USF Libraries
USF Digital Collections

A natural analogue for long-term passivity

MISSING IMAGE

Material Information

Title:
A natural analogue for long-term passivity
Physical Description:
Book
Language:
English
Creator:
Monson, Raymond E
Publisher:
University of South Florida
Place of Publication:
Tampa, Fla.
Publication Date:

Subjects

Subjects / Keywords:
passive behavior
corrosion
josephinite
nuclear waste
Dissertations, Academic -- Civil Engineering -- Masters -- USF   ( lcsh )
Genre:
government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Monson ABSTRACT The U.S. Department of Energy (DOE) has been engaged in a viability study for a potential underground geological repository in Yucca Mountain, Nevada. The repository is being designed for disposal of high level nuclear waste. A reference design for the repository has focused on the use of natural and manmade barriers to assure that radionucleide release will not be significant though an extended time period on the order of 10,000 years. The reference design utilizes manmade metallic components that are expected to last for this time period.The specified metallic materials depend on a phenomenon known as metallic passivity to achieve their expected service lives. It is difficult to demonstrate this type of service life for these metallic materials as they have only been in commercial use for less than 100 years. There have been metal artifacts and metallic materials that have survived for long time periods, however, little is known about whether these artifacts have been exposed to conditions where they have been immune to corrosion, exhibiting passive behavior, or actively corroding at an extremely low rate. A demonstration of metallic passive behavior being maintained over many thousands of years would greatly increase confidence in the expectation that passive behavior could be maintained on the repository waste packageA demonstration of metallic passive behavior being maintained over many thousands of years would greatly increase confidence in the expectation that passive behavior could be maintained on the repository waste package materials. Long-lived metallic materials, such as iron, copper, nickel, and alloys based on these metals are materials that demonstrate passive behavior and have been identified in the literature as possible analogues, potentially useful to provide additional confidence in making projections of such long-term passive behavior.1, 4, 28, 45 This paper presents a study into some aspects of the corrosion behavior of Josephinite.Josephinite is a naturally occurring assemblage of a metallic alloy of nickel and iron in conjunction with a host rock. The typical metallic composition is approximately 70% nickel and 30% iron. The material has been reported in association with geologic features with age into the millions of years. The study used corrosion measurement techniques to assess the behavior of the mineral immersed in aqueous solutions of various pH. Corrosion measurement techniques utilized included potentiodynamic polarization, open circuit corrosion potential, and electrochemical impedance spectroscopy.Other techniques utilized in the study included visual and metallographic examinations with both optical and scanning electron microscopy. Test results from this study indicate that passive behavior characterizes Josephinite specimens immersed in naturally aerated buffered aqueous solutions in a range of pH from 6 to 9. This range has been reported for the geographic area where Josephinite materials are found in southwest Oregon. This suggests that passive behavior may be responsible for the material longevity as opposed to the material being immune or undergoing slow but active corrosion.
Thesis:
Thesis (M.S.C.E.)--University of South Florida, 2003.
Bibliography:
Includes bibliographical references.
System Details:
System requirements: World Wide Web browser and PDF reader.
System Details:
Mode of access: World Wide Web.
Statement of Responsibility:
by Raymond E. Monson.
General Note:
Title from PDF of title page.
General Note:
Document formatted into pages; contains 152 pages.

Record Information

Source Institution:
University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001416913
oclc - 52786399
notis - AJJ4765
usfldc doi - E14-SFE0000051
usfldc handle - e14.51
System ID:
SFS0024747:00001


This item is only available as the following downloads:


Full Text

PAGE 1

A NATURAL ANALOGUE FO R LONG-TERM PASSIVITY by RAYMOND E. MONSON A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Engineering Department of Civil Engineering College of Engineering University of South Florida Major Professor: Dr. Alberto A. Sagues, Ph.D. Committee Member: Dr. Stanley C. Kranc, Ph.D. Committee Member: Dr Je ffrey G. Ryan, Ph.D. Date of Approval: July 1, 2003 Keywords: corrosion, passive behavior, nuclear waste, josephinite Copyright July, 2003, Raymond E. Monson

PAGE 2

TABLE OF CONTENTS LIST OF TABLES..............................................................................................................iii LIST OF FIGURES...........................................................................................................iv ABSTRACT......................................................................................................................vii 1. NUCLEAR WASTE ISSUE...........................................................................................1 2. REFERENCE DESIGN FOR NUCLEAR WASTE CONTAINMENT.............................2 3. PROJECT OBJECTIVE AND APPROACH...................................................................6 4. REVIEW OF PASSIVE METALS..................................................................................7 4.1 Potential/pH Diagrams............................................................................................9 5. EXAMPLES OF LONG LIVED METALS.....................................................................11 5.1 The Josephinite Example.....................................................................................12 6. ANALOGUE AND MODERN MATERIAL SELECTION..............................................16 7. EXPERIMENTAL TECHNIQUES................................................................................18 7.1 Visual Observation and Measurements of Josephinite Specimens......................18 7.2 Metallographic Observations................................................................................18 7.3 Elemental Analysis...............................................................................................19 7.4 Solutions Used In Corrosion Testing....................................................................20 7.5 Specimens Used In Corrosion Testing.................................................................21 7.6 Potentiodynamic Polarization...............................................................................23 7.7 Corrosion Potential...............................................................................................24 7.8 Electrochemical Impedance Spectroscopy...........................................................24 8. EXPERIMENTAL RESULTS AND DISCUSSION.......................................................27 8.1 Visual Observation and Measurements of Josephinite Specimens......................27 8.2 Metallographic Observation..................................................................................28 8.3 Elemental Analysis...............................................................................................29 8.4 Potentiodynamic Polarization...............................................................................30 8.5 Corrosion Potential...............................................................................................32 8.6 Electrochemical Impedance Spectroscopy...........................................................33 9. EXPERIMENTAL POTENTIAL/PH DIAGRAM............................................................38 10. CONCLUSIONS........................................................................................................40 11. RECOMMENDED ADDITIONAL WORK...................................................................43 i

PAGE 3

REFERENCES................................................................................................................45 APPENDICES.................................................................................................................90 Appendix A: Nickel 200 Potentiodynamic Polarization Results..................................91 Appendix B: E-NiFe Potentiodynamic Polarization Results........................................97 Appendix C: Josephinite Potentiodynamic Polarization Results...............................103 Appendix D: Nickel 200 EIS Results.........................................................................104 Appendix E: E-NiFe EIS Results..............................................................................110 Appendix F: Josephinite EIS Results........................................................................116 Appendix G: Test Material Certifications..................................................................139 Appendix H: Project Related Correspondence.........................................................143 ii

PAGE 4

LIST OF TABLES Table 1 Elemental analysis of tested modern specimens............................................49 Table 2 Test matrix of specimens................................................................................49 Table 3 Buffered solutions used in testing...................................................................50 Table 4 Resistivity of aqueous solutions......................................................................50 Table 5 Elemental analysis of Josephinite specimens..................................................51 Table 6 Slopes from potentiodynamic polarization.......................................................52 Table 7 Summary of potentiodynamic polarization test results....................................53 Table 8 Summary of EIS tests and modeling results...................................................54 iii

PAGE 5

LIST OF FIGURES Figure 1 Geographic distribution of Nuclear Waste needing long-term storage ........55 Figure 2 DOE projected flow of nuclear waste to disposal site..................................55 Figure 3 Reference design waste package................................................................56 Figure 4 Reference design of natural barrier system.................................................56 Figure 5 Reference design of engineered barrier system..........................................57 Figure 6 Typical potentiodynamic polarization curve showing areas of interest........57 Figure 7 Theoretical potential-pH diagram for nickel, from Pourbaix.........................58 Figure 8 Experimental potential-pH diagram for nickel, from Pourbaix......................59 Figure 9 Schematic of Josephinite corrosion specimen mounting.............................50 Figure 10 Corrosion specimen mounting.....................................................................61 Figure 11 Test Circuit used for verification of EIS instrumentation..............................62 Figure 12 Smithsonian Josephinite specimen............................................................63 Figure 13 Commercial Josephinite specimen .............................................................63 Figure 14 Scratches on exterior metallic portion of Smithsonian Josephinite specimen .................................................................................64 Figure 15 Scratches on exterior metallic portion of commercial Josephinite specimen .................................................................................64 Figure 16 Cross sections of commercial Josephinite specimens.................................65 Figure 17 Copper inclusion in Specimen L, unetched, 25x..........................................65 Figure 18 Nickel 200 specimen microstructure, 250x..................................................66 iv

PAGE 6

Figure 19 E-NiFe electrode specimen, microstructure, 250x.......................................65 Figure 20 Specimen L etched in Marbles reagent, large inclusion, 6.25x....................67 Figure 21 Specimen L magnified from Figure 20, 100x...............................................67 Figure 22 Specimen L magnified from Figure 21, 250x................................................68 Figure 23 Specimen L, microstructure additional area, 250x.......................................68 Figure 24 Specimen M microstructure, 250x................................................................69 Figure 25 Specimen L etching revealed banding features, 25x...................................69 Figure 26 Specimen L etching showing banding at copper inclusion, 100x.................70 Figure 27 Typical polarization scans of Nickel 200 specimens.....................................71 Figure 28 Typical polarization scans of E-NiFe electrode specimens..........................72 Figure 29 Typical polarization scans of Josephinite specimens...................................73 Figure 30 Peak and passive current densities for Nickel 200, E-NiFe and Josephinite specimens........................................................................74 Figure 31 Open circuit corrosion potential for Nickel 200 specimens..........................75 Figure 32 Open circuit corrosion potential for E-NiFe electrode specimens................76 Figure 33 Open circuit corrosion potential of Josephinite specimens..........................77 Figure 34 Randles Circuit used for modeling EIS behavior..........................................78 Figure 35 Nyquist Diagram for Nickel 200 specimens in various pH solutions............79 Figure 36 Nyquist Diagram for E-NiFe electrode specimens in various pH solutions................................................................................................80 Figure 37 Nyquist Diagram for Josephinite specimen L1 in pH 7 solution...................81 Figure 38 Nyquist Diagram for Josephinite specimen S in pH 7 solution.....................82 Figure 39 Rp value over time for specimens L1 and S in pH7 solution........................83 v

PAGE 7

Figure 40 Josephinite Specimen M after 1,632 and 10,512 hours exposure in pH 7 solution..........................................................................84 Figure 41 Estimated corrosion rates for Nickel 200, E-NiFe and Josephinite based on EIS measurements..................................................85 Figure 42 Corrosion dehavior dependence on solution pH and nickel content............86 Figure 43 Experimental potential pH diagram for Nickel 200.......................................87 Figure 44 Experimental potential pH diagram for E-NiFe electrode.............................88 Figure 45 Experimental potential pH diagram for Josephinite.....................................89 vi

PAGE 8

A NATURAL ANALOGUE FOR LONG-TERM PASSIVITY Raymond E. Monson ABSTRACT The U.S. Department of Energy (DOE) has been engaged in a viability study for a potential underground geological repository in Yucca Mountain, Nevada. The repository is being designed for disposal of high level nuclear waste. A reference design for the repository has focused on the use of natural and manmade barriers to assure that radionucleide release will not be significant though an extended time period on the order of 10,000 years. The reference design utilizes manmade metallic components that are expected to last for this time period. The specified metallic materials depend on a phenomenon known as metallic passivity to achieve their expected service lives. It is difficult to demonstrate this type of service life for these metallic materials as they have only been in commercial use for less than 100 years. There have been metal artifacts and metallic materials that have survived for long time periods, however, little is known about whether these artifacts have been exposed to conditions where they have been immune to corrosion, exhibiting passive behavior, or actively corroding at an extremely low rate. A demonstration of metallic passive behavior being maintained over many thousands of years would greatly increase confidence in the expectation that passive behavior could be maintained on the repository waste package materials. Long-lived metallic materials, such as iron, copper, nickel, and alloys based on these metals are materials that demonstrate passive behavior and have been identified in the literature as possible vii

PAGE 9

analogues, potentially useful to provide additional confidence in making projections of such long-term passive behavior. 1, 4, 28, 45 This paper presents a study into some aspects of the corrosion behavior of Josephinite. Josephinite is a naturally occurring assemblage of a metallic alloy of nickel and iron in conjunction with a host rock. The typical metallic composition is approximately 70% nickel and 30% iron. The material has been reported in association with geologic features with age into the millions of years. The study used corrosion measurement techniques to assess the behavior of the mineral immersed in aqueous solutions of various pH. Corrosion measurement techniques utilized included potentiodynamic polarization, open circuit corrosion potential, and electrochemical impedance spectroscopy. Other techniques utilized in the study included visual and metallographic examinations with both optical and scanning electron microscopy. Test results from this study indicate that passive behavior characterizes Josephinite specimens immersed in naturally aerated buffered aqueous solutions in a range of pH from 6 to 9. This range has been reported for the geographic area where Josephinite materials are found in southwest Oregon. This suggests that passive behavior may be responsible for the material longevity as opposed to the material being immune or undergoing slow but active corrosion. viii

PAGE 10

1. NUCLEAR WASTE ISSUE High level nuclear waste material has been accumulated by many countries that utilize nuclear materials. These nuclear materials have been used to produce electricity, provide propulsion for naval vessels, and for the manufacture of nuclear weapons. Some elements of the waste are radioactive isotopes that are hazardous for long periods of time. Safe containment of these radioactive isotopes requires their isolation until they no longer pose a significant risk to human health and the environment. As of December, 1998, the United States had accumulated 38,500 metric tons of used, or spent nuclear fuel from commercial power plants. The commercial spent fuel is currently stored in 33 states at 72 power plants and one commercial storage facility. The amount of spent fuel is expected to double by the year 2035 if all of the currently operating nuclear plants complete their initial 40-year licensing period. By 2035, the United States is expected to accumulate an additional 2,500 metric tons of spent nuclear fuel from nuclear weapons and other defense related programs. Figure 1 shows the current location of nuclear waste needing long-term storage. Figure 2 illustrates the DOE projected flow of waste to the disposal site. Geologic disposal of radioactive waste has been a focus of scientific research for more than 40 years. As early as 1957, a National Academy of Sciences report to the Atomic Energy Commission recommended burial of radioactive waste in geologic formations with the objective of isolating waste long enough for the hazardous radioactive products to decay to low levels. 26 1

PAGE 11

2. REFERENCE DESIGN FOR NUCLEAR WASTE CONTAINMENT The U.S. Department of Energy (DOE) has been engaged in a viability study for disposal of high level nuclear waste using a reference design for a potential underground geological repository in Yucca Mountain, Nevada. The Yucca Mountain site is approximately 150 miles northwest of Las Vegas and is located in a currently semi-arid environment receiving about 7 inches of precipitation annually. The purpose of the repository is to protect people from harmful radionucleide releases for an extended period of time on the order of 10,000 years. 1, 2 Reference design parameters for the repository call for a storage density of 80 to 100 metric tons of uranium (MTU) per acre. (One MTU is the amount of spent fuel that contained 1,000 kilograms of uranium before irradiation). The repository is designed to provide for a total loading of 70,000 MTU contained within the approximately 1,200-acre site. Most of the waste will consist of spent nuclear fuel from civilian reactors. Recent reference designs published by the DOE 26 for the repository have focused on the combined use of both natural and engineered barriers to provide multiple layers of defense against release of radioactive materials into the environment. A portion of the engineered barrier system calls for utilization of double-walled, all metal waste packages to hold the nuclear materials. A concept drawing of the waste packages is provided in Figure 3. The waste is to be isolated in approximately 10,000 individual containers, with The viability study was conducted as part of a site characterization effort to assess whether the Yucca Mountain Site was suitable for long-term storage of nuclear waste. The site is currently (2003) in the license application preparation stage. 2

PAGE 12

each package holding up to 21 pressurized water reactor or 44 boiling water reactor waste assemblies. The waste packages would be approximately 1-1/2 to 2 m diameter and 3-1/2 to 6 m long depending on the type of waste. The reference design calls for the waste packages to be placed in single rows within stabilized horizontal tunnels, or drifts, which are to be excavated in the unsaturated rock zone of Yucca Mountain, Nevada. The tunnels are to be placed approximately 300 meters below the surface of the mountain and 300 meters above the existing water table. The placement is part of the natural barrier system in the reference design, which is depicted in Figure 4. After the waste packages are placed into the drifts, the drifts are to be sealed and the repository placed in a monitored status for 50 to 100 years. Reference design plans call for the repository to be closed and permanently sealed after this monitoring stage. A recent reference design called for the outermost wall of these packages to be fabricated from a 20-mm thick shell of nickel base Alloy 22. (UNS N06022, nominal composition, by wt. 56% Ni, 22% Cr, 13% Mo, 2.5% Co, 3% W, and 3% Fe). 1, 13 The second, or inner wall, of the packages is a 50-mm thick type 316NG stainless steel material. For design purposes, the Alloy 22 is primarily present for corrosion resistance and the 316NG stainless shell for providing mechanical strength. 25 An earlier waste package design called for a 50-mm outer layer of plain carbon steel and a 20-mm inner layer of Alloy 22. 2 An additional engineered barrier in the reference design calls for use of drip shields to cover the waste packages in an effort to minimize water dripping onto the packages and to limit mechanical damage from possible falling debris. The reference design for the 3

PAGE 13

drip shield calls for the covers and structural supports to be made from titanium and feet fabricated from Alloy 22. The reference design plans do not call for installation of the drip shields until completion of a long-term monitoring stage when the site is to be sealed and closed, after perhaps 100 years or more. The pallets for support of the waste packages are to be made from a welded assembly of Alloy 22. A concept drawing for the engineered barrier system is shown in Figure 5. Alloy 22 material is a chromium-rich nickel base alloy. Nickel, chromium, and other important alloy components are not thermodynamically stable in the expected repository conditions. Alloy 22 derives its corrosion resistance from a phenomenon known as metallic passivity. When passive, a thin film sometimes only a few atomic layers deep, forms on the surface of the metal and separates the potentially reactive metal from the environment. The Alloy 22, 316NG stainless steel container, and the titanium drip shield materials all depend on passive behavior for corrosion resistance. Projections of system performance indicate that the engineered barrier portion of the repository is critical to achieving the desired system performance. In the DOE viability assessment, the Alloy 22 outer wall of the waste package has been given primary credit for providing corrosion resistance through projected passive behavior. Corrosion rates in the passive state are often less than 0.01 m/year and such rates will support a projected waste package design life in excess of 10,000 years. Since passivity is the key to the corrosion resistance of Alloy 22, it is essential that this portion of the waste package remain in the passive state over the extremely long service period. As an engineered material, however, Alloy 22 has only been in use for a few decades so predictions of the performance of Alloy 22 over the expected design life cannot be based on direct observation. 1,4 In addition, there is only approximately 100 years of service 4

PAGE 14

experience with engineered materials maintaining passive behavior (e.g. chromium stainless steels). In fact, documented examples of any metallic material maintaining passive behavior over many thousands of years do not seem to be available. Without direct evidence, the possibility exists for unknown mechanisms of deterioration to occur over many thousands of years. In summary, the relatively short service history of Alloy 22, and engineered passive metallic materials in general, brings into question the reliability of extrapolating the behavior of the material out to 10,000 years. 28 In light of the above, a demonstration of metallic passive behavior of a suitable analogue material being maintained over many thousands of years would greatly increase confidence in the expectation that passive behavior could be maintained on the waste packakge materials. 1, 4, 28, 45 The use of an analogue material would provide a look back in time to assess what type of corrosion behavior might have been responsible for a demonstrated long life. In searching for a demonstration of long-term passive behavior, it is important to recognize that metallic materials can be long lived for reasons other than passivity. For example, the material may have been immune to corrosion, or undergoing active corrosion at a very low rate. Iron, copper, nickel, and alloys based on these metals are examples of long lived materials which have been identified in the literature as potential natural analogues to study for comparative behavior to modern day metals exhibiting passive behavior. 4 The potential analogues are not directly representative of the waste package alloys, but are similar in that passive behavior may be responsible for a demonstrated long life. 5

PAGE 15

3. PROJECT OBJECTIVE AND APPROACH In light of the above issues associated with projections of such long-term passive behavior, this project was created to attempt to identify a metallic material that may have exhibited passive behavior over an extremely long period of time, and the environmental conditions leading to the behavior. To accomplish this, the following four tasks were established: Review the main characteristics of metallic passivity. Identify a candidate metallic material for use as an analogue in demonstrating long-term passive behavior. The candidate material must have demonstrated a long life in excess of 10,000 years. The candidate material would also have to be available for use in destructive corrosion and metallographic study. The candidate material could be either a natural or a manmade item. Assess the corrosion behavior of the selected candidate analogue and related metallic engineered modern materials under aqueous exposure conditions of controlled pH similar to those that may have been experienced by the analogue material in its environment. The experimental techniques utilized would need to be able to distinguish between immune, active, and passive behavior. Organize the information in an experimental potential-pH diagram using the general test methodology outlined by Verink 5 6

PAGE 16

4. REVIEW OF PASSIVE METALS Jones 15 has defined passivity as a condition of corrosion resistance due to formation of thin surface films under oxidizing conditions with high anodic polarization. Passive behavior is associated with the formation of a thin, thermodynamically stable oxide or hydroxide film on the surface of a metal. Many modern commercial metals owe their usefulness as structural materials to this passive behavior. Metals such as aluminum, nickel, chromium, titanium, and iron along with some of their alloys exhibit passive behavior. Iron containing a sufficient amount of chromium to become stainless steel is an example of one such alloy. While passive, these metals exhibit very low corrosion rates. A metal or alloy showing passivity will typically display a transition from active corrosion to passive behavior when subject to anodic polarization. This transition will typically be exhibited by the formation of an S-shaped dissolution curve when plotting current, or current density, versus applied potential on a semi-logarithmic scale as shown in Figure 6. While undergoing anodic polarization, metals exhibiting a transition from active to passive behavior initially undergo exponentially increasing corrosion rates as measured by current density. On further increases in potential, the corrosion rate decreases to a much lower value and remains low over a considerable range of potential. The magnitude of the reduction in corrosion rate from the active to the passive regions can be on the order of 10 3 to 10 6 14, 15 Additional increases in potential lead to a marked increase in corrosion rate when the transpassive/oxygen evolution region of behavior is reached. 7

PAGE 17

The initial zone of exponentially increasing corrosion rate is the region of active corrosion behavior. The zone of reduced corrosion rate is identified as the region of passive behavior. Nickel based metals are well represented in the literature as a material for study of passive behavior. Researchers have experimentally identified a variety of films present on passive nickel base materials. MacDonald 16 reported on Surface Analysis by Laser Ionization (SALI) techniques performed using nickel specimens in both phosphate and borate buffer aqueous solutions. He reported Ni(OH) 2 as the primary constituent in the passive film formed with no significant difference between passive films formed in either of the buffer solutions. Graham 17 reported that the passive films on nickel are entirely NiO and 0.9 1.3m thick. Macdougal 18 also indicated NiO as the passive film in borate buffer solutions. Hummel and Verink 19 provided a summary of various literature which suggested that a variety of films such as Ni(OH) 2 NiO, NiOOH, Ni 3 O 4 Ni 2 O 3 NiO 2 NiO 1.5-1.7 or chemisorbed oxygen were responsible for passive behavior. Their own research identified Ni(OH) 2 as the primary film with NiO and NiOOH identified at various pH/potential ranges with in-situ testing by use of differential reflectometry (DR). Although the exact elemental compositions of the layer responsible for passive behavior are not resolved, 16 the effects of passive behavior can be experimentally observed by measuring changes in current. Despite the lack of resolution on the mechanism, Pourbaix 6 and Verink 5 have devised methods for mapping out conditions of active and passive corrosion behavior based on specimen potential and aqueous solution pH as discussed in the next section. 8

PAGE 18

4.1 Potential/pH Diagrams Pourbaix 6 created a series of potential/pH diagrams that show reaction products that will be thermodynamically stable under equilibrium conditions in water of various pH. The diagrams may be thought of as a map showing whether a metal, metal ion, metal oxide or hydroxide, will be stable for various conditions of potential and pH in an aqueous electrochemical system. The diagrams show conditions of potential and pH where a metal in aqueous exposure can be immune to corrosion where the metal is stable, subject to corrosion where the metal ion is stable, or passive where an oxide or hydroxide form of the metal is stable. The diagrams are useful in identifying conditions of exposure where corrosion may be possible or where it is impossible. The diagram based on thermodynamic stability of nickel and its oxide or hydroxide forms is reproduced as Figure 7. Pourbaix developed the boundary lines of the theoretical diagram by use of the Nernst equation, with consideration provided for the activity levels of the metal ions in solution. 15 The theoretical diagrams are published only for pure metals and do not predict rates of corrosion, or how quickly a metal may passivate. 16 In addition to the theoretically based diagrams, Pourbaix also published a probable experimental potential/pH diagram for nickel using the corrosion behavior reported by various researchers. 6 This diagram based on empirical information has been reproduced as Figure 8. Verink 5 outlined a method to produce potential/pH diagrams for metal alloys based on experimental testing. The general test methodology consisted of conducting a series of polarization scans on a specimen material in solutions of various pH and plotting the potentials at which active corrosion and passive behavior are observed. This method 9

PAGE 19

permits creation of the potential/pH diagrams for metallic alloys and solutions other than pure water. 10

PAGE 20

5. EXAMPLES OF LONG LIVED METALS Johnson and Francis 3 reported many examples of native metals, meteorites, and archeological objects that have survived quite well over extended periods of time. Their study included man-made items from alloys rich in metals such as gold, silver, copper, lead, iron and tin. The longest lived of the man-made items identified were gold artifacts from 6000 to 7000 B.C. Surviving iron and nickel based meteorites were estimated to have been exposed to terrestrial conditions for 5,000 to over 100,000 years. Manmade copper artifacts have been dated to 9,000 years old. Native copper deposits in Michigan have also been reported to be approximately 500 million years old. Abrasions on the copper deposits were linked to a glaciation period and dated to at least 8,000 years ago. For surviving man-made artifacts, Johnson and Francis estimated a range of corrosion rates from 0.002 to 7.6 m/year for iron specimens and 0.008 to 3 m/year for copper specimens that were not submerged under water. For iron, both the high and low ends of the range occurred on artifacts buried in tombs in arid climates. Other iron specimens with corrosion rates between the extremes were found exposed in various atmospheric and aqueous environments. The copper specimens were reported buried in a variety of materials such as gravel, soil, clay, as well as under atmospheric exposure conditions. Johnson and Francis compared their estimates of corrosion rates to those published by Uhlig 27 for materials under modern rural exposure conditions. Uhlig reported rates of 1.8 to 12.2 m/year for iron and 0.4 to 1.3 m/year for copper. Johnson and Francis commented that the modern rates reported by Uhlig corresponded with the mid-range of 11

PAGE 21

their estimates, and that the most durable artifacts have been subject to exceptionally low corrosion rates. Robbiola, Blengino, and Fiaud 21 reported on natural patinas formed on archeological bronze (Cu-Sn) alloys buried for approximately 3,000 years. They estimated corrosion rates of 0.5 to 4 m/year for exposure duration of 20 years or less and decreasing with time, tending towards zero. It should be noted however, that copper exhibits a large range of potential and pH conditions where it is immune to corrosion by having a thermodynamically stable metallic form. Review of a published potential/pH diagram 15 for copper indicates that the range of metal stability is substantially larger than for other metals such as iron, nickel, aluminum, or chromium. With a significant range of stability, the possibility exists for the copper artifacts to have been in a condition where they were immune to corrosion. It appears that little or no attention has been given in the literature as to whether the durability of these archeological and natural specimens was due to exposure conditions where the metals had been immune to corrosion, actively corroding, or exhibiting passive behavior in their environment. Thus there is much uncertainty as to whether any of the long lived metal specimens represent examples of long-term passive behavior. 5.1 The Josephinite Example The potential of Josephinite as a natural analogue to demonstrate long term passive behavior has been pointed out by McNeil and Moody. 4 Josephinite is a naturally occurring assemblage of metallic alloy of nickel and iron in conjunction with a host rock. The typical ratio of nickel to iron is approximately 3:1. Josephinite specimens are found in Josephine County in southwestern Oregon and were first described in 1892. 9 Similar 12

PAGE 22

mineral assemblages have been found at other locations in the world and have been identified as Awaruite. 4, 5 The variation in terminology in the literature appears to revolve around whether the mineral specimens from Josephine County are regarded as unique apart from similar specimens found elsewhere. For the purposes of this study the term Josephinite will refer to the metallic and host rock assembly of minerals found in and around Josephine County. Naturally occurring deposits of both nickel and iron occur in various locations throughout the world, but they generally occur as metallic ores. The ores are typically sulfide or oxide forms of these metallic elements. 33 Large iron ore deposits are located in the Ural Mountains of the former Soviet Union and near Lake Superior in the United States. Large nickel ore deposits are located in the Soviet Union and eastern Canada. Josephinite specimens are found as metallic nuggets instead of the ores more characteristic of the primary metal constituents. Josephinite has been reported as placer deposits found in streams or streambeds, and as embedded deposits located within a host geological formation. Masses of Josephinite up to 50 kg have been reported. 3 Centimeter sized nuggets are commercially available. The presence of large amounts of reduced metal in natural exposure, including oxidizing conditions, strongly suggest that passive behavior may have played an important role in the preservation of the metal alloy over geologic time frames. Josephinite is reportedly found as irregularly shaped nuggets of the metal surrounded by harzburgite, serpentinized olivine, an ultramafic host rock. 9, 10 Ultramafic rocks are generally composed of ferromagnesium silicates, metallic oxides and sulfides, and native metals on rare occasions. 8 Olivine is a mineral identified as being closely 13

PAGE 23

associated with the Josephinite nuggets. Olivine is subject to serpentinization which occurs during exposure to water according to the following reaction 9 : 6 Mg 1.5 Fe 0.5 SiO 4 + 7 H 2 O 3 Mg 3 Si 2 O 5 (OH) 4 + H 2 + Fe 3 O 4 (Olivine) (Serpentine) As shown above, the serpentinization occurs by the metamorphism (especially hydration) of a mineral, such as olivine. The most common serpentine color is reported as being green, however the rocks are reported to weather to an orange-brown color. 8 The serpentinization of the olivine host rock indicates that the Josephinite nuggets have been exposed to aqueous solutions for some portion of the geologic time frame. Josephinite bearing placers were found by Dick 10 to be closely associated with serpentine shear zones and diabase dykes. Dykes are bodies of igneous rock cutting across the structure of adjacent rock and result from intrusion of magma. 8 Dykes associated with Josephinite nuggets have been dated by K-Ar methods to 150-155 million years. 9, 10 Dick 10 has suggested that the intrusion of the dykes caused an increase of hydrothermal activity and circulation of water in the adjacent rocks. He proposed that this hydrothermal activity led to the development of the serpentine and the formation of nickel-iron deposits by reduction of nickel sulfides and iron in the local vicinity of the dyke. This suggests a relatively close association of age between the formation of the dikes and the formation of the nickel-iron nuggets. Leavell 29 expressed similar views on the origin of the material. Bird 41 suggested that the Josephinite metallic material had its origins in the earth mantle region and was deposited with the dykes. With either origin, the presence of serpentine, the formation of the nickel-iron deposits, and the presence of Josephinite placer deposits, suggest aqueous exposure which is 14

PAGE 24

consistent with the suggestion that passive behavior may be responsible for the metal longevity. 15

PAGE 25

6. ANALOGUE AND MODERN MATERIAL SELECTION Based on the reported longevity, availability, and reported exposure conditions of the deposits, Josephinite was selected as a material to use in examining the tendencies of this natural analogue towards passive or active corrosion behavior under aqueous exposure. Manmade artifacts of sufficient age (10,000 years) for this study were typically one of a kind museum type items and were not considered good candidates for destructive testing. 3 Josephinite specimens from two sources were included in the study. A specimen nugget of Josephinite was obtained on loan from the Smithsonian Institute for the purposes of performing non-disruptive visual observations and elemental analysis using EDS techniques. Three additional specimens of Josephinite were obtained commercially for use in performing chemical, metallurgical, and corrosion testing. The commercial specimens were obtained from Excalibur Minerals, Inc. of Peekskill, New York. Detailed information on the Josephinite specimens is presented in Section 8.1. Two modern alloys were selected for comparison of corrosion behavior against the Josephinite specimens. The composition of the two alloys was selected such that the nominal nickel/iron ratio of Josephinite fell between the nickel/iron ratio of the two alloys. One of the alloys was Nickel 200 (UNS N02200), a commercially pure nickel, which was supplied in the form of 1 cm diameter x 30 cm long rod. The second alloy was a nominal 55% nickel-45% iron core wire from a commercially available E-NiFe class of welding electrode within the American Welding Society A5.15 specification. The E-NiFe alloy 16

PAGE 26

was supplied as 0.64 cm diameter x 58 cm long rod. Both of the modern materials were supplied in the mill-annealed condition, with mill test reports as provided in Appendix E. A summary of the elemental analysis as reported for the specimens on the respective mill test reports is shown in Table 1. Both the Nickel 200 and the E-NiFe specimens were supplied in a clean surface condition and were reported to have been pickled. 17

PAGE 27

7. EXPERIMENTAL TECHNIQUES A variety of techniques were used to examine and evaluate the specimens of this study. These techniques included: visual observations, metallographic observations, elemental analysis, potentiodynamic polarization, corrosion potential, and electrochemical impedance spectroscopy. Table 2 provides a matrix of the experimental techniques utilized on each type of specimen. 7.1 Visual Observations and Measurements of Josephinite Specimens Densities of the commercial specimens were calculated by weighing them in air and immersed in water using a triple beam balance. Visual observations were made utilizing a reflected light microscope with magnifications up to 250x. 7.2 Metallographic Observations The three commercial Josephinite specimens were sectioned for optical examination of the specimen interiors and for preparation of corrosion test specimens. Sections were cut using a low speed Buehler wafering wheel (diamond wheel cutting blade) and Buehler Metadi cutting fluid. One section from each nugget was mounted, polished and etched for metallographic examination. Buehler Bakelite thermosetting material was used for mounting. Etching was performed using Marbles reagent, a mixture of hydrochloric acid and copper sulfate. 32 Metallographic observations were made of the Nickel 200 and E-NiFe specimens for comparison. 18

PAGE 28

Surface preparation for all of the metallographic work was performed by abrading the specimens with progressively finer silicon carbide paper discs through 600 grit and then progressively finer polishing through 0.05 micron alumina. After polishing, sections of each specimen were observed under magnification both with and without etching. 7.3 Elemental Analysis Elemental analysis was performed on various areas of the Josephinite specimens using a JOEL JSM 840 scanning electron microscope (SEM), and a Tracor Northern TN 5500 energy dispersive x-ray spectrometer (EDS). Analysis was performed on the specimen exteriors before sectioning and interiors after sectioning. The Smithsonian specimen was not sectioned for analysis, however elemental analysis of the specimen exterior was performed. In the SEM, a beam of electrons impinges on the surface of the specimen being analyzed. At the impingement point, electron and x-ray emissions are produced. EDS utilizes the energy spectrum of the x-rays given off by the specimen to identify the type and quantity of elements present on the material surface. The EDS process allows measurement of the elemental composition of the material specimen for elements heavier than sodium. Materials to be used in the SEM for EDS must be conductive or coated with a conductive sputtered layer. The specimen must be clean, and small enough to fit into the machine vacuum chamber. 32 19

PAGE 29

7.4 Solutions Used in Corrosion Testing A pH range of approximately 6 to 9 was reported for natural surface waters for areas near the location of Josephinite deposits in Oregon. 34, 35 Aqueous solutions with pH bracketing and extending through this range were used to assess corrosion behavior of the Josephinite and modern material specimens. An assumption was made that these pH conditions have existed in the Oregon location for an extended period of time and are representative of the natural exposure conditions experienced by the Josephinite materials. Buffered aqueous solutions of pH ranging from 4 to 12 were utilized for conducting potentiodynamic polarization scans, measurements of corrosion potential, and EIS of the Nickel 200, E-NiFe, and Josephinite specimens. The compositions of the buffered solutions utilized are summarized in Table 3. The compositions were taken from the CRC Handbook 38 and were similar to those used by Verink 5 The pH of each solution used was verified to be within 0.1 units of the nominal value prior to use with a Corning 140 pH meter using commercial buffer solutions for system calibration. Resistivities of several of the buffered solutions were measured and are reported in Table 4. The measured resistivity of these solutions is lower than the values reported for natural waters in the vicinity of Josephine County. In the case of non-uniform active corrosion, the lower resistivity of these solutions may be expected to produce a higher corrosion rate than for the natural waters. However onset of passive behavior should result in extremely low corrosion rates independent of solution resistivity. Temperature of the solutions during corrosion testing was 21 +/1.7 o C in all cases. The corrosion cell glassware used was in general accordance with the ASTM G5 7 standard. 20

PAGE 30

For potentiodynamic polarization, the solutions were stirred using a magnetic stirring plate and deareated. Deareation was performed by bubbling commercial, high-purity, nitrogen through the solution for a minimum of one hour prior to the start of the polarization scans. The solutions used for measurements of corrosion potential and EIS were naturally aerated, being left open to the atmosphere. The solutions were not stirred during the course of the measurements. A Gamry Instruments potentiostat was used in conjunction with a corrosion cell consisting of a saturated calomel electrode (SCE) reference electrode, Lugin probe, two graphite counter electrodes and the specimen being tested as the working electrode. The probe tip to specimen distance was typically 5mm. For this report, all measurements of electrochemical potential were converted to the standard hydrogen scale by adding 0.241 volts to the SCE measurement. 7.5 Specimens Used in Corrosion Testing Corrosion test specimens of the modern nickel base alloys consisted of solid cylindrical specimens made from the supplied rods. The Nickel 200 corrosion specimens measured approximately 1.25 cm long by 0.93 cm diameter. The E-NiFe corrosion specimens measured approximately 2.25 cm long by 0.54 cm diameter. Exposed surface area of the specimens was approximately 5 cm 2 and 4 cm 2 for the Nickel 200 and E-NiFe specimens respectively, after subtracting the area of the Teflon gasket used in mounting the specimens. Mounting was in general accordance with ASTM G5. 7 Photographs showing the configuration of the Nickel 200 and the E-NiFe corrosion specimens are provided in Figure 10. 21

PAGE 31

Corrosion specimens for Josephinite consisted of cut cross sections of the supplied nuggets. The sectioned specimens of Josephinite were irregularly shaped and were estimated to have effective surface areas from 0.62 to 0.32 cm 2 The estimated metallic area of the sections was based on dimensional measurement of the approximately oval shaped sections. Based on the appearance of the unetched cross sections, it was estimated that approximately 75% of each cross section consisted of a metallic surface with the remainder assumed to be a non-conductive rock. To verify the assumption of non-conductivity, measurements of electrical resistance were made using pointed tips of probes placed on the rock and metallic areas of the cross sections and a multimeter at 200 ohm full scale reading. The meter indicated no conductivity between the rock and metallic areas on all of the specimens while readings of zero ohms were obtained within the metallic areas. The Josephinite specimens were embedded in a two-part epoxy, Buehler Epoxide, to isolate the sectioned face as the exposed surface for corrosion testing. The specimens were in contact with a copper conductor buried within the epoxy. A schematic of the mounting is shown in Figure 9. Photographs showing the configuration of the embedded Josephinite specimens are provided in Figure 10. All corrosion specimens were prepared by polishing with progressively finer silicon carbide paper down to 600 grit followed by a wash in distilled water and subsequent immersion into the various pH buffered solutions. The specimens were repolished and washed for each subsequent use. 22

PAGE 32

7.6 Potentiodynamic Polarization Potentiodynamic polarization scans were performed on the Nickel 200, E-NiFe, and Josephinite specimens. The test methodology was in general accordance with ASTM G5 7 except for differences in the test solutions, and polarization scans were started at potentials below the hydrogen evolution potential at each pH level tested. All potentiodynamic polarization specimens were prepared by polishing as described earlier within 30 minutes of specimen immersion. Polarization scans were started 55 minutes after specimen immersion as described in the ASTM G5 standard. Potentiodynamic scans were carried out in the anodic direction until passive behavior was established. Figure 6 depicts a plot of a generic potentiodynamic scan showing selected areas of interest in the potentiodynamic scans performed. To verify the performance of the experimental potentiodynamic polarization techniques and equipment, specimens of type 430 stainless steel were run to the ASTM G5 standard. The standard addresses potentiodynamic polarization of type 430 stainless steel in an aqueous solution of 1N sulfuric acid. Standard results for type 430 stainless specimens are published in ASTM G5 for comparison against those measured to verify the techniques utilized. The specimens of 430 stainless steel were run at various times during the course of the experimental data collection to assure that the machine and techniques being utilized were reliably performing and recording the potentiodynamic scan. The test results were within the prescribed ASTM-G5 bands of laboratory performance. 23

PAGE 33

7.7 Corrosion Potential Nickel 200, E-NiFe and Josephinite specimens were immersed in naturally aereated, buffered solutions of various pH to measure the open circuit potential achieved. The Nickel 200 and E-NiFe specimens were tested in pH 4, 5, 6, 8, and 10 prepared solutions. Josephinite specimens were tested in solutions of pH 5, 6, 7, and 8. 7.8 Electrochemical Impedance Spectroscopy Electrochemical Impedance Spectroscopy (EIS) was used as an additional test method to assess whether the Nickel 200, E-NiFe or Josephinite specimens were passive or actively corroding at the measured open circuit potentials. Specimens were immersed in buffered solutions of various pH and subjected to EIS to estimate the specimen corrosion rates. The testing apparatus was a Gamry Instruments with potentiostat and frequency response analyzer (FRA) using CMS-100 software. The EIS scans were all run at zero applied DC voltage (at the open circuit potential), in a corrosion cell open to the atmosphere. The cell consisted of a glass corrosion cell and specimens in general accordance with ASTM G61. Two graphite counter electrodes were used, with a SCE reference electrode positioned close to the specimen through use of a Luggin probe. Testing was typically performed from 5000 Hz down to a 0.1 mHz frequency at an amplitude of 10 mV RMS. To verify the performance of the EIS equipment, a Randles type dummy cell was created as a test circuit to provide a simulated model of a corroding electrode. The test circuit consisted of a nominal 1k (measured 989 ) resistor connected in series to a parallel combination of a nominal 100F capacitor and 850k (measured 852 k) resistor. A schematic diagram of the test cell is shown in Figure 11. An EIS scan was 24

PAGE 34

performed on the test circuit. Plots of the modeled and recorded impedance response of the dummy cell are also provided in Figure 11. The respective plots show good agreement, indicating proper functioning of the measurement and test equipment. The modeling variables for the Rp and Rs resistors differed from the measured values by 0% and 0.8% respectively. Measurements for the capacitor portion of the circuit differed from the labeled capacitor value by 10%. EIS measurements were performed on Nickel 200 specimens in pH 4, 5, 6, 7, 8, and 10 solutions. E-NiFe specimens were tested at pH 5, 6, 7, 8 and 9. Josephinite specimens were tested at pH 5, 6, 7, and 9. EIS measurements were made using the same specimens and corrosion cells that were being used for measurement of open circuit potential. EIS measurements were taken after various immersion times up to approximately 1000 hours. Specimen preparation was identical to that used for the potentiodynamic polarization specimens described earlier. The test data was analyzed by modeling as a simple corroding electrode represented by a resistor in series with a parallel combination of a resistor and a non-ideal capacitor. Circuit modeling was performed using Gamry Framework analysis software. The polarization resistance, Rp, was obtained as an output function of the models. Estimates of corrosion rate were obtained through the following equation as applies to cases of simple activation polarization but was used otherwise to obtain nominal values. 30 25

PAGE 35

Icorr = B_ Rp where: B = ba bc______ (2.303)(ba + bc) Icorr = corrosion current density (a/cm 2 ) B = composite Tafel parameter (V) Rp = polarization resistance (ohm-cm 2 ) ba = anodic slope (V/decade), potential-log i corr bc = cathodic slope (V/decade), potential-log i corr Values of 0.1V for the anodic and 0.1V for the cathodic slopes were used in the above equation from estimates provided by Jones. 15 The resulting calculated value of the composite Tafel parameter, B, was 0.022. 26

PAGE 36

8. EXPERIMENTAL RESULTS AND DISCUSSION 8.1 Visual Observations and Measurements of Josephinite Specimens The Smithsonian specimen was received with an adhesively attached paper tag identified with the number 149489. The specimen weighed 62.5 grams, was irregularly shaped, and measured approximately 5 by 4 by 2 cm. A photograph of the Smithsonian specimen is shown in Figure 12. The commercial specimens were smaller than the Smithsonian specimen with the largest dimension of the three specimens ranging from approximately 2.5 to 1 cm and mass ranging from 11.07 g to 2.56 g. A photograph of one of the commercial specimens is shown in Figure 13, the other two commercial Josephinite specimens were similar in appearance. Densities of the commercial specimens were calculated as 7.05 g/cm 3 for the largest specimen, and 5.51 and 5.56 g/cm 3 for the two smaller sized specimens. Measurements for density of the Smithsonian specimen were not performed to avoid potentially disruptive immersion of the specimen in water. The exterior surfaces of all of the Josephinite specimens exhibited a polished luster with some portions having a shiny metallic appearance and other areas with a reddish-brown or black polished rock appearance. This is similar to Josephinite features reported in the literature 9, 10, 45 As shown in Figures 14 and 15, the specimens contained scratches and gouges with random orientations generally covering the metallic portions. The gouges may be due to abrasion or abrasion erosion 40 which might be caused by particle gouging action under either wet or dry conditions. Under magnification, the shiny metallic areas of the Josephinite surfaces were noted to have small black cavities. 27

PAGE 37

8.2 Metallographic Observations Typical unetched cross sections of the three commercial Josephinite nuggets are shown in Figure 16. Figure 17 shows a representative sample of inclusions observed in the cross sections. At least one section from each of the two larger nuggets contained copper colored inclusions. The largest specimen was noted to have the most prevalent copper colored inclusions. The copper colored inclusions were typically in close proximity to the black colored inclusions as can be seen in Figures 17 and 20. EDS analyses of one of the copper colored inclusions in Specimen L showed it to be nearly pure copper (see Table 5). All of the Josephinite specimens exhibited the internal black-colored inclusions. The copper and other inclusions appear similar to those reported by Botto. 9 Based on visual observations of the unetched sections, it was estimated that approximately 75 percent of the typical cross-sectional area was metallic with the balance being inclusions. The sectioned Nickel 200 and E-NiFe specimens were etched and observed under magnification up to 250X. The Nickel 200 specimens displayed grain sizes approximately 20 to 80 m across. A representative micrograph of the Nickel 200 specimen is shown in Figure 18. The E-NiFe specimens displayed a much smaller grain size typically on the order of 5 to 10 m per grain as shown in Figure 19. The appearance of the etched Nickel 200 and E-NiFe compared favorably with those reported in ASM Metals Handbook. 39 The grains were generally equiaxed, with no evidence of cold work noted. The equiaxed grain structure tends to confirm the reported annealed state of the Nickel 200 and E-NiFe supplied material. 28

PAGE 38

Metallographic etching of the Josephinite specimen revealed a variety of structures ranging from apparent complex mixture of phases to nearly equiaxed grains nominally 100 m in size. Micrographs showing these features are provided in Figures 20 through 26. The black area at the center of Figure 20 is the dark area appearing at the center of Specimen L and highlighted by the arrow in Figure 16. Etching in some areas produced a banding effect as seen in Figures 25 and 26. The lack of homogeneity in the Josephinite etching behavior may be due to natural variations in the formation process of the material. 9 8.3 Elemental Analysis The elemental analysis from various portions of the specimens is shown in Table 5. The table has been divided into four parts differentiating between specimen interiors, exteriors, metallic and non-metallic appearing regions. Elemental analysis of the Smithsonian and commercial Josephinite specimen exteriors showed good agreement with the reports of Josephinite and serpentine host rock reported in the literature 9, 10, 11, 12 EDS analysis of the black inclusions showed some to be similar in composition to the mainly Mg-Si of the host rock noted on the specimen exteriors. Other similar appearing areas of the specimen interiors displayed differing ratios of Ni, Fe, Mg, Si, and Ca. The elemental analysis results from interior portions of the three commercial specimens exhibited good agreement with the external portions as well as with the exterior of the Smithsonian specimen except in one regard. The largest commercial specimen, L, contained approximately 3% copper within the metallic portion along with isolated islands of almost pure copper. The mid-sized Josephinite specimen also had similar islands of copper colored inclusions but did not have the overall copper content observed in the larger specimen. The finding of native copper and copper inclusions in 29

PAGE 39

association with Josephinite was reported by Botto. 9 The copper colored inclusions appeared to be mainly located in association with dark colored inclusions internal to the metallic nuggets. The presence of copper was not noted on the exterior of the specimens. Copper may be present on the specimen exterior but buried under the host rock material, or may have been removed from the exposed surfaces by corrosion or erosion of the surrounding nickel-iron matrix. The metallic areas noted on the exterior of the Josephinite specimens exhibited black spots as local depressions. The specimens also exhibited reddish/brownish areas as noted in the literature. 9, 10 The literature reports black colored magnetite surrounding some Josephinite specimens 9 however, EDS analysis of the Josephinite specimens used in this study showed no areas of high iron concentrations as would be expected out of a layer of magnetite (Fe 3 O 4 ). It is suspected that the black/brown/red color variations may be due to a differing level of oxidation of the iron, or other elements present in the host rock. 8.4 Potentiodynamic Polarization A compilation of typical polarization scans for the Nickel 200 specimens at various pH values are shown in Figure 27. Similar polarization scans for the E-NiFe and Josephinite specimens are shown in Figure 28 and 29 respectively. A summary of the Epp, i pass and i crit values obtained from the polarization testing is presented in Table 7. It was noted that the Epp values for the E-NiFe specimens were consistently lower than the corresponding values for Nickel 200 at pH values between 6 and 10. Comparison of the theoretical potential-pH diagram by Pourbaix for nickel and iron show that iron might be expected to passivate at a lower potential than nickel in this range. It is suspected 30

PAGE 40

that the iron in the E-NiFe specimens is allowing them to passivate at lower potentials with more iron-like behavior characteristics than the Nickel 200 specimens. It was also noted that the E-NiFe specimens generally exhibited a higher peak corrosion current density (i crit see Figure 6) than the Nickel 200 specimens, roughly by an order of magnitude. The passive current densities (i pass see Figure 6) measured were similar for the two materials. The data indicates that the E-NiFe specimens experienced a higher corrosion rate than the Nickel 200 specimens while actively corroding under the test conditions. Review of the experimental and theoretical diagrams for nickel by Pourbaix indicates that the material should spontaneously passivate and not be subject to active corrosion at approximately pH 9 through 12. Figure 30 shows the measured peak and passive current densities obtained from the potentiodynamic polarization scans on Nickel 200, E-NiFe and the Josephinite specimens. The results show general convergence of the peak corrosion current density towards the passive current density as the solution pH approaches 10. The values of peak and passive current densities differ by less than 10 percent at pH 9. These experimental results provided general verification of spontaneous passive behavior indicated by Pourbaixs delineation between active corrosion and passive behavior at pH 9 in Figure 8. As shown in Figure 29, the Josephinite specimens exhibited a pattern of decreasing peak current densities as the solution pH increased from 6 to 9, similar to the Nickel 200 and E-NiFe specimens. Variations of approximately 50 percent in the corrosion current density with minimal change in the passivation potential were noted between duplicate specimens in the same pH. This may be due to naturally occurring variations in the 31

PAGE 41

specimens, or interactions between the metallic Josephinite and the serpentine internal inclusions present in each section, or to variations in the true versus estimated surface areas of the exposed faces of the Josephinite specimens. Jones 15 reported a ba value of 0.10V for a nickel electrode in a 0.12 N NaOH solution. He reported experimental ba values from 0.06V to about 0.12V and bc values from 0.06V to infinity, with the later case corresponding to diffusion control by a dissolved oxidizer. Jones suggested use of a nominal value for ba and bc as 0.1V, which yields a composite Tafel parameter of 0.022V to obtain a reasonably good estimate of the corrosion rate. As discussed earlier, this value was used in making corrosion rate estimates from EIS experiments. 8.5 Corrosion Potential The open circuit corrosion potential measured over time for the Nickel 200, E-NiFe and Josephinite specimens are plotted on Figure 31, 32, and 33. Figure 31 shows the measured potential for Nickel 200 specimens (converted to Standard Hydrogen Electrode Scale, SHE) on a linear time scale and shows a somewhat stable potential of approximately 0.2 volts SHE, or higher, being reached after 100 to 200 hours of immersion. However, when plotted with time on a logarithmic time scale as done in the bottom of Figure 31, the potentials were noted to continue on an upward trend through approximately 600 hours. The general upward trend was noted for the E-NiFe and Josephinite specimens as well. The upward trend is in agreement with predictions offered by MacDonald 28 showing potentials increasing for one year on passive C22 material. 32

PAGE 42

As shown in Figure 32, the open circuit corrosion potential measured for E-NiFe specimens in pH 6 solutions were noted to increase dramatically after formation of a dark gray or black film on the surface of the specimens. Film formation was noted after approximately 30 hours. Prior to formation of the film, the corrosion potentials were below the Epp values obtained from potentiodynamic polarization, indicating active corrosion behavior. After film formation, the corrosion potentials moved to values above the Epp, which suggests a transition to passive behavior. However, the EIS measurements discussed later in this report indicated that a substantially higher corrosion rate was still occurring on the specimens immersed in the pH 6 solution compared to the pH 7 and higher solutions. The film appeared to affect the measured corrosion potential, but did not appear to offer corrosion protection. 8.6 Electrochemical Impedance Spectroscopy Curve modeling was performed using a Randles circuit modified to include a constant phase angle element (CPE) in place of a plain capacitor. The CPE is a fictitious circuit element related to charge storage at the metal-electrolyte interface. 5, 7, 42, 43 The circuit incorporates solution resistance, an interface capacitance, and polarization resistance values to model simple corrosion effects. A schematic diagram of the circuit is shown in Figure 34. The CPE element used in modeling the EIS behavior accommodates non-ideal interface capacitance. An ideal interface capacitance would be expected to show on the Nyquist plot as a semi-circle centered on the real impedance (Z) axis. The Nyquist plots obtained from the EIS tests on the tested specimens were typically semi-circles with the centers depressed below the real Z axis. The Nyquist plots representing various exposure conditions for the Nickel 200, E-NiFe and two Josephinite specimens are shown in Figures 35, 36, 37 and 38, respectively. 33

PAGE 43

Summary data from the EIS testing is provided in Table 8. In general, the plots show a trend of increasing semi-circle diameter (increasing Rp values) with increased exposure time and with increases in pH of the solutions. Nyquist plots for the Josephinite specimens under exposure to pH7 solution for up to approximately 1000 hours are presented in Figures 37 and 38. Results generally indicate decreasing corrosion rate with increasing exposure time, similar to the Nickel 200 and E-NiFe specimens. Figure 39 shows the change in the modeled value of Rp over time for the Josephinite specimens immersed in pH 7 solution for approximately 100 hours. The modeling results show increasing Rp values with increasing exposure times. This indicates decreasing corrosion rates as exposure time is increased. This behavior is in general agreement with the observations on passive behavior by Li. 37 A photograph of Josephinite specimen M after 1,632 and 10,512 hours exposure in the buffered pH7 solution is provided in Figure 40. Although the specimens became electrically disconnected from the copper conductor used to make electrochemical measurements, specimens M and L2 were allowed to remain in pH7 solution, with observations made through 10,512 hours. The surfaces remained bright, with the original polish marks visible. No change was noted in the appearance after 10,512 hours of exposure. Similar behavior was noted for Specimen L2. Estimated corrosion rates for the Nickel 200, E-NiFe and Josephinite specimens are presented graphically in Figure 41. For Nickel 200, the estimate of corrosion current density for solutions pH 5 or higher, was a very low rate of dissolution in order of 34

PAGE 44

magnitude from 10 -2 to 10 -3 A/cm 2 indicative of passive behavior. These rates correspond to a corrosion rate of less than 0.075 m/year. The corrosion rate estimates show a value of approximately 3.5 m/year at pH 4 and a decrease of approximately 2 orders of magnitude in the rate for pH 5 through 10. This marked decrease suggests a change from active corrosion to passive behavior between pH 4 and 5 as suggested by the experimental potential-pH diagram of Figure 43, which is discussed in the next section. It was also noted that the Nickel 200 specimens turned black in the pH 4 solution, but stayed bright and shiny in pH 5 through 10 solutions. For the E-NiFe specimens in buffered solution above pH6, the estimated corrosion rates were less than 0.015 m/year. These rates compare favorably to the rates estimated by Johnson and Francis 3 for long-lived metallic artifacts. The E-NiFe corrosion rate estimates at pH 6 show a value of approximately 15 m/year and a decrease of approximately 3 to 5 orders of magnitude in the rate for pH 7 through 10. This marked decrease suggests a change from active corrosion to passive behavior between pH 6 and 7 as indicated by the experimental potential-pH diagram of Figure 44, which is discussed in the next section. Similar to the corroding Nickel 200 specimens in pH 4, the E-NiFe specimens turned black in the pH 6 solution, but stayed bright and shiny in the pH 7 through 10 solutions. Estimated corrosion rates for the Josephinite specimens ranged from 28 to 0.24 m/year in the tested solutions. The results showed a similar behavior as the Nickel 200 and E-NiFe electrode specimens with a one to two order of magnitude decrease in corrosion rate as pH was increased to higher values. The large decrease in rate suggests a change from active corrosion to passive behavior between pH 5 and 6 as indicated by 35

PAGE 45

the experimental potential-pH diagram of Figure 45, which is discussed in the next section. As additional confirmation of this behavior, the exposed face of the Josephinite specimens turned black in pH 5, but stayed shiny in the pH 6 through 9 solutions. Corrosion rates estimated from the EIS measurements for the Josephinite specimens were higher than the corresponding rates for the Nickel 200 or the E-NiFe specimens by factors of 10 to 100. This may be due to variations in the naturally occurring specimens, or interactions between the metallic Josephinite and the serpentine host material present in each section. Some of the difference may also be attributed to an assumption made that 75 percent of the exposed Josephinite specimen surface area being metallic. The presence of crevices may substantially add to the exposed surface areas that were not taken into account in the estimates. As an additional factor, it was noted that the EIS modeling results for the Josephinite specimens required use of Alpha correction values between 0.5 and 0.6 while the Nickel 200/E-NiFe specimens required Alpha values typically much closer to unity. This indicates significant depression of the center of the Nyquist plot semi-circles below the real Z axis. McKubre 43 listed several causes for the depression as: reference electrode shielding, current divergence at the electrode perimeter, poor reference probe placement, electrode surface heterogeneity, poor electrode orientation, and surface roughness. As discussed in the section on visual observations, the Josephinite electrode surfaces used in these experiments were noted to have highly heterogeneous features with non-symmetric geometry, particularly when compared to the manufactured Nickel 200 and E-NiFe specimens. Sagues 42 and McKubre have suggested that significant error may be present in the impedance results due to this depression effect. It is suspected that these conditions may be resulting in a significant overestimation of corrosion rate for the Josephinite specimens. 36

PAGE 46

The Josephinite specimens exhibited similar general trends as the Nickel 200 and E-NiFe. Namely, that the corrosion rates in low pH solutions were several orders of magnitude higher than at higher pH solutions. The demarkation between higher and lower rates occurred at different pH with an apparent dependence on the nickel content. The occurrence of higher corrosion rates versus pH appeared to follow the inverse of the nickel content; that is, the higher the nickel content, the lower the pH where passive behavior was observed. The relationship is shown graphically in Figure 42. Nickel 200 appears to be actively corroding in the pH 4 solution, while the material appears to demonstrate passive behavior from pH 6 to pH 12. For Josephinite with approximately 70% nickel, the specimens were active in pH 5, but appeared to be passive in pH 6 to pH 9. For the E-NiFe electrode with approximately 55% nickel, the specimens were active in pH 6, but appeared to be passive in pH 7 to pH 10. 37

PAGE 47

9. EXPERIMENTAL POTENTIAL/PH DIAGRAM Figure 43 shows the values of the open circuit potentials and primary passive potentials (Epp) obtained from the series of polarization scans conducted on Nickel 200 specimens immersed in various buffered pH solutions. The Epp values were taken as the measured potential at the point of peak current density, indicating the onset of passive behavior. In cases where two peak current density values were present, such as seen for Nickel 200 in pH 6 solution (Figure 27), the more noble potential was taken as the Epp value. Figure 43 shows the Epp values obtained from these experiments overlaid on the experimental nickel potential-pH diagram from Pourbaix for comparison showing good agreement. This comparison provided confidence that the technique could provide results corresponding to other researchers and could reasonably delineate areas of active and passive behavior. As indicated by the measured open circuit potentials, the experimental potential-pH diagram for Nickel 200 as shown in Figure 43 suggests that a Nickel 200 specimen will be actively corroding in pH 4 but passive in pH 5 through 12 under the test conditions. The results are in agreement with estimated corrosion rates from EIS presented in Figure 41. This figure shows a marked decrease in the estimated corrosion rates as pH changes from 4 to 5. In a similar manner as used for Nickel 200, values of the open circuit potentials and primary passive potential (Epp) from the E-NiFe specimens were plotted in Figure 44. This experimental potential-pH diagram includes the experimental diagram for nickel 38

PAGE 48

from Pourbaix for reference. The diagram suggests that the E-NiFe specimens were actively corroding in pH 6, but passive in pH 7 through 12. This is in agreement with the estimated corrosion rates shown in Figure 41, which shows a high rate of corrosion in pH 6, but substantially lower rates in the higher pH solutions. Values of the open circuit potentials and primary passive potential (Epp) from the Josephinite specimens were plotted in Figure 45. This potential-pH diagram includes the experimental diagram for nickel from Pourbaix for reference. The diagram suggests that the Josephinite specimens were actively corroding in pH 5, but passive in pH 6 through 9. This is in agreement with the estimated corrosion rates shown in Figure 41, which shows a high rate of corrosion in pH 5, but substantially lower rates in the higher pH solutions. A range of pH from 6 to 9 has been previously identified for natural waters in the geographic region where Josephinite specimens are found in southwest Oregon. The results of this project indicate that the Josephinite metallic material displays passive behavior in the controlled, buffered, aqueous solutions under oxidizing conditions used in these experiments and therefore may be a useful natural analogue material representing long term passive behavior. 39

PAGE 49

10. CONCLUSIONS The experimental results indicate that the Nickel 200, and E-NiFe specimens tested exist in the passive state in the tested naturally aerated, buffered solutions of various pH equal to or greater than approximately 5 for Nickel 200 and 7 for the E-NiFe specimens tested. Potentiodynamic polarization, open circuit potential measurements and EIS methods have tended to confirm this behavior. The behavior of the Josephinite specimens showed similar trends with passive behavior indicated for the tested pH 6 and greater solutions. Information on the pH of natural waters in areas surrounding the Josephinite deposits suggests that passive behavior may be expected in the native waters. Within the range of pH 6 to 9, the open circuit potential achieved by the Josephinite specimens indicates significant anodic polarization takes place in the tested solutions. The measured open circuit potentials place the behavior in the corrosion prone area of the theoretical potential-pH diagram by Pourbaix for both nickel and iron. Despite the anodic polarization and the thermodynamic tendency for the primary constituent materials of nickel and iron to corrode, the metalic Josephinite displays a substantial resistance to corrosion as indicated by the EIS results. This shows substantial conformance to the definitions of passive behavior presented by Uhlig 27 The estimated corrosion rates from EIS measurements for the Josephinite were less consistent than for the Nickel 200 and the E-NiFe electrode specimens. True surface area, non-homogeneous electrode surfaces, non-uniform geometry, as well as 40

PAGE 50

interactions between the inclusions and crevices are considered possible sources of some of the inconsistencies. Potential-pH diagrams were constructed using the results from potentiodynamic polarization techniques, and measured open circuit potentials with the materials tested. The potential-pH diagram produced for Nickel 200 was similar to that produced by other researchers. The potential-pH diagrams resulting from these tests show a more restrictive zone of active corrosion for the E-NiFe specimens than the experimental diagram for nickel produced by Pourbaix. The experimental diagrams produced for nickel were similar to the theoretical zone shown by Pourbaix and others 23, 6 in the regions of corrosion behavior. Measurement of open circuit potential alone is not adequate to differentiate between active and passive behavior. EIS measurements in conjunction with the OCP were more accurate at defining the regions of behavior. The OCP achieved by the E-NiFe electrode and the Josephinite specimens under what appeared to be corroding conditions where a visible corrosion product formed, placed the behavior in the passive regions of the respective experimental potential-pH diagrams. Despite the OCP, EIS results indicated that a high rate of corrosion was being experienced by the specimens. A significant feature noted in review of the corrosion rates was the marked decrease in rate for Nickel 200 as the solution pH changed from 4 to 5, for Josephinite from pH 5 to 6, and for the E-NiFe electrode from pH 6 to 7. The marked decrease provides an indication of the onset of passive behavior in the higher pH solutions. As reported 41

PAGE 51

previously, aqueous solutions with pH from approximately 6 to 9 have been reported in the vicinity of Josephine County. This suggests that passive behavior may be expected from Josephinite under field exposure conditions. 42

PAGE 52

11. RECOMMENDED ADDITIONAL WORK Additional analyses to better characterize the metallurgical structure of the Josephinite material. Etching characteristics in some areas were very different from the Nickel 200 and the E-NiFe alloys tested. Some specimens were heavily banded when etched. Judging by composition alone, the effects of etching was expected to have produced features similar to the Nickel 200 and E-NiFe specimens. SEM work at higher resolutions than used in the optical microscopy employed and additional EDS analysis traversing the banded areas is recommended. Continue measurement of the open circuit corrosion potential and corrosion rates over longer periods of time. Work by Sagues and Li 37 indicates that the corrosion rate may be expected to decrease over time. This information may be useful in demonstrating long life of Josephinite specimens. Perform potentiodynamic scans and open circuit potential measurements on additional specimens of Josephinite in buffered solutions of pH 5 to 9 to obtain a better representation of the available nuggets. Additional work is recommended to isolate the cavities and inclusions in the Josephinite specimens from areas of the metallic surface and obtain a more homogenous electrode. Removal of the inclusion areas, or isolating them by coating are two possibilities, as well as restricting the exposed surface to perhaps a circular area. Another route would be to prepare the Nickel 200 and the E-NiFe specimens as planer electrode surface in lieu of 43

PAGE 53

the cylindrical ones utilized. This should act to minimize the differences between the specimens due to geometric factors. These would remove the possible effect of these conditions on the metallic corrosion rate estimates by EIS and provide a better measure of the corrosion rate by removing possible significant errors due to these factors. Perform similar experiments using aqueous specimens from the area of Josephine deposits in southwest Oregon. These waters are reported to have higher resistivity than the buffered solutions used in these experiments. Other ionic species, such as chlorides are likely present in the natural waters, which may affect the results. Perform elemental analysis of the corrosion product observed on the Josephinite and the E-NiFe electrode specimens in pH 5 and 6 respectively to identify the primary constituents. Testing for elements such as nickel and iron as metallic elements and sodium, potassium, and phosphate as elements from the buffer solutions used in testing. 44

PAGE 54

REFERENCES 1 Sagues, A.A, Nuclear Waste Package Corrosion Behavior in the Proposed Yucca Mountain Repository, University of South Florida, Draft -October. 1998 2 U.S. Nuclear Waste Technical Review Board, Report to the U.S. Congress and the U.S. Secretary of Energy, November, 1999 3 Johnson Jr. A.B., Francis, B., Durability of Metals from Archeological Objects, Metal Meteorites, and Native Metals, Pacific Northwest Laboratory, Prepared for U.S. Department of Energy under Contract DE-AC06-76RLO 1830, September 1980 4 McNeil, M.B. Moody, J.B., Corrosion Model Validation in High Level Nuclear Waste Package Research, Materials Research Society Symposium Proceedings, Volume 294, Materials Research Society, 1993 5 Verink, Elias, Application of Electrochemical Techniques in the Development of Alloys, Electrochemical Techniques for Corrosion Engineering, NACE, 1978, ed. R. Baboian 6 Pourbaix, M., Atlas of Electrochemical Equilibria, National Association of Corrosion Engineers, Houston, TX, 1986 7 Standard Reference Test Method for making Potentiostatic and Potentiodynamic Anodic Polarization Measurements, ASTM G5 8 Hyndman, Donald, W. Petrology of Igneaus and Metamorphic Rocks, McGraw-Hill, 1972 9 Botto, Robert, and Morrison, George, Josephinite: A unique Nickel Iron, American Journal of Science, Volume 26, March 1976, p. 241-274 10 Dick, Henry, Terrestrial Nickel-Iron from the Josephinite Peridotite, Its Geologic Occurrence, Associations, and Origins, Earth and Planetary Science Letters, 24 1974, p. 291-298 11 Basset, et al, Josephinite: Crystal Structures and Phase Relations of the Metals, Physics of the Earth and Planetary Interiors,, 23, 1980, p. 225-261 12 Bird, John, et al, Widmanstatten Patterns in Josephinite, a Metal Bearing Terrestrial Rock, Science, Vol. 206, 16 November 1979, p. 832-834 45

PAGE 55

13 Reference Design Description for a Geologic Repository, Revision 2, January 1999, Civilian Radioactive Waste Management System 14 Fontana, Mars, Corrosion Engineering, McGraw Hill, Third Edition, 1986 15 Jones, D. Principals and Prevention of Corrosion, Prentice Hall, Second Edition, 1996 16 MacDonald, D. D., et al, SALI Analysis of Passive Films On Nickel Alloys, Corrosion Science, 1990 17 Graham, M.J., The Application of Surface Techniques in Understanding Corrosion Phenomena and Mechanisms, Corrosion Science, Vol 37, No 9, 1377 1397, 1995 18 Macdougal, B., et al, The Use of Electrochemical and Surface Analytical Techniques to Characterize Passive Oxide Films on Nickel, Corrosion, Vol. 28, No. 2, February 1982 19 Hummel, R. E., Verink, E. D., Smith, R. J., The Passivation of Nickel in Aqueous Solutions 1. The Identification of Insoluble Corrosion Products on Nickel Electrodes Using Optical and ESCA Techniques, Corrosion Science, Vol. 27, No. 8, 803-813, 1987 20 MacDonald, D. D, The Point Defect Model for the Passive State, Journal Electrochemical Society, Vol. 139, No. 12, December 1992 21 Robbiola, L., Blengino, J. M., Fiaud, C., Morphology and Mechanisms of Natural Patinas on Archaeological Cu-Sn Alloys, Corrosion Science, Vol. 40, No. 12, pp. 2083 2111, 1998 22 Friend, Wayne, Z., Corrosion of Nickel and Nickel Base Alloys, John Wiley and Sons, 1980 23 Silverman, David C., Revised EMF-pH Diagram for Nickel, Corrosion, Volume 37, No. 9, pp. 546-548, September 1981 24 J.R. Scully, Electrochemical Methods for Laboratory Corrosion Testing, ASTM STP-1000, edited by R. Baboian and S. Dean, 1990. p. 361 25 DiBella, Carl, Memorandum to participants in International Workshop on Long-Term Extrapolation of Passive Behavior, Background information on Waste Package Environment, June 9, 2001 26 Reference Design Description for a Geologic Repository, TDR-MGR-SE-000008-Rev 03 ICN 01, available at: http://www.ymp.gov/documents/seda06m3_b/main.htm 27 Uhlig, H, Corrosion and Corrosion Control, John Wiley and Sons, 1985 46

PAGE 56

28 Sagues, Alberto and DiBella, Carlos, EDS. Proceedings from An International Workshop on Long-Term Extrapolation of Passive Behavior, July 19-20, 2001 29 Leavell, Damiel, The Origin of Metal Alloys in the Alpine-type Peridotites, The Josephinite Example, Ohio Journal of Science, Volume 83 Number 2, 1983 30 Silverman, D.C., Carrico, J.E., Electrochemical Impedance Technique A Practical Tool for Corrosion Prediction, Corrosion, Volume 44, No. 5, May 1988 31 Kern, Raymond and Weisbrod, Alain, Thermodynamics for Geologists, Freeman, Cooper & Company, 1967 32 ASM Metals Handbook, Desk Edition, Metallography, Edited by Howard Boyer and Timothy Gall, 1985 33 Carter, G.F., Principles of Physical and Chemical Metallurgy, American Society for Metals, 1979 34 Wolfe, Victor, D., Macnab, Stephen, H., Corrugated Metal Pipe Comparison Study, Report Number ODOT Official Publication 76-3, Oregon Department of Transportation, July 1976 35 Private Communication, Chris Anderson of the Illinois Valley Soil and Water Conservation District, District covers Josephine County, Oregon 36 Bockris, John, Reddy, Amulya, Modern Electrochemistry, Second Edition, Kluwer Academic/Plenum Publishers, 2000 37 Sagues, A., Li, Lienfang, Metallurgical Effects on Chloride Ion Corrosion Threshold of Steel in Concrete, Report to Florida Department of Transportation, 2001 38 CRC Handbook of Chemistry and Physics, 54 th Edition, 1973, Chemical Rubber Company 39 ASM Metals Handbook, Volume 7, Atlas of Microstructures, 8 th Edition, American Society for Metals 40 ASM Metals Handbook, Volume 11, Failure Analysis and Prevention, 9 th Edition, American Society for Metals 41 Bird, J.M. and Weathers, M.S., Origin of Josephinite, Geochemical Journal, Vol. 13, 1979 42 Sagues, A.A., Kranc, S.C., Moreno, E.I., The Time Domain Response of a Corroding System With Constant Phase Angle Interfacial Component: Application to Steel in Concrete, Corrosion Science, Vol. 37, No. 7, 1995 43 McKubre, Michael, C.H., Techniques for AC impedance Measurements in Corrosion Systems, Paper 480 presented at NACE Corrosion, March, 1987 47

PAGE 57

44 Sagues, A.A, Corrosion Performance Projection of Yucca Mountain Waste Packages, Material Research Society Symposium Proceedings, Volume 713, 2002 45 Sridhar, N., Cragnolino, G., Evaluation of Analogs For The Performance Assessment of High Level Waste Container Material, Center for Nuclear Waste Regulatory Analysis for U.S. Nuclear Regulatory Commission Contact NRC-02-97-009, March 2002 48

PAGE 58

Table 1 Elemental analysis of tested modern specimens Specimen Ni Fe Mn Si Cu C Ti Cr Sulfur Nickel 200 99.69 0.01 0.21 0.05 0.03 0.01 0.003 AWS A5.15, E-NiFe 55.25 44.07 0.45 0.05 0.04 0.06 0.25 0.01 0.002 not reported, data from mill test reports Table 2 Test matrix of specimens Test pH Nickel 200 ENiFe Josephinite Specimen S Josephinite Specimen M Josephinite Specimen L* Visual N/A X X X X X Metallographic N/A X X X X X Elemental Analysis N/A X X X X X 4 X X 6 X X X 7 X X 8 X X 9 X X X X 10 X X Potentiodynamic Polarization 12 X X 4 X X 5 X X X X 6 X X X X 7 X X 8 X X X 9 X Corrosion Potential 10 X X 4 X 5 X X X 6 X X X X 7 X X X X X 8 X X 9 X X Electrochemical Impedance Spectroscopy 10 X X *Josephinite Specimen L was divided into two sections for corrosion testing, L1 and L2 49

PAGE 59

Table 3 Buffered solutions used in testing pH Buffered Solution 4 500 ml of 0.1 molar Potassium Hydrogen Phthalate (KH 6 C 8 H 4 O 4 ) and 13 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume 5 500 ml of 0.1 molar Potassium Hydrogen Phthalate (KH 6 C 8 H 4 O 4 ) and 226 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume 6 500 ml of 0.1 molar Potassium Phosphate Monobasic (KH 2 PO 4 )and 56 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume 7 500 ml of 0.1 molar Potassium Phosphate Monobasic (KH 2 PO 4 )and 294 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume 8 500 ml of 0.1 molar Potassium Phosphate Monobasic (KH 2 PO 4 )and 467 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume 9 500 ml of 0.1 molar Sodium Borate (Na 2 B 4 O 7 ) and 9 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume 10 500 ml of 0.1 molar Sodium Borate (Na 2 B 4 O 7 ) and 183 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume 12 500 ml of 0.1 molar Sodium Phosphate Dibasic (Na 2 HPO 4 ) and 269 ml of 0.1 molar Sodium Hydroxide (NaOH) plus distilled water for 1 liter volume Solutions prepared and verified for pH using pH meter prior to use. Buffered solution mixtures are as published in the CRC Handbook. 38 Table 4 Resistivity of aqueous solutions pH Data Source Resistivity, /cm 5 Measured buffered solution 167 6.2 Reference 34, Oregon water 6,600 7 Measured buffered solution 146 8 Measured buffered solution 119 8.45 Reference 34, Oregon water 2,805 9 Measured buffered solution 505 7 to 8.91 Reference 35, Oregon waters in nearby counties 12 4.8 50

PAGE 60

Table 5 Elemental analysis of Josephinite specimens Location Ni Fe Mg Si Al Ca Cu Sulfur Metallic areas Specimen Exterior Metallic-Sm 67.79 30.16 0.85 0.5 0.56 0.13 Nd Metallic-Sm 71.37 27.48 0.45 0.46 0.16 0.08 Nd Metallic-Sm 71.31 27.9 0.17 0.31 Nd 0.23 0.08 Metallic-Sm 71.79 28.21 MetallicL 69.02 30.54 0.44 Metallic -M 73.77 26.23 Metallic -S 62.43 25.77 1.62 10.17 Metallic areas Specimen Interior Section-L 66.75 28.40 0.76 0.49 3.60 Section M 73.60 25.81 0.17 Section S 63.24 33.59 0.62 2.21 0.34 Literature 9 68.2 28.9 <0.02* <0.008* 0.21* 0.041* Section-L near copper 22.49 72.93 0.53 0.46 3.58 Section-L near copper 9.89 25.27 16.03 0.80 25.7 22.33 Section-L copper area 2.48 0.56 96.69 Dark areas Specimen Exterior Brown-Sm 8.98 13.97 33.13 42.70 0.49 0.46 0.26 Brown-Sm 5.77 15.59 35.02 43.29 0.33 Black-Sm 11.95 11.59 35.94 39.15 Nd 1.07 0.30 Black-Sm 5.07 8.17 40.68 45.8 Nd Nd 0.29 dark-L 2.99 8.76 34.43 51.00 1.29 1.52 Dark areas Specimen Interior Section-L 19.29 30.56 16.48 26.92 6.75 Section-L 41.43 31.09 4.26 5.72 17.5 Section-M 20.5 13.87 33.22 32.41 Literature 8 12.35 34.02 43.5 3.99 3.46 Nd (not detected), (not reported), (reported as oxide) Sm Smithsonian specimen, L, M, S Commercial specimens 51

PAGE 61

Table 6 Slopes from potentiodynamic polarization Specimen pH Value Slope, volts/decade 4 bc 0.15 6 bc 0.22 8 bc 0.17 Nickel 200 12 bc 0.14 Nickel 200 Average bc 0.17 Nickel 200 4 ba 0.19 Nickel 200 Average ba 0.19 8 bc 0.19 10 bc 0.14 E-NiFe 12 bc 0.11 E-NiFe Average bc 0.15 4 ba 0.07 E-NiFe 6 ba 0.09 E-NiFe Average ba 0.08 bc 0.16 Nickel 200 and E-NiFe group average ba 0.14 bc 0.1 Nominal values suggested by Jones 15 ba 0.1 Composite Tafel Parameter using nominal values suggested by Jones B = ba bc____ __= 0.022 (2.303)(ba + bc) 52

PAGE 62

Table 7 Summary of potentiodynamic polarization test results Solution Scan Rate, mV/sec Epp, volts SHE Ipeak, Amps/cm 2 Ipass, Amps/cm 2 Nickel 200 pH4 0.167 0.156 3.48E-5 1.40E-6 pH4 0.778 0.166 5.10E-5 4.70E-6 pH4 0.167 0.271 2.97E-5 4.50E-6 pH6 0.167 0.186 6.29E-6 1.31E-6 pH6 0.778 0.144 1.50E-5 4.26E-6 pH6 0.167 0.141 3.95E-6 1.07E-6 pH8 0.167 -0.114 6.87E-6 1.46E-6 pH8 0.778 -0.08 1.37E-5 5.53E-6 pH8 0.778 -0.08 1.56E-5 5.50E-6 pH9 0.167 -0.244 1.03E-6 9.77E-7 pH9 0.778 -0.285 5.95E-6 3.54E-6 pH10 0.167 -0.029 1.13E-6 9.88E-7 pH10 0.778 -0.155 1.96E-6 1.57E-6 pH10 0.167 -0.009 4.90E-7 4.33E-7 pH10 0.167 -0.064 1.97E-6 9.01E-7 pH12 0.167 -0.294 1.27E-6 7.46E-7 pH12 0.778 -0.238 4.80E-6 3.21E-6 E-NiFe pH4 0.778 0.0113 1.23E-5 3.30E-6 pH4 0.167 0.21 4.88E-6 8.40E-7 pH4 0.167 0.251 5.43E-7 8.43E-7 pH6 0.778 -0.113 2.44E-4 3.09E-6 pH6 0.167 -0.129 2.35E-4 5.5E-7 pH8 0.778 -0.225 4.93E-5 2.80E-5 pH8 0.167 -0.254 4.22E-5 8.10E-7 pH8 0.167 -0.239 1.72E-5 8.15E-7 pH9 0.167 -0.169 1.13E-6 7.44E-7 pH9 0.778 -0.166 4.28E-6 3.00E-6 pH10 0.778 -0.358 4.32E-5 2.97E-5 pH10 0.167 -0.214 1.43E-6 1.13E-6 pH12 0.167 0.138 9.9E-7 8.33E-7 Josephinite pH6, m 0.167 -0.105 6.90E-5 3.44E-6 pH6, L1 0.167 -0.104 1.23E-4 1.51E-5 pH7, m 0.167 -0.169 2.99E-5 2.66E-6 pH7, L1 0.167 -0.144 2.91E-5 7.33E-6 pH9, m 0.167 0.0233 6.96E-6 4.92E-6 pH9, L1 0.167 0.087 3.63E-6 2.72E-6 53

PAGE 63

Table 8 Summary of EIS test and modeling results Solution Hours exposure OCP vs SCE, volts Rp, Rp, -cm2 Ru, Rc, F Alpha Estimated corrosion rate, m/year Nickel 200 pH4 48 -0.09 1.45E4 6.96E4 7 8700 0.77 3.41E0 pH5 504 0.017 9.5E5 4.56E6 10 8500 0.85 5.20E-2 pH6 100 -0.016 5.1E5 2.45E6 7 5100 0.87 9.69E-2 pH6 360 0.003 7E5 3.36E6 8 4700 0.93 7.06E-2 pH8 192 -0.029 1E6 4.8E6 4 5700 0.91 4.94E-2 pH10 96 -0.070 2E6 9.6E6 7 7800 0.9 2.47E-2 E-NiFe pH6 137 -0.49 1.5E3 6.15E3 29 1176 0.80 3.86E1 pH6 213 -0.018 4E3 1.64E4 7 1176 0.80 1.45E1 pH7 504 -0.012 4E6 1.64E7 4 7300 0.92 1.45E-2 pH8 234 -0.061 5.15E6 2.11E7 4 12000 0.92 1.12E-2 pH10 131 -0.104 8E6 3.28E7 7 12000 0.89 7.23E-3 pH10 560 -0.034 2.55E7 1.04E8 7 9000 0.97 9.31E-3 Josephinite Specimen S pH5 216 -0.342 5.8E3 1.64E3 93 480 0.55 1.45E2 pH6 120 -0.029 4.6E4 1.3E4 21 6500 0.44 1.82E1 pH7 95 -0.003 4.4E4 1.25E4 70 752 0.61 1.91E1 pH7 123 0.004 4.9E4 1.39E4 76 759 0.57 1.71E1 pH7 144 0.013 5.8E4 1.64E4 72 450 0.56 1.45E1 pH7 168 0.026 6.3E4 1.78E4 65 851 0.57 1.33E1 pH7 240 0.044 6.9E4 1.95E4 65 1000 0.6 1.22E1 pH7 318 0.041 7.5E4 2.12E4 65 1000 0.61 1.12E1 pH7 960 0.041 1.1E4 3.11E4 65 1100 0.63 7.62E0 pH9 264 -0.02 3E5 8.49E4 45 11700 0.42 2.79E0 Josephinite Specimen L1 pH5 120 -0.358 9E3 2.56E3 108 650 0.73 1.29E2 pH5 342 -0.308 6.5E3 1.85E3 100 100 0.70 9.28E1 pH7 117 0.09 2.9E5 8.24E4 70 861 0.65 2.88E0 pH7 141 0.91 3.3E5 9.37E4 65 700 0.63 2.53E0 pH7 168 0.93 3.7E5 1.05E5 65 800 0.6 2.26E0 pH7 240 0.96 1E6 2.84E5 70 800 0.62 8.35E-1 pH7 288 0.89 1.1E6 3.12E5 60 800 0.61 7.60E-1 pH7 1008 0.48 5E6 1.42E6 56 1700 0.57 1.67E-1 pH9 120 -0.14 1.1E6 3.12E5 70 54000 0.79 7.60E-1 pH9 316 -0.277 1.1E5 3.12E4 286 6000 0.83 7.60E0 Josephinite Specimen M pH6 120 0.058 8E5 6.86E5 50 41000 0.43 4.26E-1 pH6 318 0.043 6.5E5 5.57E5 63 14000 0.44 3.46E-1 pH7 120 0.026 1.5E6 1.29E6 25 25000 0.41 1.85E-1 54

PAGE 64

Figure 1 Geographic distribution of Nuclear Waste needing long-term storage 26 Figure 2 DOE projected flow of Nuclear Waste to disposal site 26 55

PAGE 65

Figure 3 Reference design waste package 26 Figure 4 Reference design natural barrier system 26 56

PAGE 66

Figure 5 Reference design for engineered barrier system 26 log Current Density(-) Potential (+) TranspassivePassiveActiveCorrosion EppIcritIpassMMn+ + neFigure 6 Typical potentiodynamic polarization curve 57

PAGE 67

Theoretical Potential/pH Diagram, Nickel-1-0.8-0.6-0.4-0.200.20.40.60.811.21.401234567891011121314pHPotential, (SHE ) O2 Stability H2 Stability Theoretical line from Pourbaix 6CORROSIONPASSIVEIMMUNE Figure 7 Theoretical potential-pH diagram for nickel, from Pourbaix 6 58

PAGE 68

Experimental Potential/pH Diagram, Nickel-1-0.8-0.6-0.4-0.200.20.40.60.811.21.401234567891011121314pHPotential, (SHE ) O2 Stability H2 Stability Experimental line from Pourbaix 6 PASSIVECORROSIONIMMUNE Figure 8 Experimental potential-pH diagram for nickel, from Pourbaix 6 59

PAGE 69

60 10 GAGE INSULATED COPPER WIRE1st LAYER EPOXYKEYDRILL AND TAP FOR 3-38 THREADVIEW A1. EMBED JOSEPHINITE SAMPLE IN EPOXY.2. DRILL AND TAP INTO JOSEPHINITE SAMPLE FOR 3-38 THREADS.3. INSERT THREADED END OF COPPER WIRE WITH SOME INSULATION REMOVED.1st LAYER EPOXY2nd LAYER EPOXY4. COVER EXPOSED COPPER WIRE TO SOUND INSULATION WITH 2nd LAYER EPOXY.5. CHECK FOR ELECTRICAL CONTINUITY BETWEEN EXPOSED JOSEPHINITE FACE AND OPPOSITE END OF COPPER WIRE.JOSEPHINITE SAMPLE MOUNTED IN EPOXYJOSEPHINITE WORKING ELECTRODESEE VIEW A Figure 9 Schematic of mounting for Josephinite corrosion specimens

PAGE 70

61 Figure 10 Corrosion specimen mounting. E-NiFe at top left, Nickel 200 at top right, Josephinite at bottom

PAGE 71

62 Figure 11 Test circuit used for verification of EIS instrumentation. Modeling results are shown in the three top graphs and consisted of three representative variables: Rs Solution Resistance, ohms; Rp Polarization Resistance, ohms; Rc Interface Capacitance, farads F i 1 1 T t i i t d f i f i t i f E I S i t t t i Rs = 989 ohm resistormodel as 996.6 ohmRp =852 k ohm resistormodel as 852 k ohm Ru = 100 miFro farad capacitormodel as 110 micro Farad 2.003.004.005.006.00-4.00-2.000.002.004.006.00Log Frequency, Hz Cell Response Model -100.00-80.00-60.00-40.00-20.000.00-4.00-2.000.002.004.006.00Log Frequency, HzPhase Angle, Degrees Cell Response Model 0.E+001.E+052.E+053.E+054.E+055.E+050.E+001.E+052.E+053.E+054.E+055.E+05Real, OhmsImaginary, Ohm s Cell Response Model

PAGE 72

Figure 12 Smithsonian Josephinite specimen, scale in inches Figure 13 Commercial Josephinite specimen, scale in inches 63

PAGE 73

Figure 14 Scratches on exterior metallic portion of Smithsonian Josephinite specimen. 25x. Scale at lower right is 10m/division Figure 15 Scratches on exterior metallic portion of commercial Josephinite specimen. 25x. Scale at lower right is 10m/division 64

PAGE 74

Figure 16 Cross sections of commercial specimens, M, L, S, top to bottom. Arrow points to dark area seen at center of Figure 20. Scale at bottom is 1mm/division Figure 16 Cross sections of commercial specimens, M, L, S, top to bottom. Arrow points to dark area seen at center of Figure 20. Scale at bottom is 1mm/division Figure 17 Copper inclusions in specimen L, unetched. 25x. Scale at lower right is 10m/division Figure 17 Copper inclusions in specimen L, unetched. 25x. Scale at lower right is 10m/division 65 65

PAGE 75

Figure 18 Nickel 200 specimen microstructure, Marbles reagent, 250x. Scale at lower right is 10m/division Figure 19 E-NiFe electrode specimen microstructure, Marbles reagent, 250x. Scale at lower right is 10m/division 66

PAGE 76

Figure 20 Specimen L etched in Marbles reagent. Large inclusion at center, numerous copper inclusions visible. 6.25x. Arrow is area magnified in Figure 16. Scale at lower right is 1mm/division Figure 20 Specimen L etched in Marbles reagent. Large inclusion at center, numerous copper inclusions visible. 6.25x. Arrow is area magnified in Figure 16. Scale at lower right is 1mm/division Figure 21 Specimen L magnified from arrow area of Figure 20. 100x. Arrow is area magnified in Figure 19. Scale at lower right is 10m/division Figure 21 Specimen L magnified from arrow area of Figure 20. 100x. Arrow is area magnified in Figure 19. Scale at lower right is 10m/division 67 67

PAGE 77

Figure 22 Specimen L magnified view of arrow area from Figure 21. 250x. Scale at lower right is 10m/division Figure 23 Specimen L, microstructure of additional area. 250x. Scale at lower right is 10m/division 68

PAGE 78

Figure 24 Specimen M microstructure. 250x. Scale at lower right is 10m/division Figure 25 Specimen L etching revealed banding features. 25x. Scale at lower right is 10m/division 69

PAGE 79

Figure 26 Specimen L showing banding at copper inclusion. 250x. Scale at lower right is 10m/division 70

PAGE 80

71 Ni Potentiodynamic Polarization Scans, 0.167mV/sec-1.5-1.0-0.50.00.51.01.51.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-02Current Density (A/cm2)Potential vs. SHE pH4 Ni pH6 Ni pH8 Ni pH10 Ni pH12 Ni Figure 27 Typical potentiodynamic polarization scans of Nickel 200 specimens

PAGE 81

72 NiFe Potentiodynamic Polarization Scans, 0.167mV/sec-1.5-1.0-0.50.00.51.01.51.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-02Current Density (A/cm2)Potential vs. SHE pH4 NiFe pH6 NiFe pH8 NiFe pH9 NiFe pH10 NiFe pH12 NiFe Figure 28 Typical potentiodynamic polarization scans for E-NiFe electrode specimens

PAGE 82

73 Josephinite Buffered Polarization Scans, 0.167mV/sec-1.5-1.0-0.50.00.51.01.51.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-02Current Density (A/cm2)Potential vs. SHE pH6 Joseph M pH6 Joseph L1 pH7 Joseph M pH7 Joseph L1 pH9 joseph M pH9 Joseph L1 Figure 29 Typical potentiodynamic polarization scans for Josephinite specimens

PAGE 83

74 0.0E Current Density, E-NiFey = 1.614e-1.4339xR2 = 0.85870.0E+001.0E-042.0E-043.0E-044.0E-045.0E-045678910Solution pHCurrent Density, (Amps/cm2) ENiFe Passive CurrentDensity ENiFe Peak CurrentDensity Peak Current DensityCurve Fit Passive Current DensityCurve Fit Current Density, Josephinitey = 0.0268e-0.9574xR2 = 0.95360.0E+002.0E-054.0E-056.0E-058.0E-051.0E-041.2E-041.4E-045678910Solution pHCurrent Density, (Amps/cm2) Josephinite Passive CurrentDensity Josephinite Peak CurrentDensity Passive Current Density CurveFit Peak Current Density CurveFit Current Density, Niy = -2E-07x + 3E-06R2 = 0.4033y = 0.0003e-0.5898xR2 = 0.8513+001.0E-052.0E-053.0E-054.0E-055.0E-05345678910Solution pHCurrent Density, (Amps/cm2) Ni Passive CurDes Ni Peak CurDens Passive Current DensityCurve Fit Peak Current DensityCurve Fit Figure 30 Peak and passive current densities for: Top Nickel 200, Center E-NiFe, Bottom Josephinite Specimens

PAGE 84

75 -0.3-0.2-0.10.00.10.20.30.40100200300400500600700Time, hoursPotential, SHE NipH4 NipH5 NipH6 NipH8 NipH10 -0.3-0.2-0.10.00.10.20.30.40.11101001000Time, hoursPotential, SHE NipH4 NipH5 NipH6 NipH8 NipH10 Figure 31 Open circuit corrosion potential for Nickel 200 specimens, Top linear time scale, Bottom logarithmic time scale

PAGE 85

76 -0.3-0.2-0.100.10.20.30.40200400600800100012001400Time, hoursPotential, SHE CP2 NiFe pH6 CP3 NiFe pH6 NiFepH7 NiFepH8 NiFepH10 N i cke l I r o n Open Ci rc ui t P o t ent i a l -0.3-0.2-0.100.10.20.30.40.11101001000Time, hoursPotential, SHE CP2 NiFe pH6 CP3 NiFe pH6 NiFepH8 NiFepH10 NiFepH7 Figure 32 Open circuit corrosion potential for E-NiFe electrode specimens, Top linear time scale, Bottom logarithmic time scale

PAGE 86

-0.3-0.2-0.100.10.20.30.40.11101001000Time, hoursPotential, SH E pH5, L1 pH5, S pH6, M pH6, S pH7, S pH7, S(2) pH7, L1 pH8, M pH9, S -0.3-0.2-0.100.10.20.30.40.1110100100010000Time, hoursPotential, SHE pH5, L1 pH5, S pH6, M pH6, S pH7, S pH7, S(2) pH7, L1 pH8, M pH9, S Figure 33 Open circuit corrosion potential for Josephinite specimens. Note the marked difference between the specimens in pH5 and the other solutions. Top linear time scale, Bottom logarithmic time scale 77

PAGE 87

78 RsCPERpRcAlpha Figure 43 Randles circuit used for modeling EIS behavior. Model consists of four variables: Rs Solution resistance, ohms Rp Polarization resistance, ohms Rc Interface capacitance, Farads Alpha factor for non-ideal interface capacitance

PAGE 88

79 Nickel0.E+001.E+062.E+063.E+064.E+065.E+066.E+067.E+068.E+069.E+061.E+070.E+001.E+062.E+063.E+064.E+065.E+066.E+067.E+068.E+069.E+061.E+07Z Real, ohm-cm2Z Imaginary, ohm-cm2 Ni pH4 48 hour Ni pH6 100 hour Ni pH6 360 hour Ni pH8 192 hour Ni pH10 96 hour NipH4 48 hour model NipH6 100 hour model NipH6 360 hour model NipH8 192 hour model NipH10 96 hour model0.15mHz0.23mHz0.1mHz Figure 35 Nyquist diagram for Nickel 200 specimens in various pH solutions, typical EIS plots and curves used for modeling shown

PAGE 89

80 Nickel Iron0.E+001.E+062.E+063.E+064.E+065.E+066.E+067.E+068.E+069.E+061.E+070.E+001.E+062.E+063.E+064.E+065.E+066.E+067.E+068.E+069.E+061.E+07Z Real, ohm-cm2Z Imaginary, ohm-cm2 NiFe pH6 144 hour NiFe pH6 216 hour NiFe pH7 504 hour NiFe pH8 240 hour NiFe pH10 144 hour NiFe pH10 552 hour NiFe pH7 504 hour model NiFe pH8 240 hour model NiFe pH10 144 hour model NiFe pH10 552 hour model0.23mHz0.1mHz 0.23 mHz, pH6 1mHz0.5mHz Figure 36 Nyquist diagram for E-NiFe electrode specimens in various pH solutions, typical EIS plots shown

PAGE 90

81 pH 7 EIS Sample L10.E+001.E+032.E+033.E+034.E+035.E+036.E+037.E+038.E+030.E+001.E+032.E+033.E+034.E+035.E+036.E+037.E+038.E+03Z real (ohm-cm2)Z Imag (ohm-cm2) 117 hours 117 hours model 141 hours 141 hours model 168 hours 168 hours model 240 hours 240 hours model 288 hours 288 hours model 1008 hours 1008 hours model0.4 mHz Figure 37 Nyquist diagram for Josephinite specimen L1 in pH 7 solution

PAGE 91

82 Figure 38 Nyquist diagram for Josephinite specimen S in pH 7 solution pH 7 EIS Sample S0.E+001.E+032.E+033.E+034.E+035.E+036.E+037.E+038.E+030.E+001.E+032.E+033.E+034.E+035.E+036.E+037.E+038.E+03Z real (ohm-cm2)Z Imag (ohm-cm2) 95 hours 95 hours model 123 hours 123 hours model 144 hours 144 hours model 168 hours 168 hours model 240 hours 240 hours model 312 hours 312 hours model 960 hours 960 hours model

PAGE 92

83 Figure 39 Rp value over time for two specimens in pH7 buffered solution Rp value over time, pH7, Sample L10.E+001.E+062.E+063.E+064.E+065.E+066.E+06010020030040050060070080090010001100Time, hoursRp, ohms Rp value over time, pH7, Sample S0.E+002.E+044.E+046.E+048.E+041.E+051.E+05010020030040050060070080090010001100Time, hoursRp, ohms

PAGE 93

84 Figure 40 Top -Josephinite specimen M after 1,632 hours exposure in naturally aerated pH7 solution. Bottom Same specimen after approximately 10,512 hours

PAGE 94

85 Estimated Corrosion Rate by EIS, um/year1.0E-041.0E-031.0E-021.0E-011.0E+001.0E+011.0E+021.0E+03pH4pH5pH6pH7pH8pH9pH10 Ni NiFe Josephinite Figure 41 Estimated corrosion rate for Nickel 200, E-NiFe and Josephinite Specimens based on EIS measurements. Note Josephinite rates are average of at least two specimens

PAGE 95

86 Corrosion Behavior Dependence on Solution pH and Nickel Content02468101214020406080100Nickel ContentSolution pH Specimen Corroding Specimen Passive Passive Behavior Active Corrosion Figure 42 Corrosion behavior dependence on Nickel Content and Solution pH

PAGE 96

87 Figure 43 Experimental potential-pH diagram produced for Nickel 200 specimens Experimental Potential/pH Diagram, Nickel-1-0.8-0.6-0.4-0.200.20.40.60.811.21.401234567891011121314pHPotential, (SHE) Ni Epp Ni OCPNi Epp O2 Stability H2 Stability Experimental Line from Pourbaix 6 Approximate range of measured open circuit potentials in naturally aerated solutions in pH range 6 12PassiveCorrosion Inert Spontaneous Passivation

PAGE 97

88 Figure 44 Experimental potential-pH diagram for E-NiFe electrode specimens. Corrosion potential values for pH 6 specimens are prior to formation of dark film on specimen surfaces. After film formation, the corrosion potentials shifted to above the NiFe Epp line Potential/pH Diagram, E-NiFe-1-0.8-0.6-0.4-0.200.20.40.60.811.21.401234567891011121314pHPotential, (SHE) NiFe Epp NiFe OCPNiFe Epp O2 Stability H2 Stability Nickel Experimental Line from Pourbaix 6 Passive Corrosion Inert Approximate range of measured open circuit potentials in naturally aerated solutions, pH ran g e 7 12

PAGE 98

Potential/pH Diagram, Josephinite-1-0.8-0.6-0.4-0.200.20.40.60.811.21.401234567891011121314pHPotential, (SHE) Joseph Epp Joseph OCPO2 Stability H2 Stability Nickel Experimental Line from Pourbaix 6 A pproximate range of measured open circuit potentials in naturally areated solutions, p H ran g e 6 9 Josephinite Epp Figure 45Experimental potential-pH diagram for Josephinite specimens. Corrosion potential values for pH 5 specimen are prior to formation of dark film on specimen surfaces. After film formation, the corrosion potentials shifted to above the nickel passive/corrosion boundary line Passive Corrosion Inert 89

PAGE 99

APPENDICES 90

PAGE 100

Appendix A: Nickel 200 Potentiodynamic Polarization Results Nickel pH4 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH4 Ni 0.167 pH4 Ni 0.167 b p4 Ni 0.778O2 stabilityH2 stability Figure A1 Nickel 200 pH4 91

PAGE 101

Appendix A: (Continued) Nickel pH6 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH6 Ni 0.167 pH6 Ni Scan C 0.167 pH6 Ni 0.778 bO2 stabilityH2 stability Figure A2 Nickel 200 pH6 92

PAGE 102

Appendix A: (Continued) Nickel pH8 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH8 Ni 0.167 pH8 Ni 0.778 A pH8 Ni 0.778 BO2 stabilityH2 stability Figure A3 Nickel 200 pH8 93

PAGE 103

Appendix A: (Continued) -1.5-1.0-0.50.00.51.01.51.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-02Current Density (A/cm2)Potential vs. SH E pH9 Ni .167 mV/sec pH9 0.778 mV/secO2 stability H2 stability Figure A4 Nickel 200 pH9 94

PAGE 104

Appendix A: (Continued) Nickel pH10 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH10 Ni 0.167 pH10 0.167 e pH10 0.167q pH10 Ni 0.778H2 stabilityO2 Stability Linear (H2 stability) Linear (O2 Stability) Figure A5 Nickel 200 pH10 95

PAGE 105

Appendix A: (Continued) Nickel pH12 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH12 Ni 0.167 pH12 0.778O2 StabilityH2 stability Linear (O2 Stability) Linear (H2 stability)O2 stability H2 stability Figure A6 Nickel 200 pH12 96

PAGE 106

Appendix B: E-NiFe Potentiodynamic Polarization Results E-NiFe pH4 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH4 NiFe 0.167 b pH4 NiFe 0.167 c pH4 NiFe 0.778H2 stabilityO2 stability Figure B1 E-NiFe pH4 97

PAGE 107

Appendix B: (Continued) E-NiFe pH6 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH6 NiFe .167 a pH6 NiFe .778 Linear (H2 stability) Linear (O2 Stability) Figure B2 E-NiFe pH6 98

PAGE 108

Appendix B: (Continued) E-NiFe pH8 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH8 NiFe .167 a pH8 NiFe .167 b pH8 NiFe .778 Linear (O2 Stability) Linear (H2 stability) Figure B3 E-NiFe pH8 99

PAGE 109

Appendix B: (Continued) E-NiFe pH9 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH9 NiFe 0.167 pH9 NiFe 0.778O2 stability H2 stability Figure B4 E-NiFe pH9 100

PAGE 110

Appendix B: (Continued) E-NiFe pH10 Buffered Polarization Scan-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHE pH10NiFe .167 a pH10 NiFe .778 Linear (O2 Stability) Linear (H2 stability) Figure B5 E-NiFe pH10 101

PAGE 111

Appendix B: (Continued) E-NiFe pH12 Buffered Polarization Scan, 0.167mV/sec-1.5-1.0-0.50.00.51.01.51.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-02Current Density (A/cm2)Potential vs. SHEO2 stability H2 stability Figure B6 E-NiFe pH12 102

PAGE 112

Appendix C: Josephinite Potentiodynamic Polarization Results Josephinite Buffered Polarization Scans, 0.167mV/sec-1.5-1.0-0.50.00.51.01.51.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-02Current Density (A/cm2)Potential vs. SHE pH6 Joseph M pH7 Joseph M pH9 Joseph M pH6 Joseph L1 pH7 Joseph L1 pH9 Joseph L1 Figure C1 Josephinite pH 6, 7 and 9 103

PAGE 113

Appendix D: Nickel 200 EIS results Figure D1 Nickel 200, pH4, 48 hours 104

PAGE 114

Appendix D: (Continued) Figure D2 Nickel 200, pH5, 504 hours 105

PAGE 115

Appendix D: (Continued) Figure D3 Nickel 200, pH6, 100 hours 106

PAGE 116

Appendix D: (Continued) Figure D4 Nickel 200, pH6, 360 hours 107

PAGE 117

Appendix D: (Continued) Figure D5 Nickel 200, pH8, 192 hours 108

PAGE 118

Appendix D: (Continued) Figure D6 Nickel 200, pH10, 96 hours 109

PAGE 119

Appendix E: E-NiFe EIS Results Appendix E: E-NiFe EIS Results 110 Figure E1 E-NiFe pH6, 137 hours 110

PAGE 120

Appendix E: (Continued) Figure E2 E-NiFe, pH6, 213 hours 111

PAGE 121

Appendix E: (Continued) Figure E3 E-NiFe, pH7, 504 hours 112

PAGE 122

Appendix E: (Continued) Figure E4 E-NiFe. pH8, 234 hours 113

PAGE 123

Appendix E: (Continued) Figure E5 E-NiFe, pH10, 131 hours 114

PAGE 124

Appendix E: (Continued) Figure E6 E-NiFe, pH10, 560 hours 115

PAGE 125

Appendix F: Josephinite EIS Results Figure F1 Josephinite S, pH5, 216 hours 116

PAGE 126

Appendix F: (Continued) Figure F2 Josephinite S, pH6, 120 hours 117

PAGE 127

Appendix F: (Continued) 118 Figure F3 Josephinite S, pH7, 95 hours

PAGE 128

Appendix F: (Continued) 119 Figure F4 Josephinite S, pH7, 123 hours

PAGE 129

Appendix F: (Continued) 120 Figure F5 Josephinite S, pH7, 144 hours

PAGE 130

Appendix F: (Continued) 121 Figure F6 Josephinite S, pH7, 168 hours

PAGE 131

Appendix F: (Continued) 122 Figure F7 Josephinite S, pH7, 240 hours

PAGE 132

Appendix F: (Continued) 123 Figure F8 Josephinite S, pH7, 318 hours

PAGE 133

Appendix F: (Continued) 124 Figure F9 Josephinite S, pH7, 960 hours

PAGE 134

Appendix F: (Continued) Figure F10 Josephinite S, pH9, 264 hours 125

PAGE 135

Appendix F: (Continued) Figure F11 Josephinite L1, pH5, 120 hours 126

PAGE 136

Appendix F: (Continued) 127 Figure F12 Josephinite L1, pH5, 342 hours

PAGE 137

Appendix F: (Continued) 128 Figure F13 Josephinite L1, pH7, 117 hours

PAGE 138

Appendix F: (Continued) 129 Figure F14 Josephinite L1, pH7, 141 hours

PAGE 139

Appendix F: (Continued) 130 Figure F15 Josephinite L1, pH7, 168 hours

PAGE 140

Appendix F: (Continued) 131 Figure F16 Josephinite L1, pH7, 240 hours

PAGE 141

Appendix F: (Continued) 132 Figure F17 Josephinite L1, pH7, 288 hours

PAGE 142

Appendix F: (Continued) 133 Figure F18 Josephinite L1, pH7, 1008 hours

PAGE 143

Appendix F: (Continued) Figure F19 Josephinite L1, pH9, 120 hours 134

PAGE 144

Appendix F: (Continued) Figure F20 Josephinite L1, pH9, 316 hours 135

PAGE 145

Appendix F: (Continued) Figure F21 Josephinite M, pH6, 120 hours 136

PAGE 146

Appendix F: (Continued) Figure F22 Josephinite M, pH6, 318 hours 137

PAGE 147

Appendix F: (Continued) Figure F23 Josephinite M, pH7, 120 hours 138

PAGE 148

Appendix G Test Material Certifications Figure G1 E-NiFe Material Certification 139

PAGE 149

Appendix G (Continued) Figure G2 Nickel 200 Material Certification 140

PAGE 150

Appendix G (Continued) Figure G3 Nickel 200 Additional Material Certification 141

PAGE 151

Appendix G (Continued) Figure G4 Josephinite Supplier Certification 142

PAGE 152

Appendix H: Project Related Correspondence Appendix H: Project Related Correspondence 143 143


xml version 1.0 encoding UTF-8 standalone no
record xmlns http:www.loc.govMARC21slim xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.loc.govstandardsmarcxmlschemaMARC21slim.xsd
leader nam Ka
controlfield tag 001 001416913
003 fts
006 m||||e|||d||||||||
007 cr mnu|||uuuuu
008 030729s2003 flua sbm s000|0 eng d
datafield ind1 8 ind2 024
subfield code a E14-SFE0000051
035
(OCoLC)52786399
9
AJJ4765
b SE
040
FHM
c FHM
1 100
Monson, Raymond E.
2 245
A natural analogue for long-term passivity
h [electronic resource] /
by Raymond E. Monson.
260
[Tampa, Fla.] :
University of South Florida,
2003.
502
Thesis (M.S.C.E.)--University of South Florida, 2003.
504
Includes bibliographical references.
516
Text (Electronic thesis) in PDF format.
538
System requirements: World Wide Web browser and PDF reader.
Mode of access: World Wide Web.
500
Title from PDF of title page.
Document formatted into pages; contains 152 pages.
520
Monson ABSTRACT The U.S. Department of Energy (DOE) has been engaged in a viability study for a potential underground geological repository in Yucca Mountain, Nevada. The repository is being designed for disposal of high level nuclear waste. A reference design for the repository has focused on the use of natural and manmade barriers to assure that radionucleide release will not be significant though an extended time period on the order of 10,000 years. The reference design utilizes manmade metallic components that are expected to last for this time period.The specified metallic materials depend on a phenomenon known as metallic passivity to achieve their expected service lives. It is difficult to demonstrate this type of service life for these metallic materials as they have only been in commercial use for less than 100 years. There have been metal artifacts and metallic materials that have survived for long time periods, however, little is known about whether these artifacts have been exposed to conditions where they have been immune to corrosion, exhibiting passive behavior, or actively corroding at an extremely low rate. A demonstration of metallic passive behavior being maintained over many thousands of years would greatly increase confidence in the expectation that passive behavior could be maintained on the repository waste packageA demonstration of metallic passive behavior being maintained over many thousands of years would greatly increase confidence in the expectation that passive behavior could be maintained on the repository waste package materials. Long-lived metallic materials, such as iron, copper, nickel, and alloys based on these metals are materials that demonstrate passive behavior and have been identified in the literature as possible analogues, potentially useful to provide additional confidence in making projections of such long-term passive behavior.1, 4, 28, 45 This paper presents a study into some aspects of the corrosion behavior of Josephinite.Josephinite is a naturally occurring assemblage of a metallic alloy of nickel and iron in conjunction with a host rock. The typical metallic composition is approximately 70% nickel and 30% iron. The material has been reported in association with geologic features with age into the millions of years. The study used corrosion measurement techniques to assess the behavior of the mineral immersed in aqueous solutions of various pH. Corrosion measurement techniques utilized included potentiodynamic polarization, open circuit corrosion potential, and electrochemical impedance spectroscopy.Other techniques utilized in the study included visual and metallographic examinations with both optical and scanning electron microscopy. Test results from this study indicate that passive behavior characterizes Josephinite specimens immersed in naturally aerated buffered aqueous solutions in a range of pH from 6 to 9. This range has been reported for the geographic area where Josephinite materials are found in southwest Oregon. This suggests that passive behavior may be responsible for the material longevity as opposed to the material being immune or undergoing slow but active corrosion.
590
Adviser: Sagues, Alberto A.
653
passive behavior.
corrosion.
josephinite.
nuclear waste.
0 690
Dissertations, Academic
z USF
x Civil Engineering
Masters.
049
FHME
090
TA145
773
t USF Electronic Theses and Dissertations.
4 856
u http://digital.lib.usf.edu/?e14.51