skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: General Corrosion and Passive Film Stability

Abstract

We have studied Alloy 22 corrosion and passive film stability in nitrogen-purged Na-K-Cl-NO{sub 3} brines having NO{sub 3}:Cl ratios of 7.4 at 160 C and NO{sub 3}:Cl ratios of 0.5 and 7.4 at 220 C in autoclave experiments under a slight pressure. The experiments were done to show the effect of high nitrate brines on the durability of the Alloy 22 outer barrier of the waste canisters. Ratios of NO{sub 3}:Cl used in this study were lower than expected ratios for the repository environment at these temperatures and atmospheric pressures (NO{sub 3}:Cl > 25), however they were thought to be high enough to inhibit localized corrosion. Localized corrosion occurred on the liquid-immersed and vapor-exposed creviced specimens under all conditions studied. Crevice penetration depths were difficult to quantify due to the effects of deformation and surface deposits. Further characterization is needed to evaluate the extent of localized corrosion. The bulk of the surface precipitates were derived from the partial dissolution of ceramic crevice formers used in the study. At this time we do not know if the observed localized corrosion reflects the corrosiveness of Na-K-Cl-NO{sub 3} solutions at elevated temperature over nine months or if it was an artifact of themore » experimental protocol. Nor do we know if much more concentrated brines with higher NO{sub 3}:Cl ratios formed by dust deliquescence will initiate localized corrosion on Alloy 22 at 160 and 220 C. Our results are consistent with the conclusion that nitrate concentrations greater than 18.5 molal may be required to offset localized corrosion of Alloy 22 at 160 and 220 C. Stability of the passive film and general corrosion were evaluated on the liquid-immersed and vapor-exposed non-creviced specimens. Elemental depth profiles of the vapor-exposed specimens are consistent with the development of a protective Cr-rich oxide near the base metal. The combined passive film and alloy oxide of the immersed specimens was much thicker than for the vapor-exposed specimens. This may be attributed to the inability to transport reactants away from the surface with limited amount of fluid in the condensate compared to the large reservoir for the liquid-immersed specimens. Elemental depth profiles of the liquid-immersed specimens suggest that Cr(III) and Mo(II) in the passive film are oxidized to Cr(VI) and Mo(VI) and are dissolved in the high nitrate brines, because the alloy oxide layers were enriched with Ni relative to Cr and Mo in the base metal. An alumino-silicate-chloride precipitate was identified on specimens immersed in solutions with a NO{sub 3}:Cl ratio of 0.5 at 220 C. Further characterization is needed to identify all secondary phases. The inability to extract reliable rates from weight loss measurements suggests that other techniques are needed to evaluate long-term general corrosion of Alloy 22.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
889973
Report Number(s):
UCRL-TR-217393
TRN: US0604513
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ALLOYS; ATMOSPHERIC PRESSURE; AUTOCLAVES; BRINES; CERAMICS; CONDENSATES; CONTAINERS; CORROSION; DEFORMATION; DISSOLUTION; DUSTS; NITRATES; OXIDES; PENETRATION DEPTH; STABILITY; TRANSPORT; WASTES

Citation Formats

Dixit, S, Roberts, S, Evans, K, Wolery, T, and Carroll, S. General Corrosion and Passive Film Stability. United States: N. p., 2005. Web. doi:10.2172/889973.
Copy to clipboard
Dixit, S, Roberts, S, Evans, K, Wolery, T, & Carroll, S. General Corrosion and Passive Film Stability. United States. doi:10.2172/889973.
Copy to clipboard
Dixit, S, Roberts, S, Evans, K, Wolery, T, and Carroll, S. Tue . "General Corrosion and Passive Film Stability". United States. doi:10.2172/889973. https://www.osti.gov/servlets/purl/889973.
Copy to clipboard
@article{osti_889973,
title = {General Corrosion and Passive Film Stability},
author = {Dixit, S and Roberts, S and Evans, K and Wolery, T and Carroll, S},
abstractNote = {We have studied Alloy 22 corrosion and passive film stability in nitrogen-purged Na-K-Cl-NO{sub 3} brines having NO{sub 3}:Cl ratios of 7.4 at 160 C and NO{sub 3}:Cl ratios of 0.5 and 7.4 at 220 C in autoclave experiments under a slight pressure. The experiments were done to show the effect of high nitrate brines on the durability of the Alloy 22 outer barrier of the waste canisters. Ratios of NO{sub 3}:Cl used in this study were lower than expected ratios for the repository environment at these temperatures and atmospheric pressures (NO{sub 3}:Cl > 25), however they were thought to be high enough to inhibit localized corrosion. Localized corrosion occurred on the liquid-immersed and vapor-exposed creviced specimens under all conditions studied. Crevice penetration depths were difficult to quantify due to the effects of deformation and surface deposits. Further characterization is needed to evaluate the extent of localized corrosion. The bulk of the surface precipitates were derived from the partial dissolution of ceramic crevice formers used in the study. At this time we do not know if the observed localized corrosion reflects the corrosiveness of Na-K-Cl-NO{sub 3} solutions at elevated temperature over nine months or if it was an artifact of the experimental protocol. Nor do we know if much more concentrated brines with higher NO{sub 3}:Cl ratios formed by dust deliquescence will initiate localized corrosion on Alloy 22 at 160 and 220 C. Our results are consistent with the conclusion that nitrate concentrations greater than 18.5 molal may be required to offset localized corrosion of Alloy 22 at 160 and 220 C. Stability of the passive film and general corrosion were evaluated on the liquid-immersed and vapor-exposed non-creviced specimens. Elemental depth profiles of the vapor-exposed specimens are consistent with the development of a protective Cr-rich oxide near the base metal. The combined passive film and alloy oxide of the immersed specimens was much thicker than for the vapor-exposed specimens. This may be attributed to the inability to transport reactants away from the surface with limited amount of fluid in the condensate compared to the large reservoir for the liquid-immersed specimens. Elemental depth profiles of the liquid-immersed specimens suggest that Cr(III) and Mo(II) in the passive film are oxidized to Cr(VI) and Mo(VI) and are dissolved in the high nitrate brines, because the alloy oxide layers were enriched with Ni relative to Cr and Mo in the base metal. An alumino-silicate-chloride precipitate was identified on specimens immersed in solutions with a NO{sub 3}:Cl ratio of 0.5 at 220 C. Further characterization is needed to identify all secondary phases. The inability to extract reliable rates from weight loss measurements suggests that other techniques are needed to evaluate long-term general corrosion of Alloy 22.},
doi = {10.2172/889973},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Nov 29 00:00:00 EST 2005},
month = {Tue Nov 29 00:00:00 EST 2005}
}
Copy to clipboard
Technical Report:
View Technical Report
DOI:  10.2172/889973
Save / Share:
Export Metadata
Save to My Library
You must Sign In or Create an Account in order to save documents to your library.

  • ; ; ; ...
    This report summarizes both general corrosion of Alloy 22 from 60 to 220 C and the stability of the passive (oxide) film from 60 to 90 C over a range of solution compositions that are relevant to the in-drift chemical environment at the waste package surface. The general corrosion rates were determined by weight-loss measurements in a range of complex solution compositions representing the products of both the evaporation of seepage water and also the deliquescence of dust previously deposited on the waste canisters. These data represent the first weight-loss measurements performed by the program at temperatures above 90 C.more » The low corrosion rates of Alloy 22 are attributed to the protective oxide film that forms at the metal surface. In this report, changes in the oxide film composition are correlated with weight loss at the higher temperatures (140-220 C) where film characterization had not been previously performed. The stability of the oxide film was further analyzed by conducting a series of electrochemical tests in progressively more acidic solutions to measure the general corrosion rates in solutions that mimic crevice or pit environments.« less

  • ; ; ; ...
    This report summarizes both general corrosion Alloy 22 from 60 to 220 C and the stability of the passive film from 60 to 90 C over a range of solution compositions that are relevant to the in in-drift chemical environment at the waste package surface. The general corrosion rates were determined by weightloss measurements in a range of complex solutions representing the evaporation of seepage water and more concentrated brines representing brines formed by the deliquescence of dust deposited on the canisters. These data represent the first weightloss measurements performed by the program at temperatures above 90 C. The lowmore » corrosion rates of Alloy 22 are attributed to the protective oxide film that forms at the metal surface. In this report, changes in the oxide composition are correlated with weightloss at the higher temperatures (140 related 140-220 C) where film characterization had not been previously performed. The stability of the oxide film was further analyzed by conducted a series of electrochemical tests in progressively more aggressive acid solutions to measure the general corrosion rates in solutions that mimic crevice or pit environments.« less

  • ; ; ; ...
    An iron-based amorphous metal, Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4} (SAM2X5), with very good corrosion resistance was developed. This material was prepared as a melt-spun ribbon, as well as gas atomized powder and a thermal-spray coating. During electrochemical testing in several environments, including seawater at 90 C, the passive film stability was found to be comparable to that of high-performance nickel-based alloys, and superior to that of stainless steels, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates. This material also performed very well in standard salt fog tests. Chromium (Cr), molybdenummore » (Mo) and tungsten (W) provided corrosion resistance, and boron (B) enabled glass formation. The high boron content of this particular amorphous metal made it an effective neutron absorber, and suitable for criticality control applications. This material and its parent alloy maintained corrosion resistance up to the glass transition temperature, and remained in the amorphous state during exposure to relatively high neutron doses.« less

  • ; ; ; ...
    This report consists of the following four parts: Field Ion Microscopy Studies of the Interaction of Hydrogen with Selected Metals and Alloys; The Role of Noncrystalline Films in Passivation and Breakdown of Passivation; Effect of Chromium Depletion on the Repassivation Kinetics 18-10 Austenitic Stainless Steel in Sodium Chloride Solutions; and Composition of Surface Films Formed During the Repassivation of Iron and Iron-Molybdenum Alloys.

  • ;
    This report consists of four parts as follows: (1) A study of the influence of Mo in Fe-Mo alloys on crevice corrosion. It was found that >5% Mo is needed to affect repassivation in a crevice. (2) The description of a new technique for measuring repassivation rates in a crevice. (3) A description of alloys prepared to simulate the composition of metal near grain boundaries of sensitized austenitic stainless steel. These alloys are used for studies of the effect of sensitization on repassivation kinetics. (4) A review of new approaches in the study of localized corrosion.