The influence of chloride on the corrosion of copper in aqueous sulfide solutions

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1 6 The influence of chloride on the corrosion of copper in aqueous sulfide solutions J. M. Smith Kinectrics, 800 Kipling Avenue, Toronto, ON, M8Z 6C4, Canada Z. Qin and F. King Integrity Corrosion Consulting, Nanaimo, BC, V9T 1K2, Canada D. W. Shoesmith Department of Chemistry, University of Western Ontario, London, ON, N6A 5B7, Canada 6.1 Introduction A proposed method of disposal of Swedish/Finnish/Canadian high-level nuclear waste is to place it in corrosion-resistant containers and bury it approximately 500 m to 1000 m deep in a granitic environment [1 3]. One option is that the containers be emplaced in bore holes and surrounded by compacted bentonite. The residual excavated space would then be backfilled with a mixture of bentonite and crushed granite. Copper is selected primarily because of its thermodynamic stability in the aqueous anoxic environments anticipated in such repositories [4], and the design of the container has been discussed elsewhere [5,6]. A model based on mixed potential principles has been developed to predict container lifetimes [7]. This model shows that corrosion during the early repository lifetime, when a significant O 2 concentration exists, should be minimal, since >80% of the available O 2 in the repository will be consumed by reaction with Fe(II) minerals and organic materials [7]. This model predicts a conservative maximum depth of general corrosion and pitting of 7.6 mm after 10 6 years [7]. However, possible components of the immediate repository environment, as well as the bentonite clay itself, contain pyrite (FeS 2 ) and sulfate (SO 4 2 ) both of which are potential sources of sulfide, the latter following reduction by sulfate-reducing bacteria, which can convert sulfates to sulfides [8]. Various factors will ensure that there is negligible microbial activity in the vicinity of the container [8]; however, remotely produced sulfide could be slowly transported through the compacted buffer to the copper container surface. In the presence of sulfides, Cu becomes a base metal since its corrosion to produce extremely stable and insoluble copper sulfides can be sustained by the reduction of water [9,10]. Whether or not this causes significant corrosion will depend on the supply of sulfide and the protectiveness of the sulfide films formed on the copper surface. The corrosion and electrochemistry of copper and copper alloys (especially Cu/Ni alloys) in sulfide-containing solutions have been studied primarily with an emphasis 109

2 110 Sulphur-assisted corrosion in nuclear disposal systems on their behavior in polluted seawater. These studies have been reviewed [11]. The possibility of sulfide-induced copper container corrosion has been considered [12 14]. Early models [13,14] were based primarily on thermodynamic principles and the assumption that the corrosion rate would be controlled by the transport of sulfide to the copper surface. More recently, the mixed potential model of King and Kolar [7] was extended to include an indirect effect of sulfide [15]. According to thermodynamic considerations, a combination of high chloride concentrations, low ph (<1), high temperature (80 to 100 ), and O 2 free conditions could support the general corrosion of Cu [4,16] by reaction with water Cu + 2Cl + H +! CuCl 2 + 1/2 H 2 [6.1] To sustain corrosion, the flux of the Cu I chloride complex and the dissolved H 2 away from the copper surface would displace this reversible reaction to the right. The model considers the consequences of increasing this flux, and hence the corrosion rate, by precipitating Cu 2 S at locations remote from the container surface by reaction with sulfide minerals (MeS) 2CuCl 2 + MeS Cu 2 S + Me(II) + 4Cl [6.2] However, none of these models consider the direct influence of sulfide on the corrosion process, which has recently been shown to be important [16]. Our previous studies show that the properties of the sulfide surface film exert a key influence on the corrosion rate [16], and that there is a possibility that Cl could influence the properties of this film. Electrochemical studies show that, in the absence of diffusion effects, the formation of Cu 2 S films on Cu proceeds via a rapid equilibrium adsorption step Cu + SH = Cu(SH) ads + e [6.3] followed by a slower, rate-determining formation of Cu 2 S Cu + Cu(SH) ads + SH Cu 2 S + H 2 S + e [6.4] However, Cu I is also soluble as CuCl 2 and, under conditions of low [SH ] and high [Cl ], the complexation and dissolution of Cu I as CuCl 2 could compete with the film formation, step 6.4 Cu(SH) ads + 2Cl CuCl 2 + SH [6.5] In this study, we have investigated the influence of chloride concentration on the properties of Cu 2 S films on Cu, under both electrochemical and natural corrosion conditions. 6.2 Experimental results Electrochemical cell and anaerobic chamber All experiments were performed in a Pyrex cell using a conventional three-electrode configuration. The counter electrode was a Pt sheet and the reference electrode a commercial saturated calomel electrode (SCE, 241 mv vs. SHE). All potentials are quoted on the SCE scale. Electrochemical experiments were performed in the open laboratory in Ar-purged solutions. Longer term natural corrosion experiments were performed within an Ar-purged anaerobic chamber (Canadian Vacuum Systems

3 The influence of chloride on the corrosion of copper 111 Ltd.), which was maintained at a positive pressure (2 4 mbar) by a glove box control system (MBraun). An MBraun oxygen probe, installed within the chambers gas circulation system, verified the operability of the online O 2 removal catalyst, thereby ensuring experiments were performed under relatively anoxic conditions (<1 ppm in the gas phase). Electrochemical measurements were made with either a Solartron 1287 or 1284 potentiostat running Corrware software (Scriber Inc.). Electrochemical impedance spectroscopy (EIS) measurements were performed with a Solartron 1255B frequency response analyzer, using a ±10 mv potential perturbation over a frequency range from 10 6 Hz to 10 3 Hz. Steady-state conditions were verified by recording a small number of data points on a reverse frequency scan. Rotating disc experiments were performed using an analytical rotator (Pine Instruments) or a low noise portable rotator (Radiometer) Electrode and solution preparation Disk electrodes were fabricated from Cu machined from a bulk sample of oxygenfree, phosphorus-doped Cu, supplied by the Swedish Nuclear Fuel and Waste Management Company, Stockholm. Electrodes were then either painted with an insulting lacquer or encased in cylindrical Teflon holders with epoxy resin, to ensure that only a flat circular face was exposed to the solution. Before experiments, the electrodes were polished with SiC paper (down to 1200 grit) and then to a mirror finish with a series of alumina-silicate suspensions (to 500 Å). Samples were then rinsed and sonicated in deionized water to remove polishing residue, and dried in a stream of Ar. Before all experiments, electrodes were cathodically cleaned to remove air-formed oxides by polarizing at 1.15 V for 60 s. Electrolyte solutions were prepared with ultra-pure deionized water (18.2 Mohm. cm), obtained from a Milli-Q Millipore System, and reagent grade chemicals. To achieve anoxic conditions, solutions used in open laboratory experiments were Ar-purged before and throughout the experiment. For experiments within the anaerobic chamber, solutions were prepared within the chamber using Ar-purged water to avoid evaporative concentration of solutions at the low pressure experienced in the chamber introduction port Surface analytical instrumentation X-ray diffraction was performed with a Bruker D8 DISCOVER 2D GADDS microdiffractometer. Spectra were recorded using a Cu κα1 + κα2 X-ray source at a power of 40 kev and 40 ma with a beam diameter of 500 µm. Scanning electron microscopy was performed with a Hitachi S-4500 scanning electron microscope. Images were recorded with an accelerating voltage of 10 kev and a beam current of 20 µa at a 15 mm working distance. 6.3 Results and discussion Natural corrosion experiment Figure 6.1 shows a series of SEM micrographs recorded on specimens allowed to naturally corrode for various time periods in solutions containing 10 3 mol/l Na 2 S

4 112 Sulphur-assisted corrosion in nuclear disposal systems 6.1 SEM micrographs recorded on Cu electrodes after natural corrosion in solutions containing 10 3 mol/l Na 2 S and various amounts of NaCl for various exposure times: (A) 0.1 mol/l NaCl; (a) 1 h, (b) 5 h, (c) 30 h; (B) 1.0 mol/l; (a) 1 h, (b) 5 h, (c) 30 h; (C) 5.0 mol/l; (a) 1 h, (b) 5 h, (c) 30 h and either 0.1 mol/l, 1.0 mol/l, or 5.0 mol/l NaCl. The progression of the corrosion process in all cases is clear, and the morphology of the films formed is clearly dependent on the chloride concentration. In 0.1 mol/l solution, EDX/SEM results indicate a thin layer of sulfide exists on the surface after only 1 h exposure. The micrographs in Fig. 6.1A show the presence of a base layer with some porosity (a) and, with time, an outer deposited layer (b, c) is formed which uniformly covers the electrode surface. At higher chloride concentrations (Fig. 6.1B and C), a similar progression from an initially formed base layer to the deposition of an outer layer is also observed. However, the morphologies of the layers vary with Cl concentration. As the Cl concentration is increased, the rapidly formed base layer present after 1 h of exposure increases considerably in roughness and porosity and the outer deposited layer appears less well-formed and less uniform. XRD analyses of layers grown under these conditions indicate the coexistence of chalcocite (Cu 2 S) and digenite (Cu 1.8 S) in all cases. Since Cu 2 S is always the dominant phase, it seems likely that this is the thicker, outer deposited layer, while the thin inner

5 The influence of chloride on the corrosion of copper 113 base layer is Cu 1.8 S. A similar claim has been made by previous authors [18]. Thermodynamic calculations [18] and potential ph diagrams [10] show that stability fields exist for a range of copper sulfides; namely, chalcocite (Cu 2 S), djurleite (Cu S), digenite (Cu 1.8 S), and anilite (Cu 1.75 S) and, for slightly more oxidizing conditions, covellite (CuS). Of these phases, the stability field for chalcocite extends beyond (i.e. to lower potentials than) the stability field for water in the presence of sulfide at concentrations as low as 10 5 mol/l, making Cu 2 S the most stable phase under the conditions of the experiments described here. Given that the base layer formation is expected to involve solid state growth via a defect transport process, the presence of the highly non-stoichiometric Cu 1.8 S is not surprising. The slower formation of the outer layer would involve transport of Cu I species over a considerable distance, i.e. from the reacting metal surface to the deposition site. Since this process involves the deposition of solution or surface diffusing species, and occurs considerably more slowly than base layer formation, the formation of the more thermodynamically stable Cu 2 S is expected EIS measurements A series of natural corrosion experiments was performed in the same three solutions as described in Section and an EIS spectrum was periodically recorded. The spectra recorded in 0.1 mol/l NaCl are shown in Fig Two clear time constants are observed and the increase in total impedance ( Z ) at the low frequency limit (10 3 Hz) indicates a small but steady increase in the impedance of the Cu/Cu 2 S/SH solution interface with time. The higher frequency time constant (at ~10 Hz) is attributed to charge transfer at the Cu metal surface and the lower frequency time constant to the properties of the Cu 2 S surface film. As shown for the shortest and longest exposure times in Fig. 6.3, the spectra can be accurately fitted to the two time constant equivalent circuit shown in Fig. 6.4 provided that constant phase elements are used to account for the non-ideality in the capacitances. As described above, the surface film comprises a flawed base layer and a deposited outer layer. Thus, in this equivalent circuit, R ct, is the charge transfer resistance at the base of fault (pore) sites in the base layer and C dl is the double layer capacitance. Since Cu 2 S films are electronically conductive, a large fraction of the potential drop across the interface will polarize the Cu 2 S/SH solution interface [18]. For this reason, C dl is placed at this interface in the equivalent circuit rather than in parallel with R ct at the base of the flaws. The nature of the flaw sites in the base layer varies with Cl concentration (Fig. 6.1) and is not well defined. It is likely that such sites contain polarizable charge-carrying species including both solution-soluble and surface-adsorbed species. In the equivalent circuit, the properties of these flaws are represented by a parallel combination of a capacitance, C pore, and a resistance, R pore, the latter representing the dimensional constraints of the pore. It is acknowledged that this combination may not fully represent the process determining the interfacial properties since diffusional effects could be incorrectly incorporated into the R pore C pore combination. However, the inclusion of a porous structure in the equivalent circuit provided a better fit to the experimental data than a Warburg impedance used previously to fit EIS data in Cl free solutions [16]. The values associated with the constant phase elements show that this circuit is a reasonable representation at the lowest Cl concentration; however,

6 114 Sulphur-assisted corrosion in nuclear disposal systems 6.2 EIS spectra recorded after natural corrosion for various times in a solution containing 10 3 mol/l Na 2 S mol/l NaCl: (a) phase angle (h) vs. log frequency; (b) log impedance (Z) vs. log frequency there is a significant deviation from ideality at the higher chloride concentrations, as discussed below. The parameter values obtained by fitting the spectra are shown in Figs. 6.5 and 6.6. The observed increases in R ct and especially R pore, indicate a closing of the flaws in the deposit with time, as observed in Fig With the exception of the value for the shortest experiment, C dl varies little with time as is expected if this capacitance is associated with the Cu 2 S/solution interface. The decrease in C pore with time is also consistent with the closing of pores since this would decrease the number of polarizable species within these locations. The trend in all parameters towards time-independent values suggests that the deposited layer is compact and eventually enforces a steady-state protective condition. The impedance spectra obtained in the 1.0 ml/l NaCl solution are shown in Fig With the exception of the spectra recorded for the shortest exposure time, there is very little change in the spectra over the 38.5 h of the experiment. As observed in 0.1 mol/l NaCl, the spectra contain two distinct time constants, both at slightly higher values, ~40 Hz and ~10 1 Hz, than at the lower concentration. While these

7 The influence of chloride on the corrosion of copper Examples of the fits of the EIS spectra in Fig. 6.6 to the electrical equivalent circuit in Fig Electrical equivalent circuit used to fit EIS spectra: R ct, charge transfer resistance; C dl, double-layer capacitance; R pore, capacitance associated with polarizable species in pores; R S, resistance of the bulk solution 6.5 Charge transfer resistance (R ct ) and double-layer capacitance (C dl ) as a function of the duration of natural corrosion of Cu exposed to 10 3 mol/l Na 2 S mol/l NaCl. Values obtained by fitting the EIS spectra plotted in Fig. 6.2 to the electrical equivalent circuit shown in Fig. 6.4

8 116 Sulphur-assisted corrosion in nuclear disposal systems 6.6 Pore resistance (R pore ) and pore capacitance (C pore ) as a function of the duration of natural corrosion of Cu exposed to 10 3 mol/l Na 2 S mol/l NaCl. Values obtained by fitting the EIS spectra plotted in Fig. 6.2 to the electrical equivalent circuit in Fig. 6.4 spectra could be fitted to the equivalent circuit in Fig. 6.4, the fits were not as good as at the lower concentration, especially for the spectra recorded after the longest exposure time (Fig. 6.8). As indicated in the figure, the fit to this spectrum was limited to frequencies >10 1 Hz in an attempt to minimize errors. The parameter values obtained from these fits are plotted in Figs. 6.9 and The most obvious difference between the impedance behavior in the two Cl concentrations is found in the pore characteristics. Whereas, in 0.1 mol/l NaCl, R pore increased from ~30 kohm.cm 2 to ~100 kohm.cm 2, the value recorded in 1.0 mol/l decreases from a similar early value (~35 kohm.cm 2 ) to a final value of ~12 kohm. cm 2. This indicates the occurrence of a pore opening process at the higher concentrations as opposed to the pore sealing process observed at the lower concentration, consistent with the SEM micrographs in Fig The increase in C pore, while small, supports this suggestion since an increase in polarizable species would be expected within the opening pore. The spectra recorded in 5.0 mol/l NaCl are shown in Fig These spectra cannot be fitted to the equivalent circuit in Fig The inclusion in the equivalent circuit of an additional parallel RC combination does lead to visually well-fitted spectra but unreasonably large capacitance values (3 to 5 mf.cm 2 ) are obtained, a clear indication that diffusive processes are important at this concentration. Despite this inability to fit the spectra, a number of pertinent qualitative observations can be made. 1. The impedance at the low frequency limit (10 3 Hz) is an order of magnitude lower than at the two lower Cl - concentrations, suggesting a much lower degree of surface protection of the surface by the deposited sulfide layer. 2. If the intermediate time constant (at ~1 Hz) can be attributed to the R pore C pore combination, then the small decrease in impedance in this region indicates that there is a slight tendency for the pores in the base layer to open with time.

9 The influence of chloride on the corrosion of copper EIS spectra recorded after natural corrosion for various times in a solution containing 10 3 mol/l Na 2 S mol/l NaCl: (a) phase angle (h) vs. log frequency; (b) log impedance (Z) vs. log frequency 3. The time constant at high frequencies (~10 3 Hz) indicates an unimpeded charge transfer at the base of the faults in the base layer. The value of R ct (estimated by visual inspection of Fig. 6.11) is in the range 1 to 3 ohm.cm 2. Such a low value indicates that the metal surface at the base of flaws in the base layer is unprotected at all times by any deposition process in the flaws. This is consistent with the SEM micrographs in Fig. 6.1, which show the presence of an exposed porous base layer and a non-protective deposited layer at all times Cyclic voltammetry The above experiments clearly show that as the Cl concentration is increased from 0.1 mol/l to 5.0 mol/l, the Cu 1.8 S base layer becomes more porous and the outer deposited Cu 2 S layer less protective. This suggests that the coupling of reactions 6.3 and 6.5 competes with the coupling of reactions 6.3 and 6.4 as the Cl concentration is increased. To investigate this possibility more thoroughly, a series of voltammetric scans to various anodic limits was performed in 0.1 mol/l and 5.0 mol/l NaCl (Figs and 6.13).

10 118 Sulphur-assisted corrosion in nuclear disposal systems 6.8 Examples of the fits of the EIS spectra in Fig. 6.7 to the electrical equivalent circuit in Fig Charge transfer resistance (R ct ) and double-layer capacitance (C dl ) as a function of the duration of natural corrosion of Cu exposed to 10 3 mol/l Na 2 S mol/l NaCl. Values obtained by fitting the EIS spectra plotted in Fig. 6.2 to the electrical equivalent circuit shown in Fig. 6.4 The anodic behavior observed on the forward scan is similar at both concentrations although the currents were higher at the higher Cl concentration. An oxidation peak with the shape typical of a diffusion-controlled process is observed. Although not shown here, scans performed on rotating disc electrodes yield considerably larger currents and a current independent of potential at positive potentials, confirming that the anodic process is controlled by the diffusive flux of SH to the electrode

11 The influence of chloride on the corrosion of copper Pore resistance (R pore ) and pore capacitance (C pore ) as a function of the duration of natural corrosion of Cu exposed to 10 3 mol/l Na 2 S mol/l NaCl. Values obtained by fitting the EIS spectra plotted in Fig. 6.2 to the electrical equivalent circuit shown in Fig. 6.4 surface. However, the reverse voltammetric scans show that the films formed anodically in the two solutions are significantly different. At the lower Cl concentration, scans to various anodic potential limits produce a single reduction peak at a potential between 1.0 V and 1.1 V. The exact position of this peak depends on the extent of sulfide film formation, which is proportional to the area under the cathodic reduction peak. The presence of a single peak indicates the formation of a compact, dense layer of sulfide in good electrical contact with the electrode surface, which is consistent with the SEM observations in Fig Although unimportant in terms of the present study, it is worth noting that the anodic formation and subsequent reduction of this layer leads to a very large enhancement of the current for water reduction for potentials < 1.3 V. This indicates that the reduction of the sulfide film leads to a fine particulate Cu layer with a very large surface area. For the higher Cl concentration, a similar single reduction peak is observed providing the anodic scan limit is not too positive (Fig (a, b)). This is consistent with the formation of a Cu 1.8 S base layer in good electrical contact with the Cu surface and hence reduced at a similar potential to the layer formed at the lower Cl concentration ( 1.0 V to 1.1 V). However, when the anodic potential limit is extended to more-positive values, not only does this peak become larger but a second reduction peak is observed at more-negative reduction potentials. The observation of two distinct reduction peaks suggests the reduction of two separate layers as opposed to the single compact layer formed at the lower Cl concentration. Thus, the reduction occurring at more negative potentials can be attributed to a more loosely attached deposit formed on top of the base layer but not necessarily within the pores of the base layer. In this regard, the observed behavior is consistent with the SEM observations in Fig. 6.1, for natural corrosion experiments. For potential scans to more-positive anodic limits, the anodic film formation process is under diffusion control. This means that the SH concentration at the

12 120 Sulphur-assisted corrosion in nuclear disposal systems 6.11 EIS spectra recorded after natural corrosion for various times in a solution containing 10 3 mol/l Na 2 S mol/l NaCl: (a) phase angle (h) vs. log frequency; (b) log impedance (Z) vs. log frequency metal surface will be very low compared with the Cl concentration, especially in the 5 mol/l NaCl solution. Thus, the maintenance of open porosity in the base layer leading to the formation of a less compact and less-readily reducible outer deposit in 5.0 mol/l is consistent with the coupling of reactions 6.3 and 6.5. This would lead to the transport of Cu I species away from the metal surface and their deposition as Cu 2 S on the outer surface where the SH concentration would approach bulk solution values. This enhanced Cu I transport via soluble CuCl n (n 1) species does not appear to compete with sulfide film formation at 0.1 mol/l NaCl leading to the formation of a more compact protective sulfide deposit. In an attempt to determine whether dissolution of Cu I plays an important role in the overall anodic process at higher [Cl ], the anodic (Q A ) and cathodic (Q C ) charges were calculated by numerical integration of the anodic and cathodic areas in Figs and The ratio Q C /Q A, which is a measure of the fraction of anodic charge recovered by reduction of the sulfide films formed during the anodic part of the scan, is plotted as a function of anodic potential limit in Fig For short anodic excursions (i.e. to potentials 0.90 V), this ratio is small, indicating that dissolution, as opposed to sulfide film formation, is dominant at the low anodic

13 The influence of chloride on the corrosion of copper Cyclic voltammograms recorded on Cu immersed in a solution containing 10 3 mol/l Na 2 S mol/l NaCl. The plots were recorded at a potential scan rate of 2 mv/s and reversed at (a) 0.92 V; (b) 0.90 V; (c) 0.85 V; (d) 0.80 V; (e) 0.70 V. The curves are offset by 0.4 ma/cm 2, as indicated by the vertical arrow 6.13 Cyclic voltammograms recorded on Cu immersed in a solution containing 10 3 mol/l Na 2 S mol/l NaCl. The plots were recorded at a potential scan rate of 2 mv/s and reversed at (a) 0.95 V; (b) 0.93 V; (c) 0.90 V; (d) 0.85 V; (e) 0.80 V; (f) 0.75 V; (g) 0.70 V. The curves are offset by 0.25 ma/cm 2, as indicated by the vertical arrow

14 122 Sulphur-assisted corrosion in nuclear disposal systems 6.14 The cathodic to anodic charge ratio (Q C /Q A ) as a function of anodic scan limit. The charges were calculated by integrating the anodic reactions (Q A ) and cathodic film reduction reactions (Q C ) of the voltammetric scans plotted in Figs and 6.13 currents achieved up to these potential limits. For more-positive potential limits, sulfide film formation dominates and the ratio approaches 1, i.e. the great majority of oxidized Cu becomes trapped in the Cu 1.8 S/Cu 2 S surface layers and is hence available for cathodic reduction on the reverse scan. While this last plot clearly suggests that dissolution contributes significantly at potentials close to those prevailing in natural corrosion experiments ( 0.95 V), it does not confirm that higher Cl concentrations lead to more extensive dissolution, since no significant difference in the Q C /Q A ratio is observed between the two solutions. 6.4 Summary and conclusions The possibility that the corrosion of copper in aqueous sulfide solutions is influenced by chloride present in groundwaters in a nuclear fuel waste repository has been investigated under natural corrosion and electrochemical conditions. Sulfide films were observed to grow initially as a thin base layer of Cu 1.8 S which developed porosity allowing the further growth of a much thicker outer deposited layer of Cu 2 S. In 0.1 mol/l chloride solution, this outer layer was dense and compact and eventually sealed the pores in the base layer, a situation which would lead to low corrosion rates. When the chloride concentration was increased to 1.0 mol/l, the base layer became more porous and the outer layer less dense and compact, and the pores in the base layer were not sealed. At 5.0 mol/l chloride, EIS data indicate that open pores are present in the base layer allowing rapid reaction to produce Cu I species (as surface adsorbed CuSH species), a situation that could lead to a significant increase in corrosion rate.

15 The influence of chloride on the corrosion of copper 123 A possible explanation for this influence is that, when the chloride to sulfide concentration ratio is high, Cu I species, originally formed as surface adsorbed CuSH species can be complexed by chloride to produce soluble species (CuCl n (n 1) ). Transport of these species away from the metal surface would maintain porosity in the base layer and limit the deposition of the outer protective Cu 2 S deposit. Acknowledgements This research was funded by the Swedish Nuclear Fuel and Waste Management Company (SKB), Stockholm. We are grateful to Surface Science Western (University of Western Ontario) for the use of their scanning electron microscope. References 1. F. King, Corrosion of Copper in Alkaline Chloride Environments. TR Swedish Nuclear Fuel and Waste Management Company, Stockholm, J. McMurry, D. A. Dixon, J. D. Garroni, B. M. Ikeda, S. Stroes-Gascoyne, P. Baumgartner and T. W. Melnyk, Evolution of a Canadian Deep Geologic Repository: Base Scenario, Ontario Power Generation Report No REP R00, J. McMurry, B. M. Ikeda, S. Stroes-Gascoyne and D. A. Dixon, Evolution of a Canadian Deep Geologic Repository: Defective Container Scenario, Ontario Power Generation Report No REP R00, I. Puigdomenech and C. Taxen, Thermodynamic Data for Copper. Implications for the Corrosion of Copper under Repository Conditions. TR Swedish Nuclear Fuel and Waste Management Company, Stockholm, C. Anderson, Development of Fabrication Technology for Copper Canisters with Cast Inserts. Status Report in August 2001, TR Swedish Nuclear Fuel and Waste Management Company, Stockholm, P. Maak, Used Fuel Container Requirements, Ontario Power Generation Report No PDR R01, F. King and M. Kolar, The Copper Container Corrosion Model Used in AECL s Second Case Study, Ontario Power Generation Report No REP R00, K. Pedersen, Microbial Processes in Radioactive Waste Disposal, TR Swedish Nuclear Fuel and Waste Management Company, Stockholm, F. King and S. Stroes-Gascoyne, Microbially influenced corrosion of nuclear fuel waste disposal containers, in Proc International Conference on MIC, 35/1 35/14. NACE International, Houston, Texas, USA, M. Pourbaix and A. Pourbaix, Geochim. Cosmochim. Acta 56 (1992), J. M. Smith, The corrosion and electrochemistry of copper in aqueous, anoxic sulphide solutions, Ph.D. thesis, The University of Western Ontario, London, Canada, SKB, Final Storage of Spent Nuclear Fuel. KBS3, Volumes I IV. Swedish Nuclear Fuel and Waste Management Company, L. Werme, P. Sollin and N. Kjellbert, Copper Canisters for Nuclear High Level Waste Management Company, Report No. TR-92-26, F. King, L. Ahonen, C. Taxen, U. Vuorinen and L. Werme, Copper Corrosion Under Expected Conditions in a Deep Geologic Repository, Report No. TR Swedish Nuclear Fuel and Waste Management Company, Stockholm, B. Beverskog and I. Puigdomenech, Pourbaix Diagrams for the System Copper Chlorine at C, SKI Report No. 98:19. Swedish Nuclear Power Inspectorate, J. M. Smith, Z. Qin, F. King, L. Werme and D. W. Shoesmith, Corrosion, 63 (2007), M. R. G. de Chialvo and A. J. Arvia, J. Appl. Electrochem., 15 (1985), K. Rahmouni, M. Keddam, A. Srhiri and H. Takenouti, Corros. Sci., 47 (2005), 3249.