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Comments on “The corrosion of copper-nickel alloys in sulfide-polluted seawater: the effect of sulfide concentration”
Corrosion Science, Vol. 36, No. 10, p. 1809, 1994 Elsevier Science Ltd Printed in Great Britain 0010-938x/94 $7.00+0.00
Pergamon
Comments on "The corrosion of copper-nickel alloys in sulfidepolluted seawater: the effect of sulfide concentration" by J.N. Al-Hajji and M.R. Reda M. B. McNeil Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, D.C. 20555
The recent paper The Corrosion of Copper-Nickel Alloys in SulfidePolluted Seawater: the Effect of Sulfide Concentration by J. N. Al-Hajji and M. R. Reda (Corrosion Science 34, 163 (1993)) argues that the first sulfide mineral precipitated during sulfiding corrosion of Cu and Cu-Ni alloys is covellite, CuS, and that chalcocite (Cu,S), the most commonly observed sulfide corrosion product, is produced by cathodic alteration of covellite. This thesis is based on three assumptions. First, it is assumed that the Cu dissolves as Cu" and that the primary precipitation reaction is Cu"
+ S' ----> cus
Second, it is assumed that the very low solubility product calculated for this reaction will lead to precipitation of covellite before any other mineral. Third, it is assumed that covellite alters readily to chalcocite at STP. Covellite is not a cupric compound. Traditionally, it has been viewed as containing equal numbers of Cu' and Cu" ions', but X-ray photoelectron spectroscopy' has shown it to contain only Cu'. Geochemical studies3.4,5 show that solubilities of Cu (and other metal ions) in sulfide solutions cannot be reliablv estimated from the mineral K.. values for sulfide ion/metal ion reactions, ignoring complex ions. Labgratory studies6 also show that the solubility of covellite depends very strongly on crystallinity and particle size. It is also unclear how the covellite is to be rapidly converted to chalcocite (nearly quantitatively, to judge by published data on sulfiding corrosion of copper alloys). It would be helpful if the authors could put forward a balanced equation for this process and an explanation of why the proposed reaction should be rapid at STP.
1. D. T. Rickard, Mineralium
Deposita 7, 180 (1972). 2. I. Nakai, M. Izawa, Y. Sugitani, Y. Niwa, and K. Nagashima, Mineraloqical Journal 8, 135 (1976). 3. L. R. Gardner, Geochimica et Cosmochimica Acta 38, 1297 (1974). 4. J. Boulegue, C. L. Lord III, and T. M. Church, Geochimica et Cosmochimica A& 46, 453 (1982). 5. A. W. Rose, Mobility of Copper and Other Heavy Metals in Sedimentary Environments in Sediment-Hosted Stratiform Copper Deposits (ed. R. W. Boyle et al), Geoloqical Association of Canada Special Paper 36 (1989) p.97. 6. P Shea and G. R. Helz, Geochimica et Cosmochimica Acta 38, p. 229 (1989). 1809
Pergamon
Comments on "The corrosion of copper-nickel alloys in sulfidepolluted seawater: the effect of sulfide concentration" by J.N. Al-Hajji and M.R. Reda M. B. McNeil Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, D.C. 20555
The recent paper The Corrosion of Copper-Nickel Alloys in SulfidePolluted Seawater: the Effect of Sulfide Concentration by J. N. Al-Hajji and M. R. Reda (Corrosion Science 34, 163 (1993)) argues that the first sulfide mineral precipitated during sulfiding corrosion of Cu and Cu-Ni alloys is covellite, CuS, and that chalcocite (Cu,S), the most commonly observed sulfide corrosion product, is produced by cathodic alteration of covellite. This thesis is based on three assumptions. First, it is assumed that the Cu dissolves as Cu" and that the primary precipitation reaction is Cu"
+ S' ----> cus
Second, it is assumed that the very low solubility product calculated for this reaction will lead to precipitation of covellite before any other mineral. Third, it is assumed that covellite alters readily to chalcocite at STP. Covellite is not a cupric compound. Traditionally, it has been viewed as containing equal numbers of Cu' and Cu" ions', but X-ray photoelectron spectroscopy' has shown it to contain only Cu'. Geochemical studies3.4,5 show that solubilities of Cu (and other metal ions) in sulfide solutions cannot be reliablv estimated from the mineral K.. values for sulfide ion/metal ion reactions, ignoring complex ions. Labgratory studies6 also show that the solubility of covellite depends very strongly on crystallinity and particle size. It is also unclear how the covellite is to be rapidly converted to chalcocite (nearly quantitatively, to judge by published data on sulfiding corrosion of copper alloys). It would be helpful if the authors could put forward a balanced equation for this process and an explanation of why the proposed reaction should be rapid at STP.
1. D. T. Rickard, Mineralium
Deposita 7, 180 (1972). 2. I. Nakai, M. Izawa, Y. Sugitani, Y. Niwa, and K. Nagashima, Mineraloqical Journal 8, 135 (1976). 3. L. R. Gardner, Geochimica et Cosmochimica Acta 38, 1297 (1974). 4. J. Boulegue, C. L. Lord III, and T. M. Church, Geochimica et Cosmochimica A& 46, 453 (1982). 5. A. W. Rose, Mobility of Copper and Other Heavy Metals in Sedimentary Environments in Sediment-Hosted Stratiform Copper Deposits (ed. R. W. Boyle et al), Geoloqical Association of Canada Special Paper 36 (1989) p.97. 6. P Shea and G. R. Helz, Geochimica et Cosmochimica Acta 38, p. 229 (1989). 1809