NaHSおよびNa₂S水溶液によるAu-Ag合金の腐食

抄録

Corrosion experiments on Au, Ag and Au-Ag alloys of various composition in 1mol/L solutions of NaHS and Na₂S have been carried out at 150°C over 120 days. Ag₂S was formed in NaHS solutions on Au₂₅Ag₇₅, Au₁₀Ag₉₀ and Ag₁₀₀ (pure silver) and in Na₂S solutions on Au₅₀Ag₅₀, Au₂₅Ag₇₅, Au₁₀Ag₉₀ and Ag₁₀₀, but its morphology differed: The Ag₂S formed in the NaHS solutions was platy, while that formed in the Na₂S solutions was mostly whisker-like. It is thought that Ag₂S morphology was controlled by HS^- and S^2- concentrations in the solutions and by the rate of sulfidation. The remarkably developed Ag₂S scale seen on Ag₁₀₀ was found to consist of an outer layer formed by the outward diffusion of Ag⁺ and an inner layer formed by the inward diffusion of S^2-.