Spectral and Gravimetric Analysis of Completely Oxidized Amalgam Systems

Abstract

Analysis of the soluble solution species, insoluble solution precipitate, adherent corrosion products, and microstructural changes of the substrate amalgam after selected polarization to -0.2v and +0.5v in a chloride solution is reported. Results indicate only small concentrations of soluble species, high concentrations of a Sn insoluble solution precipitate at -0.2v, and high concentrations of a Cu precipitate at +0.5v, related to CuCl₂·3Cu(OH)₂. The completely oxidized amalgam microstructure indicates a thin outermost layer of predominantly Sn-Cl, a thick corroded layer of Ag-Sn-Hg-Cl, and the remaining substrate amalgam. The compound of (SnO) 160 is also associated with the thick corroded layer. The microstructure of the substrate amalgam exhibits, besides the normally occurring phases and products, four new phases or alterations due to the redistribution of Sn, Cl and O from the gamma–2 corrosion products, (1) the reappearance of voids, (2) a grey Ag-Sn-Cl phase with and without Cu localized at specific sites in the gamma-1 matrix, (3) dark areas or partially filled voids containing the same elements as in (2) and formerly occupied by the gamma-2 products, and (4) a Cu-rich phase from the deterioration of the Cu₆Sn₅ phase and also included within the matrix. These changes, particularly (1), (2) and (3) occur with the onset of the gamma-1 deterioration. Unreacted Ag₃Sn including the additions of the Cu₃Sn component is the last phase to be attacked in the composite amalgam.