Mechanism by which Silver Additions Inhibit Anodic Corrosion of 4·5% Antimony-Lead Alloys

Abstract

The effect of up to 0·20 wt.-% additions of silver on the anodic corrosion of 4·5 wt.-% antimony–lead alloy, when corroded in sulphuric acid at potentials exceeding the PbO²/PbSO⁴ potential has been established. Silver reduces significantly both the rate and magnitude of corrosion in silver–antimony–lead alloys. The corrosion resistance of these alloys is shown to be concentration-dependent increasing with increase of silver content.

Microstcuctures indicate. that in 4·5 wt.-% antimony–lead alloys, corrosion takes place by the selective dissolutwn of antimony-rich phase, which forms a continuous network in as-cast and a discontinuous network in homogenised–quenched alloys. Whereas, in silver–4·5 wt.-% antimony–lead alloys, corrosion takes place mostly by the oxidation of lead-rich phase and no preferential attack of the antimony-rich phase occurs zn homogenised–quenched alloys. An electron-beam microprobe has been used to establish the distribution and location of silver and antimony at, or in the vicinity of, grain and mterdendritic boundaries, and in the grain interior of the anodically corroded as-cast and homogenisedquenched ternary alloy.

The distribution and location of silver and antimony in ternary alloy structure, morphology, type of distribution of phases, nature and type of corrosion attack as revealed by the microstructures, form the basis m explaining the mechanism by which silver inhibits anodic corrosion of these alloys in sulphuric acid.