The electrochemical corrosion behaviour of quaternary gold alloys when exposed to 3.5 % NaCl solution

Abstract

Lower carat gold alloys, specifically 9 carat gold alloys, containing less than 40 % gold, and alloying additions of silver, copper and zinc, are commonly used in many jewellery applications, to offset high costs and poor mechanical properties associated with pure gold. While gold is considered to be chemically inert, the presence of active alloying additions raises concerns about certain forms of corrosion, particularly selective dissolution of these alloys. The purpose of this study was to systematically study the corrosion behaviour of a series of quaternary gold-silvercopper-zinc alloys using dc potentiodynamic scanning in saline (3.5 % NaCl) environment. Full anodic/cathodic scans were conducted to determine the overall corrosion characteristics of the alloy, followed by selective anodic scans and subsequent morphological and compositional analysis of the alloy surface and corroding media to determine the extent of selective dissolution. Varying degrees of selective dissolution and associated corrosion rates were observed after anodic polarisation in 3.5 % NaCl, depending on the alloy composition. The corrosion behaviour of the alloys was determined by the extent of anodic reactions which induce (1) formation of oxide scales on the alloy surface and or (2) dissolution of Zn and Cu species. In general, the improved corrosion characteristics of alloy #3 was attributed to the composition of Zn/Cu in the alloy and thus favourable microstructure promoting the formation of protective oxide/chloride scales and reducing the extent of Cu and Zn dissolution.

Enhancing aluminum foil performance in aqueous and organic electrolytes: dual-secure passivation with phthalocyanine as a corrosion inhibitor

“…4,5 The corrosion current density (I corr ) and corrosion rate are oen inversely related. [43][44][45] This indicates that the corrosion current value is more signicant in estimating the actual corrosion rate of a material; 46,47 the calculated results are also shown in Table S2. † The corrosion potential (E corr ) increases with the addition of the Pc corrosion inhibitor.…”