Tarnishing of AuAgCu alloys. Effect of the composition

✍ Scribed by J. P. Randin; P. Ramoni; J. P. Renaud

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: German
• Weight: 689 KB
• Volume: 43
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.19920430305

✦ Synopsis

Abstract

The tarnishing resistance of two AuAg binary, one AuCu binary, three AuAgCu ternary and one AuAgCuZn quaternary alloys was investigated using two accelerated tarnish testing procedures. The flower of sulphur test carried out in the gaseous phase and the Tuccillo‐Nielsen method performed in an aqueous liquid solution were used. The tarnished layers were characterized by colorimetric and coulometric measurements. For most of the alloys, the colour turned both reddish and yellowish after tarnishing. A linear trend was found between the colour change and the cathodic charge, indicating that the thickness of the tarnished layer is small enough to be in the range where the reflectivity is linearly related to film thickness. For the high‐silver alloys, the tarnished layer was thick enough to give rise to interference effects and therefore the tarnish is best characterized by the cathodic charge. It was found that the silver content is the dominant parameter influencing the tarnish resistance, but the copper content also plays a role. The tarnishing of AuAg binary alloys was interpreted as a quadratic function of silver content, while that of the ternary and quaternary alloys was found to be a simple additive effect of the silver and copper contributions.