EFFECTS OF IN AND ZN ON PROPERTIES OF LOW NOBLE-METAL ALLOYS

Four low noble metal alloys with high In and Zn contents were investigated with regard to porosity in castings, structure, tarnish, hardening mechanism and cytotoxicity. Fumes were observed above the melt, due to the high Zn content and low boiling point of this metal. This Zn evaporation during melting created a small amount of porosity in the castings. This porosity diminished when the Zn content was reduced from 4 to 2%. Scanning electronmicroscopy, microprobe analyses and X-ray diffraction analyses revealed a face-centred cubic (fcc) matrix enriched in Au and Ag and a body-centred cubic (bcc) phase enriched in Pd, In and Zn which had a yellow gold-like appearance. After immersion in a 2% Na2S solution for 72 h, no tarnish attack was observed on the PdInZn-rich phase. The matrix phase was found to be slightly tarnished. The alloys remained yellow by visual inspection. The agar overlay technique displayed a very slight cytotoxic effect of a sandblasted specimen and no cytotoxic effect of a polished specimen.