Structural changes in the oxidation zones of gold alloys for porcelain bonding containing small amounts of Fe and Sn.

The oxidized surfaces of cross-sections of gold alloys containing a total of 1.5 mass % Fe and Sn, oxidized at 1000 degrees C for one hr, have been studied by various techniques, including secondary electron micro-analysis, X-ray micro-analysis, X-ray diffraction, and thermogravimetry. Over the composition range (0.30-1.50 mass % Fe), an external oxidation zone containing only Fe oxides was formed. The quantity of Fe2O3 was greater than that of SnO2 for 0.45-1.50 mass % Fe. With an Fe content below 0.45 mass %, the amount of SnO2 was greater than that of Fe2O3. Traces of Fe3O4 were formed in high Sn content alloys. Internal oxidation particles composed of Fe2O3 and SnO2 precipitated deep in the alloy matrix (0.90-1.50 mass % Fe), and these changed to an internal oxidation band composed mainly of SnO2 for 0.3 mass % Fe.