High-temperature oxidation behaviors and surface oxide color of Pd-free, Au-Pt-based metal-ceramic alloys for dental applications

Abstract

The effects of small additions of oxide-forming elements (In, Fe, Sn, or Zn) on high-temperature oxidation behaviors and surface oxide colors in experimental Pd-free, Au-Pt-based metal-ceramic alloys for dental applications were investigated by means of spectrophotometric colorimetry, thin-film X-ray diffraction, and field-emission electron probe microanalysis. Three mirror-polished plate samples sized 10 × 10 × 0.5 mm3 from each alloy were subjected to the oxide-forming heat treatments at 950 °C for 10 min in air and then submitted to the above-mentioned investigations. The sole addition of Fe or Sn to the parent Au-10 at.% Pt alloy (AP10) formed very thin external oxide layers of Fe2O3 or SnO2, respectively. Chromaticity indices for these oxidized surfaces largely varied with concentrations of Fe or Sn due to light interference phenomena. On the other hand, the sole addition of In to the parent AP10 alloy developed In2O3 precipitates by the internal oxidation mechanism. Their surface colors did not change significantly regardless of In concentrations. It was highlighted that the combinative addition of 2 at.% In and Fe or Sn to the AP10 alloy well developed In2O3 precipitates in the Au-Pt alloy substrate by the internal oxidation mechanism. Owing to this significant effect of In inclusion, all of the oxidized ternary AP10-In and quaternary (AP10-In2)-Fe/Sn alloys showed similar surface oxide colors with a* coordinates (red-green direction) of nearly +4 and b* coordinates (yellow-blue direction) of nearly +11, which were pale yellow-brown subjectively. Results of this study are expected to be useful in designing esthetic and novel Pd-free, Au-Pt-based metal-ceramic alloys for dental applications.