Optical properties and microstructures of Pd-free Ag–Au–Pt–Cu dental alloys

Abstract

Nine experimental Pd-free Ag-Au-Pt-Cu dental alloys containing 10 at.% Pt and 10 to 35 at.% Au were prepared and their optical properties and microstructures were investigated by means of spectrophotometric colorimetry, optical microscopy, and electron probe microanalysis. All the alloys were annealed at 850°C and mirror-polished to observe their reflectance curves in the visible spectrum and three-dimensional color coordinates. All the alloys were composed of a major phase of Ag-Au-rich matrix and a minor and almost colorless Pt-Cu-rich phase. It was found that the color of the alloys was substantially controlled by the Ag-Au-rich matrix and that with increasing Au/Ag atomic ratio from 0.130 to 0.996, the yellow-blue chromaticity index b* increased from 8.0 to 14.4, giving a pale yellow color. This systematic increase in yellowness was caused by a continuous shift of the absorption edge of reflectance curve towards longer wavelengths with increasing Au/Ag atomic ratio.

On the hot pressing of coloured high-gold alloys powder compacts applied to the manufacturing of innovative jewellery items

“…The higher reflectance for high wavelengths exhibited by alloys A, B and C are in agreement with Shiraishi et al [29] findings for gold alloys with high gold content. The same authors showed that the three pure elements composing these alloys, i.e.…”

“…The L* value registered for the different samples did not significantly differ within each group, ranging from ∼55 to ∼59. These luminance values are relatively lower than those reported by Shirishi et al [29], but such differences are related to colour measuring experimental set up, particularly with the reduced area of the samples that was used for measuring the colour.…”

“…The alloy C displayed the highest value for a* coordinate (6.5 to 7.2) and relatively low values for b* coordinate, which makes this alloy looks red. Finally, the alloy D exhibited low a* (2.3 to 2.7) and b* (10.1 to 11.8) coordinate values, which is typical of metals with white colour such as pure silver and pure platinum [29]. Figure 7 shows the reflectance curves for the hot pressed coloured gold samples, processed at 700°C for 30 min.…”

Tarnish resistance evaluation of experimental Pd-free Ag-Au-Pt-Cu dental alloys

“…According to the authors' previous study using electron probe microanalysis, it was found that the matrix was rich in Ag and Au while the secondphase small grains were rich in Pt and Cu 10) . The PtCu-rich second-phase grains were well protected from the tarnish attack in all the samples, as shown in Fig.…”

Corrosion resistance evaluation of Pd-free Ag-Au-Pt-Cu dental alloys

“…In our previous study, the chemical compositions of the matrix and second-phase small grains in alloy C were determined by EPMA 24) . The matrix was rich in Ag and Au, whereas the second-phase small grains were rich in Pt and Cu 24) . In this study, only the Ag-Au-rich matrix was corroded after the CV forward scan (Figs.…”