The silver–indium system: thermal analysis, photomicrography, electron microprobe, and X-ray powder diffraction results

Abstract

In the system Ag–In, the isothermal phase transformation at 281 °C previously assumed by Weibke and Eggers has been found not to exist. Metastability of the γ phase and of the indium phase is persistent at room temperature. The boundaries of the intermediate phases have been redetermined. At room temperature, the equilibrium γ phase (hexagonal) exists between 71.0 and 70.3% silver. At 325 °C and higher temperatures, the γ-phase region extends to higher indium concentrations than those given by Weibke and Eggers. The order–disorder transformation of the γ phase, postulated by Hellner, does not appear to exist. The liquidus is found to lie approximately 8 °C higher than that determined by Weibke and Eggers.At room temperature, the ε phase exists between 67.5 and 65.0% silver. At these compositions, the cubic cell edges of the ε phase are a = 9.878 ± 0.004 and 9.887 ± 0.004 Å, respectively. The γ/(γ + ε) phase boundary has been redetermined and extended.A new α′ phase is claimed to exist at approximately 73.8 wt. % silver. It is formed by a peritectoid phase reaction at 187°. In the α′ phase the silver atoms occupy the face-centered positions and the indium atoms, the corner positions of the cubic lattice. The intensities of diffraction lines were calculated using such a model and were found to be in reasonable agreement with the observed intensities of the α′ phase. The cell edge of the α′ phase is 4.144 + 0.004 Å, at room temperature, and this is identical, within experimental error, with that of the α phase.A new phase diagram for the Ag–In system has been constructed.