Determination of the equilibrium miscibility gap in the Pd-Rh alloy system using metal nanopowders obtained by decomposition of coordination compounds

Highlights: • The Pd-Rh phase diagram has been experimentally reinvestigated. • The true equilibrium was achieved with the two-way approach. • The critical point of the miscibility gap lie at 58 at.% Rh and 820 °C. - Abstract: The Pd-Rh phase diagram has been reinvestigated in the subsolidus region using X-ray diffraction, scanning and transmission electron microscopy. The true equilibrium at the miscibility boundary was achieved with the two-way approach. Nanosized powders of metastable solid solutions and two-phase palladium-rhodium mixtures were used to shorten the time required to equilibrate the system. The initial samples were prepared by decomposition of coordination compounds [Pd(NH₃)₂Cl₂], [Rh(NH₃)₅Cl]Cl₂, [Pd(NH₃)₄]₃[Rh(NO₂)₆]₂ and [Pd(NH₃)₄][Rh(NH₃)(NO₂)₅]. The obtained phase diagram exhibits miscibility gap wider than generally accepted with the critical point of solubility at 58 at.% Rh and 820 °C