THERMODYNAMICS AND LOCAL ATOMIC ARRANGEMENTS OF GOLD-NICKEL ALLOYS

An e.m.f. apparatus with an oxygen-ion conducting solid electrolyte, differential thermal analysis, powder diffractometry, density measurements, and transmission electron microscopy (TEM) were used to determine thermodynamic quantities, the phase boundaries in the solid and liquid, and the microstructure of gold-rich solid solutions. Alloys with x(Ni) = 0.03, 0.06, 0.10, 0.15, 0.21, 0.35, 0.55, 0.73, 0.87 and 0.93 were investigated. The thermodynamic activities deviate positively from Raoult's law in the liquid and solid states. The heats of formation and excess entropies exhibit positive values. This causes a large miscibility gap in the solid state. TEM, however, reveals short-range order in the alloys annealed above the miscibility gap.