Thermographic study of the contact melting of metals. II. Binary systems with intermediate phases

Abstract

Differential thermal analysis, metallography, and local x-ray spectral analysis were used to study the heat effects and structural changes occurring upon heating powder mixtures of pairs of elements whose binary phase equilibrium diagrams contain one or more intermediate phases. It was found that contact melting in these mixtures is accompanied by exothermal heat effects in both the solid and liquid states, related to the formation of intermetallic compounds. The temperatures at which strong exothermal effects were observed coincide with the melting temperatures of eutectics in the various systems. The magnitudes of the heat effects are determined by the differences between the exothermal heats of formation of the intermediate phases and the endothermal heats of formation of the liquid phases which formed simultaneously. In the systems containing phosphorous, interaction was controlled by the sublimation of this component. Phosphides were formed at low temperatures as a result of the rapid exothermal reaction of phosphorous vapor with the metals.