LINK BETWEEN THE DISSOLUTION MECHANISMS OF A SOLID METAL IN A LIQUID BINARY ALLOY AND THE SHORT-RANGE ORDER IN THE MELT

In the frame of the regular associate model, a calculation of the enth alpy of mixing of an A - B liquid alloy with strong negative deviation s to ideality shows that a negative curvature with respect to composit ion corresponds to repulsive interactions between A atoms (in excess i n the melt) and the A(a) B(b) associates whereas a positive curvature corresponds to attractive interactions. Moreover, the theoretical mode ling of the dissolution process shows that the dissolution time of the solid metal B in the A(1-x)B(x) liquid alloy increased when the trans itory transformation of an A(a) B(b) layer is assumed at the solid-liq uid interface. The dissolution mechanisms have been connected to the s tructure of the melt by the way of experimental determinations: i) In the case of the Ag - Te system, the enthalpy of mixing exhibits a nega tive curvature and the dissolution process of solid Ag in the liquid A g - Te melt takes place through the transitory formation of an Ag2Te l ayer. ii) In the case of the Ge - Te system, the enthalpy of mixing sh ows a positive curvature and a direct diffusion mechanism of Ge in the melt is pointed out. It can be concluded that repulsive interactions hinder the spreading of the associates in the melt, favour the formati on of the transitory solid compound layer and increase the time of dis solution.