CONFIGURATIONAL HEAT-CAPACITIES - ALKALI VS. ALKALINE-EARTH ALUMINOSILICATE LIQUIDS

The heat capacities of three aluminosilicate glasses and liquids have been determined from drop-calorimetry measurements made between 400 an d about 1800 K. At the glass transition, the observed C-p changes vary from 16% to 36%, increasing when the SiO2 content decreases or when a lkaline-earth are substituted for alkali elements. Whereas empirical m odels for calculation allow the heat capacities to be calculated accur ately for glasses, they give less good results for liquids owing to st rong interactions between alkali or alkaline-earth elements with alumi num for which there are no current accounts. Such comparisons nonethel ess demonstrate that the configurational properties of complex composi tions can be predicted from measurements performed on simple systems. The variations of the configurational heat capacity as a function of t emperature and composition are discussed with reference to short-range order around cations. (C) 1998 Elsevier Science B.V. All rights reser ved.