Compositional dependence of fragility and glass forming ability of calcium aluminosilicate melts

The compositional dependence of glass forming ability (GFA) of two series of calcium aluminosilicate melts is studied by measuring their viscous behavior and crystallization tendency. The first series consists of five compositions on the joining line between the eutectic point of anorthite–wollastonite–tridymite and that of anorthite–wollastonite–gehlenite. The series includes the eutectic compositions as end members. The second series consists of five compositions on a line parallel to the joining line on the alumina rich side. In the present work, GFA is described in terms of glass stability. The Hrubÿ parameter (K_H) [A. Hrubÿ, Czech. J. Phys. B 22 (1972) 1187] obtained from calorimetric data is used as a measure of glass stability. From the viscous behavior of the undercooled melts studied by viscometry the fragility (m) is derived. The results show that m is inversely proportional to K_H for the two series of melts, proposing m as an indirect measure of GFA. However, this proportionality is only valid for comparison of the glasses in the series of systematic substitutions of components. In general, the melts on the joining line between the two eutectic compositions are found to have superior GFA. Within each series GFA increases as a function of the network polymerization.