Abstract
Critical cooling rate Q* for glass formation was determined by means of DTA method for a non-alkali multicomponent system of 39.8SiO2·10.1Al2O3·24.4CaO·12.6ZnO·11.1TiO2·2.0B2O3mol% composition. Q* was found to be 1.5×10-2°C/sec. Viscosity of the system was measured by the beambending and the counter balancing method. The liquidus temperature T1 of the system was determined by DTA method. From the viscosity and T1 data, the Liquidus viscosity η1 was obtained (logη1/PaS=0.94). The Q*-η1 relationship of the non-alkali system was compared with those of alkali silicate and alkali borate systems.It was found that the present non-alkali system has a critical cooling rate equivalent to 94SiO2·6Li2O, 75B2O3·25Li2O or 85B2O3·15Na2O glass. The fusion entropy ΔSf was calculated from eq. (2) using the values of liquid parameters of the non-alkali system. It became apparent that the non-alkali system has a considerably high ΔSf value compared with the alkali borate or alkali silicate system. This was regarded to indicate that the present system is composed of various polyhedra, including SiO4, AlO4 or TiO4 tetrahedra, thus easing a glass formation of a SiO2 poor melt.
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