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Published online by Cambridge University Press: 15 February 2011
Several glass forming systems have been studied by in situ scanningcalorimetry and by solution calorimetry in Molten 2PbO.B2O3 at 973 K. In systems which showmacroscopic glass-glass phase separation on annealing, namely K2O-La2O3-SiO2 and Li2O-SiO2, the enthalpies of solution of opticallyclear quenched glasses and milky annealed glasses are almost identical. Thisbehavior, coupled with a linear variation of heat of solution withcomposition along joins which have a large change in overall degree ofpolymerization, support the contention from spectroscopy that short rangeclustering dominates even in nominally single phase Materials, withexsolution observed as the initially present heterogeneous regions grow insize. Alkali titanosilicate melts show Cp anomalies consistentwith breakdown of alkali titanate complexes or changes in Ti coordination.Calorimetry is a sensitive quantitative probe of crystallization as afunction of time in both ceramic and geologic systems.