Determination of Crystal Growth Rates in Glasses Over a Temperature Range Using a Single DSC Run.

In this work, we propose and test a simple and accurate technique capable of determining the crystal growth rate, U(T), over a fairly wide temperature range by means of a single differential scanning calorimetry run. This method is based on using 50-200 μm-thick samples with parallel rough surfaces so that crystal growth is effectively unidirectional and the crystallization fronts have a constant area during the entire crystallization process. Growth rates are calculated from the expression U(T) = L·q· DSC (T)/Apeak, where DSC( T) is the value of the differential scanning calorimetry ( DSC) crystallization curve at each temperature T, Apeak is the overall peak area, L is half the sample thickness, and q is the heating rate. This method has been tested for different values of L and q for three glasses undergoing predominantly surface nucleation, that possess distinctly different crystallization behaviors: stoichiometric lithium disilicate and diopside (CaO·MgO·2SiO2) and a nonstoichiometric lithium-calcium metasilicate. Growth rates spanning temperature intervals of more than 100 K, including temperature ranges where literature data are scarce due to experimental difficulties, were determined using a single DSC run. The resulting U(T) data were compared with literature data obtained using optical microscopy. The growth rates determined using the proposed method show excellent agreement with the published data for both stoichiometric glasses and only small errors for the nonstoichiometric glass. [ABSTRACT FROM AUTHOR]