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The rates for nucleation (I) and crystal growth (U) for a lithium disilicate (Li 2 O⅐2SiO 2 , LS 2 ) glass were determined, as a function of temperature, using a new differential thermal analysis (DTA) technique. This technique requires in situ nucleation and crystal-growth heat treatment of a small amount of powdered sample inside the DTA apparatus, which then are followed by a DTA scan at a constant heating rate. The I and U values that have been determined at selected temperatures for the LS 2 glass are in excellent agreement with those reported in the literature. The technique also has been used to determine the concentration of quenched-in nuclei in LS 2 glasses prepared from melts that have been quenched at different rates, which are in reasonable agreement with those estimated from theoretical considerations. This new DTA technique is less tedious, requires a smaller amount of sample, and is at least 10 times faster than the conventional methods that have been used to measure I and U. Also, no special sample preparation, other than simply grinding and screening the glass to a particle size that is suitable for use, is required in this technique, whereas grinding, polishing, or etching is required in conventional methods. The excellent agreement in the I or U values that have been determined for the LS 2 glass via the present and conventional methods demonstrates the accuracy, validity, and usefulness of this DTA method for rapid determination of the nucleation and crystal-growth rates in glasses.

The crystallization of lithium disilicate (Li20 * 2Si02) glass nucleated at various temperatures was studied by differential thermal analysis (DTA). A plot of the DTA crystallization peak height versus nucleation temperature closely resembles the classical nucleation rate curve for lithium disilicate glass whose maximum is at 453°C. The glass becomes saturated with internal nuclei when heated at 453°C for 10 h. The DTA technique is a rapid, alternative method for determining the temperature for maximum nucleation. The activation energy for crystallization, E, and the heat of crystallization, H, are independent of the concentration of nuclei and are 249 f 10 and 67 -+ 3 kJ/mol, respectively. The Avrami exponent, n, depends strongly on the concentration of nuclei in the glass. [

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