Determining crystal growth rate-type of curves in glasses by differential thermal analysis

Abstract

Abstract A crystal growth rate vs. temperature ( U vs. T )-type of curve for a Li 2 O.2SiO 2 glass was determined up to a temperature of 690 °C using a differential thermal analysis (DTA) method. As determined from this ( U vs. T )-type of curve, the temperature corresponding to the onset of crystal growth was 570±3 °C which is in excellent agreement with the same value determined by the conventional method. The complete range of temperature where crystal growth can occur and the temperature ( T max ) where the crystal growth rate is a maximum for this glass could not be determined. It is concluded that for temperatures T max , the DTA method can delineate only a small, initial portion of the ( U vs. T )-type of curve, where the crystal growth rate is sufficiently low so that the glass does not totally crystallize after the required (for at least 5 min) isothermal heat treatment at these temperatures. For temperatures > T max , the curve cannot be determined by the DTA method if the temperature for isothermal heat treatment is approached by heating the glass from room temperature. For determining the curve for temperatures > T max , the desired temperature (> T max ) for isothermal heat treatment of the glass is suggested to be approached from the melting temperature of the glass.