DEVITRIFICATION OF FLUOROINDATE GLASSES

Most fluoride glasses are likely to devitrify when heated for some tim e between the glass transition and melting temperatures. The crystalli zation kinetics of some fluoroindate glasses were studied by isotherma l and non-isothermal methods using differential scanning calorimetry. The heating rate a varied between 1 and 10 K min(-1). The value of Avr ami's exponent n lay between 1 and 2.5, corresponding to a diffusion-c ontrolled growth of crystals. The apparent activation energy for cryst allization, E, varied from 45 to 50 kcal mol(-1). These values of n an d E are low by comparison with those of other fluoride glasses, which suggests high stability against devitrification.