Nucleation and Growth of Lead Titanate from a Glass

The temperature dependence of the rate of growth of PbTiO 2 crystals from a PbO‐B 2 O 3 ‐TiO 2 glass was experimentally determined. The Brown‐Ginell equation describing the temperature dependence of the growth rate provided an excellent fit for the data. The activation energy for the growth of PbTiO 3 crystals was 34 kcal per mole. Within the same temperature range the activation energy for viscous flow was 75 kcal per mole. Differential thermal analyses of both powdered and solid samples of glass showed that the exotherm associated with crystal growth occurred at 100° to 150°C below that of the maximum rate of crystal growth and corresponded to a temperature at which the rate of surface nucleation was relatively high although the rate of crystal growth was low.