Nucleation and growth of crystals in a ZBLYALiPb glass

The surface and bulk crystallisation of a ZBLYALiPb glass has been investigated. The crystalline phases grown after thermal treatments were observed by optical and scanning electron microscopy and identified by X-ray diffraction (XRD). The nucleation frequency is very low (maximum value 3 x 10(3) m(-3) s(-1)). Growth is linear. Its rate can be described with an Arrhenius equation in the temperature range from 568 to 603 K. The apparent activation energy is 397 kJ mol(-1). Values of activation energy published up to now for crystallisation in fluorozirconate glasses are collected. They range from similar to 150 to similar to 500 kJ mol(-1). The spread can be explained by comparison with the apparent activation energy for viscous flow which presents a huge variation in the undercooled regime above the glass transition temperature. From the temperature dependence of the activation energy for crystallisation of different fluorozirconate, glasses it is concluded that the rate of crystal growth is controlled by viscous flow. (C) 2001 Elsevier Science B.V. All rights reserved.