EFFECT OF GRAIN-SIZE ON THE CRYSTALLIZATION KINETICS OF COPPER VANADATE GLASSES

The crystallisation kinetics of V2O5.BaO.ZnO glasses were studied usin g DTA technique as a function of particle size of the glass powder. Th e order of the crystallisation reaction was obtained by using Ozawa's method. Using this method indicated that the Avrami coefficient equals three for particles less than 125 mu m in size and equals two for oth er particle sizes. It means that the crystallisation process could be changed from bulk to surface as the particle size increased. The activ ation energy for crystallisation was calculated by using six different methods. The average value for each particle size was evaluated. The most consistent results were found to be the Ozawa-Chen method. It gav e deviations between 1.7 to 8.1% for all particle sizes. Particles in the range 90<G<160 mu m needed less energy for crystallisation than ot her grain sizes.