CALORIMETRIC STUDIES ON THE CRYSTALLIZATION OF LI2S-B2O3 GLASSES

xLi(2)S . (1 - x)B2O3 system glasses have been prepared by liquid nitr ogen quenching technique at a cooling rate of about 15 degrees C/s in the absence of water and oxygen. On the basis of Johnson-Mehl-Avrami e quation, the isothermal and non-isothermal crystallization kinetics of xLi(2)S . (1 - x)B2O3 glasses have been studied using differential sc anning calorimetry. The crystallization activation energy, E, Avrami e xponent, n, and crystallization enthalpy, -Delta H, have been estimate d. It is found that in xLi(2)S . (1 - x)B2O3 oxysulfide system, glasse s can be formed within the composition range of x less than or equal t o 0.45. The x = 0.25 glass shows the strongest stability against cryst allization, while the x = 0.45 glass is the least stable composition a mong glass samples. The results indicate that the crystallization is a thermally activated process and it is mainly controlled by a surface nucleation mechanism. The activation energies of crystallization are m aximal for glass samples with a particle size of 180-100 mu m. Crystal lization enthalpy, -Delta H, and peak temperature, T-p, are linearly d ependent. (C) 1998 Elsevier Science E.V. All rights reserved.