Effect of ZrO_2 on Crystallization and Phase Transformation in Low-temperature Processed BaO-Al_2O_3-SiO_2 Glass-ceramics

BaO-Al_2O_3-SiO_2(BAS) glass-ceramics with stoichiometric and off-stoichiometric celsian composition were fabricated,doped with B_2O_3 for melting and sintering.Crystallization and phase transformation characters of two groups of BAS glass-ceramics with and without ZrO_2 were investi- gated by differential scanning calorimetry (DSC),X-ray diffraction (XRD) and dilatometry.Results show that for both BAS glasses,the sintering temperature is lower than 850℃and crystallization peak temperature is lower than 900℃.The crystallization characteristic of hexacelsian in each sample is bulk nucleation and three-dimensional growth because Avrami exponent is 2.8-3.9.The crystallization characteristic of monocelsian in the sample doped with ZrO_2 is surface nucleation and one-dimensional growth because Avrami exponent is 0.95,while it is bulk nucleation and three-dimensional growth be- cause Avrami exponent is about 3.0 in the sample without nucleation agent.It reveals that crystalliza- tion peak temperature and activation energy get lower in stoichiometric BAS glass-ceramics doped with ZrO_2,while the crystallization peak temperature get higher in off-stoichiometric BAS glass-ceramics doped with ZrO_2.Stoichiometric BAS glass-ceramics doped with ZrO_2 crystallized at 850℃for 12h is completely transformed into monocelsian.Monocelsian will not be detected in off-stoichiometric BAS doped with ZrO_2 crystallized at 850℃for 100h.