Crystallization Behaviors Of MgO-Al₂O₃-SiO₂ Glass Ceramic

The crystallization kinetics of MgO-A12O3 -SiO2 system glass was investigated by different thermal analysis (DTA). The crystallization activation energies and crystallization kinetics parameters of MgO-Al2O3-SiO2 system glass were calculated by Augis-Bennett method, modified Kissinger method and Ozawa method. The effect of nucleation agent on the crystallization activation energies and crystallization kinetics parameters of MgO-A12O3-SiO2 system glass was studied.The crystallization behaviors of MgO-A12O3-SiO2 system glass-ceramic were investigated by the method of FIIR absorption spectra (IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The coordination change of titanium ions in MgO-A12O3-SiO2 system glass-ceramic was studied by IR. The effect of nucleation agent on the crystallization behaviors of MgO-A12O3-SiO2 system glass-ceramic was studied by XRD.The results showed that TiO2 and ZrO2 as nucleation agent clearly affect crystallization activation energies, crystallization kinetics parametersand crystallization behaviors of MgO-AL2O3-SiO2 system glass. The crystallization activation energies obtained from both Augis-Bennett method and Kissinger method are almost the same. The crystallization activation energies obtained from Ozawa method are bigger than those from Augis-Bennett method and Kissinger method, but Ozawa method is simple. The frequency factor v obtained from Augis-Bennett method is one magnitude lower than that from modified Kissinger method. The crystallization activation energy and temperature of crystallization peak were obviously decreased by the addition of nucleation agent. Diversified crystallization kinetic criterions of MgO-AL2O3-SiO2 system glass were calculated, but only crystallization kinetic criterion ky(T)(T = Tg,Tx,Tp)fits well for judging the stability of MgO-AL2O3-SiO2 system glass. The stability of MgO-AL2O3-SiO2 system glass was decreased with the increase of nucleation agent. Glasses have interlinked SiO4, A1O4 tetrahedron as their most fundamental units. Titanium ions were four-coordination at low temperature and were found to be of six-coordination with the increase of temperature. TiO2 was in the form of magnesium aluminum titanate, Zr/Ti solid solution and rutile in the calefactive process. ZrO2 was in the form of Zr/Ti solid solution in glass- ceramic and XRD did not detect other forms of zirconium. When MgO-AL2O3-SiO2 system glass did not have nucleation agent, the primary crystalline phase was -cordierite , glass began to crystallization from the surface. When 6% TiO2 was added to the MgO-AL2O3-SiO2 systemglass, the primary crystallization phase was magnesium aluminum titanate, glass was bulk crystallization. Then when TiO2 was added to MgO-A12O3-SiO2 system glass, phase-separation was promoted, the primary crystalline phase changed, crystallization velocity expedited.