Study of the Non-Isothermal Crystallization Kinetics of Lithium Disilicate Glass Ceramic

Abstract

The glass ceramic with the crystals of lithium disilicate Li2O · 2SiO2 (LS2) as the main crystal phase is one of the prospective materials in the field of restorative dentistry. In this study, the crystallization kinetics of LS2 glass ceramic obtained from the base glass of the system SiO2–Li2O–Al2O3–K2O–P2O5 were investigated by the non-isothermal method using differential thermal analysis at four different heating rates. The DTA curves showed different exothermic crystallization peaks over the temperature ranges of 645–683 and 807–845°C. The lithium metasilicate, Li2O · SiO2 (LS), and the lithium disilicate, crystallized over these respective temperature ranges, was established by XRD technique. The crystallization kinetic parameters were calculated by the Kissinger plot and Augis-Bennett equations for non-isothermal analysis. The calculated activation energy of crystal growth, EC1= 236 kJ/mol, EC2 = 340 kJ/mol, and the Avrami parameters, n1 = 1.46–1.67, n2 = 2.73–2.91, together with the results from SEM observations, indicated that the crystallization mechanism of LS was substantial surface crystallization while the crystallization mechanism of LS2 was dominant bulk crystallization. The calculated activation energy of glass transition was also determined EV = 516 kJ/mol.