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

Resumo

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, E_C1= 236 kJ/mol, E_C2 = 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 E_V = 516 kJ/mol.