Influence of Al₂O₃ and B₂O₃ on Sintering and Crystallization of Lithium Silicate Glass System

Abstract

This article reports on the effect of Al 2 O 3 and B 2 O 3 added as dopants on the preparation of glass-ceramics (GCs) belonging to the lithium silicate glass system. The GCs are prepared by sintering route using glass powders. The reasons for the crystallization of the metastable crystalline phase lithium metasilicate (LS) are discussed and the impact of the dopants on the thermodynamics and kinetics of crystallization is investigated. The addition of dopants modifies the thermodynamic equilibrium of the system and this change is mainly entropy driven and also slowdown the kinetics of crystallization. Differential thermal analysis and hot-stage microscopy are employed to investigate the glass-forming ability, sintering, and crystallization behavior of the studied glasses. The crystalline phase assemblage studied under nonisothermal heating conditions in the temperature range of 800°C-900°C in air. Well sintered and dense glass-ceramics are obtained after sintering of glass powders at 850°C-900°C for 1 h featuring crystalline phase assemblage dominated by lithium disilicate (LS 2 ).

Structure and crystallization behavior of Al containing glasses in the CaO–B2O3–SiO2 system

“…It reveals that the amount of SiO 4 increase while the BO 4 units reduce in glass system with the Fig. 4 NMR spectra of (a) 11 B, (b) 27 Al and (c) 29 Si of experimental glasses.…”

“…Deconvolution of (a) 11 B, (b) 27 Al and (c) 29 Si NMR spectra for glass with x ¼ 5. 19,20 Their relative areas are depicted in Fig.…”

“…Fig. 4(b) revealed the 27 Al MAS-NMR spectra of the glasses with x ¼ 1, 5 and 10. The spectra showed a narrow peak centered at 55 ppm are associated with Al IV unit 23 and the peak is sharper with the increasing of x, which shows the enhancement of Al units in glasses.…”

“…This can be ascribed to the addition of Al 2 O 3 dopants, dissolved in glass system, modies the thermodynamic equilibrium of the system and this change is mainly entropy driven and also slowdown the kinetics of crystallization. 27 The addition of Al 2 O 3 leads to the reconnection of fractured silicon oxygen tetrahedron and a large extent of atomic rearrangements. This will make the glass need higher thermal energies to crystallize, resulting the increasing of crystallization temperature ( Fig.…”