­Effect of sintering treatment time on the sintering behaviour and thermal shock resistance of Li₂O-Al₂O₃-SiO₂ glass-ceramics

Abstract

In order to determine the correlation of flexural strength and thermal shock resistance properties, the sintering behavior of Li 2 O-Al 2 O 3 -SiO 2 (LAS) glass-ceramics at different sintering treatment times and the effect of thermal shock cycles on LAS glass-ceramics were investigated. The LAS glass-ceramics were isothermally treated at 1100°C from 1.5 to 4.5 h. Phase transformation of major crystalline of β-spodumene and minor crystalline of ZrTiO 4 revealed unchanged as sintering treatment time increased. The physical properties of LAS glass-ceramics that were sintered for 3.5 h demonstrated an increased density (2.45 g/cm 3 ) and less porosity percentage (0.62%). The prolonged sintering treatment affected the microstructure whereby the mean grain size increased from 0.55 to 0.67 µm which also demonstrated the increase of microhardness in the range between 3.90 and 5.47 GPa. The flexural strength of LAS glass-ceramics revealed an enhancement of 158 MPa when sintered for 3.5 h. The thermal shock resistance properties were assessed at 500°C from one to seven cycles via thermal shock tests. After four thermal shock cycles, LAS glass-ceramics showed an improvement of 82% of residual strength from its original strength, due to a decrease in the formation of pores and an increase in the crystallinity and percentage of β-spodumene.

Preparation study for the low thermal expansion spodumene/mullite composites

“…24 For the samples sintered at 1300 • C, the grain continued to grow to produce boundary stress, leading to the expansion of pores and a slight decrease in the degree of densification. 25 As can be seen from Figure 6B, at the same temperature, the bulk density of the samples increased with the increase of the spodumene content. At different sintering temperatures, the bulk density of the samples was found to first increase and then decrease.…”

“…In the middle and later stages of sintering, the grain growth led to the formation of pores, and the samples reached their densest state 24 . For the samples sintered at 1300°C, the grain continued to grow to produce boundary stress, leading to the expansion of pores and a slight decrease in the degree of densification 25 …”

“…An excessive amount of the liquid phase gathered on the grain boundary, which no longer was able to support the larger external force, thereby leading to a decrease in the bending strength of the material. In general, the sintering process is a densification process, in which the bulk density and bending strength of the material increase and the corresponding porosity decreases 25 …”

“…In general, the sintering process is a densification process, in which the bulk density and bending strength of the material increase and the corresponding porosity decreases. 25…”

Ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics containing multiphase nanocrystals

“…[34][35] Chen et al 36 studied the effect of Li 2 O content in LAS glass on the crystal phase and CTE and found β-quartz solid solution-based crystal phases precipitation in glass-ceramics, and CTE in 30-300 • C range decrease with Li 2 O content increase. Lutpi et al 37 investigated the relationship between thermal treatment duration and thermal shock behavior of LAS glass, confirmed that the extension of thermal durations resulted in the growth of nanocrystals, from 0.55 to 0.67 μm, and induced microhardness increase, from 3.90 to 5.47 GPa. Keyvani et al 38 found that Al 2 O 3 contents in LAS glass had critical effect on crystallization processes and the microstructure of glass-ceramics by SiO 2 consumption.…”