Effect of high pressure in the Li2O–2SiO2 crystallization

Abstract

The aim of this work was to investigate the effect of previous treatments at high pressures on the crystallization kinetics of monolithic samples of a Li 2 O-2SiO 2 (LS 2 ) glass. The glass transition temperature (T g ) and the temperature of the onset of crystallization (T p ) obtained by differential thermal analyses (DTA) were measured for LS 2 glass samples submitted to isostatic pressures ranging from 2.5 to 7.7 GPa during 5 min at room temperature. The observed systematic changes in T g and T p were probably related to the cracks induced by high pressure inside the monolithic samples and in its surface. Away from the cracks, the nucleation density slightly decreased as a function of pressure but along the cracks, the nucleation density was significantly higher.

Lithium Disilicate Glass‐Ceramics by Heat Treatment of Lithium Metasilicate Glass‐Ceramics Obtained by Hot Pressing

“…The reported IPS Empress 2 Li 2 Si 2 O 5 material, with strength of 400 ± 40 MPa, has been prepared by the hot‐pressing technology . The flexural strength of ~440 MPa for Li 2 Si 2 O 5 glass‐ceramics prepared by hot‐pressing technology was also reported, which is favorable for the application as dental crown, but unfavorable for the machinability and costs of CAD/CAM or other processing. For the dental application of the Li 2 Si 2 O 5 glass‐ceramics by hot pressing, a new processing for preparing Li 2 Si 2 O 5 glass‐ceramics should be proposed by considering the machinability of metasilicate and the high strength of disilicate in the final product, which had been applied for the bulk Li 2 Si 2 O 5 glass materials in the dental crown fabrication .…”

Thermal stability of lithium metasilicate produced under high pressure from lithium disilicate glass

“…The temperature and processing times under high pressure were chosen to obtain three different stages of nucleation and growth. According to previous results on LS 2g at atmospheric pressure, 455°C corresponds to the maximum nucleation rate temperature, while 610°C corresponds to the ideal temperature to promote crystal growth up to detectable sizes . In the first group of samples investigated in this work, the LS 2g glass cylinders were processed at 7.7 GPa and 500°C for 2 hours.…”

“…Toroidal type high‐pressure apparatus was used to process monolithic samples of LS 2g glass under HPHT to produce the LS m crystalline phase. The specific configuration used for the high‐pressure processing and calibration procedures are described elsewhere . The samples consisted of cylinders with dimensions of 2.3 mm in height × 3 mm in diameter.…”

“…In particular, LS 2g glass has been investigated under high pressure by Fuss et al and by Buchner et al The formation of LS m was clearly confirmed by X‐ray diffraction and Raman spectroscopy after processing LS 2g glass simultaneously at high pressure and high temperature (HPHT) . In a previous work, it was shown that heat treatment of the glass at 2.5 and 4 GPa induced the crystallization of LS 2c (treatment at 455°C and 500°C for nucleation and at 610°C for crystal growth).…”

“…This replacement was detected by a shift of the peaks in the XRD pattern. The results obtained by Buchner et al indicated that the LSm phase, while produced as a stable phase at HPHT, remained present at atmospheric pressure and room temperature but as a metastable phase.…”