engleski

EX SITU XRD, TEM, IR, RAMAN and NMR spectroscopy of crystallization of lithium disilicate glass at high pressure

The structure of a Li2O∙ 2SiO2 (LS2) glass was investigated after the glass was subjected to a uniform hydrostatic pressure of 4.5 or 6 GPa up to a temperature of 750 oC. The structure of the processed samples was investigated using XRD, TEM, IR, Raman and NMR spectroscopy. Glass densified at 6 GPa has an average Si-O-Si bond angle ~7o lower than that found in glass processed at 4.5 GPa. At a pressure of 4.5 GPa crystal of lithium disilicate crystallizes from the glass while at 6 GPa, the densified glass crystallizes to a new high pressure form of lithium silicate. The new high pressure phase that forms at 6 GPa has a complex structure with at least 4 different Si sites. NMR of the 6 GPa sample showed the presence of Q4 species with (Q4)Si-O-Si(Q4) bond angles of ~157o. This is the first time that Q4 species with such large bond angles have been reported in alumina free alkali silicate glass. No presence of five or six coordinated Si was found.

Lithium Disilicate Glasses ; Crystallization ; Pressure

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