SOLID-STATE SI-29 NMR AND FT RAMAN-SPECTROSCOPY OF THE DEVITRIFICATION OF LITHIUM METASILICATE GLASS

Lithium metasilicate glass was found to devitrify in two steps. In the primacy step the glass undergoes a transformation which is exothermic and in which there is almost no crystal growth. The nature of this pr ocess and the modification that it causes in the glass has been invest igated by a combination of solid state Si-29 nuclear magnetic resonanc e spectroscopy and Raman spectroscopy. During the primary step a redis tribution of Q(N) units occurs as shown by changes in the intensities of the Si-29 resonances associated with these structural units. The ab sence of narrow resonances in samples heated to the primary step sugge sts that most of the sample is not crystalline. This amorphous state i s consistent with the powder X-ray diffraction where only diffraction peaks with small intensities are seen. (C) 1998 Elsevier Science B.V.