Mesoporous calcium silicate glasses. I. Synthesis

The conventional method of preparing glasses is quenching a melt. However, as with many multicomponent glasses, only a certain range of CaO-SiO2 compositions can be melt derived. Sol-gel processing allows one to produce gel-glasses with compositions lying within the liquid-liquid immiscibility dome of the CaO-SiO2 system. Crack-free silica-calcia xerogel monoliths of various shapes and sizes of compositions expressed by the following formula xCaO . (1 - x)SiO2, where 0 less than or equal to x less than or equal to 0.5 mole fraction, were prepared via the sol-gel technique, starting from tetraethyl orthosilicate and calcium nitrate. In this paper the processing technique is described. The materials produced were characterised using X-ray diffraction, infrared (FTIR) spectroscopy, energy dispersive scanning electron microscopy (SEM-EDS) as well as differential thermal analysis (DTA). The gel-glasses produced are confirmed to be amorphous even after stabilisation at 600degreesC, with crystallisation temperatures above 850degreesC. When sintered at 1000degreesC they form crystalline phases in accordance to the CaO-SiO2 phase diagram. Acid digestion analysis confirms that the compositions of the gel-glasses are similar to that of the computed values. The gel-glasses are homogeneous throughout the monolith. (C) 2002 Elsevier Science B.V. All rights reserved.