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⩽x⩽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 600 °C, with crystallisation temperatures above 850 °C. When sintered at 1000 °C 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.