Z-PHASE SYNTHESIS USING REAGENTS AND INDUSTRIAL WASTE MATERIAL SILICA GEL

Abstract

The process of synthesis of calcium silicate hydrate, called Z-phase, was examined under hydrothermal conditions (200 ºC under a saturated water steam pressure) using both pure CaO (98.7%) and amorphous SiO₂·nH₂O. The fineness of the starting mixture was found to have a crucial influence on the formation of the mentioned compound: the finer the SiO₂·nH₂O, the faster Z-phase is formed. For example, only traces of this calcium silicate hydrate were identified when the specific area of SiO₂·nH₂O was ~400 m²/kg, but when this parameter was increased to ~2 000 m²/kg, Z-phase was the dominant compound in the synthesis products. Also, attempts to synthesize Zphase from industrial material have been made. Silicagel, a waste of AlF₃ production, was used as the main component because of its high amorphous SiO₂ content (78.9%), adding a calculated amount of pure CaO (98.7%). The results have shown that the process of Z-phase formation in this case is analogous as compared with that of pure SiO₂·nH₂O with the specific area of about 2 000 m²/kg and that the mentioned compound is stable when the duration of the synthesis is 4–8 hours. Also, the transition of Z-phase into gyrolite – thermodynamically most stable phylosilicate compound group – occurs faster (after 24 hours instead of 48 when using pure SiO₂·nH₂O).

DOI: http://dx.doi.org/10.5755/j01.ct.59.1.1524