Notes. Crystallization of amorphous silica into quartz

Crystallized quartz has been obtained from amorphous silica prepared by the hydrolysis of silicon alkoxide containing calcium or magnesium alkoxide (10 mol %). The crystallization of CaSiO3 and MgSiO3 is observed prior to that of quartz. Crystallization isotherms are described by the contracting cube equation 1 –(l –f)⅓=k(t–t0) and activation energies have been determined as 435 and 498 kJ mol–1 in the presence of Ca2+ and Mg2+ respectively.