Solid-phase synthesis of wollastonite in natural and technogenic siliceous stock mixtures with varying levels of calcium carbonate component

Abstract

Solid-phase synthesis of wollastonite has been determined to be primarily affected by the structural and mineralogical properties of the siliceous stock – its chemico-mineralogical composition (purity and presence of amorphous component) and granularity, as well as variations in phase change behaviour at high temperatures. Wollastonite synthesis occurs most completely in the mixtures of calcium carbonate with amorphous (microsilica) or semi-crystalline (gaize or diatomite) siliceous stock, yielding 92–96% wollastonite at 1200°С. For natural quartz-based stock (marshallite), wollastonite yield does not exceed 60–80%. Solid-phase wollastonite synthesis in mixtures of reactive amorphous or semi-crystalline siliceous stock with varying quantities of calciferous stock (10–50wt% CaO) produces wollastonitic ceramics chemically resistant to molten aluminium with the specific gravity of 1.1–1.7g/cm3 and the compressive strength of 28–76MPa, which exceeds the requirements for ceramics in foundry equipment by a factor of 3–3.5.