Wollastonite from Hydrothermally Synthesized Calcium Hydrometasilicate Obtained from Various Modifications of Silica

Abstract

A hydrothermally CaO–SiO2–H2O system was investigated at 150°–200°C, 2.5 h (CaO:SiO2=0.95) using various modifications of SiO2 in the presence of a mineralizer. Synthetic (stabilized) γ‐tridymite is the most reactive among SiO2 modifications. In the reaction mixture, the optimal concentration of the mineralizer (KOH) is 2% (versus the solid phase). The binding degree of CaO with SiO2 practically is 100% at 150°C. It is impossible to synthesize CSH free of C2SH on the basis of β‐cristobalite and β‐quartz under the investigation conditions without the use of mineralizer. The calorimetric effects as well as heat of de‐hydration of hydrosilicates were determined during their transformation into wollastonite. The entropy change at the peaks has been calculated.

Synthesis and characterization of wollastonite-2Mby using a diatomite precursor

“…As far as synthesis of wollastonite is concerned, experimental procedures refer to the phase reaction method (Kurczyk and Wuhrer, 1971; Kridelbaugh, 1973; Kurczyk, 1977; Kotsis and Balogh, 1989; Ibañez et al , 1990; Grigoryan et al , 2010), the hydrothermal process (Glasser and Taylor, 1978; Grigoryan et al , 2006, 2008, 2010), the glass ceramic method (Philip and Binet, 1971), the sol-gel method (Villegas and Fernandez Navarro, 1988); the molten salts technique (Trubnikov et al , 1989); the microwave method (Vichaphund et al , 2011) and the hydrothermal microemulsion method (Lin et al , 2006).…”