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Growth of 2M-Wollastonite Polycrystals by a Partial Melting and Recrystallization Process for the Preparation of High-Aspect-Ratio Particles
L. Zhu, H.Y. Sohn
Abstract
A polytype of wollastonite, 2M-wollastonite, that breaks into acicular particles under external forces was synthesized in a partial melting and recrystallization process using relatively pure component materials. In the first step, samples containing SiO2 and CaO and small amounts of various additives were pressed into discs and sintered at 1270 °C. These temperatures are lower than the melting points of the major components but higher than the melting points of most of the additives so as to partially melt the samples. The samples were then cooled to below 550 °C at an average rate of 2 – 3 K/min. At the end of this stage, alpha-wollastonite was formed and the particles produced from it displayed little or no acicularity. In the second step, when the samples were further heated at 1070 °C for 5 – 8 hours and then cooled to room temperature, 2M-wollastonite (one of the beta-wollastonite polytypes) was formed. The particles obtained from this phase displayed high acicularity with some particles having aspect ratios as high as 15:1. In addition, the effects of the types and amounts of additives, processing temperature and time on the aspect ratio of the final products were determined.
Keywords
Wollastonite, partial melting, acicular, high aspect ratio, synthesis
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