Wollastonite polytypes in the CaO-SiO2 system. |
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| Authors: | E Mazzucato A F Gualtieri |
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| Institution: | (1) Dipartimento di Scienze della Terra, Università di Modena e Reggio Emilia, Via S. Eufemia 19, 41100 Modena, Italy e-mail: alex@unimo.it Fax: +39-059-417399, IT |
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| Abstract: | This work deals with the identification and kinetics of crystallisation of the wollastonite polytypes which form in the system
CaO-SiO2 in the temperature range 700–1000 °C. The kinetics of phase transformations in the system have been determined from analysis
of in situ synchrotron X-ray powder diffraction data. Two different systems with the same compositions were investigated:
one is more reactive, having grains with a larger surface area per unit volume, the other is less reactive, being composed
of grains with a smaller surface area per unit volume. 1T-wollastonite forms first and progressively transforms in an intermediate
1Td-wollastonite disordered form. Both phases in turn transform into 2M-wollastonite polytype. Differences in the polytypes
forming and reaction kinetics were observed for the two systems. In the more reactive system, the conversion 1T to 1Td polytypes
is the dominant process. The kinetic parameters calculated using the Avrami models fully describe the reaction process of
formation of both polytypes and transformation of one polytype into the other.
Received: 3 August 1999 / Accepted: 20 March 2000 |
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| Keywords: | Wollastonite Reaction kinetics Polytype In situ synchrotron XRPD |
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