Thermal properties and devitrification behaviour of (1+x)CaO·(1−x)MgO·2SiO2 glasses
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The thermal properties (glass transformation, Tg, and softening, Ts, temperatures), the crystalline phases formed during heating in a differential thermal analysis (DTA) apparatus, the kinetic parameters and the mechanism of the devitrification process, of glasses of the system diopside-wollastonite were investigated. The substitution of CaO by MgO induces an increase in Tg and the crystal growth activation energy, Ec; this is probably linked to the greater coordination number of Caz+ ions with respect to the Mg2+ ions. The substitution of CaO by MgO lowers the nucleation rates of the diopside phase; wollastonite solid solution nuclei form whose growth appears to leave a glassy matrix in which diopside formation is inhibited. Only surface nucleation was observed, but, in finely powdered samples, which soften and efficiently sinter before devitrifying, surface nuclei behave as bulk nuclei. When bulk crystallization occurs, the Avrami parameter m was found to be 2 for all glasses, except the diopside one, for which m=3.
KeywordsActivation Energy Thermal Property Differential Thermal Analysis Coordination Number Nucleation Rate
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