Crystallization kinetics terbium-doped aluminophosphate glass studied by DSC, XRD and SEM

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Crystallization kinetics and thermal transformation analysis were investigated for a transparent Tb-doped aluminophosphate glass, with a composition based on the system Tb2O3-Li2O-BaO-Al2O3-La2O3-P2O5, which was prepared by a wet non-conventional raw materials preparation method, followed by a melt-quenching process. The crystallization parameters (crystallization activation energy (Ec) and Avrami exponent (n)) were evaluated from the experimental data obtained by differential scanning calorimetry (DSC) performed at different heating rates. DSC curves exhibited an endothermic peak associated with the glass transition and an exothermic crystallization peak. The glass dependence of the transition (Tg) and of the crystallization (Tp) temperatures on the heating rate (b) were evaluated by Lasocka method. There was a close agreement between the values of the glass transition (Eg) and crystallization (Ec) activation energies determined by Kissinger, Moynihan and Ozawa methods. Considering the variation of the fraction of crystallization (c), 0.1 ≤ c ≤ 0.9, calculated from the thermal analysis experimental data for the exothermic peak, the value of activation energy (Ec(c)) slightly decreased from 360 to 310 kJ/mol, and the Avrami exponent (n(c)) varied from 0.85 to 1, suggesting a surface nucleation mechanism in the crystallization process. X-ray diffraction analysis (XRD) indicated the formation of a predominant aluminium metaphosphate phase, Al(PO3)3, that was present with some aluminium phosphate (AlPO4). Observation by scanning electron microscopy (SEM) of the microstructures of bulk glass samples, after heat-treatment at 600 ºC, revealed the presence of spherulitic-shaped crystals in the glass matrix and confirmed that crystallization was predominantly initiated from the surface of the samples.
Original languageUnknown
Publication statusPublished - 1 Jan 2013

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