Crystallization kinetics of gehlenite glass microspheres
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Crystallization kinetics of gehlenite glass microspheres Melinda Majerová1 · Anna Prnová2,3 · Alfonz Plško3 · Peter Švančárek2,3 · Jana Valúchová2,3 · Róbert Klement3 · Dušan Galusek2,3 Received: 9 August 2019 / Accepted: 9 January 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The glass of gehlenite composition was prepared by flame synthesis in the form of microspheres. The powder precursor was synthesised by standard solid-state reaction method using S iO2, Al2O3 and C aCO3. The prepared glasses were characterized from the point of view of surface morphology, phase composition and thermal properties by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The prepared samples contained only completely re-melted spherical particles. SEM did not reveal any features indicating the presence of crystalline phases. However, traces of crystalline gehlenite were detected by XRD. The high-temperature XRD measurements (HT XRD) were carried out to identify the phase evolution during glass crystallization. In the studied temperature range, gehlenite phase was identified as the main crystalline phase. Non-isothermal DSC analysis of prepared glass microspheres was carried out from room temperature up to 1200 °C at five different heating rates: 2, 4, 6, 8 and 10 °C/ min to determine the thermal properties of microspheres. In order to study the crystallization kinetics, the DSC curves were transformed into dependence of fractional extent of crystallization (α) on temperature. The Johnson–Mehl–Avrami–Kolmogorov model was found to be suitable for description of crystallization kinetics. Frequency factor A = 5.56 × 1029 ± 1.73 × 1029 min−1, apparent activation energy Eapp = 722 ± 3 kJ mol−1 and the Avrami coefficient m = 2 were determined. In the studied system, the linear temperature dependence of nucleation rate, diffusion controlled crystal growth interface and a 2D crystal growth were confirmed. Keywords Gehlenite · Solid-state reaction · Flame synthesis · Glass microspheres · Crystallization kinetics
Introduction Gehlenite (Ca2Al2SiO7) is a sorosilicate from the family of melilites, which are a large family of tetragonal, noncentrosymmetric materials. C a2Al2SiO7 crystallizes in the tetragonal crystal system with a space group P 4̄ 21 m, and the lattice parameters of the unit cell were a = b = 7.868 Å, c = 5.068 Å and V = 299.390 Å3. In the structure of the * Melinda Majerová [email protected] 1
Department of Magnetometry, Institute of Measurement Science, Slovak Academy of Sciences, Dúbravská cesta 9, 842 19 Bratislava, Slovak Republic
2
Vitrum Laugaricio – Joint Glass Center of The IIC SAS, TnU AD and FCHPT STU, Študentska 2, 911 50 Trenčin, Slovak Republic
3
Centre for Functional and Surface Functionalized Glass, Alexander Dubček University of Trenčin, Študentska 2, 911 50 Trenčin, Slovak Republic
gehlenite, the Al3+, Si4+ and Ca2+ cations are localized at three types of sites: A l3+ ion
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