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The structure of glasses of the binary system CaO-P 2 O 5 was investigated by the comparison of the results of the thermodynamic model of Shakhmatkin and Vedishcheva constructed using the molar Gibbs energies obtained from the FACT database with the results obtained by the analysis of Raman spectra of xCaOÁ(100 -x)P 2 O 5 (x = 35, 40, 45, 50, 55) glasses performed by the principal component analysis (PCA) method and spectral decomposition by the method of Malfait. The PCA method identified three independent components in the studied spectral series. On the other hand, the thermodynamic modeling resulted in three components with significant abundance in the studied glasses, i.e., P 2 O 5 , CaP 2 O 6 , and Ca 2 P 2 O 7 . Using the method of Malfait, partial Raman spectra of P 2 O 5 , CaP 2 O 6 , and Ca 2 P 2 O 7 were calculated. The experimental spectra were reproduced with very good accuracy. The multivariate curve resolution (MCR) method was used for the analysis of the experimental spectra. It was found that MCR loadings are practically identical with the partial Raman spectra obtained from the results of thermodynamic model by the method of Malfait. All the obtained results confirmed the structural information acquired from the thermodynamic model.

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 SiO 2 , Al 2 O 3 and CaCO 3 . 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 × 10 29 ± 1.73 × 10 29 min −1 , apparent activation energy E app = 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.

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