Identification of surface active components in glass forming melts by thermodynamic model

Nine compositional series of 15(Na2O, K2O)center dot 10(CaO, ZnO)center dot 75(ZrO2, SiO2) glass-forming melts were studied, all with the ZrO2 content of 0, 1, 3, 5 and 7 mol.%. The investigated glass compositions were obtained by equimolar substitutions ZrO2 / SiO2, ZnO / CaO and K2O / Na2O. Surface tension of studied glassforming melts was de-termined by the sessile and pendant drop profile numerical analysis in the temperature range (1250 1500) degrees C. The experimental values of melt density were used. The linear temperature dependence of surface tension was observed for all samples with only small differences between values obtained from sessile and pendant drop profiles. The Shakhmatkin and Vedishcheva thermodynamic model (TDM) was evaluated for each glass melt at temperature of 1400 degrees C. The total number of 36 components was considered in TDM. Only 26 components were present with non-negligible equilibrium amount. The surface tension was described by the multilinear function of equilibrium amounts of statistically independent non-negligible components of the TDM. The surface active components were identified by negative values of their coefficients. Such way the N3S8 and C2ZrS4 were identified as "strongly" surface active and NCS5 and KS4 as probably surface active. Regarding the oxide compositional point of view, the surface tension was mostly influenced by ZnO (increase with the addition of the oxide) and by K2O (decrease with the addition of the oxide)

Structure and Raman spectra of binary barium phosphate glasses

[EN] The structure of xBaO·(1 − x) PO (x = 0.30, 0.35, 0.40, 0.45, and 0.50) glasses was studied by Raman spectroscopy and thermodynamic model Shakhmatkin and Vedishcheva (SVTDM). The seven system components (defined as stable crystalline phases of the BaO–PO binary phase diagram) were considered in the SVTDM: BaO, PO, 4BaO·PO (B4P), 3BaO·PO (B3P), 2BaO·PO (B2P), BaO·PO (BP), and BaO·2 PO (BP2). Only the equilibrium molar abundances of BP and BP2 were non-negligible in all studied glass compositions. Therefore, in the next step, multivariate curve analysis (MCR) of the baseline—subtracted, thermally—corrected experimental Raman spectra, was performed for two components (BP2 and BP). MCR resulted in the Raman spectra (loadings) and relative abundances (scores) of each considered component. The MCR method reproduced 98.93% of the spectral data variance. Then, the decomposition of Malfait was used. The perfect fit between the MCR loadings and the partial Raman spectra of BP2 and BP, obtained by Malfait’s decomposition, was found, confirming the validity of thermodynamic model.This paper is created in the frame of the Project FunGlass that has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 739566. This work was supported by The Slovak Grant Agency for Science under Grant No. VEGA 1/0064/18, and the Project Centre for Functional and Surface Functionalized Glass (CEGLASS), ITMS code is 313011R453, operational program Research and innovation, co-funded from European Regional Development Fund

Crystallization kinetics of Ni-doped Ca2Al2SiO7 glass microspheres

The Ni-doped Ca(2)Al(2)SiO(7)glass systems were prepared by flame synthesis. Solid-state reaction was used to prepare the powder precursors. The concentration of Ni was 0.5, 1 and 3 mol%. Polydisperse systems were prepared with diameters between 5 and 140 mu m. Detailed examination of morphology of the glass microbeads by SEM revealed no features indicating the presence of crystalline phases. However, X-ray diffraction analysis showed that the samples GNi0.5 (0.5 mol% of Ni) and GNi1.0 (1.0 mol% of Ni) contained traces of crystalline gehlenite. HT-XRD was used to determine the temperature dependence of phase composition. For all prepared compositions, only one crystalline phase (Ca2Al2SiO7) was observed. DSC measurements in the temperature range 30-1200 degrees C at five different heating rates were carried out to study the thermal behavior. The DSC curves of all glasses contained one exothermic peak, which was attributed to crystallization of the gehlenite. The maximum of the peak decreased with increasing Ni content in the microspheres. The kinetic parameters (frequency factorA, apparent activation energyE(app)and the Avrami coefficientm) of the crystallization were determined using the Johnson-Mehl-Avrami-Kolgomorov model. In case of GNi0.5 and GNi1.0 glasses, the nucleation's rate had linear temperature dependence, the crystal growth interface is controlled by chemical boundary and the crystal growth is one-dimensional. The rate of nucleation is linear, the crystal interface growth is controlled by diffusion and one-dimensional crystal growth prevails in crystallization of the GNi3.0 (3.0 mol% of Ni)

Structure, thermal properties and crystallization behavior of binary Y2O3–Al2O3 glasses with high alumina content

Five compositions in the system Al2O3–Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 °C, with slow crystallization of θ- and α-Al2O3 phases detected in the temperature interval 980–1450 °C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 °C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and α-Al2O3 phase in the samples crystallized at 1500 °C and the presence of a trace amount of θ-Al2O3 in the sample crystallized at 998 and 1300 °C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected

Structure and magnetic properties of Bi-doped calcium aluminosilicate glass microspheres

Bi-doped CaO-Al2O3-SiO2 glass microspheres with Ca2Al2SiO7 (gehlenite) composition were prepared by combination of solid-state reaction and flame synthesis. The concentration of Bi was 0.0, 0.5, 1 and 3 mol %. The chemical composition of prepared glass microspheres was determined by X-ray fluorescence (XRF). The structural and magnetic properties of prepared glass microspheres and their polycrystalline analogues were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy and SQUID magnetometry. The closer inspection of glass microspheres surface by SEM confirmed smooth surface and revealed no features indicating presence of crystalline phases. All Bi-doped microspheres are X-ray amorphous, however in case of undoped microspheres XRD detected traces of crystalline gehlenite. XRD analysis of samples crystallized at 1273 K for 10 h revealed the presence of gehlenite as the main crystalline phase. The presence of gehlenite in crystallized samples were also confirmed by Raman spectroscopy. All samples (glass microspheres and their crystalline analogues) showed diamagnetic or weak ferromagnetic behavior at room temperature, whereas paramagnetic or weak ferromagnetic behavior was observed at 2 K