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.

Investigation of the structure glass-ceramic materials according to data of IR spectroscopy

The efficiency of the use of IR spectroscopy in studying the structure of magnesium-aluminosilicate glass-ceramic materials was analyzed. It was established that the formation of the structure of these glass-ceramic materials during the heat treatment is associated with a distortion of the cordierite structure. The presence of solid solutions, high and low cordierite in the structure of the materials under study was detected according to the systems of bands F2, E2, C2 and D2, depending on the temperature of their heat treatment. The mechanism of phase formation in magnesium-aluminosilicate glass-ceramic materials has been determined, which consists in the formation of future crystals of -cordierite and spinel at the initial stages of nucleation, and crystals of -cordierite and mullite at the stage of crystallization. Formation of a finely dispersed glass-ceramic structure with a predominant content of -cordierite or mullite under conditions of low-temperature heat treatment is a decisive factor in ensuring high thermal and mechanical properties of glass-ceramic materials. This allows them to be used as structural elements of devices and equipment under thermal and mechanical loads.

Lithium aluminosilicate glass-ceramics for low-temperature anodic sealing of MEMS sensors

The results of a study of the anodic bonding parameters of transparent glass-ceramics based on lithium aluminosilicates which are promising as structural materials of MEMS and MOEMS sensors are presented. A comparison of the optical transmittance of these materials and classical for MEMS industry glasses has been carried out. The glass-ceramics electrical conductivity in a wide temperature range has been measured. The procedure of hermetic sealing of glass-ceramics by the anodic bonding at temperatures of 150 – 250 °C has been worked out. A prototype of glass-ceramic atomic cell has been fabricated.

Effect of Different Concentrations of Titanium Oxide (TiO2) Addition on the Crystallization Behaviour and Some Properties of Alkaline Earth Aluminosilicate Glass-Ceramics

Glass-ceramics in the CaO-MgO-Al2O3-SiO2 quaternary base glass system was produced via melting technique using feldspar, limestone and magnesite as sources of starting materials. Glass-ceramics production involves making a base glass, annealing and cooling to room temperature and then reheating the base glass to nucleation and crystal growth temperatures. Characterization of the produced glass-ceramics was carried out using a scanning electron microscope (SEM). The effects of the crystallization process on some properties such as hardness, chemical durability in acid and alkali media of samples were determined. The results portrayed that glass-ceramic samples to which various amounts of TiO2 (2,4,6,8 and 10 wt.%) were incorporated showed the formation of crystalline phases dispersed in the matrix of their respective residual glassy phases. Significant improvement in hardness, as well as minimum weight loss, were recorded for all the glass-ceramic samples. On the contrary, the glass samples did not crystallize despite subjecting them to heat treatment, their hardness values were low and they were not resistant to acid (1M HCl) and alkali (1M NaOH) attacks. The inability of TiO2 addition to fully transform them into glass-ceramics remains a shortcoming. However, the glass-ceramic samples obtained from this study can be used for tiling works.