Glass Physics and Chemistry最新文献

A method is developed for producing primary catalyst carriers in the form of honeycomb blocks using additive technologies. The composition of the molding slip is developed and its rheological properties are optimized. Block catalysts based on primary supports formed by 3D printing are obtained. It is shown that these products are highly productive in the process of the catalytic oxidation of CO with atmospheric oxygen and it is possible to further increase it due to the formation of channels of complex geometric shapes, which make it possible to intensify the processes of heat and mass transfer.

Anion-deficient structures based on a Sr_0.5Ba_0.5Co_1 – xFe_xO_3 – δ composition, synthesized from a melt in a solar oven in a flux of concentrated solar radiation with a density of 100–200 W/cm² are studied. Briquettes in the form of tablets based on a stoichiometric mixture of carbonates and oxides of the corresponding metals (SrCO₃ + BaCO₃ + Co₂O₃ + Fe₂O₃) are melted in the focal zone of the great solar furnace. Melt drops flow into the water, cooling at a rate of 10³ deg/s. The castings were ground to a fineness of 63 µm, dried at 400°C, and molded into tablets (samples) with a diameter of 20 mm and a height of 10 mm. Samples of the material are sintered in the temperature range 1050–1250°C. The samples are used to study the structure, water absorption, and destruction in a carbon dioxide environment. The crystal lattice of the material has a perovskite structure with the unit cell parameter a = 4.04 Å. Samples of the material show resistance to water vapor. The observed values of the structural parameters indicate that the material of composition Sr_0.5Ba_0.5Co_0.8Fe_0.2O_2.78 can be used as a catalyst for the generation of hydrogen and synthesis gas through reforming and methane oxidation.

When low molecular weight ammonium polyphosphate interacts with polyethylene polyamine, thermoplastic polymers containing fractions with glass transition temperatures T_glass ≥ –95°C are obtained. Their thermal and heat resistance, as well as moisture resistance, is measured at a humidity of 40–50%. The structure and chemical scheme for the formation of interaction products are proposed.

In this work we prepared boro-telluride glass samples while varying the concentration of TeO₂ (0.00, 10.00, 20.00 mol %) by melt quenching technique and study their physical, optical and luminescence properties by various characterization methods. We found that band gap lies in the 2.88–2.18 eV range, showing decreasing trend with increasing concentration of TeO₂. The emission spectra shows four emission peaks under 378 nm excitation centered at 486, 545, 590 and 620 nm because of the transition from ⁵D₄ state to ⁷F_J (where, J = 6, 5, 4, 3) lower levels. Whereas the intensity decreases with increasing concentration of TeO₂, indicating that the non-radiative energy transfer through cross relaxation (CR) increases with increasing concentration of TeO₂. The color coordinates for all studied glasses fall in green region and were (x = 0.304, y = 0.605). The CCT obtained value for all prepared glasses is 6000 K. Above study suggests that these glasses can be potentially used in green light LEDs and in other solid state lighting applications.

A series of lithium aluminosilicate glasses with the composition of 70SiO₂–10Al₂O₃–5K₂O–15Li₂O–xNaCl (x = 0.5, 1.5, 2.5, 3.5 and 4.5 wt %) were prepared by the melt-quenching method. The effect of NaCl addition on mechanical properties was assessed. It was found that both the glass density and the hardness decreased with increasing content of NaCl from 0.5 to 3.5 wt %. Interestingly, Vickers hardness of the glass increased when NaCl content increased by 4.5 wt %. Raman test results show that NBO/T in the glass increases with NaCl, that is, the decrease of the degree of polymerization of the glass network due to the breaking of Si–O–Si bonds. Since the Si–O–Si covalent bond is the strongest bond in the silicate glass, the glass structure tends to be depolymerized, and the density and Vickers hardness decrease. Thus, we attribute the hardness increasing at 4.5 wt % NaCl addition to the fact that Na⁺ enters the network pores acting as network modifier.

Two compositions of heat-resistant electrical insulating organosilicate coatings are developed using fine glassy additives in the compositions: aluminoborosilicate and vanadium antimony phosphate glass. The coatings have a heat resistance of 700 and 800°С and resistance to sudden temperature changes from the maximum permissible temperature to 20°С three times. The electrical insulating and physical-mechanical properties of the coatings are determined.

The combinatorial-topological analysis and self-assembly of crystal structures of Yb₇₂Sn₄₆-tP118 (a = 11.076 Å, c = 36.933 Å, V = 4530.86 ų, pr. group P4/mbm) intermetallic compounds is modeled using computer methods (the ToposPro software program). For the crystal structure of Yb₇₂Sn₄₆-tP118, 195 variants of a cluster representation of a 3D atomic grid with 5 (24 variants), 6 (86 variants), and 7 (85 variants) structural units are established. The variant of the fastest self-assembly involving three types of clusters-precursors forming layers of octahedra K6 = 0@6(Yb₄Sn₂) with symmetry g = 4/m, from polyhedra K11 = Sn@10(Yb₈Sn₂) with symmetry g = –1, and polyhedra K15 = Yb@14(Yb₁₀Sn₄) with symmetry g = 2 mm, as well as Yb and Sn spacer atoms, is considered. The symmetry and topological code of the processes of the self-assembly of 3D structures from clusters-precursors are reconstructed in the following form: primary chain → layer → framework.

To prepare 0.5LaPO₄–0.5ZrO₂ and 0.5LaPO₄–0.5Y₂O₃ ceramic composites, a microwave assisted sol-gel procedure for the synthesis of nanosized 0.5LaPO₄·nH₂O–0.5ZrO(OH)₂ and 0.5LaPO₄· nH₂O–0.5Y(OH)₃ precursor powders was developed. Ceramic composites were prepared by microwave sintering of powders at 1100°C after preliminary heat treatment of precursor powders at 850°C, as well as by conventional stepwise sintering at 1000, 1100 and 1200°C for 24 h. The unit cell parameters of monoclinic LaPO₄ were calculated depending on sintering method and temperature. The values of specific surface area of the samples, Vickers microhardness, and thermal conductivity were determined; fracture surface of ceramic samples was studied. Such a complex study of 0.5LaPO₄–0.5ZrO₂ and 0.5LaPO₄–0.5Y₂O₃ composites is presented for the first time. The influence of sintering method, temperature and addition of zirconia and yttria to LaPO₄ on the resulting composite’s properties, phase composition and type of ceramic fracture surface is discussed.

Thermal expansion of SrBi₂B₂O₇ borate was investigated by in situ powder X-ray diffraction in the temperature range from –175 to 25°C. Compositional deformations of Sr_1 – xBa_xBi₂B₂O₇ solid solutions were calculated. The band gaps for solid solutions were determined by the absorption spectroscopy. A similarity of thermal and compositional deformations has been established. These deformations were compared with the crystal structure of Sr_1 – xBa_xBi₂B₂O₇ solid solutions.

Polymer dielectric composites consisting of polytetrafluoroethylene, silicon dioxide and barium titanate mixed in various proportions were successfully synthesized by low-temperature sintering. The structure of the obtained composite samples was studied by the X-ray diffraction, the electron microscopy, and the weight method. Electrical characteristics (dielectric permittivity and losses) of samples were investigated at a frequency of 1 MHz. According to structural analysis, the synthesized samples are a mixture of amorphous polytetrafluoroethylene and silicon dioxide, and crystalline ferroelectric BaTiO₃, the ratio of which determines the electrical properties of the composites. Depending on the content of barium titanate, the studied samples show a permittivity from 4 to 6.5 with a dielectric loss level of 0.06–0.14. It is shown that the significant influence on the dielectric properties of the polytetrafluoroethylene/silicon dioxide/barium titanate system is exerted by heat treatment modes.