Glass Physics and Chemistry最新文献

Glass composition of 6Na₂O 22B₂O₃·70SiO₂·2Cr₂O₃ is studied by scanning electron microscopy, X‑ray powder diffractometry (XRPD), and differential thermal analysis, depending on the duration of heat treatment at a temperature of 550°C. It is established that during heat treatment for 24–96 h, a phase separation structure with interpenetrating phases is formed in the studied glass, and a crystalline phase of eskolaite—Cr₂O₃ is also formed. With the maximum heat treatment duration of 96 h, cristobalite is formed in the bulk of the glass, which is accompanied by a decrease in the glass transition temperature of the low-viscosity phase. In this case, the intensity of eskolaite peaks decreases. Cr₂O₃ and SiO₂ crystallize apparently due to the substance of the low-viscosity phase.

The physicochemical processes occurring in glasses of the PbO–CdO–SiO₂–B₂O₃–Al₂O₃ system after high-temperature contact with oxides of various metals—CuO, NiO, Al₂O₃, TiO₂, Nb₂O₅, and WO₃, as well as the electrical resistance of the obtained glasses—are studied by X-ray phase analysis, infrared spectroscopy, and electron paramagnetic resonance. It is established that these properties are determined by the acid-base and redox properties of the oxides and glasses, which directly depend on the content of the O^2– ion in each specific composition.

The results of research on the production of porous glass materials for thermal insulation based on silica-containing technogenic waste and nepheline are presented. The effect of modifying additives on the physical and technical properties of foamed materials is studied, and their optimal quantity and ratio are determined. It is shown that the introduction of a mixture of chalk and gypsum into the charge can significantly increase the strength (by a factor of 1.8–2) and reduce the water absorption of foam glass materials.

Based on the data obtained by complex methods of physicochemical analysis on studying various sections of ternary Tm–As–S(Se) systems and using the published data, the boundary of the glass formation region of the Tm–As–S and Tm–As–Se system is determined. It is established that at a cooling rate of 10 deg/min in the Tm–As–S system, the glass formation area of the system’s glass is 33 at % of the total area of the triangle; and at a cooling rate of 10² deg/min, 51 at % of the total area of the triangle. In the Tm–As–Se system under the specified cooling regimes, the glass area is 35 and 54 at %, respectively.

Synthesis of layered perovskite-like niobates APb₂Nb₃O₁₀ (A = Rb, Cs), being promising visible light active photocatalysts, has been conducted by the ceramic method under variable conditions to obtain the samples with the highest possible phase purity. The oxides prepared were shown practically not to undergo protonation and hydration of the interlayer space upon keeping in water. Both phases APb₂Nb₃O₁₀ were used to yield corresponding protonated hydrated forms H_xA_1 − xPb₂Nb₃O₁₀∙yH₂O via acid treatment. It was found that the propensity of the samples to the substitution of interlayer cations by protons depends clearly on the A⁺ cation: while the Rb-containing niobate is capable of complete protonation (x = 1) upon a single treatment with 6 M nitric acid, the Cs-containing counterpart gives a high enough protonation degree (x ≥ 0.9) only after several renewals of the acid solution. The protonated niobates obtained were exposed to an additional water treatment under hydrothermal conditions, which allowed producing new hydrated derivatives with the enhanced thermal stability towards interlayer dehydration as compared with the protonated precursors.

Hydroxylclinohumite Mg₅(SiO₄)₂(OH,F)₂ is a common monoclinic orthosilicate of the humite group, which, on the one hand, is a prototype of promising materials, and, on the other hand, is an important source of information about both the transport and the presence of water in the Earth’s mantle, and therefore studying its thermal behavior is of particular interest. In this paper, the mineral is studied by powder X-ray diffraction for the first time in a wide temperature range (–180 ≤ T ≤ 1000°C). The temperature limits for the existence of the phase are established, the principal values of the thermal expansion tensor are calculated, and a structural interpretation of thermal expansion is given.

The effect of the hydrothermal synthesis conditions (temperature, duration, mixing), composition, and presynthetic processing of narrow fractions of cenospheres of fly ash, which act as a template and source of Si and Al, on the production of microspherical zeolite materials of the given structural type in the Na₂O–H₂O–(SiO₂–Al₂O₃)_glass of two molar compositions is studied. The synthesis products are characterized by XRD, SEM-EDS, and low-temperature nitrogen adsorption, and their sorption properties in relation to Cs⁺ and Sr²⁺ are studied. The factors contributing to the predominant formation of NaX zeolite of the faujasite structural type are revealed. It is established that zeolite products based on cenospheres with a glass phase content of about 95 wt % demonstrate the highest sorption parameters, including the maximum capacity for Cs⁺ and Sr²⁺ of up to 250 and 180 mg/g, distribution coefficient of about 10⁴ and 10⁶ mL/g, and degree of extraction of 99.1 and 99.9%, respectively.

The SiO₂, Gd₂O₃–SiO₂ and Eu₂O₃–SiO₂ were synthesized by two ways: using the silicon oxide isolated from kaolin and using the silicon oxide obtained by hydrolysis of tetraethoxysilane. Agar-agar (polysaccharide) was added as a structure-forming agent and the freeze-drying was used for obtaining powders. DSC and TG up to 700°С revealed endothermic effects corresponding to the loss of free moisture, the decomposition of metal hydroxide and hydroxogroups (≡Si–OH) from the silica surface. The powders calcined at 700°С are X-ray amorphous. The morphology of the samples was studied using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The hydrodynamic size of the particles synthesized from kaolin, determined using DLS method, exceeds the particle size established by TEM. The hydrodynamic size of the nanoparticles obtained from tetraethoxysilane is within the particle size determined by TEM. The agglomerates formed by particles synthesized from tetraethoxysilane are less strong than those obtained from kaolin. In the Eu₂O₃–SiO₂ system obtained using tetraethoxysilane, nanocrystallinity with a particle size of 8–40 nm was detected. The luminescence excitation spectra for the Eu₂O₃–SiO₂ samples synthesized by both ways differ in the ratio of the supersensitive ⁵D₀–⁷F₂ and magnetodipole ⁵D₀–⁷F₁ transition bands. For the Gd₂O₃–SiO₂ nanopowder obtained from tetraethoxysilane, an increase in the ⁵D₀–⁷F₂ intensity, as well as the appearance of a second ⁵D₀–⁷F₁ peak were observed.

The main cause of global warming is the steady increase in greenhouse gases in the atmosphere. The largest share of greenhouse gases is carbon dioxide CO₂. Therefore, it is important to efficiently separate it in different gas systems. The article examines the sorption of carbon dioxide from polysilicic acid—silica gels modified with hydroxyethyl carbamate (HEC). It is shown that the modification is optimal in 30% HEC solutions. The fact of modification is confirmed by the presence of amino, hydroxyl, and carbonyl groups in the sorbents. Thermal stability is studied by the thermogravimetric method. Sorption at high pressures is studied by the gravimetric method and sorption at atmospheric pressure is studied by the thermogravimetric method. It is found that the presence of amino groups contributes to the sorption of carbon dioxide by silica gel more than doubling. The highest sorption rates are found to be 8.8% of the mass of the sorbent at 30°C. After five cycles of sorption/desorption processes in sorbents, the maximum sorption capacity decreased by 10%. The sorption rate increases at high pressures of up to 3 atm. Sorbents modified with a 30% HEC solution at 3 atm sorb up to 9.96 mol CO₂/g. The relatively fast growth of the sorption rate at high pressures and its relatively slow growth at low pressures prove that the process corresponds to type-2 sorption. Such sorption systems are promising for use in various technological systems containing CO₂.

The results of studies on the intensification of the dealkalization process of alkaline silicate industrial and synthesized glasses with acid gases are analyzed and summarized. The composition of the reaction products of glasses with gaseous reagents is identified using X-ray phase analysis, X-ray spectral electron probe microanalysis, thermal analysis, flame photometry, and quantitative chemical analysis. The physicochemical properties of industrial glassware modified with gaseous reagents are determined in laboratory and factory experiments. Ways of intensifying the dealkalization process of silicate glasses with acid gases are discussed.