Glass Physics and Chemistry最新文献

The process of the formation of diamond-like carbon films on the surface of monocrystalline silicon is studied. The film is formed as a result of the plasma-chemical decomposition of hydrocarbons (propane, butane) and subsequent annealing in a vacuum. The carbon film is formed in the form of diamond-like nanoparticles with a diameter of about 8 nm. Silicon–carbon bonds are formed at the boundary of the silicon substrate and the carbon film, which ensures strong adhesion.

Nanosized (1 – x)ZrSiO₄–xHf(OH)₄ precursor powders are synthesized using the sol-gel method with the separate precipitation of components for obtaining (1 – x)ZrSiO₄–xHfO₂ ceramic composites. The thermal behavior of the precursor powders is studied using the differential scanning calorimetry and thermogravimetry (DSC/TG) method. By sintering powders precalcined at 850°C in air in the temperature range of 1000–1300°C, ceramic composites with high microhardness are obtained. The phase composition is determined by the XPA method.

Using the methods of the cocrystallization and coprecipitation of hydroxides, xerogels and powders based on zirconium dioxide are synthesized and ceramics based on them are obtained. The influence of the synthesis conditions on the physicochemical properties of the obtained materials is assessed.

In the Cs₂O–B₂O₃–SiO₂ system, samples with different stoichiometric ratios of Cs₂O : B₂O₃ : SiO₂—1 : 3 : 2 (CsSiB₃O₇) and 1.25 : 2.5 : 2—were obtained by solid-phase reactions. The phase formation of cesium borosilicate СsSiB₃O₇ was studied. In samples with a stoichiometric ratio of 1 : 3 : 2, CsSiB₃O₇ crystallizes with impurities of kirchhoffite and CsB₃O₅ at 680°C. At 750°C, melting is observed with the formation of cubic boropollucite CsBSi₂O₆. In samples of nonstoichiometric composition, Cs₂B₄SiO₉ crystallizes at 680°C along with CsB₃O₅. With an increase in temperature to 750°C, only boropollucite is formed.

In accordance with the developed original method of the sol-gel synthesis of compositions, based on the separate precipitation of components (using the reverse precipitation technique) followed by their mixing and sintering, ceramic composites based on the LaPO₄–ZrSiO₄ system are obtained. The developed sol-gel synthesis technique is based on the separate preparation of colloidal solutions of LaPO₄·nH₂O and zirconium hydroxide ZrO(OH)₂, formed after adding ammonia solution (sols) and an alcohol solution of TEOS (gel) by reverse precipitation and subsequent mixing of the sols and gel with the addition of the ammonia solution to obtain the corresponding compositions ((1 – x)LaPO₄·nH₂O–x(H₂SiO₃‒ZrO(OH)₂)) in the form of gels. The physicochemical properties of the powders are studied using the X-ray diffraction, DSC/TG, and sorption methods. The Vickers microhardness of the ceramic samples sintered in the temperature range of 1000–1300°C is measured. A Russian patent was obtained for the method of synthesizing composites based on LaPO₄. Mineral-like matrices based on the LaPO₄–ZrSiO₄ system are intended to be used for the immobilization and disposal of individual isotopes of the actinide–rare earth fraction of high-level waste (HLW).

Bismuth-containing composite materials (CMs) with variable yttrium oxide content are synthesized by impregnating porous silicate glass matrices in acidified aqueous-salt solutions of Bi(NO₃)₃·5H₂O in the presence of Y(NO₃)₃·6H₂O with their subsequent heat treatment at 650 or 870°C, and their luminescent properties are studied. It is found that the synthesized materials exhibit photoluminescence in a wide spectral range (230–900 nm) due to the presence of various active centers (=Si⁰, Y³⁺–({text{O}}_{3}^{{2 - }}), Si-BAC (silicon-associated bismuth active centers), radicals , Bi³⁺ and Bi²⁺ ions, Bi³⁺ pairs, silicon–oxygen defects), as well as the Bi³⁺ → Y³⁺ MMCT (metal-to-metal charge transfer) transition, as a result of which they can be considered as new promising solid-state phosphors.

This article presents the results of a study of the concentration limits of the existence of the hollandite phase in the Cs₂O–Al₂O₃–TiO₂ system. A number of samples with different ratios of cesium, aluminum, and titanium are obtained by combustion of citrate–nitrate compositions. The phase composition and microstructure of the obtained materials are studied using X-ray phase analysis and scanning electron microscopy. When studying the electrical properties, it is found that the Cs_1.16Al_1.84Ti_6.33O₁₆ (σ = 5.45 × 10^–5 S/cm at T = 750°C) has the highest specific electrical conductivity.

Using computer methods (ToposPro software package), a combinatorial-topological analysis and modeling of the self-assembly of crystal structures of the La₈Ni₄₀As₂₄–oP72 (V = 1069.3 ų, etc., Pnma group) and Ca₁₂Fe₃₂Pd₄As₂₄-oP72 (V = 1155.89 ų, etc., Pnma group) families are carried out. For the crystal structure of La₈Ni₄₀As₂₄–oP72, 79 variants are established for identifying cluster structures with the number of clusters N = 2 (1 variant), 3 (18 variants), 4 (30 variants), and 6 (30 variants). A variant of the self-assembly of a crystal structure with the participation of clusters-precursors forming the packing is considered: double tetrahedra-dimers K6(4a) = 0@6(La₂Ni₂As₂) and K6(4b) = (Ni₂As₂Ni₂) with symmetry g = –1, tetrahedra K4 = 0@4 (LaNi₂As), rings K3 = 0@3(Ni₂As), and spacer atoms Ni7 and As5. For the crystal structure of Ca₁₂Fe₃₂Pd₄As₂₄-oP72 93 variants are established of the cluster representation of a 3D atomic grid with the number of structural units equal to 2 (2 variants), 3 (15 variants), 4 (49 variants), and 6 (29 variants). A variant of self-assembly of the crystal structure of Ca₁₂Fe₃₂Pd₄As₂₄-oP72 with the participation of the clusters-precursors forming the packing is considered: double tetrahedra-dimers K6(4a) = 0@6(Ca₂Fe₂As₂) with symmetry g = –1, tetramers K12(4b) = 0@12 (CaFeFe₂As₂)2 with symmetry g = –1, tetrahedra K4 = 0@4(CaFe₂As), rings K3 = 0@3(Fe₂As), and Pd and As spacer atoms. The symmetry and topological code of the self-assembly processes of the 3D La₈Ni₄₀As₂₄–oP72 and Ca₁₂Fe₃₂Pd₄As₂₄-oP72 structures is reconstructed from clusters-precursors in the following form: primary chain → layer → framework.

This paper presents the results of determining the content of various acid-base sites (Brønsted basic, Brønsted acid, Lewis basic) on the inner surface of the pore space of high-silica porous glasses (PGs), obtained as a result of the through leaching of alkali borosilicate glass with a two-frame structure and modified by isothermal exposure at various temperatures in the range of 120–750°C. The relationship between changes in the content of the centers under consideration and the processes of hydroxylation and dehydroxylation of the PG surface is analyzed depending on the heat treatment temperature.