Glass Physics and Chemistry最新文献

The temperature dependences of the specific heat capacity of glasses based on bismuth and sodium borates, obtained by comparison under conditions of melt cooling into the environment, have been studied. An interpretation of the observed effects is given on the basis of the features of the molecular structure and the thermal mobility of its fragments. Viscosity changes of the melt and cooling rate strongly affects the temperature dependence of c_p, s/c_p max at temperatures above the glass transition temperature. The calculated specific heat of the melt increases with decreasing cooling rate, increasing viscosity and it approaches the values of the specific heat at the maximum corresponding to the temperature vitrification. Adding NaOH to borate glass affects the value and position of the maximum specific heat to a lesser extent than the Bi₂O₃ addition.

La₂O₃–SiO₂ systems are synthesized from kaolin and tetraethoxysilane. The thermal decomposition of images after freeze-drying when heated to 1000°C is studied using thermogravimetry and differential scanning calorimetry. The morphology of the samples is studied by transmission electron microscopy (TEM) and dynamic light scattering (DLS); the acid–base properties of the surface are determined by the indicator method. During the heating of samples in the temperature range of 25–600°C, endothermic effects are discovered, accompanied by weight loss. The structure of the kaolin sample is heterogeneous; nanoparticles (10 nm) of lanthanum oxide are located on the surface of microparticles (220–270 nm) of silicon oxide. The sample obtained from tetraethoxysilane has a homogeneous nanostructure with particle sizes of 5–13 nm, but is characterized by less intense sorption values at Brønsted acid sites (pK_a 1.7; 3.46) compared to the sample from kaolin. This is due to the production of the La₂O₃–SiO₂ system already in solution and the blocking of silanol groups on the surface of silicon oxide. A significant increase in specific adsorption at pK_a 9.2 for both the kaolin and tetraethoxysilane samples proves the existence of La³⁺ metal ions and OH^– hydroxyl groups on the surface of silicon oxide.

Mechanochemical activation of the impact-shear type of air-dry mixtures of clinoptilolite-stilbite and clinoptilolite rocks together with 25, 33, and 50 wt % potassium hydrogen phosphate trihydrate is carried out. The structure, phase, elemental, and granulometric composition, morphology, and physical properties of the powders are studied using infrared spectroscopy, differential scanning calorimetry, X-ray phase analysis, energy-dispersive X-ray spectrometry, sieve analysis, scanning electron microscopy, gravimetry, and air permeability. The electrical conductivity of tablet samples is measured in the temperature range from 25 to 580°C. It is found that the electrical conductivity of clinoptilolite-stilbite rock containing 50 wt % potassium hydrogen phosphate trihydrate, subjected to impact-shear action with the absorption of a mechanical energy dose of 5.04 kJ g^–1, is equal to 7.06 × 10^–2 S m^–1 at 560°C. It has been shown that mechanochemical activation of zeolite together with potassium hydrogen phosphate crystal hydrate contributes to an effective increase in conductivity and is a promising method for obtaining solid electrolytes.

Composite materials (CMs) based on matrices of high-silica porous glasses activated by Cu²⁺ and Y³⁺ ions are synthesized. The influence of the composition of composites (concentration and ratio of copper and yttrium introduced) and the temperature of their heat treatment (in the range of 50–870°C) on their spectral properties is studied. Examining samples using optical and IR spectroscopy reveals absorption bands related to Cu²⁺ ions and caused by vibrations of the Y–O bonds in Y₂O₃. It is established that, depending on the synthesis conditions, the obtained materials possess UV, blue-green, and IR luminescence due to the presence of various active centers (defects and oxygen vacancies in CuO, Cu²⁺ ions, radicals , and F centers in Y₂O₃, =Si⁰ centers, E' centers (O₃≡({text{Si}} cdot )), neutral oxygen vacancies (O₃≡Si–Si≡O₃), and nonbridging oxygen defect centers in the silica matrix of glass.

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 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).

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.