Abstract—This article discusses the possibility of obtaining dense ceramics based on zirconium dioxide powder using the gel casting method. The microstructure has been investigated, and the physical and mechanical properties of the obtained samples have been studied. An experimental selection of the composition of the water-based zirconium dioxide powder suspension was carried out. The apparent density of the samples obtained from the suspension after sintering was 5.91 g/cm3, with a relative density of 97.7

To produce highly porous ceramics with total porosity of 78-80 %, hollow corundum microspheres (HCMs) with the following characteristics were used: diameter - 140-180 mu m, wall thickness - 2-9 mu m, bulk density - 0.7 g/cm(3). These HCMs were obtained by plasma spheroidization (manufacturer: LLC << Kit-Stroy >>, St. Petersburg). Liquid glass (Na2O& sdot;SiO2& sdot;H2O) was used as a hardening binder for molding green bodies. Previously, aluminum powder consisting of flake particles was introduced into the volume of liquid glass. Such particles created a reinforcing framework within the structure of green bodies. In this case, liquid glass and aluminum powder together performed the function of a sintering activator during the subsequent heat treatment of the samples in air. Reaction sintering at a temperature of 600 degrees C, solid-phase sintering with the manifestation of the "zonal compaction" effect at 1200 degrees C and liquid-phase sintering in the range of 1600-1850 degrees C were recorded. The evolution of the structure and phase composition of ceramics was studied depending on the sintering temperature in the selected temperature range from 600 degrees C to 1850 degrees C. Depending on the sintering temperature, the compressive strength of ceramics was 4.0-17.3 MPa. Discrete fracture of the samples during deformation was recorded. The developed highly porous ceramics can be used as high-temperature thermal insulation.

Mesoporous hydroxyapatite (HA) is widely used in various applications, such as the biomedical field, as a catalytic, as a sensor, and many others. The aim of this work was to obtain HA powders by means of chemical precipitation in a medium containing a polymer—polyvinyl alcohol or polyvinylpyrrolidone (PVP)—with concentrations ranging from 0 to 10%. The HA powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, atomic emission spectroscopy with inductively coupled plasma, electron paramagnetic resonance, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The specific surface area (SSA), pore volume, and pore size distributions were determined by low-temperature nitrogen adsorption measurements, and the zeta potential was established. The formation of macropores in powder agglomerates was determined using SEM and TEM. The synthesis in 10% PVP increased the SSA from 101.3 to 158.0 m2/g, while the ripening for 7 days led to an increase from 112.3 to 195.8 m2/g, with the total pore volume rising from 0.37 to 0.71 cm3/g. These materials could be classified as meso-macroporous HA. Such materials can serve as the basis for various applications requiring improved textural properties and may lay the foundation for the creation of bulk 3D materials using a technique that allows for the preservation of their unique pore structure.

Определены кинетические закономерности образования нитридов сплавов Zr–Nb (содержание Nb 0.1, 2.5 и 5 мас. %) при температуре 1900°C. Процесс азотирования характеризуется двухстадийностью, где обе стадии описываются экспоненциальным законом. Скорость химической реакции на второй стадии значительно меньше, чем на первой. Охарактеризован состав формирующихся гетероструктур Zr 1– х Nb х N–ZrN 1– n /β-твердый раствор циркония в ниобии–Zr 1– х Nb х N, установлена последовательность нитридизации компонентов исходного сплава. На первой стадии процесса происходят образование α-твердого раствора азота в Zr и его переход в нестехиометрический нитрид. Кинетическая зависимость на второй стадии описывает нитридизацию фазы β-Nb, образовавшейся при распаде твердого раствора Zr〈Nb〉. Показано, что продолжительность второй стадии процесса определяется количеством ниобия в исходном твердом растворе. Экспериментально подтверждена возможность создания однофазной керамики с активными добавками нитридизацией сплавов Zr–М в одностадийном процессе с сохранением исходной формы металлической заготовки.

The ceramic material was produced by sintering green bodies made of thin-walled hollow corundum microspheres (HCMs) obtained by plasma spheroidization. Highly concentrated aqueous solutions of metal chlorides (AlCl3 center dot 3H(2)O and a mixture of ZrOCl2 center dot 8H(2)O with YCl3 center dot 6H(2)O), hardened upon drying, were used as a binder for molding green bodies. As a result of the thermal decomposition of these metal chlorides in air, oxides Al2O3 and ZrO2-Y2O3, sintering activators, were formed within the areas between HCMs. Solid-phase sintering occurred due to the formation of Al2O3 within these areas, while the formation of ZrO2 - Y2O3 within these areas provided liquid-phase sintering as a result of the appearance of a eutectic melt in the Al2O3 - ZrO2 - Y(2)O3 system. In the first case, sintering took place at the points of contact between HCMs (compressive strength of ceramics is 0.4 - 1 MPa, density - 0,85 g /cm(3), total porosity - 80%), and in the second case, "necks" were formed between the HCMs, significantly strengthening the structure of ceramics (compressive strength of ceramics - 15 MPa, density 1,4 g /cm(3), total porosity - 65%).

We have demonstrated general kinetic aspects of the formation of nitrides of Zr–Nb alloys (containing 0.1, 2.5, and 5 wt

Ceramic nitride samples of tailored composition and shape have been prepared by controlled nitridation of Ti–V metal pairs. We have obtained kinetic and current–voltage curves for the interaction of the Ti–V metal pairs with nitrogen. In different parts of the metal pairs, the nitridation process follows different mechanisms. In the case of the pure metals, the formation of nearly stoichiometric ceramics involves the formation of three- and two-layer graded structures. Nitridation of the junction region, containing a Ti–V solid solution, is determined by the chemical affinity of titanium and vanadium for nitrogen. The formation of titanium nitride leads to decomposition of the Ti–V solid solution in the junction and vanadium metal separation on grain boundaries. The rate of vanadium nitridation increases as the titanium content of the solid solution decreases. The thermoelectric voltage of the Ti–V system in the temperature range from –195.7 to +550°C has been evaluated as a function of the degree of nitridation. The thermoelectric voltage and Seebeck coefficient of metal–ceramic and ceramic structures have been determined as functions of temperature. Characteristically, the thermoelectric voltage of all the nitrided pairs rises monotonically over the entire temperature range studied. Nitrided titanium–vanadium pairs with tailored composition can be used as ceramic thermoelectric converters.

We describe a sequence of structural transformations characterizing high-temperature nitridation of zirconium–niobium alloys containing 0.1–10 wt % niobium. High-temperature saturation of solid solutions of niobium in zirconium with nitrogen is accompanied by decomposition of the Zr〈Nb〉 solid solution and the formation of Zr1 – хNbхN–(ZrN1 – n/β-solid solution of Zr in Nb)–Zr1 – хNbхN composite structures. During nitridation of the heterostructures, zirconium nitride reacts with β-niobium, which is the final step of the nitridation of the parent Zr〈Nb〉 solid solution. Characteristically, the ceramics thus prepared have near-surface porosity reproducing the surface porosity of the as-rolled material.

Ceramics based on hafnium carbide of a given shape have been synthesized by direct carbidization of rolled hafnium in a hydrocarbon atmosphere. Excess carbon resulting from high-temperature pyrolysis of hydrocarbons forms on the surface of ceramic hafnium carbide an easily detachable layer consisting of graphite with an admixture of amorphous carbon. The final formation of ceramics occurs at a temperature of 2400 °C in an atmosphere of an inert gas — argon. The phase composition and structure of the synthesized ceramics are characterized.

Stoichiometric niobium carbide (NbC) samples with a tailored shape have been synthesized by direct carburization of rolled metallic niobium in an atmosphere of an argon + ethylene gas mixture. Ceramics have been produced by reacting niobium metal with ethylene gas, through absorption of the carbon released on the niobium surface as a result of ethylene decomposition. Complete carburization has been shown to be accompanied by the formation of an anisotropic inner cavity, reflecting the initial shape of the sample, which is characteristic of ceramics produced using the oxidation-assisted engineering approach. We have studied the substructure, superconducting properties, and mechanical properties of NbC synthesized via high-temperature carburization of niobium foil.

The article proposes a variant of constructing an information and analytical system that makes it possible to control the refractive properties of the environment (atmosphere) based on the actual values of its parameters, as well as to determine the numerical values of the refractive index of the atmosphere. Its operation is based on a method that makes it possible to detect errors during measurements by optical systems in a real atmosphere. The main feature of the method under consideration is the comparison of the refractive indices in a real and ideal atmosphere. The difference in the corresponding values of the refractive index of the atmosphere makes it possible to correct the results obtained during measurements by optical systems. This article describes the operation of the software algorithm, which allows not only measuring and evaluating based on information on hydrometeorological parameters and refractive properties of the surface layer of the atmosphere, but also visualizing the results of measurements carried out by optical systems. Experimental studies carried out confirm the high adequacy of the models underlying the described complex.

A model for studying the movement of avalanche-hazardous snow masses based on the method of smoothed particles is presented. This approach has been shown to be most appropriate in modelling environments prone to fragmentation. The impact of the snow avalanche on vehicles and the dependence of the affecting factors on the thickness of the snow cover and the terrain have been investigated. It has been found that with snow cover thickness up to 0.5 m, avalanche does not lead to loss of vehicle controllability. The results of the modelling at a qualitative level coincide with the real effects of the avalanche on the vehicle, which confirms the adequacy of the model developed.

Production aspects are considered for preparing porous ceramic based on α-Al2O3 using the effect of zonal compaction during powder workpiece sintering of very fine combustion products in air of flaky aluminum powder PAP-2 particles. It is shown that formation of a porous structure in sintered material proceeds by a local breakage mechanism through boundaries of aggregates with formation of pores between agglomerates, and also due to occurrence of a closed intergranular pore system. Properties of the ceramic obtained are: density 2.45 g/cm3, total porosity 39%, open porosity 30%, closed porosity 9%, the and ultimate strength in bending 50 – 60 MPa.

The predictive model for determining of water volume depending on the level of flooding based in the article proposed. The model includes the coastal zone and part of the intermediate zone between the depressions and the mounds of the bottom. The model makes it possible to outpace the potential danger of a hydrological emergency in terms of water volume, depending on a small number of parameters.

The cross section of atomic electron Compton scattering gamma + e -> gamma' + e' was measured in the 4.400-5.475 GeV photon beam energy region by the PrimEx collaboration at Jefferson Lab with an accuracy of 2.6% and less. The results are consistent with theoretical predictions that include next-to-leading order radiative corrections. The measurements provide the first high precision test of this elementary QED process at beam energies greater than 0.1 GeV. (C) 2019 The Author(s). Published by Elsevier B.V.

The engineering aspects are regarded for the porous α-Al2O3 eramics' preparation under the zonal densifcation during the powder blanks sintering formed out of the fnely dispersed end products of the alumina powder PAP-2's flake particles air combustion. It was demonstrated that the porous structure in the sintering material was forming by means of local pulloff mechanism which had effect at the agglomerated particle boundaries creating the open interagglomerate porous, as well as by the sealed intragranular porous system's arising. The obtained ceramics properties are the following: the density is 2,45 g/cm3, total porosity is 39 %, open porosity is 30 %, sealed porosity is 9 %, the ultimate bending strength 50‒60 MPa.Ill. 6. Ref. 16. Tab. 1.