Microstructure defects arising in the manufacture of oxide ceramics based on aluminum oxide were studied. Several common problems arising in the manufacture of ceramic materials from fine-grained starting powders with high sintering activity as well as differences in the optimal properties of materials intended for use at high and moderate temperatures were considered. Samples of ceramic materials of the mullite–corundum system modified with zirconium dioxide were obtained by co-deposition of the initial powders followed by their grinding, pressing, and sintering. The fracture surfaces of samples were examined on a scanning electron microscope to study defects in the microstructure of powder ceramics. Characteristic defects in the microstructure were identified. The reasons for their appearance were explained. Possible ways to solve the problems of degradation of the properties of oxide ceramic materials were proposed based on technical literature data and the experimental results.

The article presents an overview of the existing types of binders for heat and sound insulation made of glass and mineral fibers. The interest in the development or modification of binders for the manufacture of thermal insulation used in the transport, construction, and industrial sectors is due to increased requirements for their operational characteristics, as well as fire and environmental safety requirements. Trends in the development of binders for fibrous thermal insulation materials that meet modern requirements are indicated: thermal protection systems must have sufficient strength and flexibility to maintain their integrity during manufacture, transportation and installation in target volumes, sufficient elasticity to restore volume after compression, low specific gravity, low coefficient of thermal conductivity, resistance to flame, low smoke emission and resistance to moisture gain during heating and cooling.

Gel casting is one of the new and promising methods for producing ceramics. Modern research on the production of ceramic materials by gel casting covers a wide range of materials, including both dense and porous ceramic materials. The advantages of this method, such as ease of processing, the use of technological equipment of traditional methods, increased productivity, the possibility of obtaining products of large shapes and complex geometry, gave impetus to new research and development. This article provides an overview of publications devoted to research in recent decades on the production by gel casting of both dense ceramics for the manufacture of structural elements and porous ceramics for the manufacture of thermal insulation, porous filters and membranes.

Gel casting is one of the new and promising methods for producing ceramics. Current research on the production of ceramic materials by gel casting covers a wide range of materials, including dense as well as porous ceramic materials. The advantages of this method, such as ease of processing, use of the process equipment of conventional methods, heightened productivity, and possibility of obtaining products having large shapes and complex geometries, are creating a surge in new R D. This article reviews publications devoted to research conducted during recent decades on the production of both dense ceramics for the manufacture of structural elements and porous ceramics for the manufacture of thermal insulation, porous filters, and membranes by the gel casting method.

The composition and morphology of a ceramic material based on magnesium oxide and their influence on its thermophysical and physicomechanical properties are studied. It is established that the matrix component has the same morphological features and is cubic magnesium oxide when different initial precursors are used. The dependences of the physical and mechanical properties on the type of precursor and method of molding were studied on experimental samples.

This study proposes to use synthetic discrete refractory fiber, grade NDA-17-42-2, based on alumina and silica (in the weight ratio 85 and 15%, respectively) with a diameter from 1 to 3 μm as a friction component in tribotechnical materials. Due to high hygroscopy in combination with a high specific surface area up to 400 m2/g (comparable to asbestos) it is possible to expect high efficiency as a tribotechnical additive to frictional materials. Specimens based on iron, bronze, and copper with addition of fibers have been produced using the methods of powder metallurgy. Tribotechnical behavior of iron and copper-based specimens is comparable both in terms of functions of sliding speed and load on friction contact, and of respective values. Tests of copper-based specimens have demonstrated decrease in the coefficient of friction from 0.44 for pure copper to 0.18 and its stabilization. In addition, despite lower mechanical strength of the copper specimen with fibers in comparison with bronze and iron ones, its wear is not higher and in certain regimes is even significantly lower. It has been established that tribotechnical behavior of copper-based specimens with frictional additive of fibers qualitatively differs from that of iron and bronze-based specimens with the same frictional additive of alumina-based fibers. The difference in tribotechnical behavior of copper-based specimens with fibers is related to formation of an adhesive ceramic layer on the friction track. Formation of a similar layer on iron and bronze specimens is not observed. The formed ceramic layer separates friction surfaces, preventing formation of scores, sticking of friction materials, the coefficient of friction is stabilized, and the wear decreases in wide range of sliding speeds and loads. As a consequence, the operation ranges regarding the allowable sliding speed and loads are significantly expanded.

The dependences of the physicomechanical, thermophysical, and dielectric properties of a ceramic composite based on magnesium oxide on the sample formation method are studied. The main reasons for the sample behavior in tests and the advantages and disadvantages of slip casting and pressing methods are discussed. The influence of the sample formation method on the distribution of the reinforcing component is studied.

A possible approach to obtaining a high-temperature composite material with an aluminum oxide based matrix reinforced with zirconium oxide is considered. A method of producing samples of a ceramic composite material (CCM) is described. A comparative study of the compositions and technological methods of producing CCM is performed. A promising outlook for CCM composition based on mullite modified with zirconium oxide is substantiated. The advantage of obtaining CCM by semi-dry pressing is described. A direction for further development is substantiated.

The article considers the influence of a concentrated solar radiation flux at the focus of a Big Solar Furnace (BSF) on the formation of hierarchical structures of heat-shielding ceramic composite materials based on refractory oxide fibers. A flat front of irradiation with a concentrated solar flux in the focal spot of the BSF creates a uniform thermal field over the surface, which has a sharp temperature gradient deep into the sample along the z-axis, forming isothermal planes with a uniform temperature. It means that in these planes a certain hierarchical self-organization of a structure with a certain crystal structure takes place. At such concentrated solar irradiation, a high-density flux falls on the sample surface, a nonlinear, non-equilibrium temperature field arises, which shows that the processes in the solar furnace belong to the category of “Complexity” processes. Samples of heat-shielding materials were irradiated on the BSF at a concentrated solar radiation flux density of 380 and 460 W/cm2 until partial destruction in order to obtain a sintering and reflow zones on the samples to determine phase and structural changes in the samples. Investigations of microstructure of fused samples of VMK-5 and VMK-6 ceramic composite materials, heat-treated with a solar energy concentrated flow at T = 1800–1900°С, showed that a hierarchically self-organized structure with cubic and acicular crystals is formed in the samples. Studies of the microstructure of the fused VTI-17 samples showed that the structure of the samples passed to a new hierarchical level, from a chaotic distribution of fibers with non-fibrous inclusions in the initial samples to a hierarchically self-organized microstructure in the form of large grains. A further increase in temperature transfers the system to a new hierarchical level, crystals of cubic and lamellar shape grow from the grains.

The particulars of mullite crystallization during the synthesis of the ceramic composite material ‘mullite – zirconium oxide,’ obtained from a two-phase gel by co-precipitation combined with sol-gel synthesis, were studied. Powders of the ceramic composite material ‘mullite – ZrO 2 ‘ were obtained. They were heat treated at 1150 and 1350°C. Samples of the ceramic composite ‘mullite – zirconium oxide’ were made from the obtained powders by semi-dry pressing. The microstructure and phase composition of the ceramic were studied.

The article presents the results of a study of the behavior of a composite material, a matrix based on an organic polymer filled with fibers of partially stabilized zirconium dioxide, under exposure to air at temperatures above 2000°C. The discovered phase and structural changes lead to the formation of a new, low-temperature phase, while the fibrous structure of the material was maintained. The study makes it possible to evaluate the use of a composite material with an organic matrix reinforced with refractory zirconium oxide fibers under conditions of short-term exposure to extremely high temperatures.

В работе предложено использование синтетического дискретного тугоплавкого волокна марки НДА-17-42-2 на основе оксида алюминия и кремния (в массовом соотношении 85 и 15% соответственно) диаметром от 1 до 3 мкм в качестве фрикционного компонента в триботехнических материалах.Благодаря высокой гигроскопичности в сочетании с высокой удельной поверхностью до 400 м 2 /г (сравнимой с асбестом) позволяет, надеется на высокую эффективность в качестве триботехнической добавки в состав фрикционных материалов.Методом порошковой металлургии изготовлены образцы на основе железа, бронзы и меди с добавкой волокон.Триботехническое поведение образцов на железной и бронзовой основе сопоставимо по характеру зависимостей от скорости скольжения и нагрузки на контакт трения, так и по значениям величин.Испытания образца на медной основе показали снижение коэффициента трения с 0,44 для чистой меди до значения 0,18 и его стабилизацию.Также, несмотря на меньшую механическую прочность медного образца с волокнами по сравнению с бронзовым и железным, его износ не больше, а при некоторых режимах даже значительно ниже.Установлено, что триботехническое поведение образца на медной основе с фрикционной добавкой волокон качественно отличается от поведения образцов на железной и бронзовой основах с такой же фрикционной добавкой волокон на основе оксида алюминия.Отличие триботехнического поведения образца на медной основе содержащего волокна, связано с образованием адгезионного керамического слоя на дорожке трения.Образования подобного слоя на железном и бронзовом образцах не наблюдается.Формирующийся керамический слой разделяет трущиеся поверхности предотвращая образование задиров, прихвата трущихся металлов, стабилизируется коэффициент трения, и снижается износ в широком диапазоне скоростей скольжения и нагрузок.

The effect of transparent ceramic fiber texture on strength is evaluated. Three types of continuous fibers of composition Al2O3–SiO2 produced overseas, as well as experimental fibers of a similar composition prepared under laboratory conditions, are studied. It is established that all of the fibers analyzed have a highly perfect texture, but the texture of experimental batch fibers differs significantly from standard specimens. Conclusions are drawn about reasons for appearance of texture in these specimens, and its possible effect on user properties is analyzed. Ways are proposed for improving properties of domestically developed fibers of a similar class.

Heat and sound insulating carbon-polymer composites are produced and described. The heat and sound insulation properties, namely, the heat conductivity coefficient and the difference of temperatures between the heater and the opposite side or the layer of the sample of these composites are investigated. The sound insulation properties are characterized by losses of sound pressure during passage through the composite. It is demonstrated that carbon-polymer composites can be used in Far North and Arctic conditions.

The objects of investigation are foam ceramic materials based on aluminum oxide, magnesium oxide, and alumina-magnesia spinel. The results of investigations on the sintering of spinel ceramic using aluminum and magnesium oxides as the initial components are presented. It is shown that the optimal range of the sintering temperatures for obtaining materials with open-cellular pore structure is 1600 – 1700°C. Materials with interconnected porosity up to 85% and strength in compression up to 1.4 MPa were obtained.

The results of work on obtaining titanium nitride whiskers from the gas phase are reported. A theoretical assessment of the possibility of homogeneous formation of microsubstrates of various types and compositions in the gas phase, the conditions for condensation of the titanium nitride phase, and the growth of whiskers was made previously. Based a thermodynamic analysis of the system under study, calculations of the active critical supersaturations were performed and the rates of homogeneous condensation in the gas phase of titanium and titanium nitride were estimated. Thermodynamic calculations of the compositions of the Ti–Cl–H, Ti–Cl–N, and Ti–Cl–Ar subsystems determined the structural elements of the laboratory setup and the technological features of the process of growing titanium nitride crystals. Samples of titanium nitride whiskers were obtained and studied.

The paper presents the results of testing a heat-protective material based on Al 2 O 3 and SiO 2 fibers under exposure to a concentrated solar energy flux and highly non-uniform thermal and light field conditions. Avariation in the material structure and morphology depending on the heat treatment temperature is shown. The material retains its properties during extended exposure to temperatures of 1,600 – 1,700°C due to the formation of a stable mullite and α-Al 2 O 3 structure. Above the mullite melting point (~1,840°C), the material undergoes deformation and melting, and loses its physical, mechanical, and thermal insulation properties.