The coating based on the MoSi2–MoB–HfB2 system on the substrate of the C/C–SiC composite is prepared by the in situ reaction synthesis using the slurry-roasting deposition of the powder composition at 1620°C under an argon expansion pressure of 1 Pa. The reaction mechanisms in the Mo–HfSi2–SiB4–C system predetermining the synthesis of secondary phases MoSi2, MoB, HfB2, and HfC are proposed. Thermodynamic calculations of possible chemical reactions are performed. Probable causes for a high porosity of the prepared coating are analyzed.

The oxidation resistance of a coating, which is formed by firing deposition of layers from a ZrSi2–MoSi2–ZrB2–Si powder mixture, on a C/C–SiC composite substrate is studied. Oxidation resistance tests are carried out under interaction with a high-speed air plasma flow at temperatures up to 2200°C. The performance of the coating is ensured by the formation (and evolution during operation) of a heterogeneous oxide film based on borosilicate glass modified with zirconium, which is an efficient barrier to oxygen diffusion and promotes the passivation of oxidation processes. An increase in the operating temperatures above 1750–1800°C leads to glass phase evaporation from the surface and the formation of a porous thermal barrier layer based on ZrO2 and containing secondary phases Mo/MoO2, Mo3Si, and Mo5Si3. The temperature gradient across the coating thickness favors partial preservation of the glass phase in the inner layers due to a decrease in the vapor pressure, which results in the retardation of oxygen diffusion deep into the material. The temperature–time ranges of performance; the characteristics of mass loss, catalytic activity, and emissivity of the coating; and the main factors limiting the efficiency of its protective action are determined.

A coating based on the MoSi2–MoB–HfB2 system on a C/C–SiC composite substrate is obtained by in situ reaction synthesis using the technology of slurry–roasting deposition of a powder composition at 1620 °C and an argon rarefaction pressure of ~ 1 Pa. Mechanisms are proposed for the reaction interaction in the Mo–HfSi2–SiB4–C system, which determine the synthesis of the secondary phases MoSi2, MoB, HfB2 and HfC. Thermodynamic calculations of possible chemical reactions are carried out. Potential reasons of the high porosity of the resulting coating are analyzed.

This article contains the results of research on the development of a Cf/C-UHTC carbon fabric composite based on a viscose precursor and a combined matrix consisting of partially sintered ceramics in a system consisting of HfC-HfB2-NbC-NbB2-TiC-TiB2-B4C-SiC, amorphous carbon, and pyrocarbon. The SiC fraction does not exceed 8.5‒9.0 wt%. In its initial state, the composite has open porosity, with apparent and true densities of 18‒22%, 2.25‒2.29 g/cm3 and 2.79‒2.91 g/cm3, respectively. The bending strength and the elasticity modulus are 27.8 ± 0.7 MPa and 7.8 ± 0.2 GPa, respectively, and the fracture strain is 0.85 ± 0.05%. The tests for resistance to oxidation and ablation were carried out in a gas dynamic flow regime and non-equilibrium air plasma heating at flow rates of 4.5‒4.8 km/s and breaking enthalpy of 45‒50 MJ/kg. Heating was performed in the temperature range Tw = 1400‒2700 °C at the critical point on the front surface of the samples. The average linear ablation rate and mass loss rate of the composite are 6.3 ± 0.3 μm/s and 6.22 ± 0.44 mg/s. The estimated value of the conductivity factor is 0.280‒0.285 W/(m·K). The performance ability of the composite arises from the formation and evolution of a passivating heterogeneous oxide film consisting mainly of titanium niobate Ti2Nb10O29, mixed solutions of Hf1-xTixO2, (Ti1-xHfx)1-yNbyOz and (Ti1-xHfx)NbO4 with broad homogeneity ranges, and also encapsulated carbide and boride particles. It is shown that the oxidation resistance of the composite increases as a result of the transition through a number of phases into a liquid state as the working temperature increases.

The C-f/C composite oxidation of polyacrylonitrile-based carbon fibers with a combined carbon matrix at 600(degrees)C up to a weight loss of 80 wt% has been investigated. The changes in the open porosity, specific surface area, apparent and true densities of the composite, as well as the ultimate strength and elastic modulus during three-point transverse bending tests have been analyzed. An analytical model for obtaining qualitative and semi -quantitative estimates of the change in integral pore size during oxidation of heterophase materials has been developed. The change in pore size is estimated through the evolution of open porosity P and materials specific surface area S. The model has been validated in the C-f/C composite oxidation study. The composite's mechanical properties dependences on the value of the integral pore size are obtained and analyzed. The structural parameter P/S characterizes the change in the interphase interaction during pores formation and development. It is established that the failure mechanism depends on the value of the parameter P/S and dynamically changes with the oxidation of C-f/C composite. The use of P/S parameter as a criterion for estimation and control of composite materials structural integrity in open systems is proposed.

The modification of polydimethylphenylsilazane with an epoxy oligomer for use as a binder in the technology of producing ceramic matrix composites (CMCs) is considered. As a result of the modification, the yield of pyrolysis residue increased from 21 to 60 wt

Исследована окислительная стойкость покрытия на подложке из C/C-SiC композита, сформированного методом обжигового наплавления слоев из порошковой смеси в системе ZrSi2-MoSi2-ZrB2-Si. Испытания окислительной стойкости проводили в условиях взаимодействия с высокоскоростным потоком воздушной плазмы вплоть до 2200оC. Работоспособность покрытия обеспечивается образованием и эволюцией в процессе эксплуатации гетерогенной оксидной пленки на основе боросиликатного стекла, модифицированного цирконием, которая является эффективным барьером для диффузии кислорода, что способствует пассивации процессов окисления. Увеличение рабочих температур свыше 1750-1800оС приводит к испарению стеклофазы с поверхности и образованию пористого термобарьерного слоя на основе ZrO2, содержащего вторичные фазы Mo/MoO2, Mo3Si и Mo5Si3. Градиент температуры, наблюдаемый по толщине покрытия, способствует частичному сохранению стеклофазы во внутренних слоях из-за снижения упругости пара, что приводит к замедлению диффузии кислорода вглубь материала. Определены температурно-временные пределы работоспособности, характеристики уноса массы, каталитической активности и излучательной способности покрытия, а также основные факторы, ограничивающие эффективность его защитного действия.

The interaction of leucosapphire single crystals with high-enthalpy gas fluxes is studied in a system modeling the aerodynamic flow around aircraft surfaces and their heating at flight altitudes of 80–100 km. The recombination rate constant K w at the surface of leucosapphire with orientation (1120) in an atmosphere of dissociated air and nitrogen is calculated. The microstructure, phase composition, and chemical composition of the surface are investigated. The results cannot readily be explained by existing theories of catalytic recombination and aerodynamic surface heating of aircraft components.

An analytical model is developed to obtain qualitatively and semiquantitatively estimate the changes in the integral pore size during the oxidation of heterophase materials. The model is tested on studying the oxidation of CCCM with a pyrocarbon matrix at 600°C up to a mass loss of 75 wt %. The change in the pore size is analyzed to quantify the structural degradation of the composite.

An analytical model is developed for obtaining qualitative and semi-quantitative estimates of changes in the integral pore size at the oxidation pro-cess of heterophase materials. The model was tested in the study of the C/C composite oxidation at 600°C with a mass loss up to 75 % wt. To quantify the structural degradation of the composite, the nature of the change in the size of the formed pores is analyzed.

The relevance of the study is conditioned by the fact that the most popular and irreplaceable materials that have found wide application in the aerospace industry are composites based on quartz materials. These materials are distinguished by their high mechanical and electrical strength, chemical and corrosion resistance. In this regard, it is of interest to obtain a composite material that combines a low specific gravity, processability of polymers, and thermal stability of ceramics. The aim of this work was to study the effect of the temperature of thermal oxidative destruction of a polymer binder, which is a semi-finished product of a pyrolysis matrix, on the electrophysical parameters of a composite material. The paper investigates a composite material based on woven quartz material with a pyrolysis matrix of an organosilicon binder and functional additives. This composite was considered as a material for creating an electric rocket engine chamber. Thermogravimetric analysis was used to evaluate the effect of the temperature of thermooxidative degradation of the polymer binder on the electro-physical parameters of the obtained material. The tests were carried out according to standard test methods on an Instron 5969 universal testing machine with Bluehill software until the samples failed. In the course of the study, it was found that the processes that occur up to 400°C are mainly associated with the course of the reaction for non-entered functional groups, the telomerisation reaction, intramolecular rearrangement of macromolecules and the removal of low-boiling substances. According to the results of the study, the obtained characteristics of the test material turned out to be suitable for its use in structural elements of electric propulsion engines.

The oxidation of carbon-carbon (C/C) composite materials with a pyrocarbon matrix at temperatures of 570-600oC to a mass loss of 90% by weight was studied. The formation of micropores with a size of up to 2 nm on the surface of carbon fibers is proved by the method of small-angle X-ray scattering. Tests for three-point transverse bending of C/C composite samples with the extent of reaction X-c = 0-0.6 were performed. A decrease in the tensile strength and elastic modulus during bending was found in the intervals from 315 to 1 MPa and from 60 to 0.2 GPa, respectively. This is the result of violations of the adhesive interaction in the filler-matrix system, increasing the degree of defect structure because of burnout pyrolysis residue of the binder, nucleation and evolution of microporosity, and also due to the decrease in cohesive strength of the fibers as a result of increase of their defects. The use of the specific surface area as a parameter for evaluating and controlling the structural stability of composite materials in open systems is proposed.

The low-temperature oxidation process of carbon-carbon composite materials (CCCM) with a pyrocarbon matrix has been examined. Oxidation at temperatures of 450 to 700 °C is characterized by internal burnout of the carbon phase without a noticeable change in the experimental samples external volume. Oxidation resistance analysis of CCCM structural components was performed. CCCM and carbon fibers specific surface area were estimated by the low-temperature adsorption of nitrogen and krypton using the Brunauer-Emmett-Teller model and the theory of density functional model. Pore size distribution was calculated by the semi-empirical Horvath-Kawazoe method. A significant increase (about 10-15 times) in specific surface area of the composite material, together with a rise in free volume ~5%, was accompanied by total weight loss of about 5%. Specific surface area changes occur as a result of anisotropic etching of carbon fibers surface with the formation of micropores with 0.5–2.0 nm diameter range. Although macropores are formed mainly due to the oxidation of thermosetting binder pyrolysis residue, they do not contribute to the specific surface increase but solely provide access to micropores. Microporosity evolution leads to an increase of structural discontinuity degree and, ultimately, to the loss of matrix-filler contact boundary. As a result, an overall weakening of material mechanical characteristics is to be noted. Thus, oxidative degradation is closely related to the increase in void space. A follow-up study is on-going. In fact, an open question remains, namely whether the oxidative process occurs differently in the micropores of diameter less than 2 nm and how it may contribute to the oxidative stress resistance behavior of CCCM.

Electric rocket engines are widely used in space technology. Furthermore, at present, electric propulsion engines are also used as mid-flight engines for flights in interplanetary space. On modern spacecraft, the following types of electric propulsion are mostly used: SPT and grid ion thruster. When using these engines as sustainers, it is important is to increase the total power for obtaining the required thrust and specific impulse. With an increase in total power, the volume of the discharge chamber increases, which leads to technological difficulties in the manufacture of discharge chambers from ceramic materials. Thus, the task of finding alternative ceramic materials is relevant and necessary in the development of high-frequency ion thrusters. The article discusses the issues of creating a composite material based on woven quartz materials and organosilicon binder as a precursor filled with silicon nitride for the manufacture of gas discharge chamber (GDC) of high-frequency ion thruster (RFIT). By thermos-gravimetric analysis, a thermosetting binder, which meets the requirements of vibration resistance and electromagnetic permeability of GDC in the megahertz range, was selected. Based on the binder filled with silicon nitride powder, reinforced by quartz woven fabrics, manufactured GDC. The resulting product was tested as part of the laboratory electric propulsion device with a diameter of 100 mm and power of 200W.

A technology is developed for 3D printing of the large-diameter gas-discharge chambers of electric rocket engines. The material employed is a ceramic composite based on silicon nitride.

This study discusses the creation of heat-resistant dielectric composite material based on organosilicon polymers for the manufacture of gas discharge chamber (GDC) for the electric rocket engine (ERE). A binder has been proposed that meets the high requirements for vibration resistance and electromagnetic permeability of GDC in the megahertz range of electromagnetic waves. Based on this binder filled with silicon nitride powder, GRС was designed; this product was fully tested as part of laboratory 200 kW ERE. The research of structural transformations that occur during heating of materials was carried out by synchronous thermal analysis. The material obtained in the result of the experiment, the basis of which was SiSiB®PVMQ filled with Si3N4 60% by mass, is characterized by a number of properties that are structured and described in this study. As a result of the study, it was demonstrated that the studied material is characterized by heat resistance up to 400 ºС. On the basis of these materials, the authors produced a GDC, which was tested as part of a laboratory model. It was established that the increase in mass loss over 400 °C is due to the initiation of the process of thermal degradation of the main polymer chain.

This article presents the results of the binder jetting technology application for the silicon nitride ceramics production. A modified version of the Plan-B 3D printer with an epoxy-based binder was used for silicon green bodies preforming. Silicon powder was pre-coated with epoxy resin, and the curing agent was added during 3-D printing of green bodies using a standard cartridge. Curing and removal of organics was carried out during the high-temperature vacuum drying of the printed preforms. Reaction-bonded silicon nitride was obtained by using pressureless sintering. An additional compaction of green bodies is proposed to reduce the porosity of green bodies and sintered ceramics. It is shown that the proposed methods allows to improve the mechanical properties of sintered specimens.

Results are given for a study of the microstructure, composition, and mechanical properties of ceramic based on silicon nitride prepared using three-dimensional printing technology and reaction sintering. In order to prepare workpieces of silicon powder an experimental three-dimensional printing unit is used, operating by binder injection technology. Synthesized specimens have high porosity and consist predominantly of α-Si3N4.