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We have studied the spontaneous comminution of cast materials consisting of a Mn-doped Cr2AlC MAX phase and chromium, manganese, and aluminum carbides and aluminides. The materials were prepared in the form of ingots by self-propagating high-temperature synthesis (SHS) in a 3-L reactor at an argon pressure p = 5 MPa. The starting mixtures consisted of manganese(IV) oxide, chromium(III) oxide, aluminum (ASD-1), and carbon. The presence of aluminum carbide (Al4C3) in a cast material has been shown to lead to spontaneous comminution of the cast material (without mechanical or chemical influences) into powders with a crystalline particle size under 100 μm. The particle size reduction has been shown to result from reaction between aluminum carbide and atmospheric moisture. The synthesized materials have been characterized by X-ray diffraction and X-ray microanalysis, and we have studied structural and phase states of particles of the desired products obtained as a result of self-comminution of a cast SHS material.

A material based on a (VCr)2AlC solid solution has been obtained for the first time by self-propagating high-temperature synthesis from a powder reaction mixture of vanadium(V) and chromium(III) oxides with aluminum and carbon (graphite). The synthesized material has been studied by X-ray diffraction and microstructural analyses. It has been shown that the product also contains vanadium and chromium carbides and intermetallics. The presence of these phases seems to be associated with the nonequilibrium character of the synthesis process due to a short “lifetime” of melt and its fast cooling and crystallization. The synthesized material is an electrical conductor, which demonstrates a metallic character of conductivity throughout the entire measured temperature range of 300–1300 K. The room-temperature specific resistance of the composite material based on a (Cr,V)2AlC solid solution is 1.14 µΩ m, which is higher than the specific resistance of the materials based on the Cr2AlC and V2AlC MAX phases. The microhardness of the synthesized material is 6.9 GPa.

High-temperature synthesis of cast composite materials in the Cr–Mn–Al–C system with various ratios between the Cr2AlC MAX phase and chromium and manganese aluminides and carbides was studied. Experiments were performed in a universal 3-L reactor under argon pressure Р = 5 MPa. Mixtures of powders of chromium(III) and manganese(II, IV) oxides and calcium peroxide with aluminum (ASD-I) and carbon were used as a charge. The synthesis features and the phase composition and microstructure of the target products are significantly influenced by the reactant ratio in the charge. At the stoichiometric ratio of the components corresponding to the Cr2AlC phase, a cast composite material consisting of the Cr2AlC MAX phase, chromium carbides Cr7C3 and Cr3C2, and chromium aluminide Cr5Al8 is formed. In the course of combustion of the charge with the component ratio corresponding to the Mn2AlC phase, a cast composite material consisting of manganese carbides (Mn3AlC, Mn0.545Al0.42C0.035) and aluminide (MnAl) is formed. When these compositions are combined in an 0.75 : 0.25 ratio, the final product is a composite material consisting of a solid solution based on the Cr2AlC MAX phase, manganese carbides (Mn3AlC), and chromium aluminides (Cr2Al). When these compositions are combined in an 0.5 : 0.5 ratio, the final product is a composite material consisting of the manganese-doped Cr2AlC MAX phase and of manganese (Mn14Al86, Mn22.5Al77.5) and chromium (Cr5Al8) aluminides. The final products were characterized by X-ray diffraction and local microstructural analysis.

–A material based on the V2AlC MAX phase has been obtained for the first time by the method of self-propagating high-temperature synthesis (SHS) using a reaction mixture of vanadium oxide(V) and (IV) powders with aluminum and carbon (graphite). The obtained material was characterized by X-ray diffraction and energy-dispersive X-ray spectroscopy. The Rietveld method was used to perform quantitative analysis. The synthesized material based on the V2AlC MAX phase is an electrical conductor that demonstrates the metallic behavior of conductivity in the entire measured temperature range of 300–1300 K in the vacuum of 2 × 10–3 Pa. It has been suggested that the V2AlC phase makes a decisive contribution to the electrical resistance of the synthesized material that may be caused by the formation of V2AlC nanolaminate grains contacting with each other in the bulk of the material.

Using the method of self-propagating high-temperature synthesis (SHS metallurgy), cast composite materials were produced in the Cr–Ti–B system. The experiments were carried out in universal SHS reactors with an initial argon pressure of Рin = 5 MPa. Mixtures of CaCrO4, TiO2, Al, and B powders were used as batch. It was shown that by varying the mass ratio α of CaCrO4/2Al/2B and 3TiO2/4Al/6B mixtures in a batch, it is possible to significantly affect the synthesis patterns, phase composition, and microstructure of the target products. The initial mixtures are capable of burning in the range of α 0–20%. The phase separation limit occurs at α = 15%. The introduction of a highly exothermic CaO2 + Al additive into the mixture made it possible to expand the phase separation limit to α = 20%. As α increases, the amount of titanium boride in the final product increases. The resulting composite material consists of titanium-chromium boride distributed in a matrix of chromium boride. The synthesized materials were characterized by X-ray and local microstructural analysis. The structural phase states of the target products produced under various conditions were studied.

Experimental data are presented on the high-temperature synthesis of cast composite materials in the Cr–Al–C system with different relative amounts of the MAX phase Cr2AlC and chromium carbides and aluminides. The experiments were carried out in multipurpose self-propagating high-temperature synthesis (SHS) reactors at an argon pressure p = 5 MPa. The starting mixtures consisted of calcium chromate (CaCrO4), aluminum (ASD-1), and carbon powders. It has been shown that varying the percentage of carbon in the starting mixture may have a significant effect on the synthesis process and the phase composition and microstructure of the final products. It has been found that, in the case of the stoichiometric starting mixture composition, the synthesis yields cast composite materials consisting predominantly of the MAX phase Cr2AlC and containing the lower chromium carbide Cr7C3 and the chromium aluminide Cr5Al8. The addition of excess (superstoichiometric) carbon to the starting mixture leads to an increase in the percentage of the MAX phase Cr2AlC in the synthesis product, disappearance of the chromium aluminide Cr5Al8, and the formation of the higher chromium carbide Cr3C2 instead of the lower carbide. The final synthesis products have been characterized by X-ray diffraction and local microstructural analysis. The structure and composition of the synthesis products obtained under various conditions have been determined.

The regularities of synthesis by the SHS metallurgy method of cast materials in the Mo-W-Si system are studied. The experiments were carried out in SHS reactors with a volume of 3, 20 and 30 L under the pressure of an inert gas (argon) P = 5 MPa. In the experiments, high-calorie mixtures of molybdenum (6) and tungsten (6) oxides with aluminum and silicon were used. Thermodynamic calculation of combustion parameters of the initial systems according to the Thermo program showed that they have high adiabatic combustion temperatures exceeding the melting points of the initial reagents and final products of synthesis. Studies have shown a strong effect of the ratio of the initial reagents on the regularities of synthesis. Cast (ingots) single-phase disilicides of molybdenum (MoSi2) and tungsten (WSi2), as well as their solid solutions MoSi2–WSi2, are obtained with any given ratio between them. Their microstructure and elemental and phase composition were investigated. Optimal modes of mechanical conversion of the obtained ingots of the target products into the powders of the required fractions are developed. The influence of the composition of composites on the strength and oxidation of sintered samples in air at different temperatures was studied. It was shown that sintered composites from MoSi2–WSi2 solutions have higher strength and are less susceptible to oxidation compared to ceramics obtained by solid-phase sintering from powders of individual MoSi2 and WSi2.

In this paper, we studied the reaction mechanism of chemical transformations of the initial components in the combustion wave of MoO3/TiO2/Al/Si mixtures of the thermite type in the synthesis of molded molybdenum disilicide (MoSi2) and binary molybdenum titanium silicates ((MoTi)Si2). Syntheses were carried out in a high-temperature synthesis reactor at an initial argon pressure of P0 = 5 MPa. The effect of the ratio of initial reagents and geometric factors on the laws of synthesis of these materials was experimentally studied. The intervals of the component ratios, at which molybdenum and titanium silicides can be synthesized with specified compositions, are determined. We carried out experiments on stopping the combustion front. The chemical transformation of the components of the initial MoO3/TiO2/Al/Si mixtures in the combustion wave is shown to proceed in stages, and chemical reactions can be considered as chemically conjugated processes. The obtained results provide the scientific basis for the creation of promising molded silicide ceramics with high performance properties.

This paper reports the preparation of cast dimolybdenum pentaboride by a self-propagating high-temperature synthesis (SHS) metallurgy method. Experiments were carried out in SHS reactors at an initial excess gas (Ar) pressure p0 = 5 MPa. In the experiments, we used thermite-type starting mixtures consisting of molybdenum oxide, aluminum, boron oxide, and elemental boron powders. The combustion of such mixtures yields two types of final product: Mo2B5 and Al2O3. The combustion temperatures of the starting mixtures used in our experiments have been shown to exceed the melting points of the final products, which are thus formed in a liquid (cast) state. Under the effect of gravity, the heavier phase Mo2B5 settles down to form a lower ingot, whereas the lighter phase Al2O3 forms an upper ingot. The synthesis products have been characterized by X-ray diffraction and local microstructural analysis. The results demonstrate that the composition and amount of the starting mixture have a significant effect on the synthesis parameters and the composition and microstructure of the Mo2B5. We have optimized conditions for the preparation of single-phase cast dimolybdenum pentaboride.

The possibility of combustion of a mixture of chromium peroxide with aluminum nitride is shown experimentally. The effect of initial pressure of nitrogen and ratio of reagents on an average linear burning rate, as well as on a relative mass loss in the combustion of a CrO3/AlN mixture is studied. The concentration limits of the burning rate of the test mixture are determined. The microstructure and phase and chemical compositions of the combustion products of the chromium–nitride-aluminum mixture are described.

The combustion of a highly exothermic mixture of calcium chromate with aluminum and boron has been studied. It has been shown that these mixtures are able to burn in a wide range of reactant ratios. The autowave chemical transformation is accompanied by decomposition of calcium chromate, the chemical reaction of the decomposition products with aluminum and boron, the formation of a two-phase melt of the combustion products with its subsequent gravity separation, and crystallization of the layers. The results of the study may be useful for obtaining chromium borides.

Experimental data are presented on the high-temperature synthesis of cast inorganic materials in the MgO–Al2O3 system. Experiments were carried out in multipurpose self-propagating high-temperature synthesis (SHS) reactors at an argon pressure p = 5 MPa. The starting mixtures used in the experiments consisted of molybdenum(VI) and magnesium(II) oxides and aluminum. It has been shown that, varying synthesis parameters, one can control the phase composition and microstructure of the final oxide products. We have optimized synthesis conditions for the preparation of single-phase magnesium aluminate spinel, MgAl2O4. The SHS products have been characterized by X-ray diffraction and local microstructural analysis.

This work investigates the regularities of autowave chemical transformation of MoO3/Al/AlN mixture, gravity separation of its combustion products, and formation of composition and structure of end product (aluminum oxynitride). It is demonstrated that the mixtures of MoO3, Al and AlN are capable of burning in wide ranges of reagent ratios. In the general case, this process is composed of three consecutive stages: stage 1—combustion and chemical transformation of MoO3, Al, and AlN mixture into two-phase melt of end products (autowave synthesis); stage 2—gravity separation of combustion products (metallic and oxide phases), where two layers are generated: upper layer of “light” oxynitride (Al2O3–AlN) and bottom layer of “heavy” intermetallic compound (Mo–Al); stage 3—cooling and generation of phase composition and crystalline structure of metallic and oxide layers. It is established that variation of the aluminum content in the initial mixture at constant content of nitride additive significantly influences the combustion and autowave chemical transformation of the mixture and the phase composition and structure of the end product (aluminum oxynitride). Optimum compositions are determined for obtaining aluminum oxynitrides with high nitrogen content (up to 6–9 wt %) and impurity content (Al7O3N5 and AlN) below 3 wt %. The obtained cast aluminum oxynitride and method of its production are promising for production of high-strength transparent ceramics.

The regularities for the autowave synthesis (SHS) of a cast oxide composite material (Al2O3–Cr2O3 · ZrO2) were studied by example of combustion of thermite-type systems under an inert gas pressure. The ratio of starting reagents with optimal zirconia content was determined for the synthesis of the desired product on the basis of analysis of published data and thermodynamic calculations (Thermo program). In the experiments, it was shown that combustion temperature and sample mass are the most important parameters influencing the composition and microstructure of the final product. Optimal conditions for the process control were defined. The final product includes solid solution Al2O3–Cr2O3 grains located on the boundaries of ZrO2 particles. The material is promising for production of machine parts working in conditions of intense wear and shock loads in corrosive environments at elevated temperatures (for example, sintering of ceramic cutting tools).

Composites in the MoSi2 + Si3N4 system containing 1.0, 2.5, and 5.0 wt % Si3N4 were synthesized by hot pressing at the temperature of 1650°C and the pressure of 30 MPa. Silicon nitride powders of two types of were used as reinforcing additives: one with isometric equiaxed crystals and one with fibrous structure. The samples were characterized by microstructural and phase analyses; the relative density and the flexural strength were determined. Composites with the flexural strength of up to 410 MPa were synthesized. The resistance to low-temperature oxidation of MoSi2 + Si3N4 composites in air at the temperature of 750°C was studied. The increase in the resistance to oxidation of composites with silicon nitride in air compared to pure molybdenum disilicide for both types of silicon nitride powders was established. For all the composites obtained, the parabolic oxidation rate constants were calculated.

The combustion and chemical transformation of a Fe2O3/Al/Zr mixture has been studied. From the results of thermodynamic calculations and experiments, it has been found that the ratio of Al and Zr affects the phenomenology and features of the combustion and the composition of cast combustion products. The range of obtaining oxide materials (Al2O3 and ZrO2) is determined. A qualitative model for the combustion of thermite systems with two parallel reactions is proposed.

The processes of combustion and phase separation in thermite SHS systems in the synthesis of cast composite materials based on the silicides of molybdenum, tungsten, niobium, and titanium in a wide range of ratios between them have been studied. Thermodynamic calculations for the hot MoO3/2Al/2Si and WO3/2Al/2Si systems have shown that the pressure has a the strong effect on the combustion temperature and yield of gaseous products, and for the cold 3Nb2O5/10Al/12Si and 3TiO2/4Al/6Si systems, this effect has not been found. The effect of the ratio of the initial reagents and the activating high-temperature additive (CaO2 + Al) on the combustion and phase-separation parameters have been studied experimentally.

It is shown that critical conditions (temperature and pressure) in a fuel cell (metal tube piece) of a model nuclear reactor can be produced by burning energetic thermite SHS systems. The heating temperature of the zirconium or steel tube can be controlled by varying the composition of the thermite mixture, the gap between the thermite pellet and the tube wall, and the design of the thermite pellet. The results of the studies show that a WO3-2Al based thermite mixture can be used to model an emergency situation (without the use of radioactive fuel) in the reactor fuel cell.

The possibility of producing multicomponent master alloys with low-melting-point (Mg) and refractory (Ni, Mo, W) metals, which are used for the manufacture of high-temperature alloys in metallurgy, by SHS metallurgy is studied. The experiments are performed at a high inert gas pressure in a reactor. Highly exothermic powder mixtures of nickel oxide, molybdenum, tungsten, elementary magnesium, and elementary aluminum are used for synthesis. The experimental results demonstrate a strong effect of the ratio of the reagent masses, the gas pressure, and the magnesium and aluminum particle sizes on the laws of synthesis and the formation of the composition and microstructure of the end products.

This paper reports the high-temperature synthesis of cast Cr2AlC from mixtures of chromium(III) oxide, chromium(VI) oxide, aluminum, and carbon at an increased inert gas (Ar or N) pressure in a 3-L self-propagating high-temperature synthesis reactor at an initial argon pressure pi = 5 MPa. The reaction products were characterized by X-ray diffraction and X-ray microanalysis. The results indicate that the ingots obtained under optimized conditions consisted of Cr2AlC and Cr3C2 with a ratio of about 85 : 15.

The method of self-propagating high-temperature synthesis (SHS) is applied to prepare cast oxynitride ceramics using a Fe2O3 + 4Al thermite mixture. The nitrogen-containing components of the mixture were AlN and Si3N4 additives. The synthesis was performed in a reactor at an initial nitrogen pressure of 8MPa. The nitrogen-containing additives are demonstrated to influence the burning rate and combustion limits of the mixtures, as well as the yield and chemical composition of the cast ceramics.

Samples of MoSi2-WSi2 composite materials with additions of magnesium alumosilicates are obtained by solid phase sintering at 1650–1800°C in an argon atmosphere of powdered mixtures of initial components and disintegrated cast samples of 70% MoSi2–30% WSi2 (Mo0.7W0.3Si2), synthesized in an SHS reactor. The influence of the content of tungsten and oxide additive on oxidation of samples in air at 750°C for 100 h is studied. It is found that 70% MoSi2–30% WSi2 composite materials are less exposed to oxidation than MoSi2 and WSi2, and addition of 20 vol % magnesium alumosilicates decreases the rate of low temperature oxidation.

The possibility of obtaining cast aluminum oxynitrides in the combustion of iron-aluminum termite in a nitrogen atmosphere is shown. The combustion was carried out in a sealed reactor at an initial nitrogen pressure up to 10 MPa. The effect of the initial nitrogen pressure and aluminum content (in excess of stoichiometric) in the initial mixture on the bound nitrogen content in the oxide product of the synthesis is studied. Based on thermodynamic calculations and experimental results, a model was proposed for the chemical transformation of the initial mixture in the combustion wave with formation of a two-phase high melt.

This work examines general trends in the autowave synthesis of cast Mo-W-Si ceramics in a reactor at an elevated gas pressure using highly exothermic mixtures of molybdenum oxide, tungsten oxide, aluminum, and silicon. The results indicate that the gas (N2, Ar) pressure in the reactor and reactant ratio have a strong effect on the combustion process. We have obtained cast solid solutions with a controlled MoSi2: WSi2 ratio.

Aluminum oxynitrides Al22O30N2 and Al23O27N5 and a number of Al-O-N solid solutions with a nitrogen content of 2.3 to 6.5 wt % were prepared from (CrO3-Al-Al2O3-AlN) thermite-type mixtures with a high combustion temperature (2950–3200 K) by using the autowave synthesis method. The synthesis was conducted in a hermetically sealed reactor at an initial nitrogen pressure of 4.0 to 8.0 MPa. The aluminum nitride content was demonstrated to influence the nitrogen content in cast aluminum oxynitrides and on their microstructure and phase composition.

Regularities of synthesis and sintering of molybdenum disilicide are studied. The synthesis is carried out in the combustion mode (self-propagating high-temperature synthesis) with the use of high-caloric mixtures of molybdenum oxide with aluminum and silicon. The cast synthesis product (MoSi2) is subjected to grinding and subsequent sintering. The studies show that the basic parameters that influence the process of synthesis and its regularities are gas pressure in the reaction vessel and sizes of silicon particles. The sintering process, microstructure, and characteristics of sintered samples may be controlled through varying the sintering temperature and ratios of the ZrO2 and Y2O3 additives.

The influence of temperature on cation exchange on phenol groups of macroporous materials based on phenolformaldehyde resins (PFRs) was studied for Amberlit XAD 761 with irregularly shaped grains obtained by breaking up polycondensation resin blocks and FFS-1.4/0.7 with spherical granules. An increase in temperature caused some decrease in the sorption capacity of PFRs in the alkaline region, but almost did not influence the selectivity of alkali metal ion exchange. The sorption capacity and selectivity of PFRs did not change after multiple (dozens of cycles) transfer of phenol groups from the hydrogen to salt form and back. Ion exchangers of this type can effectively be used for separating mixtures of alkali metal ions containing cesium and rubidium.

The influence of temperature on the exchange of calcium and sodium ions from solutions of 2.3–2.8 g-equiv/l concentrations on KB-2e4 gel polyacrylic cationite, KB-4P2 and KB-4 gel polymethacrylic cationites, and Purolite C104 polyacrylic cationite was studied over the temperature range 273–400 K. It was shown that, simultaneously with a substantial increase in selectivity with respect to calcium ions, the differential enthalpy of the ion exchange reaction increased linearly on all polyacrylic and polymethacrylic cationites as the temperature grew.

The sorption and separation of a mixture of two electrolytes with a common ion on an ion exchanger saturated with this ion with elution by water was exemplified by the sorption separation of mixtures of 4 N HCl and KCl solutions with different compositions on an AV-17x8 anion exchanger in the Cl form. It was noted that the front of a mixture was always diffuse. It was found that situations can occur when a zone of a purified more weakly sorbed component with a constant concentration is accumulated. A procedure for the calculation of a single-step separation factor based on the results of separation experiments is described.

The combustion synthesis, microstructure, chemical composition, and phase composition of cast Al2O3-Cr2O3 materials are described. The synthesized solid solutions are based on corundum or chromia, depending on the Al2O3 and Cr2O3 contents. Using self-propagating high-temperature synthesis, a cast aluminum oxynitride is obtained for the first time.

The basic results on the effect of temperature on the equilibrium and thermodynamic characteristics of ion-exchange systems and the use of this effect in developing reagentless methods for ion-exchange separation are considered.