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Macrokinetic characteristics of the combustion of mixtures in the (100% − X)(Ti + 0.5C) + X(Ta + C) system with a variable mixing parameter X and initial temperature T0 of charge heating are considered. For compositions with X = 10 and 30%, an abrupt increase in the velocity Uc and temperature Tc of combustion as a result of passing two parallel chemical reactions of titanium and tantalum carbide formation is established. The Uc (T0) and Tc (T0) dependencies are linear for the mixture with X = 50%. By hardening the combustion wave, it is revealed that the primary structure formation in the combustion region starts from the selection of submicron grains of nonstoichiometric titanium carbide from the supersaturated titanium melt. In the investigated range of parameter X, synthetic products are single-phase and represent titanium-tantalum carbide. An increase in X results in a decrease in the size and microhardness of (Ti, Ta) C grains and a reduction of the relative density of compact synthetic products. The kinetics of high-temperature oxidation of alloys on the basis of carbide (Ti, Ta) C is studied. Ceramics produced at X = 10% are most heat-resistant.

Preparation of high-porous TiAl foam by volume combustion synthesis (VCS) was investigated. It is shown that the optimum conditions for pore formation are attained when gas evolution coincides in time with melting of the reactants.

Time-resolved synchrotron radiation diffraction analysis was applied for detecting structure and phase transformations during heterogeneous reactions in lamellar intermetallic composites obtained by mechanical activation and magnetron deposition. Results show that reactions in these systems start at lower temperature, as compared to common powder mixtures of the same composition. This method can be useful for understanding intrinsic mechanisms of heterogeneous reactions in micro- and nano-lamellar systems.

The combustion of pressed specimens of a stoichiometric Fe2O3-TiO2-Al-C powder mixture burning in the SHS regime is studied. It is found that the final product has the same shape and size as the initial specimen. The composition and structure of the final product, which is highly porous high-melting Al2O3-TiC-Fe(Ti) composite ceramics, are studied. The mechanism of phase and structure formation in the examined system is proposed.

This article describes results obtained during the study of the combustion syntheses of intermetallic Al–Ti films, starting from elemental nanoscaled multilayers of Al and Ti. The original multilayers were prepared by plasma sputtering and the combustion synthesis was started by local or general heating, depending on the case. Atomic scanning tunneling microscopy, scanning and transmission electron microscopy, X-ray diffraction, and differential scanning calorimetry have been used to study the slow and self propagating reaction modes. Self-sustained reaction starts at temperature 600 K, which is much lower than the value for powder mixtures of similar composition and may be explained by abnormally fast diffusion along grain boundaries. Formation of product “bridges” across the nanolayers was observed at the first stages of the reaction. The combustion product (TiAl) inherits the texture of initial Ti and Al layers. An interpretation of the reaction mechanisms for the formation of TiAl and TiAl 3 is given and discussed.

Fine-particle tungsten carbide powders are produced from tungsten(VI) oxide by self-propagating high-temperature synthesis. The starting-mixture composition is shown to have a significant effect on the phase composition, morphology, and particle size of the WC powder. A procedure is described for recovering tungsten carbide from intermediate products using chemical dispersion. The influence of the dispersion agent on the morphology and particle size of the resultant powder is examined. The results indicate that the use of organic solvents for chemical dispersion prevents the formation of solid agglomerates, enhances the dissolution rate of impurities and defect-rich intercrystalline layers, and makes it possible to obtain tungsten carbide powders with a predominant particle size no greater than 0.05–0.2 μm.

Ti–Al multilayer foils were produced magnetron vacuum deposition. The microstructure period varied in the range of 5–110 nm, the number of layers was 150–4700, and the total thickness of a multilayer foil reached 15–20 μm. The gasless combustion of the foils was studied. Steady‐state and pulsating combustion regimes were revealed; combustion temperatures were determined for both regimes. It was shown that the most probable mechanism of the self‐propagating reaction is the diffusion of Al in β‐Ti at a temperature close to the temperature of the α → β transition.

The possibility of preparing ultrafine boron nitride powders by self-propagating high-temperature synthesis (SHS) is examined. The results demonstrate that, by varying SHS conditions (starting-mixture composition, combustion rate, cooling rate, and intermediate grinding time), one can control the morphology and particle size of the resultant hexagonal BN powder. Systematic data are presented on the chemical dispersion of SHS products for separating nanometer-sized particles. The effect of chemical dispersion (composition of the dispersion medium, process temperature, and dispersion time) on the particle size, morphology, and chemical and phase compositions of boron nitride powders is analyzed. Hexagonal boron nitride powders are obtained with a purity of 99.5+%, particle size of 0.1–0.2 μm, and specific surface of up to 65 m2 /g.

Experimental data are presented on the self-propagating high-temperature synthesis of aluminum nitride from Al + AlN starting charges, containing no gas-generating additions. The effect of the charge composition on the combustion temperature, powder morphology, and the chemical composition of the synthesis products is analyzed. The results are used to optimize the process conditions.

The basic macrokinetic stages of a gas-free thermal explosion in an Nb-Al system with different stoichiometric ratios of the reagents are determined using scanning differential calorimetry, electron metallography, and microanalysis. Chemical interaction begins when aluminum melts (993 K) and proceeds slowly up to a temperature of 1020-1040 K, at which dramatic self-heating and acceleration of the reaction (thermal explosion) occur. Migration of the melt from the center of the sample to the surface layers and growth of droplets on the sample surface are observed at the stage of slow reaction, and the drops penetrate again into the sample at the stage of thermal explosion. The phases NbAl3 and Nb2Al are formed in the thermal explosion regardless of the initial stoichiometry of the composition; the differences are manifested only in the ratio of these phases and in the amount of residual (nonreacted) niobium.

The laws of heat transfer and eutectic liquid mixtures redistribution between layers of bimetallic powder materials in the process of consolidation while self-propagating high temperature synthesis mode were investigated. It was determined that temperature gradients exist on both sides of the interface between layers of porous nickel and an exothermal mixture of 15% Al–85% Ni. The temperature decreased from the interface to the centers of the layers. Inhomogeneous temperature distribution was the cause of liquid phase transfer from the combustion zone (near the interface) to the cold peripheral zones of the inert powder layers. The observed laws were confirmed by the results of physical metallurgy investigation.

Self-propagating high-temperature synthesis (SHS), also known as combustion synthesis, is a modern technique for producing refractory compounds and materials [1]. This method is based on the use of internal chemical reaction heat rather than external (furnace) heating for material synthesis and processing. Initial mixture consists of two or more powders, which are able to react exothermically with each other. Being locally initiated, the reaction becomes self-sustaining, heat produced in the reaction front igniting the nearest part of the mixture. Ceramic-intermetallic composites, composed of ceramic grains (TiC, TiB2, etc.) and TiAl intermetallic binder, possess attractive properties for potential applications as cutting tools, aerospace materials, hard and refractory structural materials. As the enthalpies of reaction between Ti and C, B or Al are large, these materials can be produced through combustion synthesis (SHS) by means of heterogeneous reactions in the ternary mixtures of elemental powders. Formation mechanisms of the materials have been studied in the present work. Since the characteristic features of SHS are fast temperature variations and short duration of the product formation (usually from a few seconds to a few minutes), Time-Resolved Synchrotron Radiation Diffraction (TRSRD) is used for monitoring phase transformations. This method, firstly developed for investigation of SHS in the Ni–Al system [2], have been further improved in order to reach extremely short temporal resolution of 5 ms per diffraction pattern [3], or to combine it with thermal vision system [4]. Powders of Ti (∼ 40 μm average size, 99.8% purity), C (carbon black, ∼0.1 μm, 99% purity) and B (amorphous black, ∼0.1 μm, 99% purity) were dry-mixed and pressed into rectangular (20 × 10 × 5 mm) samples with a remainig porosity of roughly 40%. Two initial compositions were studied: 2Ti+Al+2B and 2Ti+Al+C. The samples were put in a specially designed chamber with an X-ray transparent window [4], under He atmosphere at normal pressure. Radiation, produced by one of L.U.R.E. (Orsay, France) synchrotron source, was monochromized and focused on the lateral surface of the sample. Radiation wavelenght was chosen equal to 2.53 A, intensity of the incident beam was ∼1010 photon per second. The sample surface exposed to synchrotron radiation (region of analysis), was a rectangle of 0.1 mm × 1.5 mm, with its long side parallel to the reaction front. Reaction was initiated locally by an electrically heated W wire. A gasless combustion front propagated along the sample with a velocity of 3 cm/s (Ti–Al–B) or 0.4 cm/s (Ti– Al–C), maximum averaged temperatures in the reaction zone were 2200 and 1960 K, respectively. Synchrotron ray diffraction patterns were recorded continuously (before, during and after reaction) by a curved linear detector which covered the range (theta) from 28 to 73 ◦, divided into 512 or 1024 channels. Sequence of 1024 SRD patterns was stored without time interval on a PC during 40.96 s. Hence, every pattern represents information about sample current phase composition during an interval of 40 ms. The stored data files were further converted into bitmap images, where larger intensity of radiation correspond to darker areas. These images give general information about phase evolution during combustion synthesis of the materials. TRSRD pattern of phase transformations in the Ti– Al–B system is shown in the Fig. 1. Lines of Ti and Al can be observed before reaction, amorphous boron does

The aim of this work is the preparation and study of the mechanisms of structure formation of dense ceramics based on the TiC–TiB2–MeO system obtained by pressure–assisted Self-propagating High-temperature Synthesis. SHS systems were selected on the basis of thermodynamic analysis as suitable to realise regimes of synthesis with formation of liquid phase allowing a full densification. It was observed that at the adiabatic temperature the liquid phase formed in the SHS products consists of either melted oxides or eutectic TiC–TiB2. The results of microstructural observations and mechanical characterization confirm that the metal oxides effectively promote the densification of the final products and the grain refinement of the SHSproduced ceramic materials.

International audience; Gasless combustion of a mechanically activated Ni-Al mixture is experimentally studied; the process is compared with the characteristics of combustion of a nonactivated Ni-Al mixture. Mechanical activation of the Ni-Al mixture is shown to form layered conglomerates consisting of numerous layers of the initial components. As a result, the structure of the medium becomes very similar to a cellular structure, which forms the basis for advanced microheterogeneous models of gasless combustion. A relation between the local (microscopic) and global (macroscopic) parameters of gasless combustion is found. Modification of the microstructure of the initial medium by means of mechanical activation allows obtaining products whose microstructure differs significantly from the microstructure of products obtained from nonactivated mixtures.

Ferrites with composition of NiMnxFe1-xO4, (with x = 0 ÷ 1.0) have been synthesized by self-propagating high-temperature synthesis (SHS). The particle size of the synthesized ferrite powder was about 10 nm. Additional heat treatment at 1270 K during 50 min allowed us to obtained product with the single phase composition NiFe2O4. We found out that the increasing of the manganese content (x) increased the lattice constant of the ferrites from 0.833896 nm (x = 0) up to 0.836369 nm (x = 1). The synthesized powder contains two types of ferrite particles that are varied in size and shape. The magnetic properties significantly depend on the microstructure and chemical composition of synthesized ferrites. It has been found that the coercive force Hc increased from 1.75 (x = 0.2) to 2.85 (x = 1). By using of IBSD technology thin film of NiFe2O4 was sputtered on the Si (100) substrate. All sputtered films were X-ray transparent. The structure of ferrite films consisted of agglomerate less than 35 nm. The thickness of the sputtered film was about 600 nm. Additional heat treatment at 770 K during 90 min resulted to homogeneity of the film microstructure. The temperature range 400-750 K corresponds to working temperature range of gas-sensing devices. The ferrite compounds were studied by TOF-SIMS (Time-of-Flight Secondary-Ion-Mass-Spectrometry) for all depth of film. The resistivity R of synthesized film was 39 kΩ. Measurement of gas-sensing sensitivity RCH4/Rair for gas (2%v. CH4) – air mixture showed increase of R up to 12% at the present of methane at 403 K. For further research we plan to replace iron to manganese ions in chemical compounds of ferrite.