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This paper describes the effect of preliminary low-energy mechanical activation of nickel powder on the thermal explosion of a Ni3Al intermetallic compound. Two synthesis methods are considered. The first method requires that a mixture is continuously heated by an external energy source. The second method requires that an external source is turned off upon reaching a certain temperature. It is revealed that low-energy mechanical activation of nickel intensifies the Ni3Al synthesis. With continuous heating, the ignition temperature does not depend on activation time and is equal to the melting point of aluminum. In the case of heating with an external source turned off, preliminary activation of nickel reduces the solid-phase ignition temperature. It is established that nickel activation in a laboratory mill allows one to eliminate its passivation factors. [ABSTRACT FROM AUTHOR]

The processes occurring during the induction of a thermal explosion in titanium and aluminum powder mixtures are analyzed. The role of the oxide film on aluminum particles and the heating rate of samples during interaction between titanium and aluminum is considered, and various mechanisms of the oxide film destruction at temperatures near the melting point are proposed. It is shown that, depending on the heating rate of the samples, there are three possible mechanisms of formation of direct contact between titanium and aluminum: mechanical destruction of the oxide film on aluminum, the reaction of aluminum oxide with titanium, and the reaction of aluminum oxide with aluminum. Mechanical activation of the powder mixture lowers the ignition temperature by 20–30°C. As the average titanium particle size reduces from 90 to 10 m, the ignition temperature is lowered by 100°C. It is shown that a two-stage ignition mechanism is observed in a number of cases. The isothermal section of aluminum melting is followed by the stage of a slow temperature rise up to 700–800°C, after which the temperature rise rate increases tenfold. [ABSTRACT FROM AUTHOR]

Phase composition of thermal explosion products in compacts made of Ti–C–Al powder mixtures with an equiatomic ratio of titanium and black carbon (soot) and with an aluminum content of 10–40% (wt.) is studied. The compacts are heated at a rate of °C/min in an argon atmosphere. Self-ignition temperature of all compositions was close to the melting point of aluminum (660°C). Peak temperatures and the maximum rate at which temperature increment becomes larger as the aluminum powder content in the mixtures increases. Synthesis products contain titanium carbide and Al3Ti titanium trialuminide, whose ratio depends on the aluminum content in the mixture. Pretreatment of reaction mixtures in a planetary mill flattens aluminum particles, thereby preventing the formation of a melt. The spreading of a melt over the titanium surface with subsequent reaction diffusion and the formation of Al3Ti increases the synthesis temperature in compacts made of nonactivated mixtures. [ABSTRACT FROM AUTHOR]

Synthesis products in mechanically activated powder mixtures of titanium and nickel of three compositions corresponding to double intermetallic compounds are studied. The mixtures are mechanically activated in a planetary mill at a rate of 40 g and a processing duration of 20 min. Synthesis is carried out by a thermal explosion: the mechanically activated mixtures are heated in a sealed reactor in an argon atmosphere at an average heating rate of 70°C /min. The phase composition of the powder products after synthesis and additional annealing is studied by X-ray diffraction analysis, and the results are discussed using the reference data on the temperature dependences of the Gibbs energy of intermetallic compounds. It is revealed that, regardless of the elemental composition of the mixtures, the TiNi3 intermetallic compound, which has the highest negative Gibbs energy, is predominantly formed during synthesis. Therefore, a single-phase target product can be obtained only from a TiNi3 mixture. Thermal explosion products in mixtures of the other two compositions are multiphase. Annealing causes no qualitative changes in the phase composition, and the quantitative changes in the phase content are negligible. [ABSTRACT FROM AUTHOR]

Combustion of mechanically activated mixtures in 2Co–Ti–Al and Co–2Ti–Al is investigated, and alloys based on them are obtained by self-propagating high-temperature synthesis (SHS). Microstructural, X-ray, and differential-thermal studies are performed. A Heusler phase Co2TiAl-based alloy is obtained for the first time by means of mechanical activation. Conditions for the mechanical activation of a reacting powder mixture for the formation of a single-phase material is experimentally selected. [ABSTRACT FROM AUTHOR]

Combustion and the formation of structures and phases in a 2Co–Ti–Al system during self-propagating high-temperature synthesis in a thermal explosion are under study. It is determined that a single-phase product (a Co2TiAl Geissler compound) can be obtained in this system. Morphology, microstructure, and physical-magnetic properties of combustion products of the system are investigated. [ABSTRACT FROM AUTHOR]

Synthesis is carried out in a Ti + Al mixture prepared by two methods, namely preliminary mechanical activation (MA) or preheating. Synthesis occurs in the cases of layer-by-layer combustion (SHS) and thermal explosion. The dependences of burning rates of activated Ti + Al mixtures on the MA duration are investigated. The relationships between the initial temperature and the rates and maximum combustion temperatures of initial mixtures along with the elongation of samples after combustion are determined. The phase composition of the initial mixtures after activation and of the synthesis products is described. The MA duration (12 min) at which the burning rate of the mixture is maximum is experimentally determined. For this mixture (12-min long MA), the dependence of the burning rates and maximum combustion temperatures along with the elongation of samples after combustion on the initial temperature is studied. Synthesis at which the content of the main phases (TiAl and Ti3Al) in the products is maximized is established. [ABSTRACT FROM AUTHOR]

We have studied the effect of preload and the time delay in pressure application to the product of high-temperature synthesis by thermal explosion of a stoichiometric powder mixture on the grain size in the synthesized Ni3Al compound, on the nature of its fracture, strength, and ductility. [ABSTRACT FROM AUTHOR]

Single-phase aluminum diboride was obtained by thermal explosion of an aluminum-boron mixture mechanically activated in a planetary ball mill. The additional mechanical treatment of the products of thermal explosion was found to reduce the coherent scattering area size of AlB2 to nanometer values. The results of x-ray phase and electron microscopy of the mechanocomposites and products of thermal explosion are presented. [ABSTRACT FROM AUTHOR]

This paper describes the calculation of the relationship of the critical ambient temperature at which lead α-azide is ignited and the relationship of the critical temperature of self-heating with the thickness of plane crystals with the use of the Semenov criteria and numerical solution of the differential equation of heat balance. The stability of the heat balance equation is analyzed. Analytical expressions for the determination of critical ambient temperatures and self-heating temperatures. The calculations are carried out with the parameters of the heterogeneous reaction of thermal decomposition of lead azide in the mode of decreasing volume. The calculations results are in good agreement with the known experimental data. It is shown that the larger the activation energy of the exothermic reaction, the stronger the relationship of the critical temperature of ignition of lead α-azide with the thickness of plane crystals. [ABSTRACT FROM AUTHOR]

A new criterion for thermal explosion in exothermically reacting systems for the case of arbitrary one-step conversions is proposed. The computation method is based on the analysis of the equation of maximum temperatures obtained for closed systems taking into account reactant consumption. The dependence of the maximum temperature on the Semenov and Todes parameters is bistable and the critical conditions are determined by the extremum conditions on the relevant parametric diagrams. The demarcation lines of ignition in the Todes criterion-Semenov criterion parametric plane are calculated for second-order exothermic reactions. Comparison of numerical and analytical calculations shows that they are in satisfactory agreement. [ABSTRACT FROM AUTHOR]

The mathematical model of thermal explosion and synthesis of products in a mechanically activated 3Ni + Al mixture is simulated in macroscopic approximation. It is shown that activation of original components significantly increases the formation rate of a NiAl intermetallide. The experimental data are used to determine the thermophysical and kinetic constants of the process. [ABSTRACT FROM AUTHOR]

A mathematical model of synthesis in a mechanically activated SiO + Al mixture is constructed in the macroscopic approximation. It is demonstrated that preliminary mechanical activation makes it possible to obtain solid-phase ignition and to ensure synthesis of AlO and Si products in the thermal explosion regime. Based on experimental data, thermophysical and thermokinetic constants of the process are determined. [ABSTRACT FROM AUTHOR]

The dependences of the critical energy density required to initiate the explosive decomposition of lead azide and the radius of the most heated nanoparticle on the pulse duration of the first harmonic of neodymium laser (1064 nm) are calculated within the framework of the micro-hotspot model of thermal explosion. The calculations are carried out with account for the dependence of the absorption efficiency factor of the laser pulse on the lead nanoparticle radius. With the maximum value of the absorption efficiency factor (1.18), the lead nanoparticle radius (in lead azide) becomes 74 nm. If the pulse duration is short (smaller than 40 ns), the radius of the most heated lead nanoparticle in the lead azide matrix varies slightly (less than 15%) and equals 63.5 nm within the range of short pulse durations. Accounting for the dependence of the absorption efficiency factor of the laser pulse on the nanoparticle radius makes it possible to resolve the paradox of small particles. [ABSTRACT FROM AUTHOR]

A superadiabatic regime of the thermal explosion in mechanically activated stoichiometric mixtures of tungsten and carbon black is obtained. Regimes of preliminary mechanical activation of mixtures and the subsequent thermal explosion that allow obtaining a single-phase carbide WC with a submicron grain size are determined. The mechanical energy accumulated in the sample as a result of preliminary activation is estimated. Results of the x-ray diffraction analysis and electron microscopy of mechanically activated samples and thermal explosion products are reported. [ABSTRACT FROM AUTHOR]

Self-heating processes in binary homogeneous mixtures are studied based on the analysis of phase trajectories on the heating rate-temperature plane. The proposed approach allows determining the characteristic regions of exothermic reactions in the parametric diagram of the Todes criterion versus the Semenov criterion. Generalized strict criteria for the degeneration of thermal explosion are determined for reactions with low activation energy and reactions with a low thermal effect for any reaction orders. An approximating formula describing the dependence of the Todes criterion on the Semenov criterion is derived for calculating the critical conditions of thermal explosion up to its complete degeneration for reaction orders higher (or equal to) one. A criterion for the applicability of the classical thermal explosion theory as a special case of the proposed model is found. A diagram of the critical parameters in the introduced new variables is considered to predict and control the self-heating kinetics of mixtures. [ABSTRACT FROM AUTHOR]

The effect of preliminary mechanical activation of low-calorific-value powdered formulations in a planetary ball mill on the main parameters of the subsequent thermal explosion has been studied. It has been found that in mechanically activated compositions, the initiation temperature of thermal explosion is reduced by hundreds of degrees. The maximum decrease (1300°C) is observed for the Ti + 4 wt.% C system. Regimes of preliminary mechanical activation of reaction mixtures and the subsequent thermal explosion conditions producing TiAl and NiAl single-phase intermetallic compounds with nanometer grain size were determined. For the 3Ni + Al composition, the energy accumulated during mechanical activation was evaluated. It is shown that the initiation temperature of thermal explosion in the MA compositions studied can be used to estimate the temperature that develops in the mill drums. [ABSTRACT FROM AUTHOR]

A thermal explosion and self-propagating high-temperature synthesis in low-calorific SiO-Al mixtures subjected to preliminary mechanical activation are obtained. Results of x-ray and electron-microscopic investigations of the microstructure and phase composition of activated mixtures and reaction products are reported. It is found that complete reduction of quartz by aluminum occurs only in the thermal explosion mode. [ABSTRACT FROM AUTHOR]

In this paper, we study a micro-hotspot model for the laser initiation of explosive decomposition taking into account the melting of the matrix of the energetic material and the nanometallic inclusion contained in its volume. The heating features of the nanoparticle in an inert matrix are investigated, and the dependence of the maximum temperature on the surface of the inclusion on its radius is constructed. It is shown that melting leads to a reduction in the maximum heating temperature and a slight change in the radius of the most heated nanoparticle. The dependences of the critical initiation energy density of explosive decomposition of pentaerythritol tetranitrate (PETN) with aluminum nanoparticles on the inclusion radius with and without melting are calculated. With melting taken into account, the model gives higher critical initiation energy density of explosive decomposition. In the case of inclusions of large radius, the formation of the reaction site of explosive decomposition occurs before complete melting of the metal inclusion, which results in solidification of the melt during the induction period. [ABSTRACT FROM AUTHOR]

The problem of thermal explosion in a semi-batch reactor is solved. The critical conditions for the thermal explosion are studied. It is shown that the ignition resulting from the chemical reaction is possible both during the stage of feeding of the second reactant solution and after its completion. The dynamic behavior of the reactor depending on the temperature of the heat exchanger and the volumetric feed rate of the second reactant is analyzed. It is shown that ignition at the feeding stage occurs at high temperature of the heat exchanger and involves two macroscopic stages. In the first stage, the temperature increases with increasing rate (thermal explosion regime), and in the second stage, its further increase occurs in the regime of combustion of the second reactant. The critical ignition conditions are found to be independent on the feed rate of the second reactant in a particular range of its values. [ABSTRACT FROM AUTHOR]

A mathematical model of the self-heating of dispersed solid mixtures is considered taking into account the boundary kinetics of formation of the intermediate product phase. It is shown that decreasing the ratio of the characteristic diffusion time to the characteristic reaction time can lead to a transition from the diffusion regime to the kinetic regime, resulting in a change in the effective activation energy of the synthesis and the growth pattern of the product layer. This change may be due to decreases in the heterogeneity scale of the mixture and the ratio of the activation energy of the formation of the new phase to the activation energy of diffusion. An analytical model of the solid-state reaction in the kinetic regime was developed and used to obtain temperature dependences of the coordinates and velocities of the boundaries of the growing layer. [ABSTRACT FROM AUTHOR]

Qualitative features of self-heating regimes for first-order homogeneous reactions are considered by analyzing the structure of the phase trajectories. Consideration of the temperature dependence of the heating rate makes it possible to extend the main results of Semenov's theory of thermal explosion and pass to a two-dimensional parameter diagram, which allows the determination of the critical ignition conditions taking into account kinetic inhibition. It is found that the diagram of the Todes criterion versus the reciprocal of the Semenov criterion has four characteristic regions with different kinetics, two of which are limiting and two transitional ones. The boundaries of the regions are calculated, and the classical theory of thermal explosion is shown to be a special case of the projections of these boundaries on the range of the Semenov criterion. [ABSTRACT FROM AUTHOR]

An analytical solution of the problem of thermal explosion of an annular layer is obtained for two cases: 1) the inner cylinder is thermally insulated (heat exchange with the environment through the surface of the outer cylinder follows Newton's law); 2) the outer cylinder is thermally insulated (heat exchange through the surface of the inner cylinder follows the same law). The dependence of the critical value of the Frank-Kamenetskii parameter on the ratio of the radius of the inner cylinder to the radius of the outer cylinder is constructed for various values of the Biot number. The limiting cases where this ratio tends to zero and unity are considered. [ABSTRACT FROM AUTHOR]

A statistical approach is used to study the influence of a random field of temperature in the ambient medium on the thermal stability limits of a particle with an exothermal chemical reaction. Temperature fluctuations in the ambient medium are modeled with a spatially uniform, statistically stationary, random Gaussian process with a finite time of autocorrelation function decay. A closed equation for the particle temperature probability density is derived by the method of functional differentiation. Stochastic drift of the particle in the temperature space, which makes the particle reach the critical temperature of the thermal explosion, is studied with the use of the Kolmogorov backward equation for the transition probability density. On the basis of the numerical solution of the equation for the particle temperature probability density, the stationary distribution of this probability is demonstrated to have a bimodal structure. The influence of the time of thermal relaxation of the particle and the integral time scale of temperature fluctuations in the ambient medium on the loss of thermal stability of the particle with volume heat release is examined. [ABSTRACT FROM AUTHOR]

mathematical model for thermal explosion in a mechanically activated heterogeneous system was constructed and tested. The model includes equations of thermal balance, chemical transformation, and dynamics of excess energy in condensed substances. The model was analyzed by analytical methods. Relations determining the characteristics of thermal explosion were obtained. The accuracy of analytical estimates was verified by numerical simulation. [ABSTRACT FROM AUTHOR]

qualitative analysis of structural types of phase trajectories and corresponding thermograms with various values of the Semenov and Todes criteria for systems with intense self-deceleration is performed. A rigorous criterion of degeneration of the thermal explosion is found. Physical mechanisms of various regimes of self-heating processes are analyzed. An approximate functional dependence of the critical value of the Semenov parameter on the self-deceleration parameter is obtained, and the limits of its applicability are determined. [ABSTRACT FROM AUTHOR]

nonstationary model of gas combustion in a porous cylindrical heat generator with allowance for heat losses inside the body and from the outer surface is proposed and numerically analyzed. The flow pattern is demonstrated to depend on the ratio of the outer and inner radii of the working region. Critical conditions separating the stationary operation mode and the thermal explosion are found. [ABSTRACT FROM AUTHOR]

Specific features of heating of a mechanically activated 3Ni + Al mixture during synthesis in the thermal explosion mode are considered. Based on the authors’ criterion of the minimum curvature of the heating rate logarithm as a function of inverse temperature, the activation energies of the synthesis process in the above-mentioned system are determined and the temperature intervals of the Arrhenius dependence and self-deceleration segments on thermograms are found. A kinetic function structure analysis shows that synthesis follows the laws of homogeneous kinetics with the reaction order close to unity. The calculated activation energies are anomalously low, as compared with conventional self-propagating high-temperature synthesis in this system. [ABSTRACT FROM AUTHOR]

Conditions of a static thermal explosion in mechanically activated Ti-C-Ni mixtures are studied. Mechanical activation of the mixtures in a planetary ball mill during 30–180 sec is found to reduce the reaction-initiation temperature by 1000–600°C, as compared with traditional self-propagating high-temperature synthesis. Results of x-ray diffraction analysis and electron microscopy of activated mixtures and thermal explosion products are described. The result of the synthesis is a TiC compound in a solid nickel matrix. [ABSTRACT FROM AUTHOR]

Results of studying the thermal explosion of 3Ni-Al mixtures after their preliminary mechanical activation in a planetary ball mill are described. Reduction of the initiation temperature and effective energy of activation of interaction between the reagents to anomalously low values is found. Results of an x-ray diffraction analysis and an electron-microscope study of the thermal explosion products and initial mixtures with different times of mechanical activation are given. [ABSTRACT FROM AUTHOR]

Stochastic phenomena in the kinetics of chemical reactions induced by a thermal explosion are studied. The statistical analysis is performed on the basis of nonlinear differential equations for gas temperature and concentration of reacting particles with random initial conditions, and also corresponding equations for the probability density function of the state variables of the system. The results of the numerical solution of these equations are presented in the graphical form as a statistical set of an ensemble of kinetic curves of concentration of reacting particles and gas temperature and as the time evolution of their probability density function. Small random fluctuations of gas temperature and particle concentration at the beginning of the reaction are demonstrated to induce significant fluctuations of the induction period. [ABSTRACT FROM AUTHOR]

This paper gives the results of temperature measurements at the beginning of fast decomposition of nine commercial azo dyes under heating. The enthalpies of formation of three azo dyes are measured, and the parameters of their explosive transformation are calculated. It is shown that for the flash temperatures obtained using the kinetic parameters of decomposition reactions and calculated heats of explosion of azo dyes, the average deviation from experimental values is 4.5%. [ABSTRACT FROM AUTHOR]

Specific features of formation of temperature and concentration fields during self-propagating high-temperature synthesis in the thermal explosion regime in a cylindrical reactor are studied by methods of mathematical modeling. The calculations are performed with allowance for melting of one (chemically active) component in the approximation with the high-melting component being non-soluble in the melt of the low-melting component. It is shown that the conditions of complete conversion of the original components in the volume of the reacting mixture depend on relations between the Biot criterion of the system, the ambient temperature, and the thermal effect of the reaction. After the thermal explosion, which occurs when the melting front reaches the geometric center of the reactor, a front of complete conversion is formed. This front moves from the cylinder centerline to the periphery with a gradually decreasing velocity. The diagram of the critical values of the Biot criterion at which the components burn down completely in the entire reaction volume is calculated. [ABSTRACT FROM AUTHOR]

The conditions and regimes of thermal ignition of a reactive porous layer are investigated under asymmetric conditions on its lateral surfaces and with an oxidizer supply to the layer by diffusion or filtration through the cold boundary. For a zero-order reaction, an analytical dependence of the critical value of the Frank-Kamenetskii parameter on the Zel’dovich parameter is obtained, which separates the regions of steady-state and unsteady regimes. A numerical analysis is made of the critical value of the Frank-Kamenetskii parameter on the Zel’dovich parameter, the Todes parameter, which determines the oxidizer consumption, and the parameter determining the oxidizer supply to the layer: the Lewis numbers or the filtration analog of the Peclet parameter. [ABSTRACT FROM AUTHOR]

The combustion of hydrogen and silane is studied. It is established that the chain initiation reaction on quartz in the zone of hydrogen and silane combustion is manifested as an autocatalytic reaction which is able to initiate a chain explosion and participate in the initiation of a thermal explosion. It is shown that in the case of an oxyhydrogen gas, the assumption of a branching-chain nature of the third limit is inconsistent with Semenov’s law, which includes double exponential dependences of the chain reaction rate on time and temperature. A criterion for the participation of branching chains in complex processes is proposed based on the presence or absence of short delays of a thermal explosion (≈1 sec). According to the criterion, the explosion of an oxyhydrogen gas at atmospheric pressure with delays markedly exceeding 1 sec proceeds without the participation of branching chains and is consistently explained by the joint action of autocatalytic processes on the reactor wall and gas-phase processes. [ABSTRACT FROM AUTHOR]

A model of phase-formation processes in the regime of a static thermal explosion of a powder mixture at temperatures higher than the melting point of the low-melting component is developed on the basis of the equilibrium diagram of state of a Ti-Al system. Numerical diagrams of the critical parameters of the system are constructed for different ratios of the original components. The dynamics of motion of the boundaries of phase homogeneity regions is calculated. For the ratio of the components in the mixture corresponding to the TiAl compound, the composition of the resultant product of the synthesis is demonstrated to depend on the conditions of heat transfer between the system and the ambient medium, which may offer a principal possibility of controlling phase-formation processes in the system mentioned. [ABSTRACT FROM AUTHOR]

Conditions of origination of the thermal explosion in a cylindrical chemical reactor equipped by a certain number of symmetrically located stirrers ensuring forced convection of the reacting mixture are considered in the approximation of an infinite Peclet number and under the assumption of laminar motion of the fluid. The critical value of the thermal explosion parameter (Frank-Kamenetskii parameter) is found as a function of the number of stirrers and the distance between the centerlines of the stirrers and reactor. As the number of stirrers increases, the calculations predict a lower probability of the thermal explosion, and the critical value of the parameter can severalfold exceed its classical value. It is found that the thermal explosion parameter substantially depends on the location of the stirrers, responsible for heat removal from the reactor. [ABSTRACT FROM AUTHOR]

A new method is developed for specimen preheating with subsequent loading by shock waves and conservation of the products of shock consolidation; the method is based on the use of the chemical furnace energy produced by a thermal explosion or combustion of SHS systems. The use of the thermal explosion expands the range of pre-shock heating temperatures up to 3000 °C and the range of mean pressures in the cylindrical ampoule up to 25 GPa. Two variants of preheating are considered: an inert specimen is heated by heat release in a reacting SHS system or the specimen under study itself is an SHS system. [ABSTRACT FROM AUTHOR]

A problem of thermal ignition of an exothermic mixture with an inert filler in a thick-walled container is formulated. It was found that synthesis can be performed under conditions of a weakly changing temperature if an inert filler is added to the mixture. Variation of critical conditions separating different thermal regimes with different values of model parameters is examined: ignition and extinction or ignition and slow transformation. [ABSTRACT FROM AUTHOR]

The specific features of dynamics of the thermal explosion in systems porous reagent- active gas-solid product under conditions where the heat-transfer and mass-transfer regions are separated from the ambient medium are considered. In addition to the competition of heat release and heat removal, the process of initiation of exothermal chemical interaction in these systems under normal pressures depends significantly on conditions of filtration transport of the gaseous reagent. The induction and post- induction periods of the thermal explosion are studied. The theoretical analysis of thermal-explosion issues is supplemented by an experimental study of the process for the porous titanium-nitrogen-titanium nitride system. [ABSTRACT FROM AUTHOR]

The problem of the thermal explosion of a reactant in the shape of a hollow cylinder under third-kind boundary conditions is solved by an inverse method. Methods for determining the critical parameters in the general and particular cases are given. Transcendental equations are derived whose roots are used to determine the critical values of the Frank-Kamenetskii parameter. The results of a numerical analysis are presented and approximating functions are given to determine the critical Frank- Kamenetskii parameter as a function of the Biot number. [ABSTRACT FROM AUTHOR]

Analytical and numerical methods are used to solve the problem of size reduction of a solid reactant in a reactive gas as applied to problems of synthesis in solid–gas systems and safe grinding of powders. Formulas are obtained that describe the dynamics of temperature, the degree of conversion, particle size, and specific interfacial area. The conditions of explosive and nonexplosive syntheses and safe grinding are determined. [ABSTRACT FROM AUTHOR]

A complete solution of the unsteady‐state filtration problem of thermal explosion incorporating the postinduction period is given for the first time. The paper describes a study of the temperature‐field dynamics, pore‐gas pressure, and the degree of condensed‐phase conversion versus the reactive‐gas deficiency in a reactive porous material. Focus is on the formation and propagation of frontal regimes of exothermic chemical reactions (their number, direction, and velocity of propagation, degree of condensed‐phase conversion at the front). The study revealed “double self‐ignition” phenomena and combustion‐wave propagation regimes with incomplete conversion at the front. A surface regime of thermal explosion limited by gas filtration from the outside was considered. The regularities in the dynamics of the exothermic chemical reaction found in the present study allow one to qualitatively control high‐temperature synthesis under thermal explosion conditions. [ABSTRACT FROM AUTHOR]

A pointwise mathematical model of sintering of a compact of an ultrafine metal powder in the thermal explosion mode is developed. A condition for occurrence of this reaction mode is found. The model is verified by results on the delay and temperature of the beginning of Pt-black powder sintering. [ABSTRACT FROM AUTHOR]