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The mechanochemical synthesis of titanium nitride during double mechanical activation of titanium powder is studied in argon and in nitrogen gas. The duration of mechanical activation of titanium in argon and nitrogen is varied in experiments. As suggested by the analysis of powder mixture morphology, X-ray diffraction analysis, and microanalysis, the preliminary mechanical activation of titanium in argon contributes to accelerating the mechanochemical synthesis of titanium nitride. Analytical relationships are obtained and theoretical estimates are given that make it possible to predict the process of double mechanical activation of titanium. [ABSTRACT FROM AUTHOR]

This paper describes synthesis in 5Ti + 3Si + Al( %) activated mixtures and in an 5Ti + 3Si + 10% Al initial mixture. The effect of mechanical activation and aluminum content on burning rate, maximum combustion temperature, morphology, elongation, integrity, and phase composition of combustion products is studied. Mechanical activation expands the limit of Al content to 40% at which samples can burn without preheating. The following intermetallic alloys are synthesized on the basis of Ti–Si–Al: solid solutions based on Ti(Si Al titanium silicide and those based on Ti(Al Si aluminide titanium. [ABSTRACT FROM AUTHOR]

Effect of mechanical activation of components and external pressure on the combustion of a heterogeneous Ti + C mixture under SHS compaction is under study. It is shown that the presence of pressure (15 MPa) results in low-rate layered combustion (4–7 cm/s) and the absence of any external pressure causes unsteady combustion at a high burning rate (50–70 cm/s), namely surface-annular combustion and volumetric combustion, both based on convective heat and mass transfer. This paper proposes a mechanism for convective combustion at a high burning rate, based on the ignition of a heterogeneous mixture by a hot impurity gas released in a combustion wave and filtered through layered cracks and other macrodefects in the volume of charge compacts, which form during the pressing of powder mixtures. The mechanical activation of the reaction mixture components reduces the density and strength of the compacts and increases the efficiency of the formation of macrodefects. External pressure has the opposite effect as it prevents crack formation and the propagation of hot impurity gas through cracks. The consolidated samples of titanium carbide with a relative density of up to 95% are obtained in volumetric combustion. [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]

This paper describes experimental studies and a mathematical model of mechanical activation and high-temperature synthesis during the Nb–2Si combustion. The model is constructed in the macroscopic approximation. Synthesis regimes are determined depending on the duration of joint mechanical activation of the reagents. The kinetic parameters of grinding of the initial powder mixture and the mechanochemical synthesis of the reaction product are obtained on the basis of experimental data by the inverse problem method. [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]

This paper describes a study of the influence of mechanical activation (MA) and Mn content on burning rate, maximum combustion temperature, sample elongation during combustion, size of composite particles, mixture yield after MA, phase composition, and morphology of synthesis products in a Ni + Al + Mn mixture. The mechanical activation of the Ni + Al + Mn mixture expands the manganese content limit at which the combustion of samples without preheating is possible, from 14 to 49% (by weight). Preliminary MA makes it possible to synthesize a compound containing all three initial metals: the (Ni, Mn)Al phase being an ordered solid solution of variable composition based on NiAl. Moreover, mechanical activation causes an increase in the burning rate, elongation, and porosity of samples of products, as well as a decrease in the maximum combustion temperature. An increase in the fraction of manganese in Ni + Al + Mn causes a decrease in the size of composite particles, the elongation of product samples, and the maximum combustion temperature, as well as an increase in the mixture yield after MA. The dependence of the burning rate on the fraction of manganese in the activated Ni + Al + Mn mixture has a maximum. [ABSTRACT FROM AUTHOR]

This paper describes a study of the effect of a Fe + Co + Cr + Ni + Al metal binder content and mechanical activation (MA) on burning rate, maximum combustion temperature, the elongation of samples during combustion, the mixture yield after MA, the size of composite particles after MA, and the morphology and phase composition of combustion products in a Ti + 2B + (Fe + Co + Cr + Ni + Al) system. Self-propagating high-temperature synthesis (SHS) is used to obtain a composite material consisting of ceramics and a high-entropy alloy. The MA increases from 60 to 80% the maximum content of a metal binder in the mixture, at which SHS is carried out at room temperature. The addition of a Fe + Co + Cr + Ni + Al binder to the activated Ti + 2B mixture prevents mechanochemical synthesis from proceeding during 5-min long MA. [ABSTRACT FROM AUTHOR]

Ti3AlC2 and Ti3SiC2 single-phase MAX phases were obtained by preliminary mechanical activation (MA) of initial mixtures of powder reactants in a high-energy planetary ball mill and subsequent self-propagating high temperature synthesis (SHS). The products of MA and SHS were studied by X-ray diffraction and electron microscopy. [ABSTRACT FROM AUTHOR]

This paper describes the effect of preliminary mechanical activation (MA) and Ti content on maximum temperature, maximum burning rate, composite particle size, mixture yield after MA, sample elongation during combustion, and the phase composition and morphology of combustion products in the Ni–Ti–Al system. The preliminary MA of a Ni + Al + Ti mixture expands the limit of titanium content at which samples can burn without preheating, from 17 to 59% (by weight). Mechanical activation is followed by a drop in the number of phases in the products and an increase in the burning rate, while the maximum synthesis temperature decreases. The augmentation of the Ti content in the Ni + Al + Ti mixture reduces the burning rate and maximum combustion temperature of both initial and mechanically activated mixtures. Moreover, as the titanium content increases, the average size of composite particles decreases and the yield of the activated mixture becomes larger. In the combustion of mechanically activated mixtures with a high (24–52%) titanium content, the Ti2Ni phase and the Ni2TiAl Heusler phase predominate in the products, while the traces of melting are visually observed. In the activated Ni + Al + Ti mixture, the Ti content at which the Heusler phase content in the combustion products becomes maximum is revealed. Most of the observed dependences are explained. [ABSTRACT FROM AUTHOR]

The Hedvall effect was implemented in self-propagating high-temperature synthesis (SHS) in TiNi + 1.1C and Ni3Al + 1.2Si low-calorific-value compositions using preliminary mechanical activation (MA) in a high-energy planetary ball mill. The dependences of the initiation temperature and the maximum reaction temperature on MA time were obtained. MA conditions that provide the solid-state mode of the self-propagating reaction were determined. The results of X-ray diffraction and electron microscopy of MA and SHS products are given. [ABSTRACT FROM AUTHOR]

Mathematical models constructed in the macroscopic approximation are used to perform a theoretical study of volume and wave synthesis in a hybrid mixture consisting of nonactivated and activated powders of the same composition. Synthesis dynamics depending on the fraction of activated powder at different values of the preliminary mechanical activation parameters is considered. Analytical formulas are obtained for approximate estimates of the temperature and time of synthesis in nonactivated and activated compositions. [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]

This study describes the effect of preliminary mechanical activation and SiO2 quartz content on combustion rate, maximum combustion temperature, sample elongation during combustion, compressibility of mixtures, composite particle size, phase composition, and the structural features of combustion products in a Ni–Al–SiO2 system. In Ni–Al–SiO2 initial mixtures, not subjected to mechanical activation, it is not possible to initiate combustion at room temperature if the mass content of SiO2quartz exceeds 10%. Preliminary mechanical activation of the Ni–Al– x SiO2reaction mixture expands the limit of quartz content in the mixture, at which it is possible to realize the combustion of pressed samples at room temperature, up to 40%. The burning rate and sample elongation during combustion increase significantly after the reaction mixtures are mechanically treated, and the relative density of the samples, obtained at a fixed pressing pressure, decreases. The increasing quartz content in the Ni–Al– x SiO2reduces the combustion rate, the maximum combustion temperature, and the sample elongation during the combustion of both the initial and mechanically activated mixtures. Moreover, as the quartz content increases, so does the sample density reached at a fixed pressing pressure in the case of initial mixtures, while the density in the case of mechanically activated mixtures is virtually not affected. The increasing quartz content also reduces the composite particle size after mechanical activation and increases the number of phases formed in the reaction products. An explanation for most of the observed relationships is proposed. [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]

Effect of carbon content in a Ni–Al–C system and preliminary mechanical activation on a burning rate, sample elongation, and mixture yield after mechanical activation, as well as on the structural features of combustion products is under study. Combustion in pressed samples from a mechanically preactivated Ni + Al mixture at room temperature could not be activated. The addition of carbon [2, 4, and 6% (by weight)] into the reacting Ni + Al mixture allows for combustion in Ni–Al–C based pressed samples. Preliminary mechanical activation of the reacting Ni + Al + xC mixture expands a carbon content limit in the mixture at which the combustion of pressed samples is possible. In addition, mechanical activation, as well as an increase in the carbon content in the Ni–Al–C system reduces the burning rate. The observed relationships are explain. [ABSTRACT FROM AUTHOR]

This paper describes the influence of mechanical activation of coals on ignition and thermal-oxidative degradation using two independent methods: thermogravimetric analysis and ignition of a coal suspension in a vertical pipe furnace. It is determined that the ignition temperature of mechanically activated coals decreases and that mechanical activation affects the further process of thermal-oxidative degradation. [ABSTRACT FROM AUTHOR]

A method of preliminary mechanical activation is used to implement the combustion of a Ti + Ni mixture, which does not burn at room temperature. The dependences of the burning rate, maximal temperature of combustion, and elongation of samples on the mechanical activation time of the Ti + Ni powder mixture are described for the first time. Moreover, the microstructure and phase composition of activated mixtures of their combustion products are studied. The mechanical activation time (9 min) during which the burning rate of the mixture and the content of the main phase (TiNi intermetallide) are maximal in the combustion products is experimentally determined. In these conditions, the combustion propagates within a narrow zone—the maximal temperature corresponds to that in the combustion front. [ABSTRACT FROM AUTHOR]

A mathematical model of synthesis in a mechanically activated 3Ni–Al system is constructed in a macroscopic approximation. Different combustions as the functions of duration of mechanical activation and the duration of isothermal exposure of the mechanical mixture are determined. Experimental data are used to calculate kinetic constants that characterize the conversion of the substance during mechanical treatment. [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]

Detailed results of an x-ray diffraction analysis of equimolar mixtures of nickel and aluminum with different particle sizes before and after shock loading in flat recovery ampoules are reported. [ABSTRACT FROM AUTHOR]

This paper describes the study of the effect of mechanically activated grinding of coal on its flammability. Coal treated in a ball pulverizer and mechanically activated coal exposed to air are compared in experiments. The experiments show a decrease in the chemical activity of mechanically activated coal. [ABSTRACT FROM AUTHOR]

Self-propagating high-temperature synthesis in both the modes of both layer-by-layer combustion and dynamic thermal explosion was carried out using preliminary mechanical activation of BC-Ti powder mixtures in a planetary ball mill. Preliminary mechanical activation conditions of reaction mixtures that provide a reduction in the reaction initiation temperature to 600 ± 20◦C were determined. The reaction products consist of mixtures of TiC and TiB with submicron grain size. The results of x-ray diffraction and electron microscopy studies of activated samples and reaction products are presented. [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]

The detonation properties of mechanically activated mixtures of ammonium perchlorate and aluminum were studied. The deflagration-to-detonation transition for low-density charges was investigated. Dependences of the detonation velocity of pressed charges with different types of aluminum on the activation time, density, and diameter of the charges were obtained. For compositions with nanosized aluminum, it is was found that the detonation velocity depends nonmonotonically on the inverse charge diameter and remains almost unchanged in a certain range of charge diameters. It is shown that the joint use of mechanical activation and nanosized components of the composite explosive significantly increases the detonability, reduces the critical diameter, and shifts the maximum of the detonation velocity as a function of density to higher charge densities. [ABSTRACT FROM AUTHOR]

This paper describes a study on the burning of pressed and bulk-density samples from a Ni + Al mixture subjected to mechanical activation. It is shown that mechanical activation and dispersion have a different impact on the burning rate of the samples under study. The gas flow hardly changes the burning rate of the bulk-density mixtures. The linear burning rate of the dispersed bulk-density mixture is 1.7 times greater than that of the pressed mixture, and the mass burning rates are equal to each other. The calculations showed that the conductive heat transfer mechanism in the combustion wave of the dispersed bulk density mixture is the principal mechanism. [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]

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]

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]

The effect of the activation time of the Ti + 2B mixture on the burning rate of cylindrical samples and thin foils is studied. For cylindrical samples, combustion of samples activated in argon is compared with combustion of samples activated in air. The burning rates are almost identical in these two cases. It is demonstrated that the burning rate of cylindrical samples continuously increases with increasing activation time. The burning rate of thin foils remains almost unchanged as the activation time increases up to 4 min and then drastically increases and reaches a value twice greater than the burning rate of cylindrical samples. For the titanium and boron powders used in this study, the time needed to reach the maximum burning rate is 7 min in the case of activation in air and 5 min in the case of activation in argon; if the activation time is longer, then the product of combustion is formed. The features of combustion observed in this study can be explained from the viewpoint of convective-conductive model of combustion wave propagation. [ABSTRACT FROM AUTHOR]

Preparation of mechanically activated energetic composites (MAECs) based on solid fuels (Al, Mg, and Si) and oxidizers (S, MoO, (-CF-), KClO, NH ClO, etc.) is considered. Compared to conventional mechanical mixtures, the burning rate of MAECs is significantly increased, and in some cases high-velocity detonation can be obtained. The propagation of the reaction in MAECs is accompanied by high energy release comparable to the heat of explosion of powerful aluminized explosive materials. The composites are highly sensitive to heat treatment and are capable of rapid transition from combustion to detonation. The results obtained in this work show that MAEC based formulations are promising energetic materials for a wide range of applications, from igniting and initiating compositions to components to small charges in microsystem devices. [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]

Burning rates were measured for samples of the starting mixture of Ni + Al and the same mixture subjected to mechanical treatment in argon and then in water. The dependences of the burning rate on the diameter of the samples of the original and mechanically activated mixtures are similar. The burning rate passes through a maximum as the diameter increases from 8 to 12 mm. It is found that the burning rate of 270-360 µm thick films obtained by rolling the starting mixture of Ni + Al and the mixture mechanically activated and then activated in water (dispersed) is 4-20 times the burning rate of cylindrical samples 8-12 mm in diameter, pressed from the same powders. The data obtained in this study were explained using a convective-conductive model of combustion-wave propagation. [ABSTRACT FROM AUTHOR]

The method of self-propagating high-temperature synthesis (SHS) was used to synthesize spinel ceramic pigments. Producing aluminum-nickel and aluminum-cobalt pigments in a finely dispersed state is a complex stepwise (combined) process involving a reduction stage and simultaneous natural air filtration. In the case of small-diameter samples, a flat combustion front is observed and in large samples, the front is formed of many hot spots. The dependence of combustion rate on porosity is presented. The maximum combustion rate of these systems are recorded for porosity of 50-60%. Powdered SHS pigments were obtained for the first time. [ABSTRACT FROM AUTHOR]

The possibility of producing Cu/ZrO composites by combining mechanical activation and self-propagating high-temperature synthesis (SHS) is studied using x-ray diffraction and electron microscopy. It is shown that Cu/ZrO composites are formed in SHS using CuO/Cu/Zr mechanocomposite as a precursor. [ABSTRACT FROM AUTHOR]

The influence of mechanical activation on the structural state and reactivity of a Ni—Al powder mixture is studied. Mechanical activation of the Ni—Al mixture is demonstrated to have an induction period that involves accumulation of deformation defects of the crystal structure of the species; the NiAl phase of the reaction product is not yet registered in this period. Partial amorphization of aluminum increasing the system reactivity is revealed. Based on results of a diffraction analysis, a quantitative criterion of the state of the species during their activation is proposed: the value of stresses of the second kind. The system becomes unstable and autogenerates a synthesis reaction when microstresses are accumulated in the initial material to the level of the yield stress of the corresponding substance. [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]

The current status of research in the field of combustion of heterogeneous nanostructural systems is reviewed. Four classes of reactive media are considered: nanothermites, sol-gels, mechanically activated nanocomposites, and multilayer nanofilms. Based on the summary of publications, possible mechanisms of combustion in such systems and prospects of their further applications are discussed. [ABSTRACT FROM AUTHOR]

Laws of self-propagating high-temperature synthesis in 3Ti + 2BN reactive mixtures after preliminary mechanical activation in a planetary ball mill are studied. A discontinuity caused by specific features of the dynamics of formation of mechanocomposites is observed on the plots of the burning rate and temperature versus time. Regimes of preliminary activation are determined, which ensure the solid-phase combustion regime. Results of x-ray diffraction phase analysis and electron microscopy of combustion products and initial mixtures for different times of mechanical activation are presented. [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]

Mechanical activation of a mixture of silicon oxide and aluminum is studied by methods of infrared spectroscopy, differential thermal analysis, and x-ray diffraction. If a SiO2/Al mechanocomposite is used as a precursor, then a Si/Al2O3 composite with a small grain size and a uniform distribution of the components can be obtained by the method of self-propagating high-temperature synthesis. [ABSTRACT FROM AUTHOR]

Experiments aimed at studying the ignition of coal dust obtained by coal disintegration in high-energy mills are performed in a tubular furnace. Effective kinetic constants of ignition of coal dust ground in a vibrational-centrifugal mill and in a disintegration mill under conditions of rapid heating are determined for the first time. It is shown that the volatile release rate depends on the method of coal grinding. [ABSTRACT FROM AUTHOR]

It was found that mechanical activation of a mixture containing iron, aluminum, and oxide iron resulted in mechanochemical reduction of iron oxide and formation of a Fe/Al/Al2O3 nanostructural mechanocomposite. High-temperature self-propagating synthesis (SHS) using this composite as a precursor yielded a FeAl/Al2O3 composite, which retained the morphology and dimensional characteristics of the precursor. During mechanical activation of a mixture of iron, aluminum, and chromium oxide, complete reduction of the latter did not occur but SHS also led to the formation of an intermetallide/oxide nanocomposite, in which chromium atoms were incorporated in the structure of iron aluminide. [ABSTRACT FROM AUTHOR]

A mathematical model of nonisothermal synthesis in a mechanically activated system with allowance for the phase transition in one reagent is constructed. Results of studying the influence of the phase transition on the kinetics of nonisothermal chemical interaction of a pre-activated mixture for two different limiting synthesis regimes (wave and volume synthesis) are presented. [ABSTRACT FROM AUTHOR]

This paper considers the mechanisms of structure formation during gas detonation spraying of coatings of TiAl3 and Ni3Al intermetallic compounds produced under equilibrium and nonequilibrium synthesis conditions. The coating sprayed from TiAl3 has the same phase composition as the initial powder, regardless of the synthesis conditions. During spraying of Ni3Al, the structure of the coating also does not depend on the synthesis conditions and consists of two phases — Ni3Al and NiAl, with the crystal structure varying along the coating thickness. Comparative impact abrasion tests of the coatings showed advantages of TiAl3 coatings over coatings based on Ni3Al and titanium diboride. [ABSTRACT FROM AUTHOR]

A new method is developed for obtaining powder nanocomposites consisting of a metallic or intermetallic matrix and ceramic nanometer particles as a reinforcing phase. This method involves the following consecutive processes: short-time mechanical activation of the mixture of powder reagents in a high-energy planetary ball mill, self-propagating high-temperature synthesis, and additional mechanical activation of the synthesis products. Specific features of the reinforcing phase synthesis in matrices are examined by an example of TiB2-Cu and TiB2-TiNi systems. Compaction conditions that allow obtaining volume nanostructural materials with high strength characteristics are found. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Results from experimental studies of the nonisothermal mechanochemical reaction in the titanium-nitrogen system. Experimental data are compared with simulation results. The effective kinetic parameters of mechanical activation of the reactant and the chemical reaction are determined from analytical relations. It is shown that the developed mathematical model is suitable for the analysis of the macrokinetics of nonisothermal chemical reactions in solid reactant-reactive gas systems. [ABSTRACT FROM AUTHOR]

A mathematical model for the combustion of preliminary activated heterogeneous systems is proposed which includes equations describing heat conduction, chemical kinetics, and the dynamics of the excess energy accumulated in condensed reagents at the stage of preliminary mechanical treatment. The excess energy decreases as a result of structure normalization and chemical transformation, whose activation energy, in turn, depends on the excess energy in the condensed reagents. The case of stationary combustion is analyzed in detail. The effect of mechanical activation on the velocity of the synthesis wave and its structure is analyzed by numerical modeling. The main conclusions are compared with available experimental data. [ABSTRACT FROM AUTHOR]