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The problem of thermal stability of a cylindrical sample with nonlinear heat generation placed in a medium with the ambient temperature random walk was studied. The behavior of this system was examined depending on the parameters of the problem (heat generation intensity, random walk variance). A numerical algorithm based on averaging multiple random trajectories of the ambient temperature was proposed. A numerical method was developed for solving the heat transfer problem with the heat source and stochastic boundary which combines both explicit and implicit schemes for linearized transfer equations and the Euler–Maruyama method. The distributions of ignition characteristics and their moments were obtained. Their dependencies on the parameters of the problem were investigated.

Objectives: Coating treatment on the surface of diamond particles is an important technique to effectively overcome the problem of difficult bonding between diamond and substrate, and the thermal explosion reaction is a common surface coating technique for diamond particles. However, this technology has disadvantages such as difficulty in separating diamonds from the product and a low proportion of diamonds, which increases its complexity and production costs, greatly limiting the promotion and application of this technology. This article aims to introduce polytetrafluoroethylene (PTFE) into thermal explosion reaction technology to form a coating mainly composed of TiC on the surface of diamond particles. It is expected to optimize the coating preparation process and promote the popularization and application of thermal explosion reaction technology in the field of diamond plating, so as to improve the wear resistance and service life of the diamond tools. Methods: Using two raw material systems, Ti/carbon black/diamond and Ti/carbon black/PTFE/diamond powders, the thermal explosion reaction of Ti/carbon black/diamond is induced by the chemical furnace method, and the intense chemical reaction between PTFE and titanium at low temperature ensures that the Ti/carbon black/PTFE/diamond system directly undergoes a thermal explosion reaction. At the same time, the TiC coating can be generated on the surface of diamond particles by adjusting the ratio of raw materials and triggering the thermal explosion reaction under high temperature conditions. The macroscopic morphology of diamond particles before and after coating is observed and compared by optical microscope to roughly infer the plating condition, and the phase compositions of the coating were analyzed by X-ray diffraction. Then the scanning electron microscope and the energy dispersive spectroscopy are used to observe the surface morphology of diamond particles, determine the elemental compositions, and infer the surface reaction state. Results: The thermal explosion reaction of both raw material systems can form a TiC coating on the surface of diamond. The main phase of the binder reaction product is TiC, and the main phases of the coating on the surface of diamond particles are TiC and Ti. But for the Ti/carbon black/diamond system, the chemical furnace method is needed to induce a thermal explosion reaction. When the diamond mass fraction in the raw material is 30% or lower, the TiC coating on the surface of the diamond particles is good. When a small amount of PTFE is introduced into the Ti/carbon black/diamond system, the reaction between Ti and PTFE releases a large amount of heat, which induces the thermal explosion reaction between Ti and carbon black and synthesizes TiC, and finally forms a TiC coating on the surface of diamond particles. In addition, the system does not need the chemical furnace method to detonate. When the diamond mass fraction in the raw material is less than or equal to 60%, the diamond particle surface coated with TiC coating is good. At the same time, appropriately reducing the content of carbon black in the raw materials can enable diamond to obtain a good TiC coating on its surface even when the mass fraction of diamond is 90% or higher. Conclusions: TiC coatings are prepared on the surface of diamond particles using thermal explosion reaction technology, and the important effects of raw material compositions and PTFE additives on the formation of diamond particles' surface coating are revealed. Adding an appropriate amount of PTFE can directly induce the thermal explosion reaction, which greatly promotes the increase of the proportion of diamond in the raw material, and effectively improves the formation quality of the coating. This can greatly save binder powder, thereby reducing production costs, while obtaining loose powder products that are easy to separate from diamonds. In addition, drawing on the work of this study, other carbide materials (such as SiC) can be analogously extended for coating on the surface of diamond particles, thereby promoting the promotion and the application of thermal explosion reactions in diamond coating.

Porous NiAl intermetallics were synthesized from Ni-50at.%Al powder compact using an energy-saving and facile method of thermal explosion (TE). The effect of preheating treatment at 470 °C for 2 h on exothermic behavior, macroscopic appearance, phase composition and microstructures are investigated. Results shown that the combustion temperature decreases from 1645 to 1516 °C and the synthesized porous NiAl compounds possess a complete cylindrical shape. Some Ni2Al3 and NiAl3 phases preferentially generate in the preheating process through the solid-phase diffusion reaction. Afterward, the eutectic reaction of Al-NiAl3 and the melting of Al promote the occurrence of an obvious exothermic reaction even at a low temperature. After TE reaction, three-dimensional interconnected pore channels are formed among the product skeletons with a high porosity of 60%, indicating the pore structures of porous NiAl sintered compact can be well controlled. The oxidation kinetics curve suggests that porous NiAl compounds exhibit excellent oxidation resistance at high temperature. [ABSTRACT FROM AUTHOR]

Co-Al porous materials were fabricated by thermal explosion (TE) reactions from Co and Al powders in a 1:1 ratio using NaCl as a space retainer. The effects of the NaCl content on the temperature profiles, phase structure, volume change, density, pore distribution and antioxidation behavior were investigated. The results showed that the sintered product of Co and Al powders was solely Co-Al intermetallic, while the final product was Co4Al13 with an abundant Co phase and minor Co2Al5 and Co-Al phases after added NaCl dissolved out, due to the high Tig and low Tc. The open porosity of sintered Co-Al compound was sensibly improved to 79.5% after 80 wt.% of the added NaCl dissolved out. Moreover, porous Co-Al intermetallic exhibited an inherited pore structure, including large pores originating from the dissolution of NaCl and small pores in the matrix caused by volume expansion due to TE reaction. The interconnected large and small pores make the open cellular Co-Al intermetallic suitable for broad application prospects in liquid–gas separation and filtration. [ABSTRACT FROM AUTHOR]

The goal of this research is to design the Gudermannian neural networks (GNNs) to solve a type of two-point nonlinear singular boundary value problems (TPN-SBVPs) that arise within thermal-explosion theory. The results of these investigation are provided for different neurons (4, 12 and 20), as well as absolute error along with the time complexity. For solving the TPN-SBVPs, a genetic algorithm (GA) and sequential quadratic programming (SQP) are used to optimize the error function. The accuracy of designed GNNs is provided by using a hybrid GA–SQP combination, which is based on a comparison of obtained and actual solutions. Furthermore, statistical analysis of the data is proposed in order to establish the competence as well as effectiveness of designed and the efficacy of the designed computing framework for solving the TPN-SBVPs. [ABSTRACT FROM AUTHOR]

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This work focused on the production of the MoAlB MAB phase through self-propagating, high-temperature synthesis in the thermal explosion mode. The influence of the method of a Mo-Al-B-powder reaction mixture preparation on the combustion temperature, mechanism, and stages of the MAB phase formation in the combustion process was investigated. The combustion temperatures of the mixtures obtained in the rotary ball mill and high-speed planetary ball mill were 1234 and 992 °C, respectively. The formation of intermediate compounds Mo3Al8 and α-MoB in the combustion front, along with MoAlB, was established using the time-resolved X-ray diffraction method. In the case of the mixture prepared in a ball mill, the primary interaction in the combustion front occurred through the Al melt, and in the case of using a planetary mill, solid-phase reactions played an important role. The mechanical activation of the mixture in a planetary mill also accelerated the processes of phase formation. The method of a reaction mixture preparation has virtually no effect on the MoAlB MAB phase content in combustion products (92–94%), but it does affect their structure. The synthesis products have a lamellar structure composed of MAB grains with a thickness of ~0.4 μm and a length of ~2–10 μm. [ABSTRACT FROM AUTHOR]

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 process of creating a porous metal-ceramic material based on Ni-Al alloy and gadolinium-doped cerium oxide (CGO) using the thermal explosion method has been investigated. This study aims to analyze the effect of CGO on the thermal explosion parameters and the architecture of the resulting Ni-Al-CGO materials. In this regard, the influence of adding CGO powder to the Ni-Al system on the synthesis process and structure formation during controlled heat loss thermal explosion has been studied. Dependencies of temperature and time characteristics of the thermal explosion on initial parameters have been measured. It has been demonstrated that the concentration of CGO in the initial mixture and heat dissipation from the sample significantly affect the rate of the exothermic reaction. The phase composition of the obtained porous materials, depending on the CGO content and the temperature of subsequent vacuum annealing, was analyzed using X-ray diffraction. The chemical composition and microstructure of the synthesis products were examined through electron microscopy and energy-dispersive X-ray spectroscopy. The possibility of forming metal-ceramic composites with a porosity of 60–65 % for use as supporting substrates for solid oxide fuel cells with a NiO/CGO anode has been shown. An anodic layer of NiO/CGO was applied to a metal-ceramic base of the composition (Ni+25 %Al)+5 %CGO using screen printing, which was then annealed in an air atmosphere at 1300 °C and reduced at 900 °C in a hydrogen atmosphere. The dilatometric method determined that adding 40 wt.% Cr to a mixture of Ni-Al powders reduces the average coefficient of thermal expansion of the new material.

High-entropy carbides are a new class of inorganic compounds promising for a wide range of applications. A new concept was proposed for the synthesis of powders of high-entropy carbides by self-propagating high-temperature synthesis (SHS) in the gasless thermal explosion mode from previously mechanically synthesized and structured reaction mixtures. For the first time, high-entropy carbides TaTiNbVWC5 and TaNbVMoWC5 were produced by this method, and their crystal structure was determined and compared with those of similar compounds synthesized by sintering. [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]

Porous TiAl3 materials were prepared by a time- and energy-saving thermal explosion (TE) method with Ti-75 at% Al mixture powders. Cyclic oxidation tests were performed in air at 650 °C, 800 °C, and 900 °C. Only a weak peak of the oxide phase was detected by X-ray diffraction when the oxidation temperature was below 800 °C. The pore structures remained stable without pore blockage or collapse due to the thin protective oxide layer formed on the surface of the product skeleton at 650 °C, which was confirmed to be Al2O3. The thickness of the oxide scale increased with increasing the oxidation temperature from 800 °C to 900 °C. The compressive strength of the oxidized sample was inversely proportional to its corresponding porosity. Additionally, the antioxidant mechanism at high temperature was further investigated, indicating excellent oxidation resistance. Therefore, porous TiAl3 intermetallic can be considered as promising materials for applications such as filtration, separation, and catalysis at a high temperatures up to 800 °C.

In this study, the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition. The criticality conditions for a slab, an infinite cylinder, and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system. Exact solution for a Semenov model with convection heat loss was also presented. The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared. The critical parameter δ is calculated and compared with those of Frank-Kamenetskii solution values. The validation of the calculated ignition temperatures with other exact solution and experimental results were offered. The relation between critical parameters form Semenov and F.K. models solution was introduced.

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]

MoAlB ceramics containing a small amount of Al2O3 and MoB as impurities were synthesized by thermal explosion technique using Mo, Al, and B2O3 as the raw materials. The effect of Al content on the reaction synthesis of MoAlB materials was investigated. Results showed that adding excess Al could compensate for the Al volatilized during the thermal explosion reaction Moreover, it could remarkably promote the formation of gaseous AlO and inhibit the synthesis of solid-phase Al2O3. Thus, it substantially promoted the synthesis of MoAlB. High-content MoAlB ceramics were prepared at 800 °C for 1 min by using 2Mo/4.6Al/B2O3 as the raw materials. The MoAlB grains were flaky and had a thickness of 500 nm and a length of 1–5 μm.

Fe2AlB2 material was prepared through spark plasma sintering (SPS) by using Fe/Al/B mixed powder as the raw material. The effects of sintering temperature, holding time, and Al content on the phase composition and microstructure of the product were studied to obtain materials with high Fe2AlB2 content. Results showed that when the sintering temperature was increased to approximately 1000°C, SPS induced a thermal explosion reaction, resulting in the formation of a dense sintered sample with high Fe2AlB2 content. The sample contained a small amount of FeB and FeAl3 impurities. The synthesis of Fe2AlB2 could be promoted by optimizing holding time and increasing Al content in the raw materials. The most suitable process parameters for the synthesis of materials with high Fe2AlB2 content were 1000°C, no holding, and 2Fe/1.1Al/2B raw material. The Fe2AlB2 sample had good mechanical properties. Its Vickers hardness and bending strength were 10.5 GPa and 352 MPa, respectively. Given that the synthesized Fe2AlB2 material was unstable, continuously increasing the temperature or extending the holding time would cause it to decompose.

Heat generation as a result of the exothermic reaction reaches the environment mainly due to the conduction through the walls of the vessel. The balance between the heat generated and the heat conducted away, resulting in the explosion is described by the Frank-Kamenetzkii (FK) parameter ρ. The critical value of FK for which the explosion occurs depends upon the shape of the vessel, which requires the solution of governing singular nonlinear Poisson-Boltzmann equation. Owing to the exponential nonlinearity and singularity the analytical exact solution for the non-integer k values does not exist. This work focuses on implementing the polynomial collocation by exploiting the global optimization features of the genetic algorithm to solve the Poisson-Boltzmann equation for integer and non-integer shape factors (k). The governing equation was converted into coupled nonlinear algebraic equations and an objective function was formulated. The method was examined for six different configurations of the control parameters of GA to find the best set of parameters. The solution for temperature distribution is obtained for cylindrical (k = 1), parallelepiped (k = 0.438, 0.694), and an arbitrary shape (k = 0.5) respectively. The solution obtained from Polynomial Collocation Genetic Algorithm (PCGA) remained in good agreement with the corresponding analytical results for k = 1, with the minimum absolute error of 10−10. The critical values of the FK are obtained as 1.5,1.4,and1.7 for shape factor k=0.438,0.5,and0.694 respectively with the convergence of the order of 10−6to10−5. The obtained solution is fairly stable over appropriate independent runs with the variation in the fitness value ranging from 10−05to10−03. Further simulations were performed to validate the results through statistical error indices. The diminutive errors of the order of 10−6 confirm reliable optimum solution, accuracy, and stability.

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]

Variational formulations are proposed for equations describing the stationary states of nonisothermal one-dimensional reactors, including those under convective transfer. Several versions of a numerical solution are considered for the proposed variational formulations on the basis of the method of local variations and the Rayleigh–Ritz method. The special features of using numerical methods to solve the problems under consideration are discussed: convergence and ratio of a spatial grid step to the degree of an approximating polynomial. Modifications of the thermal ignition problem with account for convective transfer and heat losses are considered. A variational principle is proposed that determines the structure of a combustion front at a given propagation velocity. It is shown that this variational principle can be used along with the principle of minimum entropy production for a complete solution to the problem of stationary propagation of an exothermic reaction wave. [ABSTRACT FROM AUTHOR]

In this study, the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition. The criticality conditions for a slab, an infinite cylinder, and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system. Exact solution for a Semenov model with convection heat loss was also presented. The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared. The critical parameter d is calculated and compared with those of Frank-Kamenetskii solution values. The validation of the calculated ignition temperatures with other exact solution and experimental results were offered. The relation between critical parameters form Semenov and F.K. models solution was introduced. [ABSTRACT FROM AUTHOR]

Ceramics with high MoAlB content were rapidly synthesized via thermal explosion by using Mo/Al/B mixed powders as the raw materials. The effects of raw material ratio and heating mode on the phase composition of the products were studied through DSC, X-ray polycrystalline diffractometer, and SEM. Results showed that ceramics with high MoAlB contents could be prepared from 1.1Mo/1.2Al/1.05B powders by using a tubular furnace at 800 °C for 1 min. They could also be obtained from 1.1Mo/1.1Al/1B powders through spark plasma sintering at 1000 °C without holding. Finally, the reaction mechanism of MoAlB material synthesis via thermal explosion was proposed on the basis of thermodynamics analysis.

Co–Al porous intermetallics were fabricated by an efficient and energy-saving method of thermal explosion (TE) reactions. The effects of Co/Al molar ratios on the temperature profiles, phase compositions, expansion behaviors, density, pore characteristics, and oxidation resistance were investigated. When the target furnace temperature was set at 700°C, there was an obvious exothermic peak in the temperature profiles. The ignition temperatures were in the range of 600–645°C, and the combustion temperatures were in the range of 984–1,421°C. Co–Al porous intermetallics had the open porosity of 27–43%, and the pores were from nonfully dense green compacts and explosion behaviors of TE. The specimen with Co:Al = 2:9 possessed a higher open porosity of 42.8%, the lowest density of 1.86 g cm−3, and the largest volume expansion of 76.7%. The porous specimens with Co:Al = 1:1 possessed the highest open porosity of 43.2%, the lowest volume expansion of 12.3%, and the highest density of 3.42 g cm−3. All Co–Al porous intermetallics showed excellent oxidation resistance at 650°C in air, especially the specimen with Co:Al = 1:1 had the highest oxidation resistance.

High-energy ball milling (HEBM) of powders is a complex process involving mixing, morphology changes, generation and evolution of defects of the crystalline lattice, and formation of new phases. This review is dedicated to the memory of our colleague, Prof. Michail A. Korchagin (1946–2021), and aims to highlight his works on the synthesis of materials by self-propagating high-temperature synthesis (SHS) and thermal explosion (TE) in HEBM mixtures as important contributions to the development of powder technology. We review results obtained by our group, including those obtained in collaboration with other researchers. We show the applicability of the HEBM mixtures for the synthesis of powder products and the fabrication of bulk materials and coatings. HEBM influences the parameters of synthesis as well as the structure, phase composition, phase distribution (in composites), and grain size of the products. The microstructural features of the products of synthesis conducted using the HEBM precursors are dramatically different from those of the products formed from non-milled mixtures. HEBM powders are also suitable as feedstock materials for depositing coatings by thermal spraying. The emerging applications of HEBM powders and future research directions in this area are discussed. [ABSTRACT FROM AUTHOR]

Results of receiving a diborid of magnesium are given in work by magniathermal oxidation of boron composite compounds at different argon pressures and temperatures. The relevance of a research is proved by superconducting properties of magnesium diboride. Synthesis of magnesium diboride itself accelerates, due to wall burning and thermal explosion of exothermic mixture of the reaction products of magniathermal. It is shown that the use of SHS method at high argon pressure and temperature allows to obtain magnesium diboride of high purity.

Fe2AlB2 material was prepared through spark plasma sintering (SPS) by using Fe/Al/B mixed powder as the raw material. The effects of sintering temperature, holding time, and Al content on the phase composition and microstructure of the product were studied to obtain materials with high Fe2AlB2 content. Results showed that when the sintering temperature was increased to approximately 1000°C, SPS induced a thermal explosion reaction, resulting in the formation of a dense sintered sample with high Fe2AlB2 content. The sample contained a small amount of FeB and FeAl3 impurities. The synthesis of Fe2AlB2 could be promoted by optimizing holding time and increasing Al content in the raw materials. The most suitable process parameters for the synthesis of materials with high Fe2AlB2 content were 1000°C, no holding, and 2Fe/1.1Al/2B raw material. The Fe2AlB2 sample had good mechanical properties. Its Vickers hardness and bending strength were 10.5 GPa and 352 MPa, respectively. Given that the synthesized Fe2AlB2 material was unstable, continuously increasing the temperature or extending the holding time would cause it to decompose. [ABSTRACT FROM AUTHOR]

The volume filling degree (VFD) is a universal property of materials whose influence is often overlooked in the assessment of their property and performance. The present work exemplifies its significance by evaluating its influence on the thermal explosion of a typical 1,3,5-trinitro-1,3,5-triazinane (RDX) energetic material (EM) and the related underlying mechanism, with experimental measurements of the critical temperature for an explosion delay of 5 ​s (T5s), and reactive molecular dynamics (MD) simulations. Three samples with different VFDs are accounted for in the T5s measurements, whereas seven RDX-containing models are established for our MD simulations, considering two kinds of surfaces, four VFDs of 1, 0.5, 0.1, and 0.05, and three heating styles. The experimental measurements show that a higher VFD leads to a lower T5s, or readier thermal decay. The origin of the VFD influence on T5s is that a smaller VFD favors dissociation reactions such as the NO2 partition, and disfavors the combination ones such as NO2 consumption in rapid complete decay to obtain final stable products and enhance heat release. Particularly, the reduced VFD increases the energy required to complete decay, lowers the decay rate and heat release, and results in reduced temperature, pressure elevation and explosion power, in agreement with the experimental observation that a higher VFD causes a lower T5s. Moreover, the origin of the VFD influence is principally from the pressure effect. Therefore, the VFD is crucial in the thermal decomposition of EMs because various VFDs can cause a significant difference in power. Moreover, the difference in the surface effect on the thermal decay of RDX between the (021) and (210) faces is clearly discriminated under adiabatic heating, because more activated molecules are found around the (021) face owing to the higher internal energy. In summary, the influence of VFD is significant when dealing with issues related to the surfaces of EMs.

This work investigates possible factors that lead to acetone-water explosion in a hydrothermal extraction reactor that happened in our laboratory. To begin with, acetone-water reactivity was checked in CAMEO. Next, pressure build-up curves at varying operating conditions were simulated in Aspen Batch Modeler. Analysis of variance (ANOVA) was conducted in IBM SPSS Statistical Software to determine the most significant factors causing the explosion. Results from CAMEO showed that the explosion was a boiling liquid expanding vapour explosion (BLEVE). Outputs from Aspen simulation indicated that the reactor pressure rise increased with the increment of acetone ratio, heating temperature and reactant total volume. The reactor wall ruptured as the pressure exceeded the maximum allowable working pressure. IBM SPSS showed that the heating temperature was the most significant factor causing the pressure to build-up within the reactor, followed by the acetone-water ratio and total reactant volume. Among all three factors, the heating temperature added to largest pressure build-up, especially when the temperature was increased near to 360 °C. The time required to trigger explosion was predicted to be within 13.8–15 min of heating.

The personal awareness of explosion protection increases consequently with the terrorist threat throughout the world in recent years, so explosion protection becomes a worldwide problem. People pay more and more attentions to the explosion-proof of building. Glass window is the weakest component of a building. Therefore, it is very important to study the explosion-proof performance of glass windows for improving the building protection capability. The experiment is the most intuitive method to detect the explosion-proof performance of glass windows. The critical safety distance of the glass window under small explosion load was measured by experiment in this paper. However, due to the high risk and cost of explosion experiments, so the experiment data were rather rare. For comprehensive understanding the explosion-proof performance of laminated glass windows, the critical charge for double laminated toughened glass under explosion was simulated. According to the fitting curve of critical charge, the empirical formulas for calculating the critical charge for laminated glass windows with three panel sizes, three glass thicknesses and four interlayer thicknesses are obtained at different distances. The error analysis shows that the empirical formulas are accurate and available, which can provide some reference for the anti-explosion design of laminated tempered glass.

The goal of this work was to separate the reaction and spark plasma sintering (SPS) effects during the in-situ synthesis of TiC in mechanically milled Ti–C–3Cu powder mixtures. The powders were milled for 3–10 min in a high-energy planetary ball mill. Structural changes occurring in the reaction mixtures during thermal explosion (TE) in a furnace and SPS in a graphite die were compared. Although the maximum temperature of TE reached the melting point of copper in some samples, no evidence of extensive melting was observed in the microstructure of the products of TE. The ignition and maximum temperatures of TE were found to decrease with increasing milling time of the mixture. In the mixture milled for 10 min, the maximum temperature of TE was only 820 °C. Melting of copper at the inter-particle contacts during SPS was observed in samples milled for 5–10 min (SPS at 900–980 °C) and caused the formation of TiC-depleted regions in the microstructure. Those regions were the re-solidified melt partially filling the pores between the agglomerates. Based on the analysis of the TE parameters in the mixtures and microstructures of the products of TE and SPS, melting during SPS was attributed to the effect of electric current (a high electric current density at the inter-particle contacts) and not to the heat of reaction. The hardness, compressive strength and Young's modulus of the sintered composites are reported. A TiC–Cu composite (milling time 5 min, SPS at 980 °C, relative density 93%) shows a compressive yield strength of 890 MPa and an ultimate compressive strength of 920 MPa. [ABSTRACT FROM AUTHOR]

Silicon oxynitride nanopowders were successfully prepared by thermal explosion of the Si and SiO 2 mixed powders with the different particle sizes in various molar ratio (x / y = 2.0, 1.5) under N 2 , supplemented by the subsequent gravity separation strategy. The effects of Si/SiO 2 molar ratio, preheating temperature and insulation time on the phase composition of the as-oxynitrided products in the thermal explosion strategy were investigated. Meanwhile, the effects of sedimentation time on the phase composition and oxygen content of the as-obtained products in the gravity separation strategy were also discussed. It is shown that the by-products are absent in the as-oxynitrided products with a 1.5:1 M ratio. Prolonging the insulation time or preheating temperature is beneficial to improve the content of Si 2 N 2 O phase with a 2.0:1 M ratio. All the by-product phases are disappeared in the as-oxynitrided products with a 2.0:1 M ratio after sedimentation treatment of 120 s. The as-obtained silicon oxynitride nanopowders with 58% of recovery and 16.2% of oxygen content are close to the theoretical stoichiometric ratio of Si 2 N 2 O. The preparation mechanism of silicon oxynitride nanopowders was proposed. [ABSTRACT FROM AUTHOR]

In this paper is presented a simple possible model which can explain the thermal explosion problem, the existence of an induction period and a sudden rapid temperature rise. As state variables used for modeling are: the pressure, the temperature and the concentration. The time evolutions of these state parameters are analogically modeled using ordinary differential equations. The numerical simulations of the obtained model are made in Matlab/SimulinkTM. The validation of the model is realized by comparison between experimental data and simulation results, presenting a good accuracy. [ABSTRACT FROM AUTHOR]

In the present paper, the trace B doped Ni3Al alloy was prepared by the thermal explosion and hot extrusion (TH/HE) technique. Its micro-structure characterization and mechanical properties were carried out by OM, XRD, TEM, compression and micro-hardness tests. Micro-structure examinations exhibit that the TH/HE technology has transformed the powders into Ni3Al alloy with less porosity. In the synthesized part, coarse and ultrafine Ni3Al grains comprise the dual-scale grain structure with segregated Al2O3 particles along grain boundary. TEM observations reveal that γ-Ni, Al2O3 and Ni3Al phases coexist in the synthesized part. Moreover, the Al2O3 particles in the synthesized part have α-Al2O3 and γ-Al2O3 two crystal structures. In addition, there is a transition region along the interface of Al2O3 and Ni3Al grain. The subsequent hot extrusion optimize the micro-structure of the extruded part by homogenizing the Ni3Al grain, uniformly distributing Al2O3 and generating massive substructures. The great deformation results in the pile-up of dislocations, intersected dislocations and substructures. Moreover, the movement of dislocation promotes the formation of micro-twinning in the Ni3Al grain, which is accompanied with the stacking faults and nano-structure. The mechanical properties exhibit that the micro-structure optimization caused by the TE/HE technology improves the compressive ductility and strength of the Ni3Al alloy obviously. DOI: http://dx.doi.org/10.5755/j01.ms.24.4.19460

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]

In the present paper, a mathematical modeling of high-temperature synthesis process in powder system Ni+Al under linear heating conditions was carried out. A comparative analysis of numerical modeling results and experimental data which were obtained for mechanically activated powder mixtures is presented. The criterion for determining the characteristic ignition temperature in the case of forced ignition was proposed. This criterion makes it possible to establish a relationship between the thermokinetic parameters at the ignition limit. With the use of the model, the dependencies of the ignition temperature, the induction time, and the conversion degree on the effective activation energy were established. It was found that these dependencies are close to linear that allows making the predictive estimates. It was shown that the ignition temperature depends most significantly on the activation energy of the synthesis while its dependence on other kinetic parameters is of secondary importance. Based on the criterion proposed, an alternative method for determining the effective activation energy of synthesis was considered. [ABSTRACT FROM AUTHOR]

To achieve the low energy consumption and high strength joining between Ti and Ni, a novel joining method (rapid thermal explosion, TE) was developed for joining dissimilar metals using Ti-Al mixture powders as flux. The TE reaction temperature of Ti-Al flux was measured, and the microstructure and mechanical properties of Ti/Ni joint were investigated. The results reveal that the combustion temperature of the Ti-Al powder interlayer is 1103 °C, which is higher than the joining temperature, and an obvious self-exothermic phenomenon lasts 20 s. The intermetallic compound diffusion layers formed at both interfaces mainly owing to the diffusion of Al and the growth activation energy of diffusion layers near both interfaces are 79.68 kJ/mol and 38.26 kJ/mol, respectively. Based on the sheer strength and diffusion layer, the formation mechanism of Ti/Ni joints is metallurgical bonding through atomic diffusion and formation of the diffusion layer. [ABSTRACT FROM AUTHOR]

We consider the model of auto-ignition (thermal explosion) of a free round reactive turbulent jet introduced in [11]. This model falls into the general class of Gelfand-type problems and constitutes a boundary value problem for a certain semi-linear elliptic equation that depends on two parameters: α characterizing the flow rate and λ (Frank-Kamenetskii parameter) characterizing the strength of the reaction. Similarly to the classical Gelfand problem, this equation admits a solution when the Frank-Kamenetskii parameter λ does not exceed some critical value λ ⁎ (α) and admits no solutions for larger values of λ. We obtain the sharp asymptotic behavior of the critical Frank-Kamenetskii parameter in the strong flow limit (α ≫ 1). We also provide a detailed description of the extremal solution (i.e., the solution corresponding to λ ⁎) in this regime. [ABSTRACT FROM AUTHOR]

In this work, NiAl-WC composite was synthesized by a mechanical activated thermal explosion process from the powder mixture of nickel, tungsten, aluminum, and graphite. The phase, morphology, and microstructure development during milling and after the thermal explosion process were evaluated by XRD, FE-SEM, and TEM-EDS analysis techniques, respectively. The results indicated that after the thermal explosion of an as-mixed powder mixture, unreacted starting powder remained, and some new phases like Al 0.42 Ni 0.52 and W 2 C formed, which confirmed that the synthesis reactions were not completed. But, the final product of 5 h milled powder after the thermal explosion consisted of desired phases, NiAl and WC. XRD results of 5 h milled powder showed that the mechanical activation had two effects on NiAl-WC composite synthesis, reduction of crystallite and particle size, and better mixing of reactant powders and formation of W 2 C phase as an intermediate phase. These effects increased kinetics of reactions, and finally, NiAl-WC composite formed. [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]

The urgency of the discussed issue is caused by the need to find a new technology of obtaining aluminum nitride. The main aim of the study to justify the possible mechanism of aluminum nitride crystal formation under thermal explosion during combustion of aluminum nanopowder in air and to propose the phenomenology model of these processes. The methods used in the study: X-ray diffraction studying with high time resolution (synchrotron radiation), SEM-microscopy, thermodynamic calculation. The results: It was established experimentally during combustion of aluminum nanopowder in air under thermal explosion the micro size monocrystals are formed in homogeneous magnetic field and elongated nonlinear crystals with faceting are formed in inhomogeneous magnetic field. The authors have proposed the phenomenology model of aluminum nitride crystal formation under thermal explosion during aluminum nanopowder combustion. The faceting crystal formation is the result of magnetic field influence on stabilization of combustion product and their subcooling. Monocrystals grow in heat wave as a result of transition of X-ray amorphous phase in stable monocrystal condition.

The relevance. The preparation of refractory nitrides in the air under the conditions of thermal explosion of aluminum nanopowder mixtures with metal oxides presents practical interest both for materials science and for the theory of the reactivity of air at high temperatures. This synthesis is the least energy-intensive, and it does not require complicated equipment. Only the heating of the initial charge is necessary for synthesis, then the process proceeds spontaneously. The main aim of the research is to determine experimentally the composition of combustion products of aluminum nanopowder mixtures with niobium pentaoxide in the air, to substantiate theoretically the stabilization of niobium nitride Nb2N in the air. Object: powder containing niobium nitride obtained by burning a mixture of aluminum nanopowder with niobium pentoxide in the air. Methods: x-ray analysis (diffractometer Difrey-401), differential thermal analysis SDT Q600 Instrument company. On the basis of the results of the differential thermal analysis the authors have calculated four parameters of the mixtures activity: temperature of oxidation beginning (tst.ox., °C), oxidation degree (α, %), maximal oxidation speed (vmax, mg/min), specific thermal effect (ΔН, J/g). X-ray analysis was used for investigating crystal structure of oxidation ending products. Results. Combustion of mixtures of aluminum nanopowder with niobium pentaoxide in the air proceeded in two stages with formation of niobium nitride Nb2N. According to the x-ray analysis in the combustion products, the mixture of NP Al:Nb2O5=3:1 reached maximum of 47 rel. %. The calculation of the isobaric-isothermal potential showed that niobium nitride should be oxidized by air oxygen. The reason of stabilization of Nb2N crystalline phase is the air oxygen deactivation by emission of burning aluminum nanopowder.

We have studied the influence of a preload applied to a starting elemental powder mixture and the strain in the product of high-temperature synthesis during a bulk exothermic reaction on the grain structure of the Ni3Al intermetallic compound and the temperature dependence of its strength. The results demonstrate that, during the bulk exothermic reaction responsible for the formation of the intermetallic compound under pressure in a closed press die, the average grain size varies along a vertical cut, from the minimum value on the upper and lower surfaces of the synthesized sample to the maximum value in its central part. As the preload applied to the starting powder mixture is raised, the average grain size decreases, whereas the general character of the grain size distribution in a cross section of the sample remains unchanged. Deformation of the high-temperature synthesis product in a press die with partial extrusion causes an appreciable grain size reduction, significantly averaging the grain size in the bulk of the synthesized sample, and raises the tensile strength of the intermetallic compound in the temperature range 20–1000°C. [ABSTRACT FROM AUTHOR]

In situ synchrotron studies of structure and phase formation dynamics in mechanically activated (t = 7 min, power density 40 g) and mechanically activated with subsequent irradiation by γ‐quanta 60Co powder mixture (Ti 64 wt% + Al) during high‐temperature synthesis by the method of thermal explosion using induction heating are described. In situ high‐temperature synthesis was carried out on the created experimental complex adapted for synchrotron X‐ray diffraction methods. The sequence of formation and time–temperature interval of the metastable and main phases were determined. The impact of preliminary mechanical activation and of γ‐irradiation on the macrokinetic parameters of the synthesis were studied experimentally in situ. It has been established that the impact of γ‐irradiation on the mechanically activated powder mixture of the composition Ti 64 wt% + Al leads to a change in the thermal parameters of combustion: the maximum synthesis temperature and the burning rate decrease. The heating rate for the non‐irradiated mixture is 204.8 K s−1 and that for the irradiated mixture is 81.6 K s−1. The dependences of mass fractions of the synthesized compounds on time and temperature were calculated from the stage of preheating until completion of the thermal explosion. A single‐phase equilibrium product of the composition γ‐(TiAl) is formed in γ‐irradiated mechanically activated mixture when the system reaches maximum temperature. The synthesized product of the mechanically activated mixture without γ‐irradiation contains 72% γ‐(TiAl); TiAl3 (26%) and residual Ti (2%) are also observed. [ABSTRACT FROM AUTHOR]

Synthesis of metal matrix composites from powder mixtures is experimentally studied in a thermal explosion. A mathematical model for initiating a reaction that allows for the main physical and chemical phenomena changing the phase composition of a sample is formulated. It is shown that simulation results qualitatively agree with experimental data. [ABSTRACT FROM AUTHOR]

Highlights • The variational formulation of a steady heat conduction problem is considered. • Estimates of thermal explosion parameters are obtained. • Comparative analysis of thermal explosion parameters for a cylinder is given. Abstract The variational formulation of the nonlinear problem of steady heat conduction in an arbitrary configuration domain is applied to investigate the conditions for the existence of a steady-state temperature distribution in a stationary medium with the intensity of volumetric energy release rising with increasing temperature. Based on the relations of the time-independent theory of thermal explosion, a variational model of this phenomenon is constructed, which makes it possible to obtain estimates of the critical values of the parameters that determine the temperature state of the medium preceding the thermal explosion. The examples of a comparative analysis of such values for a solid and a hollow cylinder of finite length are given. [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]

High porosity Co-Al-Fe intermetallic with 3D-microstructures were one-step synthesized via a novel thermal explosion reaction. A link between pore structure and permeability was established using 3D-XRM technology. The corrosion resistance of the samples with different Fe contents was investigated at 900 °C under an oxygen/sulphur atmosphere for up to 120 h. The results showed that the pore structure of the samples remains stable, and the internal matrices are intact due to the formation of a thin protective layer of Al 2 O 3 and Fe 2 O 3 on the surface of the product skeleton. In addition, inward diffusion of S leads to the formation of FeS nodules. • Co-Al-Fe IMCs of high porosity (45.19%) was fabricated by rapid TE reaction. • 3D-XRM establish the link between the microstructure and corrosion behavior. • Acoustic emission is used to predict the variation of sample mechanical property. • The addition of Fe improved the anti-oxide/sulfidation performance of the samples. • Formation of FeS in sulfidation is beneficial to the densification of oxide film. [ABSTRACT FROM AUTHOR]

The temperature state of a solid body, in addition to the conditions of its heat exchange with the environment, can greatly depend on the heat release (or heat absorption) processes within the body volume. Among the possible causes of these processes should be noted such as a power release in the fuel elements of nuclear reactors, exothermic or endothermic chemical reactions in the solid body material, which respectively involve heat release or absorbtion, heat transfer of a part of the electric power in the current-carrying conductors (so-called Joule’s heat) or the energy radiation penetrating into the body of a semitransparent material, etc. The volume power release characterizes an intensity of these processes.The extensive list of references to the theory of heat conductivity of solids offers solutions to problems to determine a stationary (steady over time) and non-stationary temperature state of the solids (as a rule, of the canonical form), which act as the sources of volume power release. Thus, in general case, a possibility for changing power release according to the body volume and in solving the nonstationary problems also a possible dependence of this value on the time are taken into consideration.However, in real conditions the volume power release often also depends on the local temperature, and such dependence can be nonlinear. For example, with chemical reactions the intensity of heat release or absorption is in proportion to their rate, which, in turn, is sensitive to the temperature value, and a dependence on the temperature is exponential. A further factor that in such cases makes the analysis of the solid temperature state complicated, is dependence on the temperature and the thermal conductivity of this body material, especially when temperature distribution therein is significantly non-uniform. Taking into account the influence of these factors requires the mathematical modeling methods, which allow us to build an adequate nonlinear mathematical model of the heat conductivity process in the volume power release body. Quantitative analysis of these models requires using the numerical methods, as a rule.At the same time, such a simple body, which is an unlimited plate of the constant thickness allows us, under certain assumptions, to solve analatically a nonlinear heat conductivity problem taking into account the thermal conductivity of the plate material and the power release intensity versus temperature.This solution enables us to reveal a number of significant effects that have impact on the thermal state of the plate, including those related to conditions of available steady temperature distribution, and it can be used to test the results obtained by numerical methods.

The relevance of the research. The new proposed technology for obtaining refractory nitrides has several advantages: low energy consumption, no need for complex equipment, nitrogen is used to produce nitrides, synthesis is carried out at atmospheric pressure. The main aim of the research is to determine experimentally the composition of combustion products of aluminum nanopowder and tantalum pentoxide mixtures in air and in liquid nitrogen. Object: tantalum nitride synthesis product obtained by burning the aluminum nanopowder mixture with tantalum pentoxide in air. Methodsh: x-ray analysis (diffractometer Difrey-401), differential thermal analysis (DTA) (thermoanalyzer SDT Q600 Instrument company). According to the results of the DTA the authors have calculated four parameters of activity of the mixtures: oxidation onset temperature (Tst.ox, °C), oxidation level (α, %), maximal oxidation rate (vmax, mg/min), specific thermal effect (ΔН, J/g). Results. The authors determined the parameters of activity of aluminum nanopowder with tantalum pentoxide mixtures. It is revealed that along with nitride and aluminum oxide in the products a crystalline phase of metallic tantalum is formed. The maximum yield of tantalum was 54 rel. %. It was shown experimentally that at aluminum nanopowder combustion in air, aluminum recovers tantalum pentoxide, which interacts with air nitrogen to form crystalline Ta2N tantalum nitride. According to X-ray, in the combustion products of a mixture of aluminum nanopowder with tantalum pentoxide, the crystalline phases of α- and β-tantalum are found. At the same time, tantalum nitride was not detected when the sample was burned in liquid nitrogen.