This article reports investigation of the effects of high-rate stochastic micro-mechanics on the produced particulate size distribution during ball milling of reactive bimetallic foils (nanoheaters), by experimental and computational modeling. In particular, Ni-Al foils are ball-milled at various load charges, revolution rates and process durations, and the resulting particulate geometries are characterized by micrograph statistical analysis. Numerical simulation of the evolving particulate structure is based on coalescence and fragmentation of flexible monometallic ellipsoidal primitives, impacted by milling balls and vial walls with kinetic theory-based kinematics. Particulates are constrained by discrete compliant and continuum media and undergo conceptual ideal elastic transformations modeled by strain energy methods, and recast into inelastic frictional and plasticity-driven welding and fracture events. Finally the theoretical model predictions of particulate size distribution are validated against laboratory microscopy observations.

Highly refractory composites with predominant volume fraction of TiB2, were “in situ” synthesized and consolidated. The production process was carried out using elemental powders by means of self-propagating high-temperature synthesis under pseudo-hot isostatic pressure (SHS-pseudo-HIP). The Ti:B atomic ratio corresponded to TiB2 formation, and Cr:C atomic ratio has been established in (3:2) molar ratio.

Based on scanning electron images (SEI), very high relative density was obtained with nearly full densification in composite with intended 85vol.% of TiB2, which is sufficiently high concentration of boron from the perspective of neutron shielding. However XRD results indicated formation of CrB and TiC, next to TiB2. This clearly indicates no equilibrium in pseudo-binary TiB2-Cr3C2 system. Besides, broadened peaks in XRD patterns as well as gradient of composition in EDS maps may indicate solid solutions, especially (Ti,Cr)C. The existence of (Ti,Cr) solid solutions and ternary compounds is possible, considering Hume-Rothery rules for hypothetical mutual solubility.

Molybdenum silicides and borosilicides are promising structural materials for advanced power plants. A major challenge, however, is to simultaneously achieve high oxidation resistance and acceptable mechanical properties at high temperatures. For example, molybdenum disilicide (MoSi2) has excellent oxidation resistance and poor mechanical properties, while Mo-rich silicides such as Mo5Si3 (called T1) have much better mechanical properties but poor oxidation resistance. One approach is based on the fabrication of MoSi2−T1 composites that combine high oxidation resistance of MoSi2 and good mechanical properties of T1. Another approach involves the addition of boron to Mo-rich silicides for improving their oxidation resistance through the formation of a borosilicate surface layer. In particular, Mo5SiB2 (called T2) phase and alloys based on this phase are promising materials.

In the present paper, MoSi2−T1 composites and materials based on T2 phase are obtained by mechanically activated self-propagating high-temperature synthesis (MASHS). To obtain denser products, the so-called SHS compaction (quasi-isostatic pressing of hot combustion products) has been employed. Thermal analysis has shown that SHS compaction significantly improves the oxidation resistance. Self-sustained combustion of Mo/Si/B mixtures for the formation of T2 phase becomes possible if the composition is designed for adding a more exothermic reaction of MoB formation. These mixtures exhibit spin combustion. Oxidation resistance of the obtained multi-phase Mo−Si−B materials is independent on the concentration of Mo phase in the products. The “chemical oven” technique has been used to obtain a single Mo5SiB2 phase and an alloy consisting of α-Mo, Mo5SiB2, and Mo3Si phases.

Copper–zinc alloy (Cu/Zn) powders with different Zn to Cu molar ratios were prepared by the combustion synthesis technique using a CuO + 0.15(C2H4)n + kZn (0.2 ≤ k ≤ 1.6 mol) reactive mixture. Depending on the Zn concentration, the combustion wave developed a temperature between 950 and 1040 °C and passed through the sample with a speed of 0.04–0.08 cm/s, resulting in almost single-stage temperature distributions. Cu/Zn alloy powders with Zn concentrations ranging from 0.5 to 45 wt% were obtained. It was shown that alloy particles become spherical and well dispersed with increasing Zn concentration. Inert dilution test with KCl salt was also performed to determine the influence of temperature degradation in the combustion wave on the morphology and composition of alloy powders.

The effects of surrounding gaseous environment on the reaction behaviors and product formation for sputter-deposited Ti/2B reactive multilayers are reported. With the surrounding environment set to different air pressures, from atmospheric conditions to 10-4 Torr, Ti/2B samples were reacted in a self-propagating mode, and the average reaction wave velocities were determined through high-speed imaging. Propagation speeds for 3.0 μm-thick multilayers were in the range of 10.89 to 0.05 m/s depending on bilayer thickness (i.e., reactant layer periodicity) and ambient pressure. X-ray diffraction analysis showed that single-phase TiB2 forms within multilayers that have small bilayer thickness. Multilayers that have a large bilayer thickness developed a mixture of TiB2, TiB and TiO2.

Several binary intermetallic compounds—each containing a rare-earth (RE) element paired with a transition metal (TM)—were prepared by self-propagating, high-temperature synthesis (SHS). Thin multilayers, composed of alternating Sc or Y (RE element) and Ag, Cu, or Au (TM), were first deposited by direct current magnetron sputtering. Once the initially distinct layers were stimulated and caused to mix, exothermic reactions propagated to completion. X-ray diffraction revealed that Sc/Au, Sc/Cu, Y/Au, and Y/Cu multilayers react in vacuum to form single-phase, cubic B2 structures. Multilayers containing Ag and a RE metal formed cubic B2 (RE)Ag and a minority (RE)Ag2 phase. The influence of an oxygen-containing environment on the reaction dynamics and the formation of phase were investigated, providing evidence for the participation of secondary combustion reactions during metal-metal SHS. High-speed photography demonstrated reaction propagation speeds that ranged from 0.1–40.0 m/s (dependent on material system and foil design). Both steady and spin-like reaction modes were observed.

Monodispersed nickel oxide nanoparticles have been synthesized using solution combustion synthesis method. Size of the nanoparticles was controlled by varying different reaction parameters such as reaction temperature and reaction time. Structure and morphology of the nanoparticles were investigated using X-ray diffraction and transmission electron microscopy. BET surface area of 99.7 m2/g was obtained for the nanoparticles synthesized at 300 °C. A decrease in surface area was observed with increase in reaction temperature. The nanoparticles were compacted using spark plasma sintering technique at 950 °C and thermal conductivity was studied on compacted sample. Significant decrease in thermal conductivity was observed for nanoparticles in compared to their bulk counter-part.

Thermoelectric calcium cobalt oxide (Ca1.24Co1.62O3.86) with high Seebeck coefficient was prepared by self-propagating high temperature synthesis (SHS) followed by a short post treatment process. Synthesized samples were analyzed by XRD for their phase purity for samples prepared from different reactants mixtures. A final element model of SHS of calcium cobalt oxide was developed to study the temperature history and reaction rate change during the synthesis. This model can be used to predict reaction temperatures for various initial conditions.

The ignition and reaction mechanisms of the thermal explosion reaction in the Ni-Ti-C system under air and Ar conditions were investigated. The reaction for the formation of TiC can be initiated at a low temperature under air. The ignition temperature under air is much lower than that under Ar. Under Ar, both the ignition and reaction mechanisms consist of dissolution, reaction, and precipitation. Under air, the ignition mechanism is confirmed to be the chemical oven mechanism, and the reaction mechanism is dissolution, reaction, and precipitation. The mechanism of gas transport plays a much more minor role in the ignition and reaction processes under air.

The ignition and reaction processes of the thermal explosion reaction from the Ti–B4C system in air were studied. The thermal explosion reaction for the formation of TiC and TiB2 can be initiated at a relatively low temperature with the incorporation of air. Generally, the ignition process in air is suggested to be a chemical oven rather than gas transport, and the reaction process is proposed to be dissolution and precipitation.

In this study, the dense polycrystalline Ti2AlC was synthesized by self-propagating high-temperature combustion synthesis with the pseudo–hot isostatic pressing process (SHS/PHIP). The resultant phase purity is highly dependent on the mol ratio of raw powders. The Ti2AlC was densified by applying pressure after the SHS reaction. The resultant sample mainly contains typical plate-like nonstoichiometric Ti2AlCx (x = 0.69) with grain size of ∼6 µm. The sample shows the Vickers hardness of 5.5 GPa, highest flexural strength of 431 MPa, compressive strength of 1033 MPa, and fracture toughness of 6.5 MPa·m1/2. No indentation cracks in Ti2AlCx were observed, indicative of a damage material nature. The reaction mechanism for the formation of SHS/PHIP-derived Ti2AlC is also discussed based on differential thermal analysis and x-ray diffraction results.

Effects of Fe incorporation into Al–Ti–B4C reactants on the combustion behaviors, reaction mechanism, synthesized products, and possible natural convection of fluids were investigated. The incorporation of Fe significantly promotes the self-propagating reaction and decreases the reaction dependence on the B4C particle size. The prior reaction of Fe with B4C leads to the decomposition of B4C and formation of Fe2B and free carbon. On the other hand, the reaction of Fe with Ti and Al gives rise to the emergence of Fe–Ti and Fe–Ti–Al eutectic liquids. As a result, the diffusivity and reactivity of the dissociated carbon and boron atoms are greatly facilitated and the reaction is substantially promoted, yielding a desirable product of TiC, TiB2, and FeAl phases. Moreover, the incorporation of Fe may enhance free convection of the molten phase in the reaction zone and thus contribute to the combustion synthesis process.

This investigation analyzed the effect of reactant particle size on the stress development characteristics of NiAl synthesized through self-propagating high temperature synthesis. Four sample combinations of NiAl were synthesized based on initial particle diameters of the reactants: (i) 10 μm Al and 10 μm Ni (S1), (ii) 10 μm Al and 100 nm Ni (S2), (iii) 50 nm Al and 10 μm Ni (S3), and (iv) 50 nm Al and 100 nm Ni (S4). Characterization of NiAl was performed by parallel comparison of the distribution of residual stresses of the samples prior to and after the reaction. Residual stresses were quantified using x-ray diffraction. Upon characterization it was found that combinations S1, S2, and S3 exhibited tensile residual stresses, while combination S4 exhibited compressive residual stresses. Statistical analysis confirmed that self-propagating high temperature synthesis products derived from nanoparticle reactant sizes exhibited compressive residual stresses offering improved fatigue resistance in composite production.

The aim of the present work is to understand the effect of different parameters such as the molar ratio of metallic ions to fuel in sol-gel solution, pH of the solution, and calcining temperature on the efficiency of the combustion synthesis technique in preparing submicron lanthanum nickel ferrite using metal nitrate-citrate/glycine mixtures. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) was used to evaluate the powder morphology and elemental composition. The crystal structure of the calcined powders was evaluated by X-ray diffraction (XRD) and the thermal characteristics of the LNF precursors were examined by thermo-gravimetric analysis (TGA) in air, to identify suitable processing conditions. It was found that by increasing the molar ratio of fuel to metallic ions in the precursor solution, calcining could take place at lower temperatures. However, by increasing the molar ratio of fuel to metallic ions, the yield of the combustion process was decreased. Furthermore, the pH value of the precursor solution did not have any influence on the process efficiency over the range examined.

A combustion synthesis method for the synthesis of α-Si3N4 from a reactant compact composed of Si, NaN3, and NH4X and wrapped up with an igniting agent was investigated. Wrapping the reactant compact with the igniting agent (i.e., a mixture of Ti and C powders) was found necessary for the synthesis of Si3N4. In addition to NH4Cl, which was considered previously to function as a catalytic agent, other ammonium halides (i.e., NH4F, NH4Br, and NH4I) were found to be capable of catalyzing the synthesis reaction with NH4Cl being the most effective. Si3N4 could not be produced when NaN3 was replaced by C3H6N6. NaN3 was thus considered to exert an essential effect on the combustion synthesis reaction other than functioning as a solid-state nitrogen source as considered previously. It was proposed that Na vapor produced by decomposition of NaN3 reduces SiXx (formed by reaction of Si and NH4X), promoting the nitridation reaction to form Si3N4. NaN3 thus plays a role as a reducing agent in the synthesis reaction.

The synthesis of ultrafine tungsten carbide (WC) powder has been investigated from a WO3 + Mg + C mixture via combustion technique. The values of combustion parameters were estimated over the Mg concentration range 3 to 16 mol. Fast increasing tendency of the WC/W2C phase ratio from Mg concentration has been found in the final products. Phase pure WC was prepared with more than 10 mol Mg, and a small amount of ammonium carbonate (or urea) was blended with the WO3+ C mixture. The effects of the combustion conditions on product morphology and composition were evaluated using scanning electron microscopy and x-ray diffraction analysis. The results of the investigation indicate that carbon-containing compounds significantly enhance the combustion synthesis process; leading to higher conversion efficiencies and phase pure WC formation at 1500–1550 °C. The crystalline particles of WC showed a narrow distribution in particle size, with a mean diameter around 200 nm. The results are discussed in the context of gas-phase and solid-phase transport models.

The SHS reaction in the Ni–Ti–B4C system starts with the formation of Ni–Ti and Ni–B intermetallic compounds from the solid interacted reaction among the reactants and, subsequently, the formation of Ni–Ti and Ni–B liquid at the eutectic point. Meanwhile, some C atoms from the reaction between Ni and B4C can dissolve into Ni–Ti liquid to form TiC. The heat generated from these reactions can promote the mutual diffusion of Ni–Ti–C and Ni–B liquid and simultaneously accelerate the formation of Ni–Ti–C–B liquid. Finally the precipitation of TiC and TiB2 occur when the C and B atoms in the liquid become supersaturated. The addition of Ni not only promotes the occurrence of the self-propagating high temperature synthesis (SHS) reaction by forming Ni–Ti liquid, but also accelerates the SHS reaction by forming Ni–B liquid and dissociative C. The early appearance of dissociative C from the reaction between Ni and B4C causes the formation of TiC prior to that of TiB2.

The effects of TiO2 addition on the reaction behavior, product, and mechanism in the Ti–B4C system were investigated in this study. The reaction could be self-sustaining for the TiO2 addition no more than ∼33% of the total weight of the reactants. With an increase in the TiO2 addition, the combustion temperature and wave velocity decrease progressively, the ignition delay time first decreases and then increases, while the constituents of the reaction products do not vary significantly unless the relative addition content of TiO2 exceeds ∼22 wt%. Therefore, TiO2 could be used as a favorable reaction regulator for the Ti–B4C system. The reaction mechanism, as determined by differential thermal analysis and combustion front quenching experiment in combination with subsequent x-ray diffraction examination, is changed more or less by the addition of TiO2 with the extent depending on the addition amount.

The influence of different raw material mixtures on β-sialon (Si6−zAlzOzN8−z, 1 ⩽ z ⩽ 4) formation through mechanical activation coupled combustion synthesis (MA-CS) was investigated in low nitriding atmosphere of 1 MPa without diluent inclusions. The MA-CS performed for the first time on sialon raw materials with milling time of 18 min obtained sialons more than three times as pure as those obtained by CS of mixtures ball milled to 1 h (z = 3). The starting materials containing silicon, aluminum, and alumina (z = 4) after MA-CS had an increment of sialon amounts up to 88 mass%.

TiCx–Al2O3 composites have been synthesized by pressure-assisted combustion synthesis of (Ti + C + Al2O3) reactant powder. Different alumina contents (10–40 vol%) have been investigated to study the dilution effect on TiC microstructure. A mechanical method and a mixed chemical/mechanical method have been used to obtain (Ti + C + Al2O3) powder mixtures with different alumina distributions. Scanning electron microscopy (SEM) observations of these mixtures show that alumina is distributed inside micrometric (Ti + C) aggregates for the first method whereas alumina is located around (Ti + C) aggregates for the second one. X-ray diffraction (XRD) and SEM analyses of the composites indicate that TiCx is substoichiometric in carbon and mainly consists of submicrometric grains. A distribution of Al2O3 inside (Ti + C) aggregates is more efficient to reduce TiC grain size. For the 40 vol% Al2O3 diluted (Ti + C) mixture prepared from the mechanical route, TiCx nanocrystallites have been successfully stabilized, which demonstrates that the addition of Al2O3 diluent in a (Ti + C) mixture can be efficiently used to inhibit grain growth.