Self-propagating High-temperature Synthesis Research Articles

Production of Zirconium-Niobium Alloys for Nuclear Reactors Fuel Rods via SHS Process

This article presents the results of studies of the self-propagating high-temperature synthesis (SHS) for obtaining zirconium alloys with niobium by the method of calcium-thermal reduction of nuclear-grade zirconium tetrafluoride in the presence of niobium powder. The optimal heating temperature of the initial charge and the methods of charge mixture with different calcium content were determined. The safety of the SHS process is ensured by the formation of an optimal combustion front of the mixture to remove the released high-pressure gases. A setup for the furnace reduction of zirconium alloys with charge preheating, discharge of molten products into molds of various designs, and control of the time and rate of slag and alloy crystallization has been tested. The required performance of the installation, the degree of transition of zirconium from salt into the alloy, and the purity, structure, and uniformity of the alloy were achieved.

Synthesis of low-cost Ti3AlC2-Ti2AlC dual MAX phase with high-electrical conductivity using economical raw materials and novel compositions

Titanium-aluminum-carbide (Ti3AlC2-Ti2AlC) dual MAX phases produced with mechanical alloying (MA) of raw materials followed by a self-propagating high-temperature synthesis (SHS) approach. The low-cost dual MAX phases have been manufactured from commercial powders of Ti, Al, TiC, and agricultural wastes-based activated carbon (AC). The effects of Ti/Al/C mole ratios and carbon sources with various prices on the surface morphology, microstructure, chemical structure, and electrical conductivity of dual MAX phases have been investigated. All synthesized MAX phases have acceptable surface morphology with hexagonal particles and high purity (78.87–99.26 %). The FESEM, EDS, XRD, and XPS analyses revealed that the AC and TiC are appropriate as carbon sources for the manufacture of Ti3AlC2-Ti2AlC dual and Ti3AlC2 single MAX phases, respectively. Moreover, the purity of the MAX phases can be controlled with Al/C ratios in raw materials composition. The AC-produced Ti3AlC2-Ti2AlC dual MAX phase with 3Ti:1.25Al:2 C displayed the highest electrical conductivity (5.631 ×106 S/m), while TiC-produced Ti3AlC2 single MAX phase with 3.25Ti:2.2Al:2 C composition has comparable electrical conductivity (2.203 ×106 S/m) and highest purity (99.26 %). This study makes available an advantageous method for low-cost synthesis of high-purity MAX phases. These understandings open up a pathway to improve synthesis protocols for low-cost and high-conductivity MAX phases in the future.

An overview of the synthesis of silicon carbide–boron carbide composite powders

Abstract Recently, silicon carbide–boron carbide composite ceramics have attracted more and more attention. The most important achievements of the silicon carbide–boron carbide composite ceramics should be applied in terms of mechanical, physical, and chemical for use in various advanced industries, such as armor plates, nozzles, abrasive tools, mechanical seals, etc. To prepare silicon carbide–boron carbide composite ceramics with good performance, the synthesis of silicon carbide–boron carbide composite powders is the basis. The synthesis approaches of silicon carbide–boron carbide composite powders are systematically summarized in this review, including ball milling, high-energy ball milling, self-propagating high-temperature synthesis (SHS), and sol–gel. Particularly, nanosized silicon carbide–boron carbide composite powders can be in situ synthesized by high-energy ball milling, SHS, or sol–gel. When commercial silicon carbide and/or boron carbide powders are used as raw materials to synthesize silicon carbide–boron carbide composite powders, the pretreatment of acid etching can significantly remove oxide layers existing on the surfaces of initial powders.

Combustion synthesis of ultra-high-temperature solid solutions (ZrxNb1-x)B2. Part 1: The mechanisms of combustion and structure formation

The self-propagating high-temperature synthesis (SHS) in Zr–Nb–B system has been thoroughly investigated with a focus on its macrokinetics and phase formation mechanisms. The activation energies were determined by analyzing the relationship between the combustion rate and temperature. For compositions NbB2–40%ZrB2 and NbB2–50%ZrB2, the increase in the initial temperature has resulted in a significant change in combustion rate's dependence on temperature, signifying a possible shift in the reaction mechanisms. The quenched combustion front technique (QCF) method in conjunction with thermodynamic and ab initio calculations were used to analyze the sequence of phase formation events, including the formation of niobium and zirconium borides through gas transport reactions involving volatile boron suboxide BO in the heating zone, followed by the emergence of a zirconium-boron melt in the combustion zone and formation of main fraction of niobium and zirconium borides. Interactions between the primary niobium and zirconium borides and the melt result in the formation of solid solutions; however, at sub-optimal combustion conditions multiple non-equilibrium solid solutions are retained in the products. To address this issue, a machine learning model was developed, attaining coefficients of determination (R2) of 89% for combustion temperature and rate predictions, thus enabling the fine-tuning of macrokinetic parameters of the SHS process in the system.

COLD UNIAXIAL PRESSING OF COMOSITE MATERIALS BASED ON PTFE WITH FUNCTIONAL ADDITIVES TIC AND TIB2

In the current work a solid-phase technology of composite materials based on polytetrafluoroethylene (PTFE) with functional additives is investigated. The mentioned additives are titanium carbides and diborides was obtained by self-propagating high-temperature synthesis (SHS). The process of pressing bulk density composite powders into compact blanks in a special mold by loading in a constant speed mode has been studied. Rheological strainstress curves were obtained. The time when a progressive increasing of stress inside the sample was determined. The results of these studies were compared with data for samples without additives (pure PTFE), as well as for compositions with basalt fiber. It is shown that at stresses 171-177 MPa it is possible to achieve a density corresponding to the calculated compact density of 2.24-2.25 g/cm3. The dependence of density variation over the volume of compact specimens has been studied, and a comparative analysis of the compressibility moduli G under uniaxial cold pressing has been carried out.

Coatings Prepared by Electro-Spark Alloying with SHS Electrode Materials Based on Ti-B-Fe-AlN

In this work, the features of the phase composition, structures, and properties of coatings obtained on a high-speed steel substrate (steel R6M5) were studied. The coatings were prepared using the ESA method (electro-spark alloying). Electrode materials prepared through self-propagating high-temperature synthesis (SHS) based on (Ti-B-Fe)xAlN with the addition of nanosized AlN particles in the amount of x = 0.5, 10, 15 wt % were used as electrodes. The structure, phase composition, and physical and mechanical properties of the SHS electrode materials are reported. It was found that the coatings inherited the structure of the SHS electrode material and formed two characteristic zones for x = 0 and three zones for x = 5, 10, 15. The surface hardness of the substrate made of the high-speed steel R6M5 with the developed coatings was found to increase up to five times compared to the uncoated substrate. It was found that the wear resistance of the samples with the coating was four to six times higher than that of uncoated samples.

Microstructure and tribocorrosion behaviors of Fe–Al–Ti coatings prepared by the aluminothermic reaction

To improve the tribocorrosion resistance of 316L stainless steel in acidic media, Fe–Al–Ti coatings were prepared on 316L substrate by self-propagating high-temperature synthesis (SHS) using an aluminothermic reaction. The effects of Ti content on the tribocorrosion behaviors of Fe–Al–Ti coatings in 0.5 mol/L H2SO4 solutions were investigated. The Fe–Al–Ti coatings exhibited a multi-phase microstructure. The open circuit potential (OCP) of the Fe–Al–Ti coatings and 316L substrate decreased significantly with the onset of sliding, indicating a strong wear-corrosion synergistic effect. The hardness and tribocorrosion resistance of Fe–Al–Ti coatings increase with increasing the Ti content. The tribocorrosion volume loss of the Fe–25Al–25Ti coating was about one order of magnitude lower than that of the 316L substrate. The Fe–25Al–25Ti coating was more suitable as a tribocorrosion-resistant material than the 316L substrate.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВИДА ФЛЮСА НА СИНТЕЗ ЛИТОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА АМг2-TiC

The results are presented devoted to the study of the influence of flux type on the process of self-propagating high-temperature synthesis (SHS) of titanium carbide in aluminum flux, as well as on the structure and properties of the resulting composite material AMg2-TiC. During the research, the most promising halide salts for use as fluxes were analyzed and selected: Na3AlF6, Na2TiF6, K2TiF6, K1-3AlF4-6 (Nocolok ™ made in Germany). During the experimental synthesis, the most active signs of an exothermic reaction between titanium and carbon powders in the flux were recorded having a flux additive Na2TiF6. Then microstructural, micro X-ray spectral analysis and quantitative X-ray phase analyses were carried out, according to their results it was found out that the most homogeneous distribution in terms of material volume, the maximum content of a high dispersion of carbide phase close to the stoichiometric composition is also observed in samples obtained with the use of Na2TiF6 salt. The synthesized samples of the composite material were assessed according to physical and mechanical characteristics: hardness, porosity and electrical conductivity. It was found out that composite samples with an optimal structure are also characterized by a decrease in porosity by 1.33%, an increase in hardness by 94 MPa and a reduction of electrical conductivity by 0.3 MSm/m compared with samples obtained using other fluxes. According to the results of the studies carried out, Na2TiF6 flux is recommended for use to implement SHS composite AMg2-TiC material.

Structure of Nb-Si-C-based composite obtained by self-propagating high-temperature synthesis

Alumothermic self-propagating high-temperature synthesis was used for obtaining 2Nb-1Si-1C composite material. The morphology, structure and phase composition of the composite were studied by X-ray diffraction and scanning electron microscopy. It was found that γ- Nb5Si3, NbC, NbSi2 phases were formed in the sample.

Preparation, luminescence, and application of LiMeBO3 borates, Me = Mg, Ca, Sr, Ba, Zn, Cd. Review

The review summarises and analyses data on the preparation, structure, and spectral-luminescent properties of LiMeBO3-based borates, Me = bivalent metal. These polycrystalline borates are prepared traditionally by solid-phase reactions and self-propagating high-temperature synthesis and its modifications based on a combustion reaction. Frameworks of lithium borates with alkaline earth metals, zinc, and cadmium are formed from large metal polyhedra between which there are boron-oxygen triangles isolated from each other. Doping with rare-earth and heavy metal ions leads to the formation of solid solutions which normally have defective structures. Doped activator ions often become the main part of the luminescence centre in the phosphor. The luminescent properties of ions of rare-earth elements arise from the possibility of electronic transitions between states within the 4f-configuration. The paper discusses the most likely mechanisms of charge compensation during heterovalent substitution in LiMeBO3 borates (co-doping and formationof cation vacancies). It is shown that charge compensation during the combined introduction of ions of REEs and alkali metals into the structure has a positive effect on the emission yield. The review considers the results of thermoluminescent, upconversion, and photoluminescent properties and processes and phenomena that cause them. It also explains the mechanism of resonance energy transfer from the sensitiser to the activator using the example of Yb3+→Er3+. It discusses the possibility of using the considered borates as phosphors that emit green, blue, and red light in white LEDs and as effective materials for personnel neutron dosimetry and the dosimetry of weak ionising radiation

Study on electrothermal ignition model of self-propagation high-temperature synthesis system for samarium vaporization

The quality of short-wave radio communication in the ionosphere depends largely on the state of the ionosphere, but it is uncontrollable and unreliable. The release of gaseous samarium into the ionospheric space can form high-density plasma clouds, which is of great significance for improving the quality of shortwave radio communication. The high temperature and high heat released by the self-propagation high-temperature synthesis reaction can effectively heat and vaporize the samarium. At the same time, this method can effectively avoid the adverse impact of the reaction of individual components of the reaction material on the ionization efficiency of samarium, and greatly improve the ionization efficiency of the samarium. Therefore, self-propagation high-temperature synthesis is an important method for heating and vaporizing samarium. To study the ignition model of self-propagation high-temperature synthesis system for heating and vaporizing samarium, and to design and control the ignition process is the premise for heating and vaporizing samarium. Based on the theory of chemical reaction and heat conduction, the electrothermal ignition process is studied in detail. By analyzing the change of energy distribution in the ignition process, a theoretical model of ignition under the electric energy heating mode is proposed, and a theoretical equation for calculating the ignition time is derived. The model can be used to design and control the ignition system and explain many phenomena in the ignition process. In addition, the electrothermal ignition test was carried out for heating and vaporizing samarium in the self-propagation high-temperature synthesis system to obtain the ignition power and ignition time of different reaction systems under different samarium content and porosity, and further analyze the universality of the calculation model. The results show that the test results are in good agreement with the theoretical calculation results, and the validity of the model is verified, which provides an important support for the design of self-propagation high-temperature synthesis reaction heating and vaporizing samarium ignition system.

Structure and Phase Formation in the Ni–Al–Co System during Self-Propagating High-Temperature Synthesis

Structure and Phase Formation in the Ni–Al–Co System during Self-Propagating High-Temperature Synthesis

Investigation of the processing effect parameters on the spectroscopic properties of ZnSe nanocrys-tals for hot-pressed ceramics of the Cleartran and Multispectral classes

Problem. The problem is unavailability of inexpensive ZnSe nanocrystals for hot-pressed ceramics of the Cleartran or Multispectral classes. Goal. The goal is to investigate and improve the structural features of ZnSe nanocrystals obtained by combustion synthesis during annealing in air or nitrogen. Methodology. ZnSe nanocrystals were characterized by combustion synthesis using electron scanning microscopy, X-ray diffraction analysis, electron paramagnetic resonance, and photoluminescence analysis. Results. To improve the spectroscopic properties of ZnSe nanocrystals were synthesized by combustion synthesis method (self-propagating high-temperature synthesis) with different initial current pulses, a series of thermal annealing was carried out in the temperature range Т = 200 ÷ 800 °С with a step of Т = 100 °С at atmospheric pressure, in air or in nitrogen. The developed approach makes it possible to obtain the investigated ZnSe nanocrystals with specified properties by controlling their crystal structure. The dependences of the structure, characteristics of the magnetic field, and hyperfine structure of electron paramagnetic resonance, photoluminescence spectra during annealing in air or nitrogen from temperatures of annealing were obtained. In comparison with the initial charge, the size of nanocrystals grows by ~ 20 %, the fraction of the cubic phase increases, the parameters of nanocrystals lattice grows, and the number of dislocations and microstress decrease after annealing. It is recommended to use a current pulse of ~ 40 A, and then perform annealing at a temperature of T = 800 °C in nitrogen for the synthesis of ZnSe nanocrystals with a more perfect structure. Originality. The annealing of ZnSe nanocrystals obtained by combustion synthesis in air or nitrogen was studied. Practical value. The obtained results allow using the synthesized ZnSe nanocrystals by combustion synthesis method for various optoelectronic devices or for obtaining hot-pressed ceramics of the Cleartran or Multispectral classes.

Acetone Processing on Nickel-chromium Catalysts Produced by Self-propagating High-temperature Synthesis

The processing acetone wastes method into isopropyl alcohol (ISA) by liquid-phase hydrogenation on the new catalyst obtained by the selfpropagating high-temperature synthesis (SHS) was studied. The optimal compositions of SHS for producing nickel-chromium catalysts were identified. The comparative analysis of the activity of the SHS catalyst was carried out in comparison with the traditional one obtained as a result of coprecipitation. The surface area morphology of the obtained samples was measured. The surface morphology was studied, including the calculation of the mesopores distribution. It was found that the proposed catalyst was reduced at a higher temperature than the previously proposed one. The stability of particles to sintering was confirmed.

Ba-doped LaCoO3 perovskite as novel bifunctional electrocatalyst for zinc–air batteries

Developing efficient non-noble metal bifunctional cathode catalysts to accelerate the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a major challenge for zinc–air batteries (ZABs). In the present study, a series of La1−xBaxCoO3 (x = 0, 0.05, 0.10, 0.15, 0.20) perovskite-type oxides were prepared via self-propagating high-temperature synthesis and evaluated as the bifunctional electrocatalytic activity for ZABs. Among the samples, La0.85Ba0.15CoO3 showed the best bifunctional catalytic activity, in which the Eonset of ORR at 0.1 mA cm−2 and the Ej of OER at 10 mA cm−2 in 0.1 M KOH solution were 0.829 and 1.685 V vs.RHE, respectively. Besides, the La0.85Ba0.15CoO3 catalyst was evaluated as an air electrode for ZABs, displaying a high power density of 116.2 mW cm−2 at the current density of 233.8 mA cm−2 and a stable charge–discharge voltage gap of 0.98 V after 1200 cycles, with superior cycling stability over 200 h. Characterization analysis revealed that the enhancement of bifunctional electrocatalytic activity was attributed to the larger specific surface area and increase in oxygen vacancy. Thus, the Ba-doped LaCoO3 material is a promising bifunctional electrocatalyst for ZABs.

Synthesis, characterization, and applications of lanthanide ortho ferrites

In our current study, we demonstrate that lanthanum and yttrium ortho ferrites can be synthesized using a combustion process called self-propagating, high-temperature synthesis (SHS) using lanthanum(III) oxide and yttrium(III)oxide, chromium oxide, Iron metal, and potassium perchlorate as raw materials. Synthesized lanthanide and yttrium orthoferrites were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and thermogravimetric differential scanning calorimetry techniques. The results show that the synthesized orthoferrites are of high quality with particle sizes less than 100 nm and showing less agglomeration. Synthesized lanthanum and yttrium orthoferrites exhibited electrical conductivities around 50 kHz for different temperatures ranging from 35 to 500°C. The rise in conductivity is found to be linear with an increase in temperature. Herein, our work paves way for low-cost, large-scale production of lanthanide orthoferrites without the need for reaction solvents, which greatly opens up the scope for combustion-based synthesis approaches.

STUDY OF THE POSSIBILITY OF PROCESSING FERROVANADIUM SCREENINGS IN COMBUSTION MODE

The possibility of recycling dispersed ferroalloys using the method of self-propagating high-temperature synthesis (SHS) is demonstrated using the example of the synthesis of composite ferrovanadium nitride in the processing of ferrovanadium screenings grades FeV50 and FeV80. It has been established that in order to obtain the maximum nitrogen content in the synthesis products, it is necessary to use unshaped samples with a charge porosity of more than 50%, and the nitriding process should be carried out at a reacting gas pressure of 6-8 MPa.

Synthesis of non-stoichiometric carbides and carbohydrides of Ti and Ti-Nb using self-propagating high-temperature synthesis technique

Non-stoichiometric monocarbides are of great interest because they can be used as additives at production of hard alloys. Interestingly, the non-stoichiometric carbides of IV group metals provided with a wide range of homogeneity interact with hydrogen and form ternary compounds, carbohydrides. These compounds attract the researches as the bases for creating new hydrogen containing materials resistant at temperatures above those for known binary hydrides of transition metals. They are promising as materials for biological protection in nuclear energy. In the present work the single-phase non-stoichiometric face-centered cubic (FCC) carbides and hexagonal close packed (HCP) and FCC carbohydrides based on Ti and Ti-Nb were synthesized using Self-propagating High-temperature Synthesis (SHS) method. These syntheses were implemented in one technological stage. The high hydrogen content in the synthesized non-stoichiometric carbohydrides promoted their dispersion down to particle sizes of < 5 µm and even smaller, to the nanoscale crystallite sizes of < 50 nm. The mechanism of formation of non-stoichiometric carbides and carbohydrides in SHS was discussed. Significant advantages of a highly efficient non-energy-intensive SHS method for the synthesis of non-stoichiometric titanium and titanium-niobium carbides and carbohydrides can be of commercial and industry interest.

Influence of laser spot size on structure and properties of high-temperature CompoNIAL-M5-3 alloy produced by selective laser melting

The CompoNiAl-M5-3 high-temperature alloy based on nickel monoaluminide was obtained by selective laser melting (SLM) of a spheroidized powder with particle size in the range of 20 – 45 μm. The powder was manufactured using an integral technology including self-propagating high-temperature synthesis (SHS), briquette grinding, sieve and air classification followed with spheroidization of powder particles in a thermal plasma flow and ultrasonic purification of spheroidized particles from nanofraction. Using parametric studies, the SLM modes were tested on SLM 280H and TruPrint 1000 machines. Mechanical tests of the samples were carried out using the uniaxial compression scheme with the strain rate dε/dt = 10–4 s–1 in the temperature range 1023 – 1273 K. Scanning and transmission electron microscopy methods were used to study the influence of laser spot size on the evolution of microstructure and thermomechanical properties of the SLM-consolidated material in comparison with that obtained by hot isostatic pressing (HIP). The authors established the effect of HIP + HT (aging in vacuum) post-treatment on the structure and mechanical properties of the material. The yield strength at 1073 K of the alloy built on the additive machine with a laser spot diameter of 38 μm after SLM + HIP + HT was 500 MPa, which exceeded the yield strength of the HIP-samples by 220 MPa.

Thermophysical properties of a Cu–Ti–C–B SHS composite

The paper studies the thermophysical properties of a Cu-Ti-C-B composite produced by self-propagating high-temperature synthesis (SHS) of an initial mixture of copper, titanium, boron carbide (B4C), and carbon powders. The matrix of the composite is a supersaturated solid solution of titanium in a copper lattice with Cu4Ti nanosized particles homogeneously precipitated under cooling. The matrix microhardness is 450 HV 0.1. Particles of titanium carbide (TiC) and titanium diboride (TiB2) resulting from SHS are randomly distributed in the bulk of the composite. The microhardness of the regions with the predominance of TiC particles is 640 HV 0.1, and the microhardness of the regions with the predominance of TiB2 particles is 900 HV 0.1. The average hardness of the composite is 60 HRC. Differential scanning calorimetry demonstrates a unified wide exothermic effect at temperatures ranging from 750 to 1000 °С, with an enthalpy of 148.6 J/g, associated with the exothermic reaction between residual titanium and boron carbide (B4C), which did not react during SHS. The temperature dependences of density, thermal diffusivity, heat capacity, thermal conductivity, and the coefficient of linear thermal expansion are experimentally determined. The particles of the strengthening phases are found to reduce slightly the thermal properties of the composite compared to pure copper. It is shown that annealing at temperatures of 800 and 860°C decreases the level of residual stresses in the composite matrix.