Self-propagating High-temperature Synthesis Method Research Articles

Characteristics of phase formation during combustion of the MgO-Al2O3-Mg(NO3)2·6H2O-Al-B system

The research revealed the carbon micro traces in the synthesis products of magnesium aluminate spinel produced by the method of self-propagating high-temperature synthesis (SHS) in the MgO-Al2O3-Mg(NO3)2·6H2O-Al system with boron additives. The phase composition, structure, and morphological features of the surface of the samples were examined. The gases evolving during combustion were analyzed. IR spectroscopic analysis showed that carbon has a diamond-like lattice similar to the lattice of detonation nanodiamonds. It was shown that low-energy nuclear reactions (boron-proton reaction) proceed in the combustion wave during high-speed SHS processes under certain conditions. Based on the experimental data, the most probable mechanisms of carbon formation in the synthesized products were formulated and proposed.

Исследование порошка титана, полученного методом СВС-гидрирования и дегидрирования в вакуумной печи

The method of SHS (self-propagating high-temperature synthesis) allows the efficient synthesis of titanium hydride. The article presents new results of experimental studies of titanium powders synthesized by the method of SHS hydrogenation and dehydrogenation in a vacuum furnace. Changes in the microstructure, phase and chemical composition during hydrogenation-dehydrogenation of a titanium sponge were studied. The titanium sponge was hydrogenated in a high-pressure SHS reactor at a hydrogen pressure of 3 MPa. The content of oxygen and carbon impurities decrease in the process of SHS hydrogenation was found. After hydrogenation, the sponge is a single-phase δ-hydride of titanium with a tetragonal lattice, the particles have a fragmentary shape. In the obtained titanium hydride, an increased hydrogen content of 4.64 wt. % was noted. The hydrogenated titanium sponge was mechanically crushed in a drum-ball mill to a particle size of 40 – 250 microns. Dehydrogenation of titanium hydride powder was carried out in a vacuum furnace at a temperature of 850 °C for 220 minutes. Titanium after dehydrogenation is a single-phase α-titanium powder with a hexagonal close packed lattice, the size and shape of the particles have not changed. The technological process under study provides the possibility of obtaining high-quality titanium powders of the necessary granulometric composition for various fields of powder metallurgy.

PREPARATION AND PROPERTIES OF NITRIDE-CONTAINING COMPOSITES DURING COMBUSTION OF THE «SILICON – ZIRCON» MIXTURE IN NITROGEN

Nitriding of silicon with the addition of zircon (10-70%) was performed by the self-propagating high-temperature synthesis (SHS) method. The nitriding potential and the combustion rate were studied versus the mixture composition, nitrogen pressure, and the sample diameter. The maximum nitriding potential is achieved with the addition of 40 – 50% zircon to the starting mixture. Nitriding of the «silicon – zircon» mixture by the SHS method occurs in the autoscillatory mode. The macrostructure of the burned samples was shown to be heterogeneous. Combustion was impossible for the «50% silicon – 50% zircon» mixture with a sample diameter less than 30 mm and a nitrogen pressure less than 1.5 MPa. Varying the synthesis parameters (nitrogen pressure 1.5-6 MPa, sample diameter 30-60 mm), the phase composition of the synthesized products consists of α,β-Si3N4, ZrO2, Si2N2O and ZrSi2. The high-temperature interaction of the «40% silicon – 60% zircon» mixture with gaseous nitrogen was studied using the complex DSC-TG- analysis. It was found that zircon does not undergo physical and chemical transformations involving a weight change under controlled heating conditions in the range of 20 – 1500 °С. Silicon in the «silicon – zircon – nitrogen» system exhibits the properties of both a nitride-forming agent (Si3N4, Si2N2O phases are identified in the synthesized products), and a reducing agent ZrO2 with the formation of ZrSi2. The mechanism of chemical transformations during SHS nitriding of silicon with zircon is presented. The properties of the nitride-containing composites were investigated depending on the zircon content in the mixture.

Effect of Mg Content on Synthesis of TiC Powder from Leucoxene by Self-Propagating High-Temperature Synthesis Method

Titanium carbide (TiC) composite powder was synthesized via the self-propagating high-temperature synthesis (SHS) method using leucoxene as a source of titanium oxide (TiO2) and magnesium (Mg) as an initiator. The effect of Mg content on synthesized TiC composite powder was characterized in terms of chemical composition and morphology by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Results showed that adding 1.5 moles Mg into the reactant system leached with 0.1 M hydrochloric acid solution was the optimal condition, and TiC was apparent in the XRD analysis at a particle size of less than 150 μm.

Using infiltration and self-propagating high-temperature synthesis processes for manufacturing cermets. Review

Cermets are ceramic-metal composite materials (composites) with a relatively high content of ceramic phases from 15 to 85 % by volume. In the 20th century cermets were considered mainly as composites of high-temperature carbide, oxide, nitride, boride and silicide ceramic phases with metallic phases of the iron group, but in the 21st century the concept of cermets has significantly expanded due to the appearance of composites made of ceramic and metal phases with lower melting points including sulfides and MAX phases, as well as light and low-melting metals (Al, Mg, Cu, Ag, Pb, Sn). Therefore, cermets began to be considered not only as tool, heat-resistant and wear-resistant heavy structural materials, but also as light, strong structural materials for the production of vehicles, and as functional materials for various purposes. However, quite often cermets are characterized by such disadvantages as a tendency to brittle destruction, the difficulty in achieving structural uniformity and reproducibility, as well as fault detection, and the high cost of cermet manufacturing. It determines the need in their further development, research to improve the composition, structure and properties of cermets, searching for new applications, developing new manufacturing methods and reducing the cost of their production. Various cermet manufacturing methods are discussed such as solid-phase, liquid-phase, gas-phase, and in-situ methods. The methods of infiltration with molten metals, the effect of wetting, and the conditions for spontaneous infiltration are considered in more detail. The results of using the method of self-propagating high-temperature synthesis (SHS) are also described in detail including a new cermet manufacturing method proposed by the authors of this review based on the use of the SHS of a porous ceramic skeleton followed by spontaneous infiltration with molten metal.

Comparison of different methods for Li2MTi3O8 (M – Co, Cu, Zn) synthesis

AbstractBACKGROUNDMesoporous powders of lithium titanates Li2MTi3O8 (M – Co, Cu, Zn) of spinel structure are promising as anode materials for Li‐ion batteries.RESULTSLi2MTi3O8 (M – Co, Cu, Zn) were obtained by the sol–gel method, using self‐propagating high‐temperature synthesis (SHS) from glycine–citrate–nitrate mixtures, and also by the SHS method from aqueous solutions. The crystal structure, phase composition, microstructure and dispersion of the obtained materials were studied.CONCLUSIONIt was established that the SHS method for the synthesis of lithium titanates has several advantages compared with the sol–gel method, including not requiring solvents, reduced aggregation of particles, a higher specific surface area and low bulk density of the obtained powders. The electrode obtained on the basis of Zn‐containing Li titanate by the SHS method from glycine–citrate–nitrate mixtures showed the highest charging capacity of 160 mAh g−1 and high cyclic stability. © 2021 Society of Chemical Industry (SCI).

Production of Ferroboron from Wastes by SHS-metallurgy and influence of Ligatures on the Structure/Properties of Cast Iron

Waste, generated during the industrial process negatively affects the environment, but at the same time it is a valuable raw material and can be used to produce new marketable products. The study of the effectiveness of Self-propagating High temperature Synthesis (SHS) methods, which are characterized by the simplicity of the necessary equipment, the purity of the final product and the high processing speed, is under the wide scientific and practical interest to solve the set problem. The work describes technological aspects of production of ferro boron by the method of SHS - metallurgy from iron-containing wastes of rolled production for alloying of cast iron and results of effect of alloying element on degree of boron assimilation with liquid cast iron. Features of Fe-B system combustion have been investigated and the main parameters to control the phase composition of synthesis products have been experimentally established. Effect of overloads on patterns of cast ligatures formation and mechanisms of structure formation of SHS products was studied. It has been shown that an increase in the content of hematite Fe2O3 in iron-containing waste leads to an increase in the content of phase FeB and accordingly, the amount of boron in the ligature. Boron content in ligature is within 3-14%, and phase composition of obtained ligatures consists of Fe2B and FeB phases. Depending on the initial composition of the wastes, the yield of the end product reaches 91 - 94%, and the extraction of boron is 70 - 88%. Combustion processes of high exothermic mixtures allow obtaining a wide range of boron-containing ligatures from industrial wastes. In view of the relatively low melting point of the obtained SHS-ligature, the positive dynamics of boron absorption by liquid iron is established. According to the obtained data, the degree of absorption of the ligature by alloying gray cast iron at 1450 ° C is 80 - 85%. When combined with the treatment of liquid cast iron with magnesium, followed by alloying with the developed ligature, boron losses are reduced by 5-7%. At that uniform distribution of boron micro-additives in volume of treated liquid metal is provided.

Low-threshold field electron emission from graphene nanostructures

This paper presents the results of a study of field electron emission from two-dimensional graphene-like nanostructures synthesized by the method of self-propagating high-temperature synthesis. It is shown that this technology makes it possible to create efficient large-area field emitters. It is found that such structures exhibit the effect of low-threshold field electron emission. The possibility of obtaining high-current electron beams with currents up to several hundred amperes has been confirmed in pulsed electric fields.

Phenomenological model of synthesis of few-layer graphene (FLG) by the selfpropagating high-temperature synthesis (SHS) method from biopolymers

A phenomenological model for the synthesis of few-layer graphene (FLG) nanosheets by the method of self-propagating high-temperature synthesis (SHS) from starch, lignin, and other biopolymers is considered. We suggested that polysaccharides, in particular starch, could be an acceptable source of native cycles for the SHS process. The carbonization of biopolymers under the conditions of the SHS process was chosen as the basic method of synthesis. Chemical reactions, under the conditions of the SHS process, proceed according to a specific mechanism of nonisothermal branched-chain processes, which are characterized by the joint action of two fundamentally different process-accelerating factors - avalanche reproduction of active intermediate particles and self-heating. It is shown that the proposed model can explain the production of few-layer graphene nanosheets with linear dimensions of tens of microns and a thickness of several graphene layers.

Synthesis of Metal Matrix Composites Based on CrxNiy-TiN for Additive Technology.

The novelty of this work consists of obtaining original fundamental data on the laws of synthesis of new metal matrix composite materials for additive technologies. CrN + TiNi composites were obtained using the method of self-propagating high-temperature synthesis. In this work, analysis of the parameters of the synthesis of composite materials as well as their structure and phase composition were carried out. A scheme for the formation of a composite structure is established; it is shown that the phase composition is represented by 54.6 wt.% CrN and 45.4 wt.% TiNi. It was shown that composites based on the system are suitable for machines that make use of direct laser deposition to grow layers of materials. Sample structure and phase parameters were studied. It is shown that titanium nitride particles are uniformly distributed in the CrNi intermetallic matrix, the TiN particle size ranges from 0.3 to 9 μm and the average particle size is 2.8 μm. The results obtained indicate the possibility of synthesizing promising metal matrix composite materials for additive technologies. Such materials may have increased hardness, operating temperature and strength.

Formation of Mn2AlB2 by induction-assisted self-propagating high-temperature synthesis

Rapid formation of the MAB phase ceramic, Mn2AlB2, by the method of induction furnace-assisted self-propagating high-temperature synthesis (SHS) was investigated in this work. The effects of Al content, high-energy ball-milling and cold pressing load on phase purity and reaction behaviour were also examined. An Al content of 140% allowed the highest conversion of reactants to Mn2AlB2. Increasing ball-milling time was shown to increase phase purity and reduce SHS ignition and peak temperatures. Unpressed powder samples exhibited higher phase purities and significantly lower SHS ignition temperatures than pressed samples. It was revealed that Mn2AlB2 forms by a two-stage reaction in this process, as evidenced by the presence of two exothermic peaks in the temperature-time data. The short synthesis times and equipment scalability available using this method offer a unique solution for the large-scale fabrication of MAB phase powders.

Влияние химического состава матрицы на структуру и свойства монолитных СВС-композитов

Introduction. The development of new wear-resistant materials obtained by the method of self-propagating high-temperature synthesis (SHS) is an urgent problem in materials science. The SHS method is most widely used in the field of creating new powder materials. Much less attention has been paid to the production of monolithic non-porous composites. For monolithic composites, it is very important to identify the role of the metal matrix and phase transformations in the process of secondary structure formation after the completion of the synthesis process when the obtained material is cooled. The aim of this work was to carry out a comparative analysis of the structure and properties of SHS composites of the Fe-Ti-C-B, Fe-Ni-Ti-C-B, Fe-Ni-Cr-Ti-C-B, and Cu-TiC-B systems. Materials and research methods. Composites were obtained from powder mixtures consisting of thermoreactive components Ti, C, and B, as well as matrix Fe, Fe-Ni, Fe-Ni-Cr, and Cu. The initial powders were thoroughly mixed, loaded into a steel tube container, and the powder mixture was preliminary compacted. Then, the workpieces were heated in an electric furnace to the temperature of the onset of autoignition. After completion of the SHS, the workpieces were deformed with a force of 250 MPa in a hydraulic press at a temperature not lower than 1000 ° C. Samples were cut from the obtained sandwich plates for microstructural studies, density determination, hardness measurements, transverse bending tests and abrasive wear resistance tests. Results and discussion. All investigated composites were characterized by an uneven distribution of strengthening particles TiC and TiB2 over the volume. The use of the Fe-Ni matrix led to the formation of regions with the γ-Fe + Fe2B eutectic structure in the composite and an additional strengthening phase Ni3Ti. The use of Fe-Ni-Cr metal-matrix components led to the formation of two solid solutions in the matrix - austenite and ferrite, and Cr23C6 particles were formed along the boundaries of austenite grains. The maximum transverse bending strength was shown by SHS composites of the Fe-Ti-C-B and Cu-Ti-C-B systems with a matrix of FCC solid solutions. All composites had a hardness of 66 -72 HRC and showed the same abrasion resistance.

Production of TiC-MMCs Reinforcements in Cast Ferrous Alloys Using In Situ Methods.

This literature review aims to summarize the research conducted on the production of locally reinforced ferrous castings based on metal matrix composites reinforced with TiC (TiC-MMCs). One way to improve the wear resistance of cast components is to reinforce critical regions locally with metal matrix composites (MMCs) without changing the toughness of the component core. The in situ method of self-propagating high-temperature synthesis is one of the main approaches for the production of this enhanced material. Using this approach, the reinforcement is formed from a powder compact inserted in the mold cavity. The temperature of the liquid metal then produces the combustion reactions of the powders, which promote the formation of the ceramic phase. This paper focuses on eight powder systems used to synthesize TiC: Ti-C, Ni-Ti-C, Ni-Ti-B4C, Fe-Ti-C/Fe-Cr-Ti-C, Cu-Ti-B4C, Al-Ti-C, and Al-Ti-B4C, and provides an overview of the methodologies used as well as the effect of processing variables on the microstructural and mechanical characteristics of the reinforcement zones.

Corrosion behaviour of the NiTiX (X = Si, Mg, Al) alloy prepared by self-propagating high-temperature synthesis

Abstract The NiTi alloys are used in the biomaterial field, because of their shape memory, superelasticity, and good corrosion resistance. The influence of alloying elements on the corrosion behaviour of NiTi was studied in this research. Samples were made by the self-propagating high-temperature synthesis method, milled, and then sintered by the spark plasma sintering method. Si, Mg, and Al were used as alloying elements always in 5 wt.%. Studied materials were compared with reference cast NiTi. Polarization resistance was measured after 1 and 12 hours of stabilization in phosphate-buffered saline. It was found out that alloying elements do not have a clear effect on polarization resistance. Si increased Rp and on the other hand, Al decreased it. Measurement of cyclic potentiodynamic polarization in PBS was conducted, too. All studied samples showed signs of localized corrosion. Corrosion was probably initiated in pores, which are presented on the surface due to used manufacturing technology.

Preparation of quaternary compounds Cu2ZnSnS4 by using the self-propagating high-temperature synthesis

Possibility to prepare finely dispersed Cu2ZnSnS4 by using the method of self-propagating high-temperature synthesis has been studied in this work. Investigations of Raman scattering and IR-Fourier spectroscopy of the synthesized finely dispersed material have been carried out. The analysis of the Raman and IR-Fourier spectra showed that the synthesized material in the process of preparing is formed with a kesterite structure with the inclusion of a certain amount of secondary phases in the form of sulfides and stannites.

Influence of Co content on microstructure and hardness of AlCoxCrFeNi (0 ≤ x ≤ 1) high-entropy alloys produced by self-propagating high-temperature synthesis

In an effort to reduce energy consumption and expensive Co content, herein we report the effects of Co content on microstructure and microhardness of widely studied AlCoxCrFeNi high-entropy alloys produced by cost-efficient aluminothermic self-propagating high-temperature synthesis (SHS) method. Accordingly, the feasibility of SHS technique in the production of AlCoxCrFeNi master high-entropy alloys was discussed. In order to investigate the effect of further casting, the SHS alloys were also subjected to vacuum arc melting/suction casting process. Prior to SHS; phase diagram, raw material amounts and adiabatic temperatures were calculated via thermochemical modelling. The calculated equilibrium phase diagram suggested a full BCC structure over the whole Co range. However, according to XRD results, as-cast alloys consisted of BCC and FCC phases, having microhardness values ranging in between 385 HV and 504 HV, depending on Co content. The increase in Co content, enlarged the grains, altered the spinodal decomposition morphology and led to the formation of dual-phase (FCC + BCC) alloys, which in return had a significant effect on the microhardness values. Overall hardness values were increased due to finer microstructure obtained by suction casting. Also, Widmanstätten plate-like growth of the FCC phase inside the BCC cores was kinetically suppressed due to higher cooling rate. It was concluded that AlCoxCrFeNi master high-entropy alloys can be successfully produced by SHS method and the attained dual-phase microstructures could be beneficial in tailoring mechanical properties as well as reducing the total cost of the AlCoxCrFeNi HEAs system in addition to the significant energy reduction obtained via SHS route.

Energy-effective AlMgB14 production by self-propagating high-temperature synthesis (SHS) using the chemical furnace as a source of heat energy

In this work, AlMgB14 was obtained by self-propagating high temperature synthesis (SHS) using the chemical furnace based on titanium and silicon (Ti5Si3) as a source of heat energy. Structure and phase composition of the synthesis products were studied. AlMgB14 formation mechanism was proposed. It was found that the highest yield of AlMgB14 (94 wt %) is achieved with a 2 cm thick chemical furnace. The average size of crystal grains in the obtained AlMgB14-based powder is 1 μm. The duration of AlMgB14 formation is 138 s, which is 30–180 times faster than the duration of high-temperature vacuum sintering. In this case, the SHS method makes it possible to obtain AlMgB14 excluding the energy-consuming stage of heating to the isothermal holding temperature.

Microstructure Peculiarities of Intermetallic and Composite Coatings

Coatings were obtained by the method of electrospark deposition (ESD), using Ni-Al intermetallic alloys, steel having been used as cathodes. The structure of samples preliminarily, coated with nickel aluminides of various phase compositions (NiAl, Ni3Al), was investigated. In addition to the indicated anode materials, a complex alloyed metal matrix alloy obtained by the method of self-propagating high-temperature synthesis, was used. It was established that the coating microstructure consisted of columnar crystallites, vertically oriented to the cathode surface. X-ray microanalysis of the transverse sections showed a change in the composition of crystallites along their height. It was found that the content of the cathode components decreased from the surface of the sample to the upper part of its coating, however, the content of the anode components increased. The revealed regularities indicate the fact that the coating structure obtained at ESD, was formed through the stage of liquid-phase mixing, which explained high coating adheasion. The mechanisms of structure formation of both single-layer and two-layer coatings proved to be identical.

Effect of the cobalt content on properties of La2Ni1-xCoxO4+δ

Ruddlesden-Popper-type La2NiO4+δ oxide is considered as a potential cathode for solid oxide fuel cell applications. In this work, the tailoring possibility of the cathode material properties by doping with a small amount of Co has been investigated. The initial powders were synthesized by the self-propagating high-temperature synthesis method. The sintering kinetics, thermal expansion, electrical conductivity, catalytic activity of La2Ni1-xCoxO4+δ (0 ≤ x ≤ 0.3) as well as their interaction with Zr0.84Y0.16O2-δ (YSZ) and Ce0.73Gd0.27O2-δ (GDC) electrolytes have been studied. It was shown that the coefficient of thermal expansion of the investigated compositions increases with increasing the Co content. The Co doping leads to decreasing of La2Ni1-xCoxO4+δ conductivity in the temperature range below 600°С, whereas at higher temperatures, compositions with x = 0.2 and 0.3 have higher conductivity than La2NiO4. The polarization resistance of the cathodes in contact with YSZ increases with increasing the Co content. However, in contact with GDC the La2Ni0.8Co0.2O4+δ composition has the lowest polarization resistance of 0.4 Ω cm2 (at 800 °C), which is 1.5 times less than that of La2NiO4+δ. Therefore, it was concluded that doping with the appropriate amount of Co could further improve the properties of lanthanum nickelate cathode.

Synthesis of FeSi-Al2O3 Composites by Autowave Combustion with Metallothermic Reduction

Fabrication of FeSi-Al2O3 composites with a molar ratio of FeSi/Al2O3 ranging from 1.2 to 4.5 was conducted by the self-propagating high-temperature synthesis (SHS) method. The synthesis reaction involved metallothermic reduction of Fe2O3 and SiO2 by Al and the chemical interaction of Fe and Si. Two combustion systems were examined: one contained thermite reagents of 0.6Fe2O3 + 0.6SiO2 + 2Al, and the other had Fe2O3 + 2Al to mix with different amounts of Fe and Si powders. A thermodynamic analysis indicated that metallothermic reduction of oxide precursors was sufficiently exothermic to sustain the combustion reaction in a self-propagating mode. The SHS reaction carrying out co-reduction of Fe2O3 and SiO2 was less exothermic, and was applied to synthesize products with FeSi/Al2O3 = 1.2–2.5, while the reaction reducing only Fe2O3 was more energetic and was adopted for the composites with FeSi/Al2O3 = 2.5–4.5. Moreover, the former had a larger activation energy, i.e., Ea = 215.3 kJ/mol, than the latter, i.e., Ea = 180.4 kJ/mol. For both reaction systems, the combustion wave velocity and temperature decreased with increasing FeSi content. Formation of FeSi-Al2O3 in situ composites with different amounts of FeSi was achieved. Additionally, a trivial amount of aluminum silicate was detected in the products of high FeSi contents due to dissolution of Si into Al2O3 during the SHS process.