High-temperature Synthesis Method Research Articles

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.

Thermodynamically study of phase formation of Ni-Ti-Si nanocomposites produced by self-propagating high-temperature synthesis method

Understanding the phase formation mechanisms in self-propagating high-temperature synthesis from the thermodynamical aspect of view is important. In this study, the phase formation of the ternary system of nickel-titanium-silicon was studied by using the HSC software V6.0, and phase formation is predicted by calculating the adiabatic temperature of exothermic reaction between reagents. Then, by using X-ray diffractometer analysis, the results of the simulation were evaluated by experimental achievements. Results showed a good correlation between thermodynamical calculation and prediction with experimental. It could be concluded that the equilibrium mechanism is the dominant mechanism in phase formation in the SHS synthesis method. NiTiSi solid solution phase is obtained from the reaction between Ti5Si3 and Ni2Si and Ni.

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.

Electrolytical Carbon Nanostructures from Molten Salts: Synthesis and Properties

Carbon nanomaterials (CNMs) occupy a special place in nanoscience owing to exceptional thermal, electrical, chemical and mechanical properties. They are used in various areas of modern technologies: super-strong composite materials, supercapacitors, smart sensors, targeted delivery drugs, catalyst carriers, field emission devices, quantum wires, paints, for energy storing and conversion, for gas storing, in nanoelectronics, etc. Therefore, a great attention is given all over the world to the development of novel efficient method for the fabrication of CNMs, comprehensive investigation of their properties, and search for new applications. Today there are many methods for the synthesis of CNMs. In resent ten years, the method of high-temperature electrochemical synthesis (HTES) in molten salts has been rapidly developing. The essence of the method of HTES is the cathodic reduction of oxygen-containing carbon compounds dissolved in molten salts. There are several variants of HTES. The advantages of all variants of HTES are: (1) soft synthesis conditions, (2) simple hardware implementation, (3) the possibility of controlling the electrolysis conditions, (4) low energy consumption for electrolysis, (5) the use of cheap precursors, (6) easy doping during synthesis, (7) monodipersity of the product. An important advantage of HTES is the possibility of using carbon dioxide as a starting reagent. Global warming, caused by increase in the emission of greenhouse gases (CO2, CH4 and others), is recognized as a serious environmental problem of the mankind.The goal of this work is presentation of research results on the electrochemical transformation of carbon oxy-compounds (lithium carbonate and carbon dioxide) into nanoscale solid carbon of different structure and morphology (carbon nanotubes (CNTs), fibers (CNFs), graphene) in chloride-carbonate melts.On the basis of a voltammetric study, it has been found that direct electroreduction of CO2 dissolved in equimolar salt mixture Na,K|Cl under an excessive pressure (1 - 15 atmospheres) up to carbon at temperature 750 0C occurs in one stage at polarization rates above 0.2 Vs-1. The electrode process is controlled both by the charge transfer rate and by the rate of gas diffusion to the electrode. At polarization rates below 0.1 Vs-1, the electrode process occurs in two stages, and an Electrochemical-Chemical- Electrochemical mechanism of CO2 reduction has been suggested. The cathodic product is carbon films and powders of different structures and morphology. Typical morphologies of the electrolytic products obtained in the melts Na,K|Cl–CO2 are shown in Fig. 1.All the products obtained in the system Na,K|Cl–CO2 (10 atm.) contain CNTs, the majority of which are multi-walled and have a curved form (structural defects). Most often CNTs agglomerate into bundles, and more rarely are arranged as individual tubes. The outer diameter of CNTs varies from 5 to 250 nm, while the internal diameter from 2 to 140 nm. Almost all CNTs are filled partly with electrolyte salt. When the current density increases, the CNT diameter decreases (although every product obtained at the current densities used has CNTs of different diameters).It was found by voltammetry method that the process of reduction of Li2CO3 in Na,K|Cl melt depends on the gaseous atmosphere above the melt. In air, it includes two electrochemical stages. The preliminary chemical reaction of lithium carbonate dissociation (Li2CO3 ⇄ Li2O + CO2) leads to the formation of two electrochemically active particles: CO2 and LixCO3 2-x, which are reduced to elemental carbon at different potentials of -0.8 and -1.7 V respectively against Pt|O2/O2- reference electrode. Both processes are irreversible, and the electroreduction of LixCO3 2-x takes place with diffusion control of the delivery of the depolarizer to the electrode surface. Under of argon or carbon dioxide atmosphere over the melt, the process of lithium carbonate dissociation is suppressed; therefore, the deposition of carbon in this case occurs only from the cationized carbonate complex.X-ray diffraction, SEM and Raman spectroscopy revealed that the cathode product is a high disordered amorphous carbon. Agglomerated particles consist of degraded graphite structures with an approximate crystallite size of 30–40 nm.Figure 1. TEM micrographs (a÷e) and electron-beam images (d (inset in the upper left) and f) of carbon powders produced in the system Na,K|Cl–CO2 (10 atm.) at different current densities: (a ÷ e): i k = 13.5; 28; 42; 56; 72 mA/cm2 ; T = 750 0C; Figure 1

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.

Study and applicability of photoluminescence properties of Cr4+: LiInGeO4

This paper reports a series of Cr4+: LiInGeO4, based on a high-temperature solid-phase synthesis method and the effect of LiInGeO4-doped Cr4+ ions on the spectral properties and luminescence colors in the near-infrared region. Under 808 nm excitation, the emission spectra showed a broad band at 1000–1500 nm, with a maximum peak occurring at 1218 nm due to the 3T2→3A2 transition of Cr4+ ions. The lifetime decreases with the increasing amount of Cr4+ ions, from 8.30035 μs to 6.656 μs. The chromium's chemical composition and valence state in LiInGeO4 were analyzed by x-ray photoelectron spectroscopy. The results showed that the chromium in LiInGeO4 was tetravalent, and no trivalent chromium was found. The results show that LiInGeO4 crystals can have promising applicability in anti-counterfeiting due to the possibility of both up-conversion and down-conversion glowing.

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.

MgAl2O4:Cr3+ luminescence thermometry probe in the physiological temperatures range

Temperature sensing from the photoluminescence of MgAl2O4:Cr3+ ceramic powder is systematically investigated. Material was prepared by self-propagating high temperature synthesis method. In this host, Cr3+ experiences the strong crystal field, so the overlapping emissions from 2E and 4T2 energy levels are observed. Emission and excitation spectra were recorded from 300 K to 540 K. The broad photoluminescence attributed to 4T2→4A2 emission gains in intensity with increase in temperature on account of 2E→4A2 emission intensity until 460 K when both emissions start quenching. The emissions were separated by deconvolution at each temperature and used for the luminescence intensity ratio temperature readout method. The obtained relative sensitivity exhibited high values in the physiological range, from 3.5 %K−1 at 300 K to 2.9 %K−1 at 330 K, above 2 %K−1 below 400 K and above 1 %K−1 between 400 K and 540 K.

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.

Thermoelectric properties of phosphorus-doped van der Waals crystal Ta4SiTe4

Recently, one-dimensional van der Waals crystal Ta4SiTe4 has been reported as a promising low-temperature thermoelectric material. Extraordinarily high power factor has been reported for the one-dimensional Ta4SiTe4 single whisker and two-dimensional (PVDF)/Ta4SiTe4 composite film, but the thermoelectric properties of three-dimensional Ta4SiTe4 polycrystalline bulks have been rarely investigated. In this study, we prepared a series of phosphorus (P)-doped Ta4SiTe4 polycrystalline bulks by using the high-temperature synthesis and cold press method. Their electrical and thermal transport properties along the directions parallel and perpendicular to the pressure were systematically investigated. Upon doping P at the Si-sites to increase the carrier concentration, the electrical conductivity is enhanced while the intrinsic excitation is suppressed, resulting in significantly improved power factor approaching the theoretically optimal value. All Ta4Si1-xPxTe4 bulks possess low lattice thermal conductivities with the values below 1.2 Wm−1K−1. The weak van der Waals interaction among the [Si2Ta8Te8]n chains results in the appearance of low-lying optical modes and introduces additional scattering to phonons. A peak thermoelectric figure of merit value of 0.18 is obtained at 300 K for polycrystalline Ta4Si0·995P0·005Te4, about double that of pristine polycrystalline Ta4SiTe4.

Microstructure and thermoelectric properties of α-and γ-Al2O3 doped ZnO under high pressure

Using high pressure and high temperature (HPHT) technology to improve the thermoelectric properties of oxides is a feasible solution. To further understand the micro-physical mechanism improving the thermoelectric performance of ZnO in a higher pressure environment, the effects of α and γ lattice structure Al2O3 (α-Al2O3, γ-Al2O3) on doped ZnO were systematically studied. ZnO samples with different Al doping ratios (α-x, γ-x; x = 0.02, 0.04, 0.06, 0.08) were prepared by HPHT. Test results show that the high pressure and high temperature synthesis method effectively improves the solid solubility of α-Al2O3 and γ-Al2O3 in ZnO, among which γ-Al2O3 is more easily dissolved into the zinc oxide crystal lattice. Under the same doping ratio, the electronic conductivity of the sample synthesized with γ-Al2O3 is higher than that of the sample synthesized with α-Al2O3. In addition, the ZnAl2O4 phase precipitated out of the sample with increased Al doping. Although the ZnAl2O4 phase decreases the electrical properties of the sample, a small amount of ZnAl2O4 is uniformly dispersed in the ZnO sample, which can inhibit the growth of crystal grains, and assist grain refinement. The optimized high pressure sintering temperature was 1123 K, and the zT value of γ-0.04 was 0.17 at 973 K.

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.

Rapid High-temperature Synthesis of Nanosized ZSM-22 Zeolite

Nanosized ZSM-22 with high crystallinity was synthesized rapidly by a high-temperature hydrothermal synthesis method. The effects of synthesis conditions such as crystallization temperature, crystallization time, Si/Al ratios and crystallinity of ZSM-22 were investigated, and the relationship between crystallization temperature and crystallization time was calculated by Arrhenius equation. Meanwhile, the rapid high-temperature synthesis method was effective to synthesize ZSM-22 with Si/Al ratio from 35 to 70. The nanosized ZSM-22 exhibited high light olefin selectivity and a long lifetime in the MTO reaction.

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.