Conditions Of Self-propagating High-temperature Synthesis Research Articles

Nano- and Submicron-Sized TiB2 Particles in Al–TiB2 Composite Produced in Semi-Industrial Self-Propagating High-Temperature Synthesis Conditions

Nano- and Submicron-Sized TiB2 Particles in Al–TiB2 Composite Produced in Semi-Industrial Self-Propagating High-Temperature Synthesis Conditions

Sorption of Radium-226 on Few-Layer Graphene Synthesized under Conditions of Self-Propagating High-Temperature Synthesis

Sorption of Radium-226 on Few-Layer Graphene Synthesized under Conditions of Self-Propagating High-Temperature Synthesis

Use of Few-Layer Graphene Synthesized under Conditions of Self-Propagating High-Temperature Synthesis for Supercapacitors Applications.

Graphene nanostructures (GNSs) are among the most promising materials for producing supercapacitors. However, GNSs are still not used in creating supercapacitors due to the impossibility of obtaining large volumes of high-quality material at an acceptable cost. In our previous works, we have shown the possibility of synthesizing large volumes of few-layer graphene (FLG, the number of layers is not more than five) from cyclic biopolymers under conditions of self-propagating high-temperature synthesis (SHS). Using the SHS process makes it possible to synthesize large volumes of FLG without Stone-Wales defects. This work is devoted to the study of the possibility of using FLG synthesized under the conditions of the SHS process in the creation of supercapacitors. It was found that the synthesized FLG makes it possible to obtain better results than using classical materials, namely activated carbon (AC). It was found that the sample based on FLG had a higher specific capacitance of 65 F × g-1 compared to the sample from AC, the specific capacitance of which was 35 F × g-1; for a speed of 5 mV × s-1, these values were170 and 64 F × g-1, respectively. The drop in capacitance over 1000 cycles was 4%, indicating a sufficiently high FLG stability, allowing us to consider FLG as a prospective material for use in supercapacitors.

Carbonization of Biopolymers as a Method for Producing a Photosensitizing Additive for Energy Materials

It has been shown that defect-free Stone–Wales (SW) free few-layer graphene (FLG) can be obtained by carbonizing lignin under conditions of self-propagating high-temperature synthesis (SHS). The obtained few-layer graphene was used as a modifying additive for pyrotechnic compositions. It was found that the addition of 2.5 mass % of few-layer graphene synthesized from lignin to a pyrotechnic complex based on porous silicon and fluoropolymer leads to a significant increase in the combustion intensity of pyrotechnic compositions.

Influence of Conditions of Self-Propagating High-Temperature Synthesis on Phase Composition and Structure of Materials Based on Ti–B

Influence of Conditions of Self-Propagating High-Temperature Synthesis on Phase Composition and Structure of Materials Based on Ti–B

Few-Layer Graphene Structures as a Promising Mycotoxin Sorbent

It has been experimentally established that samples of low-layer graphene, synthesized by carbonization of plant materials (lignin, cellulose, and spruce bark) under conditions of self-propagating high-temperature synthesis, are effective sorbents for mycotoxin T-2 under conditions simulating the environment in the gastrointestinal tract of mammals, and are capable of irreversibly sorb at least 94.6% of mycotoxin with a sorption capacity of 1 mg of mycotoxins per 1 g of sorbent. Key words: few-layer graphene, self-propagating high-temperature synthesis, specific surface area, mycotoxin sorption. Keywords: few-layer graphene, self-propagating high-temperature synthesis, specific surface, sorption of mycotoxins.

Малослойные графеновые структуры как перспективный сорбент микотоксинов

It has been experimentally established that samples of low-layer graphene, synthesized by carbonization of plant materials (lignin, cellulose, and spruce bark) under conditions of self-propagating high-temperature synthesis, are effective sorbents for mycotoxin T-2 under conditions simulating the environment in the gastrointestinal tract of mammals, and are capable of irreversibly sorb at least 94.6% of mycotoxin with a sorption capacity of 1 mg of mycotoxins per 1 g of sorbent. Key words: few-layer graphene, self-propagating high-temperature synthesis, specific surface area, mycotoxin sorption.

Hardness and thermal conductivity of a composite based on aluminum modified with a hybrid material detonation nanodiamond/few-layer graphene

A hybrid carbon material of the composition few-layer graphene/detonation nanodiamonds synthesized under the conditions of self-propagating high-temperature synthesis was first tested as a modifying additive in creating of a composite material based on aluminum. It was found that the use of 0.25 mass. % of the hybrid material made it possible to increase the hardness of the metal composite up to 2 times compared to the original aluminum while maintaining the density identical to the original aluminum and a sufficiently high thermal conductivity of about 200 W/(m*K).

Synthesis of Composite Materials based on TiB2–TiC–Al2O3 and CrB2-Al2O3 in the Combustion Conditions

Borides and carbides attract the attention of developers of heat-resistant and super hard structural materials due to a unique combination of their resistance to high-temperature oxidation, high hardness, wear resistance, electrical and thermal conductivity and etc. The article presents experimental results on obtaining composites based on TiB2-TiC-Al2O3, CrB2-Al2O3 by a method combining self-propagating high-temperature synthesis (SHS) and mechanical activation (MA). The influence of the composition of the initial components, the conditions of SHS and preliminary MA on the formation of the microstructure and phase composition of the SHS-composite based on titanium carbide and titanium, chromium borides has been studied. The SHS products were examined by X-ray diffraction analysis and a scanning electron microscope. High-temperature phases of borides of chromium, titanium, aluminum oxide and their spinel are found in SHS products.

Hogweed Biomass as a Raw Material for Producing 2D Nanocarbons: An Environmental Aspect

The possibility of carbonization of the biomass of Sosnowski hogweed under the conditions of self-propagating high-temperature synthesis (SHS) was explored. It was found that carbonization of the hogweed biomass samples taken in the flowering and dead stem phases gave 30‒40% carbonized product. The yield of the carbonized product from the hogweed biomass sample taken in the early vegetative phase (before flowering) did not exceed 2%. Such a low yield may be due to the features of the formation of the nanocarbon precursor in the process of plant development. Analysis by several complementary techniques (Raman spectroscopy, X-ray diffraction) showed that, in terms of their morphometric parameters, the carbonized product particles correspond to 2D nanocarbon, specifically to graphene nanoplatelets.

The Possibility of Dense Materials Based on Obtaining an AlN–SiC Solid Solution by Self-Propagating High-Temperature Synthesis Gasostating

The synthesis and sintering of the (AlN)x(SiC)1 – x solid solution have been studied under conditions of self-propagating high-temperature synthesis (SHS) gasostating at high nitrogen gas pressures (up to 110 MPa). The phase formation during the combustion of mixtures of aluminum and silicon carbide with a different amount of Al (from 35 to 60 wt %) is studied. It is shown that the optimal amount of aluminum mixed with silicon carbide to obtain a single-phase solid solution (with the complete conversion of aluminum to aluminum nitride, and also without the dissociation of silicon carbide) is 45–50 wt %. Using a mixture with 55–60 wt % Al leads to excessively high temperatures, which in turn leads to the decomposition of silicon carbide to Si + C elements. The optimal parameters for obtaining dense material in one stage are determined. The measured porosity and density of the samples allow us to establish that, for samples with 50 wt % of the aluminum content, prepressing is essential for the final density. It is found that the additive of 5 wt % yttrium oxide increases the density of the material by almost 10%. A similar effect is also exerted by an increase in the initial gas pressure from 80 to 110 MPa. The maximum density that is achieved is 2.7 g/cm3, which is 83% of the theoretical density. The total volumetric shrinkage of the material is 10% ± 0.5, which can be almost completely leveled by the addition of 3 wt % boron. The hardness of the samples reaches up to 2000 kg/mm2.

FORMATION OF STRUCTURE OF HOOKS OF LOADING LIFTS IN CONDITIONS OF SHS

The article deals with the formation of the structure of hoists for lifting cranes in order to prevent the development of cracks by forming the structure of steel 20 by treatment in the conditions of self-propagating high-temperature synthesis (SHS) to obtain fine-grained ferrite-perlite structure. The conducted researches allow to form a rational structure of steel to exclude the development of cracks in dangerous sections of lifting hooks of hoisting and transport mechanisms working in the shops of metallurgical production. The method of structure control after SHS is developed taking into account the influence of different diameters of hooks.

High temperature X-ray powder diffraction study of boron carbide crystals of different composition

Boron carbide crystals of various compositions were studied by X-ray powder diffraction in the temperature range of 25-700 ​°C. The formation of a metastable structure of boron carbide under the conditions of self-propagating high-temperature synthesis was detected. Its metastability manifested in a decrease of the unit cell volume after the first heating-cooling cycle. The cell volume change disappeared in all the subsequent heating-cooling cycles. For B12C3 crystals this effect did not occur. The metastability of boron carbide crystals was explained by the presence of C and/or B atoms in crystalline structure channels and their motion along the channels and up to position of structural vacancies under the temperature increasing.

RESEARCH OF CORROSION RESISTANCE OF MATERIALS WORKING IN COAL RESIN AND FORMATION OF SEDIMENTS BEFORE GRINULATION OF THE PERK

The aim of the work is to study the corrosion resistance of structural materials operating in industrial conditions of coke production. Instability of loading of chemical workshops of coke production, a sharp change in the productivity of units due to the instability of the coke base, an increase in the HCN content in coke oven gas, and the use of new reagents for water purification of closed cycles increases the corrosivity of process fluids. The growing use of imported equipment requires more careful monitoring of local corrosion, which is the most dangerous. When it develops in places where metal fatigue occurs, cracks or stress corrosion cracking occur. With this type of damage, the service life of the equipment is significantly reduced. It was found that the content of insoluble quinoline and toluene in the filter cake before granulation (35.4 and 50%) indicates the presence of highly pyrolyzed particles 27-48 μm in size, which are formed, possibly, when the resin passes through the tubular furnace or by oxidation in a cube reactor. A high ash content in the filter cake was observed prior to granulation (2.59%), which was caused by the adhesion of ash particles to the cake during filtration. Detected ash particles having a regular pointed shape of 5-30 microns in size can cause abrasive wear. Effective corrosion protection of materials is confirmed by coatings obtained under conditions of self-propagating high-temperature synthesis.

SHS-Aided Joining of Ceramic Materials with the Ta Substrate

Experiments on evaluating the possibility of joining ceramic materials with a Ta substrate under conditions of self-propagating high-temperature synthesis (SHS) are explored. The sample consists of tantalum foils and pellets Ti + 0.65C and 5T + 3Si, between which a Ti + 2B igniting tape is laid. The sample is installed on a boron nitride support. A chamotte brick plate (SiO2 + Al2O3) with a load of 3360 g placed on its top is placed on a sample to decrease the heat sink. The experiments are performed in a reaction chamber in argon under a pressure of 1 atm. The samples are preheated from the bottom, and the reaction is initiated from their butt. The sample temperature is measured using W–Re thermocouples. The temperature gradient over the sample thickness, depending on the heating rate, is 50–150 K/mm. The samples with strong joining of the tantalum foil with Ti + 0.65C, as well as between two pellets, are formed. The top foil is not welded to the 5Ti + 3Si pellet, which is explained by a rather low temperature (1600°C) at the interface. When studying the interface of the tantalum foil with titanium carbide, the formation of Ti–Ta and (Ta,Ti)C interlayers is found. The possibility of joining the tantalum foil with ceramic materials during SHS is shown by investigations. The main conditions of such joining are the presence of the liquid phase and correspondence of the combustion temperature of the Ti + 0.65C composition to the melting point of the tantalum substrate. These results can be useful when fabricating multilayered functional coatings and functionally graded materials.

Development of wear-resistant coatings for automotive parts after processing in SHS conditions

Methods of obtaining chromium-coated coatings are considered and technology for the formation of boron, silicon and titanium protected layers on steels under conditions of self-propagating high-temperature synthesis is presented. Using the methods of mathematical modeling, when obtaining wear-resistant coatings on machine parts in conditions of self-propagating high-temperature synthesis, optimal compositions of SHS mixtures have been developed. When tested in sliding friction conditions, the best abrasion resistance, among the coatings under consideration, are chromoaluminium-coated coatings. Their wear resistance is 4.8-5 times higher than in uncoated samples, chromoaluminosilicated and chromoalumotated in 2.1-3.5. The gas-transport method of coating with the help of SHS makes it possible to obtain steel 50 and U8A with increased physical and mechanical properties, without requiring high energy costs and time.

SHS-aided joining of ceramics with Ta substrate

The possibility of joining ceramic materials with a Ta substrate was explored in the conditions of self-propagating high-temperature synthesis (SHS). The sample used in experiments consisted of Ta foils, Ti + 0,65C pellet, 5Ti + 3Si pellet, and a Ti + 2B igniting tape laid between them. The sample was installed onto a BN base and covered by a chamotte brick (SiO2+ Al2O3) plate with a weight of 3,36 kg placed on top in order to reduce heat sink. Experiments were performed in a closed reactor under 1 atm of Ar. Samples were preheated from the bottom, after which SHS reaction was initiated from the butt. Temperature was monitored with three W/Re thermocouples. Depending on heating rate, temperature gradient along the sample depth had a value of 50–150 deg/mm. The samples obtained exhibited strong joining between Ta foil and Ti + 0,65C and also between the two pellets. The upper foil did not stick to the 5Ti + 3Si pellet, which can be explained by low temperature at the interface (1600 °C). At the Ta–TiC interface, the formation of Ti–Ta and (Ti, Ta)C interlayers was observed. The studies conducted demonstrate the possibility of Ta foil joining with ceramic materials under SHS conditions. Main conditions for this joint are the presence of a liquid phase and Ti + 0,65C combustion temperature matching the Ta substrate melting temperature. The results may be useful for deposition of multilayer functional coatings and functionally graded materials.

Structure and phase formation of combustion products during the synthesis of γ-AlON in self-propagating high-temperature synthesis

Synthesis of aluminum oxynitride (γ-AlON) in conditions of self-propagating high-temperature synthesis (SHS) gas-statting under high pressures (10–100 MPa) of gaseous nitrogen, including the mode of so-called coupled combustion reactions (chemical furnaces) is investigated. It is shown that chemical and phase compositions of combustion products, as well as their structure and morphology of powder particles, depend on the reagent ratio in Al–Al2O3 initial mixture, as well as on nitrogen pressure, combustion temperature of highly exothermic components of chemical furnaces, and grade of initial reagents. The structure of γ-AlON powder particles are determind and its relation with operation conditions of SHS. Optimal SHS parameters for Al5O6N (γ-AlON) formation are established.

Formation of titanium and niobium aluminides induced by hydrogen in a hydride cycle

The results of our study of formation of aluminides by the hydride cycle (HC) method in Ti–Al and Ti–Al–Nb systems and of their hydrides under the conditions of self-propagating high-temperature synthesis are presented. The HC method was developed at the High-Temperature Synthesis Laboratory of the Nalbandyan Institute of Chemical Physics, Armenian Academy of Sciences. The effect of various parameters: the ratio of titanium and niobium hydrides and aluminum powders in the reaction mixture, hydride powder grain size (micro and nano size), compacting pressure during compaction of hydrides, and conditions of dehydrogenation and sintering (heating temperature and rate) on the characteristics of the obtained aluminides: crystal structure, density, etc. was studied. As a result, single-phase aluminides α2-Ti3Al, Ti2Al, γ-TiAl, TiAl3, Ti0.33Al0.34Nb0.33, Ti0.5Al0.23Nb0.27, Ti0.52Al0.15Nb0.33, TiAl6Nb, etc., and hydrides were synthesized. The HC method has significant advantages over conventional procedures: low temperature (1000–1100°C) and processing time (30–60 min), one-stage formation of single-phase aluminides, etc.

Manipulating the Combustion Wave during Self-Propagating Synthesis for High Thermoelectric Performance of Layered Oxychalcogenide Bi1–xPbxCuSeO

Novel time- and energy-efficient synthesis methods, especially those adaptable to large-scale industrial processing, are of vital importance for broader applications of thermoelectrics. We herein reported a case study of layer-structured oxychalcogenides Bi1–xPbxCuSeO (x = 0–10%) with emphases on the reaction mechanism of self-propagating high-temperature synthesis (SHS) and the impact of SHS conditions on the thermoelectric properties. The combined results of X-ray powder diffraction, differential scanning calorimetry, and quenching experiments corroborated that the SHS process of BiCuSeO consisted two fast binary SHS reactions (2 Bi+3 Se → Bi2Se3 and 2 Cu+Se → Cu2Se) intimately coupled with two relatively slow solid-state diffusion reactions (2 Bi2Se3+B2O3 → 3 Bi2SeO2 and then Bi2SeO2+Cu2Se → 2 BiCuSeO). The formation rate of the reaction intermediate Bi2SeO2 was the bottleneck in the SHS process of BiCuSeO. Importantly, we found that adding PbO in the starting materials has (i) facilitated the formatio...