SHS Process Research Articles

Preparation of ZrB2–SiC–Al2O3 composites by SHS method with aluminothermic reduction

Ternary composites composed of ZrB2, SiC, and Al2O3 with a broad composition range were produced by PTFE-activated combustion synthesis involving aluminothermic reduction of ZrSiO4, SiO2, and ZrO2. Two solid-state combustion systems were investigated: one comprised ZrSiO4, SiO2, Al, B4C, and C and the other consisted of ZrSiO4, ZrO2, Al, B4C, and B powders. It was required for the powder compacts to adopt 3 wt% PTFE as the reaction promoter to initiate and sustain their combustion reaction. The influence of the gas-phase diffusion transport induced by PTFE on the SHS process was confirmed and the activation mechanisms were proposed. With the assistance of PTFE, self-sustaining combustion was established with a distinct combustion wave characterized by a reaction temperature of 1210–1380 °C and a propagation velocity of 2.27–3.16 mm/s. Based on the XRD analysis, the products were ZrB2–SiC–Al2O3 composites with traces of Si, ZrO2, or ZrC. The synthesized products exhibited a granular morphology. The particle size of the composite powders was in the range of 1–2 μm.

Formation of zirconium silicide–Al2O3 composites from PTFE-assisted ZrO2/Si/Al combustion synthesis

Zirconium silicide–Al2O3 composites were fabricated from PTFE-assisted ZrO2–Al–Si combustion systems. PTFE acted as a reaction promoter to initiate and sustain combustion. Reactant mixtures were based on stoichiometries of 3ZrO2 + 4Al + xSi with x = 1.5, 3.0, and 6.0. With the addition of PTFE at 3 wt% of the powder mixture, self-sustaining combustion was established upon ignition. The effect of gas-phase diffusion transport induced by PTFE on the SHS process was confirmed. The composites synthesized from powder compacts of x = 1.5 and 3.0 were composed of ZrSi, ZrSi2, ZrC, and Al2O3. Formation of ZrSi2–Al2O3 composites with a trivial amount of ZrC was obtained from the Si-rich sample of x = 6.0. The microstructure of as-synthesized products exhibits a granular morphology and constituted particles have a size range of 1–2 μm.

Structural-phase state and tribological properties of the foamed self-fluxable alloy PG-10N-01 modified by the borated material

Problem. The paper presents the results of a study of the microstructure, phase composition and wear resistance of deposited coatings based on the PG-10N-01 alloy modified with the developed composite material containing titanium diboride, nickel boride, titanium oxide and iron. Goal. The aim of this work is to develop a composite material (CM) based on the powder material of the Ni-Cr-B-Si system, modified by a composite material (microns) obtained using a SHS process containing titanium borides and other elements for hardening machine parts subjected to abrasive wear. Methodology. To achieve this goal, it is necessary to develop a technology for obtaining microns and conduct studies of the structure, phase composition and abrasive wear resistance of deposited coatings from CM based on the Ni-Cr-B-Si system material modified by a composite material with elements containing boron. Results. The functional features of multi-functional road panels of pavement are revealed and their scheme on the roadway is presented. The principle of operation of the road as a unified system of multifunctional road surface panels has been researched. The scheme of implementation of road marking and automatic control of road traffic is presented. Originality. To increase the abrasive wear resistance of the deposited coatings based on the self-fluxing alloy PG-10N-01, it is proposed to use a modifying composite material containing titanium and chromium borides obtained using the SHS process. Practical value. To increase the abrasive resistance of machine parts, a charge composition has been developed to obtain a composite wear-resistant material using the SHS process. This composite material when modifying the surfaced coating with PG-10N-01 alloy increases its abrasive resistance by 1.7 times.

Reaction mechanism in SiO2-MnO2-Fe-Al system for producing ferrosilicomanganese powder

In this research, the ferrosilicomanganese powder was synthesized via mechanical alloying and SHS methods. Silicon oxide, manganese oxide, iron and aluminum powders were used as starting materials. SHS process was initiated by oxyacetylene flame. The activated and inactivated powder mixtures were used for producing ferrosilicomanganese grade 26%Si-53%Mn-21%Fe. The powder mixtures were characterized by X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Thermodynamic analysis showed that aluminothermic reduction of MnO2 is more thermodynamically favored as compared with aluminothermic reduction of SiO2. Adiabatic temperature of MnO2 and SiO2 reduction by Al was calculated about 2946 K. It was found that no reaction took place during mechanical alloying. After annealing and SHS processes, first MnO2, then SiO2 oxides were reduced by Al and ferrosilicomanganese and Al2O3 phases were produced. Due to the high adiabatic temperature, all products were formed in liquid state, leading to produce sintered ferrosilicomanganese and isolated Al2O3 particles.

Research of the foil production for the SHS process

Self-propagating high-temperature synthesis, discovered by Soviet scientists A.G. Merzhanov, I.P. Borovinskaya and V.M. Shkiro is a process with significant scientific and technological potential. It is used in industries to produce goods that have properties that cannot be reproduced by other methods. Self-propagating high-temperature synthesis may be used to obtain products of different geometric parameters and functional properties. The paper presents the results of studies on the production of a foil from Ni–Al powders for the subsequent implementation of the self-propagating high-temperature synthesis. In preliminary experiments, the properties of the initial aluminum and nickel powders were determined. Based on the results of the experiments, an assumption was made about the possibility of their use for foil production. The foil can be used for local heating of third-party products. It was proposed to obtain foil in two ways. The first method involves the powders mixture rolling in specialized powder rolling mills. The second method provides preliminary pressing of workpieces and their subsequent rolling. The study showed the rationality of the second method application. The initiation of the self-propagating high-temperature synthesis process was next performed. The most rational way to initiate the combustion process has been proposed. The analysis of the compositions of the reaction products was made.

Precision measurement of the velocity of propagation SHS wave by the method of chrono-topographical analysis

The paper presents the capabilities of the chrono-topographical analysis method for studying the discrete nature of the propagation of the SHS process on the scale of the combustion source and the reaction cell. Using the approach of chrono-topographic analysis, thermal imaging studies of the microheterogeneous combustion mode in the Ni-Al system were carried out. The regularities of the dynamics of individual foci in the SHS wave are revealed. Using chronographic maps of the SHS process, it is shown that there are two types of foci in the combustion wave, which differ in the nature of the propagation dynamics. On the scale of the reaction cells in the experiment, the relationship of the combustion dynamics with the moments of the formation of new reaction sites was studied. According to the results, it was concluded that an increase in the heat deficit in microheterogeneous combustion regimes leads to an i ncrease in the dispersion of the resulting product. This work was supported by the Russian Foundation for Basic Research in research projects No. 18-08-01475, 18-08-01152, as well as grant No. 13-01-20 / 28 "Leading Scientific School of Yugra State University".

Thermal imaging complex with tracking function for joint research of microheterogeneous processes and macrokinetics of SHS phenomenon

The paper presents the features of the method of chrono-topographical analysis of high-resolution thermal imaging data. Robotic foundations of the organization of a thermal imaging complex with a tracking function and the formation of a single chronographic map of the SHS phenomenon based on the results of temperature observations in several areas are described. It is shown that with the same measurement error of the propagation velocity of a SHS wave, a complex with a tracking function has a greater information power than a thermal imaging system with a single observation area. The approbation of the measuring complex during the investigation of SHS in the model Ni-Al system was performed. A joint analysis of heterogeneous processes revealed a similarity in the character of the propagation of combustion centers along the SHS wave front and the motion of the front itself. Based on the chronographic maps of the SHS process, it was found that there were two types of foci in the reaction wave, which differed in the dynamics of the boundary propagation along the front.

The wear resistance increasing of the deposited coatings of the Ni-Cr-B-Si system by modifying them with composite materials synthesized using the SHS process (Self-propagating high-temperature synthesis)

ABSTRACT To solve the problem of creating effective wear-resistant coatings for machine parts, studies have been carried out on the possibility of using composite materials obtained using the SHS-process as a modifier for the Ni-Cr-B-Si powder material. A composite material based on a self-fluxing PG-10H-01 alloy modified with a composite material obtained using a SHS-process containing carbide and titanium diboride, iron carbide was developed. The optimal composition of the modified composite material based on the PG-10N-01 alloy for electric arc overlaying welding was determined.

Reproducibility of a heterophase structure emergence effect when changing the ignition temperature of SHS in a layered nanosized nonstoichiometric Ti-Al system

The simulation results of SHS process in a package of alternating nanoscale layers of the crystal lattices of Ti and Al atoms for two systems with various numbers of atoms and nonstoichiometric ratios are given. For simulation the LAMMPS package supporting parallel computations and the interatomic interaction potential in the “embedded atom” model (EAM) have been used. For two systems with various numbers of atoms and nonstoichiometric ratios the sets of temperature and density profiles along the layers of the structure at successive instants of time (up to 16 ns) have been obtained. For a system with 453974 atoms and a nonstoichiometric ratio of 1.23 the heterostructure emergence with an alternation of intermetallic phases when changing the SHS “ignition” temperature has been reproduced.

The application of self-propagating hightemperature synthesis to obtain a protective-strengthening alumina-silica coatings

This article shows the possibility of using the method of self-propagating high-temperature synthesis to obtain protective and hardening coatings for the lining of various thermal installations. The development of compositions of ceramic masses for the production of SHS coatings was carried out on the basis of aluminum powder, clay raw materials, exhausting and fluxing components as well as mineralizing additives. The prepared suspension including pre-prepared and thoroughly mixed raw materials was applied with a brush or a spray gun onto the previously cleaned and moistened surface of an aluminosilicate refractory. The firing of the coating was carried out in accordance with the mode of removing the thermal unit at the operating temperature. The temperature of the initiation of the SHS process, previously established using differential thermal analysis, was in the range of 570–720 °C and depended on the chemical composition of the charge. It has been established that the presence of crystalline phases of silica, corundum, hematite and a number of solid solutions (mainly calcium and sodium aluminosilicates) in the coating structure provides the necessary combination of the thermomechanical and thermophysical characteristics of the coatings. On the basis of the conducted research, the expediency of applying the technology of self-propagating high-temperature synthesis for the production of protective and hardening coatings on the lining of thermal units is demonstrated, which is confirmed by industrial tests in the conditions of the Minsk Ceramic Factory OJSC «Keramin».

Application of SHS in the Manufacture of (NiAl/Ni3Al)/TiB2 Composite

The aim of this study was to demonstrate the advantages and the method of application of the SHS process in the manufacture of (NiAl/Ni3Al)/TiB2 composites. A comparison was made between sinters manufactured by FAST/SPS using two different routes to process the substrates, which formed the composite matrix. The evaluation criteria were based on measurements of selected physical, mechanical, and tribological properties, and on microstructure examinations. The evaluation has indicated a preferable method for the manufacture of composites, where the SHS reaction takes place during compaction of the powder mixture. This produces a sinter characterized not only by the high degree of sintering, and high values of the Young’s modulus and HV1 hardness, but also by the satisfactory resistance to tribological wear. Additionally, the use of this process saves energy and reduces product-making cost, owing to a less expensive technique of making individual substrates.

Chrono-topographical analysis of the laws of the microheterogeneous combustion mode for the production of powders by the SHS method

The paper presents the capabilities of the chrono-topographical analysis method for studying the discrete nature of the propagation of the SHS process on the scale of the combustion focy and the reaction cell. Using the approach of chrono-topographic analysis, thermal imaging studies of the microheterogeneous mode of combustion in the Ni-Al system were carried out. The regularities of the dynamics of individual foci in the SHS wave are revealed. Using chronographic maps of the SHS process, it is shown that there are two types of foci in the combustion wave, which differ in the nature of the propagation dynamics. On the scale of the reaction cells, the experiment investigated the relationship of the combustion dynamics with the moments of the formation of new reaction sites. According to the results, it was concluded that an increase in the heat deficit in microheterogeneous combustion regimes leads to an increase in the dispersion of the resulting product. The work was supported by the Russian Foundation for Basic Research in research projects no. 18-08-01475, 18-08-01152, as well as grant no. 13-01-20/28 “Leading Scientific School of Ugra State University”.

Thermally Coupled SHS Process in a Hybrid System

Thermally Coupled SHS Process in a Hybrid System

Ultra-fast fabrication of bulk ZrNiSn thermoelectric material through self-propagating high-temperature synthesis combined with in-situ quick pressing

The conventional fabrication of bulk thermoelectric materials usually involves time and energy consuming steps including melting, annealing and sintering et al, which restricts the large-scale application. Herein, high thermoelectric performance ZrNiSn bulks were synthesized by one step self-propagating high-temperature synthesis combining with in-situ quick pressing (SHS-QP). The correlation among SHS process, QP process and the critical pressure, is systematically investigated. The reduced grain size due to non-equilibrium feature of SHS-QP leads to a significant reduction in the thermal conductivity and a high figure of merit ZT ~ 0.7.

OBTAINING OF FERROSILICOCHROMIUM POWDER ALLOY BY SILICOTHERMIC REDUCTION AND STUDY OF THE MECHANISM OF THIS PROCESS


 
 
 
 The process of obtaining a powder ferrosilicochromic alloy by the method of silicothermic reduction of local chromites and slags of copper smelters was investigated. The mechanism of this process has been studied. It is established that the best results are obtained in the case of slag / chromite ratio = 1: 1, when an alloy with microdispersed structure and high strength is obtained. The optimum composition of the resulting alloy is as follows: 35,1% Fe; 36,35% Si and 28,53% Cr, with a metal yield of 98,4%. The obtained alloy powder can be used as an acidified and alloying additive to chromium- and silicon-containing stainless composite materials. The aspects of the process for obtaining FeSiCr alloy have been developed. The maximum temperature (Tc) and the linear propagation velocity of the combustion wave (Uv) are determined graphically. The mechanism of the formation of FeSiCr in the SHS process is explained.
 
 
 

Combustion Synthesis of Chromium Nitrides

This paper explores different modes of synthesis by combustion of chromium-nitrogen and ferrochromium-nitrogen alloys. The SH-synthesis of chromium nitrides and ferrochromium nitrides was performed. Regular patterns in layer-by-layer and surface modes of Cr combustion in nitrogen were investigated. The mechanism of non-stationary combustion during the synthesis of chromium was investigated. Regular patterns of chromium and ferrochromium combustion in the cocurrent filtration mode were analyzed, and the possibility to intensify the SHS process using the pressure filtration principle was assessed. The process of chromium powder combustion in the cocurrent flow of nitrogen-containing gas in the range of specific flow rates from 20 cm3/s·cm2 was investigated. Pressure filtration intensifies the process of combustion wave propagation in the Cr–N2 system. Here, the combustion rate increases while the degree of nitridation decreases. We discovered superadiabatic heating modes when the reaction zone was blown with pure nitrogen and a nitrogen-argon mixture. The tempering mode that was realized during pressure filtration allows for the uptake of high-temperature single-phase non-stoichiometric phases of Cr2N.

PRECISION MEASUREMENT OF THE VELOCITY OF PROPAGATION SHS WAVE BY THE METHOD OF CHRONO-TOPOGRAPHICAL ANALYSIS

The paper describes a method for detecting reaction cells with a given depth of response on thermal images. A technique has been developed for the formation of chronographic and topographic maps of the process from the cells that make up the combustion front. It is shown that the integral chronographic map allows us to identify the ergodicity of the SHS process and reduce by 1-2 orders of magnitude the size of the confidence interval in the estimated propagation velocity of the combustion front. A method is proposed for measuring the propagation velocity of the SHS process, which takes into account the deviation in the orientation of the regular grid of the matrix sensor of the chamber from the normal to the combustion front. The method combines the analysis of chronographic and topographic maps and integrates two approaches to determining the direction of the normal: the analysis of spatial data of thermal images; control of the delay time of appearance of the reaction front in different normal sections. The estimation of the error of the method was performed in the course of experimental studies of the SHS phenomenon in the Ni-Al system. It is shown that for high-resolution thermal imaging data (5.8 μm and 2 ms) with a sensor size of 1 MP, the error is 0.05 %, and using higher-dimensional sensors or a tracking thermal control, you can achieve a value of 0.0005 %.

A comparative study on the synthesis of oxide-free ZrB2-xZrC composites

A comparative study was done on the synthesis of oxide free ZrB2-xZrC (x = 20 and 30 wt%) through MASHS and MASPS process in the Mg/ZrO2/B2O3/C system. The effect of Mg, B2O3 on the efficiency of synthesis process was examined. In MASHS route, the addition of excessive amounts of Mg and B2O3 did not cause complete reduction of ZrO2 even if primary mixture was activated by mechanical alloying before SHS process. It was also found that mere addition of Mg was not efficacious in synthesis of pure composites in MASPS. However, when extra B2O3 was added to the primary mixture, peaks of ZrO2 were not detected in the synthesized powders when MASPS was applied. The reaction mechanism was also studied.

Graphene‐Like Carbon Nanostructures From Combustion Synthesis

Combustion synthesis (CS) (self‐propagating high‐temperature synthesis [SHS]) is a well‐known method of nanomaterials production. Among its advantages one may point out the remarkable number of materials possible to design. It starts from a mixture of a strong reducer and an oxidant and leads to a variety of materials (also metastable). The process is carried out under high pressure (up to 5 MPa) in a reaction chamber and on average after initiation by ohmic heating takes less than a few seconds. Being self‐sustainable it is environmentally friendly and favorable from the energetic point of view. The results of exploratory research on the autothermal synthesis of few‐layered graphite via a CS are presented. It has been shown before that different carbon‐related precursors can be directly converted into novel nanocarbons using strong reducers and the CS approach. In the current work such research is extended toward direct thermic reduction of standard calcium carbonate into few‐layered graphene (FLG). As the oxidizer one may use a variety of minerals: dolomite siderite and limestone. Moreover the following reactant systems have been tested: Si/PTFE/NaCl and Si/CFx in order to obtain graphene flakes and SiC nanowires. To better characterize the product, XRD analysis and Raman spectroscopy might be used. The SHS process mechanism (thermodynamics kinetics of wave propagation) and in situ diagnostics optimization and control are also discussed. Finally, the presented approach is currently under further investigation with preliminary results for the GO/Ti reagent system. It can be additionally extended by a qualitative fractal analysis of the obtained nanomaterials.

Study of the formation of the phase composition and structure of magnesium-aluminate spinel obtained by the SHS method

Magnesium-aluminate spinel was obtained by self-propagating high-temperature synthesis. Magnesium and aluminum oxides were used as initial components, and aluminum (ASD-4) with additives of amorphous boron was used as fuel. The structure and phase composition of the initial substances and reaction products were studied by means of X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. The synthesis products are shown to contain MgAl2O4 as a main phase and a small amount of α-Al2O3 corundum as an impurity. Partial substitution of Mg2+ by Co2+ and of Al3+ by Cr3+ leads to a shift of X-ray diffraction peaks towards smaller angles, increasing a parameter of the crystal lattice of spinel a, which indicates the formation of solid substitutional solutions. The colour of spinels becomes bright-blue and pink, respectively. A small amount of boron used as energetic additive forms boron oxide, low-melting borates, and eutectics in the MgO-B2O3, CoO-B2O3, Al2O3-B2O3 systems during combustion, which leads to the appearance of a liquid phase and the formation of skeletal crystals with the size of 1÷10 μm during the high-speed SHS process.