Self-propagating High-temperature Synthesis Technology Research Articles

Study of the effect of the morphology of initial powders on the structural and dimensional characteristics of SiC-based porous ceramic materials

The realization of the necessary energy-efficient technological solutions for the production of highly porous SiC-ceramic materials requires appropriate research. The results of developing energy-efficient one-step methods for the synthesis of porous SiC-based ceramics and studying the characteristics of the obtained ceramics are presented. The effect of the morphology of initial powders on the synthesized product is considered. Ultrafine silicon carbide powders of two types, identical in characteristic particle size, but quite different in the surface morphology, were used as fillers in the synthesis of experimental samples of porous ceramics. The first one was obtained by the traditional furnace method (SiCf), the second one was synthesized by the technology of self-propagating high-temperature synthesis (SiCshs). It is shown that the particle morphology of initial powder components determines the structural parameters and characteristics of synthesized porous ceramics. The pore space parameters (average pore size, specific surface area, equivalent hydraulic diameter, permeability, etc.) can vary significantly. Porous ceramic materials synthesized on the basis of SiCf have an open porosity of 47%, high liquid permeability (up to 2 mDarcy), overwhelming dominance of α-SiC phase, and a narrow pore distribution with an average pore size of about 1 μm. High open porosity (more than 58 %), highly developed nanostructured pore space surface with an area of more than 12 m2/g, and wider pore size distribution (average pore size — 140 nm) are observed in porous ceramic materials based on SiCshs. The obtained results can be used to improve energy-efficient synthesis technologies and methods for predicting the properties of highly porous SiC-based ceramic materials. This will make it possible to create highly porous SiC ceramics within a priory predicted limits of effective applicability for the processes of ultrafiltration or catalysis.

САМОРАСПРОСТРАНЯЮЩИЙСЯ ВЫСОКОТЕМПЕРАТУРНЫЙ СИНТЕЗ СИЛИЦИДА ТИТАНА В СИСТЕМЕ «КРЕМНИЙ-ГАЛОГЕНИД ТИТАНА-АЗИД НАТРИЯ»

The objective is to study the possibility of ob-taining titanium silicide using the azide technology of self-propagating high-temperature synthesis (SHS-Az) in silicon-titanium halide-sodium azide system.
 The task to which the paper is devoted is to find the optimal composition of the charge, which combus-tion gives the opportunity to obtain titanium halide by SHS-Az method.
 Research methods: the study of the titanium sil-icide synthesis in powder is carried out in the mode of solid-flame combustion in SHS-Az laboratory reactor. The synthesized powders are subjected to studies al-lowing to define the phase composition and structure. The studies are carried out using a diffractometer and a scanning electron microscope. 
 The novelty of the work is in synthesizing tita-nium silicide not only by a new method in the mode of high-temperature combustion of the heterogeneous silicon-titanium halide-sodium azide system, but also by obtaining a powder with close values to the range of nanoparticles. 
 Study results of obtaining titanium silicide by SHS-Az method from the heterogeneous silicon-titanium halide-sodium azide system show that the target product is a finely dispersed mixture of particles of equal shape but of different phase composition: Ti5Si3, TiSi2, TiN, Si, Ti. The average particle size is equal to 150-200 nm. 
 Conclusions: it is found that Ti5Si3 and TiSi2 ti-tanium silicides can be obtained in the combustion mode by SHS-Az method from silicon-titanium halide-sodium azide system.

Исследование структуры и свойств металломатричных композиционных материалов, полученных методом прямого лазерного выращивания

Due to mechanical properties, Inconel family alloys are proven to be functional materials that are used at elevated temperatures in chemically aggressive environments and under high loads. Development of additive technologies has revealed a potential of these alloys as an initial powder raw material for additive manufacturing machines. In this work, the application of metal matrix composite materials in a direct laser growing technology is studied. The technology of self-propagating high-temperature synthesis is used to manufacture the composite material. The study results show that the application of metal matrix materials in the technology of direct laser growing allows one to increase wettability of ceramic particles by a matrix metal. As a result, the quality of particle-matrix borders is improved, the porosity is decreased, and the uniformity of the distribution of particles in the matrix is increased. The structure of the obtained materials is represented by Inconel 625 matrix alloy and inclusions of TiB2 ceramics. The average size of the ceramic particles is less than 300 nm. It is shown that adding to Inconel 625 powder of a composite metal matrix SHS powder of NiTi-TiB2 in an amount of 5 wt% leads to an increase in the microhardness of the material by 1.5 times relative to the materials obtained from pure Inconel 625. At the same time, there is an increase in the ultimate strength of the materials up to 920 MPa and a decrease in the ductility by 15% relative to the samples made of pure Inconel 625 alloy.

ВЛИЯНИЕ ЭЛЕМЕНТНОГО ПОРОШКОВОГО СЫРЬЯ НА ФОРМИРОВАНИЕ ПОРИСТОГО КАРКАСА МАХ-ФАЗЫ Ti3AlC2 ПРИ ПОЛУЧЕНИИ МЕТОДОМ СВС

The ternary carbide compound Ti3AlC2 belongs to the so-called MAX-phases – a new type of ceramic materials with unique properties. A simple energy-saving method of self-propagating high-temperature synthesis (SHS) based on combustion is one of the promising methods for the production of this MAX-phase. The application of the SHS technology is to produce a Ti3AlC2 MAX-phase porous frame with the homogeneous porous structure without such defects as large pores, laminations, and cracks is of great interest. The paper investigates the possibility of producing such a porous frame with the maximum content of the Ti3AlC2 MAX-phase using powders of Ti, Al, and C elements of various grades different in particle sizes and carbon forms (soot or graphite) as initial components. Porous frame samples were produced by the open-air burning of pressed briquettes of charge of the initial powders of the selected grades without applying external pressure. The authors studied the macro- and microstructure of the obtained samples, their density, and phase composition. The study shows that using the finest titanium and carbon powders leads to the excessively active combustion with gas evolution and the synthesis of the defective porous samples with the charge briquette shape distortion, large pores, laminations, and cracks. Besides the titanium carbide by-phase, the highest values for the MAX-phase amount in the SHS-product were obtained using the titanium powder of the largest-size fraction together with the graphite powder, rather than soot. The excess aluminum powder addition to the stoichiometric ratio to the initial charge leads to an increase in the MAX-phase amount in the SHS product, compensating for the loss of aluminum due to evaporation. An increase in the sample volume (scale factor) also leads to an increase in the MAX-phase amount in the SHS product due to the slower cooling of the product after the reaction.

From the history of nitrided ferroalloys

The article considers research on the history of nitrided ferroalloys appearance and development of technologies for nitrogen-containing steels and ligatures. The most important advantages of nitrogen as an alloying element are its availability and almost unlimited reserves in nature. The technology of nitrogen extraction does not cause any harm to the environment and is not accompanied by the formation of waste. New technologies of nitrided ferroalloys and new compositions of nitrogen-containing ligatures emerged as a response to the creation of new grades of nitrogen-alloyed steels. At the same time, researchers in Europe, the United States, and the Soviet Union made the greatest contribution to the development of nitrided steel and ferroalloys technology. Nitrided ferrochrome emerged from the need for alloying stainless steels of various classes. Nitrided ferrovanadium was created for microalloying high-strength low-alloy steels. For nitrogen alloying of transformer steel, an alloying material based on silicon nitride was developed. Nitrogen-containing compositions based on manganese are universal alloying materials for a wide range of applications. Technologies of nitrided ferroalloys developed in the direction of creating compositions with the maximum nitrogen content with minimal consumption of material resources. Currently, technologies for direct introduction of nitrogen gas into liquid metal during out-of-furnace processing are being successfully developed. Alloying with its solid carriers remains a universal method for smelting nitrogen-containing steels. Nitrogen in nature occurs exclusively in a gaseous form, so for introduction to steel, it is necessary to fix it in the composition of a solid substance. At the same time, such a nitrogen-containing material must be compatible with the steel melt and technological in use. This problem is completely solved by the technology of self-propagating high-temperature synthesis (SHS), which allows obtaining composite ferroalloys based on nitrides, with properties that are unattainable for the furnace process.

Efficiency of the continuous editing process grinding circles

Conducted experimental studies have shown the high efficiency of using continuous dressing and its varieties - cleaning during grinding. The conditions that ensure the minimum wear of the ruling and working circles for various processing conditions are determined. It is established that the minimum wear of the circles takes place at a relative speed of the working and ruling circles, close to zero. At the same time, the productivity of the dressing process and the processing efficiency are practically not reduced. It is shown that the greatest efficiency of continuous dressing takes place when grinding materials that are prone to adhesive setting with the components of the abrasive wheel. Recommendations are given on choosing the ligament and firmness of the ruling circles. The mechanisms of wear of the circles at various slip coefficients are established. Ensuring the angle of intersection between the circles, as a rule, increases the efficiency of the process, in addition, reduces vibration in the editing system. An increase in the angle of crossing over 10° increases the wear of the circles. The use of continuous cleaning reduces wear on the working circle and does not distort its macro profile. It was found that the ruling circles with an abrasive, which was created using the technology of self-propagating high-temperature synthesis (SHS), have greater wear resistance than circles of a similar characteristic from elbor, but inferior to diamond.

Utilization of dispersed waste of ferroalloy production on the basis of metallurgical SHS-process

A review of methods for processing dispersed waste from f loy production was performed. In ferroalloy plants there is a problem of formation and accumulation of cyclone dust (the catch product from crushing – CPC), formed during the grinding and fractionation of ferroalloys. The drawbacks of the known methods for the disposal of such dust are shown. The authors have investigated the possibility of obtaining commercial nitrided ligatures from CPC’s and substandard ferroalloy fines using the technology of self-propagating high-temperature synthesis (SHS). On the basis of the proposed “metallurgical” SHS method, a technology has been developed and the possibility of largescale production of nitrided ferrosilicon, ferrovanadium, ferrochrome and other materials has been shown, which has demand on the world market. Synthesized SHS materials are superior in quality to nitrided ferroalloys obtained by conventional furnace method, in particular, they have a lower content of oxygen, hydrogen and other impurities, and differ in better physical and mechanical properties: density, porosity, strength, and others. Based on the method of metallurgical SHS, the production of nitrided ferroalloys and composite ligatures with the possibility of processing up to 5000 ton per year of cyclone dust of ferrosilicon and other alloys was established in Russia, Magnitogorsk on the production base of scientific and technical production company LLC “STPF “Etalon”. A new approach to the practical implementation of the SHS method is developed and the possibility of using synthesis products in metallurgy is shown. The main application of these products is the use of alloying additives in smelting of a wide range of steels and alloys: transformer, rail, stainless, high-strength structural, and others. Another popular consumer of composite “metallurgical” SHS materials is the refractory production. Modification of traditional refractories used in smelting of cast iron, steel and non-ferrous metals with new composite SHS materials based on nitrides, borides, carbides and other refractory compounds can significantly increase the service life and reduce the expenses for refractories.

High temperature synthesis of copper coatings made from a thin film layered composition “CuO -B - Glass”

The study is aimed at developing methods for producing thin-layer cermet coatings. Such coatings are promising for use in flat heating elements, thermal protective coatings. A method for producing electrically conductive coatings based on copper and borosilicate glass using the technology of self-propagating high-temperature synthesis is proposed. The wave synthesis and thermal explosion in the CuO – B – glass thin-layer system were studied using experimental methods and developed mathematical models. The effect of the reaction layer thickness and inert additive on the kinetics of the process and characteristics of final products was studied. Numerical calculations were performed to study the dynamics of the process. The thermophysical and kinetic parameters that determine the synthesis in the CuO – B – glass system are found using the inverse method.

Combustion wave in a two-layer solid fuel system

We consider the model describing propagation of a combustion wave in a system of two layers of different exothermic reacting materials under conditions of thermal contact between them through a common surface. This system is directly related to synthesis of advanced materials via the Self-propagating High temperature Synthesis technology when one of the reactants serves as a heat source (donor layer) for the other reacting material (acceptor layer) and facilitates the chemical reaction in the latter. The reaction sheet approximation is used and the parametric study of the boundaries of existence and characteristics of combustion waves in the system of layers is undertaken. The parameters of the process are identified which allow to achieve significantly superadiabatic peak temperatures of combustion in the acceptor layer.

The Influence of Aluminum Nitride Nanoparticles on the Structure, Phase Composition, and Properties of TiB/Ti-Based Materials Obtained by SHS Extrusion

Compact ceramic long-dimensional materials based on titanium monoboride modified with aluminum nitride dopants (3 and 5 wt %) were obtained via SHS extrusion. Titanium monoboride was produced using azide technology of self-propagating high-temperature synthesis (SHS-Az). Small dopants of nanoscaled aluminum nitride powder exert a strong influence on the phase composition, structure, and physicomechanical properties of samples prepared by SHS extrusion. Scanning electron microscopy data reveal the refinement of the main titanium monoboride phase grains in modified samples. The most pronounced refinement of titanium monoboride grains is observed as the AlN nanopowder content is increased to 5 wt %. The combustion characteristics (temperature and combustion rate) are measured in an installation simulating the real SHS extrusion conditions. It is established that AlN at its content of 3 wt % in the initial charge interacts with the titanium matrix during combustion with the formation of the Ti2AlN and Ti4AlN3 MAX phases. AlN at a concentration of 5 wt % undergoes decomposition during combustion with release of titanium nitrides and pure aluminum, as well as the TiB, TiB2 and Ti2AlN phases. Modified compact ceramic materials are shown to exhibit higher microhardness in comparison with samples without using nanomodified AlN dopants.

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».

Mobile Installation of Water Treatment in the Aftermath of Emergency Situations

A new technological scheme of water treatment is proposed, combining reagent methods with hydrodynamic activation of coagulation, flocculation and sorption processes, with baromembrane methods of purification. A method of organizing the process of filtering water after treatment with reagents using a tangential filter made using self-propagating high-temperature synthesis technology is proposed. Jet agitators – ejectors were developed and investigated, the efficiency of using ejectors as devices for dosing and mixing of reagents with treated water was shown. An experimental model of the installation was created and it was successfully tested on model as well as real polluted waters. Purified water obtained on an experimental sample of the installation fully complies with the hygienic requirements and standards established for drinking water.

Application of SHS auxiliary reaction of titanium carbide for introduction of AlN nanoparticles into aluminum melt

For ex-situ introduction of AlN nanopowder, obtained by azide technology of self-propagating high-temperature synthesis (SHS) or combustion synthesis in the mixture with the flux cryolite: (AlN-35%Na3AlF6), into the aluminum melt, an exothermic master powder composite (EMPC) of different composition (AlN-35%Na3AlF6) – (Ti + C) – Na2TiF6 was first used, leading to the realization of in-situ process of SHS of reinforcing phase TiC in the combustion mode in the aluminum melt. The conditions were found for reliable ignition of the EMPC and fabrication of cast hybrid nanocomposites Al-Al-TiC, including the calculated composition Al-7.7%AlN-19%TiC with an increased content of AlN reinforcing phase.

Method of Differential Chronoscopy of Unstable Regimes of Combustion Wave Distribution

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SHS Technology for Composite Ferroalloys. 1. Metallurgical SHS: Nitrides of Ferrovanadium and Ferrochromium

The development of specialized self-propagating high-temperature synthesis (SHS) for complex ferroalloys used in steel smelting and in blast-furnace technology is discussed. To that end, a new approach to the SHS process has been conceived: the metallurgical SHS process, in which the basic raw material consists of various metallurgical alloys including dusty waste from ferroalloy production. In that case, synthesis involves exchange exothermal reactions. The product is a composite based on the initial inorganic compounds; the binder is iron or an iron alloy. Depending on the state of the initial reagents, the metallurgical SHS processes may be gas-free, gas-absorbing, or gas-liberating. For each case, the combustion conditions will be very different. Thermal matching may be used in organizing the metallurgical SHS process in systems that are not strongly exothermal. The self-propagating high-temperature synthesis of nitrided ferrovanadium and ferrochrome is investigated. It is shown that the phase composition of the initial alloy strongly affects the combustion of ferrovanadium in nitrogen. In the nitriding of σ ferrovanadium, transformation of the intermetallide to an α solid solution is activated on reaching the phase-transition temperature (~1200°C). The composite structure of the nitriding products of ferrovanadium is formed under the influence of solid–liquid droplets consisting of molten iron and solid vanadium nitride. Solid-phase reaction of ferrochrome with nitrogen facilitates high degrees of nitriding. The combustion rate of ferrochrome on nitriding during coflow filtration, as in chromium, increases with increase in the nitrogen flow rate. The degree of nitriding of the ferrochrome in forced filtration (4.7–7.5% N) is much less than that in natural filtration (8.8–14.2% N).

Nanomaterials of SHS technology for tribological applications: A review

A review of results of applying the powder technology of self-propagating high-temperature synthesis (SHS) for obtaining various nanomaterials that can be used according to the tribotechnical indentation is given. First, these are low-cost nanopowders of sulfides, oxides, nitrides, carbides, borides, and metals which are suitable as solid lubricants and friction modifiers for liquid and plastic lubricating materials. Second, these are solid compact nanostructured ceramic and composite materials for the fabrication of tribotechnical construction. This type of nanomaterial can be fabricated both ex situ from SHS nanopowders by sintering or introduction into the melt both in situ in one stage from initial powders reagents by gasostatic SHS technology, forced SHS compaction, SHS casting, and SHS in the melt, which considerably simplifies and cheapens the production of such materials. Third, these are SHS materials for the deposition of nanostructured coatings of various thicknesses with a high wear resistance and low friction coefficients, such as nanostructured materials for surfacing and spraying, electrospark alloying electrodes, multicomponent targets for magnetron sputtering, cathodes for vacuum-arc evaporation, and nanodispersed fillers of electrochemical and chemical coatings.

Preparation of the highly dispersed powder of titanium carbonitride by SHS azide technology with previous partial nitriding

It is shown that the powder of very hard refractory titanium carbonitride (TiC0.5N0.5) is the basis of tungsten-free hard alloys which are prospective for application as inexpensive cutting tools. The finer the powder of titanium carbonitrideis, the moreenhanced properties of hard alloys, sintered from the powder, are. An opportunity to reduce the particle size of the titanium carbonitride powder obtained by energy-saving azide technology of self-propagating high-temperature synthesis at the cost of reducing the particle size of the initial titanium powderwas investigated. To ensure the safety of the grinding process of the initial metal titanium powder, it was offered to nitride a Ti powder partially into a TiN0.2 compound. Such partial nitriding was performed by the azidetechnology with lack of sodium azide (NaN3) as a nitriding reagent. After intensive grinding in the planetary ball mill, the TiN0.2 powder turned into a superfine powder with an ultrafine structure. This powder was capable of nitriding and carburizing in the azide technology with formation of superfine pure powder agglomerates which are composed of ultrafine and nano-particles of TiC0.5N0.5.

Development of SHS azide technology of silicon carbide nanopowder

The possibility of increasing the purity and yield of the SiC nanopowder using an intermediate synthesis of silicon nitride (Si3N4) by azide technology of self-propagating high-temperature synthesis based on the use of a powder of sodium azide (NaN3) as a nitriding reagent was investigated. As a result of combustion of the initial mixture of powders ‘19Si + 6NaN3 + (NH4)2SiF6 + 20’, a powdery product was obtained, consisting almost entirely of SiC (about 90%) with an admixture of Si3N4 and Si (about 5% each), and representing nanoparticles (80-150 nm) combined into agglomerates with the size up to 50 µm.

DEFECTS IN LARGE HOLLOW POROUS CYLINDRICAL FILTERS MADE BY SHS

The relevance of research is connected with the use of ceramic filters in biology and medicine for fine filtration of air and biological fluids abroad. Due to the unique combination of chemical and thermal resistance, high strength and thermal conductivity, ceramic filters are used to clean aggressive liquids, superheated high pressure steam and other gases. The dependence of burning rate on the relative density and granulometric composition of FeTiO 3 –Al–Si–SiO 2 –C powder mixtures is studied. The paper provides experimental results on the influence of initial charge compact density and composition on the quality of products obtained. The main types of defects appearing in the synthesis are identified. The causes of defects are found. Feedstock with particle sizes larger than specified values results in penetrations (cavities) occurring in the product. Their formation is caused by the increased liquid phase content in these regions due to decelerating reaction rate and rising temperature. Higher density results in transverse and longitudinal laminations in the product. Such laminations are formed under the pressure of gaseous products with the low gas permeability of the sample that declines as density increases. The technology of self-propagating high-temperature synthesis of large porous products is developed with the photographs of filtering elements presented: for the typical industrial gas burner GG-2, for superheated steam and demineralized water purification (filtering elements used in polyvinyl chloride process vessels at JSC «Sayanskkhimplast»), for iron removal from artesian water. Defect-free large porous products can be obtained with an optimal ratio of the sample grain size distribution and density, as well as reaction rate and heat removal rate.

Obtaining nanopowder pseudo-ligatures Cu–(SiC+Si3N4) for modification and reinforcement of aluminum alloys

The mechanical mixing and subsequent compaction of a powder mixture consisting of carrier powder (electrolytic copper (Cu) with particle size of 20–100 μm) with nanopowder modifier compound (powders of silicon carbide (SiC)—50–70%, silicon nitride (Si3N4)—20–30%, sodium hexafluoroaluminate (Na3AlF6)—10–20%) with particle size of 70–100 nm obtained by azide technology of self-propagating high-temperature synthesis (SHS) were investigated. The mixtures containing 2.5, 5, 10, 15% of the modifier were investigated. Mechanical mixing was carried out for 30–45 min at speed of 150 rpm in a Pulverizette-5 planetary mill. An analysis of mixing of the raw powder components was performed. Some physicotechnological properties of the obtained powder mixtures, such as particle size distribution, density, bulk weight, and flowability, are determined. The formation of briquettes—the nanopowder pseudo-ligatures from powder mixtures of composition Cu–(SiC + Si3N4) with different concentration of modifier—was carried out by cold pressing. Compacting of the received mixtures of powders was carried out in cylindrical mold using a PSU-50 hydraulic press under pressure of 85–310 MPa. The dependence of the relative density and porosity of the briquettes on the pressure of pressing is determined. The microstructures of pseudo-ligatures pressed at maximum pressure of pressing are presented. Briquettes—nanopowder pseudo-ligatures with diameter of 25 mm, height up to 2 mm, weight of 5 g, with relative density of 53–85% and porosity of 15–47%—intended for subsequent input to aluminum melt with the aim of inoculation are obtained.