High-temperature Synthesis Process Research Articles

Nanostructured Aluminum Matrix Composites of Al-10%TiC Obtained In Situ by the SHS Method in the Melt

The aim of this study was an investigation of the influence of technological parameters of the process of self-propagating high-temperature synthesis (SHS) on the formation of nanoparticles of titanium carbide from a mixture of powders of titanium and carbon in molten aluminum and on the properties of the obtained composite Al-10 wt. %TiC. The results show that the application of such techniques as the use of titanium powder of coarse fraction, the integrated flux of composition 30-35% NaCI, 52-57% KCI, 10-13% Na2SiF6 and adding aluminum powder to the initial charge can reduce the size of most of the synthesized particles of the carbide phase TiC to ultrafine sizes. At the same time, the replacement of 20% titanium metal powder in the charge with the titanium-containing salt Na2TiF6 makes it possible to synthesize nanoparticles of titanium carbide with size less than 0.1 μm in the composite Al-10%TiC. The produced SHS composite Al-10%TiC is characterized by a high level of physico-mechanical and tribological properties with good corrosion resistance. Reinforcement with ultrafine and nanosized particles of TiC enhances the strength characteristics of the composite Al-10%TiC by 2.5-2.9 times in comparison with pure aluminum, while the reinforcement with microsized particles of TiC (2-4 μm) only by 1.5-1.7 times; resistance to corrosion increases by 4-5 times.

Fabrication of Aluminum-Ceramic Composites with TiC-Ni Skeleton by SHS Pressing Method

One-stage technology of obtaining aluminum-ceramic skeleton composites by combining the processes of self-propagating high-temperature synthesis (SHS) of the porous skeleton and its infiltration under pressure with molten aluminum (method SHS-pressing) was considered. Experimental study of the effect of the pressure of infiltration on the distribution of the content of aluminum over the height and radius of the disk-shaped sample with SHS skeleton made of a cermet of TiC-Ni was performed. Mechanisms of the formation of structure and properties of the composite depending on the infiltration pressure were described.

Self-Propagating High-Temperature Synthesis of Composite Nanopowder AlN-BN from Systems "Sodium Azide – Halides of Aluminum and Boron"

The composite powder of AlN-BN is of interest from the point of view of the use for sintering the AlN-BN composite ceramics. The ceramics compared with AlN ceramics would have better thermal shock resistance, less britlleness, better machinability, good heat conductivity and tribological properties. Possibility of obtaining a composite powder of AlN-BN with the application of process of self-propagating high-temperature synthesis (SHS) from powder mixtures of NaN3 and precursors of aluminum and boron was investigated. Halide salts AlF3, Na3AlF6, KBF4 and NH4BF4 were used as the precursors. It was shown that these mixtures are capable of burning and obtaining agglomerated composite powders from nanosized (50-170 nm) particles.

Steel pipe-lined Fe–W<sub>2</sub>B-based composite coating by centrifugal-Self-propagating high-temperature synthesis process

Steel pipe-lined Fe–W<sub>2</sub>B-based composite coating by centrifugal-Self-propagating high-temperature synthesis process

Confined growth of Li4Ti5O12 nanoparticles in nitrogen-doped mesoporous graphene fibers for high-performance lithium-ion battery anodes

Nanomaterials with electrochemical activity are always suffering from aggregations, particularly during the high-temperature synthesis processes, which will lead to decreased energy-storage performance. Here, hierarchically structured lithium titanate/nitrogen-doped porous graphene fiber nanocomposites were synthesized by using confined growth of Li4Ti5O12 (LTO) nanoparticles in nitrogen-doped mesoporous graphene fibers (NPGF). NPGFs with uniform pore structure are used as templates for hosting LTO precursors, followed by high-temperature treatment at 800 °C under argon (Ar). LTO nanoparticles with size of several nanometers are successfully synthesized in the mesopores of NPGFs, forming nanostructured LTO/NPGF composite fibers. As an anode material for lithium-ion batteries, such nanocomposite architecture offers effective electron and ion transport, and robust structure. Such nanocomposites in the electrodes delivered a high reversible capacity (164 mAh·g–1 at 0.3 C), excellent rate capability (102 mAh·g–1 at 10 C), and long cycling stability.

Fabrication of aluminum–ceramic skeleton composites based on the Ti2AlC MAX phase by SHS compaction

A one-stage manufacturing technology of aluminum–ceramic skeleton composites by combining the processes of self-propagating high-temperature synthesis (SHS) of a porous skeleton formed by the MAX phase of the Ti2AlC composition and its impregnation by the aluminum melt under pressure (SHS compaction) is considered. A composition of the exothermic charge 2Ti + C + 22.5 wt % Al + 10 wt % TiH2, which provides the formation of a porous skeleton of the Ti2AlC phase without impurity phases by the SHS technology, is selected. It is shown that, when impregnating the hot SHS skeleton with aluminum, new phases are formed such as the MAX phase (Ti3AlC2), titanium carbide (TiC), and titanium aluminide (Al3Ti). However, the content of the basic MAX phase remains high, and the ceramic component of the material consists of Ti2AlC by 76%. When analyzing the microstructure, it is revealed that the composite has certain residual porosity after impregnation and cooling. The influence of the impregnation pressure (q = 22, 28, and 35 MPa) on the distribution of the aluminum content over the height and radius of the diametral sample section is investigated experimentally. It is shown that the nonuniform Al distribution over the sample bulk is caused by the nonuniform pressure and temperature fields, as well as the different compactibility of hot inner and colder outer sample parts. The degree of compaction of characteristic zones is leveled as the impregnation pressure increases, and the composition inhomogeneity over the sample bulk decreases. The difference in aluminum concentration over the sample bulk at q = 35 MPa does not exceed 5%. The SHS-compacted aluminum–ceramic skeleton composite based on the Ti2AlC MAX phase corresponds to high-strength Al-Zn–Mg–Cu aluminum alloys by the hardness level (HB ≈ 150 kg/mm2).

Fabrication of aluminum–ceramic skeleton composites based on the Ti2AlC MAX phase by SHS compaction

A one-stage manufacturing technology of aluminum-ceramic skeleton composites by combining the processes of self-propagating hightemperature synthesis (SHS) of a porous skeleton formed by the MAX phase of the Ti2AlC composition and its impregnation by the aluminum melt under the pressure (SHS compaction). A composition of the exothermic charge 2Ti + C + 22,5 wt % Al + 10 wt % TiH2, which provides the formation of a porous skeleton of the Ti2AlC phase without impurity phases by the SHS technology, is selected. It is shown that when impregnating the hot SHS skeleton with aluminum, new phases are formed such as the MAX phase (Ti3AlC2), titanium carbide (TiC), and titanium aluminide (Al3Ti). However, the content of the basic MAX phase remains high, and the ceramic component of the material consists of Ti2AlC by 76 %. When analyzing the microstructure, it is revealed that the composite has certain residual porosity after the impregnation and cooling. The influence of the impregnation pressure (q = 22, 28 and 35 MPa) on the distribution of the aluminum content over the height and radius of the diametral sample section is investigated experimentally. It is shown that the nonuniform Al distribution over the sample bulk is caused by the nonuniform pressure and temperature fields as well as different compactibility of hot inner and colder outer sample parts. The degree of compaction of characteristic zones is leveled as the impregnation pressure increases, and composition inhomogeneity over the sample bulk decreases. The difference of aluminum concentration over the sample bulk at q = 35 MPa does not exceed 5 %. By the hardness level (HB ≈ 150 kg/mm2), the SHS-compacted aluminum-ceramic skeleton composite based on the Ti2AlC MAX phase corresponds to high-strength Al–Zn–Mg–Cu aluminum alloys.

Applying FeAl coating on the low carbon steel substrate through self-propagation high temperature synthesis (SHS) process

Abstract In this research, a self-propagating high temperature synthesis method was applied for coating FeAl on the low carbon steel substrate. This technique is a combination of material fabrication with the coating process, simultaneously. Al and Fe were mixed regarding to have the stoichiometry of the reaction. The mixture was cold pressed at 150 MPa and was put just on the substrate at 950 °C in the air furnace without external pressure. The combustion synthesis occurred after 45–60 s and the coating was formed. Microstructure of synthesized powders and coatings was investigated by scanning electron microscopy equipped with EDS and X-ray diffraction, respectively. Wear resistance of coatings and substrate was measured by using a pin-on-disk tribometer. The results illustrated that high temperature of SHS reaction led to appropriate adherence of the coating and substrate. In addition, the tribological properties of coated specimens significantly improved. The results of the wear test demonstrated that the mass loss percentage of the substrate was almost 4 times more than that of coated specimen. The corrosion evaluations using potentiodynamic polarization test disclosed that the obtained coating had better performance than that of low carbon steel.

Evaluation of W-containing Sr1 −xBaxFe0.75W0.25O3–δ (x = 0, 0.5, 1) anode materials for solid oxide fuel cells

In this work, W-containing Sr1−xBaxFe0.75W0.25O3−δ (x=0, 0.5, 1) perovskite-related oxides have been for the first time evaluated in terms of their possible application as anode materials in solid oxide fuel cells. Crystal structure, thermal expansion coefficient, transport properties, oxygen content, chemical compatibility in relation to ceria-based electrolyte, and stability of the materials in reducing atmospheres have been studied. It was found that SrFe0.75W0.25O3−δ and Sr0.5Ba0.5Fe0.75W0.25O3−δ oxides show simple perovskite-type structure with cubic Pm-3m symmetry, while BaFe0.75W0.25O3−δ exhibits hexagonal P63/mmc structure. Small grains (~2μm) can be obtained for SrFe0.75W0.25O3−δ compound with very simple, high-temperature synthesis process in air. Large oxygen nonstoichiometry changes of Δδ≈0.36 were observed for SrFe0.75W0.25O3−δ oxide upon heating in 5vol.%H2 in argon. Seebeck coefficient and electrical conductivity measurements revealed that SrFe0.75W0.25O3−δ oxide exhibits p-type conductivity in air and n-type conductivity under reducing conditions. This oxide presents relatively good chemical compatibility in relation to Ce0.8Gd0.2O1.9 electrolyte, and chemical stability in 5vol.%H2 in argon up to at least 800°C. Electrochemical impedance spectroscopy studies for SrFe0.75W0.25O3−δ-based cells conducted in pure hydrogen and CH4 indicated the possibility of the application of SrFe0.75W0.25O3−δ as the anode material in SOFCs.

Hardening of Aluminum Alloys with Nano-Dispersed Inclusions during the Implementation of Energy-Saving Process of Self-Propagating High-Temperature Synthesis in Aluminum Melt

It was demonstrated that the application of self-propagating high-temperature synthesis as a low energy expenditure method to produce alloys of the Al-TiC system is of high priority. The process for the preparation of the charge and obtaining a composite alloywere described. The results of studies of electrical conductivity and mechanical properties of aluminum matrix composite alloys, modified with nanoparticles of titanium carbide TiC werepresented.Alloys with compositions: Al-10% TiC, Al7%Si + 10% TiC and Al9%Si + 10% TiC, as well as the original matrix materials: pure aluminum and Al9%Si werestudied. The index of plasticity was obtained by calculation. This calculated value showed that the experimental samples are small crystalline materials and nanomaterials. It was shown that the addition of nanoparticles of titanium carbide improves the mechanical properties of the initial alloy, without significantly reducing the electrical conductivity (no more than 30%).

The Effect of Rotational Speed on Steel Pipe Lined Fe-WB Based Composite Coating by Centrifugal-SHS Process

The Iron-Tungsten boride based composite was coated on the inner surface of steel pipes by centrifugal-self-propagating high-temperature synthesis (centrifugal-SHS) process. The precursors were prepared by a stoichiometric ratio of wolframite mineral (Fe (Mn)WO4), aluminum (Al) and boron oxide (B2O3). Phase composition and microstructure of composite coating were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). On this study, depending on the rotation speed, the highest rotation speed (2250 rpm) produced highest micro-hardness of the composite (1699 HV).

Fabrication of in situ Al2O3 reinforced nanostructure 304 stainless steel matrix composite by self-propagating high temperature synthesis process

Abstract 304 austenitic stainless steel reinforced by Al2O3 particles was prepared by microwave assisted self-propagating high temperature synthesis process using the Fe2O3Cr2O3NiOAlFe reaction system. Furthermore, effects of mechanical activation of the reactants and the addition of 21.2 wt.% extra Al to the chemical composition of the reactants on the chemical composition of the produced stainless steel was investigated. Atomic absorption spectroscopy analysis results indicated that by the addition of extra Al to the reactant mixture and using 30 minute mechanical activation, stainless steel containing 17.27 wt.% Cr and 7.73 wt.% Ni could be produced with its chemical composition very close to the chemical composition of 304 stainless steel. X-ray diffraction analysis showed that the stainless steel contains nanostructured austenite and ferrite phases. Also microstructural characterizations indicated that there is a uniform distribution of black particles in the steel matrix. Energy dispersive spectroscopy analysis showed that these particles are composed of Al and O elements while the matrix contains Fe, Cr and Ni elements. The presence of Al2O3 particles and nanostructure matrix improved the hardness and therefore the wear properties of the composite in comparison with the wrought 304 stainless steel plate.

Corrosion-Resistant High-Silicon Cast Iron for Chemical Engineering Components

A method is proposed for preparing corrosion-resistant high-silicon cast iron by processing fine waste from engineering enterprises in a self-propagating high-temperature synthesis process. Theoretical aspects for the SHS process and a practical procedure for implementing it are provided. Results of analyzing practical experiments are presented.

Mechanical activation process for self-propagation high-temperature synthesis of ceramic-based composites

In this study, the mechanical activation process of the Al–TiO2–H3BO3 thermite mixture was modeled and optimized before self-propagation high-temperature synthesis of Al2O3–TiB2 ceramic composite powders. For this purpose, response surface method in conjunction with full factorial design was conducted for evaluating the experiments and modeling the process. The milling speed and milling time were considered as the process input parameters. In addition, the intensity and temperature of the last exothermic peaks in DSC curves, which correspond to the occurrence of self-propagation high-temperature synthesis process, were chosen as the responses. Analysis of variance was employed for checking the accuracy of the developed models. Furthermore, the effects of milling speed and time on the responses were explored using the developed methods, in detail. The results showed that the models were significant and they predicted the responses accurately. Moreover, the milling time was obtained to be more effective parameter on the responses. The optimized condition for the mechanical activation was 340 rpm and of 17.63 h for milling speed and milling time, respectively.

Оптимизация аппаратурно-технологического оформления процессов высокотемпературного синтеза твердосплавных материалов с учетом неопределенности

Оптимизация аппаратурно-технологического оформления процессов высокотемпературного синтеза твердосплавных материалов с учетом неопределенности

Structural characterization and optical properties of dysprosium doped strontium calcium magnesium di-silicate phosphor by solid state reaction method

Dysprosium doped strontium calcium magnesium di-silicate phosphor namely: SrCaMgSi2O7:Dy3+ was prepared by the solid state reaction method. The crystal structure of the prepared phosphor was an akermanite type structure, which belongs to the tetragonal crystallography with space group P42‾1m. From field emission scanning electron microscopy (FESEM), agglomerations of particles were observed due to the high temperature synthesis process. The chemical composition of the sintered SrCaMgSi2O7:Dy3+ phosphor was confirmed by energy dispersive X-ray spectroscopy (EDX). Under the ultra-violet (UV) excitation, the characteristic emission of Dy3+ ions peaking at 478, 580 and 674nm, originating from the transitions of 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 in the 4f9 configuration of Dy3+. Commission International de I’Eclairage (CIE) color coordinates of SrCaMgSi2O7:Dy3+ are suitable as white light emitting phosphor. Decay graph indicate that this phosphor contains fast decay and slow decay process. The mechanoluminescence (ML) intensity of SrCaMgSi2O7:Dy3+ phosphor increases linearly with increasing impact velocity of the moving piston, which suggests that this phosphor can be used as sensors to detect the stress of an object. Thus the present investigation indicates that the piezo-electrically induced de-trapping model is responsible to produce ML in SrCaMgSi2O7:Dy3+ phosphor. The possible mechanism of white light emitting long lasting phosphor is also investigated.

Self-propagating high-temperature synthesis of finely dispersed titanium carbide phase of powder mixtures in aluminum melt

The process of self-propagating high-temperature synthesis (SHS) of titanium carbide particles in aluminum melt containing the mixture of titani- um and carbon powders with addition of chloride-containing flux, aluminum or halide salt (Na 2 TiF 6 ) powders in it has been investigated in produc- ing Al–10%TiC composite alloy. The use of the additives is shown to allow diminishing the size of synthesized TiС carbide phase particles to ultrafine (0,17–0,35 μm) and nanosized (less than 0,1 μm) levels.

Combustion Synthesis of TiN-BN Nanostructured Composite Powder with the Use of Sodium Azide and Precursors of Titanium and Boron

The composite powder of TiN-BN is of interest from the point of view of the use for sintering the TiN-BN composite ceramics, which compared with TiN ceramics would have less britlleness, better machinability and good tribological properties. Possibility of obtaining a composite powder of TiN-BN with the application of process of combustion synthesis (CS) or self-propagating high-temperature synthesis (SHS) from powder mixtures of sodium azide and halide salts KBF4, NH4BF4, (NH4)2TiF6 and Na2TiF6 as precursors of titanium and boron was investigated. It was shown that these mixtures are capable of burning and obtaining agglomerated composite powders. TiN-BN powder with an admixture of KF is formed only in combustion of

Studies of Ta, Al, and Carbon Sources on Combustion Synthesis of Alumina–Tantalum Carbide Composites

Alumina–tantalum carbide (Al2O3–TaC and Al2O3–Ta2C) composites were synthesized by incorporating aluminothermic reduction into a self-propagating combustion process. The test specimens adopted were composed of Ta2O5, Al, Al4C3, and carbon powders. Experimental evidence showed that the use of Al4C3 to provide Al and carbon decreased combustion exothermicity and hindered Ta2O5 from being fully reduced. In contrast, for the formation of Al2O3–TaC and Al2O3–Ta2C composites, Al4C3-free samples with molar ratios of Ta2O5:Al:C = 3:10:6 and 3:10:3, respectively, exhibited the highest combustion temperature and reaction rate in the self-propagating high-temperature synthesis process and yielded products with very few minor phases.

Microstructure and Adhesion of NiAl/Al and NiAl/Ni Coatings Formed by SHS Process

The objective of thiswork was to investigate the microstructure and adhesion of NiAl coating whichformed by self propagation high temperature synthesis (SHS) process. Ni/Almixture and an underlayer material which used Ni and Al were compacted to forma bilayer pellet and subsequently put on a steel substrate. The Ni/Al reactionwas ignited using induction heating in a combustion chamber of argon gas. Themorphology and microstructure of the products were observed using SEM and XRD.The results showed that further reactions between NiAl coating and underlayermaterials formed several intermetallic phases. The role of Al and Ni underlayeron the microstructure, porosity and the adhesion between coating and thesubstrate was observed.