Self-propagating High-temperature Synthesis Process Research Articles

Microstructural evolution and 1500 °C oxidation resistance of Mo(Al,Si)2 fabricated via an innovative two-step SHS-SPS technique

An innovative two-step approach of self-propagating high-temperature synthesis (SHS) and spark plasma sintering (SPS) was developed to rapidly fabricate MoSi2 and Mo(Al,Si)2 ceramics for high-temperature anti-oxidation applications. The SHS process predominantly promoted the synthesis of high-purity and high-yield MoSi2 and Mo(Si,Al)2 phases in the alloyed powders. Subsequently, dense and crack-free MoSi2 and Mo(Al,Si)2 ceramics were produced using SPS. 1500 °C oxidation tests of the ceramics (100 h) revealed the formation of a protective SiO2 oxide layer on the surface of MoSi2 ceramics, while an Al-Si-O composite glassy oxide layer formed on Mo(Si,Al)2 ceramics., which exhibited better thermal stability and lower oxygen permeability compared to the single SiO2 oxide layer. However, an excessive Al content (>0.05 at.%) compromised the oxidation resistance due to the emergence of a Si-depleted Mo5(Si,Al)3 layer with inferior oxidation resistance, which was caused by the high-temperature diffusion of Si. Therefore, via this novel two-step SHS-SPS technique compact and crack-free Mo(Si,Al)2 ceramics can be rapidly synthesized at high temperatures. When trace amount of Al was added (0.05 at.%), Mo(Si0.95,Al0.05)2 showed optimum high-temperature oxidation resistance.

Alumina-based ceramic coatings obtained by the SHS process for high temperature corrosion and wear protection of steel tubulars

Ceramic coatings have much potential for steel tubulars' protection against high temperature corrosion of gases and liquids, often containing abrasive solid particles, and to enhance their integrity in severe power generation, mineral and oil & gas production environments. Combining self-propagating high-temperature synthesis (SHS) with high-speed centrifugal process, alumina-based coatings were produced onto the inner surface of tubulars for these applications. According to the developed SHS batch formulation and the designed centrifugal device and process, well-consolidated composite ceramic layers with a thickness of 1.5–3 mm have been obtained. The developed SHS process does not create hazardous gases, and it takes ∼30 s for the ceramic phase formation. A high-level compaction due to centrifugal forces and a liquid phase sintering approach provided a dense gradient ceramic structure formed by oxide grains cemented by a glassy phase and bonded with a steel substrate through a thin iron layer. The coatings were successfully produced onto the inner surface of carbon and stainless steels’ tubes of up to 12 ft-lengths and standard dimensions from 2 to 3/8″ to 7.5” OD. The coatings were tested, for the first time, in wear and high-temperature corrosive environments, e.g., in steam–H2S–CO2 gases and molten salts, with encouraging results due to high contents of Al2O3 and some other oxides and consolidated ceramic structure. They can be recommended for applications in high-temperature (900 °C and greater) corrosive environments and erosive flows.

Intercalation based synthesis of Chevrel phase superconductors

This work focuses on the superconducting and magnetic properties of Chevrel phase (CP) compounds (Cu2Mo6S8 and Ni2Mo6S8) processed via a novel self-propagating high-temperature synthesis (SHS) method involving ternary cation intercalation in MoS2 high-temperature polymorphs. Green pellets of the precursor materials sealed under vacuum and exposed to 1050 °C or 1200 °C rapidly transformed from a powder mixture into submicron CPs within minutes. X-ray diffraction analysis confirmed the presence of Cu2Mo6S8 CP (67%), and Ni2Mo6S8 (93%). This group has illustrated the first time CP were formed at low energy cost and full stoichiometry. Magnetization versus temperature data obtained for the samples under different field conditions confirmed the superconducting behavior of the Cu–CP at a critical temperature of 8.3 K. The Ni–CP behaved as a superparamagnetic at low temperature (4.2 K). The results of this work suggest that the novel SHS process offers a viable scalable synthesis route for the Chevrel family of compounds and that it is worth exploring the functional applications of the new compounds of this material system.

The influence of hydrogen on the synthesis of biocompatible alloy Ti-6Al-7 Nb by a new Hydride Cycle method

The Hydride Cycle (HC) method is proposed as a new approach for synthesis of biocompatible alloy Ti-6Al-7 Nb. In this approach, preliminary, (Ti-7 Nb)H3.81 hydride is synthesised by Self-propagating High-temperature Synthesis (SHS) method. The heating of a mixture of this hydride with aluminum, (Ti-7 Nb)H3.81+6Al, at 1000°C for 30 minutes in the HC device results in the synthesis of Ti-6Al-7 Nb alloy containing the α- and β-phases of Ti, 92 wt% and 8 wt%, respectively. The alloy interacted with hydrogen in the combustion mode (SHS) forming the hydride (Ti-6Al-7 Nb)H3.17 with hydrogen content 3.07 wt%. This amount of hydrogen ensures the brittleness of the hydride and its grinding for 30–40 minutes to the agglomerates down to submicron or nano sizes. The presence of hydrogen in the crystal lattice enhances the plasticity of the hydride facilitating its compaction. The compaction of the (Ti-6Al-7 Nb)H3.17 alloy hydride and dehydrogenation under T=1000°C results in the reaction-activated sintering and the formation of practically porous less Ti-6Al-7 Nb alloy. The HC synthesis of the biocompatible alloy Ti-6Al-7 Nb compiled with SHS mode of the hydride synthesis is provided with the several advantages over the traditional methods. It is a low temperature, short duration, waste less process, proceeding by solid-state mechanism without melting of components, being an energy-saving in total. The proposed HC approach for synthesis of Ti-6Al-7 Nb alloy in combination with the high-technology SHS process for the hydrides formation can be used in manufacturing the biocompatible alloys. The hydrogenation-sintering of the alloy hydride (Ti-6Al-7 Nb)H3.17 can be used for producing of items of any designed complex form, particularly of implants.

FORMATION OF CHROMATED COATINGS ON A PRESS TOOLING IN THE PRODUCTION OF RUBBER PRODUCTS FOR ROCKET AND SPACE TECHNOLOGY

This research analyzes the influence of residual stresses formed as a result of the process of self-propagating high-temperature synthesis on the mechanical properties and durability of structural materials and protective coatings. The main emphasis is placed on the analysis of the relationship between residual stresses and adhesive strength and durability of the obtained coatings. Rubber-based composites may prove to be competitive and eventually replace traditional materials in a number of applications, as there are many advantages to using these materials. For example, rubber-based composites often have a lower density than traditional materials such as metals. This leads to a reduction in the weight of products, which is important in a variety of industries where lightness is a key characteristic. Rubber composites are characterized by cushioning, flexibility, and elasticity, which makes them able to handle dynamic loads and adapt to various forms of deformation without losing structural properties. Research was carried out on parts of press tooling used for manufacturing of rubber-technical products in rocket-space engineering. It was found that residual stresses formed during the SHS process have a significant effect on the adhesion properties of protective coatings. Residual stresses appear after SHS treatment under conditions of thermal self-ignition of SHS charges. At the cooling stage of the SHS process, residual compressive stresses appear as a result of the elastic interaction of the alloyed titanium coating and the structural material, which have different sizes and coefficients of thermal expansion. The maximum values of adhesion strength of titanium coatings on steel 45 were 120-150 MPa when alloyed with aluminum and 180-210 MPa when alloyed with chromium. This research emphasizes the importance of residual stress control for improving the strength and durability of protective coatings obtained under SHS conditions and their possible role in extending the service life of structures and equipment. Additional research in this direction may contribute to process optimization and product quality improvement in the aerospace industry.

Production of iron triad-based colored spinels by the self-propagating high-temperature synthesis

Blue, green, and khaki spinels were produced by self-propagating high-temperature synthesis (SHS) using Co3O4–ZnO–Mg(NO3)2·6H2O–Al(OH)3–Al, Ni2O3–ZnO–Cr2O3–Al(OH)3–Al, and Co2O3–Fe2O3–Al(OH)3–Al mixtures. The composition of the synthesis products was characterized by X-ray diffraction and IR spectroscopy. The oxides Co3O4, Co2O3, ZnO, Ni2O3, Cr2O3, Fe2O3, and aluminum hydroxide Al(OH)3 were used for the synthesis. Fuel was provided by aluminum powder (ASD-4). The spinel-type ceramic pigments were synthesized using layer-by-layer combustion, which involves two parallel exothermic reactions: aluminum oxidation and aluminothermic reactions. The fast self-propagating reactions and high synthesis temperatures rapidly destroy the structure of Al(OH)3 hydroxide in the starting mixture, producing gaseous reaction products that prevent the sintering of the spinels. The surface morphology of pigment powders and their composition was studied using a Quanta 3D 200i, FEI Co. scanning electron microscope and a Philips SEM 515 scanning electron microscope equipped with a local energy dispersive X-ray analysis (EDAX). The particle size of the synthesized spinels was approximately 1–5 μm. Colored spinels powders obtained by the SHS process can be used as ceramic pigments.

Thermodynamic analysis of production parameters and microstructural evolution in shape memory Ni(50-x)Ti(50)Fe(x) (x = 5, 10) alloy synthesized by combustion synthesis

This study represents an initial effort to produce NiTiFe shape memory alloys via the self-propagating high-temperature synthesis (SHS) process. The synthesis successfully yielded Ni45Ti50Fe5 and Ni40Ti50Fe10 alloys from elemental Ni, Ti, and Fe powders at three distinct preheating temperatures (240, 330, 420 °C). To support empirical findings, thermodynamic analysis using Factsage Thermodynamic Software was employed to correlate reaction propagation behavior with chemical composition. The calculation showed that the addition of 5 at.% Fe to the B2 phase did not hinder reaction self-propagation. This conclusion was supported with the ∆Hf/Cp ratio and transient liquid ratio, computed using the sub-lattice model, which closely resembled that of NiTi. Whereas 10 at.% Fe that synthesized at preheating temperature of 240 °C exhibits struggle, thus an increase in triggering time causes an effect on crystallite size and a decrease in porosity. Empirical results confirmed these findings, albeit influenced by ignition times. An increase in the liquid ratio due to the adiabatic temperature rise can also result in a reduction of NiTi content when the Fe ratio is increased, consequently diminishing the driving force for the reaction. In the sample containing – 5% Fe, the main phase is B2, and the R martensitic phase is also present. Ms is determined to be – 38.7 °C. SEM analyses revealed the presence of Ti2Ni and Ti2Ni3 phases in the upper and lower regions, while the distribution in the middle section is more homogeneous. No martensitic transformation was observed in 10% Fe. Additionally, nanocrystalline regions were detected within the samples by transmission electron microscopy, contributing to a nuanced understanding of their structural properties.Graphic abstract

Analysis of Stress Distribution of Composites Based on Hydroxyapatite by Finite Element Method

Self-propagating intermediate temperature synthesis (SIS) is a process that utilizes exothermic reactions to initiate and maintain component combustion so as to produce low porosity values and high hardness. It is necessary to know about the heat transfer phenomenon because SIS has a weakness, namely the high exothermic rate and very fast combustion rate which requires a high level of control. In addition, compression or compaction needs to be done because this method is expected to produce a homogeneous particle density distribution. The phenomenon of heat transfer and pressure that occurs in the SIS process is a simplification of the self-propagating high-temperature synthesis (SHS) process, which can be simulated and analyzed using engineering software based on finite element analysis. Stress simulation that occurs with the addition of weight percent titanium 5%, 10% and 20% using a pressure of 171 MPa and produces a normal stress. The heat transfer simulation that occurs uses a temperature of 750 °C, 850 °C, and 950 °C with a processing time of 2 hours with variations in the addition of weight percent titanium 5%, 10%, and 20% which results in an effect on heat flux and temperature distribution. Samples that were given the addition of 20% titanium by weight were given a pressure of 171 MPa to produce a normal stress of-230.44 MPa with the lowest porosity value of 22.63%. Samples processed at 850 °C with the addition of 10% weight percent titanium produced the lowest heat flux value of 0.0027220 W/m2.

Structure and phase composition of SHS composites based on Al–Ti–B system with different Al content

The paper deals with the influence of the Al content in the initial Al–Ti–B system on self-propagating high-temperature synthesis (SHS) processes, structure, and phase composition of synthesized products. It is found that the higher Al content leads to a temperature decrease of exothermic reaction and changes its wavefront propagation from layerwise to spinwise multiple locations. SHS products obtained from the Al–Ti–B system contain titanium diboride (TiB2) and aluminum (Al) phases. The weight content of phases in SHS products depends on the Al content in the initial powder mix and approximately matches the weight content of its components. The higher Al content provides a decrease in the size of the coherent scattering region for detected phases. SHS products obtained from the Al–Ti–B system with 10 wt% Al, consist of separate TiB2 particles coated with aluminum film. The Al content increased up to 30 and 60 wt%, provides the formation of the metal matrix structure. In this case, synthesis products consist of the aluminum matrix with TiB2 particles distributed inside. It is found that the growth in the Al content from 10 to 60 wt% in the initial Al–Ti–B system, results in the size reduction of TiB2 particles in SHS products from 3.37 to 0.41 μm, respectively.

Effect of Mg stoichiometry on self-propagating high temperature synthesis (SHS) of ZrC nanoparticles in ZrO2-Mg-C system

ABSTRACT It is significant to develop the production processes of Zirconium Carbide (ZrC) nanoparticles due to its superior properties. In this study, self-propagating high-temperature synthesis (SHS) followed by an acid leaching route was used to produce ZrC powder. ZrO2 was used as the zirconium source, C black as the carbon source and Mg as reductant. After modelling thermodynamically with the FactSage 7.1 software in terms of adiabatic temperature and possible phases, SHS processes were carried out with varying reductant stoichiometry (90%, 100%, 110%, 120%) and applying chemical treatment with HCl leaching for purification. The obtained products were characterised by XRD and SEM-EDS analysis. The optimum reductant stoichiometry for the production of ZrC was determined as 110%. As a result of the leaching processes, it was revealed that ZrC powders with an average particle size of 320 nm and containing a small amount of oxide residues could be synthesised. Compared to carbothermal reduction, which is the main production method of the material, the desired compounds were synthesised with much lower energy consumption and in much finer particles.

On the complex synthesis reaction mechanisms of the MAB phases: High-speed in-situ neutron diffraction and ex-situ X-ray diffraction studies of MoAlB

High-intensity in-situ neutron diffraction was used in this work to characterise the reaction mechanisms of the MAB phase ceramic, MoAlB, synthesised using both standard pressureless sintering in a vacuum furnace and induction-assisted self-propagating high-temperature synthesis (SHS). The high-speed diffractogram capture rate of 0.1–20 Hz (0.05–10 s) allowed the identification of intermediate phases with lifespans of 1–30 s. It was found that MoAlB formed during pressureless sintering through a multi-stage reaction beginning at ∼510 °C with the formation of MoAl12. An SHS reaction occurred at ∼578 °C, producing metastable β-MoB as an intermediate phase, followed by MoAlB and Mo3Al8. MoAlB was also found to be present during two separate temperature windows, initially following the SHS reaction at ∼578 °C, decomposing almost completely by ⁓1020 °C, then re-forming at ⁓1200 °C. For the induction-assisted SHS process, a reaction between the elemental powders at ∼660 °C lead to the primary formation of β-MoB as an intermediate phase, followed by a transition to α-MoB and intercalation with Al, forming MoAlB in ∼3 s from the beginning of the SHS reaction. Neutron diffraction (ND), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used post-reaction to confirm the compositions and analyse the microstructure of samples produced using both methods.

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.

Production of Zirconium-Niobium Alloys for Nuclear Reactors Fuel Rods via SHS Process

This article presents the results of studies of the self-propagating high-temperature synthesis (SHS) for obtaining zirconium alloys with niobium by the method of calcium-thermal reduction of nuclear-grade zirconium tetrafluoride in the presence of niobium powder. The optimal heating temperature of the initial charge and the methods of charge mixture with different calcium content were determined. The safety of the SHS process is ensured by the formation of an optimal combustion front of the mixture to remove the released high-pressure gases. A setup for the furnace reduction of zirconium alloys with charge preheating, discharge of molten products into molds of various designs, and control of the time and rate of slag and alloy crystallization has been tested. The required performance of the installation, the degree of transition of zirconium from salt into the alloy, and the purity, structure, and uniformity of the alloy were achieved.

Combustion synthesis of ultra-high-temperature solid solutions (ZrxNb1-x)B2. Part 1: The mechanisms of combustion and structure formation

The self-propagating high-temperature synthesis (SHS) in Zr–Nb–B system has been thoroughly investigated with a focus on its macrokinetics and phase formation mechanisms. The activation energies were determined by analyzing the relationship between the combustion rate and temperature. For compositions NbB2–40%ZrB2 and NbB2–50%ZrB2, the increase in the initial temperature has resulted in a significant change in combustion rate's dependence on temperature, signifying a possible shift in the reaction mechanisms. The quenched combustion front technique (QCF) method in conjunction with thermodynamic and ab initio calculations were used to analyze the sequence of phase formation events, including the formation of niobium and zirconium borides through gas transport reactions involving volatile boron suboxide BO in the heating zone, followed by the emergence of a zirconium-boron melt in the combustion zone and formation of main fraction of niobium and zirconium borides. Interactions between the primary niobium and zirconium borides and the melt result in the formation of solid solutions; however, at sub-optimal combustion conditions multiple non-equilibrium solid solutions are retained in the products. To address this issue, a machine learning model was developed, attaining coefficients of determination (R2) of 89% for combustion temperature and rate predictions, thus enabling the fine-tuning of macrokinetic parameters of the SHS process in the system.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВИДА ФЛЮСА НА СИНТЕЗ ЛИТОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА АМг2-TiC

The results are presented devoted to the study of the influence of flux type on the process of self-propagating high-temperature synthesis (SHS) of titanium carbide in aluminum flux, as well as on the structure and properties of the resulting composite material AMg2-TiC. During the research, the most promising halide salts for use as fluxes were analyzed and selected: Na3AlF6, Na2TiF6, K2TiF6, K1-3AlF4-6 (Nocolok ™ made in Germany). During the experimental synthesis, the most active signs of an exothermic reaction between titanium and carbon powders in the flux were recorded having a flux additive Na2TiF6. Then microstructural, micro X-ray spectral analysis and quantitative X-ray phase analyses were carried out, according to their results it was found out that the most homogeneous distribution in terms of material volume, the maximum content of a high dispersion of carbide phase close to the stoichiometric composition is also observed in samples obtained with the use of Na2TiF6 salt. The synthesized samples of the composite material were assessed according to physical and mechanical characteristics: hardness, porosity and electrical conductivity. It was found out that composite samples with an optimal structure are also characterized by a decrease in porosity by 1.33%, an increase in hardness by 94 MPa and a reduction of electrical conductivity by 0.3 MSm/m compared with samples obtained using other fluxes. According to the results of the studies carried out, Na2TiF6 flux is recommended for use to implement SHS composite AMg2-TiC material.

Preparation of high-quality FeV50 alloy by an improved SHS-EAH multi-stage process

As the most widely used vanadium intermediate alloy, ferrovanadium is mainly prepared by the self-propagating high-temperature synthesis (SHS) process with the advantages of short process and large heat release. However, there is a trade-off between the amount of reduction agent of Al and the product quality of ferrovanadium, which is caused by the thermodynamic equilibrium limitation of the reduction between Al and vanadium oxides. The reasonable adjustment of the trade-off has become an urgent problem to be solved for the preparation of high-quality ferrovanadium. In the present work, the thermodynamic equilibrium for the reduction limitation using Al as reducing agent has been thoroughly analyzed with the reference to the equilibrium phase diagram. It was found that the theoretical reduction limitation of total vanadium (T.V) in slag was decreased from 4.08 wt.% to wt. 0.86 wt.% when the Al content in alloy reached 2.0 wt.% at 1800 °C. The vanadium in slag was mainly presented in the form of MgV3O8 and coexisting with other phases of MgAl2O4, CaAl2O4, CaAl4O7, CaAl12O19. With the purpose of further decrease the high Al concentration in alloy and vanadium loss in slag, an improved SHS-EAH process was implemented by multi-stage gradient aluminum addition coefficient pattern, the average vanadium content in slag was reduced from 1.82 wt.% to 0.83 wt.%, while the aluminum content in FeV50 alloy was decreased from 1.5 wt.% to 0.4 wt.%. The SHS-EAH process was proved to be a better process with improved yield and quality for the preparation of ferrovanadium.

SHS of highly dispersed powder compositions of nitrides with silicon carbide Review

The application of the process of self-propagating high-temperature synthesis (SHS) to prepare highly dispersed powder nitride-carbide compositions from the most common refractory nitride (Si3N4, AlN, TiN) and carbide (SiC) compounds with a particle size of less than 1 μm is considered. The advantages of composite ceramics over single-phase ceramic materials and such trends of its development as the transition to nanostructured ceramics and the application of in situ processes of direct chemical synthesis of nanoparticles of components in the composite body are described. The attractiveness of the SHS process as one of the promising in situ processes characterized by simplicity and cost-effectiveness, the possibility of obtaining highly dispersed ceramic powders by burning mixtures of inexpensive reagents is shown. Considerable attention is paid to the consideration of the results of the application of azide SHS, based on the use of sodium azide and gasified halide salts as part of mixtures of initial powders of nitrided and carbidized elements during their combustion in nitrogen gas. The review of publications devoted to the application of SHS to obtain highly dispersed composite powders Si3N4–SiC, AlN–SiC and TiN–SiC, promising for use in sintering of the corresponding composite ceramic materials of submicron and nano-sized structure with improved properties, lower brittleness, good machinability, lower sintering temperatures compared with single-phase ceramic materials made of nitrides or carbides as well as for other applications, is presented. The results of the application of azide SHS are presented in detail both in the form of the results of thermodynamic calculations and the results of experimental research of combustion parameters, combustion product structure and composition. The advantages and disadvantages of using the combustion process for the synthesis of nitride compositions with silicon carbide, the causes of the disadvantages and the directions of further research to eliminate them are discussed.

Fast preparation of AgxPb20SbTe20 (x = 0.5–3) component with high thermoelectric performance

PbTe-based quaternary AgPbmSbTem+2 (LAST) has been a kind of promising thermoelectric materials due to its relatively low lattice thermal conductivity and good electrical performance. However, traditional melting or mechanical alloying methods are time-consuming, which is not suitable for applications. To solve this problem, a fast method combined self-propagating high-temperature synthesis (SHS) with spark plasma sintering (SPS) has been adopted in this work. Nanostructured n-type AgxPb20SbTe20 (x = 0.5–3) materials with high thermoelectric performance have been successfully prepared. On one hand, power factors of all samples reached over 1.6 mW·m−1·K−2 at high temperature, because Ag assembles grain boundaries and forms Ag2Te precipitates in the SHS process, enhancing the thermoelectric properties by modulation doping, energy filtering and dynamic doping. On the other hand, the Ag2Te-PbTe coherent interfaces bring multiple phonon scattering resources to reduce the thermal conductivity. As a result, a high ZT value of ∼1.32 at 773 K is achieved in Ag1.25Pb20SbTe20. This work provides a facile, rapid and energy-saving way to prepare PbTe-based materials with good thermoelectric performance.

Improved mechanical properties of porous nitinol by aluminum alloying

Aluminum alloying effects (up to 2 at %) on the macrostructure, microstructure, and mechanical properties of porous nitinol (NiTi) obtained by self-propagating high-temperature synthesis (SHS) were studied. It has been established that Ni and Ti interactions with liquid Al (0.5–1 at % Al) in the SHS process significantly change macrostructure, decrease the size of the interpore bridges, and increase their number, resulting in a larger effective cross-sectional area. An increase in the aluminum content above 1 at % leads to larger interpore bridges in the SHS product. The microhardness of TiNi(Al) increases from 305 HV 50 g to 422 HV 50 g with aluminum concentration, while the fraction of the TiNi(Al) (B2 + B19′) phases decreases from 75% to 50%. The Ti 2 Ni(Al) phase fraction increases from 25% to 50% with Al concentration. The 64 MPa tensile strength and 2.9% fracture strain of porous Ti 50 Ni 49 Al 1 alloy are higher than without Al. The increase in strength is due to the formation of a more homogeneous macrostructure and solid solution strengthening of the alloy-forming phases. Porous NiTi with 0–2 at % Al was obtained by self-propagating high-temperature synthesisNiTiAl macro and microstructure are optimal at 1 at %Al, along with mechanical properties. • Porous NiTi with 0–2 % Al was obtained by self-propagating high-temperature synthesis. • Al doping changed macrostructure and decreased interpore bridge size. • The TiNi(Al) phases fraction decreased from 75 % to 50 % with more Al. • Vickers hardness increased with Al concentration. • The optimal Al content is 0.5–1 % for improved structure and mechanical properties.

The method for efficiently releasing samarium vapor to generate artificial plasma clouds in the ionosphere

Vaporized samarium (Sm) has been released in the ionosphere for artificially creating plasma clouds, which can tailor radio propagation of information systems. The titanium-boron (Ti-B) self-propagating high-temperature synthesis (SHS) reaction can be used to vaporize Sm for releasing in the ionosphere. In this paper, a one-dimensional Fourier combustion model of Sm vaporizing by Ti-B reaction is established, based on the principle of chemical reaction and heat conduction. The Gauss-Seidel iterative algorithm is used to numerically simulate the SHS process of titanium-boron-samarium (Ti-B-Sm) system. This study first investigates the impact of different green compact porosity and content of Sm on the temperature field distribution, stable temperature and wave rate of the combustion process. The calculation shows that the porosity has little effect on the stable combustion temperature. With the increase of porosity, the stable combustion temperature remains basically unchanged, while the combustion wave rate shows a downward trend. The amount of Sm has a significant negative effect on the stable combustion temperature and the combustion wave rate. The higher the amount of Sm is, the more quickly the stable combustion temperature and the combustion wave rate decrease. The theoretical result indicates that, Sm could not exceed 35 % for being heated and vaporized. And the porosity could not exceed 52 % for efficient vaporization of Sm and stability of combustion wave. Finally, taking the Ti-B-Sm system with 30 % Sm contents as an example, several experiments were carried out using green compacts with different porosity. The experiments show that the maximum temperature of the compact during the combustion process is very close when the porosity varies from 30 % to 45 %, about 2075 K, which is in agreement with the simulation. The combustion wave rate is distributed from 5 mm/s to 8 mm/s within the range of 30 % and 50 % of porosity. Finally, the combustion products are detected by diffraction of X-rays (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). It shows that the Ti-B-Sm compact with 30 % Sm content and porosity not exceeding 52 % can effectively vaporize Sm, and the vaporization efficiency of Sm is about 75 %. The results of this study provide guidance for payloads of future experimental campaigns in the ionosphere.