High-temperature Synthesis Method Research Articles

Optimization of Aluminum Boride Synthesis in the Self-Propagating High-Temperature Synthesis Mode to Create Waste-Free Technology

This paper is the continuation of our previous paper. In this work, we optimized the synthesis of aluminum borides by the SHS method. The purpose of the research was to develop the foundations of waste-free technology. The initial components were powders of boric anhydride (B2O3), aluminum (Al), the oxide-heating additive (KNO3), various fluxing additives, including mixed ones. The optimal ratios of the initial components for increasing the yield of aluminum boride with a high boron content and obtaining slag suitable for the production of high-alumina clinkers were determined. Studies have shown that the development of a waste-free technology for producing aluminum borides by the method of self-propagating high-temperature synthesis (SHS) is possible and yields target (alloy) and by-product (slag) products that meet the requirements for chemical and phase composition.

Preparation and performance of Mg-doped spinel-structured LiMn2O4 cathode materials

The main work of this paper is to use the traditional high-temperature solid-state synthesis method to synthesize lithium manganese spinel cathode material and modify it by doping under optimized process parameters to improve its cycle performance. The doping of Mg2+ reduces the content of Mn3+ in the material. The material with Mg doping has higher structural stability and inhibits the Jahn-Teller and reduces the dissolution of Mn. LiMgxMn2−xO4 (x = 0, 0.02, 0.04, 0.06, 0.08) was synthesized by the traditional high-temperature solid-state method. The crystal structure and morphology of the synthesized powders were characterized by XRD, SEM, and FT-IR, respectively. The electrochemical performance of the battery was tested by CV, EIS, and long-term cycling. Among them, LiMg0.04Mn1.96O4 had the best cycling performance, the first discharge capacity of the material was 113.5 mAh·g−1. When it was cycled to 500 cycles at 0.1 C, still had the capacity of 92 mAh·g−1 with a capacity retention rate of 81.05%.

Synthesis and Study of Structural, Microstructural, and Magnetic Properties of Europium and Scandium 1 Mol % Doped CuFe2O4 Prepared by Self-Propagating High Temperature Synthesis Method

Synthesis and Study of Structural, Microstructural, and Magnetic Properties of Europium and Scandium 1 Mol % Doped CuFe2O4 Prepared by Self-Propagating High Temperature Synthesis Method

NiTi-SiC composite coating on Ti6Al4V alloy produced by SHS using induction heating

Abstract In this study, NiTi and NiTi-XSiC (1 wt%, 2 wt%, and 4 wt%) powders were coated on the Ti6Al4V surface by the self-propagating high-temperature synthesis (SHS) method using induction heating. Optic microscope and a scanning electron microscope (SEM) for the microstructural properties of coatings, energy dispersive spectrometry (EDS) for element distribution analysis, and X-ray diffractogram (XRD) for phase component analysis were carried out. The microhardness difference between the coating and the substrate was assessed by using the Vickers hardness scale. The microhardness increased with the addition of SiC, and the highest hardness value was 1416 Hv and detected in the sample NiTi–SiC 4 wt%. Phases formed by diffusion during solidification in the compounds Ti, Al, NiTi, NiTi2, NiAl, Ni3Al, Al3Ti, and TiO2, respectively.

Preparation, structure and photocatalytic activity of nanocomposites based on cerium oxide

Mesoporous CeO2 and MgO powders and nanocomposites based on them were synthesized by the method of self-propagating high-temperature synthesis, and the mutual influence of magnesium oxide and cerium oxide on the crystal structure, microstructure, and morphology of the obtained materials was studied. It has been established that CeO2 is formed on the surface of magnesium oxide, while the developed surface of the material is preserved. It has been established, that the sizes of CeO2 crystallites in the composition of nanocomposites change insignificantly and range from 6.5 to 7.4 nm, while the values of the specific surface area and average pore diameter of the studied samples depend on the composition and vary in the ranges of 19–41 m2/g and 11.9‒19 nm, respectively. The highest efficiency of photodegradation of dyes of acid telon blue and direct bright blue is observed for samples of MgO–CeO2 (30 mol.%) and MgO–CeO2 (50 mol.%) ‒ 98.5 and 92.5 %, respectively, taking into account the effect of direct photolytic decomposition under the influence of ultraviolet radiation.

Features of compaction in the combustion process of a system based on (Ni‒Al)/(SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, 3Al<sub>2</sub>O<sub>3</sub>∙2SiO<sub>2</sub>)

The possibility of using the method of self-propagating hightemperature synthesis to obtain high-temperature cermet materials and non-removable layer compounds based on (NiAl)/oxide, where the oxides are SiO2, Al2O3 and 3Al2O3·2SiO2, is investigated. The thermodynamic analysis of gorenje reactions was carried out and the properties of the synthesized products were investigated. An alternative method of creating a layered material with different content of oxide phases opens up wide possibilities for its use as heat insulators and special elements for high-temperature applications. Ill.8. Ref. 16. Tab. 1.

Study of the TIG weldability of aluminum matrix composite material AMg2-TiC

Subject of research: Weldability of the composite alloy AMg2-TiC.
 Purpose of research: Matrix alloy AMg2 is often used in welded joints. Reinforcement with a highly dispersed ceramic phase of titanium carbide leads to an increase in the hardness and strength of the alloy; therefore, it is necessary to study how the composite material behaves during and after welding.
 Methods and objects of research: The object of study is the AMg2-TiC composite alloy obtained by the method of self-propagating high-temperature synthesis. Microstructural analysis was carried out on a Jeol JSM 6390A scanning electron microscope. The elemental composition was determined by X-ray microanalysis on a Jeol JSM 6390A scanning electron microscope with a Jeol JED-2200 attachment. The hardness of the samples was determined on a hardness tester ZIP TK=2M using the Brinell method according to GOST 9012-59. Weldability tests were carried out by argon-arc welding using an Everlast Power TIG 210 EXT welding inventory and filler materials that most closely match the chemical composition of the matrix alloy.
 Main results of research: This paper shows the possibility of welding a composite material using the TiG method. The weldability of the composite was rated as satisfactory. Highly dispersed particles of the reinforcing phase do not dislocate from the area of ​​the base metal to the area of ​​the weld. The hardness of the composite material after argon-arc welding does not fall, but remains at the same level. The porosity in the weld zone of the composite is less than in the weld zone of the matrix alloy.

Effect of the Mass Fraction of NiTi-TiB2 SHS-Particles on the Phase Composition, Structure, and Mechanical Properties of Inconel 625-NiTi-TiB2 Composites Produced by Direct Laser Deposition.

This paper studies the impact of the mass fraction of NiTi–TiB2 particles obtained by the method of self-propagating high-temperature synthesis (SHS) on the phase composition, structure, and mechanical properties of composites made by direct laser deposition from an Inconel 625–NiTiz–TiB2 powder mixture. Composites were obtained from a powder mixture with the mass fraction of particles at 5–10 wt%, and they consisted of an Inconel 625 metal matrix wherein ceramic inclusions of titanium diboride TiB2 were distributed. Increasing the mass fraction of SHS-produced NiTi particles from 30 to 95 wt% led to the emergence of a NiTi intermetallide phase in the matrix material as well as an increase in the average TiB2 particle size and formation of their agglomerates. In addition, an increase in the microhardness of the materials was observed. The graph of tensile strength of Inconel 625–NiTi–TiB2 samples has a parabolic shape with a maximum at 1000 MPa (when the mass fraction of SHS-produced NiTi–TiB2 particles is at 30 wt%). A further increase in the mass fraction of NiTi–TiB2 led to a decrease in the tensile strength down to 400 MPa. Here the deformation of samples decreases linearly as the ratio of composite particles in the initial mixture increases. From a comparative analysis of the results obtained, the optimal mass fraction of composite NiTi–TiB2 particles in the Inconel 625-NiTi–TiB2 powder mixture was found to be 5 wt%.

THE INFLUENCE OF ULTRASOUND ACTIVATION ON MICROSTRUCTURE AND HARDNESS OF POROUS Ni-Ti SHAPE MEMORY ALLOYS

A Ni-Ti shape memory alloy with a porous structure is obtained by the method of self-propagating high-temperature synthesis (SHS) and investigated the possibility of changing its microstructure and hardness. The research aimed to study the changes in the microstructure and hardness of the Ni-Ti shape memory alloy with a porous structure when the Ni and Ti metal powders are preliminarily subjected to ultrasound activation for different periods. The microstructure of the alloy surfaces was studied with using a Hitachi scanning electron microscope (SEM), and the hardness was measured with a Brinell electronic hardness tester. The results of the experiments showed that the porosity and hardness of the Ni-Ti alloy enlarged with an increase in the time of ultrasound activation of the components. The innovative aspect of this study is that prior to the synthesis of powder elements with a purity of Ni 99.9% and Ti 99.9% with an average particle size of 40 μm, they were previously subjected separately to ultrasound activation at different periods.

Achieving electromagnetic wave absorption capabilities by fabrication of flower-like structure NiCo2O4 derived from low-temperature co-precipitation

In this work, The NiCo2O4 with 3D hierarchical multilayer flower-like structure was prepared by the low-temperature (55 °C) co-precipitation method combined with the calcination process, avoiding the traditional high-temperature hydrothermal synthesis method. The prepared flower-like NiCo2O4 with a large specific surface area was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and automatic surface area and porosity analyzer (BET) and vector network analyzer (VNA). A novel evaluation approach was proposed to evaluate the electromagnetic wave (EMW) absorbing properties of various samples (different calcination temperatures), which was to defined the ΔS as the area enclosed by the curve when the reflection loss (RL) value was less than −10. In order to take the material thickness into account, and then the effective reflection loss (RLE) value was defined ΔS/d to measure the electromagnetic wave (EMW) loss capability of the different samples. The results showed that NiCo2O4 exhibited excellent EMW absorption effect when the calcination temperature was 400 °C, and the maximum RL value reached −43.17 dB at 14.32 GHz with the thickness of 1.5 mm and the effective absorption bandwidth (fe) was 4.48 GHz (12.08 GHz–16.56 GHz). The excellent EMW absorption property was mainly due to NiCo2O4 with particular porous flower-like structure, which could achieve impedance matching to loss EMW by dielectric loss and magnetic loss.

Fabrication and oxidation resistance of the non-stoichiometric tantalum-hafnium carbonitride

This research was conducted to obtain non-stoichiometric tantalum-hafnium carbonitride powder of the Fm3m (225) structural type using a combination of mechanical activation (MA) and self-propagating high-temperature synthesis (SHS) methods. Mechanical activation for 60 min in a low-energy mode (347 rpm) forms Ta/Hf/C composite particles 1 to 20 μm in size with a layered structure and contributes to a uniform distribution of elements. SHS of a mechanically activated Ta + Hf + C mixture in a nitrogen atmosphere (0.8 MPa) leads to the formation of a single-phase tantalum-hafnium carbonitride powder with the Ta0.25Hf0.75C0.5N0.3 composition where particles feature by a ≪spongy≫ morphology with pores and caverns and consist of submicron grains. Spark plasma sintering (SPS) was used to obtain a bulk sample of tantalum-hafnium carbonitride with a grain size of 3 to 5 μm, relative density of 98.2 Ѓ} 0.3 %, hardness of 19.8 Ѓ} 0.2 GPa, and crack resistance of 5.4 Ѓ} 0.4 MPa・m1/2. The kinetics of (Ta,Hf)CN oxidation at 1200 °C in air is described by a parabolic law suggesting the formation of an Hf6Ta2O17 + mHfO2 oxide layer with a low oxygen diffusion rate where the oxidation rate is 0.006 mg/(cm2・s). A (Ta,Hf)CN oxidation mechanism is proposed, which states that Ta2O5 and HfO2 are formed on the surface of grains at the first stage that react with each other at the second stage to form a Hf6Ta2O17 homologous superstructure and monoclinic HfO2. CO, CO2, NO and NO2 gaseous oxidation products are released with the formation of pores and cracks.

Improved oxidation protective ability of SHS powder-synthesized ZrB2-MoSi2-SiC-Si coating on carbon/carbon composites

ZrB2-MoSi2-SiC-Si coatings were prepared by gaseous silicon infiltration on the carbon/carbon composites, and the powders synthesized by the self-propagating high-temperature synthesis method (SHS) were used as the raw materials to benefit the oxidation protective ability of the coatings. The ZrB2-MoSi2-SiC-Si coatings prepared from commercial powders (CP coated samples) were used as a comparison. After sintering, the structure of the coating prepared with SHS powders is denser than the CP coated sample with a density of 3.5 g/cm3. After 62 h of oxidation tests at 1500 °C, the mass loss of the SHS coated sample was only 0.28 %, which was 32 % lower than that of the CP coated sample. The ability of SHS coatings to exhibit better oxidation protection is attributed to the higher oxidation stability and sintering activity of the SHS powders than that of commercial ones.

Synthesis and Property Examination of Er2FeSbO7/BiTiSbO6 Heterojunction Composite Catalyst and Light-Catalyzed Retrogradation of Enrofloxacin in Pharmaceutical Waste Water under Visible Light Irradiation.

A new photocatalyst, Er2FeSbO7, was prepared by solid phase sintering using the high-temperature synthesis method for the first time in this paper. Er2FeSbO7/BiTiSbO6 heterojunction (EBH) catalyst was prepared by the solvent thermal method for the first time. Er2FeSbO7 compound crystallized in the pyrochlore-type architecture and cubelike crystal system; the interspace group of Er2FeSbO7 was Fd3m and the crystal cellular parameter a of Er2FeSbO7 was 10.179902 Å. The band gap (BDG) width of Er2FeSbO7 was 1.88 eV. After visible light irradiation of 150 minutes (VLGI-150min) with EBH as a photocatalyst, the removal rate (RR) of enrofloxacin (ENR) concentration was 99.16%, and the total organic carbon (TOC) concentration RR was 94.96%. The power mechanics invariable k toward ENR consistency and visible light irradiation (VLGI) time with EBH as a photocatalyzer attained 0.02296 min−1. The power mechanics invariable k which was involved with TOC attained 0.01535 min−1. The experimental results showed that the photocatalytic degradation (PCD) of ENR within pharmaceutical waste water with EBH as a photocatalyzer under VLGI was in keeping with the single-order reactivity power mechanics. The RR of ENR with EBH as a photocatalyzer was 1.151 times, 1.269 times or 2.524 times that with Er2FeSbO7 as a photocatalyst, BiTiSbO6 as a photocatalyst, or N-doping TiO2 (N-TO) as a photocatalyst after VLGI-150min. The photocatalytic activity, which ranged from high to low among above four photocatalysts, was as follows: EBHP > Er2FeSbO7 > BiTiSbO6 > N-TO. After VLGI-150min toward three periods of the project with EBH as a photocatalyst, the RR of ENR attained 98.00%, 96.76% and 95.60%. The results showed that the stability of EBH was very high. With appending trapping agent, it could be proved that the oxidative capability for degrading ENR, which ranged from strong to weak among three oxidic radicals, was as follows: superoxide anion > hydroxyl radicals (HRS) > holes. This work provides a scientific basis for the research and oriented leader development of efficient heterojunction catalysts.

Kinetics of the Synthesis of Aluminum Boride by the Self-Propagating High-Temperature Synthesis Method

The influence of certain factors on the kinetics of the process of obtaining aluminum borides (burning rate, ingot formation, and phase separation) was investigated. In this study, we report the registration of diboride using the SHS protocol. The synthesis of aluminum diboride from boric anhydride occurred by the aluminothermic method. The initial components were boron trioxide and aluminum in the form of powders. Researchers paid special attention to the degree of grinding of the charge fluxing substances. The influence this had on the rate of development of the degree of charge concentration was studied. To calculate the degree of charge, a composition was chosen according to the speed obtained from a number of experiments where melting was carried out with the following charge densities in g/cm3: 0.80; 1.08; 1.18; 1.74. The method of melting was ignition from above. The experimental results allowed us to conclude that the nature of the change in the combustion rate of the system, where there was an excess of the reducing agent in the charge, is the same. An increase in the combustion rate, where there was an excess of aluminum of up to 20%, was likely due to the fact that the reaction area of the charge components increased. In addition, an increase in speed can be explained by a decrease in heat losses due to a reduction in the melting time. With an increase in excess aluminum above 20% of the stoichiometry, the observed decrease in the combustion rate can be explained by a decrease in the specific heat of the process due to the melting of the excess aluminum, which played the role of a ballast.

High-pressure A-site manganites: Structures and magnetic properties

Compounds of general formula ABO3 are widely studied due to their versatility regarding chemical composition, structure and physical properties. The use of high-pressure and high-temperature synthesis method allows the introduction of small Mn2+ cation into the often-large A site, giving rise to the so-called A-site manganites, with a few exceptions to this rule. Polymorphism, structural features and magnetic properties of A-site manganites are revisited in this short review dedicated to Miguel A. Alario y Franco on his 80th birthday. We extend this dedication to John B. Goodenough and J. Paul Attfield on their 100th and 60th birthdays in recognition of their ground work. Happy birthday all three!

The production of corrosion alloy by self-propagating high-temperature synthesis

The subject of research: Self-propagating high-temperature synthesis (SHS) is an energetically low-cost method for obtaining materials with desired properties.
 The purpose of research: Development and approbation of the method of self-propagating high-temperature synthesis.
 Methods and objects of research: For the synthesis of a corrosion-resistant material, a thermite mixture of Al (75 %) and Fe2O3 (25 %) and the addition of MoO3 with a variable mass fraction of 10 %, 15 %, 20 %, 25 % of thermite were taken. The composition and structure of the synthesized material were determined by XRD and metallography methods. Based on the properties of the physical properties of the obtained material (porosity, electrical conductivity) and its phase composition (MoO2, Al2O3, FeMoO4), samples obtained with a 15 % addition of MoO3 were selected for testing for corrosion resistance.
 Results of research: The paper presents the results of approbation of obtaining a corrosion-resistant material by the SHS method. Conducted tests for corrosion resistance established: the rate of continuous corrosion of the synthesized material (MoO3 15 %) was 0.2 mm / year, which is close in value to corrosion-resistant steels; high resistance of the synthesized material to technical salt when tested for 14 days with a concentrated solution of the reagent 0.18 ml * eq / l. The listed properties of the synthesized material confirm the possibility of obtaining corrosion-resistant materials by the SHS method, including those for operation in the Arctic.

Metamorphosis of the properties of the gas-phase fraction of ZnS:Mn obtained by the method of self-propagating high-temperature synthesis from the charge with a different Zn/S ratio

Performed in this work is a comparative analysis of photoluminescence, photoluminescence excitation and EPR spectra of gas-phase fraction of powdery ZnS:Mn obtained using the self-propagating high-temperature synthesis from the charge with a different Zn/S ratio. It was found that the size of particles in the synthesized materials was with in the range 10–300 nm. The size that is comparable with the Debye screening length (L). The luminescence and other characteristics of the studied material were found to differ significantly from the bulk ones. This finding has been explained by a unique energy structure of crystallites. Zn/S ratio has been shown to impact significantly on the crystallites sizes and the amount of incorporated Mn. The largest crystallite sizes and the high Mn content were observed in the powder synthesized with a stoichiometric Zn/S ratio, while the minimum particle sizes - in the powders synthesized with S excess. At sulfur excess, the size of particles is close to the Debye length, and carriers can freely migrate in the conduction band to the surface, where mainly nonradiative recombination occurs. The stoichiometric Zn/S ratio or Zn excess in the charge results in the increase of the particle sizes up to the values 2L ≤ d≤3L. Such materials are characterized by minimization of non-radiative losses. This finding opens new possibilities for ZnS application.

Novel Pathway for the Combustion Synthesis and Consolidation of Boron Carbide.

A novel pathway for the magnesiothermic reduction of boron oxide and magnesium dodecaboride (MgB12) in the presence of carbon by a self-propagating high-temperature synthesis method was proposed that was aimed at the direct preparation of boron carbide nanopowder. The combined utilization of two boron sources, boron oxide and MgB12, allowed tailoring the overall caloric effect of the process, increasing the yield of the target product and lessening the laborious leaching process. In addition, it is an alternative way to utilize magnesium borides, which are inevitable side products at boron production. Multivariate thermodynamic calculations performed in the B2O3-MgB12-Mg-C system allowed estimating equilibrium compositions of the products and deducing the optimum composition of the initial mixture for obtaining B4C. For the latter, the adiabatic temperature (Tad) is 2100 °C, which is theoretically enough for the implementation of the self-propagating reaction. The combustion reaction was shown to be extremely sensitive to the initial mixture composition, external pressure, as well as sample diameter (heat losses). It proceeds in self-oscillatory mode and leads to the product of a layered macrostructure. The combustion product was then consolidated by the spark plasma sintering technique at different conditions. Vickers microhardness was measured, and the wear erosion behavior was examined. The variation in lattice parameters of boron carbide reflected the influence of synthesis, sintering and erosion conditions on the ordering/disordering of the boron carbide structure.

Analytical control for the content of small amounts of oxygen in aluminum nitride powders using a «Metavak-AK» analyzer

A method for prompt and reliable control of low oxygen content in aluminum nitride powder using a modern gas analyzer «Metavak-AK» operating in automatic mode and never used previously for this object is presented. Aluminum nitride was obtained under conditions of pilot production at ISMAN by the method of self-propagating high-temperature synthesis (SHS). A program for operation of a «Metavac-AK» analyzer has been developed for oxygen determination in AlN samples and optimal conditions of analysis were specified: reductive melting of a sample in a graphite crucible at a furnace temperature of 2700°C in the presence of a combined Sn/Ni flux in a helium flow. The total oxygen content in aluminum nitride powders and the relative standard deviation ranged within 1.01 – 1.18% and 1.75 – 9.87%, respectively.

Aurivillius Phase Bi4V3O12 with d1 Magnetic Cations, Anisotropic and Negative Thermal Expansion, Multiple Structural Transitions, and Low-Dimensional Magnetism.

Aurivillius phases are an important class of inorganic compounds as they often show ferroelectric properties, and some members of this family are used in nonvolatile ferroelectric memories. The majority of Aurivillius phases have nonmagnetic d0 cations in the perovskite block. Bi4Ti3O12 is the best-known and extensively studied compound within this family. Here, using a high-pressure, high-temperature synthesis method, we could successfully prepare a full magnetic analogue, Bi4V3O12, with d1 cations. Bi4V3O12 is unstable in air above about 520 K. However, in an inert atmosphere, Bi4V3O12 demonstrates two first-order reversible structural transitions near 525 and 760 K. The high-temperature prototypical phase is the same in both Bi4V3O12 and Bi4Ti3O12 with tetragonal (T) I4/mmm symmetry and aT = 3.85608(5) Å and cT = 32.6920(8) Å (at 850 K) for Bi4V3O12, while the low-temperature phases are different. Bi4V3O12 shows anisotropic thermal expansion above 300 K and negative volumetric thermal expansion above about 700 K. Magnetic measurements showed a broad maximum near 70 K on magnetic susceptibility, indicating the presence of low-dimensional magnetism with strong antiferromagnetic interactions between V4+ ions with the Curie-Weiss temperature of about -370 K. But no long-range magnetic ordering was found in Bi4V3O12 down to 2 K.