High-temperature Synthesis Research Articles

Electrocatalytic oxygen reduction on nitrogen-doped porous carbon spheres prepared with resorcinol–phenolsulfonic acid–formaldehyde mixed resins

Abstract The resorcinol–phenolsulfonic acid–formaldehyde (RxPS1–xF) mixed resin spheres were prepared by the high-temperature hydrothermal synthesis. Pyrolysis of the resin spheres under NH3 atmosphere produced small, porous, conductive N-doped carbon spheres. These carbon spheres promoted electrocatalytic oxygen reduction reaction (ORR) with almost 100% four-electron reduction selectivity, and their performance was comparable to that of the state-of-the-art Pt/C catalyst.

A New High-Pressure High-Temperature Phase of Silver Antimonate AgSbO3 with Strong Ag-O Hybridization.

We report on a new polymorph of silver antimonate AgSbO3 discovered with the use of high-pressure high-temperature synthesis at 16 GPa and 1380 °C. The crystal structure is determined from X-ray powder diffraction, and we find this new high-pressure phase crystallizes in monoclinic space group C2/c with the following values: a = 8.4570(3) Å, b = 9.8752(3) Å, c = 8.9291(3) Å, β = 91.1750(12)°, and V = 745.56(4) Å3. We synthesized the high-pressure (16 GPa) AgSbO3 phase from the ilmenite phase as a precursor. This high-pressure monoclinic AgSbO3 consists of a three-dimensional network of corner- and edge-sharing SbO6 octahedra with channels along the c-direction containing Ag atoms. We also synthesize AgSbO3 in the defect pyrochlore phase at 4 GPa from the same ilmenite precursor and compare the Raman spectra and the cation-anion bonding of all three AgSbO3 phases. The absence of a cubic perovskite form of AgSbO3 even at pressures of ≤16 GPa is likely due to the covalency of the Sb-O bonds and the moderate electronegativity of Ag+. Hybridization of Ag d and O p orbitals results in a variation of Ag-O distances that correlates with the band gap, which is in qualitative agreement with the density of states around the Fermi level from our density functional calculations. We compare AgSbO3 with other ABX3 compounds to elucidate the dependence of the structure on the constituent atoms.

High pressure and high temperature synthesis of a new boron carbide phase

The dense boron carbide (B-C) phases with diamond structure are predicted to be superhard, with hardness close to that of a cubic boron nitride (c-BN). At ambient conditions, graphite-like BC3 is well characterized, firstly reported by Kouvetakis et al. In this work, we have synthesized a new B-C phase from the graphite-like BC3 in a laser-heated diamond anvil cell. Interestingly, this phase could be recoverable to ambient pressure due to dynamic stabilities. The Raman spectrum and X-ray diffraction patterns give the possible structure of this new phase.

The role of hydrogen in the synthesis of High-entropy alloys and their hydrides

The aim of this work is to present the new technique processes of formation of stable hydrides of High-entropy alloys (HEAs) with high hydrogen content. The essence of the proposed method is the sequential use of self-propagating high-temperature synthesis (SHS) method for producing the metal hydrides, followed by the formation of alloys in the hydride cycle (HC) method. Preliminary, the hydrides of three compositions of metal mixtures were synthesized in SHS: 0.2TiH2+0.2ZrH2+0.2HfH2+0.2VH2+0.2NbH2, 0.3TiH2+0.15ZrH2+0.15HfH2+0.2VH2+0.2NbH2 and 0.3TiH2+0.1ZrH2+0.1HfH2+0.2VH2+0.2NbH2+0.1MgH2. From the synthesized mixtures of metal hydrides, the HEAs were produced in HC. The resultant hard alloys Ti0.2Zr0.2Hf0.2V0.2Nb0.2, Ti0.3Zr0.15Hf0.15V0.2Nb0.2 and Ti0.3Zr0.15Hf0.15V0.2Nb0.2Mg0.1 without crushing combusted in Н2 at РH2 = 5-30atm. in SHS mode. As a result, the hydrides of HEAs (Ti0.2Zr0.2Hf0.2V0.2Nb0.2)Н2.05, (Ti0.3Zr0.15Hf0.15V0.2Nb0.2)H2.05 and (Ti0.3Zr0.1Hf0.1V0.2Nb0.2 Mg0.1)H182 were synthesized with H2 content between 2.17-2.42wt.% and H/Me = 1.82-2.05. The repeating the hydrogenation-dehydrogenation processes for 1-3 times confirmed the exceptional cyclic stability of hydrides and the reversible high hydrogen storage capacity of the alloys. The regularities and the mechanism of formation of HEAs and their hydrides were elucidated. The applicability of combination of SHS and HC methods for synthesis of solid solutions of BCC structure HEAs and of their hydrogen-rich hydrides was demonstrated. The remarkable advantages of the developed efficient, low-energy consuming, waste-free and safe method for the synthesis of HEAs and their hydrides can be of commercial interest and attractive to industry, given the current needs for the development of renewable energy, in particular, the solid hydrogen storage facilities.

Mechanical and Oxidation Behavior of MoSi2-40wt.%Ti5Si3 Composites Produced by MASHS and SPS

Silicides, known for their exceptional oxidation resistance at high temperatures, are promising materials for advanced applications. Among them, MoSi₂ and Ti₅Si₃ stand out. In this study, a Ti29Mo18Si53 composition was selected to produce a MoSi2-40wt.%Ti5Si3 composite via mechanically activated self-propagating high-temperature synthesis (MASHS). Elemental powders were milled, synthesized in a tubular furnace, and sintered using spark plasma sintering (SPS). The resulting (Ti0.8, Mo0.2)Si2-MoSi2-Ti5Si3 composite maintained stability through sintering, achieving 99% of its theoretical density, a hardness of 10.9±0.4 GPa, and a fracture toughness of 5.11 MPa·m0.5. To evaluate processing effects a second sample, prepared under similar condition but with concurrent synthesis and sintering in the SPS, achieved 97% density, 7.1±0.5 GPa hardness, and 4.97 MPa·m0.5 fracture toughness. Additionally, pure Ti₅Si₃ and MoSi₂ were synthesized separately via MASHS, mixed to form a MoSi₂-40 wt.% Ti₅Si₃ composite, and then consolidated by SPS. This composite reached 96% density, 11 ± 0.6 GPa hardness, and 3.8 MPa·m0.5 fracture toughness. Moreover, the (Ti₀.₈Mo₀.₂)Si₂-MoSi₂-Ti₅Si₃ composite demonstrated superior oxidation resistance compared to Ti₅Si₃ and similar to monolithic MoSi₂ up to 1000°C.

Al/AlN-based thermal paste fillers prepared by self-propagating high-temperature synthesis (SHS)

Al/AlN-based thermal paste fillers prepared by self-propagating high-temperature synthesis (SHS)

Influence of highly dispersed phase of titanium carbide on physical and mechanical properties of alloys AM4.5Kd and AK10M2N

Dispersion-strengthened composite materials belong to the group of promising structural materials characterized by a diverse combination of properties. The work presents examples of the creation and heat treatment of composite materials based on aluminum alloys, strengthened by a dispersed phase of titanium carbide, and characterized by high hardness, elastic modulus and good wettability by the melt. The most accessible, inexpensive and effective way to obtain them is self-propagating high-temperature synthesis (SHS).The work shows the possibility of obtaining new aluminum matrix composite materials based on industrial aluminum alloys AM4.5Kd and AK10M2N by reinforcing them with 10 wt.% highly dispersed titanium carbide or AM4.5Kd–5.95 vol.% TiC and AK10M2N–5.78 vol.% TiC. The reinforcing phase is formed in alloy melts using the technology of SHS from the initial elemental components—titanium powder and carbon black. Using the obtained samples, an assessment was made of the uniformity of the ceramic phase distribution over the volume of the matrix alloys, which amounted to 0.15 and 0.12 for the samples AM4.5Kd–10%TiC and AK10M2N–10%TiC, respectively, which constitutes a high degree of uniformity.An assessment was made of physical properties such as porosity, density, electrical conductivity, as well as the coefficient of thermal linear expansion. Analysis of the data allows us to say that the final composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC have a slightly higher density (↑~4%) than the matrix alloys, due to the presence of a ceramic phase, low porosity values (~1%), lower TCLE (↓~6%) than matrix alloys and low electrical conductivity (~25% IACS). This article also presents data on the values of the mechanical properties of composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC. It has been shown that reinforcement with a ceramic phase contributes to a significant increase in hardness by 15 and 42 HB, as well as higher values of the compressive yield strength by 31 and 17 MPa, respectively, while maintaining a high level of relative deformation. The results obtained allow us to conclude that the developed composite materials can be recommended for products used under conditions of elevated temperatures and significant wear.

Study of structural and mechanical properties of composite ceramics of the AlMgB14–TiB2 system

AlMgB14 ceramics is known as a material characterized by increased hardness in combination with a low friction coefficient. Composite structures based on this ceramics have even higher strength characteristics. In the present work, we investigate the structural-phase states and physicomechanical properties of composite ceramics of the AlMgB14–TiB2 system with a variable TiB2 content, obtained by hot pressing the initial batch based on AlMgB14 and TiB2 ceramic powders preliminarily synthesized by the method of self-propagating high-temperature synthesis. It was found that the resulting materials are characterized by a composite structure represented by TiB2 inclusions distributed in the AlMgB14 matrix. The phase composition of the resulting composites is similar to the phase composition of the initial batch, with 5 to 9 wt. % of the MgAl2O4 spinel phase being formed. The microhardness of AlMgB14–TiB2 composites is up to 19.9 GPa (the hardness of AlMgB14 ceramics obtained by a similar method without additives is 7 GPa). The three-point bending strength of AlMgB14–TiB2 composite materials is 309 MPa.

Reductive pathways in molten inorganic salts enable colloidal synthesis of III-V semiconductor nanocrystals.

Colloidal quantum dots, with their size-tunable optoelectronic properties and scalable synthesis, enable applications in which inexpensive high-performance semiconductors are needed. Synthesis science breakthroughs have been key to the realization of quantum dot technologies, but important group III-group V semiconductors, including colloidal gallium arsenide (GaAs), still cannot be synthesized with existing approaches. The high-temperature molten salt colloidal synthesis introduced in this work enables the preparation of previously intractable colloidal materials. We directly nucleated and grew colloidal quantum dots in molten inorganic salts by harnessing molten salt redox chemistry and using surfactant additives for nanocrystal shape control. Synthesis temperatures above 425°C are critical for realizing photoluminescent GaAs quantum dots, which emphasizes the importance of high temperatures enabled by molten salt solvents. We generalize the methodology and demonstrate nearly a dozen III-V solid-solution nanocrystal compositions that have not been previously reported.

Effect of Synthesis Process on The Piezoelectric Properties of (1-x) NBT-xBT: A Comparative Study Between Solid State and Hydrothermal Methods

Lead-free oxide perovskite materials are produced to ensure that no toxic or dangerous waste is released into the environment, although this technique often requires a high-temperature synthesis method. Nevertheless, the development of an environmentally friendly chemical process to carry out the synthesis of perovskite material in the laboratory at low temperature is a major challenge. In this investigation, to lower the temperature of the thermal treatment, (1-x)(Na0.5Bi0.5)TiO3-xBaTiO3 (abbreviated as (1-x)NBT-xBT) ceramics were synthesized using two different methods: a hydrothermal method and a conventional calcination process (solid-state), using the same reagents. The effects of various synthesis techniques on the composition, structure, morphology, and dielectric properties of the (1-x)NBT-xBT ceramics were registered and examined. The XRD plots taken at ambient temperature were used to verify the phase formation of the samples. The occurrence of functional bands was also verified by Raman spectroscopy at ambient temperature. Using the Rietveld refinement method were able to detect the morphotropic phase boundary (MPB) near x=0.05-0.07. When the hydrothermal process was adopted, the (1-x)NBT-xBT ceramics show a single perovskite structure sintered at 1000°C. Moreover, scanning Electron Microscopy (SEM) examination revealed a uniform distribution of grains and a significant change in grain size with the increase in BaTiO3 concentration when compared to the conventional method. The microstructure of ceramics is generally strongly influenced by the method used to prepare the powders, which has a considerable impact on their performance. Piezoelectric and dielectric properties of the specimens have been compared with the properties of those prepared by the hydrothermal process. Thus, the choice of the suitable synthesis method depends on the desired properties of the (1-x)NBT-xBT materials.

Probing Ce- and Zr-Fumarate Metal-Organic Framework Formation in Aqueous Solutions with In Situ Raman Spectroscopy and Synchrotron X-ray Diffraction.

The synthesis of Ce-fumarate and Zr-fumarate metal-organic framework (MOF) is monitored for the first time with in situ Raman spectroscopy in custom-built solvothermal reactors. Several synthesis conditions were explored for Ce-fumarate at room temperature. The use of the method for high-temperature synthesis of Zr-fumarate is also demonstrated. In situ Raman monitoring provided insights into both the solution and crystalline phases of the reaction medium, revealing the dynamic interplay among precursors, modulators, and the forming MOF structure. The reaction kinetics was determined by following the characteristic peak at 1666 cm-1. The conversion was in good agreement with the reaction kinetics determined via in situ synchrotron powder diffraction. The resulting MOF products were further characterized using ex situ X-ray powder diffraction, scanning electron microscopy, thermogravimetry, and surface area measurements. This study demonstrates a simple and industrially scalable method for monitoring MOF synthesis in situ, which can provide insights into the stages and mechanisms of formation of MOFs and other compounds.

Synthesis of silica-coated polygonal Fe3O4 nanoparticles

The small size, surface effect, and tunneling effect of nanomaterials enable their applications in various fields, including catalysis, sensing. Fe3O4 has been widely used in nanotechnology owing to its excellent photoelectromagnetic properties. In this study, polygonal Fe3O4 nanoparticles were prepared through a high-temperature synthesis method. Subsequently, silica coating was applied via the Stöber method to obtain a nanomaterial with uniform particles. The prepared Fe3O4 exhibited a distinct crystal structure and an ultra-high saturation magnetization, reaching up to 134.2 emu/g. Moreover, the dodecyl trimethyl ammonium bromide (DTAB) templating agent facilitated the coating of Fe3O4 with silica. The coated Fe3O4@SiO2 particles featured a well-defined core–shell structure and corrosion resistance, making them highly promising candidates for magnetic targeting medical tools, magnetic resonance imaging agents and other biological applications.

Macroscopic perspective on phase transition behavior of natural single-crystal graphite under different pressure environments

Comprehensive understanding of the direct transformation pathway from graphite to diamond under high temperature and high pressure has long been one of the fundamental goals in materials science. Despite considerable experimental and theoretical progress, current experimental studies have mainly focused on the local microstructural characterizations of recovered samples, which has certain limitations for high-temperature and high-pressure products, which often exhibit diversity. Here, we report on the pressure-induced phase transition behavior of natural single-crystal graphite under three distinct pressure-transmitting media from a macroscopic perspective using in situ two-dimensional Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. The surface evolution process of graphite before and after the phase transition is captured, revealing that pressure-induced surface textures can impede the continuity of the phase transition process across the entire single crystal. Our results provide a fresh perspective for studying the phase transition behavior of graphite and greatly deepen our understanding of this behavior, which will be helpful in guiding further high-temperature and high-pressure syntheses of carbon allotropes.

Room-Temperature Single-Phase Synthesis of Semiconducting Metal-Covalent Organic Frameworks With Microenvironment-Tuned Photocatalytic Efficiency.

In order to improve the solubility of metallated monomers and product crystallinity, metal-covalent organic frameworks (MCOFs) are commonly prepared via high-temperature sol-vothermal synthesis. However, it hampers the direct extraction of crystallization evolution information. Exploring facile room-temperature strategies for both synthesizing MCOFs and exploiting the crystallinity mechanism is extremely desired. Herein, by a novel single-phase synthetic strategy, three MCOFs with different microstructure is rapidly prepared based on the Schiff base reaction between planarity-tunable C3v monomers and metallated monomers at room temperature. Based on detailed time-dependent experiments and theoretical calculations, it is found that there is a planarity-tuned and competitive growth relationship between disordered structures and crystal nucleus for the first time. The high planarity of monomers boosts the formation of crystal nucleus and rapid growth, suppressing the forming of amorphous structures. In addition, the microenvironment effect on selective photocatalytic coupling of benzylamine (BA) is investigated. The strong donor-acceptor (D-A) MCOF exhibits efficient photocatalytic activity with a high conversion rate of 99% and high selectivity of 99% in 5h under the 520nm light irradiation. This work opens a new pathway to scalable and efficient synthesis of highly crystalline MCOFs.

Thermal enhancing luminescence and thermal quenching luminescence of Sc2(MoO4)3: X mol% Eu3+

The synthesis of a series of Sc2(MoO4)3: x mol% Eu3+ red phosphors (x = 0, 1, 3, 5, 7, 10, 15, 20, 30, 50, 70 and 100) was successfully completed through the implementation of a high-temperature solid-phase synthesis methodology. The optimum 5 mol% Eu3+ doped Sc2(MoO4)3 were prepared at 900 °C, and no concentration quenching luminescence were observed in Sc2(MoO4)3: x mol% Eu3+ phosphors though crystalline phase varied. In particular, the 10 mol% Eu3+-doped Sc2(MoO4)3 exhibited thermal enhancing luminescence (TEL) when excited with 277 nm light. At 125 °C, the intensity reached 250 % of the initial value, while at 300 °C, it remained at approximately 190 % of the initial intensity. With 396 nm excitation, the phosphor presented thermal quenching luminescence (TQL). In the TEL Sc2(MoO4)3: x mol% Eu3+ phosphors, the optimal temperature of TEL enhanced with Eu3+ concentration increasing. For the Eu2(MoO4)3 phosphor, it only demonstrated TQL with 277 nm and 396 nm excitations. The mechanism of TEL can be ascribed to the enhancement in structural rigidity resulting from the negative thermal expansion (NTE), which was accompanied by efficient energy transfer from MoO42− to Eu3+. Furthermore, the fluorescence lifetime of the 5D0 level demonstrated a declining trend then a rising trend with elevated Eu3+ concentrations, whereas the color purity value exhibited an ascending trend always.

Coordination Compounds of Cobalt(II) Nitrate and Perchlorate with Acetamide and Carbamide: Precursors for the Synthesis of Catalytically Active Tricobalt Tetraoxide

The reactions of cobalt(II) nitrate or perchloride with acetamide (AA) or carbamide (Ur) in an aqueous medium produce coordination compounds [Co(Ur)4](NO3)2 (I), [Co(Ur)6](NO3)2 (II), [Co(AA)4(H2O)2](NO3)2 (III), [Co(AA)4(H2O)2](NO3)2 ∙ 2AA (IV), [Co(Ur)6](ClO4)2, (V), [Co(AA)4(H2O)2](ClO4)2 (VI), and [Co(AA)6](ClO4)2 (VII). The compositions of the isolated complexes are determined by physicochemical methods, and the crystal and molecular structures of compounds II, V, VI, and VII are solved. Specific features of the thermal behavior of all synthesized compounds in a wide temperature range are studied in detail. These compounds are shown to be used as precursors in the preparation of nanosized Co3O4 using self-propagating high-temperature synthesis. The catalytic activity of thus synthesized Co3O4 in the model epoxidation of allyl alcohol is studied.

SYNTHESIS AND PHYSICO-CHEMICAL PROPERTIES OF A NEW COMPLEX FERRITE

The article discusses the synthesis of new complex ferrite, radiographic and electron microscopic studies. The phase of complex ferrites was synthesized by the method of high-temperature sol-gel synthesis. For the first time, the structure of CrKFe2O5 Composite ferrite was studied by X-ray phase analysis and scanning electron microscope methods, the syngony type, elementary cell parameters, radiographic and pycnometric densities, and elemental analysis were determined. A comparative analysis of the relationship between the parameters of the Crystal cell of primary substances and the parameters of the obtained complex ferrite Crystal cell was carried out. Micro-samples were taken from different parts of the crystallite obtained through a scanning electron microscope, the elemental composition of the crystals was analyzed, and the general type of layer of the complex ferrite surface was demonstrated. As a result, the fact that the compound consists of two phases, the clarity of its construction was determined by the topography and chemical composition of the compound. As a result, it was found that the newly synthesized complex ferrite corresponds to the Formula CrKFe2O5. The particle size of the compounds formed is large (between 200 μm, 20.0 μm, 5.00 μm and 2.00 μm).

A Study of the Structure and Properties of a Ti–Al–Mg/Ti-Based Metal–Intermetallic Material Produced by Self-Propagating High-Temperature Synthesis Combined with Pressing

A Study of the Structure and Properties of a Ti–Al–Mg/Ti-Based Metal–Intermetallic Material Produced by Self-Propagating High-Temperature Synthesis Combined with Pressing

УТИЛИЗАЦИЯ МЕТАЛЛИЧЕСКОГО ПОРОШКА ВЫСОКОУГЛЕРОДИСТОГО ФЕРРОХРОМА МЕТОДОМ САМОРАСПРОСТРАНЯЮЩЕГОСЯ ВЫСОКОТЕМПЕРАТУРНОГО СИНТЕЗА (СВС)

This article discusses the methods of recycling high-carbon ferrochrome metal powder by self-propagating high-temperature synthesis. The article is devoted to the study of aspiration metal dusts formed during the production of ferroalloys. The article analyzes the composition of the source material, its physicochemical properties, and the impact on the testing process. The publication touches upon the relevance of this topic and the advantages of the self-propagating high-temperature synthesis method. Particular attention was paid to comparative analyses of this method from other traditional material processing processes. This article will help to consider the problem of environmental pollution and the impact of traditional metallurgical processes on the ecosystem. The authors also analyze in detail the physical properties of the original powder samples and their combustion temperature mode. The publication shows the process flow charts, laboratory devices, and the type of resulting material. This article provides a detailed analysis of the types of laboratory devices, their physical and mechanical properties. The publication provides a thorough and detailed chemical analysis of the resulting material. In the course of the study, the expected results were obtained, which are presented in the form of tables and a figure. The article consists of an introduction, main part, conclusion, conclusion and list of references.

Synthesis of high purity Ti2AlC MAX phase by combustion method through thermal explosion mode: Optimization of process parameters & evaluation of microstructure

Obtaining high-purity MAX-phase powders is a challenging issue. Therefore, in this article, the effects of two key parameters, including mechanical activation time (1, 2, and 3 h), and preheating temperature (800 and 1000 °C) were investigated on the formation mechanism of Ti2AlC MAX phase using mechanically activated (assisted) self-propagating high-temperature synthesis (MA-SHS) combustion method through thermal explosion mode. For this aim, a powder mixture of titanium, aluminum, and carbon with a stoichiometry ratio of (2:1:1) was used. Differential thermal analysis (DTA) was carried out to evaluate the effect of mechanical activation and preheating temperature of the formation temperature of the target MAX phase. Subsequently, the microstructural, phase analysis, chemical composition, and determination of surface chemical states studies were carried out through scanning electron microscopy (SEM), X-ray energy distribution spectroscopy (EDS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectric spectroscopy (XPS), respectively. DTA results illustrated that applying mechanical activation alters the formation temperature, which leads to an increase in the purity of the MAX phase. The quantitative measurements were carried out using the Rietveld method to determine the purity of the achieved MAX phase. The results indicated that samples subjected to 2 h of mechanical activation at a preheat temperature of 1000 °C exhibited to contain 96.1 % of Ti2AlC MAX phase, which is the highest value among other specimens and the lowest amount of secondary and oxide phases (3.9 % of TiC) during the combustion synthesis process compared to other samples.