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Efficient hydrogen production relies on cost-effective and durable non-noble metal electrocatalysts for the hydrogen evolution reaction (HER). In this work, a liquid metal-assisted solid-flame combustion synthesis (SF-CS) method was used to create transition metal carbide TMC) nanocrystals with exposed facets. The TMCs include TiC, VC, NbC, TaC, Ta 2 C, WC, and Mo 2 C. In acidic solutions, the TMC nanocrystals show enhanced conductivity and superior HER performance, as evidenced by their lower Tafel slope, higher current density, and decreased overpotential. In particular, Mo 2 C nanocrystals exhibit an overpotential of 95 mV and a Tafel slope of 26 mV dec−1. These findings highlight a noteworthy improvement over previously reported nanostructures in recent years in terms of the HER properties of Mo 2 C with particular facets. This improvement is attributed to the unique surface characteristics, such as energy and active sites, which are impacted by various factors and require more investigation to meet the intended goals. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Zirconium-based ceramics and composites such as ZrC, ZrB2, ZrC–SiC, ZrB2–SiC–ZrC, and ZrB2–SiC–ZrC–ZrSi were synthesized in fine powder form via combustion synthesis (CS) using ZrSiO4, Mg, C, B, and NaCl as raw materials. Temperature distributions in the combustion wave were measured by thermocouples and used to estimate the combustion temperature and wave propagation velocity. The influence of the NaCl mole fraction on the combustion parameters, phase composition, and particle size of the composite powders was investigated. The experimental results revealed that the combustion temperature and particle size of the composites have a stable decreasing tendency with increase in the NaCl mole fraction in the starting mixture. It was found that near the combustion limit (1.5mol NaCl), the combustion temperature drops below 1500°C and the particle size reaches the nanometer scale. [Copyright &y& Elsevier]

Abstract This paper reports the preparation of Ti microparticles that are angular and spherical in shape through the combustion of a TiO 2 + αCa (where α is moles of Ca) exothermic mixture in an inert atmosphere. The relationship between the combustion parameters and the properties of the resultant Ti particles is discussed with consideration of the effect of Ca concentration. Using excess amounts of Ca in the experiment was effective in modifying the shape of the particles from angular to spherical. The Ti powder was found to be well-dispersed and the diameter of individual particles ranged from 5 µm to 50 µm. Based on the combustion parameters, the activation energy for the redox reaction was calculated as ∼ 138 kJ/mol. This paper discusses the chemistry of the reduction process and highlights the effects of combustion temperature and the amount of liquid calcium on the characteristics of the Ti particles. Graphical abstract The combustion process in TiO 2 + Ca mixture developed a maximum temperature of about 1820 °C and resulted in Ti spherical particles. fx1 [ABSTRACT FROM AUTHOR]

In this study, a single-step combustion process for the synthesis 1-D, 2-D, and 3-D micro and nanostructures of AlN was developed. The structures were grown by combustion of Al+ k AlF 3 (or ZnF 2 )+ m NH 4 Cl reaction mixture under 4.0 MPa nitrogen atmosphere. Based on experimental data, the growth conditions, morphology, and composition, optical, and thermal properties of AlN micro and nanostructures were determined. The formation of structures was associated with the combustion temperature, liquid and gas-phase reactions, and the type of additives used in the experiments. The new insight, we gleaned from this study may help in the selective growth of AlN micro and nanostructures of different morphology, enhancing their functionality. [ABSTRACT FROM AUTHOR]

In this study, we examined the effect of potassium perchlorate (KClO 4 ) and magnesium hydroxide (Mg(OH) 2 ) additives on the combustion behavior of a ZrO 2  + 2Mg mixture to produce a fine powder of zirconium metal. The results of thermodynamic analysis and experiments imply that nearly 0.04 mol of KClO 4 is needed to initiate a combustion reaction in the ZrO 2  + 2Mg system. As the amount of KClO 4 increases from 0.04 to 0.1 mol, the combustion temperature increases from 1250 to 1850 °C. This results in formation of fine zirconium powder with a typical particle size of less than 5 µm, and with 1.4–2.2 wt% residual oxygen. Subsequent reduction of particle size to 100–500 nm, and oxygen content to <1.0 wt% was achieved by adding Mg(OH) 2 . The as-prepared Zr powder was mixed with nitrocellulose and printed onto 10–100 µm thin-layers to study their burning stability. The wave propagation in a thin layer was on the order of 0.35–30 cm/s, which is suitable for applications requiring localized power generation. [ABSTRACT FROM AUTHOR]

This study deals with combustion behavior of B 2 O 3 /Mg/NH 4 Cl/C complex systems for the synthesis of amorphous boron (B), boron carbide (B 4 C), and boron nitride (BN) nanostructures. The raw mixtures used in the experiments were prepared on the base of a B 2 O 3 –Mg precursor mixture, which is sufficiently exothermic to maintain a self-propagating regime of the combustion reaction. Thermodynamic analysis of the combustion temperatures and experimental validation indicate that the 1000–1500 °C temperature range is very effective for synthesizing the nanostructures of B, B 4 C, and BN. It was found that B-containing functional nanostructures are mainly spherical nanoparticles (B) or nanosheets (B 4 C, BN). The phase composition and microstructural characteristics of the final products were evaluated based on the combustion temperature and solid/liquid phase changes. [ABSTRACT FROM AUTHOR]

Combustion based synthesis of AlN nanoparticles using the "solid nitrogen" promotion reaction was investigated in Al2O3 + 3Mg system in nitrogen atmosphere. A controlled amount of Mg + 0.5NH4Cl mixture as a solid source of nitrogen was blended with the Al2O3 + 3Mg starting system and the synthesis reaction of AlN nanoparticles was conducted using the exothermic heat of the entire reaction system. The resulting AlN nanoparticles were characterized by X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR), PL spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller surface area techniques. The analysis results confirmed that single phase and crystalline AlN nanoparticles with an average size of 50-500 nm were obtained from the developed approach. Photoluminescence spectra of AlN nanopowders under the excitation of 230-270 nm UV light revealed that AlN emits yellow-red light having a wavelength near to 590 nm. The chemistry of the combustion process is discussed and the basic reactions that led to the formation of AlN are presented. [ABSTRACT FROM AUTHOR]

A melt-assisted solid flame synthesis approach was applied to synthesize boron nanoparticles in argon gas and air atmospheres. For this purpose, we investigated the characteristics of a thermally induced combustion wave in B 2 O 3 + α Mg mixtures ( α = 1.0–1.5 mol) in argon and air atmospheres. Utilizing stoichiometrically insufficient amounts of magnesium ensured that a large portion of molten B 2 O 3 remained in the sample, which reduced the combustion parameters and favored the formation of boron nanoparticles. Under these conditions the combustion temperature and burning velocity were controlled in the range of 1300–1580 °C and 0.065–0.18 cm/s, respectively, and boron nanoparticles in a ∼20–200 nm size range were obtained. The characteristics of boron nanoparticles (morphology, purity, specific surface area, oxidation activity, etc.) were analyzed and a reaction pathway leading to boron nanoparticles synthesis was proposed. [ABSTRACT FROM AUTHOR]

Abstract: Herein, we present the low-temperature solid-phase combustion synthesis of tantalum carbide (TaC), TaC/tantalum silicide (TaSi2), and TaC/tantalum boride (TaB) nanoparticles by the silicothermic reduction of potassium fluorotantalate (K2TaF7) in the presence of carbon, boron, and polytetrafluoroethylene (PTFE, 1 [1] BJH, Barrett–Joyner–Halenda; HRTEM, high-resolution transmission electron microscopy; MMC, metal matrix composite; PFTE, polyfluorotetraethylene; PTFE; polytetrafluoroethylene; RF, radio frequency; SAED, selected area electron diffraction pattern; T c , combustion temperature; TEM, transmission electron microscopy; U c , combustion velocities; XRD, X-ray diffractometer. (C2F4) n ). The temperature–time profiles of the combustion wave were measured by thermocouples and used to calculate the combustion parameters: temperature and wave velocity. The flame temperature was found to increase with the concentration of PTFE. Using high resolution transmission electron microscopy, a homogeneous distribution of highly crystalline nanoparticles was observed. The thermal–kinetic activation energy, the heat released during each of the individual reactions, and the chemical mechanism of the overall combustion process are discussed with respect to the final products. [Copyright &y& Elsevier]

Abstract: An experimental study on the preparation of zirconium silicides was conducted using ZrSiO4–Mg, ZrSiO4–SiO2–Mg and ZrSiO4–ZrO2–Mg powder mixtures by the combustion synthesis (CS) technique. Test specimens having different composition ratios including Zr:Si=1:2, 1:1, 5:4, 5:3, 2:1, and 3:1 were employed in this study. Temperature profiles relative to all the starting compositions were measured using thermocouples, and the values of the combustion parameters (combustion temperature and wave velocity) were estimated using the same. The formation of ZrSi, ZrSi2, Zr5Si3, and Zr3Si2 phases was confirmed by X-ray analysis; however, only ZrSi was produced as a single-phase product. The proposed method was also extended to synthesize spherical ZrSi particles having mean diameters of 0.2–3.0μm. A comprehensive chemical pathway to describe the sequence of chemical reactions in the combustion wave was also proposed. [ABSTRACT FROM AUTHOR]