Magnesiothermic Synthesis Research Articles

Novel synthesis of siligraphene/tungstates (g-SiC/AWO) with promoted transportation of photogenerated charge carriers via direct Z-scheme heterojunctions

We developed here the efficient photocatalysts for the removal of high concentrations of tetracycline under visible light by immobilizing the AWO (A = Ag, Bi, Na) nanocrystals on the surface of siligraphene (g-SiC) nanosheets. The g-SiC/AWO composites was synthesized by magnesiothermic synthesis of g-SiC and sonochemical immobilization of tungstates. These new heterojunctions of g-SiC/tungstates show superior photocatalytic activities in the degradation of high concentrations of tetracycline and 97, 98, and 94% of tetracycline were removed by using low amounts of g-SiC/Ag2WO4, g-SiC/Bi2WO6, and g-SiC/Na2WO4 catalysts, respectively. Based on band structures, the band gaps reduce and the photocatalytic activities were extremely enhanced due to the shortening of electron transfer distance through the Z-scheme mechanism. Also, the graphenic structure of g-SiC is another parameter that was effective in improving photocatalytic performance by increasing the electron transfer and decreasing the rate of electron–hole recombination. Furthermore, the π back-bonding of g-SiC with metal atoms increases the electron–hole separation to enhance the photocatalytic activity. Interestingly, g-SiC composites (g-SiC/AWO) showed much higher photocatalytic properties compared to graphene composites (gr/AWO) and can remove the tetracycline even at dark by producing the oxygenated radicals via adsorption of oxygen on the positive charge of Si atoms in siligraphene structure.

Bulk MgB2 superconductor for levitation applications fabricated with boron processed by different routes

Bulk MgB2 discs were prepared by an in situ route from mixtures of magnesium and boron powders. The boron powders were produced by two methods. The first one consisted of a self-propagating high temperature magnesiothermic synthesis (SHS) process followed by acid and fluorine cleaning and a heat treatment in inert atmosphere. This approach produced boron with purities between 86 % and 97 %, where the main impurity was Mg. Depending on the final heat treatment, these boron powders were amorphous or crystalline. In the second route, high purity nano powders (99 %) of boron were obtained by a diborane pyrolysis process. Bulks of MgB2 were characterized by structural, microstructural, and magnetic measurements. Critical current density, pinning force aspects and levitation force (including guiding force) details were assessed. Amorphous lower purity boron (86–97 %) obtained by the first processing route was found to promote the largest levitation forces of the MgB2 bulks and, among these samples, the best levitation results were recorded when using boron with a purity of 95–97 %. Use of a lower purity boron that decreases the cost of MgB2 promotes large scale production at industrial level of bulk MgB2 superconducting magnets for levitation applications and enhances the applicability potential of MgB2 superconductor. The relationship between levitation force and specific features of the samples such as pinning force details are discussed.

Effects of reductant type on the combustion synthesis of NiB

Ni–B intermetallic alloys are important filler materials which are used in brazing applications. Carbothermic and aluminothermic synthesis routes are main methods to produce NiB. Carbothermic synthesis is carried out in electric arc furnaces and consumes high amount of energy whereas aluminothermic synthesis mainly uses its own reaction energy. Thus, via aluminothermic synthesis, the consumption of energy drops. Aluminothermic synthesis is a sub-group of combustion synthesis methods and, its name is based on the Al which is used as reductant in reactions. In the present study, aluminothermic synthesis conditions of NiB (mainly containing 15% B by wt.) were investigated for increasing B2O3 stoichiometry in reactants. Moreover, some experiments were conducted to understand the magnesiothermic synthesis conditions, as an alternative reductant. Results were compared to each other and to thermochemical simulations which were carried out by using HSC Chemistry 6.12 and FactSage 7.1 softwares. Chemical analysis, SEM-EDS and XRD were the main techniques to characterize raw materials and the products. Increasing B2O3 stoichiometry and the use of the Mg as reductant positively affected the chemical content of obtained NiB phases although metal recovery yields were lower for magnesiothermic experiments than that of aluminothermic experiments. For instance, in the magnesiothermic experiment carried out with 100% B2O3 stoichiometry, the obtained metallic fraction consisted of 84.2% Ni, 15.1% B and 0.1% Mg.

Magnesiothermic synthesis of HfB2–HfC-SiC nanocomposite by spark plasma technique

The HfB2-HfC-SiC nanocomposite was produced using H3BO3, HfO2, Si, C, and Mg as starting materials by spark plasma for the first time. The reactions during synthesis indicate that the synthesis process progressed in self-propagating mode. The reaction mechanisms were investigated by the displacement-temperature-time (DTT) diagram, which was obtained during spark plasma cycles. The synthesis process of the composite was completed at the temperature of 400 °C in less than 30 min. The tendency to form the composite was investigated by thermodynamic calculations, and the formation of HfB2, HfC, and SiC phases was observed by X-ray diffraction. Finally, using the Rietveld method, the mean crystallites sizes of about 54, 26, and 43 nm were calculated for HfB2, SiC, and HfC phases, respectively.

Fabrication and characterization of mesoporous Si/SiC derived from diatomite via magnesiothermic reduction

In the past few decades, SiC and Si have been widely researched via different methods due to their unique electrical conductivity, stable physical-chemical performance and good wear-resisting performance. In this paper, we firstly used diatomite as silica source and carbon powders as carbon source to synthesize mesoporous Si/SiC via magnesiothermic reduction reaction at relative low temperature (650 °C). All samples were characterized by XRD, SEM, TEM and N2 adsorption-desorption. The XRD patterns and TEM images confirmed that diatomite was fully transformed into Si and SiC. N2 adsorption-desorption isotherms shown that Si/SiC exhibited mesoporous structure. Brunauer-Emmett-Teller (BET) gas adsorption data showed that Si/SiC had a specific surface area of 69.09 m2/g and an average pore size about 10.82 nm. The results confirmed that diatomite can fully transformed into Si/SiC. The possible chemical reactions of magnesiothermic synthesis of mesoporous Si/SiC is also discussed.

Activation Energy and Mechanism of the Molybdenum Disilicide Sintering Process

This paper presents dilatometric analysis data for the sintering of off-the-shelf molybdenum disilicide (MoSi2) powder prepared by magnesiothermic synthesis. We have obtained continuous shrinkage curves for MoSi2 powder compacts with an initial relative density of 70% at different heating rates: 5, 10, 20, and 30°C/min. From a quantitative analysis of densification curves for the compacts, the activation energy for the initial stage of sintering has been determined to be Q = 695 kJ/mol. It has been shown that the dominant process in the initial stage of MoSi2 powder sintering is volume diffusion from grain boundaries and surfaces.

Synthesis of bio-inspired N-doped SiC and investigation of its synergetic effects on Mo catalysts in oxidative desulfurization reaction

Bio-inspired N-doped silicon carbide/Mo composites have been successfully synthesized through a facile method, combining magnesiothermic synthesis of biomorphic N-doped SiC by using gelatin biopolymer and embedded molybdenum composites forming in situ. The resulting composite materials contain MoO2, Mo2C, and MoSi2 particles dispersed well on N-doped SiC matrix. The composites displayed superior catalytic properties in oxidative desulfurization of model fuel (99.6%). The comparison between catalytic activity of N-doped SiC, N-doped carbon and SiC without nitrogen dopants demonstrated that N-doped SiC composites are more promising for ODS reaction. Comparable catalytic activity, higher durability, and lower reaction time are the advantages make this composite a good ODS catalysts and a green and cost-effective alternative for practical desulfurization of fuel.

Magnesiothermic synthesis of sulfur-doped graphene as an efficient metal-free electrocatalyst for oxygen reduction.

Efficient metal-free electrocatalysts for oxygen reduction reaction (ORR) are highly expected in future low-cost energy systems. We have successfully prepared crumpled, sheet-like, sulfur-doped graphene by magnesiothermic reduction of easily available, low-cost, nontoxic CO2 (in the form of Na2CO3) and Na2SO4 as the carbon and sulfur sources, respectively. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in CO32− to form graphene, but also sulfur in SO42− from its highest (+6) to lowest valence which was hybridized into the carbon sp2 framework. Various characterization results show that sulfur-doped graphene with only few layers has an appropriate sulfur content, hierarchically robust porous structure, large surface area/pore volume, and highly graphitized textures. The S-doped graphene samples exhibit not only a high activity for ORR with a four-electron pathway, but also superior durability and tolerance to MeOH crossover to 40% Pt/C. This is mainly ascribed to the combination of sulfur-related active sites and hierarchical porous textures, facilitating fast diffusion of oxygen molecules and electrolyte to catalytic sites and release of products from the sites.

Fabrication of morphology-controlled MgO nanowhiskers and “nanocrosses” by magnesiothermic synthesis in vapor phase at 550 °C

Morphology-controlled MgO nanowhiskers and “nanocrosses” were prepared on quartz glass fibers by magnesiothermic synthesis at 550 °C.

Templated magnesiothermic synthesis of silicon nanotube bundles and their electrochemical performances in lithium ion batteries

Silicon nanotube bundles (Si NBs) have been synthesized on a large scale via a templated magnesiothermic method.

Low-temperature Magnesiothermic Synthesis of Mesoporous Silicon Carbide from an MCM-48/Polyacrylamide Nanocomposite Precursor

Mesoporous silicon carbide with high specific surface area was successfully synthesized from an MCM-48/polyacrylamide nanocomposite precursor in the temperature range of 550–600 °C (below the melting point of Mg) by means of a magnesiothermic reduction process. The MCM-48/polyacrylamide precursor nanocomposite was prepared by in-situ polymerization of acrylamide monomer in the presence of mesoporous MCM-48 synthesized by sol-gel method. The physicochemical properties and microstructures of the nanocomposite precursor and the low-temperature SiC product were characterized by X-ray diffraction (XRD), differential scanning calorimetry-thermo gravimetric analysis (DSC-TGA), transmission electron microscopy (TEM) and N2 adsorption–desorption. TEM micrographs and Brunauer–Emmett–Teller (BET) gas adsorption studies showed that the SiC powder was nanocrystalline and had a specific surface area of 330 m2/g and a mesoporosity in the range of 2–10 nm. The presence of an exothermic peak in the DSC trace corresponds to the self-combustion process of the SiC magnesiothermic synthesis. The results also show that the carbon in excess to that required to produce SiC plays a role in the reduction of the SiO2. The mechanism of magnesiothermic synthesis of mesoporous SiC is discussed.