Synthesis Of Boron Carbide Research Articles

Synthesis of Boron Carbide by the Electric Arc Method in Open Air from Carbon of Various Origins

Synthesis of Boron Carbide by the Electric Arc Method in Open Air from Carbon of Various Origins

The Hydrothermal Method of Preparing Boron–Saccharide Precursors for the Synthesis of Boron Carbide and Its Influence on the Morphology and Phase Composition of the Obtained Products

Owing to its properties, boron carbide has been applied in scientific and industrial fields. For this reason, B4C powders should be characterized by high purity and homogeneity in grain size and shape. In this study, boron carbide was prepared using precursors obtained using a hydrothermal method, and the grain morphology of the product was investigated. Boric acid and the saccharides glucose, fructose, inulin, and sorbitol were used as the precursors. Two precursor dehydration methods, freeze-drying and recrystallization, were compared. The precursors were subjected to DLS grain size and FT-IR spectrophotometric studies, and SEM observations of the precursors and products were performed, confirming that boron carbide powders could be successfully synthesized.

Synthesis of boron carbide by the electric arc method in open air from carbon of various origins

The paper presents the results of experimental studies on the implementation of electric arc synthesis of boron carbide using carbon with different morphology and origin as a feedstock: carbon fibers, flake graphite, carbon obtained by pyrolysis of plant waste, namely, pine sawdust and cedar nuts husks. A feature of the electric arc method used is its implementation using an original plasma reactor using atmospheric air as a working gas medium. Oxidation of feedstock and synthesis products in the working cycle of the reactor is prevented due to the generation of CO and CO2 gases in the reaction zone. The possibility of obtaining a material containing micron and submicron boron carbide crystals in a graphite matrix has been experimentally shown. Also, the paper presents information about the features of the oxidation processes of the obtained materials in comparison with commercial samples of boron carbide. Keywords: boron carbide, electric arc synthesis, carbon fibers, flake graphite, carbon of plant origin.

Синтез карбида бора электродуговым методом в открытой воздушной среде из углерода различного происхождения

The paper presents the results of experimental studies on the implementation of electric arc synthesis of boron carbide using carbon with different morphology and origin as a feedstock: carbon fibers, flake graphite, carbon obtained by pyrolysis of plant waste, namely, pine sawdust and cedar nuts husks. A feature of the electric arc method used is its implementation using an original plasma reactor using atmospheric air as a working gas medium. Oxidation of feedstock and synthesis products in the working cycle of the reactor is prevented due to the generation of CO and CO2 gases in the reaction zone. The possibility of obtaining a material containing micron and submicron boron carbide crystals in a graphite matrix has been experimentally shown. Also, the paper presents information about the features of the oxidation processes of the obtained materials in comparison with commercial samples of boron carbide.

Effects of glucose pretreatment and boric acid content on the synthesizability of B4C ceramics

Synthesis of boron carbide (B4C) as one of the hardest materials on planet Earth is of particular importance due to its wide range of industrial and engineering applications. For this purpose, boric acid and polymers can be used as the boron and carbon sources, respectively. From the family of saccharides in polymeric materials, glucose has shown the best performance for the synthesis of B4C. In this research, untreated and pretreated (caramelized by heating) glucose precursors were selected and mixed with boric acid for subsequent pyrolysis and synthesis processes. X-ray diffractometry and Fourier transform infrared spectroscopy confirmed that heat-treated glucose is a better carbon precursor for B4C synthesis. In order to evaluate the effect of the amount of boric acid, more than its stoichiometric ratio, additional amounts of boric acid (10-40%) were also examined and the excess amount of 30% was determined as the optimal value.

Synthesis of Submicron Boron Carbide by the Non-Vacuum Method with Indirect Supply of the Thermal Energy of a DC Arc Discharge

The results of experimental studies demonstrating the possibility of obtaining boron-carbide powder by treating a mixture of carbon and amorphous boron containing a small amount of boron oxide with DC arc discharge plasma are presented. A feature of the applied nonvacuum electric-arc method for the synthesis of boron carbide is its implementation in an open air environment due to achievement of the effect of screening the reaction zone with gaseous oxide and carbon dioxide. In this case, the initial reagents are heated to the required temperatures by a DC arc discharge plasma burning in the immediate vicinity of the initial-material mixture in the cavity of the graphite crucible. The resulting material contains particles of boron carbide with a size in the submicron range, which are characterized by the “shell–core” type structure. The scheme of the discharge circuit of a laboratory reactor with horizontal arrangement of electrodes and an indirect supply of thermal energy to the initial reagents described in the paper makes it possible to significantly increase the content of the boron-carbide phase and reduce the content of the graphite impurity phase.

Effect of Expanded Graphite on the Reaction Sintering of Boron Carbide.

This paper presents novel results of research focused on reaction sintering of a mixture of expanded graphite and amorphous boron. It has been shown that as a result of combining the synthesis from the elements with sintering under pressure, dense boron carbide polycrystals (95% TD) can be obtained in which stable structures dominate, i.e., boron carbides of stoichiometry B13C2 and B4C. Sintering was carried out on boron excess systems, and reaction mixtures with the following mass ratios (B:C = 5:1; 10:1; and 15:1) were used. Boron excess systems were used due to the presence of additional carbon during sintering since the matrix, reactor lining, and heating elements were made of graphite. 1850 °C was considered to be the optimum reaction sintering temperature for all of the systems tested. This shows that a reduction in the sintering temperature of 200–300 °C was observed with respect to traditional sintering techniques. Micro-cracks are present in the sinters, the presence of which is most likely due to the difficulty in removing the gaseous products which accompany the boron carbide synthesis reaction. The elimination of these defects of sintering requires further research.

Effect of mechanically modification process on boron carbide synthesis from polymeric precursor method

In this study, a polymeric precursor was synthesized from industrial raw materials by the sol-gel method. The organic components in the polymeric chain structure were separated with the calcination process, and a reactant consisting of carbon and B2O3 was obtained. Mechanically modification process was applied to the reactant by a ball milling, which changed the structure of the reactant. It was observed that this process promoted the crystallinity and decreased the particle size of the reactant. In addition, the bimodal structure of the reactant was transformed to a bicontinuous structure. The reactant and a mechanically modified carbon-based reactant (MMCBR) were applied to heat treatment at 1400–1700 °C for 5 h under argon gas to investigate the effect of mechanically modification process on final products. A non-uniform powder morphology with polyhedral and rod-shaped B4C particles was obtained from reactant and MMCBR. While the B4C powder obtained from the reactant was agglomerated, no agglomeration was observed at the B4C powder obtained from MMCBR. As a result, the B4C powder synthesized in this fashion contained less free carbon as compared to that prepared with MMCBR.

Influence of precursor preparation on the synthesis of boron carbide from glutinous rice flour

Boron carbide is a promising candidate for a variety of applications, including blasting nozzles, neutron moderators, and lightweight armor. Using of inexpensive and readily available starting materials which can react with boric acid to form B-O-C bonds, e.g., glutinous rice flour, is one of alternative means to produce high purity boron carbide powder at low temperature. In this study, boric acid and glutinous rice flour, boron and carbon sources, were used for synthesizing B4C powder by the carbothermic reduction. The mole ratios of boric acid to glutinous rice flour ranging from 1:1 to 2.5:1 were formulated and mixed by continuous stirring at 80℃ for 2 h to 8 h. The influence of reaction time during the mixing process on the phase formation of the synthesized powder was investigated. It was found that appropriate reaction time for condensation of 4 h facilitated the B4C phase formation during synthesis. The precursors were synthesized under Ar flow at 1350℃ to 1450℃ for 5 h without calcination. B4C powder with the purity of 90 wt% was successfully synthesized from this study. Chemical bonding, phase analysis, and morphology of the synthesized powder were identified by Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscope, respectively. The influences of starting composition and synthesis temperature on the characteristics of the synthesized powders were also discussed.

Synthesis of boron carbide from its elements up to 13 GPa

The synthesis of boron carbide from its elements (boron and carbon) has been studied under pressures up to 13 GPa and optimum parameters have been determined by varying the (P, T, reactants) conditions. Stoichiometric mixtures of amorphous boron and amorphous carbon have been subjected to a range of temperatures from 1673 K to 2273 K at the pressure values of 2 GPa and 5 GPa. The formation temperatures have been compared to those obtained from mixtures of β rhombohedral boron and graphite, and β rhombohedral boron and amorphous carbon at 2 GPa and 5 GPa. The formation temperature is thus shown to be affected by the pressure and the choice of the reactants. The carbon concentration of boron carbide is also shown to be affected by the pressure at which it is synthesised from elements, and we propose pressure as a means to control the carbon content. Temperature cycling has also been shown to reduce the formation temperature of boron carbide at 13 GPa. The formation of α rhombohedral boron as an intermediate phase is seen at 5 GPa before the formation of boron carbide.

Surface characterization and synthesis of boron carbide and silicon carbide

Knowing the surface properties of ceramic materials is important to determine the area of use. The carbide-based ceramics namely boron carbide and silicon carbide were synthesized and characterized. The surface properties of boron carbide and silicon carbide ceramic materials were examined by the inverse gas chromatography method. Experiments of inverse gas chromatography were carried out to determine the specific adsorption free energy and the specific adsorption enthalpy corresponding to the acid-base properties of both materials. The inverse gas chromatography measurements exhibited values of acidity constants of 0.137 and 0.086 and basic constants of 0.104 and 0.077 for boron carbide and silicon carbide, respectively. The values obtained for and parameters indicated that boron carbide and silicon carbide have an acidic character.

Synthesis of boron carbide reinforced aluminum castings through mechanical stir casting

Nuclear energy is the leading clean energy source in the United States with 99 nuclear power plants generating approximately 20% of the country’s electricity. While the growth of the industry helps to reduce our reliance on fossil fuels, there is also an increase in nuclear waste. The demand for on-site dry cask spent nuclear fuel storage has increased due to complications with the Yucca Mountain Project and diminishing pool capacity. A novel dry cask consisting of an aluminum metal matrix for effective thermal conductivity with boron carbide as a neutron absorbing additive was investigated using gravity sand casting techniques. X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and optical microscopy were used to characterize the resultant microstructure, including boron carbide incorporation and heterogeneity. Results indicate vortex and nonvortex mixing in air with boron carbide (1–10 µm diameter) produces large amounts of porosity and insufficient wetting. Use of a larger particle size distribution of boron carbide (20–60 µm diameter) during high speed vortex mixing prior to casting has shown significant dispersion of up to 12 wt% sufficient for neutron shielding with appropriate wall thickness. These results validate the use of gravity sand casting as a means to produce borated aluminum for an effective alternative to fuel storage.

Synthesis of boron carbide from its elements at high pressures and high temperatures

The formation of boron carbide under high pressures and from elemental reactants has been studied. To this end, stoichiometric mixtures of commercial crystalline beta rhombohedral boron and amorphous glassy carbon have been subjected to temperatures ranging from 1473 K to 2473 K at pressures of 2 GPa and 5 GPa. Similar syntheses have been repeated for crystalline boron and graphite. As the synthesis pressure increases, the temperature of formation of boron carbide is found to increase as well. Moreover, the reaction temperature is shown to be affected by the choice of the reactants.

Effect of initial compositions on boron carbide synthesis and corresponding growth mechanism

ABSTRACTThe yield of boron carbide (B4C) synthesised by carbothermal reduction (CTR) is low (40–50%) owing to the inappropriate initial composition. In this paper, thermodynamic equilibrium simulations for effects of initial compositions on B4C synthesis were performed, while initial compositions on the quality and yield of B4C synthesised by CTR from B2O3-C mixture at atmospheric pressure were systemically investigated. The reaction mechanisms for B4C synthesis process were thermodynamically analysed. Moreover, growth mechanisms for B4C particles were speculated based on the thermodynamic and experimental results. The results show that the simulations agree well with experimental results, and optimal initial composition is 1.906 (B2O3/C weight ratio). Under optimal condition, B4C powder prepared at 1973 K is high-quality with well crystallinity, purity of 93.58% and yield of 90.05%. Additionally, the prepared B4C particles show two types of morphologies, aggregate of small equiaxed particles and needle-like particle, which are formed through different reaction mechanisms, respectively.

Direct synthesis of fine boron carbide powders using expanded graphite

The paper presents a simple approach to obtain boron carbide powder by direct synthesis from elements. For the first time expanded graphite (EG) powder, which is a reactive form of carbon with a unique structure and microstructure, was used as a carbon source for the synthesis of this carbide. As a boron source, fine-grained amorphous boron powder was used. The synthesis was carried out in excess of boron, i.e.; the B to C ratio was 10:1 in mass. The simplicity of the synthesis was based on the fact, that the substrates did not require homogenization because a layer of boron powder was placed over a layer of expanded graphite in a closed graphite crucible. The reaction chamber was heated at temperatures from 1550 to 1650 °C for 2 h in argon. As a result, a fine-grained boron carbide powder (crystallite size of 20–40 nm) which did not require further chemical and mechanical treatment (aggregate size about 1 μm) was prepared. The plausible mechanism of the boron carbide synthesis was the transport of carbon towards boron via carbon monoxide (vapour phase) and its subsequent reaction leading to carbide formation.

Non-catalytic synthesis of boron carbide (B4C) nano structures with various morphologies by sol-gel process

Non-catalytic synthesis of boron carbide (B4C) powders with various morphologies is presented by sol-gel technique using boric acid, glycerol, and citric acid as starting materials. The effect of composition and processing conditions on the phase assembly, particle size and morphology of boron carbide powders were investigated. The formation of nanobelt, needle like, and polyhedral-equiaxed boron carbide particles with a wide-ranged particle size distribution in between 50 nm and 100 µm were observed after heat treatment at 1300 °C for 5 h in argon atmosphere. Furthermore, rod, plate and rhomboid-flake like boron carbide structures were produced by using relatively higher heat treatment temperature of 1500 °C.

Carbothermic synthesis of boron carbide with low free carbon using catalytic amount of magnesium chloride

Microcrystalline boron carbide was synthesized from boric acid and carbon black in the presence of a small amount of magnesium chloride by carbothermal reduction method at 1600 °C. The presence of magnesium chloride in the mixture has a determining effect in increasing the yield of the reaction and lowering the residual free-carbon content of the resulting boron carbide. We have also shown that, compared to several reported carbothermal reduction methods, the present catalyst also considerably lowers the excess amount of boron compound precursor required to afford boron carbide with negligible free carbon. X-ray powder diffraction (XRD) pattern indicated that the product was rhombohedral B4C. No peak, corresponding to free carbon, was observed in the XRD diffraction pattern of the B4C product formed from H3BO3:C:MgCl2 in the molar ratio of 1.0:1.45:0.01. Scanning electron microscopy image also showed that the product is fully crystalline and consisted of uniformly sized particles.

A low cost, low energy, environmentally friendly process for producing high-purity boron carbide

Boron carbide with purity levels higher than that achievable by traditional manufacturing processes using an electric arc furnace (EAF) was produced by a novel low cost, low energy, environmentally friendly process of carbothermic reduction of boric acid (H3BO3) with carbon using a self-designed temperature-controllable electric resistance furnace (ERF). The process is divided into three stages: the pelleting stage, the low-temperature pre-dehydration stage, and the high-temperature reduction stage. The optimal conditions are determined as a pelleting pressure of 20 MPa, pre-dehydration temperature of 400 °C, H3BO3/C ratio of 3.38, and reduction temperature of 1900–2300 °C. The formation of boron carbide changes from liquid-solid reactions to gas-solid reactions with increasing temperature. Furthermore, the decreasing CO partial pressure is verified to be beneficial for the synthesis of boron carbide. The proposed process circumvents the disadvantages caused by the evaporation of large quantities of water steam and unstable reduction temperature and B/C ratios exhibited by the traditional EAF process. Moreover, it provides a more stable and controllable reduction temperature for producing high-purity boron carbide that leads to improved energy consumption, product quality, and cost efficiency and reduces air pollution mainly caused by volatilization and condensation of boron oxides.

Low-temperature green synthesis of boron carbide using aloe vera

The unique structural and physical properties of boron carbide, which make it suitable for a wide range of applications, demands the development of low-cost and green synthesis method. In the present work, the commonly available leaves of aloe vera are hydrothermally treated to form the carbon precursor for the synthesis of boron carbide. The morphological characterization reveals the porous nature of the precursor turning into a tubular structure upon boron carbide formation. The structural characterization by x-ray diffraction and other spectroscopic techniques such as Fourier transform infrared, Raman, photoluminescence and uv-visible near-infrared spectroscopy confirm the formation of boron carbide. The thermogravimetric analysis of the sample is found to exhibit good thermal stability above 500 °C. When the sample is annealed to 600 °C, boron carbide with phase purity is obtained, which is confirmed through XRD and FTIR analyses. The optical emission properties of the sample are studied through CIE plot and power spectrum. Compared with other natural precursors for boron carbide, the aloe vera is found to give a good yield above 50%.

Boron Carbide Synthesis in Low-Voltage DC Electric Arc Initiated in Open Air

We describe a method of obtaining ultrafine boron carbide (B13C2) powder using the effect of a dc electric arc on a mixture of initial reactants containing carbon and boron. A peculiarity of the proposed method is that it can be implemented using arc discharge operating in open air without any vacuum equipment and protective inert gas atmosphere. X-ray diffraction data showed that the synthesized product in the general case contained three crystalline phases: boron carbide (B13C2), graphite (C), and boron oxide (B2O3). Electron-microscopic examination showed that the average size of boron carbide particles ranged from ~50 nm to ~2 μm.