Preparation of Boron Carbide Nanoparticles by Carbothermal Reduction Method
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Preparation of Boron Carbide Nanoparticles by Carbothermal Reduction Method Baohe Chang, Bonnie Gersten, Jane W. Adams1 and Steve Szewczyk2 Department of Chemistry and Biochemistry, Queens College, CUNY, Flushing, NY 11367 USA. 1 Weapons and Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069 USA 2 Oak Ridge Institute for Science and Education at the Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069 USA
ABSTRACT A carbothermal reaction process was employed to synthesize nano-sized boron carbide particles. The reactions were carried out by heating a mixture of boric oxide powder and amorphous carbon reactant under a flow of argon atmosphere in a conventional high temperature tube furnace at 1350-1700 °C for 1-4 h. In order to obtain stoichiometric powder product, additional pure boron powder was added to the reaction mixture to compensate for the boron loss in the form of B2O2/B2O3 vapor during the reaction. The effect of the structure and morphology of the precursor materials on that of the products was also investigated. X-ray diffraction (XRD) studies indicated that the powdered product prepared under optimized reaction conditions was crystalline boron carbide. Transmission electron microscopy (TEM) observations showed that the product nanoparticles ranged from 50 nm to 250 nm with the average size between 100 nm and 150 nm depending on the reaction conditions. Some boron carbide particles were as small as 50 nm. Energy dispersive spectroscopy (EDS) was also used to determine the stoichiometry of the boron carbide nanoparticle products. INTRODUCTION Boron carbide (B4C) is a low density non-metallic refractory material with a high-melting temperature exceeding 2400 °C and very high compressive strength and Young’s modulus [1-3]. Its hardness comes third after diamond and cubic boron nitride, but with the advantage of being stable up to very high temperatures [3,4]. It also has a high cross section for neutron capture and excellent high-temperature thermoelectric properties [5]. These properties make it an attractive material for numerous uses in micro-electronic, nuclear, military, space and medical applications. Two examples are its use as an abrasive wear-resistant material and as a neutron moderator/absorbent in nuclear reactors/industry In addition, it is of particular use in lightweight ceramic armor. Extensive research has been conducted over the past decades to produce boron carbide powders [6-11]. Boron carbide can be prepared by a variety of methods, such as direct reaction of carbon with boron [6]; carbon-thermal reduction of boron oxide over 1000 °C [7]; reduction of BCl3 by CH4 at a temperature of 1500 °C with laser [8]; metallothermic (usually magnesiothermic) reduction of B2O3 in the presence of carbon at 1000-1200 °C [9], or rapid carbothermal reduction of meltable B2O3-containing precursor at above 1900 °C [10]. Commercially, B4C is produced by a carbothermal process using boric acid and carbon at temperatures near the melting po
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