Synthesis of Nanocrystalline Boron Carbide by Direct Microwave Carbothermal Reduction of Boric Acid

The excellent physical and chemical properties of boron carbide make it suitable for many applications. However, its synthesis requires a large amount of energy and is time-consuming. Microwave carbothermal reduction is a fast technique for producing well crystallized equiaxial boron carbide nanoparticles of about 50 nm and very few amounts of elongated nanoparticles were also synthesized. They presented an average length of 82 nm and a high aspect ratio (5.5). The total reaction time was only 20 minutes, which disfavor the growing process, leading to the synthesis of nanoparticles. Microwave-assisted synthesis leaded to producing boron-rich boron carbide. Increasing the forward power increases the boron content and enhances the efficiency of the reaction, resulting in better crystallized boron carbide

Microwave synthesis of ultra-high temperature ceramic ZrC nanopowders

Ultra-high temperature ceramic zirconium carbide (ZrC) nanopowders were synthesized for the first time via a microwave-assisted carbothermal reduction reaction using zirconia (ZrO 2 ) and carbon black (C) as the starting materials. The effect of the reaction time on the formation of ZrC nanoparticles was examined. The as-synthesized samples were characterized using X-ray diffraction (XRD), helium pycnometry, Brunauer-Emmett-Teller (BET) N 2 adsorption, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The lattice constant and interplanar distance (d 111 ) were calculated, and the crystallite size was obtained using the Scherrer formula. Results from the experiment show highly crystalline ZrC, with crystallites less than 50 nm and nearly-spherical morphology, using 3 kW of power and only 50 min of reaction time, with a maximum reaction temperature of 1400 °C, lower than those involved using the conventional heating carbothermal reduction. The reaction time was ∼2 h shorter than that required by using a combined sol-gel and microwave-assisted carbothermal reduction method, used to prepare submicron ZrC powders (200–300 nm). The high heating rate achieved on the synthesis was favored by the excellent microwave absorption of carbon black, and the uniform heating at molecular level induced by the microwaves on the samples.Fil: Yasno Gaviria, Juan Pablo. Universidade Federal do São Carlos; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gunnewiek, Rodolfo F. K.. Universidade Federal do São Carlos; BrasilFil: Kiminami, Ruth H. G. A.. Universidade Federal do São Carlos; Brasi