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Thermal plasma synthesis of boron carbide

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2018
Altınok, Sertaç
Boron carbide is of interest for many applications due to unique combination of superior properties. These properties also make its production quite challenging. The net-shape boron carbide products are obtained by sintering of powders at high temperatures. So as to decrease the sintering temperature, initial particle size should be reduced to nanometer sizes. In this study, thermal plasma synthesis of boron carbide nanoparticles was investigated. For this purpose, radio frequency inductively coupled plasma system was used, operated at 25 kW. Initial experiments were carried out with boron oxide as solid precursor with methane as carbon source. This has shown that the boron carbide can be synthesized with this approach, but, the fraction in the total resulting powder was very low. To increase the conversion efficiency, a new precursor was used. This was azeotrope mixture of trimethyl borate and methanol used as both boron and carbon sources, fed into the plasma in gas phase with the use of evaporator coupled with peristaltic pump. Pure boron carbide with an average particle size of 31 nm were successfully synthesized. This powder was obtained after methanol-washing of as-synthesized nanopowder. In order to further increase the efficiency, diisopropylamine (DIPA) and nitrogen gas were used as additives. With the use of these additives the resulting powder was 70% B4C in the form of nanoparticles with an average size 51 nm.