Synthesis of boron carbide nanoparticles via spray pyrolysis
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Celaletdin Erguna) Department of Mechanical Engineering, Gumussuyu Campus, Istanbul Technical University, Taksim, Istanbul 34437, Turkey; and Prof. Dr. Adnan Tekin, Materials Science & Production Technologies, Applied Research Center, Istanbul Technical University, Maslak, Istanbul 34469, Turkey (Received 16 February 2016; accepted 24 June 2016)
A continuous process was developed to synthesize submicron boron carbide particles from boric acid and sucrose-based precursor solutions using a home-made spray pyrolysis system. A control set of samples was also prepared for comparison purposes of the microstructure and morphology of the ones synthesized via the spray pyrolysis method. Moreover, nickel nitrate was used in a precursor solution to investigate its catalyst effects on the reaction kinetics of boron carbide formation. The boron carbide phase was observed in the particles synthesized with spray pyrolysis at a reactor temperature of 1550 °C. The average particle size was approximately 0.46 lm. No effect of nickel additions was observed as a catalyst in boron carbide formation. Computational fluid dynamics software was used to model and simulate the experimental system. Simulation results provided information about the residence time and the temperature distribution along the tube reactor.
I. INTRODUCTION
Boron carbide (B4C) is a covalently bonded, strategic material with an extremely high hardness (27.4–34.3 GPa) exceeded by only that of diamond and cubic boron nitride, a high melting point (;2500 °C), a low density (2.52 g/cm3), a high elastic modulus (290–450 GPa),1 and a high neutron absorption cross section (600 barns).2 The combination of these unique properties makes B4C a suitable material for applications, such as grinding media, cutting tools, nozzles for slurry pumping, personal armor, and nuclear shielding applications. Recently, much attention has been paid to the unique thermoelectric properties of boron carbides because they have a large Seebeck coefficient, surprisingly low thermal conductivity, moderate electrical conductivity, and hightemperature stability.3–7 In particular, boron carbide’s Seebeck coefficient is approximately 300 lV/K,3–6 thermal conductivity is approximately 0.05 J/K s cm5,7 and thermal diffusion is approximately 0.01 cm2/s near room temperature, despite being hard and stiff with very high sound velocities (106 cm/s).6,8 The dimensionless thermoelectric figure-of-merit (ZT 5 a2 r/j) of boron carbide (where r is electrical conductivity, j is thermal conductivity, and a is the Seebeck coefficient) on the Contributing Editor: Tina Salguero Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2016.264
order of one was reported, whereas ZT 1 has also been predicted at high temperatures.6,9 These distinctive properties make boron carbide a strong candidate for hightemperature thermoelectric power generation.6,8–12 Due to its large Seebeck coefficient, boron carbides can also be used as neutron detectors, batteries,
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