Low-temperature synthesis of high-purity boron carbide via an aromatic polymer precursor
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nli Jinga) Department of Applied Chemistry, School of Science, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China; and Department of Applied Chemistry, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an, Shaanxi 710049, China (Received 22 February 2018; accepted 23 March 2018)
Boron carbide (B4C) is an attractive material for numerous applications including vehicle armor, cutting tools, blasting nozzles, and abrasive powder, owing to its extreme hardness, high melting point, high Young’s modulus, and excellent thermoelectric properties. However, the application of B4C is limited by the high-temperature synthesis process. The present work aims to explore a low-temperature manufacturing process for synthesizing B4C with a small amount of free carbon. Poly(resorcinol borate) with an aromatic structure and high char yield was chosen as the aromatic polymeric precursor. A combination of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy was performed to investigate the influences of the reaction temperature and holding time on the changes in the precursor microstructure. The results indicate that the rod-like structure of crystalline B4C is successfully synthesized at 600 °C, and the free carbon can be reduced to about 0.8 wt% in the final product. This is because the pyrolysis temperature controlled the carbon content of the B4C, which led to an enlarged contact domain between B2O3 and carbon, and a relatively low-temperature synthesis of B4C. I. INTRODUCTION
Boron carbide (B4C) is a strong candidate for a variety of applications, including armor plating, blasting nozzles, abrasive wear-resistant materials, low-wear bearings, neutron moderators in nuclear reactors, and mechanical seal faces, as well as grinding and cutting tools,1,2 due to its high melting point (2450 °C), high hardness (29.1 GPa), low density (2.52 g/cm3), high elastic modulus (448 GPa), high-temperature stability, high neutron absorption cross-section (600 barns), and excellent high-temperature thermoelectric properties.3,4 For these attributes, an extensive amount of research has been conducted over the past decade on producing B4C powders. Methods of synthesizing B4C can be classified as follows: (i) magnesiothermic reduction; (ii) carbothermic reduction; (iii) synthesis from elements; (iv) chemical vapor decomposition; and (v) synthesis from polymer precursors. However, commercial preparation of B4C is still hampered by a lack of feasible production techniques suitable for industrial upscaling. Although fine B4C powders can be obtained by the magnesiothermic reduction of B2O3 in the presence of carbon, this process is a)
Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/jmr.2018.97
inadequate for the production of high-purity powders, as powders are easily contaminated by magnesium compounds.5 The most commercially
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