A Non-Aqueous Solution Synthesis of Boron Carbide by Control of In-Situ Carbon

1. J. L. Wattsa,b, Ian D. R. Mackinnona, Peter C.Talbota,b, and Jose A. Alarcoa,b • a Institute for Future Environments • b Science and Engineering Faculty, School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, QLD Australia 4001 • . PRECURSOR ANALYSIS ABSTRACT FORMATION OF B4C Polymerisation time controls the amount of carbon available for reaction as confirmed by XRD (right). XRD pattern of a commercial sample of B4C (below). Synthesis of high quality boron carbide (B4C) powder is achieved by carbothermal reduction of boron oxide (B2O3) from a condensed boric acid (H3BO3) / polyvinyl acetate (PVAc) product. Precursor solutions are prepared via polymerisation of vinyl acetate (VA) in methanol in the presence of dissolved H3BO3. With excess VA monomer being removed during evaporation of the solvent, the polymerisation time is then used to manage availability of carbon for reaction. A Non-Aqueous Solution Synthesis of Boron Carbide by Control of In-Situ Carbon INTRODUCTION Boron carbide is used in a wide range of engineering applications due to a combination of properties including high hardness, a high resistance to chemical corrosion, a high melting point and a low specific weight. The most widely used commercial technique for producing B4C is the reduction of H3BO3 with carbon black (referred to as the carbothermal method) at ~1750°C in electric arc furnaces.1 The overall reaction mechanism for the carbothermal process is: 4H3BO3 + 7C → B4C + 6CO + 6H2O Commercial production methods result in high amounts of undesirable residual carbon as well a course product that requires milling. Theses issues have lead research to focus on alternative lower temperature synthesis methods that result in a fine powder with less residual carbon.2 Solution based synthesis techniques have shown promise in addressing these problems by achieving a greater degree of homogeneity between precursor components before final calcination. Specifically in this researchB4C powders without excess carbon are formed at temperatures as low as 1250°C with a 4 hour residence time. DSC of isolated and mixed components indicating bonding between precursors (above). SEM images of precursor powders before (A, B) and after (C) washing with hot DI water (right). ATR-FTIR spectra of precursor powder confirming the form of the boron phase (below). B4C PRODUCT SEM images of B4C formed from a 1 hour polymerisation (A) and a 19 hour polymerisation (B). Scale bars: 10 µm, inset image: 1 µm. CONCLUSION PRECURSOR PREPARATION The developed technique realises fine, near carbon-free B4C powders by controlling the carbon reactant via the polymerisation time. Enhanced homogeneity of precursors is achieved without the need for excess carbon in the precursor product. REFERENCES 1. J. Bigdeloo and A. Hadian, International Journal of Recent Trends in Engineering 2009, 1, 176-180. 2. M. Kakiage, N. Tahara, S. Yanagidani, I. Yanase and H. Kobayashi, Journal of the Ceramic Society of Japan 2011, 119, 422-425. Addition of VA monomer Polymerisation Solvent evaporation Homogeneous product Dissolution of H3BO3