Presentation on theme: "A Non-Aqueous Solution Synthesis of Boron Carbide by Control of In-Situ Carbon J. L. Watts a,b, Ian D. R. Mackinnon a, Peter C.Talbot a,b, and Jose A."— Presentation transcript:
A Non-Aqueous Solution Synthesis of Boron Carbide by Control of In-Situ Carbon J. L. Watts a,b, Ian D. R. Mackinnon a, Peter C.Talbot a,b, and Jose A. Alarco a,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. ABSTRACT PRECURSOR ANALYSIS FORMATION OF B 4 C INTRODUCTION Synthesis of high quality boron carbide (B 4 C) powder is achieved by carbothermal reduction of boron oxide (B 2 O 3 ) from a condensed boric acid (H 3 BO 3 ) / polyvinyl acetate (PVAc) product. Precursor solutions are prepared via polymerisation of vinyl acetate (VA) in methanol in the presence of dissolved H 3 BO 3. With excess VA monomer being removed during evaporation of the solvent, the polymerisation time is then used to manage availability of carbon for reaction. 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 B 4 C is the reduction of H 3 BO 3 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: 4H 3 BO 3 + 7C → B 4 C + 6CO + 6H 2 O 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 research B 4 C powders without excess carbon are formed at temperatures as low as 1250°C with a 4 hour residence time. PRECURSOR PREPARATION Dissolution of H 3 BO 3 Addition of VA monomerPolymerisationSolvent evaporationHomogeneous product Polymerisation time controls the amount of carbon available for reaction as confirmed by XRD (right). XRD pattern of a commercial sample of B 4 C (below). 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). B 4 C PRODUCT SEM images of B 4 C formed from a 1 hour polymerisation (A) and a 19 hour polymerisation (B). Scale bars: 10 µm, inset image: 1 µm. CONCLUSION 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. The developed technique realises fine, near carbon-free B 4 C 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.