New Production Method

About

What is the problem? Conventional processing of boron carbide powders involves the melting of boron oxide in an electric arc furnace with a graphite electrode at temperature in excess of 2500C. The interaction between the molten boron oxide and the carbon leads to the formation of boron carbide in a large solid ingot. This ingot has then to be ground down to powders with size below 10 microns. As boron carbide is the third hardest material in the world grinding is difficult. Our new Solution? A low temperature synthesis route which offers the potential to reduce energy requirements and labour costs Benefits of the new technology Low temperature process which saves on synthesis costs Production of a fine particulate form reduces grinding costs Production of uniform fine particles Background Conventional processing of boron carbide powders involves the melting of boron oxide in an electric arc furnace with a graphite electrode at temperature in excess of 2500C. The interaction between the molten boron oxide and the carbon, known as carbothermal reduction leads to the formation of boron carbide with by-product of carbon dioxide. The boron carbide is formed as a large ingot that has to be separated from the graphite electrode by mechanical means and is then ground down to powders with size below 10 microns. Since boron carbide is the 3rd hardest material in the world, the grinding process is labour intensive and costly due to wear of grinding tools. The costly grinding process combined with the energy intensive carbothermal reduction process makes the boron carbide powder very expensive.   There is also non-uniformity in the composition of the boron carbide depending where it is in relation to the graphite electrode. This occurs due to diffusion during the carbothermal reduction, giving a boron carbide composition that can vary from boron rich (away from electrode) to carbon rich (near the electrode). The low temperature synthesis route offers a potential to solve the energy and labour intensive problems. There have been many studies in the literature to use polymer precursors for the synthesis of boron carbide. This approach relies upon formation of polymer precursors made from a carbon and boron oxide in water. Once a polymer precursor is formed, it is then ground to a powder and then pyrolysed at around 600C to leave a fine mixture of elemental C and B. This is followed by heat treatment at temperatures between 1200 and 1500C to induce a reaction between C and B to form boron Carbide powders. There are several problems with the existing low temperature synthesis route. They are: (1) the polymer precursor material has to be ground down to powders prior to pyrolysis and this could lead to difficulty in controlling the starting precursor powders size and eventually the final boron carbide size and (2) cannot produce boron carbide powders to below 1 microns. Our new process combines the low temperature synthesis method with a further step which achieves more regular size distribution than can be produced by manual grinding and allows production of particles below 1 micron. Such fine particles of boron carbide powders will enhance the sintering kinetics and can reduce the consolidation temperature.