Effect of Expanded Graphite on the Reaction Sintering of Boron Carbide

This paper presents novel results of research focused on reaction sintering of a mixture of expanded graphite and amorphous boron. It has been shown that as a result of combining the synthesis from the elements with sintering under pressure, dense boron carbide polycrystals (95% TD) can be obtained in which stable structures dominate, i.e., boron carbides of stoichiometry B₁₃C₂ and B₄C. Sintering was carried out on boron excess systems, and reaction mixtures with the following mass ratios (B:C = 5:1; 10:1; and 15:1) were used. Boron excess systems were used due to the presence of additional carbon during sintering since the matrix, reactor lining, and heating elements were made of graphite. 1850 °C was considered to be the optimum reaction sintering temperature for all of the systems tested. This shows that a reduction in the sintering temperature of 200–300 °C was observed with respect to traditional sintering techniques. Micro-cracks are present in the sinters, the presence of which is most likely due to the difficulty in removing the gaseous products which accompany the boron carbide synthesis reaction. The elimination of these defects of sintering requires further research.