  The formation of boron carbide under high pressures and from elemental
reactants has been studied and optimum parameters have been determined by
varying the (P, T, reactants) conditions. To this end, stoichiometric mixtures
of commercial beta rhombohedral boron and amorphous glassy carbon have been
subjected to temperatures ranging from 1473 K to 2473 K at pressures of 2 GPa,
5 GPa and 13 GPa. Similar syntheses have been repeated for mixtures of beta
boron and graphite, and amorphous boron and amorphous carbon at 2 GPa and 5
GPa. The carbon concentration of boron carbide is shown to be affected by
pressure at which it is synthesised from elements, and we propose pressure as a
means to control the carbon content. The formation temperature is shown to be
affected by the pressure and the choice of the reactants. The effect of
temperature cycling on the formation temperature has also been studied. The
formation of alpha boron as an intermediate phase is seen at 5 GPa before the
formation of boron carbide.
