Synthesis of boron carbide from its elements up to 13 GPa

TL;DR

This study investigates the synthesis of boron carbide from elemental boron and carbon under high pressures up to 13 GPa, revealing how pressure and reactant choice influence composition and formation conditions.

Contribution

It demonstrates pressure as a key parameter to control boron carbide's carbon content during high-pressure synthesis from elements.

Findings

Carbon content in boron carbide varies with synthesis pressure.

Pressure influences the formation temperature of boron carbide.

Alpha boron appears as an intermediate phase at 5 GPa.

Abstract

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.