Effect of milling on the combustion synthesis of ternary system B2O3, Mg and C

The preparation of boron carbide nanoparticles was investigated by coupling a highly exothermic B₂O₃-Mg thermite reaction with a weakly exothermic B₄C formation reaction. An experimental study for the formation of B₄C nanoparticles was conducted by combustion synthesis in the mode of thermal explosion. The mixture of B₂O₃:Mg:C with stoichiometry 2:7:1 was milled for 1, 3, 6, 12, 24 and 36 h. The milled powders up to 12 h were used for the combustion reaction. The combustion reactions were carried out in an inert atmosphere (Ar) at 900 C. The samples are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The XRD analysis of all samples after combustion indicated that the main phase was MgO along with Mg₃(Bo₃)₂ and B₄C as secondary phases. The XRD analysis of samples after leaching of the combustion product detected boron carbide as a main phase and unreacted graphite as minor phase, while the graphite was the least for products of 12 h milled powders. The TEM image of this sample showed nanometric crystallite of less than 60 nm.