An investigation on the formation mechanism of nano CrB2 powder in the Mg–B2O3–Cr2O3 system

• CrB2 has been synthesized by starting materials Mg, Cr2O3 and B2O3.
• MSR mode reaction took place after a milling time of 2.5 h.
• Mg3(BO3)2 was largely formed during the thermal process.
• Nanoscale particles were obtained by the mechanochemical technique.

Fundamental aspects of reaction path in the Cr2O3 + B2O3 + Mg system to synthesize chromium diboride have been investigated. Phase transformation analysis and structural evaluation were carried out by means of differential thermal analysis techniques (DTA), X-ray diffractometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). According to DTA results, the magnesiothermic reductions of B2O3 and Cr2O3 incompletely occurred after the magnesium melting (830 and 1100 °C). The products obtained from the thermal synthesis consisted of MgO, Cr and the remaining starting materials, while, no chromium diboride phase achieved even up to 1300 °C. Single phase chromium diboride (CrB2) powder was in situ synthesized in self-sustaining mode by mechanochemical method with an ignition time of approximately 2.5 h. The reaction mechanism in this system was determined by studying the relevant sub-reactions. SEM and TEM observations confirmed that the range of particle size was within 100 nm.