Investigating mechanochemical behavior of Cr2O3-B2O3-Mg-C quaternary system

Fundamental aspects of reaction behavior and formation path in the Cr2O3-B2O3-Mg-C quaternary system have been studied to synthesize chromium boride-chromium carbide nanocomposite. In order to find the influence of simultaneous presence of magnesium and carbon on final products, various powder mixtures were chosen according to following reaction: B2O3 + Cr2O3 + (9 − x) Mg + x C. The value of x varied from 0 to 4. In the absence of carbon (x = 0), CrB2 was synthesize through mechanically induced self-propagating reaction (MSR). In the presence of 8 mol Mg and 1 mol C (x = 1), the dominant boride phase was CrB while no chromium carbide was detected. By increasing C content (x = 2), the magnesiothermic reduction occurred in MSR mode; whereas, the synthesis of Cr3C2 initiated after combustion reaction and completed gradually during milling for 6 h. Further increase in C amount (x = 3) resulted in formation of Mg3(BO3)2 as unwanted phases as well as CrB and Cr3C2. In the presence of 6 mol Mg and 4 mol (x = 4), no mechanical reaction was observed even after 8 h of milling. Optimum value of x for the formation of CrB-Cr3C2 nanocomposite was 2. Based on the morphological evolutions, it is evident that the mechanosynthesized powder is made up of nanometric particles.