Effect of Mg/B2O3 molar ratio and furnace temperature on the phase evaluation and morphology of SiC–B4C nanocomposite prepared by MASHS method

Abstract

In this study, SiC–B4C nanocomposite has been synthesized in situ successfully by Mechanical activated combustion synthesis method (MASHS). Initially Si, C, B2O3 and Mg powders as raw materials were weighed according to different molar ratio of Mg to B2O3. In next step theses materials were milled in a planetary mill under Ar atmosphere. The synthesis step was performed in a tube furnace equipped with controlled atmosphere system. The different furnace temperature was investigated on the phase synthesis and morphology of the products. The specimens in the various steps were studied by XRD analysis for evaluation of the phase compositions and calculation of the average crystallite size of them. The morphology of synthesized products was investigated by scanning and transmission electron microscopes (SEM&TEM). The final product contains main phases MgO, B4C and SiC. Also, In this sample byproducts were characterized such as Mg3B2O6, Mg2B2O5 and remaining carbon. XRD pattern of synthesized sample showed the considerable effect of increasing Mg to B2O3 molar ratio on reducing the amount of Mg3B2O6, Mg2B2O5 and remaining carbon. SiC–B4C composite was synthesized with more homogenous morphology by reducing the furnace temperature from 1000 to 900 °C, but reduction of temperature up to 800 °C give rise to uncompleted reaction whereas some unreacted Si remains. Average crystallite sizes of optimal sample were calculated 10.5 and 8 nm for SiC and B4C respectively. These values are consisted of the TEM results somehow while grain size was less than 70 nm. Also SEM observation showed fine grains with sizes falling in the nanometer range.