Role of Temperature and Nitrogen Flow Rate During the Carbothermic Synthesis of SiC/Si3N4 Nanocomposite Powder from Gel

This research article explores the synthesis of SiC/Si3N4 nanocomposite powder via a carbothermic reaction of silica xerogel under nitrogen atmosphere. The influence of both reaction temperature and nitrogen flow rate on the properties of the produced sample was thoroughly investigated. The results revealed that both reaction temperature and nitrogen flow rate played a very important role not only on the composition ratio of SiC/Si3N4 in the finally produced sample but also on the morphology of both phases. At 1300 degrees C, spherical particles of 40 nm grain size for both phases (SiC and Si3N4) were produced, while silicon nitride is the predominant phase. With increasing the reaction temperature, the amount of SiC increased at the expense of the amount of Si3N4 till SiC becomes the predominant phase at 1500 degrees C. At 1500 degrees C, almost both phases have the shape of nanorods with different grain sizes. At low nitrogen flow rate and reaction temperature of 1500 degrees C, SiC predominates while with increasing nitrogen flow rate the Si3N4 becomes the predominant phase. The photoluminescence spectra revealed that a strong emission was observed at 354 and 389 nm for the sample produced at low and high N-2 flow rate, respectively. On the other hand, a high surface area of 578 and 471 m2/g were produced for samples prepared under low and high nitrogen flow rate, respectively. Also, the mechanism of formation of the SiC/Si3N4 nanocomposite powder was postulated.