POLYMERIC SYNTHESIS OF SILICON CARBIDE WITH MICROWAVES

摘要

Among the several polytypes of silicon carbide (SiC), there is one that exhibits a cubic lattice and that is known as β-SiC or 3C-SiC. This carbide has a wide range of applications, but most of the industrial processes produce mixtures of the polytypes rather than a single one. Physical separation of polytypes is difficu hence processes where it is possible to control the kind of polytype that is being produced are always under study. Polymeric synthesis with microwaves for producing this carbide was the aim of this work. A polymeric precursor was prepared by means of hydrolysis and condensation reactions from pheniltrimethoxysilane, water, methanol, ammonium hydroxide and chloride acid. The precursor was placed into a quartz tube in vacuum; pyrolysis was carried out conventionally in a tube furnace, and by microwaves at 2.45 GHz in a multimode cavity. Conventional tests took place in a scheme where temperature was up to 1500°C for 120 minutes. Microwave heating rate was not controlled and tests lasted 60 and 90 minutes. Products of the pyrolysis were analyzed by means of X-ray diffraction; in the microwave case the diffraction patterns showed a strong background of either very fine particles or amorphous material, then infrared spectroscopy was also employed for detecting carbides. In both processes β-SiC was found as the only produced carbide.