Preparation and characterization of ultrafine ZrB2–SiC composite powders by a combined sol–gel and microwave boro/carbothermal reduction method

A combined sol–gel and microwave boro/carbothermal reduction technique was investigated and used to synthesize ultrafine ZrB2–SiC composite powders from raw starting materials of zirconium oxychloride, boric acid, tetraethoxysilane and glucose. The effects of reaction temperature, molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) on the synthesis of ultrafine ZrB2–SiC composite powders were studied. The results showed that the optimum molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) for the preparation of phase pure ultrafine ZrB2–SiC composite powders were 2.5 and 8.0, respectively, and the firing temperature required was 1300°C. This temperature was 200°C lower than that require by using the conventional boro/carbothermal reduction method. Microstructures and phase morphologies of as-prepared ultrafine ZrB2–SiC composite powders were examined by field emission-scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM), showing that SiC grains were formed evenly among the ZrB2 grains, and the grain sizes of ZrB2 in the samples prepared at 1300°C for 3h were about 1–2μm. The average crystalline sizes of these two phases in the as-prepared samples were calculated by using the Scherrer equation as about 58 and 27nm, respectively.