In-situ synthesis of ultra-fine ZrB2-ZrC-SIC nanopowders by sol-gel method

摘要

ZrB2-ZrC-SiC nanopowders with uniform phase distribution were prepared from cost-effective ZrOCl2 center dot 8H(2)O by a simple sol-gel method. The synthesis route, ceramization mechanism and morphology evolution of the nanopowders were investigated. ZrB2-ZrC-SiC ceramic precursor can be successfully obtained through hydrolysis and condensation reactions between the raw materials. Pyrolysis of the precursor was completed at 650 degrees C, and it produced ZrO2, SiO2, B2O3 and amorphous carbon with a yield of 39% at 1300 degrees C. By heat-treated at 1500 degrees C for 2 h, highly crystallized ZrB2-ZrC-SiC ceramics with narrow size distribution were obtained. With the holding time of 2 h, both the crystal size and the particle size can be refined. Further prolonging the holding time can lead to serious particles coarsening. Studies on the microstructure evolution of the generated carbon during the ceramic conversion demonstrates the negative effect of the ceramic formation on the structure order improvement of the carbon, due to the large amount of defects generated in it by the boro/carbothermal reduction reactions.