A study was carried out to determine the optimum parameters for synthesis of SiC-ZrO2 composite materials by carbothermal re-duction of zircon. Test samples were prepared by mixing average mesh size of less than 30 μm of carbon black and 40 μm of zircon with C/ZrSiO4 mass ratio of 0.2 and the extra addition amount of La2O3 was 0, 1 wt.% and 2 wt.%. Prepared samples were subjected to the car-bothermal reduction process at temperatures of 1723, 1753, 1773 and 1803 K for 4 h, respectively. The carbothermal reduction process was conducted in an atmosphere controlled tube furnace at an argon flow of 1.5 L/min. All products were examined by X-ray diffraction (XRD) to determine the transformation. The results showed that the best transformation of SiC-ZrO2 composite materials occurred at 1803 K for 4 h with the amount of 2 wt.%La2O3.
ZrO2-SiC composite powder was synthesized by carbothermal reduction of zircon in argon atmosphere, and it was used as the additive to prepare Al2O3-C refractories. The effects of heating temperature on the synthesis process and the addition of the synthesized composite powder on the properties of the Al2O3-C refractories were investigated. The results show that the synthesized composite powder can be easily obtained by heating the mixture of zircon and carbon black at 1 873 K for 4 h in argon atmosphere, and the relative contents of ZrO2 and SiC in sample reach about 83.7% and 16.3%, respectively. The bulk density, crushing strength and thermal shock resistance of the Al2O3-C refractories can be improved obviously by the addition of the synthesized ZrO2-SiC composite powder.
β-Sialon/ZrN bonded corundum composites were synthesized using fused white corundum,alumina micro powder,zircon and carbon black by nitridation reaction sintering process. Phase composition and microstructure of the synthesized composites were investigated by X-ray powder diffraction and scanning electronic microscope,and the formation process of the composites was discussed. The results show that the composites with different compositions can be obtained by controlling the heating temperature and contents of zircon and carbon black. The proper temperature to synthesize the composites is 1773 K.
A predominance area diagram for the Zr-Si-C-O system at 1773 K was plotted according to correlative thermodynamic data.β-SiC/ZrO2 composites were prepared based on the phase diagram by carbothermal reduction of zircon(ZrSiO4) in argon atmosphere.Zircon and carbon black were mixed according to the C/ZrSiO4 mass ratio of 0.2,and with 0,1wt% and 2wt% extra addition of La2O3.Phase evolution of the mixture was investigated at 1723-1803 K by X-ray powder diffraction,and the microstructure of the product prepared at 1803 K for 4 h was examined by scanning electronic microscope.The results show that the decomposition of ZrSiO4 and the formation of β-SiC can be promoted by increasing the heating temperature and adding La2O3.The β-SiC/ZrO2 composites can be prepared at 1803 K for 4 h in a mixture of zircon,carbon black and La2O3,and the contents of β-SiC and m-ZrO2 in the product sample with 2wt% La2O3 reach the highest values of 10.8wt% and 89.2wt%,respectively.The crystal size of the products is about 200 nm.
The optimum parameters were determined for synthesizing ZrN-Si3N4 composite powder from zircon by carbothermal reduction-nitridation (CTRN) process. The samples were prepared by mixing the carbon black of an average particle size less than 30 μm and the zircon of 40 μm with C/ZrSiO4 mass ratios of 0.2, 0.3, 0.4, and 0.5. The prepared samples were subjected to the CTRN process at temperatures of 1673, 1723, 1753, and 1773 K for 6, 9, and 12 h. The CTRN process was conducted in an atmosphere-controlled tubular furnace in a nitrogen gas flow of 1.0 L/min. All the products were examined by X-ray powder diffraction to determine the transformation. The results showed that the proper transformation of ZrN-Si3N4 occurred at 1773 K for 12 h with a C/ZrSiO4 mass ratio of 0.4.
ZrN-Si3N4 composite powder with low cost from zircon was prepared by carbothermal reduction-nitridation process.The influence of mass ratio of C to ZrSiO4(m(C)/m(ZrSiO4))and soaking time on phase composition and microstructure of the products was studied by means of XRD and SEM-EDS.The formation process of ZrN-Si3N4 composite powder was also analyzed in detail. The results show that with the increase of m(C)/m(ZrSiO4)and soaking time,the formation of Si3N4 and ZrN can be promoted obviously.The ZrN-Si3N4 composite powder with size of 1-2μm can be obtained at 1 773 K for 12 h when m(C)/m(ZrSiO4)is 0.4.
