Preparation And Properties Of Unfired Silicon Carbide Refractories

Silicon nitride bonded silicon carbide refractory blocks that are widespread used in aluminum electrolysis industry encounter many problems in applications, such as high cost and complex production process. The unfired technology of silicon carbide refractories after molding and drying, silicon carbide raw material can be sintered in the service environment, which will be studied in this paper in order to develop a new method for the low cost production of silicon carbide refractories.The different grain size silicon carbides, with room temperature binder phenolic resin and high temperature binder Si3N、AlN and Al mixed powders, molded through double-sided pressure of350MPa, are sintered at960℃(simulating the temperature during electrolyzation of alumina) to prepare products. The density, bending strength, oxidation resistance, heat shock resistance and corrosion resistance are studied in the paper. The phase composition and the morphology of fracture and cross section of the samples are studied by XRD and SEM. The results show that:1. A novel hight tempreture composite binder Si3N4-AlN-Al is obtained from experiment. SiC with best particle size gradation (mass ratio) being mixed with the binder.After being molded through double-sided pressure of350MPa and sintered at960℃for240minutes, samples with some strength are obtained. The maximum density is about2.57g-cm"3and the bending strengths are in the range of7.1-7.5MPa and the porosity is from17.5%to18.7%.2. Samples infiltrated with SiO2colloidal can get some excellent propoties. The maximum density is2.67g·cm-3and the minimum porosity is12.8%. The bending strength improved greately and the maximum bending strength is22.7MPa which is3times of the common ones.3. The phases of the sintering samples are mainly SiC, Al2O3, AlN, Si3N4and Al3.21Si0.47. The microstructure of the sample infiltrated with SiO2colloidal is uniform, with good bondings in the interfaces and the samples have better thermol shock resistance. After5times thermol shock the bending strength are still higher than the common ones.4. Under C.R=2and960℃high tempreture conditions, after eroded in electrolysis for2h,6h and18h, samples with12.5%content of binder and infiltrated with SiO2colloidal at the same time have the best corrosion resistence which is almost the same like Sialon materials sintered at high tempreture.5. Oxidation resistence of the infiltrated samples is better than the common ones, the weight gain from oxidation is also lower than the common samples. Bending strength of the samples improved with the increasing oxidation time during2h and10h.