Preparation And Properties Of Unfired Silicon Carbide Refractories

Silicon nitride bonded silicon carbide refractory blocks that are widespread used in alu-minum 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 produc-tion of silicon carbide refractories.The different grain size silicon carbides, with room temperature binder phenolic resin and high temperature binder Al2O3and B2O3powders, 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 penetration resistance are studied in the paper. The phase composition and the morphol-ogy of fracture and cross section of the samples are studied by XRD and SEM. The results show that:1. The best particle size gradation (mass ratio) obtained from orthogonal experiment is:1mm-0.3mm:45μn:5μm:1μm=45:18:24:4:9. After being molded through double-sided pressure of350MPa and dried in200℃for120minutes, the samples with dif-ferent contents of high temperature binder meet the requirement of masonry and transport. The density is about2.57g·cm-3and the bending strengths are in the range of13-21MPa.2. After sintered at960℃, the more the high-temperature binder, the higher the bending strength of the samples will be. The highest bending strength is19MPa in the samples with12.5%binder. The samples with7.5%binder have the highest density,2.55g·cm-3.3. The phases of the sintering samples are mainly SiC, Al2O3, Al4B2O9. The microstruc-ture of the sample is uniform, with good bondings in the interfaces. With the increase in the content of binder, the fracture mechanisms change from intercrystalline fracture to the mix-ture of intercrystalline fracture and transcrystalline fracture. 4. For sample after thermal shocks for5times, the bending strength loss rate increases with the content of binder. The best result appears in samples with7.5%binder, the bending strength loss rate maintaining25%in varying temperature difference and show good resis-tance in the erosion experiments. The oxidation resistance of all samples are almost the same high. The shape of the oxidation curves change from straight line at low temperatures to pa-rabola at higher temperatures.