| The oxidation behavior of Si3N4/SiC and Sialon/SiC in air at the temperature range from 800 to 950℃ was investigated by electronic balancein in nitride furnace with continuous weighing method, which provides a useful experimental basis for their practical application in aluminum electrolysis cells sidewalls. The results are as follows:(1) Si3N4/SiC and Sialon/SiC materials began to oxidize at 800℃ around.(2) With different materials and forming process, oxidation increment of three kinds of materials differs from each other. Their oxidation resistance of casting forming Sialon/SiC is the best, then the pressure forming Sialon/SiC, pressure forming Si3N4/SiC the worst. As the temperature increased, the specific oxidation increment of the above three materials all increased, namely, the oxidation became severely.(3) In the isothermal process at 800℃,850℃,900℃ and 950℃ in air, all oxidation increments of Si3N4/SiC and Sialon/SiC showed linear relations with time in the early oxidation stage; while in the late stage of oxidation, the curve became parabolic. The results indicated that in the prophase of oxidation the reaction speed was controlled by interface reaction, and in the anaphase by gases diffusion; the velocity constant of the two stages are both in agreement with the following relationships: k1223K>k1173K>k1123K>k1073K, kPN>kPS>kCS.(4) The apparent activation energy of the casting forming Sialon/SiC material was the maximal, then the pressure forming Sialon/SiC and the pressure forming Si3N4/SiC.(5) The pores in those oxidized samples were moderate. The porosity and pore size decreased compared with original samples, while the volume density increased.(6) Some gray and white substance appeared on the surface layers of all three samples after oxidation, and the layers were significantly different from their substrates within SEM. EDS and XRD analysis indicated that the layers were SiO2.
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