Study On Coated Process And Oxidation Kinetics Of SiC

SiO₂ from silica powder and silica solution was used to coated SiC powder so as to enhance the oxidation resistance of SiC. Besides the oxidation kinetics of SiC powder was studied.In the oxidation resistance experiments for SiO₂ coated SiC powder,the effect of mineralizing substance, adding amount of SiO₂, coating number, calcining etal on coated result and infrared emissivity was studied. In terms of oxidation weight gain theory, XRD, FT-IR, infrared radiation equipment, the oxidation resistance, phase composition, transmittance and emissivity were examed.In the oxidation kinetics experiment for coated SiC powder, the effect of different temperature for 36h on coated result and emissivity of SiC was studied. In addition the oxidation kinetic equations of silica powder coated SiC, silica solution coated SiC and pure SiC were obtained. Finally the oxidation activation energy was gained by Arrhenius relation.The study on SiO₂ coated SiC powder avoiding oxidation showed that whichever SiO₂ is from silica powder or silica solution, the better coated result could be obtained in 1300℃for 4h. SiO₂ was converted into cristobalite. Not only was the coated result without mineralizing substance better, but also the more complete development of quartz crystal could be gained. Compare the result of silica powder coated process with that of silica solution coated process, silica solution coated process was the better. Both the two coated processes were able to heighten emissivity of SiC. Meanwhile the emissivity of silica solution coated process was the higher.The study on oxidation kinetics of coated SiC powder showed that the trend of silica powder coated SiC under cyclic oxidation weight gain curves follow the exponential mathematical model as follows: y = 3.7759(1-10^{-0 .0316t}). The trend of silica solution coated SiC under cyclic oxidation weight gain curves follow the exponential mathematical model as follows: y = 3.698(1-10^{-0 .0228t}). The trend of SiC under cyclic oxidation weight gain curves follows the exponential mathematical model as follows: y = 1.2766t^0.3649. Arrhenius equation was used to study the relation between oxidation reaction rate constant k and oxidation temperature T. At last the oxidation activation energies of silica powder coated SiC, silica solution coated SiC and pure SiC were 41822.7456J/mol, 44366.8296J/mol and 36321.3718J/mol respectively.