Research Of SiC Based Composite Ceramic For Heat Absorbing Material In Tower Solar Thermal Generation

With the traditional fossil energy's depletion and environmental pollution increasing,it cause the race of developing new energy,solar energy become a hot issue as it's green and abundant,especially in solar thermal generation.The heat absorb material is the key to the solar thermal generation system,this study attempts to prepare SiC based composite ceramic which has good oxidation resistance for tower solar thermal generation absorb material.This paper studied two kinds of bonded phase to improve the oxidation resistance of SiC based ceramics,one method is in situ generated mullite bonded phase with shanxi coal-series kaolin and manufacture alumina,the other method is in situ generated magnesium aluminate spinel which prepared with calcined bauxite.The relationship between formula composition,performance,preparation process and microstructure was studied by XRD and SEM,the mechanism of oxidation resistance was also discussed.The results are as follows:?1?In this study,the synthesized mullite used for the bonded phase of the SiC based ceramic was prepared by shanxi coal-series kaolin and manufacture alumina and sodium sulfate by molten salt method.The microstructure and properties of the specimen was tested by modern testing techniques.The results indicate that the specimen A3?with 8%sodium sulfate?sintered at 1500?has the optimal performance,the water absorption is 0.06%,the apparent porosity is 0.17%,the bulk density is 2.82 g/cm³,the bending strength is 97.4 MPa.Sodium sulfate can significantly reduce the sintering temperature of the specimen,when the amount of the sodium sulfate is less than 10%,the sodium sulfate will promote the decomposition of mullite,and promote the formation of corundum;when the amount of the sodium sulfate is equal to 10%,mullite phase disappeared,specimens only have corundum and a little quartz;when the amount of the sodium sulfate is more than20%,sodium sulfate and corundum will react and generate nepheline,the physical properties of the specimens reduced sharply.?2?H series based on A3 formula formula was designed,SiC-corundum-mullite material was preparated by buried firing.The microstructure and properties of the specimen was tested by modern testing techniques,the results indicate that H3formula?30%bonded phase?fired at 1500?has the best performance:the bending strength is 51MPa,and it rise up to 60MPa after 30 times thermal shock cycles.The weight gain of H3 is 35.46mg/cm² after oxidized at 1300?for 100h,the surface is perfect.?3?Magnesium aluminate spinel used for the bonded phase of the SiC based ceramic was prepared with calcined bauxite and magnesia.The results indicate that the bending strength of the magnesium aluminium spinel is optical,the bending strength of E1 fired at 1480?is 248 MPa,and it's stability?159MPa to 174 MPa?when the firing temperature rises,spinel is stability at the high temperature.Phase of the samples is magnesium aluminum spinel,mullite and quartz.?4?Choose the magnesium aluminum spinel as bonded phase by analysising the performance and microstructure,design G series based on E1 formula,SiC-magnesium aluminate spinel material was preparated by buried firing.The microstructure and properties of the specimen was tested by modern testing techniques,the results indicate that the bending strength of G2^G5 samples are 44⁴9 MPa after firing at 1520?,the loss rate of the bending strength is 11%²1%after30 times thermal shock cycles,The weight gain of G2^G5 is 42⁵5mg/cm²after oxidized at 1300?for 100h,the surface of G5 is white,the surface of G2^G5become yellow and bubble.