The influence of microstructure evolution on the dynamic mechanical properties, including storage modulus and internal friction, of the 2.5D SiCf/SiCm composites after high-temperature treatment (800 °C and 1400 °C) in the air was investigated by three-point bending vibration test. The effects of test frequency and amplitude on storage modulus and internal friction were also evaluated. The results show that as-prepared samples have maximum storage modulus and internal friction. However, the composites treated at 800 °C in the air have the minimum storage modulus due to a large number of defects produced within the composite structure, and the composites treated at 1400 °C have the minimum internal friction due to the formation of α-cristobalite in the interface between the matrix and fibers, resulting in stronger interface bonding. With regard to test conditions, the storage modulus is sensitive to amplitude but not frequency; however, the internal friction is sensitive to both frequency because of anelasticity and amplitude due to the static hysteresis.
Refractory linings of waste incineration plants based on oxidation resistant SiC materials enable a long service life at suitable firing and operation conditions. Steam oxidation resistance of Si3N4-SiC, SiO2-SiC, SiAlON-SiC material at 1000°C was tested according to ASTM-C863 after 50c, 100h, 200h, 250h and300h respectively. The phase composition and microstructure before and after oxidation were analyzed by means of XRD and SEM. Results indicate that there is continuous increase of volume expansion and weight change on materials with the oxidation to the oxidation time. After 50h of oxidation, a small amount of cristobalite can be observed in these materials, which comes directly from the oxidation of SiC, Si2N2O and SiAlON or from the crystallization of glass phase. Oxidation weight gain occurs in the first 50 h, but volume expansion takes place after 50h . Compared with the three materials, SiO2-SiC material has a smaller weight change and volume expansion. Comparing the SEM these three materials, it is obvious that SiO2-SiC material has a better density after 300h. Based on the above results, conclusions can be reached that: the sample of SiO2-SiC has better oxidation resistance and is more suitable as lining material of waste incinerator.
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