China's Refractories

Abstract: Steam oxidation resistance of Si3N4 and Si2N2O as well as SiAlON bonded SiC refractories at 900 ℃ was tested according to ASTM-C863. Phase composition and microstructure before and after oxidation were analyzed by XRD and SEM. The results show that Si3N4 and Si2N2O bonded SiC refractory presents better steam oxidation resistance than SiAlON bonded SiC. For Si3N4 and Si2N2O bonded SiC, the oxidation speed is higher with more pronounced volume expansion in the early 100 h; afterwards, the volume expansion slows down gradually and starts to level off after 300 h. It is considered that the high silica glass phase formed during the oxidation covers Si3N4 and Si2N2O, and SiC as a protective layer and fills the open pores. But for SiAlON bonded SiC, the volume expands gradually and constantly with the increasing oxidation duration even after 500 h, due to the continuous formation of mullite transformed from oxidation products and Al2O3 in SiAlON.

Key words: nitride bonded silicon carbide, steam oxidation resistance, waste incinerator