High Temperature Ceramic Nozzle with excellent Thermal Shock Resistance for Oxygen Burners

摘要

The Al25 based ceramic nozzles for oxy-fuel combustion were prepared through a slip casting method and by a sintering reaction from the individual oxides after adjusting the composition of Al2O32/SiO2 for Al2TiO5 mullite. It appears that the low thermal expansion of Al2TiO5 ceramics are due to the effects of grain boundary micro-cracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. During the reheating run, the individual crystallites expanded at low temperature; thus, the solid volume of the specimen expanded into the micro-cracks, whereas the macroscopic dimensions remained mostly unchanged. As a result, the material expanded very little up to 1000 ℃ and the microcracks closed at higher temperatures. This result is closely related to thermal expansion curves, which were relatively steep. A characterization of the damage induced by thermal shock was conducted by measuring the evolution of the Young's modulus using ultrasonic analysis, aided by the density and thermal expansion coefficients.