Characterization by acoustic emission pattern recognition of microstructure evolution in a fused-cast refractory during high temperature cycling

Abstract : Fused-cast refractory materials are widely used in the glass industry, especially in the building of superstructures and side walls of fusion furnaces. The HZFC (High Zirconia Fused Cast) products are especially used as tank blocks for the fusion of highly corrosive glasses melted at very high temperature (such as LCD glass), due to their high corrosion resistance and their low generation of glass defects generation. The presence of this high amount of pure ZrO2 in the refractory can be responsible for microdamage occurrence during the cooling step after melt casting (annealing), associated to the martensitic transition of zirconia. Acoustic emission (AE) analysis is well known as a reliable tool to investigate microstuctural evolution at a very small scale. In this work, a fused-cast ZrO2 refractory has been investigated using a AE unsupervised pattern recognition procedure and a frequency-energy coupled analysis. Data gathering during thermal cycles at high temperature (typically 1500 °C) has been done thanks to an innovative self-developed testing device. The analysis of frequency and energy parameters makes it possible to detect and to characterize the occurrence and the chronology of microdamage in specific range of temperature. Hypothesis concerning different ways of microdamage formation below the temperature of the martensitic transformation of ZrO2 during the cooling stage can be proposed related to thermo-mechanical properties and the microstructure of the material. In particular, intergranular and intragranular microcracks due to CTE mismatches occurring in the material have been also investigated.