High performance refractory ceramics for the glass industry are designed to resist the extreme conditions of glass furnaces operations, namely thermal, chemical (corrosion) and thermomechanical stresses. Bonded mullite zirconia refractories withstand well these conditions. In this work, such a refractory is studied to understand the mechanisms of consolidation and damage of the product during high temperature heating cycles.
A refractory ceramic is composed of aggregates (particles larger than 200µm), a matrix (particles smaller than 200µm) and pores. The evolutions with temperature of physical (e.g. density, porosity, crystal phases), thermal (e.g. thermal mass losses, thermal expansion) and mechanical (e.g. static and dynamic modulus of elasticity, flexural strength) properties were studied to improve the understanding of the thermomechanical behavior of the material. For instance, the evolution of the dynamic modulus of elasticity shows that two main phenomena coexist in the material, namely sintering during heating and microcracking during cooling. The matrix and the aggregates were separately studied to deepen the understanding of the whole material. Consequently, it was demonstrated that microcracking was mainly driven by the difference of coefficients of thermal expansion between the matrix and the aggregates. The zirconia phase change leads to volume changes that also impact the thermomechanical behavior of the refractory [1, 2]. The binder has an influence on the consolidation steps as well.
Furthermore, a challenging in-situ experiment was implemented at the European Synchrotron Radiation Facility (ESRF) [3], to study the evolution of the microstructure as a function of temperature and relate it to the thermomechanical behavior previously observed. For this purpose, an induction furnace was designed to allow in-situ imaging of a sample by X-Ray tomography during a thermal cycle up to 1200°C and back to room temperature. The evolution of the microstructure was investigated from the 3D images acquired at two resolutions: 5 and 0.35µm.