Non-destructive thermal damage characterization of cordierite-mullite refractories

Refractory materials containing cordierite (2MgO.2Al2O3.5SiO2) and mullite (3Al2O3.2SiO2) are used as support in furnaces, because of their low thermal expansion properties which confer them a very good ability to thermal shock resistance. Composed of two phases presenting very different CTE (1.5–3×10-6 for cordierite and 4–6×10-6 K-1 for mullite), these materials can develop damage during thermal cycling due to internal stresses. The resulting network of microcracks is well known to improved thermal shock resistance of materials, since it usually involves a significant decrease in their elastic properties. This paper is devoted to the characterisation of the damage generated by this CTE mismatch, thanks to the application of a specific ultrasonic device at high temperature