Amélie BIGEARD – Consolidation and thermomechanical behavior of an alumina-mullitezirconia castable refractory during high temperature treatments

Jury

Prof. Emmanuel DE BILBAO, Université d'Orléans - Rapporteur
Prof. Marc HUGER, Université de Limoges - Rapporteur 
Prof. Sylvain MEILLE, INSA Lyon - Examiner
Prof. Pascal FORQUIN, UGA - Examiner
Dr. David JAUFFRES, UGA - Thesis director

Prof. Didier BOUVARD, Senior Scientist - Invited
Mme Camille MESNAGER, Saint-Gobain Research Provence engineer - Invited
 

Abstract

Castable refractory ceramics are used in glass furnaces for their resistance to extreme conditions, such as high temperatures, thermal shocks and corrosion. The objective of this work is to investigate the behavior of an industrial refractory during its production and use. The studied material is an alumina-mullite-zirconia refractory. Alternative formulations were developed to deepen the understanding of the material.
First, the structural (XRD), thermal (dilatometry) and thermomechanical (dynamic hot modulus of elasticity (HMOE), hot strength) evolutions of the materials during successive thermal treatments were studied. These characterizations were then coupled with microstructural observations. A setup was developed at ESRF to perform in-situ X-Ray tomography, with a voxel size of 0.35 µm, and in-situ SEM was used to follow the microstructure evolution at a finer scale, during successive thermal cycles. Two main phenomena were identified: 
- Liquid phase sintering during the first heating, with material heterogeneity (aggregates vs matrix) resulting in constrained sintering of the matrix. 
- Thermal damage by microcracking, originating from the thermal expansion mismatch between the mullite zirconia aggregates and the matrix, during cooling, and microcrack healing/closing during subsequent heating.
Then, the thermal shock resistance of this material was studied, in terms of both post thermal shock mechanical properties and microstructure changes. An in-situ thermal shock test was specifically developed to monitor the dynamic HMOE throughout a thermal shock. 
Finally, a phenomenological model of sintering and damage was proposed. The model is based on the dynamic HMOE as an accessible metric to quantify sintering and damage. It was then implemented in a FEM code, applied to a thermal gradient test and compared to experimental data.
These results propose a comprehensive description of the behavior of this industrial refractory ceramic and pave the way for the development of innovating solutions for the glass industry.