An investigation of thermomechanical behavior and microstructural properties of high chromia and alumina refractories for the glass industry

In this work two different classes of refractories, developed and produced by Saint-Gobain SEFPRO, were investigated: alumina fine grains refractories (AR) and chrome oxide fine grains and coarse grains refractories (CR). The creep behavior of AR was studied, in particular the influence of secondary phases, grain size and distribution, to verify new materials better performance compared to the AR already presents in SEFPRO catalogue. For CR with actual tests employed by Saint-Gobain SEFPRO, in particular thermal fatigue and corrosion resistance, information about crack propagation, material modes of failure, microstructural behavior, effects of secondary phases on thermomechanical resistance are limited. Furthermore these tests don’t always reflect applications and don’t allow to make a coherent hierarchy among materials with respect to microstructural observation and material composition. By introducing new tests and by observing failure surfaces new properties and microstructural behavior were observed, and a coherent hierarchy among products to understand their pertinence for several identified applications was obtained. Mechanical resistance, through 4-point bending test, and Creep behavior at 1200°C have been investigated for alumina refractories. 4-point bending, toughness tests, through SEVNB Method, at 1200°C and cyclic mechanical loading (CML) at 1200°C and 1400°C have been performed on CR. Improved creep behavior of certain alumina products was related to the lower silica content and other confidential components that control grain growth and grain boundaries sliding. Differences in transgranular and intergranular crack propagation were attributed to different matrix and grain cohesion. For CR, in the presence of interconnected large pores, toughness behavior improved, decreasing material integrity being large pores the major source of material detachment. In one class of CR zirconia was present. Despite its beneficial contribution to the thermal shock resistance, it was not so evident for toughness and induced micro-cracks were observed as crack-initiation sources. Cyclic mechanical loading was performed to simulate internal thermo-mechanical stress, despite a certain hierarchy could be established, further tests need to be performed. Finally, the parameters obtained were used to calculate thermal shock parameters according to thermal elastic approximation. A coherent hierarchy between fine grains and coarse grains chrome oxide materials was established.