Investigation of fracture behavior of typical refractory materials up to service temperatures

Abstract

In service, refractory linings experience thermal stresses typically exceeding their mechanical strength. However, this does not lead to the catastrophic failure of modern well-designed refractory linings. They rather undergo a more or less stepwise wear process and typically retain their structural stability despite existing substantial damage. Classic mechanical tests, such as modulus of rupture measurements that solely consider the maximum strength right before catastrophic fracture occurs are thereby inappropriate to quantify the resistance to damage of refractory products. Despite significant advancements in the theoretical description of fracture process and resistance to damages of refractory materials, there is still a lack of empirical data and scientific studies regarding the fracture behavior of typical refractory materials, especially at high temperature. Wedge splitting measurements, which proved very efficient to investigate the fracture behavior of refractory materials, were performed up to 1500◦C on four typical refractory materials and supported by microscopic investigations. All investigated refractory materials display a rather brittle behavior below 900◦C. While the high alumina brick almost remains in this state up to at least 1500◦C but gets mechanically weakened above 1400◦C, the cement bonded high alumina castable displays a drastic increase of its specific fracture energy above 1100◦C and no substantial loss of strength. This strongly suggests a brittle-to-ductile transition. The andalusite and silica bricks also seem to experience a brittle-to-ductile transition, even at lower temperature than for the high alumina castable; however as the andalusite brick gets dramatically weakened by the formation of liquid phase, its specific fracture energy collapses as well above 1100◦C. Much more surprisingly, silica bricks see their specific fracture energy strongly rising at about 1000◦C, but falling again above 1100◦C while retaining substantial strength, hence coming back to a rather brittle state.