Abstract

In many industrial processes refractory materials are exposed to considerable mechanical stresses at high temperatures. The wear resistance of refractories against these conditions is crucial to the service life of industrial aggregates. Therefore, an increased flexibility at elevated temperatures and an advanced thermal shock resistance constitute desirable properties for refractory materials. The formation of interlocking structures contributing to this behaviour can be found in nature; for instance itacolumite, a material based on interlocked quartz grains exhibiting large intergranular decohesions. This particular microstructure, reminding of a puzzle, enables itacolumite to resist large strains before failure when exposed to thermomechanical stresses. Inspired by this very special material behaviour, this study attempts to create refractory castables which are capable of resisting higher thermal shock stresses and show an improved flexibility. As a first step of this study, two chemically identical high-alumina castables were designed, which differ in the shape of the added Y-PSZ (Partially Stabilized Zirconia doped with 3 mol.-% yttria; size 0.2 - 1 mm) grains only: The first formulation mainly includes anisometric Y-PSZ particles, whereas the second formulation predominantly contains isometric Y-PSZ grains of the same production lot. Thereby, two different methods of material reinforcement, namely transformation toughening and the formation of interlocking structures, are intended. To evaluate their impact on the high temperature performance of the castables, the applied testing methods include cycling Resonant Frequency Damping Analysis up to 1500°C as well as Refractoriness under Load and Creep in Compression, Hot Modulus of Rupture (HMOR) tests between room temperature and 1500°C and a post mortem SEM analysis of the microstructure. The examined castables showed a very similar behavior under compressive load, but considerable difference in bending behavior. Both the HMOR measurements and SEM analysis indicated that the grain shape has a strong influence on the condition of the matrix. Since heating as well as the sudden volume change of the martensitic transformation particularly lead to expansion in axial direction of the grains in case of the elongated Y-PSZ particles, a different crack network is introduced into the surrounding matrix compared to the castable containing isometric zirconia grains which expand approximately uniform in radial direction.