Refractories containing fused and sintered alumina aggregates: Investigations on processing, particle size distribution and particle morphology

Abstract The present study investigated pressed high-purity alumina refractories containing either white fused or tabular (sintered) alumina aggregates under comparable conditions. Using factorial experiments especially the effects of the pressing pressure, the particle size distribution model and the particle morphology were evaluated. White fused alumina exhibited a higher refractoriness under load as well as a lower total compression and creep rate in creep in compression experiments. However, tabular alumina had a higher cold crushing strength and Young's modulus before and after thermal shock. Yet, no significant effect regarding the relative loss of the Young's modulus due to thermal shock was determined. Generally, a higher pressing pressure reduced the apparent porosity and increased the cold crushing strength, the Young's modulus and the refractoriness under load. The batches according to a recently suggested modified Andreasen particle size distribution model contained a considerably higher amount of the coarsest particle fraction, while the medium particle size fractions were reduced. Surprisingly, for both alumina raw materials the modified Andreasen model resulted in a virtually identical apparent density and a slightly lower apparent porosity compared to the conventional Andreasen model. Furthermore, the thermomechanical properties were essentially unaffected, while the cold crushing strength and the Young's modulus were somewhat lower. For both raw materials the addition of blocky coarse grain fractions yielded a lower apparent porosity and higher apparent density compared to angular grains due to improved particle packing. Remarkably, the creep in compression and the creep rate were reduced as well. Consequently, the modified Andreasen model together with a designed particle morphology might allow the fabrication of shaped alumina products with a much higher content of coarse grained particles resulting in at least similar or even improved physical, mechanical and thermomechanical properties irrespective of the used alumina raw material.