Properties and microstructures of lightweight alumina containing different types of nano-alumina

The key challenge in designing lightweight wear linings for industrial furnaces lies in the fabrication of porous materials with the smallest possible open porosity and pore size. In this study, in order to increase the migration velocity of the grain boundary, alumina sol and nanosized α-Al2O3 were introduced for their high temperature grain boundary superplasticity. Investigations on the effect of various types of nano-alumina additives on pore repartition and some properties of sintered lightweight alumina were carried out. The introduction of nano-alumina increased the surface stress and accelerated the division of pores. The addition of alumina sol and nanosized α-Al2O3 showed similar effects on the physical properties of lightweight alumina. Compared to samples without addition of nano-alumina, samples containing alumina sol and nanosized α-Al2O3 exhibited the increased closed porosities (from 2.8% to 7.1% and 9.2%, respectively), decreased open porosities (from 12.4% to 10.5% and 5.2%, respectively), lower thermal conductivities (decreasing amplitudes of 16% and 9%, respectively) and increased intracrystalline porosity. Furthermore, the addition of different types of nano-alumina led to microstructural differences in the samples. Abnormally grown grains, with a size of approximately 100-200grain μm, containing numerous smaller intracrystalline pores inside were observed in the sample added alumina sol. The sample containing nanosized α-Al2O3 exhibited a homogeneous distribution of grain sizes. The different grain growth rates, accompanying with various types of nano-alumina, were responsible for the differences in microstructure.