Influence Of Microfine Powders On Microstructure And Properties Of Corundum-based Castables

In this paper, the corundum-based castables with microfine powders of reactive alumina, nano alumina particle, and ultra fine silica were studied respectively. After heating treatment at 110℃×24h, 1100℃×3h and 1500℃×3h, the typical physical properties and microstructure characteristics of castabbe samples, such as apparent porosity, bulk density, pore size distribution, permanent linear change, cold modulus of rupture (CMOR), cold crushing strength (CCS) and hot modulus of rupture (HMOR), thermal shock resistance were studied. The morphology and mineral phases were studied by techniques of scanning electron microscopy (SEM) and X-ray diffraction (XRD). A correlation study of pore size distribution and strength was also included in this paper.The addition of reactive alumina or nano alumina powders increases the compactness of castable samples, resulting higher bulk density and lower apparent porosity, the pore size can be reduced, and thus, the microstructure of castable sample can be improved. The addition of reactive alumina or nano alumina powders can promote the sintering process, which improved the CMOR and CCS, and resulting higher density. The addition of reactive alumina or nano alumina powders can also improve the sample's HMOR and thermal shock resistance. After heating treatment at 110℃×24h, 1100℃×3h and 1500℃×3h, the correlative between the grey relational degrees between pore size and mechanical sthength was investigated. It was found that high correlative between pore size of less than 0.2μm and CMOR existed, it was also found that the grey relational degrees between the pore size of less than 0.5μm and CCS of the samples is high.After heating treatment at 110℃×24h, 1100℃×3h and 1500℃×3h, the castable with Al₂O₃/SiO₂ gel addition exhibits high CMOR and CCS, however, the properties of apparent porosity, bulk density, HMOR and thermal shock resistance were deteriorated. When the addition of Al₂O₃/SiO₂ gel is 6wt%, the samples exhibited poorest HMOR and thermal shock resistance. For the castable samples with 110⌒?4h and 1100℃×3h heating treatment, the grey relational degree between the pore size of less than 0.2μm and 0.5～1μm and CMOR/CCS is high; for the castable sample with 1500℃×3h, the grey relational degree between the pore size of 1～3μm and larger than 9μm and CMOR/CCS is high.The addition of ultra fine silica can fill the interspaces within castable structure effectively, thus, the compactness of castable sample can be improved. The addition of ultra fine silica enhanced sintering process, which resulting higher density, CMOR and CCS. Also, the addition of ultra fine silica increased the samples'HMOR significantly, and the samples'HMOR reach its peak value when the addition of the ultra fine silica is 6wt%, however, the thermal shock resistance became the worst. It was also found that the grey relational degrees between pore size of 45⁹0μm and the samples strength is high. The grey relational degrees between pore size and the CMOR are higher than that of the grey relational degrees between pore size and the CCS. With the increase of heating treatment temperature, the gray relational degrees between pore size and CMOR were increased, and the gray relational degrees between pore size and CCS were increased firstly and decreased thereafter.