Fracture behavior and microstructure of Al2O3–SiO2 castables containing andalusite

Abstract

Abstract To evaluate the andalusite role on the fracture behavior of Al2O3–SiO2 castables and reveal the improvement mechanism of flexibility, Al2O3–SiO2 castables with various andalusite additions (0, 10, 20, 30, 40, and 50\xa0wt%) were prepared adopting homogenized bauxite, andalusite, calcium aluminate cement, microsilica and ultrafine α-Al2O3 powder as raw materials. Wedge splitting test was used to determine fracture behavior of Al2O3–SiO2 castables. The improvement mechanism of toughness was discussed according to the analysis of microstructure. The results show that incorporation of andalusite is an effective way to change fracture behavior and improve the flexibility of the Al2O3–SiO2 castables. The force-displacement curve of the Al2O3–SiO2 castables without andalusite addition is featured with a linear fracture behavior, while the force-displacement curves of the Al2O3–SiO2 castables containing andalusite are characterized by a nonlinear fracture behavior. The flexibility parameter (GF/σNT ratio) rises markedly from 35.3\xa0μm of the castable without andalusite to 197.8\xa0μm of the castables with 40% of andalusite addition, which increases more than twice. Microcracks toughening plays one major role in the improvement of the flexibility of Al2O3–SiO2 castables containing andalusite. The formation of microcracks can be attributed to mismatch of coefficient of thermal expansion between andalusite particles and matrix, caused by anisotropic behavior of andalusite aggregates and mullitized andalusite aggregates. The interlocking microstructure of in situ formed mullite grain in the matrix is the second reason for the toughness improvement of Al2O3–SiO2 castables containing andalusite.