Ceramic composites based on in situ calcium hexaaluminate/aluminum titanate prepared from ferrotitanate slag

Abstract

Ferrotitanium slag has attracted attention owing to its high aluminum content, which can partly replace the alumina in the traditional alumina/silicon carbide multiphase refractory materials. Alumina/calcium hexaaluminate ceramic composites have been prepared using ferrotitanium slag. However, previous studies neglected the utilization of valuable titanium resources in ferrotitanium slag. Therefore, in this study, calcium hexaaluminate/aluminum titanate composite ceramics were prepared using ferrotitanium slag and aluminum hydroxide as the main raw materials and titanium dioxide (TiO2) as an additive. The influence of TiO2 concentration on the phase composition, microstructure, and mechanical and thermal expansion properties of the ceramics was studied. The results showed that calcium hexaaluminate and aluminum titanate were generated in situ and the composite was reinforced by calcium hexaaluminate, providing flexural strength to the material. The Mg2+ and Fe3+ impurities present in the ferrotitanium slag formed a solid solution with aluminum titanate, accelerating the production of aluminum titanate while inhibiting its thermal decomposition. With the addition of TiO2 (2–20 wt%), the aluminum titanate formed in the ceramic effectively reduced the thermal expansion coefficient of the material. However, at concentrations > 5 wt%, the rutile phase and excessive liquid phase in the sample resulted in a significant reduction in the flexural strength at room temperature. At 5 wt% TiO2, the main crystal phases of the ceramic composite were calcium hexaaluminate and aluminum titanate. The composite exhibited a flexural strength of 19 MPa at room temperature(≈25 ℃), and a thermal expansion coefficient lower than 4 × 10−6 °C−1 at 1100 °C.