Preparation Process Of Alumina Fiber And Characterization For Their Coating Properties

Al2O3 fiber is a kind of inorganic ceramic fibers with the property of extraordinary heat resistance, high-temperature oxidation resistance and good corrosion resistance in both acid and alkaline environment. Among ceramic fibers, Al2O3 fiber as a useful candidate material due to its low raw material costs and simple production process has been widely used in such fields as industrial, military, and civilian engineering. The present work is mainly focused on preparing technique of Al2O3 fiber, whose porosity can be controlled by adjusting processing parameters. Here, sol-gel method was used, followed by centrifugal spinning, drying and calcining. The study contents include following three main aspects.(1) Al2O3 fiber precursor was prepared using Al(H2PO4)3 sol, which was obtained by the reaction of HPO4 with Al(OH)3, followed by centrifugal spinning. Al2O3 fiber precursor had 4-12μm in diameter. The preparation process has obvious advantages:e.g. the reaction time is short, and manipulation is relatively simple. AlPO4-Al2O3 composite fibers can be easily obtained after drying and calcination of Al2O3 fiber precursor. Their calcination curves were drafted according to TG-DTA data, XRD analysis, and SEM observation. The effect of different calcination temperature on the phase composition and morphology of obtained fibers was also studied. α-Al2O3 phase appeared after the calcination at 1580℃. However, there was still AlPO4 phase in the fibers. The pure α-Al2O3 phase can not be obtained via this route, thus further exploration must be done on the preparation technique of Al2O3 fibers.(2) Since pure α-Al2O3 fiber was not obtained by Al(H2PO4)3 sol, we choose the reaction of AlCl3·6H2O and Al powder to prepare inorganic aluminum sol. Oxide doping technique was also used for improving the density of Al2O3 fibers by respectively adding Y2O3, Y2O3 stabilized ZrO2 and Sm2O3 into the aluminum sol. It was mainly focused on the effect of different dopants and calcination temperature on porosity, phase composition, and density of Al2O3 fibers. The results showed that doping with Y2O3 stabilized ZrO2 can remarkably suppress grain growth in Al2O3 fibers during high-temperature calcination, and that Sm2O3 doping can effectively control the porosity of Al2O3 fibers.(3) The porous Al2O3 fibers can be used as substrates on which photocatalysts grow for easy separation following photocatalytic process. In present study, Bi2WO6 photocatalyst was successfully grown in-situ on porous alumina fibers by a hydrothermal method. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. At 180℃, the influence of hydrothermal holding time and pH value on the formation of Bi2WO6 and its crystalline morphology was mainly investigated, and their photocatalytic degradation performance under visible-light irradiation also evaluated. The results show that Bi2WO6 crystallites formed on porous alumina fibers have needle-like crystalline morphology, and dense and homogeneous microstructure. Moreover, their crystalline morphology and photocatalytic performance were also affected by hydrothermal holding times and pH values. The desirable crystalline morphology of Bi2WO6 crystallites can be grown on porous alumina fibers when the holding time is 9 h, and pH value is 1, while the samples still possess porous structure. Their degradation rate of RhB solutions under visible light can reach 99.5% within 90 min.