Preparation And Charaterization Of Alumina Fiber By Sol-Gel Technology

Alumina fibers were prepared by the sol-gel technology in this paper. After heat treatment, alumina fibers in different crystalline phases were obtained, which were γ-Al2O3and α-Al2O3. The effects of the aluminum sources on the formation of spinnable sol and the gel fibers, the morphology and microstructure of calcined fibers and their thermal properties were discussed. Meanwhile, alumina fibers containing different amounts of SiO2were fabricated, and the effects of SiO2on the sol spinnability, the morphology and microstructure of alumina fibers and the thermal properties have been investigated.1. Preparation and characterization of alumina fiber by sol-gel technologyIn this study, alumina fibers were prepared by a sol-gel combined centrifugal spinning technology. The effects of different aluminum salts (Al(NO3)3·9H2O and AlCl3·6H2O) on the formation of spinnable sols and alumina fibers were discussed. And also the proper heat treatments were performed as to alumina fibers derived from different aluminum salts. In addition, thermal conductivity of the calcined fibers was measured. The initial sol was composed of two different sol systems. One was formed by the hydrolysis of aluminum isopropoxide (AIP) in aluminum salt solution. The other was the solution of aluminum carboxylates stabilized by the excessive acid, and the sol was prepared with aluminum powder, formic acid (HCOOH), acetic acid (CH3COOH) and water as raw materials and copper chloride (CuCl2·2H2O) as the catalyst. The two systems were mixed well by stirring before aging in a water bath at60℃. After the proper solvent evaporation and condensation, spinnable sol was formed. The conditions, such as temperature and humidity of the surroundings, rotating speed and right viscosity of the sol, play important roles in forming desired gel fibers. The fibers were characterized by XRD、IR、TG-DSC and thermal conductivity analysis, indicating that there barely existed obvious differences in microstructure and thermal conductivity between the calcined fibers prepared by aluminum nitrate as the aluminum source and the one with aluminum chloride as aluminum sources. The thermal conductivity of γ-Al2O3fibers lumps prepared by aluminum chloride was0.06595W/m·K, which was the lowest, while the thermal conductivities of α-Al2O3fiber lumps prepared by aluminum chloride and aluminum nitrate were0.1665W/m-K and0.1778W/m-K, respectively. Namely, alumina fibers have potential applications in high temperature insulating materials. However, the pulverization of α-Al2O3fibers needs to be solved, and it needs more improments in the processing of fiber preparation.2. Preparation and characterization of alumina fibers containing SiO2Spinnable sol was prepared with AlCl3·6H2O、AIP and Al powder as aluminum source and TEOS as source of silica. Gel fibers were obtained by centrifugal spinning method. The effect of TEOS in forming spinnable sol was discussed in this paper, which demonstrated that hydrolysis of TEOS could accelerate formation of linear polymer and correspondingly shorten the aging time. However, excess TEOS could lead to three-dimensional polymerization, which could make the sol hardly spinnable. Therefore,1wt%and2wt%were chosen as the appropriate amount of TEOS. Moreover, fibers containing1wt%and2wt%SiO2were characterized by TG-DSC、 XRD、IR、SEM and measurement of thermal properties, and the effects of SiO2in morphology and microstructure of alumina fibers were discussed. It was also studied that SiO2could inhibit the growth of α-Al2O3grains and make fibers much denser. The measurement indicated that the lowest thermal conductivity was0.07156W/m·K for γ-Al2O3fibers lumps containing1wt%SiO2, while thermal conductivities of α-Al2O3fibers containing1wt%SiO2and2wt%SiO2were0.1292W/m·K and0.1261W/m·K, respectively. Besides, the existence of SiO2mitigated the pulverization of α-Al2O3fibers, indicating better heat insulating property than pure α-Al2O3fibers.