Investigation On Preparation And Properties Of MgAl₂O₄ Fibers And Fibers Board

The paper presents a new sol-gel synthesis method of MgAl2O4 spinel fibers. Polyaluminium chloride solution was sythesized from a mixture of anhydrous aluminum chloride and aluminum powder firstly. Precursor spinning solution was sythesized from a mixture of polyaluminium chloride solution and magnesium salts solution secondly. Small diameter polycrystalline MgAl2O4 spinel fibers with a certain flexibility were successfully prepared by centrifugal spinning followed by heat-treatment in air atmosphere. The molecular structure of precursor fibers was deduced from the characterization of Fourier transform infrared spectroscopy (FT-IR);The heat treatment of precursor fibers was determined by the differential scanning calorimetry (DSC-TG);The microstructure of fibers was studied by he microscope and scanning electron microscope (SEM).As the result, the spinel precursor decomposes directly to crystalline spinel at 585℃ without any evidence of phase separation. Green fibers were firstly heated at 3℃/min to 600℃ and then heated at 5℃/min to 1000℃/2h/air to sinter. The grain size of The final fibers that are 5～8 μm in dia and 100mm in length can be reduced to 25 nm.MgAl2O4 spinel fibers board was prepared by wet molding in this paper. The MgAl2O4 spinel fibers board with flat surface, uniform thickness and controllable density was successfully prepared by vacuum filtering molding process and pressure to level technique. Wet fibers board was fabricated using MgAl2O4 spinel fibers as base materials and precursor spinning solution diluted with water as the binder. After drying and calcining, the MgAl2O4 spinel fibers board was obtained. The permanent heating conductivity of length, width and thickness directions of the MgAl2O4 spinel fibers board prepared by MgAl2O4 spinel fibers pre-heated at 1000℃ were no more than 7.5%, when the fibers board sintered at 1600℃ for 12 hour. The thermal conductivity was 0.34W/m-K for the MgAl2O4 spinel fibers board with a density of 0.54 g/cm3 in 400℃. The compressive strenth was 0.39MPa when the MgAl2O4 spinel fibers board was compressed 10% in thickness direction.MgAl2O4 spinel fibers board was also prepared by colloidal molding in this paper. The MgAl2O4 spinel fibers board with flat surface and uniform controllable thickness was successfully prepared by colloidal molding.Wet fibers board was prepared using MgAl2O4 spinel fibers as base materials and polyaluminium chloride solution as the binder. Compared with vacuum filtering molding process and pressure to level technique, the compressive strenth of the MgAl2O4 spinel fibers board prepared by colloidal molding was stronger. The compressive strenth was up to 1.5MPa when the MgAl2O4 spinel fibers board was compressed 10% in thickness direction. The permanent heating conductivity of length and width directions of the MgAl2O4 spinel fibers board prepared by MgAl2O4 spinel fibers pre-heated at 1000℃ were only 1.4%, when the fibers board sintered at 1600℃for 12 hour. The thermal conductivity was 0.56W/m-K for the MgAl2O4 spinel fibers board with a density of 0.91g/cm3 in 400℃.