Preparation and characterisation of Al₂O₃film on hollow glass microspheres by the sol-gel process

Hollow microspheres are usually used as a lightweight filler in syntactic foams. In this work, Al₂O₃sols were selected and prepared under optimised conditions. A layer of Al₂O₃film was prepared on hollow glass microspheres by the sol-gel process. The phase and element evolution of Al₂O₃gel powders during exsiccation and heat treatment was investigated by infrared spectroscopy (IR) and X-ray diffraction (XRD). The 1-3 layers of coatings were prepared using a dipping method and characterised by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The results show that clear stable sols can be obtained at 80-90°C with n(H₂O):n(Al³+) greater than 150:1 and pH 2·7-3·5. After exsiccation, AlOOH, the precursor of Al₂O₃sols, can be totally eliminated and turned into Al₂O₃. Coatings with double layers have the best effect for covering the hollow microspheres.