SOL-GEL COATING OF ALUMINA FIBER-BUNDLES

A procedure for coating alumina fibre bundles with fibrillar boehmite particles is described. Fibrillar boehmite particles, having a specifi c surface area of 150 m(2)/g, were adsorbed onto the surface of the al umina fibres. The surface of the alumina fibres was first charge rever sed by adsorption of a charge reversing agent. Polyvinylsulphate (PVS) proved to be an excellent charge reversing agent, whereas citric acid and Tiron (3,5-pyrocatecholdisulphonic acid disodium salt) were unabl e to reverse the surface charge of the alumina fibres. By using polyvi nyl-sulphate (PVS), it was possible to adsorb an arbitrary number of l ayers of fibrillar boehmite particles. The coating of the alumina fibr e bundles resulted in an increase in specific surface area from 0.09 m (2)/g for the uncoated fibres, to 0.7 m(2)/g for alumina fibres coated with four layers of fibrillar boehmite particles. The adsorbed boehmi te particles were fixed onto the alumina fibre surface by calcination at 550 degrees C for 120 min, during which the boehmite was transforme d into gamma-Al2O3. The coated alumina fibre bundles were characterize d by krypton adsorption and scanning electron microscopy (SEM). (C) 19 97 Elsevier Science Limited.