Preparation of Chromium Oxide Coatings on Aluminum Borate Whiskers by a Hydrothermal Deposition Process

IntroductionAluminum borate( 9Al2 O3 · 2 B2 O3 ,abbreviated to9A2 B) whiskers have been synthesized successfullyin potassium sulfate flux from aluminum sulfateand boric acid13 ] .Since then this new material hasgained a great deal of attention owing to itssuperior properties such as low density,highspecific strength and low thermal expansioncoefficient.One of the applications of 9A2 Bwhiskers is to reinforce aluminum alloys to producelight and strong composites that can be used forthe fab…

Preparation of Chromium Oxide Coatings on Aluminum Borate Whiskers by a Hydrothermal Deposition Process

Aluminum borate whiskers (9Al2O32B2O3) can be used to reinforce aluminum alloys to produce light and strong composites. However, the adverse interfacial reactions between the whiskers and the aluminum alloys inhibit their practical uses; therefore, a protective coating is needed on whiskers. In this work, aluminum borate whiskers were coated with chromium-coating deposits in a hydrothermal solution containing CrCl3, Na2C4H4O6, NaPH2O2, and H3BO3. The presence of the impurity P in the hydrothermal deposits can be avoided by reducing the amount of NaPH2O2 in the coating solution. Thermodynamic analysis was used to discuss the behavior of ions in the coating process. The subsequent heating of the hydrothermal products in air at 800 ℃ yielded smooth Cr2O3 films with a thickness of 0.060.07 μm.