Preparation of Al₂O₃/Mo nanocomposite powder via chemical route and spray drying

A route to prepare nanometer-sized Mo particulates in Al₂O₃ was attempted by a combination of solution reactions in molecular scale and forcing precipitation by a spray-drying technique. MoO₃ was first dissolved in ammonia water and then added in the slurry with high purity, submicrometer Al₂O₃ powder. Mixed suspension was spray-dried, and then the dried granules were reduced by hydrogen gas and further hot-pressing to a bulky composite at various temperatures. Dissolution of Mo oxide, adsorption reactions on the alumina surface, and surface potential of alumina particles in homogeneous ammonia suspension were studied. Characterization of the granules, including compactability, flowing properties, surface morphology, grain growth of Mo and Al₂O₃, and mixing homogeneity, were examined. Homogeneity of the spray-dried granules was determined by the calculation of mixing index and the observation of the microstructure of the sintered body. The existence of intergranular, intragranular, and nanosized Mo particulates within Al₂O₃ grains was observed by transmission electron microscopy (TEM). All the evidence revealed that homogeneous composites with nanometer-sized Mo had been successfully prepared by this attempt with the proposed chemical roue and following the spray-drying process.