Hydrothermal Synthesis of Porous Al2O3/Al Metal Ceramics: I. Oxidation of Aluminum Powder and Structure Formation of Porous Al(OH)3/Al Composite

The properties of ASD-1 aluminum powder and its oxidation with water at 100°C were studied. It was found that the microstructure of a surface oxide film and the conditions of oxidation significantly affected the dynamics of changes in the pH of the solution and in the degree of aluminum conversion into the hydroxide. Experimental data on the oxidation in combination with electron-microscopic measurements and the determination of adsorption and texture characteristics resulted in the conclusion that colloid-chemical processes, which include the dissolution of aluminum and the formation and precipitation of the hydroxo complexes of aluminum, are fundamental for the synthesis of porous metal ceramics.     

Hydrothermal Synthesis of Porous Al2O3/Al Metal Ceramics: IV. Synthesis of Composite Porous Ceramics in the Presence of Microporous and Mesoporous Adsorbents

The formation of the structure and properties of mesoporous composite ceramics based on an ASD-1 aluminum powder and commercial adsorbent powders (zeolites and active alumina) was studied. It was found that the mechanism of the formation of contacts between the particles of commercial adsorbents and aluminum is analogous to the mechanism of synthesis of an Al(OH)₃/Al composite. The dissolution of aluminum and the precipitation of the hydroxo complexes of aluminum from solution to the region of interparticle contacts are responsible for this mechanism. The resulting composite ceramics exhibited a polydisperse pore structure and high values of mechanical strength, gas permeability, and thermal conductivity; it can be used as a block adsorbent and catalyst support.     

Synthesis of mesoporous precursors of yttrium aluminate with the perovskite structure

Mesoporous precursors of nanocrystalline yttrium aluminate YAlO₃ with the perovskite structure (a cubic lattice) are synthesized by the coprecipitation of Y³⁺ and Al³⁺ cations from deanionized yttrium-aluminum nanosols with ammonium hydroxide. Samples thus prepared are studied with the X-ray diffraction, IR spectroscopic, differential thermal, and thermogravimetric analyses. Isotherms of benzene vapor adsorption-desorption by samples calcined at 923 and 1373 K are measured. The types of the isotherms and capillary-condensation hysteresis are determined; specific surface areas, average sizes of mesopores, and mesopore size distribution are calculated. The mean size of perovskite-like crystallites that resulted form the templated precipitation of the precursor is no larger than 300 nm.