The influence of Al₂O₃ content on Al₂O₃-ZrO₂ composite-textural structural and morphological studies

In this work binary Al₂O₃-ZrO₂ composites with 25, 50, and 75%, w/w Al₂O₃ were synthesized by the sol-gel method, to find out the better Al₂O₃ amount that improve the texture, structure, and morphology. The composites presented high surface area, porosity and microcrystalline structure due to high cations dispersion induced by a good intermingling of the components. We found that structure of Al₂O₃-ZrO₂ composites include AlO₄ (tetrahedral), AlO₅ (pentahedral) AlO₆ (octahedral) polyhedral units. An increment of AlO₄ and AlO₆ species for low Al₂O₃ amount in the composites was observed. This was possibly related with segregated particles caused by progressive removal of hydroxyl groups. Otherwise, for high Al₂O₃ amount the fraction of AlO₅ species was high, this behaviour was associated with an appropriate distribution of cations within the network of the composites as derived from condensation reactions. A suitable distribution of the Al³⁺ and Zr⁴⁺ cations in the network of the composites is observable by Z-contrast where for high Al₂O₃ concentrations an homogeneous arrangement was observed. Besides, for low Al₂O₃ concentrations rods of ZrO₂ with an average length at ∼250 nm are observable. Finally, by XPS analysis the non-lattice and lattice oxygen ratio presented similar values for Al₅₀Zr₅₀ composite, associated with the same available vacancies where Al³⁺ and Zr⁴⁺ cations have mayor mobility in the bulk and the superficial of the composite. (paper)