Nano-oxides: syntheses and functionalization

The need to produce materials with more and more demanding technological performance addressed the interest of scientists towards the engineering of the synthesis of starting solid phase. For this reason, a fundamental part of the ceramic process is now reserved to the processes of powders synthesis and functionalization. A strict control of the chemical-physical evolution of forming species is been possible through the introduction of the so-called chemical routes. These chemical routes are based on the transformation of cation precursor solutions into nano particles dispersion (sols). The correlation of the parameters of synthesis with the thermodynamic and kinetic factors involved, allows the control of fundamental properties such as: size distribution, morphology, purity, surface functionalization, colloidal stability of synthesized particles. The sols production, their evolution to gels or precipitates, increase the application field of the produced solid phases: sols are used as oxide or metal based nanofluids, gels can be deposited as films with several techniques, the powders recovered by liquid medium is used for its high reactivity and purity as solid precursor for the production of full density materials. In ISTEC several techniques such as sol-gel, precipitation or co-precipitation in aqueous medium, in some cases assisted by microwave heating, are applied to the production of oxide based powders. The crystallinity of powders is increase with post synthesis thermal treatment (calcination). Together with traditional chemical routes, instantaneous solvent removal techniques have been developed such as spray-drying from precursor solution or sol-gel combustion. These techniques promote the formation of aggregates with large specific surface area and high porosity in the meso and macropore ranges. Processes based on forced hydrolysis of precursor cations in glycol medium at high temperature (polyol synthesis) have also been developed, allowing the direct formation of oxide or metal based nano particles, stably dispersed in the organic medium.