Nanometal Oxides

A simple and efficient methodology has been established for the selective synthesis of anatase and rutile [58], as well as their mixtures with various precursors using ultrasound irradiation; the products, the particle sizes of which are nanometric (<9 nm), are dependent both upon the reaction temperature and the precursor used; a substantial reduction in reaction time as well as reaction temperature is observed as compared to the corresponding hydrothemal processes. Zhu and co-workers [59] developed a process for the formation of titania whiskers and nanotubes with the assistance of sonication; titanate whiskers are obtained as a slender sheet with a length of about 1 /m and a width of 60 nm; arrays of titania whiskers with a diameter of 5 nm are prepared from the titanate whiskers; titania nanotubes with a diameter of about 5 nm and a length of 200-300 nm are also synthesized.

Xu and co-workers [60] reported the magnetic size effects and phase transformation in sonochemically synthesized Fe2O3 nanoparticles. Annealing in vacuum at temperatures Ta between 240 and 450 "C produced nanophases of y-Fe2O3 with average particle size ranging from 4 to 14 nm, depending on Ta. Phase transformation into a-Fe2O3 occurred directly by annealing in air, or via an intermediate Fe3O4 phase by annealing in vacuum at temperatures higher than 450 "C. Mapping the correlation between the magnetic properties and the annealing conditions enables control of the annealing process to obtain nanocrystals of y-Fe2O3, a-Fe2O3, or Fe3O4 with different particle sizes and magnetic properties.

0 0

Post a comment