Sintesi e caratterizzazione di nanopolveri composite allumina-zirconia

This thesis reports the synthesis of alumina-zirconia nanopowders, by means of three different routes (cooprecipitation, citrate route, microwave hydrothermal synthesis), followed by thermal treatment (calcination), performed by using conventional (muffle furnace) and alternative method (microwaves furnace). The aim of this work is to identify, over the experimented routes, the most convenient and suitable one, for the production of 95 mol% Al2O3 ࢠ5 mol% ZrO2 nanocrystalline powders and to examine the effects, on powder features, of the microwave thermal treatment respect to conventional heating. The obtained results have shown that, among the tested routes, microwave hydrothermal synthesis is the most advantageous method, and that microwave hydrothermal heating is favourable respect to conventional treatment in the calcination step. It has been demonstrated that microwave hydrothermal synthesis allows to obtain nanocrystalline powders with unique characteristics, that can be easily grinded because of the absence of hard agglomerates. The so obtained powders are composed, since after the synthesis stage (200à,°C/2 hrs), of zirconium oxide and the crystallization of aluminium oxides was reached by using low temperature and short time (400à,°C/5 min) of calcination. Furthermore, the thermal treatment, performed by using microwave source, allows the formation of the desired crystalline phases at significant lower temperature and with reduced processing time (as observed for the synthesis) respect to conventional thermal treatment. The possibility to undergo, for the calcination steps, the powders to lower temperature and reduced time avoid the formation of hard aggregates and contrast grain coarsening, preserving the nanostructure of the powders and their innovative properties.