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In this work, iron oxide nanoparticles with various morphologies were synthesized by the precipitation method from aqueous solutions of iron oxide chlorides and urea in the absence or presence of chitosan. Synthesis conditions were selected to yield magnetite nanoparticles with three different morphologies. By adding chitosan, we were able to change the morphologies of the Fe 3 O 4 nanoparticles from cubo-octahedral, flower-like, and rod-like structures to cubic, quasi-spherical, and rice-seed-like structures, respectively. The size of these iron oxide structures were in the range of 28125 nm, while the longitudinal sizes of the rod-like and rice-seed-like structures were 1101000 and 75290 nm, respectively. Transmission electron microscopy (TEM) results showed that the magnetite nanostructures synthesized in the presence of chitosan have a mesoporous structure and are composed of many nanocrystals. The mechanisms responsible for the formation of differently shaped iron oxides in the presence or absence of chitosan are analyzed and discussed. We observed that the growth mechanism changed from the classical route to the reverse growth mechanism, when chitosan was added to the synthesis solution.

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Weakly agglomerated 1.75 and 3 mol% yttria stabilized zirconia nanopowders were used in this study after six years of storage in vacuum-processed plastic containers. The proper storage conditions of the Y-TZP nanopowders avoided the hard agglomeration. Untreated and bead-milled nanopowders were used to obtain dense ceramics by slip casting and subsequent low-temperature sintering. Fully dense nanostructured 1.75Y-TZP and 3Y-YZP ceramics with and without doping of 1 wt% Al2O3 were produced by an optimized spark plasma sintering (SPS) technique at the temperatures of 1050-1150 degrees C at a pressure of 100 MPa. The SPS has revealed the clear advantage of consolidation of the weakly agglomerated nanopowders without preliminary deagglomeration. The Vickers hardness of both the low-temperature and spark plasma sintered samples was found to lie in the range of 10.98-13.71 GPa. A maximum fracture toughness of 15.7 MPa m(1/2) (average 14.23 MPa m(1/2)) was achieved by SPS of the 1.75Y-TZP ceramic doped with 1 wt% Al2O3 whereas the toughness of the 3Y-TZP ceramics with and without alumina doping was found to vary between 3.55 and 5.5 MPa m(1/2).