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The synthesis of nanosized superparamagnetic hematite particles by dissolving ferric salts in hydrochloric acid and heating at 100• C is described. A hydrolysis reaction causes the formation of hematite particles. The influence of the sequence of additions on the resulting precipitates was studied using TEM and XRD. The magnetic behavior was characterized by magnetization measurements. It was found that small changes in the reaction conditions led to remarkable changes in final size and shape of the hematite crystallites. A well-defined subrounded morphology and an average diameter of 41 nm were obtained for superparamagnetic hematite particles. This is the largest size reported thus far for superparamagnetic hematite particles. C 2002 Elsevier Science (USA)

The effect of low concentrations of Fe203, AI203 and Bi203 on the sintering behaviour of (ZrO2)o.83 (YO1.s)o.17, made by alkoxide synthesis, has been investigated. The best results are achieved with Bi203 as a sinter agent and a relative density of 95% is obtained at 1200 K. The effects of these impurities on the electrical conductivity of the bulk and the grain boundaries has been investigated using frequency dispersion analysis (101-106 Hz). All investigated impurities have a negative influence on both the bulk and grainboundary conductivity. For Fe203 and AI203 grain-boundary segregation factors of about two are calculated.

The surface-and grain boundary composition of Y, Ce and Ti doped zirconia were studied by X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy/Scanning Auger Microscopy. The grain boundaries and free surfaces showed the same enrichment levels. After heat treatment _> 1000~ all yttria doped samples showed yttrium enrichment. In the ZrO=-Y203 system the yttrium enrichment did not depend on the bulk concentration and amounted 30-34 mol% Y01.~ in all cases. As a consequence the segregation factor increases with decreasing solute concentration in the bulk. The thickness of the segregation layer was about 2-4 nm. In the ternary Y doped systems yttrium is the main segregant. In ceria-doped tetragonal zirconia polycrystals (Ce-TZP) systems significant segregation of cerium starts at T_> 1300~ and is mainly attributed to Ce 3 § In Y,Ti-TZP systems also strong segregation of Ti 4+ occurs. The absolute value of the increase of the surface concentration in fine grained material is smaller than in coarse grained material. This is mainly due to depletion of the bulk.

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