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Alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) are currently the materials of choice to meet the need for tough, strong, and bioinert ceramics for medical devices. However, the mechanical properties of ZrO2/Al2O3 dispersion ceramics could be considerably increased by reducing the corresponding grain sizes and by improving the homogeneity of the phase dispersion. Here, we prepare nanoparticles with an intraparticular phase distribution of Zr(1−x)AlxO(2−x/2) and (γ-, δ-)Al2O3 by the simultaneous gas phase condensation of laser co-vaporized zirconia and alumina raw powders. During subsequent spark plasma sintering the zirconia defect structures and transition alumina phases transform to a homogeneously distributed dispersion of tetragonal ZrO2 (52.4 vol%) and α-Al2O3 (47.6 vol%). Ceramics sintered by spark plasma sintering are completely dense with average grain sizes in the range around 250 nm. Outstanding mechanical properties (flexural strength σf = 1500 MPa, fracture toughness KIc = 6.8 MPa m1/2) together with a high resistance against low temperature degradation make these materials promising candidates for next generation bioceramics in total hip replacements and for dental implants.

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Crystalline magnetic iron oxide nanopowders are prepared by CO 2 laser vaporization (LAVA) of a hematite (α-Fe 2 O 3 ) raw powder. Condensation at normal pressure leads to maghemite (γ-Fe 2 O 3 ) as the main phase in the nanopowders. With an increasing oxygen partial pressure in the zone of condensation, an increasing amount of Fe 2 O 3 polymorph ε-Fe 2 O 3 is found. The LAVA-prepared Fe 2 O 3 nanopowders are characterized by X-ray diffraction, transmission electron microscopy, and chemical analysis and with respect to their magnetic properties. A mechanism for the initial nucleation is proposed to explain the formation of ε-Fe 2 O 3 with an increasing oxygen content in the condensation atmosphere. The model is based on the evidence of ozone in oxygen-rich condensation atmospheres. Density functional theory calculations indicate that ozone facilitates the formation of 6-fold oxygen-coordinated Fe ions acting as building units for the emerging crystal structure during the solidification of the nanoparticles. This insight into early nucleation stages will be useful for the functional design and crystal engineering of either isostructural materials like alumina (Al 2 O 3 ) or, more generally, vapor phase synthetic routes for ceramic materials.

Bacterial nanocellulose (BNC) is an extraordinary biopolymer with a wide range of potential technical applications. The high specific surface area and the interconnected pore system of the nanofibrillar BNC network suggest applications as a carrier of catalysts. The present paper describes an in situ modification route for the preparation of a hybrid material consisting of BNC and photocatalytically active anatase (TiO(2)) nanoparticles (NPs). The influence of different NP concentrations on the BNC biosynthesis and the resulting supramolecular structure of the hybrids was investigated. It was found that the number of colony forming units (CFUs) and the consumption of glucose during biosynthesis remained unaffected compared to unmodified BNC. During the formation of the BNC network, the NPs were incorporated in the whole volume of the accruing hybrid. Their distribution within the hybrid material is affected by the anisotropic structure of BNC. The photocatalytic activity (PCA) of the BNC-TiO(2) hybrids was determined by methanol conversion (MC) under UV irradiation. These tests demonstrated that the NPs retained their PCA after incorporation into the BNC carrier structure. The PCA of the hybrid material depends on the amount of incorporated NPs. No alteration of the photocatalyst's efficiency was found during repeated PCA tests. In conclusion, the in situ integration of photocatalytically active NPs into BNC represents an attractive possibility to extend its fields of application to porous filtering media for drinking water purification and air cleaning.

The CO 2 laser vaporization (LAVA) method was used to prepare titania nanopowders. Because this versatile method does not require special precursors, a coarse anatase raw powder was applied as starting material. Powder samples produced under varied process parameters were characterized by transmission electron microscopy (TEM), X-ray diffraction measurements, and Brunauer-Emmett-Teller surface area measurements. The laser-generated powders consist of spherical, single crystalline and pure anatase nanoparticles, merely softly agglomerated by weak van der Waals forces. Using TEM analysis, the influence of the process parameters on the resulting particle size distribution was investigated. The results are discussed with respect to the particle formation by gas phase condensation. The potential of a process integrated, i.e. in situ, coating procedure for the surface modification of the anatase nanoparticles is demonstrated. As an exemplary representative of organic layer materials stearic acid was chosen. The organic coating was characterized by TEM and Raman spectrometry. Because of the unavoidable soft agglomeration the coating covers entire agglomerates rather than individual primary particles. Thus, the influence of the LAVA process parameters on the agglomerate sizes was systematically studied using a scanning mobility particle sizer.

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The atomic structure and properties of nanoparticulate Fe2O3 are characterized starting from its smallest Fe2O3 building unit through (Fe2O3)n clusters to nanometer-sized Fe2O3 particles. This is achieved by combining global structure optimizations at the density functional theory level, molecular dynamics simulations by employing tailored, ab initio parameterized interatomic potential functions and experiments. With the exception of nearly tetrahedral, adamantane-like (Fe2O3)2 small (Fe2O3)n clusters assume compact, virtually amorphous structures with little or no symmetry. For n = 2-5 (Fe2O3)n clusters consist mainly of two- and three-membered Fe-O rings. Starting from n = 5 they increasingly assume tetrahedral shape with the adamantane-like (Fe2O3)2 unit as the main building block. However, the small energy differences between different isomers of the same cluster-size make precise structural assignment for larger (Fe2O3)n clusters difficult. The tetrahedral morphology persists for Fe2O3 nanoparticles with up to 3 nm in diameter. Simulated crystallization of larger nanoparticles with diameters of about 5 nm demonstrates pronounced melting point depression and leads to formation of ε-Fe2O3 single crystals with hexagonal morphology. This finding is in excellent agreement with the results obtained for Fe2O3 nanopowders generated by laser vaporization and provides the first direct indication that ε-Fe2O3 may be thermodynamically the most stable phase in this size regime.