Impurities in ceramic powders or in the sintering atmosphere can have a strong influence on the densification and microstructure development during sintering. Our sintering studies have shown that the presence of bulk platinum and adsorbed minor amounts of adsorbed impurities during the sintering process can affect the microstructural and property development of materials via the gas phase. Four different oxide powders were shaped into green bodies and sintered in presence and absence of bulk platinum. Analyses of the materials after sintering show clear differences in the microstructure and the electronic properties between samples sintered in a furnace environment and those sintered in contact or in the close vicinity of platinum foil. When Pt foil had been present in the sintering set-up, trace chemical analysis detected accumulations of the platinum metal and other trace impurities at crucible surfaces which had not been in direct physical contact with Pt foil.

The aim of this study was to develop a depth filter working on the electrostatic adsorption principle based on a microporous diatomaceous earth water filter element. The internal surface area of the highly porous elements was coated with a colloidal nanodispersion of hydrated yttrium oxide and subsequently heat-treated under reducing conditions to yield filters featuring uniformly distributed electropositive Y2O3 coatings. Filters prepared in this fashion exhibit a flowrate of 60 l/h at 3 bar and remove in excess of 99.99% of 25 nm diameter MS2 bacteriophages from feed water between pH 5 and 9.

The purpose of this study was to test the feasibility of modifying commercial microporous ceramic bacteria filters to promote adsorption of viruses. The internal surface of the filter medium was coated with ZrO2 nanopowder via dip-coating and heat-treatment in order to impart a filter surface charge opposite to that of the target viruses. Streaming potential measurements revealed a shift in the isoelectric point from pH <3 to between pH 5.5 and 9, respectively. While the base filter elements generally exhibited only 75% retention with respect to MS2 bacteriophages, the modified elements achieved a 7log removal (99.99999%) of these virus-like particles. The coating process also increased the specific surface area of the filters from ≈2m2/g to between 12.5 and 25.5m2/g, thereby also potentially increasing their adsorption capacity. The results demonstrate that, given more development effort, the chosen manufacturing process has the potential to yield effective virus filters with throughputs superior to those of current virus filtration techniques.

Barium titanate-based thermistors in the shape of fine rods between 500 and 150μm in diameter have been prepared via thermoplastic powder extrusion. Processing of the filaments is complicated by their large surface area-to-volume ratio which results in the volatilization of components during sintering. Due to their negligible size and thermal mass, these ultra-small thermistors exhibit much faster responses to changes in their operating conditions than millimeter-scale positive temperature coefficient of resistivity (PTCR) elements.

A new 3D‐microscopy method, focused ion beam‐nanotomography (FIB‐nt), has been applied to the statistical particle shape analysis and for topological characterization of granular textures in cement samples. Because of its high resolution (15 nm), FIB‐nt reveals precise microstructural information at the submicrometer scale, which cannot be obtained with conventional tomography methods. It is demonstrated that even from complex granular textures with dense agglomerates, it is possible to identify the individual sub‐grains. This is the basis for reliable statistical shape analysis. For this purpose, moments of inertia were determined for particles from five different grain size fractions of a given cement, which provides important input data for future modeling of rheology and hydration processes. In addition, FIB‐nt was used for topological characterization of the particle–particle interfaces in the dense and fine‐grained granular textures. The unique 3D‐data obtained with FIB‐nt thus open new possibilities for quantitative microstructure analysis and the data can be used as structural input for object‐oriented modeling.

Silica glass fibers with triangular and rectangular cross-sections have been produced by two different means, namely preform drawing and powder extrusion. For the preform drawing method, silica glass rods were machined and polished to yield preforms with the desired cross-sections. These were then heated to temperatures in excess of 1600 degrees C and drawn to fibers with approximately 265 mu m x 265 mu m x 265 mu m triangular and 275 mu m x 100 mu m rectangular cross-sections exhibiting tensile strengths between 300 and 400 MPa and bending radii smaller than 50 mm. For the extrusion route, a silica nanopowder was compounded at approximate to 150 degrees C with a polyethylene-based binder and extruded at similar temperatures through dies with the desired exit cross-section. The fibers were debound by thermally decomposing the binder and sintered at 1100 degrees C to yield amorphous glass fibers with approximately 205 mu m x 205 mu m x 205 mu m triangular and 275 mu m x 90 mu m rectangular cross-sections. Although the two manufacturing processes are radically different, both involve flow of a fluid with a temperature-dependent viscosity and this dictates that shape trueness (i.e. flat faces and sharp corners) is a function of the drawing and extrusion rates and the temperature during drawing and sintering.

A commercial submicrometer BaTiO3 powder was analyzed using X‐ray photoelectron spectroscopy. The analysis revealed the powder surfaces to be covered with a layer of physisorbed H2O and chemisorbed –OH ions. A BaCO3 residual not detected with XPS was shown to be present in the powder using X‐ray diffraction, suggesting that the carbonate takes the form of discrete particles rather than of a continuous surface layer. A relaxed surface phase detected in previous XPS analyses of bulk BaTiO3 was also shown to be present. Depth profiling revealed the powder surfaces to be Ti‐rich, confirming the presence of a phase, or phases, to stoichiometrically balance the barium carbonate.

Previous research has shown that vacuum filtration of particulate YBa/sub 2/Cu/sub 3/O/sub 7-x/ (Y123) suspensions in an applied magnetic field under ambient conditions, followed by partial melt processing can produce well textured Y123 thick films. In addition, the microstructural development and magnetic properties were shown to be enhanced in the presence of platinum during heat treatment. Thermal analysis revealed that platinum reduces the decomposition temperature of pure Y123 (1030/spl deg/C in O/sub 2/) by 70/spl deg/C. The current focus of this research is to further exploit this effect and develop a better understanding of the role of platinum during heat treatment. We have successfully duplicated the magnetic and microstructural enhancements observed in earlier work by adding Pt powder directly to the Y123 suspensions and heat treating the films on inert MgO substrates. The enhancement in the magnetic properties was shown to persist independent of any grain size effects resulting from improved microstructural development.<>

The effects of magnetic alignment, heat treatment, and substrate interactions on the microstructural development and properties of YBa2Cu3O7−x (Y123) thick films were studied. Aligned films were formed by vacuum filtrating a particulate suspension in a 7 T applied field. These films and nonaligned control films were fired on either platinum (Pt) foil or magnesium oxide (MgO) substrates to various maximum temperatures between 930 and 1040 °C. Optical microscopy revealed large differences in microstructural development between the various films. Aligned Y123 films fired on Pt foil exhibited the best microstructural properties. Via plasma emission spectroscopy and secondary ion mass spectroscopy, approximately 0.1 wt % Pt was found distributed throughout the films fired on platinum, while negligible amounts of Mg were detected in the films fired on MgO substrates. Differential thermal analysis revealed that, in the presence of Pt, the peritectic temperature (1030 °C for pure Y123 in O2) is reduced 70 °C, thereby opening a substantial thermal processing window for partial melt assisted growth of textured Y123. SQUID measurements of magnetic hysteresis and Tc provided quantitative evidence that, relative to the films fired on MgO, those fired on Pt exhibited enhanced texture development [ΔM(Happ∥c axis)/ΔM(Happ⊥c axis)=2.6 at 5 K, 1 T] and properties (Bean model Jc,m=5×104 A/cm2 at 5 K, 4 T) without degradation of the Tc characteristics.