Monoclinic Zirconia Bodies by Thermoplastic Ceramic Extrusion

Two ultrafine, undoped ZrO₂ powders with median primary particle sizes of 9 and 25 nm were used to prepare ceramic suspensions for thermoplastic extrusion. The organic vehicle consisted of an industrial-grade poly(ethylene- co -vinyl acetate) (EVA) or polyethylene (PE-HD) and decanoic acid as a dispersing agent. The powder volume loadings achieved were 44% and 52% by volume for the two powders, respectively. The amount of dispersant needed was calculated from a new model based on available chemisorption sites on the powder surface. Mixing and extrusion were conducted using a conventional modular plastic processing unit. Green bodies were dewaxed up to 450°C in an inert atmosphere and sintered to full density in air at 1060° and 1100°C, respectively. Analysis of the ceramic phase content and the microstructure of the bodies is presented.     

Die Rolle des Experiments in der Verfahrensentwicklung

Experiments in process development . Design data for the improvement of existing plants or for the development of new chemical processes are determined by experiments in laboratories or pilot plants. These frequently expensive testruns should lower the scaling-up risk for industrial plant and should ensure its long-term functioning and its economy. The various methods of scaling-up and the influence of errors are discussed. Some examples will show how an exact planning of the experiments can minimize the costs of development and product.     

Rare-earth diiodides and derivatives

The rare-earth diiodides, MI₂, may be synthesized from the corresponding triiodides, MI₃, by reduction with their metals at elevated temperatures or, alternatively, through so-called metallothermic reduction reactions with alkaline or alkaline-earth metals. In these cases, ternary iodides may be obtained that may be derived from the binary diiodides by either formal addition or substitution. Prominent formula types that are thus obtained are A^IMI₃, or the mixed-valent A^I₅M^II₂M^IIII₁₂ and A^IIMI₄ with A^I and A^II representing alkaline or alkaline-earth elements (and their analogues), respectively. Further iodides that are relevant in these systems are, for example, Pr₂I₅, Ba₆Pr₃I₁₉ and interstitially stabilized phases such as {Er₁₄(N₂)(C₂)₂}I₂₄, La₉O₄I₁₆ and Ba{Ce₄N₂}I₈.     

Preparation of monolithic crystalline lead titanate aerogels

Lead titanate gels were prepared via sol–gel synthesis and dried either in supercritical carbon dioxide or isopropanol. Both types of aerogels were characterized by means of thermal analysis and transmission electron microscopy. Helium pycnometry and nitrogen adsorption measurements were performed on samples that had been annealed at temperatures up to 600°C. Phase transformations and the crystallization of tetragonal PbTiO3 were monitored by X-ray diffraction. While aerogels supercritically dried in carbon dioxide disintegrate upon heat treatment, samples dried in isopropanol can be transformed to the crystalline state as monoliths. With an envelope density of 0.75 g cm-3 these ceramics exhibit a porosity of 90%. © 1998 Chapman & Hall     

Nachwuchspreis der Akademie für Ethik in der Medizin e.V. 2003

Ohne Zusammenfassung     

Response of a superconductor to a supercritical current pulse

We investigate the response of a one-dimensional homogeneous superconductor nearT _c if a current larger than the maximum supercurrent is suddenly imposed. We determine the time dependence of the order parameter, the voltage, and the quasiparticle distribution function. The delay time between the switching on of the current and the time when the system becomes normal, which is marked by the appearance of a voltage, is determined. Good agreement with experimental results is found.