The optical quality attainable in coarse-grained polycrystalline alumina is severely limited by grain-boundary scattering, which is inherent to non-cubic materials. The optical properties of sub-micrometre polycrystalline alumina are of growing interest triggered by the fact that a decrease in the grain sizes of the final sintered material yields an improvement in the optical quality while the scattering mechanism changes as the grain size becomes comparable with the wavelength of light. To achieve transparent alumina ceramics with a fine-grained microstructure, however, porosity and other defects must be avoided. This necessitates the optimization of processing and sintering procedures. Electrophoretic deposition (EPD) is a colloidal process in which ceramic bodies are directly shaped from a stable suspension by application of an electric field. Electrophoretic deposition enables the formation of homogeneous, uniform green microstructures with high density, which can be sintered to transparency. It is a simple and precise technique to synthesize not only monoliths, but also composites with complex geometries [1]. Alumina green bodies were deposited from stabilized aqueous suspensions with and without doping. Green alumina compacts were evaluated based on their pore size distribution and density. Densification behaviour was characterized by dilatometric studies conducted at constant heating rate. Samples were sintered at different temperatures with subsequent post-densification by hot isostatic pressing. Transparency was evaluated by means of spectroscopic measurements. The measured in-line transmission of the samples at 645 nm was more than 50 % and that is 58 % of the value of sapphire. The influence of dopings on transparency was investigated. The mechanical properties of the samples were tested.

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A simple, economical, and environmentally compatible methodology for the fabrication of layered ceramics is presented herein. Water‐based electrophoretic techniques and polymeric templating were combined to fabricate graded‐porosity ceramic foams with controlled pore size, pore geometry, and excellent pore connectivity. Dense ceramic films can be laid either on top of the porous ceramic or in a sandwich‐style configuration. A single fabrication step suffices when working a single material (or material composition). Else, two or more fabrication steps are required. The two‐step manufacture of a half solid‐oxide‐fuel‐cell is presented. The yttria‐stabilized zirconia (8YSZ) solid electrolyte layer was deposited on top of the templated graded‐porosity nickel‐oxide/8YSZ electrode. The present methodology promises alternatives to current fabrication processes.

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In this paper, we present chronopotentiometric results of direct current (DC) membrane electrophoretic deposition (DC-M-EPD) experiments and analyse the influence of the parameters solid concentration, particle size and electrical conductivity of colloidal fumed silica model suspensions on voltage-current curves. The expected streamline patterns are numerically modelled based on coupled mass balances, Ohmic law, Navier-Stokes and Nernst-Planck equations. The results confirm that overlimiting current condition is an obligatory condition for the formation of EPD green deposits under suitable DC-M-EPD conditions. Furthermore, micro-EPD experiments in external alternating current (AC) fields (micro-AC-EPD) using video microscopy come to the conclusion that the observed formations of microvortices are in accordance to the numerically modelled streamline patterns. Finally, the formation of AC-EPD microdeposits exhibiting a torus-like microstructure is substantially explained based on microfluidic streamline pattern analysis.