Jan Tabellion

Effect of Particle Size Distribution and Sedimentation Behaviour on Electrophoretic Deposition of Ceramic Suspensions

By systematic interaction of sedimentation and electrical field in electrophoretic deposition the particle size distribution of the deposited green body can be influenced. This can be employed for producing coatings with a very smooth surface by deposition of only the nanosized fraction of a conventional powder with broad or non-monomodal size distribution, thus avoiding preceding classification. In this paper, the preparation of stabilised slurries is described focussing on the criteria particle size distribution, zeta-potential and sedimentation behaviour. The effectiveness of the interaction of sedimentation and electrophoretic deposition is to be shown.

Influence of Dopants on the Suspension Properties and Reactive Electrophoretic Deposition (REPD)

Doped glasses are usually manufactured by melting of silica. As the melting point of silica is 2100 °C, most of the suitable dopants evaporate. Hence, alternative processes for the fabrication of glasses are needed. Sintering of nano-sized silica powders to full densety and transparently occurs at 1400 °C because of its large sintering activity. Green bodies can be doped by means of gas infiltration, by soaking of green bodies with salt solutions or by using mixtures of different powders. A further development of the electrophoretic deposition (EPD) is the reactive electrophoretic deposition (REPD), where soluble salts are added into a suspension. The dissolved ions are adsorbed on the surface of the particles and can be deposited with the particles resulting in a homogeneously doped green body. Shaping of a green body and doping can be achieved within only one process step via REPD. The feasibility of this process was shown first for a suspension of SiO2 containing different amounts of boric acid or/and cobalt chloride. First of all, the influence of different quantities of boron acid or cobalt chloride on suspension properties like viscosity, stability and zeta-potential was investigated. Secondly, green bodies were shaped by REPD and characterized regarding deposition rate, green density and amount of dopant. Finally, sintering was carried out at different temperatures. Thus, it was shown that green bodies doped with boric acid could be sintered to full density at lower temperatures compared to undoped ones. However, the sintering temperature depends on the amount of boric acid added into the suspension.

Distribution of the Local Electric Field during Electrophoretic Deposition of an Alumina Suspension on a Membrane

The spatially distributed local electric field strength during the electrophoretic deposition (EPD) of alumina suspensions on a membrane is within the scope of the present article. The water-based alumina suspensions were optimized in order to achieve stable suspensions, high deposition rates and maximum green densities of the deposited bodies. In-situ measurements of the local potential drop inside the EPD-cell were carried out using a computer assisted process control set-up with electronic data acquisition. The behaviour of the spatial- and time-dependent electric field distribution was calculated from measured potential drops. The influence of varrying input voltages on the output parameters, such as deposition rate and green density for EPD on membranes was investigated and is discussed. It is shown that the distribution of the local electric field depends on the applied voltage and on time for the case of higher voltages. A dependance of the local electrical fields on the deposition rate is suggested as well.