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BIOGRAD Résumé de rapport

Project ID: G5RD-CT-2000-00354
Financé au titre de: FP5-GROWTH
Pays: Belgium

Basic knowledge on the electrophoretic deposition process

The electrical field drop over a deposit during EPD influences the deposition rate. Due to the large practical consequences of a potential drop over the deposit, a procedure was developed to calculate it from current-conductivity measurements during EPD. The suspension composition determines whether an extra potential drop over the deposit is present or not. Alumina suspensions based on MEK and n-butylamine showed no potential drop over the deposit, while suspensions based on ethanol and an acid caused an extra potential drop over the deposit. The potential drop over the electrode is determined by the interparticle interactions in the deposit, i.e, the surface charge and potential of the pore wall and the Debye screening length that is related to the ionic strength. For ethanol-based suspensions with HNO3 addition, the specific deposit resistivity and the concomitant potential drop over the deposit was found to increase with increasing potential in the centre of the pores of the deposit, as calculated from the zeta potential of the particles in suspension, the Debye screening length and the measured average pore size. An increased pore potential inhibits ion movement through the pores of the deposit, increasing the resistivity of and the potential drop over the deposit. The very thin double layer relative to the pore diameter explained the absence of an extra potential drop for MEK, n-butylamine suspensions. These findings allow developing suspensions for specific applications. Suspensions with a high potential drop over the deposit are suitable for thin homogeneous coatings on rough surfaces, while suspensions with a low potential drop are suitable for EPD of thick bulk components.

A mathematic model was developed to describe the deposition yield during electrophoretic deposition, taking into account the influence of the powder concentration in the suspension, the deposition efficiency and accounting a changing electrical field during deposition. By means of this new equation, a relation was found between the electrophoretic mobility and the deposition efficiency for ethanol based alumina suspensions. The deposition efficiency increased with decreasing electrophoretic mobility (zeta potential).

Reported by

K.U.Leuven - Department of Metallurgy and Materials Engineering
Kasteelpark Arenberg 44
3001 Leuven
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