Papers by Author: Li Zhang

Abstract: The development of texture was studied during electrophoretic deposition in alumina suspensions containing plate shaped alumina particles. The mechanism of platelet orientation during EPD was examined with respect to the influence of the electric field, gravity and hydrodynamic forces. This was realized by using two different deposition cells, with vertically or horizontally positioned deposition electrode. The texture of the green deposit was further enhanced during sintering by templated grain growth in which the platelet shaped alumina particles were growing at the expense of the fine grained matrix. The sharp ‘fiber texture’ obtained after templated grain growth during sintering of the deposit was characterized by means of x-ray diffraction and Electron Backscatter Diffraction (EBSD).

Abstract: Deposition experiments in a Hull cell showed that high conductivity suspensions yield uniform deposits while low conductivity suspensions result in non-uniform deposits. This difference in deposition behavior is related to the resistance increase of the deposit during EPD. Impedance measurements during EPD showed that the ratio of the deposit resistance to the suspension resistance increases much more for high than for the low conductivity suspensions. They also showed that the total resistance of the EPD cell dropped almost to the suspension resistance after the electric field was turned off. This means that the deposit has no inherent resistance, but that its resistance during polarization is caused by the interaction of ions with the deposit and by the depletion of ions at the deposition electrode. The change in ion concentrations near the deposition electrode changes the acid/base properties of the particles in the deposit, as proven by adsorbed pH indicators on the particles. The change in acid/base behavior is quasi irreversible and results in a memory effect of the deposit resistance when the voltage is reapplied.