Role of ion depletion in the electrophoretic deposition of alumina powder from ethanol with increasing quantities of HCl

Under certain conditions of conductivity and at constant current, electrophoretic deposition (EPD) of alumina powder from an acidic suspension is accompanied by an anomalous voltage rise across the deposited particulate layer. This voltage rise, which is much greater than can be accounted for by the blocking of the electrode by non-conducting particles, is the signal of the formation of a very uniform, dense alumina deposition layer. To determine the conditions necessary to induce this effect and discover its origins, a series of systematic EPD trials with increasing quantities of HCL is comprehensively examined. It is shown that both of these effects can be accounted for by the formation of an ion depleted conduction layer in the solvent at the deposition electrode, which is marked by extremely high voltage gradients. The resulting electrophoretic force on particles in this layer is several orders of magnitude higher than the force on particles in the rest of the system and consolidates the particles to form the observed densely compacted layer. This high voltage gradient layer also results in a significant self-leveling effect for deposition thickness. A complete description of the various types of deposition observed in this series of trials is then given in which EPD is treated as a series of three steps: accumulation, deposition, and consolidation. This description identifies the origin of several effects seen during EPD and is intended to help the reader identify the conditions necessary to induce ion depletion enhanced, automatic leveling electrophoretic deposition.