Electrophoretic deposition: a quantitative model for particle deposition and binder formation from alcohol-based suspensions

We investigated electrophoretic deposition from a suspension containing positively charged particles, isopropanol, water, and Mg(NO3)2, with the aim of describing the deposition rates of the particles and Mg(OH)2, which is formed due to chemical reactions at the electrode, in terms of quantitative models. LaB6 particles were used as a model system. The particle layer is consolidated by simultaneous precipitation of Mg(OH)2 which acts as a binder to hold the particles together. The Mg(OH)2 content was determined solely by the amount of charge passed through the cell. Quantitative precipitation of all OH¿ formed at the electrode was observed, except at very low current. The occurrence of a minimum current was ascribed to a threshold for Mg(OH)2 deposition. The same minimum current was observed for particle deposition. In combination with results using NaNO3, where no adherent layer was formed, this illustrates that Mg(OH)2 binder is necessary for consolidation. Once the minimum current was exceeded, it was found that all particles that migrate to the electrode under the influence of the electric field contribute to the formation of the layer, i.e., the "sticking coefficient" for the particles equals 1.0. The applicability of the particle and Mg(OH)2 deposition models was tested by variation of the Mg(NO3)2 concentration, pH, and water content