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

We investigated electrophoretic deposition from a suspension containing pos itively charged particles, isopropanol, water, and Mg(NO3)(2), with the aim of describing the deposition rates of the particles and Mg(OH)(2), which i s formed due to chemical reactions at the electrode, in terms of quantitati ve models. LaB6 particles were used as a model system. The particle layer i s consolidated by simultaneous precipitation of Mg(OH)(2) which acts as a b inder to hold the particles together. The Mg(OH)(2) content was determined solely by the amount of charge passed through the cell. Quantitative precip itation 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 f or Mg(OH)(2) deposition. The same minimum current was observed for particle deposition. In combination with results using NaNO3, where no adherent lay er was formed, this illustrates that Mg(OH)(2) binder is necessary for cons olidation. Once the minimum current was exceeded, it was found that all par ticles that migrate to the electrode under the influence of the electric fi eld contribute to the formation of the layer, i.e., the "sticking coefficie nt" 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) concentr ation, pH, and water content. (C) 2000 Academic Press.