Electrophoretic Deposition: Fundamentals, Mechanisms and Examples with an In Depth Examination of the Ion Depletion Effect

Open Access
Author:
Van Tassel, Jonathan J.
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 02, 2004
Committee Members:
  • Clive A Randall, Committee Chair
  • James Hansell Adair, Committee Member
  • Leslie Eric Cross, Committee Member
  • Digby D Macdonald, Committee Member
  • Gary Lynn Messing, Committee Member
Keywords:
  • Electrophoretic Deposition
  • Alumina Surface Charge
  • Electroconvection
  • PZT Films
  • Ion Depleted Conduction
Abstract:
A definition of what is and what is not EPD is presented. This definition then serves as a guide to the presentation of the basic science necessary to understand this process, including electrochemistry, colloid and surface chemistry, and electrohydrodynamics. Analysis of this basic science leads to a list of possible mechanisms by which EPD can occur. Some of these mechanisms have already been documented in the literature, while some are still hypothetical. One of the most interesting of these mechanisms, ion depletion enhanced - automatic leveling deposition, is chosen for in-depth analysis. The first step is a complete analysis of the suspension of alumina powder in ethanol with added HCl which is used for deposition. It is shown that alumina develops a significant positive surface charge in ethanol by the dissociative adsorption of ethanol molecules to the surface and the preferential desorption of ethoxide ions from the surface. The addition of HCl leads to a large rise in surface charge due initially to reduction in ethoxide activity. After this initial rise the surface charge is set by a competitive adsorption equilibrium of chloride and ethoxide ions to positive surface sites on the powder. Analysis of the development of ionic and charge gradients in the electrolyte at the deposition electrode show the inevitability of a transition to convective transport without particles. A dramatic change in conduction behavior in the presence of particles is shown to be due to the stabilization of an ion depleted, unbalanced charge conduction layer. Extremely high voltage gradients in this layer exert a strong consolidating force on positively charged alumina particles, generating a densely packed deposition layer. The high voltage gradient also leads to a strong equilibrating force to maintain a uniform thickness of the compact deposited layer. Demonstrations are also made of the potential of EPD to address problems in the manufacture of electroceramic devices. The deposition of silver/palladium powder is used to demonstrate the ability to create both very thin layers and narrow conductor lines. The EPD of PZT is used to demonstrate the formation of an intermediate thickness film with well controlled stoichiometry.