The objective of this work is to advance the mechanistic understanding of cathodic electrocoating. These efforts are focused on the initial processes responsible for deposition, which are examined through direct experimentation and simulation. Electrocoating is a global industrial process providing a corrosive resistant base paint to automobile bodies. Presently, empirical models are used to model coating thickness; these models tend to overpredict deposition in occluded areas. Convection is implemented to study the behavior of adhered surface H2 bubbles on the substrate surfaces. The impact of surface H2 bubbles and early e-coat deposition on the local current density is studied using simulations. Results show an increased local current density around surface H2 bubbles and early e-coat deposition influences film growth. When surface H2 bubbles are displaced before sufficient e-coat is deposited the lack of increased local current density slows deposition. However, when sufficient e-coat is deposited and then surface H2 bubbles are displaced, the induction period is unaffected since the early deposition is sufficient to keep the local current density high enough to drive deposition. Solution factors are qualitatively studied using a diluted e-coat dispersion and a anionic exchange membrane cell. Experiments demonstrate a visual change in the solution near the cathode and indicates a coagulation of micelles in this region. Experiments also demonstrate a rise in pH is associated with the induction time, but is not necessary for e-coat deposition. Film resistance is used to understand film growth and film morphology during industrial electrocoating. Interruption experiments demonstrate H2 bubbles may influence film resistance. Film density and resistivity results cannot be completely explained with understood physics, underlining the importance of future resistance studies. These results provide an increased understanding of fundamental processes responsible for initial deposition, which is the foundation needed for advanced physics-based models of the electrocoating process.
College and Department
Ira A. Fulton College of Engineering and Technology; Chemical Engineering
BYU ScholarsArchive Citation
Marlar, Tyler James, "Investigation of Electrocoating Mechanisms" (2019). Theses and Dissertations. 7753.
electrocoating, e-coat convection, surface H2 bubbles, e-coat coagulation, anionic exchange membrane, electrochemical resistance, current density simulation