Electrochemistry Modeling

Electroplating and other electrodeposition operations generally want to create a smooth deposit with roughly uniform thickness over a part sometimes with a complex shape. Modeling electrochemical processes presents several particularly difficult challenges, such as nonlinear boundary conditions and linking of phenomena at very different length scales. Opennovation's electrochemistry modeling capabilities range from macroscopic boundary element calculations of current density distribution at centimeter to meter scales without volume meshing, down to detailed modeling of micron-scale dendrites.

A paper whose writing Principal Adam Powell led for the May 2007 issue of JOM summarizes electrochemistry modeling techniques over all lengthscales; that paper reference is:

A. Powell, Y. Shibuta, J. Guyer and C. Becker, "Modeling Electrochemistry in Metallurgical Processes," JOM 59(5):35–43 (May 2007). (DOI: 10.1007/s11837-007-0063-y)

Macroscopic Modeling

The goal of macroscopic modeling is to predict the distribution of current density at the electrodes for various process design parameters. This enables the engineer to control the uniformity of metal plating, to determine whether some regions will plate with a rough instead of smooth surface, and to calculate the distribution of heat generation in some processes. Such modeling is also crucial for the design of cathodic protection systems for corrosion prevention.

The image on the right shows the output of a boundary element simulation of molten salt magnesium electrowinning using solid oxide membranes (SOM). The three blue test tube-shaped electrodes are the anodes, which are encased in a yttria-stabilized zirconia SOM, which permits oxygen ions to pass through but blocks electrons. The uniform blue color indicates that the current density through the SOM is uniform, resulting in uniform heat generation. This is very important to maintaining the integrity of the fragile ceramic membranes. The other tubes are stainless steel cathodes where magnesium gas is produced. The intensely localized red color indicates high cathodic current, and thus the location where most of the magnesium vapor is produced.

Boundary element modeling using the open source Julian package is a robust method for macroscopic electrochemistry modeling. The SOM processes for producing magnesium, titanium and tantalum, and for deoxidizing copper, are described in the following paper:

U. Pal and A. Powell, "The use of solid-oxide-membrane technology for electrometallurgy," JOM 59(5):46-51 (May 2007).

Microscopic Modeling

Electroplating is an inherently unstable process, in that it tends to form a rough deposit made up of tiny metal dendrites. It is possible to avoid this by either using very low current (which is slow), or periodically reversing the current, or adding chemical additives to the plating bath. In some circumstances, such as the production of powder metal, this can be beneficial: one can control the shape and rate of growth of metal powder particles. In other circumstances, one can tune the current over time to engineer the shape of dendrites in a rough deposit.

In these cases, a microscopic model is helpful for predicting and understanding how such deposited structures will form. Phase field is a method for calculating the formation of dendritic structures, which was first used to simulate spinodal decomposition and dendritic solidification. My research group at MIT first used it to simulate electrochemical deposition processes such as electroplating and liquid metal reduction from a molten salt or slag.

Useful results of such calculations include:

  1. A. Powell and W. Pongsaksawad, "Phase field modeling of phase boundary motion due to transport-limited electrochemical reactions," in V.G. DeGiorgi, C.A. Brebbia and R.A. Adey eds. Simulation of Electrochemical Processes II, WIT Press, May 2007, pp. 43–52.
  2. W. Pongsaksawad and A. Powell, "Phase Field Modeling of Transport-Limited Electrolysis in Solid and Liquid States," J. Electrochem. Soc. 154(6):F122-F133 (June 2007).
  3. M. Suput, R. DeLucas, S. Pati, G. Ye, U. Pal and A. Powell, "Solid Oxide Membrane (SOM) Technology for Environmentally Sound Production of Titanium," in F. Kongoli and R. Reddy eds. Advanced Processing of Metals and Materials Vol. 4: New, Improved and Existing Technologies: Nonferrous Materials Extraction and Processing, pp. 273-284 (August 2006).
  4. U. Pal, S. MacDonald, D. Woolley, C. Manning and A. Powell, "Results Demonstrating Techniques for Enhancing Electrochemical Reactions Involving Iron Oxide in Slags and C in Liquid Iron," Metall. Mater. Trans. 36B:209-218 (2005).

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