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,
Electrochemistry in Metallurgical Processes," JOM
59(5):3543 (May 2007).
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
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).
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
Useful results of such calculations include:
- Prediction of deposit morphology under straight DC current or AC waveform
- AC current waveform design for fast planar growth, producing a dense
deposit with smooth surface without chemical additive contamination
- AC current waveform design for producing metal powder with desired size
(or size distribution) and morphology
- A. Powell and W. Pongsaksawad,
field modeling of phase boundary motion due to transport-limited
electrochemical reactions," in V.G. DeGiorgi, C.A. Brebbia and
R.A. Adey eds.
of Electrochemical Processes II, WIT Press, May 2007,
- 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).
- 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).
- 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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