Title

THE MODELING OF GALVANIC CORROSION SYSTEMS USING NUMERICAL METHODS WITH PARTICULAR ATTENTION TO BOUNDARY CONDITIONS OF NONLINEAR POLARIZATION (ELECTROCHEMISTRY, FINITE-ELEMENT METHODS)

Date of Completion

January 1986

Keywords

Engineering, Materials Science

Degree

Ph.D.

Abstract

The objective of this research was to develop a method for a-priori quantitative prediction of electrochemical potential and current distributions in systems of dissimilar metals submerged in an electrolyte, the motivation being mitigation of corrosion effects by material selection, geometric configuration, and cathodic protection design. Specificially, the method would employ existing numerical techniques for solving the Laplace equation, applying them in an electrochemical analysis technique for any specified geometry of electrodes having known electrode kinetics. Particular emphasis was placed on characterization of electrodic behavior using analytical expressions to represent the boundary conditions while retaining physical significance.^ A literature search examined analytical and graphical methods of the past half-century and numerical methods which began to appear in the latter 1970's. Herein, the partial differential equation governing the electric potential distribution in electrolytes was derived and unique boundary conditions representing complete nonlinear electrodics of submerged metals were developed. Modern numerical finite difference, finite element, and boundary element methods with applicability to modeling electrochemical phenomena were investigated.^ A particular finite element formulation was developed to preserve charge conservation, a required condition to include mixed potential theory in electrochemical modeling. The mathematics analogy between electrical and thermal conduction was identified and a commercially-available heat conduction computer program was selected and modified for electrochemical analysis by programming for the particular boundary conditions representing nonlinear electrode kinetics.^ The method of galvanic modeling and analysis was demonstrated by the several examples. One problem simulated one of simple geometry and idealized linear electrode kinetics previously solved exactly in the literature. Two problems with measured results for correlation were solved, one of a laboratory-scale experiment with two dissimilar metals submerged in the electrolyte, and a second of a macroscopic field problem of a shipboard seawater tank with the electrolyte enclosed by wetted metals. All three demonstration problems predicted electrochemical potential distributions in very good agreement with the exact solution or measured results.^ It was concluded that the electrochemical modeling method developed in this research embodies both mixed potential theory and full electrodic behavior of metal/electrolyte systems with demonstrated accuracy. ^