Optimizing coating performance for diffusion under cyclic moisture exposure

Abstract

Fickian diffusion is often used to model moisture transport through barrier coatings, where the goal is to protect an underlying substrate from the onset of corrosion caused by buildup of water or other aggressive species. Such coatings are often exposed to cyclic moisture, either in laboratory testing or in service due to natural environmental fluctuations. In this paper, we use lattice Boltzmann numerical techniques to investigate the effects of reservoir cycling on moisture propagation and concentration at the substrate where corrosion onset occurs. We examine both the simple case of constant diffusivity, representing idealized Fickian diffusion, and diffusivity that depends on concentration via either a step or linear function, representing polymer network swelling. The use of a coating subject to swelling is shown to lead to highly variable equilibrium behavior. We show that the nature of the functional diffusivity has large effects on water concentration at the substrate, and has implications for material design and analysis to avoid corrosion.

Moment Independent Expansion for Fourth-Order Corrections in Lattice Boltzmann Methods

“…Since its initial development in the late 1980s, lattice Boltzmann methods have been growing as a powerful tool in computational physics. Originally introduced for simulating hydrodynamic systems [1][2][3], the lattice Boltzmann methods have been an active area of research which consistently is being improved and finding new applications in other fields of physics, namely phase separation [4,5], electrostatics [6], quantum mechanics [7], diffusion [8][9][10], and moisture transport through barrier coatings [11,12]. As a consequence of the many developments in lattice Boltzmann methods, deeper analysis on the fun-Email address: kyle.t.strand@ndsu.edu (Kyle Strand) damental methods have been required for better understanding as to how the method treats any given system [13].…”