The formation and arrangement of pits by a corrosive gas

TL;DR

This paper presents a lattice model simulating pit formation by corrosive gases, explaining how regular pit patterns and geometries emerge based on particle dynamics and surface interactions.

Contribution

It introduces a simple lattice-based model that captures the formation and geometry of pits caused by corrosive gases, linking physical parameters to observed patterns.

Findings

Regular pit patterns emerge from the model.

Pit geometry depends on particle bias and absorption probability.

The formation process can be described by a PDE.

Abstract

When corroding or otherwise aggressive particles are incident on a surface, pits can form. For example, under certain circumstances rock surfaces that are exposed to salts can form regular tessellating patterns of pits known as "tafoni". We introduce a simple lattice model in which a gas of corrosive particles, described by a discrete convection diffusion equation, drifts onto a surface. Each gas particle has a fixed probability of being absorbed and causing damage at each contact. The surface is represented by a lattice of strength numbers which reduce after each absorbtion event, with sites being removed when their strength becomes negative. The model generates regular formations of pits, with each pit having a characteristic trapezoidal geometry determined by the particle bias, absorbtion probability and surface strength. The formation of this geometry may be understood in terms of a first order partial differential equation. By viewing pits as particle funnels, we are able to relate the gradient of pit walls to absorbtion probability and particle bias.