Ion Transport and Precipitation Kinetics as Key Aspects of Stress Generation on Pore Walls Induced by Salt Crystallization

TL;DR

This study investigates how salt crystal growth causes transient stress on pore walls, emphasizing the importance of interface supersaturation and reaction kinetics, with implications for understanding damage in porous materials.

Contribution

It introduces a simple stress diagram linking pore aspect ratio and reaction kinetics to stress generation during salt crystallization.

Findings

Stress build-up occurs in less than 1 second.

Interface supersaturation is critical for stress.

A stress diagram relates pore geometry and reaction kinetics.

Abstract

The stress generation on pore walls due to the growth of a sodium chloride crystal in a confined aqueous solution is studied from evaporation experiments in microfluidic channels in conjunction with numerical computations of crystal growth. The study indicates that the stress build-up on the pore walls as the result of the crystal growth is a highly transient process taking place over a very short period of time (in less than 1s in our experiments). The analysis makes clear that what matters for the stress generation is not the maximum supersaturation at the onset of the crystal growth but the supersaturation at the interface between the solution and the crystal when the latter is about to be confined between the pore walls. It is shown that the stress generation can be characterized with a simple stress diagram involving the pore aspect ratio and the Damkh{\"o}ler number characterizing the competition between the precipitation reaction kinetics and the ion transport towards the growing crystal. This opens up the route for a better understanding of the damage of porous materials induced by salt crystallization, an important issue in earth sciences, reservoir engineering and civil engineering.