Framework Integrated with Flow Cell Experiments and Simulations for Understanding Etching in Chemical Conversion Treatments

Abstract

Abstract In this study, a new framework integrates simulations and flow cell experimentation to quantitatively understand the mechanism of chemical treatment reactions.
Using this framework, the mechanisms of etching reactions induced by weak and strong acids were specifically investigated.
A flow cell system experiment was developed for the etching experiment.
Two acids (HNO3 and HF) were used, along with HNO3 without electrolytes.
Flow rate and the molar flux of Fe2+ions was measured.
A concentration field simulation of the etching reaction in the flow cell was conducted.
The concentration field within the boundary layer was visualized to understand the mechanism of H+ion supply to the metal surface. 
In the case of weak acid solutions, H+ions are primarily supplied by dissociation. 
In contrast, they were supplied by diffusion in strong acid solutions. 
A boundary layer formed within 100 μm from the metal surface. 
The experimental and simulated molar flux of Fe2+ions were compared.
The molar flux attributed to weak acid etching was more than 10 times that attributed to strong acids. 
The reaction rate constant of the H+reduction reaction was evaluated through a parameter study. 
The influence of supporting electrolytes on the etching process was also investigated.