The role of emerging grain boundary at iron surface, temperature and hydrogen on metal dusting initiation

We conduct a multiscale modeling of different iron systems exposed to carbon-rich atmospheres by means of density functional theory and reactive molecular dynamics in order to evaluate the effects of temperature, gas content and surface defects such as emerging grain boundaries and grooves on CO dissociation rate. Comparative density functional theory calculations of carbon adsorption energies on clean surface and the groove area show that grooves have preferential binding sites, explaining why emerging grain boundaries are more severely attacked by metal dusting corrosion. Molecular dynamical simulations using a ReaxFF potential on iron Sigma 3 and Sigma 5 emerging grain boundaries on (111) and (210) surfaces, respectively, also demonstrate the enhanced CO dissociation rate within the grooves area. Analysis of CO dissociation and recombination events on these systems demonstrates quantitatively the dual role of hydrogen as a CO dissociation enhancer and reactant with dissociated carbon atoms. By carefully characterizing reaction mechanisms as a function of reactant content, we provide a linear correspondence between CO dissociation variation as function of temperature and the experimental measurement of metal dusting corrosion rate.