NH.sub.4Cl precipitation can present deleterious effects on refinery surfaces when it combines with condensed water vapor to produce highly concentrated chloride and ammonia solutions. Density functional theory ("DFT") methods were used to compute the adsorption energies for various species including NH.sub.x, OH.sub.x, Cl and H on the lowest energy iron-containing surface of a metallic component. The adsorption energies were combined with thermodynamic analysis to develop phase diagrams for the various species that may dominate the surface adsorption coverage. N, O, Cl, and H each possess regions of predominance on surface Pourbaix diagrams at 25.degree. C. and 130.degree. C. in the presence of a saturated NH.sub.4Cl solution. N typically does not interfere with O adsorption and hence is unlikely to depassivate any protective oxide films. However, Cl can overlap regions of O surface stability to provide a competitive mechanism for hindering repassivation and/or accelerating the rate of metal dissolution.
STATEMENT REGARDING FEDERAL RIGHTS
 This invention was made with government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The government has certain rights in the invention.