The dissolution of a Ni (111) thin film exposed to a 0.1 M NaCl (pH4) solution was monitored for a period of 816 hours using X- ray reflectometry. The dissolution rate of the Ni (111) film decreased from approximately 9 angstrom/h at the beginning of the immersion experiment to 0.05 angstrom/h after 816- hour exposure. After reaching a steady state between formation and dissolution, the thickness of the NiO passive film remained constant at approximately 18 angstrom during the immersion experiment. (C) 2017 The Electrochemical Society. All rights reserved.