Effect of Products of Nitric Acid Reduction on Active Dissolution and Passivation of Nickel

V. P. Razygraev* and M. V. Lebedeva

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow

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Received March 27, 2008

Abstract — For nickel in HNO₃ solutions, the passivation process is impeded and the range of its active dissolution is broadened, as opposed to in solutions of nonoxidative acids, which is stipulated by the interaction processes between metal surface and the products of cathode reduction of the solution. It has been shown that the products of cathode reaction promote the occurrence of a new electronegative reaction of nickel dissolution in the form of a complex with ammonia, the ligand formed on the cathode. Moreover, the intermediate products of NO reduction to NO₂ by interacting with nickel surface displace passivating oxygen and, therefore, retard the process of electrode passivation. The kinetic control of the cathode reaction of HNO₃ reduction within the potential range of active dissolution of nickel is connected with the complicated NO desorption from nickel surface, which virtually eliminates the possibility of the development of homogeneous autocatalysis within a certain potential range.