On the Passivation of Nickel Monocrystal Surfaces.
MARTIN MARIETTA CORP BALTIMORE MD RESEARCH INST FOR ADVANCED STUDIES
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Steady state potentiostatic polarization measurements on low index nickel monocrystal surfaces in 1N H2SO4 indicate a strong anisotropy in passive current densities. The nature of this orientation dependence appears to be related to such properties of the solid state as the crystal growth axis. For example, in the case of crystal growth parallel to the 110 axis, the degree of protection provided by the passive film on a 111 surface is greater than that on either 110 or 100 faces, i.e., the passive current densities are in the following order 111 110 100. It is interesting to note that an identical anisotropy has been reported in the rate of gaseous oxidation on nickel surfaces. On the other hand, precisely the reverse dependence is observed in passivation studies when the growth direction of the monocrystal is parallel to the 100 axis. The above results are examined in terms of the crystallography and defect structure of the film, the metalfilm interface, and the metal substrate and their relevance to current theories of passivation is considered. Author
- Properties of Metals and Alloys