Passive Film on Nickel

In a sulfuric acid solution, the formation of PbO during the corrosion of lead without any other phase of PbO (1 < x < 2) has been observed the sensitivity of the method approached the monolayer level [742]. Passive films on nickel and iron surfaces have been studied both with polychromatic and monochromatic light [739]. Characteristic data of the semiconducting surface layers (fiatband potentials, charge carrier densities, bandgap energies) could be obtained. The limitations of the traditional band model that is used in solid state physics for ideal crystalline solids with practically unlimited periodicity have been pointed out and the additional difficulties caused by the polycrystalline or even amorphous nature of these films were stressed. 

The diagnostic features of this analysis have been used by Chao et al. [1982] in their investigation of the growth of passive films on nickel and Type 304 stainless steel in borate and phosphate buffer solutions. Typical complex plane and... 

Melendres, C.A. and Pankuch, M. (1992) On the composition of the passive film on nickel a surface-enhanced Raman spectroelectrochemical study. Journal of EJectroanalytical Chemistry, 333, 103-113. 

Macdonald, D.D. and Smedley, S.I. (1990) An electrochemical impedance analysis of passive films on nickel(lll) in phosphate buffer solutions. Electrochimica Acta, 35,1949-1956. Macdonald, D.D. and Urquidi-Macdonald, M. (1985) Application of Kramers-Kronig transforms in the analysis of electrochemical systems I. Polarization resistance. Journal of The Electrochemical Society, 132, 2316-2319. 

Penetration of chloride ions this mechanism [first discussed by Hoar et al. (1965)] involves, following the adsorption of Cl" on the passive film surface, the entry of Cl" into the film and its transport through the passive film to the metal/oxide interface, where it causes breakdown of the passive film. The accumulation of Cl" at the interface or the formation of metal chloride may cause the film breakdown. Support of this mechanism is provided by the observation of chlorides in the inner oxide part of the passive film on nickel (Marcus and Herbelin, 1993), Fe-Cr (Yang et al., 1994), and aluminum (Natishan etal., 1997). 

The passive film on nickel can be formed quite readily in contrast to the formation of the passive film on iron. Differences in the nature of the oxide film on iron and nickel are responsible for this phenomenom. The film thickness on nickel is between 0.9 and 1.2 mm, whereas the iron oxide film is between 1 and 4 mm. There are two theories as to what the passive film on nickel is. It is entirely NiO with a small amoimt of nonstoichiometry, giving rise to Ni cation vacancies, or it consists of an inner layer of NiO and an outer layer of anhydrous Ni(OH)2. The passive oxide film on nickel, once formed, cannot be easily removed by either cathodic treatment or chemical dissolution. 

The combined ellipsometry-reflectance method—three-parameter ellipsometry—has been subject to error analysis. Cahan showed that, while it is possible in principle to obtain an unambiguous solution for the optical constants and thickness of a film by three-parameter ellipsometry, the method does not guarantee that a solution can be obtained in practice. He also pointed out, by working with sample data from electrochemically produced films, that the numbers obtained as the solution are not necessarily physically real when the three-layer model is inadequate for the particular system. Chung, Lee, and Paik" studied the forward and reverse sensitivity analyses for three-parameter ellipsometry to obtain the forward sensitivity coefficients (dMldoi) > and the reverse sensitivity coefficients for a passive film on nickel (here... 

Figure 8 Changes in (a) A, (b) [jj, and (c) R at vanous angles of incidence for simulated passivation films on nickel surface The real line in each diagram is for the actual passivation film The dashed, dotted, and dash-and-dot lines are for simulation of deviating , t, and k values, respectively...

Figure 9. Surfaces of constant (a) ij/, (b) A, and (c) in the space of ri2-k2-x coordinates calculated for a passive film on nickel. (Reproduced from Ref. 48, by courtesy of Korean Chemical Society.)...

The reaction scheme of Bode [11] was derived by comparison of the X-ray diffraction patterns of the active materials with those for the model compounds. How the 8-Ni(OH)2 in battery electrodes differs from the model compound is discussed in Section 5.3.I.3. In recent years, the arsenal of in situ techniques for electrode characterization has greatly increased. Most of the results confirm Bode s reaction scheme and essentially all the features of the proposed a/y cycle. For instance, recent atomic force microscopy (AFM) of o -Ni(OH)2 shows results consistent with a contraction of the interlayer distance fiom 8.05 to 7.2 A on charge [61-63]. These are the respective interlayer dimensions for the model a-Ni(OH)2 and y-NiOOH compounds. Electrochemical quartz crystal microbalance (ECQM) measurements also confirm the ingress of alkali metal cations into the lattice upon the conversion of a-Ni(OH)2 to y-NiOOH [45,64,65]. However, in situ Raman and surface-enhanced Raman spectroscopy (SERS) results on electrostretching modes that are consistent with a weakening of the O-H bond when compared with results for the model a- and 8-Ni(OH)2 compounds [66]. This has been ascribed to the delocalization of protons by intercalated water and Na ions. Similar effects have been seen in passive films on nickel in borate buffer electrolytes [67]. 

D. D. Macdonald and S. I. Smedley, An electrochemical impedance analysis of passive films on nickel (111) in phosphate buffer solutions, Electrochim. Acta 35 1949 (1990). 

The lateral dimensions of the crystalline grains forming the passive films on nickel are relatively well documented. Values determined from the morphology observed by STM and AFM (Figure 5.64) have been reported to range from 2 nm in the initial stages of 2D growth... 

Most of the work to date on the use of the reflection geometry has been of an exploratory nature, and the data often do not appear to have been fully analyzed. As an example, Figure 22 contains some results obtained by Bosio et for passive films on nickel. This figure shows k-weighted xik) data for the electrode before and after passivation and, for comparison, curves for Ni and NiO. An example of the use of the energy-dispersive mode is the study... 

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