Passivity film growth

The measurements presented here illustrate impressively that it is essential to consider the effect of substrate heterogeneities on passive film growth. Measurements of passive films on macroscopic surfaces can, in principle, not be quantitatively understood in terms of classical models without taking texture effects into account, as macroscopic measurements can yield only averaged values. 

FIGURE 8.5 Passive film growth according to Muller s model. (A) Observer s B view and (B) Observer s A view. 

Fig. 14 Passive film growth on Cr following application of a potential step from (a) 0.0 to 0.4 V and (b) 0.4 to 0.8 V. Full line is film thickness calculated from QCM frequency response (with widely spaced dots indicating uncertainty, 2or). The predictions of the interface and high-field models (explained in main text) are also indicated by the line-styles marked IFM and HFM, respectively. Electrodes Crfilm on Au supported on 10-MHz AT quartz crystal. Solution ...

Table 44.2. Comparison of Distinct Passive Film Growth Models... 

The generally accepted model for passive film growth, illustrated in Fig. 3-14, is of field-assisted film formation, which is essentially a modified Cabrera-Mott model originally established for gaseous oxidation and the formation of thin oxide films in a gas at low temperature (Cabrera and Mott, 1948-1949 Fehlner and Mott, 1970). This classical theory describes the growth, in the direction perpendicular to the surface, of an oxide layer completely covering the substrate surface, by a hopping mechanism. The... 

Figure 3-14. Model of passive films growth under an applied electric field adsorption of hydroxyl groups at the film surface and formation of metallic cations at the metal/film interface, followed by cations hopping via the vacancies of the film towards the film/ electrolyte interface where reaction with the adsorbed hydroxyl groups takes place.

Fig, 4. 22 shows the double-log plots of current density with time for two alloys. For passive films on two alloys, k = -0.5 is obtained and there is no obvious difference in the k value. Therefore, the passive films on two alloys are loose and passive film growths are at the control of diffusion process. 

T. Eliades, Passive film growth on titanium alloys physicochemical and biologic considerations, International Journal of Oral and Maxillofacial Implants, vol. 12, no. 5, pp. 621-627, 1997. 

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