Oxide-nucleation

Benard, J., Adsorption of Oxidant and Oxide Nucleation , in Oxidation of Metals and Alloys, Seminar, 1970 American Society for Metals, Ohio, 1 (1971)... 

Co step. Previously it had been observed for the C0/AI2O3 O)/ Ni/Si02 (10), and Fe/Si02 (11, 12) systems that highly dispersed oxide species (small particles) were more difficult to reduce than their corresponding bulk or bulk-like oxides. Nucleation, interaction with the support, and reaction with the support were given as possible explanations for these differences. Further experiments are needed to determine the reasons for the observed particle size effect on the Co/Si02 system. 

Our conclusion then for the oxygen interactions with metals is that because of the specific association of cluster ion intensities with particular types of oxygen rather than total coverage, the technique is not suitable for monitoring coverages or kinetics in an independent manner. Once it is established which type of oxygen a particular cluster ion is representative of, then that ion may, in favorable circumstances, be used for quantification. In the case of Ni, it seems that the negative ions are very sensitive to the initiation of oxide nucleation. In the case of W(IOO), the WOj, WO+ and WOj ions may fill a similar role. 

Coverage and Secondary Ion Yield Relationship for Ni(100)/CO. We showed above the enormous variation in yields that occurred on going from adsorption to oxide nucleation. In the case of Ni(100)/CO, one can perform more subtle bonding changes by changing the CO coverage. Below 0 O.4 ML, no ordered LEED structure is formed, and vibrational spectroscopy (HRELS) indicates... 

It is important to realize that corrosion rates may be controlled by any of several thermodynamic or kinetic properties of the alloy-scale-environment system and not just by surface or interface reactions. The three stages of high temperature oxidation of a metal, shown schematically in Fig. 1, serve as an example (7). The first or transient stage includes initial gas adsorption, two-dimensional oxide nucleation, initial three-dimensional oxide formation and finally, formation of the dominant oxide that will control the oxidation rate in Stage II. Various portions of Stage I have been widely studied using surface analytical techniques, but its duration can be very short and it is usually assumed (not always correctly) that Stage I has little impact on ultimate corrosion properties of the material. 

Fig. 2. Dislocation sites and sites of oxide nucleation on a ill surface of germanium. Etched in CP4 and oxidized in poor vacuum.

Figure 10 Four helix bundle of the L chain of ferritin showing iron oxide nucleating site (Glu61, Glu64, and Glu67). Quaternary structure of ferritin displaying mineralized ferrihydrite particle...

FIGURE 2.22. (a) The reaction path leading finally to condensation of Si-OH and formation of strained Si-O-Si bridges (b) the local development of oxide nucleated by Si-OH groups on the surface. (Reprinted with permission from Graf et al. 1989, American Vacuum Society.)... 

A site is found in L ferritins from horse (HoLF) and human (HuLF) which is not present in the H ferritins, but is proposed to be an oxidation/nucleation site [4, 7, 8, 58], This site comprises glutamates 57, 60, 61 and 64 (H chain numbers) all of which lie on the inner siuface of the molecule [4, 7, 58]. Although faster than that of free iron, the initial rate of Fe(II) oxidation in HoLF or HuLF is about one-tenth that of HuHF and the L subunit is therefore unlikely to play a major role in Fe(II) oxidation in H, L copolymers. However in the heteropolymers, the combination of... 

Probably this material is too soluble to play a role in manganese oxide nucleation. 

Adsorption has been assumed to be the rate-determining process during early oxide-film formation. When a clean surface is exposed to an oxidizing gas, each molecule impinging on the surface may either rebound or adsorb. The fraction, a, that remains adsorbed on the metal surface should be constant for a constant temperature and oxygen partial pressure. Therefore, under these conditions a constant reaction rate is expected. However, the value of a is markedly lower on those parts of the surface covered with a monolayer or oxide nuclei. Thus, as adsorption or oxide nucleation proceeds, the reaction rate is expected to decrease accordingly until complete coverage of the surface by oxide has been achieved, when a much lower rate is expected to be observed. 

Oxide nucleation and growth over the entire metal surface... 

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