Oxide inner layer

STM data have shown the crystallinity of the inner layer of the passive film on chromium (Maurice et al., 1994a Zuili, 1998 Zuili et al., 1999). However, in sharp contrast to the case for nickel, on which large crystals of NiO are formed, the crystals of Cr203 formed on chromium can be very small in passivation conditions where the oxide inner layer is not fully developed, and where the passive film is highly hydrated and consists mainly of hydroxide. A typical image is presented in Fig. 3-13, which... 

Some metals oxidise at a rate which decreases, rather than increases (Type 2 in Fig. 1.89). Cerium behaves in this fashion at temperatures between 40°C and 130°C, and Loriers has suggested that the curve derives from the competition between the two oxides Ce20j and Ce02. It was proposed that the inner layer Ce2 0j was continuous and grew under diffusion control but transformed at a constant rate to an outer layer of Ce02. That is, if we writer and z as the thickness of the inner and outer layers respectively, then... 

For Fe in steam, water vapour or COj below 570°C, a two-layered Fej04 layer is observed, the inner layer growing by Oj diffusion inwards. Similarly, Potter and Mann reported the formation of a duplex Fej04 layer during the oxidation of mild steel in steam between 300°C and 550°C. 

In 1929 Pfeil" published a most interesting account of the way layered structures form and the manner in which they influence oxidation rates. From detailed studies of the growth and composition of scales he was able to show clearly how the formation of barrier layers reduced scale formation by hindering outward diffusion of iron through the scale. Naturally, this work had to be largely based on the study of scales of sufficient thickness so that the mechanism of the early stages of oxidation could not be studied in this way. Pfeil analysed the outer, middle and inner layers of scales formed... 

It is presumed that the global-quenching criteria of premixed flames can be characterized by turbulent shaining (effect of Ka), equivalence ratio (effect of 4>), and heat-loss effects. Based on these aforemenhoned data, it is obvious that the lean methane flames (Le < 1) are much more difficult to be quenched globally by turbulence than the rich methane flames (Le > 1). This may be explained by the premixed flame shucture proposed by Peters [13], for which the premixed flame consisted of a chemically inert preheat zone, a chemically reacting inner layer, and an oxidation layer. Rich methane flames have only the inert preheat layer and the inner layer without the oxidation layers, while the lean methane flames have all the three layers. Since the behavior of the inner layer is responsible for the fuel consumption that... 

Radiotracer techniques involving lsO in the anodization process are used with subsequent neutron activation analysis84 or SIMS.85 Another method involves implantation of inert ion markers into the surface layer of the sample prior to anodization and examination of the position of the markers after the oxide film has grown to a certain thickness.86 Assuming immobility of the inert species, the ratio of the cation to the anion transport number, t+/, should be equal to the ratio of the outer to the inner layer thickness. Numerous experimental determinations72,87 suggest t+ and f to be 0.4 and 0.6, respectively. 

Takahashi et a/.,79 in their work on the structure of the barrier layer [cf. Section IV(2)], have considered phosphate ions, which are found in the outer layer of the oxide, as immobile markers and, from the position of the boundary between the outer and the inner layer, deduced the transport number of the cation to vary between 0.73 and 0.81 in the current density range between 0.05 and 10 mA/cm 2. 

Both rust and oxide scales are usually mixtures of iron oxides vith other Fe (e. g. siderite) and non-Fe compounds (CaCOs). In some cases there is a more or less random mixture of components, vhereas in others, the different oxides are arranged in layers to form duplex or triplex scales. Layer-type rust arises as a result of potential or chemical gradients across the film. As these gradients vary ivith film thickness, the composition of the rust changes with the distance from the metal. On the whole, if Fe " and Fe" are present, the oxide containing Fe" is found in the inner layer of the rust. 

Fig. 18.5), overlain by magnetite (Fig. 18.4 B), with goethite and lepidocrocite at the outer surface of the tubercle (Fig. 18.4A). The magnetite probably formed by oxidation of the green rust. In the interior of the older tubercles, magnetite was oxidized to maghemite. The carbonate form of green rust was also identified in the inner layers of rust tubercles in pipes for drinking water (Stampfl, 1969).

The oxide film formed in dry air at room temperature consists of a spinel phase, probably a solid solution of magnetite and maghemite. Such films form on magnetic tapes. They are around 1.5-2.0 nm thick, and in a dry atmosphere, can provide indefinite protection (e.g. the Delhi pillar). Ali and Wood (1969) found that with time and at a relative humidity of 46%, some hematite developed as well. At higher temperatures (200-300 °C) well defined duplex films with an inner layer of magnetite... 

Melanin granules are secreted by melanocytes in the hair papilla and distributed to keratin in the hair cortex and inner layers of the hair sheath during normal development. Melanogenesis is subject to hormonal control and has been the focus of intensive genetic studies. Two main forms of melanin exist in human skin—eumelanin and phaeomelanin, both of which are derived from tyrosine through the action of tyrosinase (a cupro-enzyme) and possibly other key enzymes (with nickel, chromium, iron, and manganese as cofactors). Tyrosine is converted to dihydroxyphenylalanine and, via a series of intermediate steps, to indole-5,6-quinone, which polymerizes to eumelanin. Phaeomelanins are produced by a similar mechanism but with the incorporation of sulfur (as cysteine) by a nonenzymatic step in the oxidation process. 

Another approach to improving the properties of starch-filled polyolefin materials involves the use of ethylene-acrylate copolymers in blends with PE.45 Addition of copolymers of ethylene with methyl acrylate, ethyl acrylate or butyl acrylate were shown to improve the properties of PE films, allowing for higher starch contents. Coextrusion of starch-containing films with outer layers incorporating oxidative pro-degradants has also been utilized 46 The inner layer can contain up to 40% starch the... 

---