Iron diffusion

Camire (2002) showed that texturization does not seem to have a great effect on mineral retention and bioavailability. Others have reported increased retention of ascorbic acid in rice- and maize-based snacks (Hazell and Johnson, 1989 Plunkett and Ainsworth, 2007), increased iron diffusibility and absorption of iron-complexed protein (Poltronieri et al, 2000 Watzke, 1998), and no difference in iron and zinc absorption in human subjects fed textured bran-flour (Fairweather-Tait et al, 1989). 

Although a few elements (Fe, Cr, Ni, etc.) diffuse from the bulk of the steel specimen across Layer I, iron diffusion seems to be dominant. The... 

Z. Jurasz, M. Daniliewski, R. Filipek. Calculations of iron diffusion coefficients -high-temperature oxidation in air in a cylyndrical geometry // Defect Diffusion Forum.-2001.- V.194-199.- P.1719-1724. 

Lord, C.J., III., and Church, T.M. (1983) The geochemistry of salt marshes sedimentary iron diffusion. Sulfate reduction, and pyritization. Geochem. Cosmochim. Acta 47, 1381-1391. 

The rates of oxidation of both pyrite and pyrrhotite at 25 °C and standard atmospheric oxygen indicate that pyrrhotite can react 20-100 times faster than pyrite. During oxidation of a particle of pyrrhotite, iron diffuses to the exposed surface, thereby creating a sulfur-enriched inner zone that contains disulfide and polysulfide-hke species (Mycroft et al., 1995). 

Another interesting effect is the co-precipitation of some trace constituents with phases created by cycles of a more abundant substance. For example, as ferrous iron diffuses upward, other trace metals or phosphate may co-precipitate with the oxyhydroxides when oxygen or nitrate is encountered. These constituents may re-dissolve as the ferric oxyhydroxides are buried more deeply. 

Some other effects causing corrosion take place in the NPP, such as iron diffusion through passivated protective oxide film, high steam generator pressure, etc. 

Iron diffusion from steel into titanium >800... 

At temperatures below about 2250 F (1232 C), iron diffusion is much slower than oxygen availability. Scale formation is controlled by the temperature and the rate of diffusion of iron atoms toward the scale surface and oxygen moving toward the load surface. At temperatures above 2250 F (1232 C), the iron diffusion rate is high enough that availability of oxygen controls the reaction rate. 

Bainite is a crystalline constituent that can be formed during heat treatment of steel by isothermal transformation or continuous cooling in the temperature range between those of perlite and martensite. Here, iron diffusion is no longer possible, while... 

The deviation from stoichiometry 8 in (Cr,Fe)3 504 was measured at 1200°C and was found lower flian 0.01. Two defects may be present cation vacancies which governs iron diffusion at low oxygen activities and cations intersticials which governs iron diffusion at high oxygen activities. 

The oxidation mechanism proposed by all authors in that case is that the inner scale grows in the vacant space left by iron diffusion outwards to form the outer scale. Both scales, the outer and the inner ones, are made of Fe304 (with Fc203 at the oxide—gas interface), and for the inner scale to grow the oxidizing CO2 species must have an access to the underside. The reaction of CO2 molecules in the vacant space left below the outer oxide layer leads to oxidation and carbon transfer as observed by the carbon... 

The beneficial effects of Ce02 are also reported in the literature. It was found that sulphidation of FeAl alloys was retarded because the nanoparticles inhibit iron diffusion and act as traps for the sulphur ions [26]. Cabot and Foissy also demonstrated that silica layers stabilised with CeOz nanoparticles led to significant improvements in the corrosion resistance of zinc-coated steels [27]. Cerium oxides are also reported as having a pronounced stabilising effect on the passive state of steels and then-corrosion resistance [28]. 

Samples of allophane are, by definition, amorphous to X-rays, and their X-ray powder diffraction patterns show no pronounced X-ray powder diffraction maxima. The general scatter of X-rays by allophane samples mounted, for instance, on glass plates is, however, greater than that of the glass itself, particularly at low angles. This scatter differs for different samples, often as a result of differences in particle size or differing amounts of constituents other than allophane such as compounds of iron. Diffuse bands near 10 A, sometimes reported, are possibly due to hydrated halloysite. 

---