Intermediate oxides oxygen diffusion

A third situation that is possible is intermediate between the two extreme cases shown in Figs. 8.7a and b. In this case, the boundary between the reacted and unreacted composite is not sharp, and a region of semi-reacted SiC particles separates the two (Fig. 8.7c). This case can occur in two circumstances. When the oxygen diffusion rate through the oxidation product is comparable to, but slightly slower than, through the matrix, a semi-reacted zone will appear, the thickness of which depends on the SiC particle size. A similar situation will arise when the initial oxidation production reacts with the... 

When the polypropylene sample is irradiated in air, as is the case during a sterilization cycle, the oxidative process is initiated at the onset of irradiation. As a consequence of oxygen diffusion during irradiation a spectrum intermediate between the alkyl and peroxy radicals is generally observed (Figure 3). Whether oxygen is present during irradiation or added later, the peroxy radical becomes the dominant radical species with time. 

Vospemik et al. (2006) calculated the profile concentration along the porous catalytic layer by assuming the gas-liquid interface at the border between an intermediate porous catalytic layer and the coarse support (at about 50 pm from the top-layer surface). In their model they considered the complete depletion of oxygen in the reaction zone during the catalytic oxidation of formic acid. Their model did not take into account the catalyst distribution along the cross-section. They found the limiting influence of oxygen diffusion on the overall reaction rate. 

Oxygen diffuses in ond Nitric oxide attacks out of reduced [Cu(I)] SOD transient Cu(I)-oxygen intermediate... 

A PP sample after ozonization in the presence of UV-irradiation becomes brittle after 8 hrs of exposure, whereas the same effect in ozone is noticeable after 50-60 hours.Degradation of polymer chain occurs as a result of decomposition of peroxy radicals. The oxidation rapidly reaches saturation, suggesting the surface nature of ozone and atomic oxygen against of PP as a consequence of limited diffusion of both oxygen species into the polymer. Ozone reacts with PP mainly on the surface since the reaction rate and the concentration of intermediate peroxy radicals are proportional to the surface area and not the weight of the polymer. It has been found that polyethylene is attacked only to a depth of 5-7 microns (45). 

Some of the earliest studies of triplet carbenes in frozen media by epr spectroscopy revealed that these intermediates react rapidly with molecular oxygen (Trozzolo and Gibbons, 1967). This should not come as a surprise since the combination of a triplet carbene with triplet oxygen is a spin-allowed process. Indeed, recent measurements show that this reaction proceeds with a rate that is approximately at the diffusion limit. The product of this reaction (17) is the expected carbonyl oxide (Werstiuk et al., 1984 ... 

---