Oxygen diffusion times

The measurement of oxygen diffusion is usually made by the use of as die labelling isotope. If a gas containing an initial concentration C, of in O , and Co is the initial conceiiuation of in a right cylinder oxide sample of thickness 21, and a is the ratio of oxygen atoms in the original gas phase compared widi that in the solid, dieii after a time t, when the concentration in the gas phase is C/... 

The recombination of fragments stemming from one macromolecule, at times shorter than the diffusion time, prevents the linear increase in RD with the absorbed dose per pulse, as not all main-chain scissions result in the formation of fragments. The effect of molecular oxygen on RD in the case of PBS can be interpreted by formation of peroxyl radicals, e.g. 

In that pioneering study28 it was not possible to obtain a time resolved distribution of the backspillover oxygen species despite the fast, 40 ms, time resolution of the video-frames. If the spillover distance is 100 pm, this implies surface spillover oxygen diffusivities as high as 10 3 cm2/s. If, however, microcracks exist in the film, which is very likely, then the spillover distance is much shorter and thus much lower diffusivities would suffice to escape time-dependent detection. 

Isotopic exchange reaction rates and oxygen diffusion coefficients of Pt/M-CZ, S-CZ and R-CZ at 41 are listed in Table V (Dong et al., 2004a). The surface diffusion rate for R-CZ (Rg) is nearly 4 times larger than the bulk diffusion rate or the equilibrium isotopic exchange rate (R ), while it is... 

Oxidations for varying times showed systematic variations in the U +/U + ratios that fell into three values stable for significant periods of time (Fig. 5). These ratios of U +/U + = 0.5, 1.0 and 2.0 are believed to correspond to the presence of U3O7 (U02 U02 U03), U205 (U02 U03), and U30g (U02-U03-U03), respectively. The surface film composition is controlled by various rates of surface dissolution, oxygen diffusion into the UO2 and precipitation. Film dissolution is believed to occur upon oxidation to UO3. Because no appreciable layer of UO3 was found on the surface, it is concluded that dissolution of UO3 occurs at a rate faster than solid-state oxidation. 

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