Oxygen diffusion profiles

This model which associates the beginning of the distribution profile with an apparent diffusion coefficient has been recently discussed by Fielitz et al. [78] who proposed that the first part of the oxygen diffusion profile in polycrystalline mullite corresponded to the bulk diffusion coefficient in the B regime and not to the apparent diffusion coefficient. 

Fig. 12. Auger electron spectroscopy (AES) sputter-depth profile of CAA-treated titanium after various exposure.s in vacuum (a) as anodized, (b) 450°C for 1 h, and (c) 7(X)°C for 1 h. The sputter etch rate is 1.5 nm/min. The line indicates the original interface. The arrow denotes oxygen diffused into the substrate. Adapted from Ref. [51].

FIGURE 10.8 Profiles of the relative oxygen diffusion-concentration product across the DMPC bilayer containing 0 (O) and 10mol% zeaxanthin ( ) at 25°C. The approximate locations of nitroxide moieties of spin labels are indicated by arrows. The value of the oxygen diffusion-concentration product in water can be obtained from the oxygen diffusion coefficient and oxygen concentration in water equilibrated with air at 25°C. (From Subczynski, W.K. et al., Biochim. Biophys. Acta, 1068, 68, 1991. With permission.)... 

The degradation profile can be detected by measuring a property, such as microhardness, as a function of depth after ageing so that the magnitude of any effect from the limitation of oxygen diffusion could be measured for any temperature and material combination. The effect of a degradation profile on a bulk property will depend on the particular... 

Figure 3-4 Calculated oxygen isotope diffusion profile from both sides of a plane-sheet mineral, initial 5 0 in the mineral is l%o. The surface 8 0 is 10%o. The diffusivity D = 10 m /s. Compare this with Figure l-8b.

We will try our hand at applying the diffusion equation to a couple of mass transport problems. The first is the diffusive transport of oxygen into lake sediments and the use of oxygen by the bacteria to result in a steady-state oxygen concentration profile. The second is an unsteady solution of a spill into the groundwater table. 

Recently ICLwas used to follow the diffusion-limited oxidation of hydroxyl terminated polybutadiene at various temperatures and oxygen pressures. The CL intensity profiles were found to correlate well with theoretical oxygen concentration profiles [137]. 

Figure 50. Snapshots of oxygen incorporation experiments in Fe-doped SrTi03, recorded by in situ time and space resolved optical absorption spectroscopy.256 Rhs column refers to the corresponding oxygen concentration profiles, in a normalized representation. Top row refers a predominantly diffusion controlled case (single crystal), center row to a predominandy surface reaction controlled case (single crystal), bottom row to transport across depletion layers at a bicrystal interface.257,258 For more details on temperature, partial pressure, doping content, structure see Part I and Ref.257-259 Reprinted from J. Maier, Solid State Ionics, 135 (2000) 575-588. Copyright 2000 with permission from Elsevier.

The reaction between 02 and l e(ll)l l)TA2 is slow. The oxygen concentration profile is almost linear, characteristic of pure diffusion. Therefore, we can safely assume that the oxidation reaction takes place mainly in the liquid bulk. 

Figure 54. (a) Profiles for half the sample on rapid exchange of the surface concentration on both sides by x = L/2. The value x = 0 refers to the center of the sample. The parameter on the curves is D t/(L/2)1. (b) Concentration profiles during oxygen diffusion into SrTiCh (848 K), as a function of space and time. The smooth curves are obtained by fitting with a constant Dfl. The introduction of a concentration dependence only alters the result slightly.214... 

The nature of intermediates formed in diffusion flames is similar to the premixed ones, albeit differences in the contacting pattern. In Fig. 11, the species concentration profiles in a laminar ethylene diffusion flame front are presented. The fuel and oxygen diffuse toward each other undergoing virtual annihilation within the flame zone concomitant with the establishment of a peak temperature of about 1600°C. Because premixed systems provide a better control of combustor temperature, and many practical combustion devices operate under diffusion limited conditions, considerable effort has been expended to ensure the rapid mixing of fuel and oxygen in combustion chambers and approach premixed conditions. 

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