Oxygen concentration profiles

Figure 3.5 Schematic pH eind oxygen concentration profiles in an active tubercle. Below the magnetite shell oxygen concentration decreased sharply. pH rises above the magnetite shell due to cathodic hydroxyl-ion generation emd falls below the shell due to concentration of acidic anion, (Courtesy of National Association of Corrosion Engineers, Corrosion 91 Paper No. 84 by H. M. Herro.)...

At steady-state condition the oxygen concentration profile would be an exponential model ... 

In principle, one can take the interpretation further and calculate what oxygen concentration profile fits the measurements of the O/Ag ratio best. In fact, Baschenko et al. [39] did this and concluded that the subsurface oxygen resides mainly in the third and fourth atomic layer below the surface. Although the result appears plausible, it should be noted that such calculations are only permitted when the surface satisfies the requirements of lateral homogeneity and absence of roughness discussed above. As the O/Ag experiments were done with polycrystalline foils, one might wonder whether too detailed an analysis is warranted. Anyhow, the work forms a nice illustration of what angle-dependent XPS can achieve on catalytically relevant adsorbate systems. 

The chemical structure of plasma-treated PE was examined using XPS, the oxygen concentration profile was determined from RBS measurement and the concentration of free radicals was determined by EPR technique [78], The -CH a -CH2 (of pristine PE), oxidized (-C=0, -COO, -COC-), -NH2, and also -C=C-groups (typical for aromates) were reported present at Ar plasma-treated high-density PE (HOPE) [70],... 

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. 

EXAMPLE 2.1 Steady oxygen concentration profile in lake sediments (steady-state solution with a first-order sink)... 

Given a concentration, Co, in the overlying water, and a first-order sink of oxygen in the sediments, develop an equation to describe the dissolved oxygen concentration profile in the sediments (see Figure E2.1.1). 

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 3.29 (a) Oxygen concentration profile at the inlet and outlet of the compartments of the high-throughput micro reactor. The inlets of the sampling tubes have to penetrate into the compartments to minimize flow cross-over, (b) Area averaged oxygen concentration at one capillary outlet. Total flow velocity 50 (1), 75 (2) and 100 cm3 min-1 (3) [55] (by courtesy of ACS). 

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.

Dissolved oxygen concentration profiles with organic removal... 

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. 

Oxygen concentration profiles predicted by Equations (8.38) and (8.41), for the cases with and without myoglobin respectively, are illustrated in Figure 8.5. Only when the oxygen concentration falls near zero does the presence of myoglobin... 

The solution of Eqs. 85 with 86 will yield the oxygen concentration profile along the fluidized bed combustor. 

If the values of ncCE SAE fixed, the parameter a of Eq. 91 has a definite value. The oxygen concentration profiles are then changed by altering the value of the parameter b. By assuming b as 2.5, 4.5 and 6.5, the computed oxygen distribution in the bed is obtained as shown in Figure 5. The effect of these profiles is examined for two values of k3(To),... 

Figure 6. Effect of oxygen concentration profile on limestone requirement for different assumed -qsAE and f...

Fig. 26. (a) Translational temperature profiles along the 36° line of sight as a function of altitude, (b) Atomic oxygen concentration profiles along the 36° line of sight as a function of altitude. 

Figure 11-16 Oxygen concentration profile shown from the external radius of the pellet (/ ) to the pellet center. The gas-carbon interface is located atli.

We see that as the reaction proceeds, the reacting gas-sohd moves closer to the center of the core. The corresponding oxygen concentration profiles at three different times are shown in Figure 11-17. 

Figure 11-17 Oxygen concentration profile at various times. At, the gas-carbon interface is located at l (t ) at ti it is located at Ritj)-...

Figure 23. Axial oxygen concentration profiles for the fetal channel for transient conditions after step change V2 = 0.125 normal for case including axial gradients...

Figure 24 shows the axial oxygen concentration profiles for the fetal channel for the same transient conditions that were just discussed but for the case which neglected axial dispersion. These may be compared directly with the profiles in Figure 23 which represent the case which includes axial dispersion. As in the previous discussion, comparison of these figures shows that at this reduced maternal blood velocity the results are essentially the same, and the effects of axial diffusion are negligible. 

Fig. 6.22 Oxygen concentration profile measured with an in situ optode technique (after Wenzhofer et. al. 2001b).

An oxygen concentration profile such as the one which has been measured in situ (Fig. 3.5) or modeled (Fig. 15.5) is mostly interpreted in terms of a stationary condition (steady state) resulting from the consumption of oxygen in the sediment and its resupply by means of diffusion. Its consumption in the sediment is due to the oxidation of organic matter and other redox processes, such as the re-oxidation of divalent manganese. But how long does it take until such a stationary condition is reached ... 

The Pd-O bond also varies with the extent of oxidation of Pd. During the methane combustion reaction, the catalyst surface is a non-equilibrium, kineti-cally controlled structure. The oxygen concentration profile in the particle results from a combination of particle reconstruction, oxygen adsorption, bulk diffusion, and oxygen removal. This concentration profile varies as a function of time, and as the oxygen content increases, the Pd-O bond strength decreases. This increase is accompanied by an increase in the specific activity. The most widely accepted reaction pathway is the Mars and van Krevelen redox mechanism, which involves lattice oxygen and uneoordinated Pd centers as active species. Inhibition by products (H2O and CO2) and impurities (SO2) is a major drawback for low temperature combustion. The effect of sulfur is particularly important for catalytic converters for NGV applications because it drastically reduces the methane combustion activity. 

Closterhuis NMG, Kossen NWE (1983) Dissolved oxygen concentration profiles in a production-scale bioreactor. Biotechnol Bioeng 26 546-550... 

Figure 10.4 Predicted oxygen concentration profiles in a PP at I I0°C (Rincon-Rubio L. M. et at, Polym. Degrad. StabiL, 74, 177, 2001) Elsevier.

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