Partial pressure dependences

J. Xue, and R. Dieckmann. Oxygen partial pressure dependence of the oxygen content of zirconia-based electrolytes in Ionic and Mixed Conducting Ceramics Second International Symposium 94-12, 191-208 (1994) ES Meeting San Francisco, California. 

Figure 1 Conversion as a function of Figure 2 Partial pressure dependency of temperature 0.1 kPa N2O and space time Co-ZSM-5 at a space time of 1.52 10 1.44 10 g.s/mol g.s/mol...

The difference between the total dissolved carbon in the surface and in deep-sea reservoirs depends on productivity. And the difference between the alkalinity in these reservoirs depends on productivity and also corat, the calcium-carbonate-to-organic-carbon ratio. The carbon dioxide partial pressure depends on the difference between total carbon and alkalinity in the surface reservoir, and all these depend on the total amount of carbon and alkalinity at the start of the calculation in the three reservoirs combined. By adjusting the values of these various parameters and repeating the calculation, I arrive at the following values for a steady-state system that is close to the present-day ocean with a preindustrial level of atmospheric carbon dioxide ... 

The partial pressure dependence is readily explained using Eq. (8.1c). The equilibrium constant, K, is... 

FIGURE 1.39 Oxygen partial pressure dependency of (a) total conductivity and (b) electronic conductivity of Sm0 2Ce0 8O19 [160]. 

Models based on chemisorption and kinetic parameters determined in surface science studies have been successful at predicting most of the observed high pressure behavior. Recently Oh et al. have modeled CO oxidation by O2 or NO on Rh using mathematical models which correctly predict the absolute rates, activation energy, and partial pressure dependence. Similarly, studies by Schmidt and coworkers on CO + 62 on Rh(l 11) and CO + NO on polycrystalline Pt have demonstrated the applicability of steady-state measurements in UHV and relatively high (1 torr) pressures in determining reaction mechanisms and kinetic parameters. 

Fig. 6. The CO partial pressure dependence at constant oxygen pressure for single crystal Rh, Ru, Pt, Ir, and Pd catalysts. (From Refs. 71, 73.) —...

Finally, the term A/to can be expressed as a function of the molar fractions C and Coo (he. concentration, or activity, or partial pressure, depending on the system), the concentrations near the growing surface, and around an infinite planar surface of the sohd formed, respectively. The supersaturation parameter S is generally defined as the ratio C/Coo, thus ... 

The C02 partial pressure depends on the altitude as follows (McElwain 2004) ... 

The general forms of rate expressions in heterogeneous systems can have concentration or partial pressure dependences in both numerator and denominator along with various exponents. In heterogeneous reactors, it is not unusual to derive kinetic expressions that are more complicated than just a power-law expression. This, of course, has implications on how the reactor is controlled and the potential for runaway in exothermic systems. In some cases, where kinetics are very fast relative to mass transfer rates, the reactor behavior is governed by mass transfer and the variables that affect it. 

Figure 16. Oxygen partial pressure dependence of the electrical conductivity of doped Ce02. The steep decrease is due to excess electrons, the flat behavior to oxygen vacancies. If we refer to typical oxygen partial pressures in an SOFC, viz. to 10" bar at the cathode and 0.2 bar at the anode, we see that the conductivity changes from ionic into n-type within a high temperature Ce02 based fuel cell. Reprinted from M. Godickemeier and L.J. Gauckler, J. Electrochem. Soc. 145 (1998) 414-421. Copyright 1998 with permission from The Electrochemical Society, Inc.

For broad partial pressure regimes, however, only two mobile defects, or one mobile defect and the dopant, play a role in the electroneutrality equation (Eq. (11)). In theses cases simple partial pressure dependences, namely power laws with concentrations being proportional top 02)", can be calculated (see e.g. Refs. [57, 80, 89, 90]). One example of such a simplified situation has been examined above (Eq. (10)). 

Assuming that only the doubly charged zinc interstitials (or oxygen vacancies) contribute to the excess electrons leads to the following oxygen partial pressure dependence of the conductivity ... 

Figure 4-33 Oxygen partial pressure dependence of the change in Raman band intensity ratio for samples with Ba/Ti = 0.9999 (R = I713/I525, AR = R R0). (Reproduced with permission from Ref. 51.)...

Activation energies for methanation over Ni and Ru were the same for both the fresh and the aged catalysts (Table XVII). In contrast, activation energies for methanation over aged Co and Fe were lower by 50 and 25 kJ/mol, respectively as compared to fresh Co and Fe (Table XVII). In the case of Co the CO partial pressure dependence changed from a negative order in the upper pseudosteady state to a positive-order dependence in the lower pseudosteady state (Table XVIII). The dependence on H2 partial pressure was positive one-half order in both upper and lower pseudosteady states. For Fe the kinetic behavior was not investigated. 

Li zn defects increase Ojon. The detailed partial pressure dependence follows through integration. 

For a Pbg3Li] 7 liquid metal wall, the total chamber pressure ranges between 0.047 and 3.6 mPa (3.5 x 10 7 and 2.7 X 10 5 Torr) as temperature increases from 400 to 500°C (Figure 25). The Li partial pressure is negligible. The H2 partial pressure depends on the solubility as discussed above two possible solubility cases are plotted. The lines labeled "Case 1" correspond to high hydrogen solubility. In this case, H2 pressure is negligible as it is with the other liquid metal. Helium pressure is then also treated as before (set... 

Kuo, C.K., Tan, A., Sarkar, P., and Nicholson, P.S., Water partial pressure-dependent conductance and humidity effects on hydronium-p"-Al203 ceramics, Solid State Ionics, 58, 311-314 (1992). 

Figure 4 Oxygen partial pressure dependence of the defect concentrations of Log Sro j FeO gOt 1273 K, as obtained from model calculations ...

Strictly speaking the partial pressures depend on the total pressure, but it is readily shown, as in 1, that the variation is negligible at ordinary pressure because of the small molar volumes of condensed phases. Equation (21.53) therefore reduces to the Duhem-Margules equation, ... 

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