Effect of oxygen stoichiometry

The approach described in Sections 8.2.3 and 8.2.4.5.3 was used to construct quasi-2D (Q2D) analytical and semi-analytical models of PEFC [246, 247] and DMFC [248, 249], The Q2D model of a PEFC [246] takes into account water management effects, losses due to oxygen transport through the GDL, and the effect of oxygen stoichiometry. The model is fast and thus suitable for fitting however, the systematic comparison of model predictions with experiment has yet not been performed. Q2D approaches have been employed to construct a model of PEFC performance degradation [250], to explain the instabilities of PEFC operation [251, 252] and to rationalize the effect of CO2 bubbles in the anode channel on DMFC performance [253, 254],... 

Effects of Oxygen Stoichiometry on Structure and Properties in Ba2YCu30 ... 

To rationalize the effect of oxygen stoichiometry X on the potential loss, consider first the case of a small cell current. In this case, the local polarization curve is given by Equation 5.43. To calculate the polarization curve as a function of mean cell current density rjo (/), it is advisable to divide the terms under the logarithms in Equation 5.43... 

Another example of the effects of non-stoichiometry on diffusion is to be found in U02+. Here the defect consists of interstitial oxygen ions of high... 

The effect of various stoichiometry VO2 powders on temperature and heat of phase transition has not been reported so far. In this paper, the heats and the temperatures of transition from VO196 to VO207 in the crystalline state were measured from DSC scans. The results are listed in Table 1, indicating that the heats of the oxygen-deficient VO2 are less than those of the oxygen-rich VO2, and the VO2 02 has the maximum transition heat. The transition temperature is increased about 10°C from VOi 95 to VO2.07- Those results are not consistent with the results observed by determination of electrical resistivity of monocrystals reported in the literature, and the results in the literature are also contradictory [16,17]. The IR spectra of various size, crystalline state and stoichiometry VO2 are observed, showing the effects of size, crystalline state and stoichiometry [18]. 

As Tc depends on the oxygen stoichiometry, changes that occur with reduction may provide the key to superconductivity in these materials. The most dramatic structural effect of oxygen removal is the loss of connectivity in the 1-D chains that run along the b axis. This may indicate that conductivity occurs along these chains. An alternate explanation (26)... 

The study reported here was prompted by the still unsettled question of just how the reaction takes place. This chapter includes studies of the reaction kinetics and stoichiometry and covers the effects of oxygen and NO. 

Finally, the effects of oxygen we observed cannot be fully explained. However, expecting the chemistry related to the charge separation to be affected by oxygen is reasonable because donor-acceptor complexes between aromatic hydrocarbons and 02 are known (20). The formation of HONO in the nitration ultimately leads to the 1V6 stoichiometry reported by other workers. As described by Eberson and Radner (7), HONO decomposes to water, NO, and N02. However, in our case, NO must be oxidized by oxygen or other oxidants present in the system back to N02. Alternatively, HONO could be oxidized its reaction with oxygen in solution very rapid (21). 

Very small deviations from oxygen stoichiometry can change drastically the superconducting properties of the thallium cuprates without destroying the structure. This is the case of the thallium cuprates for which a spectacular effect of oxygen... 

If the formation of products is derived from the unilateral diffusion of anion and cation, the effect of non-stoichiometry is related to the proportions of Do and Da- When Da > Do and non-stoichiometric phase is in defect of metal ion, the reaction rate is faster than that in stoichiometric phase. If Da < Do and reaction is throughout the transition in defect of oxygen, it may speed up access to the same effect. 

A.S. Nowick, K.C. Liang, Effect of non-stoichiometry on the protonic and oxygen-ionic conductivity of Sr2(ScNb)06 a complex perovskite. Solid State Ionics 129,201-207 (2000)... 

We have now found that replacing water in the melt by methanol leads to large increases in pyridine solubility of product from the treatment, even without tetralin addition. In this paper we characterize the effects of temperature, time, hydrogen pressure, reaction stoichiometry, and addition of various inorganic and organic additives. Because oxygen removal Present Address Chevron Research Co., Box 1627, Richmond, CA 94804. 

The Incentive to modify our existing continuous-flow microunit to incorporate the square pulse capability was provided by our work on perovskite-type oxides as oxidation-reduction catalysts. In earlier work, it had been inferred that oxygen vacancies in the perovskite structure played an important role in catalytic activity (3). Pursuing this idea with perovskites of the type Lai-xSrxFeg 51 10 503, our experiments were hampered by hysteresis effects which we assumed to be due to the response of the catalyst s oxygen stoichiometry to the reaction conditions. 

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