Temperature equilibrium oxygen pressure, composition

After a series of experiments has been performed as a function of temperature, we can obtain the relation between the composition, equilibrium oxygen pressure, and temperature as shown in Fig. 1.2 (the curves for different temperature never cross on the F,-composition plane). In this case, only phase (I) and (II) are assumed to be existent. Phase (I) is known as a... 

The behavior of dissociating oxides at high temperatures is briefly reviewed. At low pressures the composition of the oxide will correspond to an equilibrium oxygen pressure quite different from the ambient oxygen pressure. Evaporation rate studies on cuprous oxide in various atmospheres show that this oxide dissociates according to CuiO (solid) — 2Cu (gas) + iOi (gas). 

Vapor pressures and vapor compositions in equilibrium with a hypostoichiometric plutonium dioxide condensed phase have been calculated for the temperature range 1500 I H 4000 K. Thermodynamic functions for the condensed phase and for each of the gaseous species were combined with an oxygen-potential model, which we extended from the solid into the liquid region to obtain the partial pressures of O2, 0, Pu, PuO and Pu02 as functions of temperature and of condensed phase composition. The calculated oxygen pressures increase rapidly as stoichiometry is approached. At least part of this increase is a consequence of the exclusion of Pu +... 

The temperature dependences of the total pressures In equilibrium with the condensed-phase composition PuOj gQ, PuOl.96> and P11O1.994 are compared in Figure 4. The differences shown In Figure 4 are due to the differences In oxygen pressures for the different compositions. 

Figure 7.7 Equilibrium oxygen partial pressure for a nonstoichiometric oxide YBa2Cu3Ox (a) composition, x, versus temperature under an oxygen partial pressure of 1 bar (b) oxygen partial pressure versus temperature for a composition of YBa2Cu306.5 and (c) oxygen partial pressure versus composition, x, for a temperature of 600°C. [Adapted from data in P. Karen, J. Solid State Chem., 179, 3167-3183 (2006).]...

Under the condition of constant temperature, there is no freedom at equilibrium, which means that both the pressure (P02) and the compositions of the coexisting solid phases are definitely determined. This is the reason why the composition versus the oxygen pressure curves in the two phase region shows a straight line parallel to the abscissa as shown in Fig. 1.2. The result of Fig. 1.3 can be explained in a similar way. Thus, eqn (1.46) is very important in understanding the phase equilibrium. Table 1.1 summarizes the relationship between the composition, the pressure (Pof), and the temperature for the binary M-O and ternary O systems for the case of the... 

One object of this investigation was to determine the equilibrium composition of sodium superoxide-sodium peroxide mixtures with oxygen at various pressures and temperatures. A group of experiments was performed in which the temperature was varied from 450 to 550 0. and the oxygen pressure from 102 to 137 atm. Both cadmium oxide and titanium oxide catalysts were used. The product composition, expressed in oxygen content, for various exposures at these conditions, is tabulated in Table I. 

Logarithmic plots of the equilibrium total conductivity versus the partial pressure of oxygen for LaSr2Fe3.yOg+5 at 950°C are shown in Fig.l as an example. The low-pressure segments of the isotherms near the minima, where deviations of the oxygen content from the nominal stoichiometric composition are very small, i.e. 6 1, are important for the analysis of the oxide ion contribution. Such minima are typical in oxides when oxygen pressure variations at constant temperature result in nearly equal concentrations of electron- and hole-like carriers. There may be another, pressure independent contribution in the conductivity and its presence is signaled by a smooth shape of the minima. Therefore the experimental results near the conductivity minima were approximated with the known relation... 

---