THERMODYNAMICS OF OXIDES

Theimodynamically, the driving force for the oxidation of a metal in gaseous environments is the Gibbs free energy offormation (AG) and consequently, the occurrence of an oxidation chemical reaction depends on the magnitude of AG. Mathematically, AG at a constant pressure is defined by 

AS° (To) = Standard entropy change kJ/mol. K) at To = 298 /f Cp = Heat capacity kJfmol. K) at constant pressure 

Notice that MxOy is the common composition of an oxide scale. Pq, Pcoi boj) Phu and Ph o are partial pressures. However, if AG 0, then it is a measure of negative deviation from equilibrium and the reaction proceeds from 

Combining eqs. (e) through (g) yields the oxygen pressure profile in the Ni NiCh interface 

Applying eqs. (10.5a ) and (10.5b) to reactions (a) through (b) yields the equilibrium constants and activities 

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If results are required at very high temperatures, as in experiments related to steel making, even short-term survival makes severe demands on the construction of the cell (Komarek and Ipser 1984). However, oxygen concentration cells have been employed with molten ionic slags to determine the thermodynamics of oxide formation in iron between 1500-1600°C (Kay 1979). Other applications include the use of YSZ for studies of semiconducting systems (Sears and Anderson 1989, Lee et al. 1992). 

Earlier work in the literature on the defect thermodynamics of oxides containing CS planes is based on conventional TEM studies of CS planes on static oxide systems. However, much of the earlier work contains the implicit assumption that all point defects due to the oxide anion loss are eliminated to produce CS planes. Several workers have made important contributions to understanding defect thermodynamics in oxides containing a finite number of... 

Thus it is important to take into accoimt the thermodynamics of oxide formation and any additional electrochemical... 

Excellent reviews on the thermodynamics of alloy oxidation have been given by Whittle [20] and Douglass [21]. In this chapter, we will refer mainly to the analyses proposed by Wang etal. [13] in discussing the thermodynamics of oxidation for binary alloys. 

Thermodynamics of oxide nucleation at the alloy surface and in the alloy substrate... 

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