Activity of oxygen in liquid In-Sb alloys
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0
0.07
0.15
0.30
0.45
0.60
0.80
0.90
1
8.24
8.96
9.64
10.80
11.71
12.59
13.35
13.57
13.64
These results differ significantly from those predicted by Jacob and Alcock's equation and by Wagner's equation combined with Chang et al's correlation of the energy parameter, h. However, by modifying Chang et al's definition of (Vb/Va), the Wagner's equation has been found to be capable of approximately describing the compositional dependence of the activity coefficient of oxygen in liquid In-Sb alloys.
DUE to the technological importance of the thermodynamic behavior of oxygen in liquid alloys, a relatively large number of investigators have measured the activity coefficients of oxygen over the entire composition range of various binary liquid alloys. Also, several attempts have been made to derive suitable solution models to describe the thermodynamic properties of oxygen dissolved in liquid alloys) -7 In predicting the variation of the activity coefficients of oxygen with alloy composition, Chang et al 6,8 have recently reported that the value of (Vb//Va) 2 plays an important part as well as (AG~ - AG~ where V a, V b, AG~ ) and AG~ denote the metallic valences and the standard Gibbs energies of solution of oxygen for solvent A and B, respectively. All the published data on the oxygen activity over the entire composition range of the solvent had been limited to the systems satisfying the conditions of (Vb/Va) 2 ~ 1 or -- 1", and AG~ ~ 5G~ In order * This covers the whole interval which is less than one, equal to, or slightly more than one.
to provide fundamental insights into the role of the ratio of the solvent metallic valences, experimental data are needed for systems satisfying the conditions of (Vb/Va) 2 >> 1 and AG~ ~ AG~ In the present investigation, a superior modified coulometric titration described in previous paper ~H has been carried out in order to determine the activity coefficients of oxygen in liquid In-Sb alloys. This system is one of typical systems satisfying the above conditions, ((Vb/Va) 2 >> 1 and AG~ ~ AG~ The significance of the values of the ratio of the solvent metallic valences has been discussed on the basis of the present experimental results. SHINYA OTSUKA is Research Associate and ZENSAKU KOZUKA is Professor, Department of Metallurgical Engineering, Faculty of Engineering, Osaka University, Osaka, Japan. Manuscript submitted May 23, 1980. METALLURGICAL TRANSACTIONS B
E X P E R I M E N T A L PRINCIPLE The electrochemical cell of cylinder type used in the present experiments is shown in Fig. 1 and described schematically by Q in liquid A-B alloys/ZrO2(+ CaO)/Air, Pt, (Cell I) P'02
P "02 = 0.21 atm
where P'o2 and P"o2 are the oxygen partial pressures at the liquid alloy-electrolyte interface and in the reference gas, respectively. The initial open-circuit emf, E~ (r) of the cell (I) is related to the initial oxygen concentration in the liquid alloy, C~ by Eq. [1]~2: RT P"o2 R El(r ) = ~ f f l n p--~- = 2 4 1 n 02
ao
~/0.21 [l] ~ • 100 2F 3'oC1 where R is the gas constant
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