Activities of oxygen in liquid lead and antimony from electrochemical measurements
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O in liquid Pb or Sb/ZrO2(+CaO)/Air,
Pt.
After measuring the equilibrium emf, the liquid metal was deoxidized by imposing a preselected voltage on the electrodes. The fairly low oxygen concentration in liquid metal could be easily determined by a modified analysis of the quantity of electrical charge passing through the cell. The standard free energies of solution of oxygen in liquid lead and liquid antominy for the reaction of 1/20z ~ O (I at. pet) were determined respectively to be: AG ~ (in Pb) = --28,300 + 3.38 T (• 300) e a l / g - a t o m = --118,600 + 14.1 T (• 1300) J / g - a t o m , AG ~ (in Sb) = - 3 2 , 8 8 0 + 5.20 T (• 350) c a I / g - a t o m = - 1 3 7 , 6 0 0 + 21.8 T (• 1500) J / g - a t o m , where the r e f e r e n c e state for d i s s o l v e d oxygen was an infiniteIy dilute s o l u t i o n . B Y u s i n g a c o u l o m e t r i c t i t r a t i o n method e m p l o y i n g a g a l v a n i c ceil, the oxygen c o n c e n t r a t i o n in s o m e liquid m e t a l s has been d e t e r m i n e d without c h e m i c a l a n a l y s i s . A l c o c k and Belford 1,2 and R i c k e r t and W a g n e r 3 used this method for the m e a s u r e m e n t s of the oxygen c o n c e n t r a tion in liquid lead, tin, and copper at c o m p a r a t i v e l y high oxygen c o n c e n t r a t i o n s . T h i s method can be i m p r o v e d in the r e g i o n of low oxygen c o n c e n t r a t i o n where the e l e c t r o n i c conduction in a solid e l e c t r o l y t e may not be n e g l e c t e d . Although Rapp et al 4-6 r e c e n t l y have avoided any e r r o r due to the e l e c t r o n i c conduction for the d e t e r m i n a t i o n of the oxygen diffusivity and s o l u b i l ity in liquid m e t a l s , t h e i r a n a l y s i s was t e s t e d or m o d i fied in this study. Although s e v e r a l i n v e s t i g a t o r s have m e a s u r e d the a c t i v i t y of oxygen in liquid lead, s e r i o u s d i f f e r e n c e s have b e e n o b s e r v e d in t h e i r r e s u l t s . 1,s-9 T h e r e is a l s o a s c a r c i t y of r e l i a b l e data for the a c t i v i t y of oxygen in liquid a n t i m o n y . R e l i a b l e data for t h e s e liquid m e t a l s a r e n e c e s s a r y to e n l a r g e our p r e s e n t knowledge of the t h e r m o d y n a m i c b e h a v i o r of oxygen d i s s o l v e d in liquid metals. In the p r e s e n t i n v e s t i g a t i o n , p o t e n t i o s t a t i c e x p e r i m e n t s a r e u n d e r t a k e n u s i n g the following c o n v e n t i o n a l e l e c t r o c h e m i c a l cell: O in liquid P b or S b / Z r O z ( + C a O ) / A i r , Pt, and a modified a n a l y t i c a l method is p r o p o s e d for the d e t e r m i n a t i o n of the v e r y low oxygen c o n c e n t r a t i o n in the liquid m e t a l .
RT P62 RT . 0(-6~.21 R T l n / ~ 0 . 2 1 E l ( r ) = ~-~ In p~---~ = ~ - In a o - 2~ ~C~
[1]
where R is the g a s c o n s t a n t , T(K) the e x p e r i m e n t a I t e m p e r a t u r e , F the F a r a d a y ' s c o n s t a n t , a_o the a c t i v i t y
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