The activity coefficient of nitrogen in binary liquid metal alloys
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I. C O M P A R I S O N O F T H E O R Y W I T H E X P E R I M E N T A L DATA I.I T h e Theoretical Equations T h e theoretical equation derived by W a g n e r for the activity coefficient of a solute X in binary liquid m e t a l alloys is: In
= 1/2 in
-In
0
{ i = z z F lx ] Z ~-i[x']i i~0 ( i ) L ~ I / 2 z J ~l/zZ
where "Y~(A) and 7~ (B) are the activity coefficients of X in pure A and in pure B respectively, Z is the coordination number, I, is 7°X(A~/~°g(B~ , R is the gas constant and T is the absolute temperature. Eq. [1] is the same as Eq. [25] of Ref. 1. The corresponding equations for the first-order and secondo r d e r Gibbs energy interaction parameters are:
and ~/Z [-Z- 1 pB(A) = [EB(A)]2_ Z ( Z - 1 ) { 1 - 2 ~ exp L-~-~--- hi
The + sign in the exponent of I, r e f e r s to E~, pB and the - sign r e f e r s to eAX, pA. Eqs. [21 and [3] are Eqs. [10] and [11] of Ref. 2. Since the Wagner equation is adequate in describing the compositional v a r i a tion of In ~ with alloy composition as t o be shown later, the corresponding two-parameter equations for o ~X A ( B ) and PX A ( B ) are not g i v e n h e r e . They a r e In YX, Eqs. [7], [8] and [9] of Ref. 2. VOLUME 8B, JUNE 1977-293
1.2
Thermodynamic Properties of B i n a r y Metal-Nitrogen Liquid Solutions
1.2.1 F e - N . A large number of investigators 3-49 has m e a s u r e d the thermodynamic properties of nit r o g e n in liquid i r o n . Since the number of m e a s u r e ments i s s o l a r g e , for the sake of c l a r i t y the l i t e r a ture v a l u e s e x p r e s s e d in t e r m s of AG°N(Fe) are s u m m a r i z e d in T a b l e I instead of presented graphically. ,0 The t e r m AGN(Fe) i s the relative partial m o l a r Gibbs e n e r g y of nitrogen with respect to N2(g) as r e p r e s e n t e d by the following reaction, 1/2 N2(g) = N (1 at. pat). The suggested v a l u e s of AG~(Fe) b a s e d on the r e s u l t s of Pehlke and Elliott 22 are e x p r e s s e d in t e r m s of a linear function of temperature and are g i v e n in T a b l e III. The uncertainty of t h e s e v a l u e s is estimated to be ± 500 J/gatom. As shown in T a b l e I, the A G ° - ~ . v a l u e s determined by m o s t of the investigators at 1873 K a g r e e well with the s e l e c t e d v a l u e of 27,260 + 500 J/gatom. For the temperature dependence of AG~(Fe ) , the r e s u l t s of Humbert and Elliott, iv Gomersall, McLean and Ward, 36 Turnock and E l l i o t t ,3~
Fedorchenko, 37 and Surovoi, Okorokov and Nefebova 4° are a l s o in good agreement with the suggested v a l u e . 1.2.2 N i - N . The suggested v a l u e s of LxG~t Ni}. g i v e n in T-T---able-m- ~ e b a s e d on the data of Wada e t ar7 at high temperatures and t h o s e of Humbert and Elliott, 17 B l o s s e y and Pehlke, 5° Lange and Schenck, sl Stomakhin, B a y e r and Polyakov52 and Krivosheya53 at t e m p e r a t u r e s near 1873 K a s shown in Fig. 1. The data of Kojima et a l , 43 and Schenck et a l 2~ at 1873 K are l o w e r than the s u g g e s t e d v a l u e . The v a l u e s of 0
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