Activity of sulfur in pyrrhotite at 1073 K
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Table I. Sulfur Activities in Pyrrhotite at 1073 K (The Standard State is S2(g)) Xs
PH~S/PH2
0.4995 0.4998 0.4999 0.5003 0.5007 0.5007 0.5011 0.5015 0.5015 0.5015 0.5022 0.5027 0.5029 0.5041 0.5045 0.5048 0.5059 0.5071 0.5071 0.5081 0.5092 0.5100 0.5107 0.5114 0.5124 0.5150
2.30 X 3.24 × 3.64 × 3.39 X 4.67 × 4.73 × 4.82 X 5.10 X 6.33 X 7.66 X 7.20 × 1.11 X 8.92 × 1.98 × 1.43 × 2.85 X 3.10 × 5.49 × 6.42 × 5.82 × 9.69 X 1.43 × 1.57 X 2.09 X 2.75 × 4.21 X
In as
10"3 10"a 10.3 10"a 10-3 10-3 10-3 10-3 10"3 10-3 10-3 10.2 10-3 10-2 10-2 10-2 10-2 10-2 10"~ 10"2 10-2 10"1 10"1 10"1 10"l 10"1
-10.29 -9.95 9.83 -9.90 -9.58 -9.57 -9.55 -9.49 -9.28 9.09 -9.15 8.72 -8.93 8.14 -8.46 -7.77 7.69 7.12 -6.96 -7.06 -6.55 -6.16 -6.07 -5.78 5.51 -5.08
and nonmetal activity equations. In their t h i r d paper on the activities of T e in FeTe (NiAs) it was found the assumption that vacancies o c c u r in every other m e t a l l a y e r was not correct. Instead they made the assumption that m e t a l vacancies o c c u r in every metal layer. The theoretical activity equations obtained are given below:
l n a F e = l n ( ~ ) - R8///( ×~ ) + C1 T
[1]
0.(3
-I.C
-2.C
,~ -3£
-4.C
-5.(3
-6.0
0.0
0.01
X
O02
0.05
F i g . 1 - - A c t i v i t y of s u l f u r i n p y r r h o t i t e as a function of c o m p o s i t i o n for t h e t e m p e r a t u r e i n t e r v a l , 943 t o 1373 K. VOLUME 8B, JUNE 1 9 7 7 - 3 4 5
RT
+ C2,
[2]
Eqs. [1] and [2] correspond to Eqs. [6] and [7] of Ref. 11 except for the different nomenclature used. The term C~ in Eq. [1] equals (-INK + H J R T ) of Eq. [6] of Ref. 11; C2 of Eq. [2] is the constant term of Eq. [1] of Ref. 11. Both C~ and C2 are functions of temperat u r e , T. The term InK represents all the nonconfigurational contributions t o the Gibbs energy and H[] is the enthalpy of formation of m e t a l vacancies. The other t e r m s in Eqs. [1] and [2] are defined below: aFe and as are the activities of the m e t a l and nonmetal component element, × = xs - 0.5 and Hi is the enthalpy of interaction between vacancies. It was found by Ipser and Komarek that the data for FeTe could be described by these equations. The detailed defect structure of pyrrhotite has not been studied. However, based on the findings of Popma and Bruggen n that m e t a l vacancies o c c u r in every m e t a l l a y e r in CrS (NiAs), it is reasonable to a s s u m e that the defect structure in pyrrhotite is s i m i lar. Accordingly, Eqs. [1] and [2] are used t o c o r r e late the experimental data of pyrrhotite. Since B u r g mann et al5 reported an extensive amount of experimental data as a function of sulfur composition and temperature, t h e i r data were used to obtain the values of Hi, C1 and C2. The value of Hi = 215.7 k J / g atom was obtained by plotting values of log [aS(exp) x (1 + 2×)/2×] vs those of y¢/(1 + 2×)2 for various temperatures between 973 and 1373 K and for X > 0.004. Knowing the v a l u e of H i and the values of aS(exp) and those of aFe obtained numerically from Gibbs-Duhem integration
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