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Thermodynamic Modeling of the Zn-‐S and Fe-‐Zn-‐S System Youngeun Kim, Supervisor: Prof. In-‐Ho Jung
Department of Mining and Materials Engineering, McGill University
Zn-‐S System Fe-‐Zn-‐S System
Introduc:on Objec0ve To complete the thermodynamic op:miza:on of the Zn-‐S binary system and the Fe-‐Zn-‐S ternary system Thermodynamic Op0miza0on • Obtaining opEmized equaEons of the Gibbs energies
of different phases that best represent the exisEng experimental data
• A computer soLware, FactSage, performs calculaEons based on the thermodynamic data
• The accuracy & internal consistency of all the equaEons are tested by comparing with data
Fe-‐Zn-‐S System : Welding • Zn is oLen used as a protecEve coaEng in order to prevent Fe or steel
from rusEng • Due to its relaEvely low melEng point, Zn melts into the grain
boundary of Fe during the welding process • S forms a very stable compound with Zn, hence being a potenEal flux
to remove Zn from Fe
Fe Zn Fe Zn Zn
Liquid Solu0on: Modified Quasichemical Model
• Atom A and B form (A-‐A), (B-‐B) and (A-‐B) pairs and the interacEon
between the atoms determines the equilibrium condiEon • Accounts for short-‐range ordering and clustering, therefore
overcomes the limitaEon of Regular Solu<on Model which only approximates random mixing in a single sublaTce, requiring a large number of parameters
Ternary Interpola0on: Toop Technique • Chosen for Fe-‐Zn-‐S soluEon modeling due to the the similar negaEve interacEon forces exisEng in S – Fe and Zn – S binary systems and almost 0 interacEon in Fe – Zn system.
Results
Discussion • There is insufficient thermodynamic data available for the Zn-‐
rich region in Zn-‐S binary system • The soluEon of Zn-‐rich region of the Zn-‐S system was
assumed to behave similarily to that of the S-‐rich region • Though there is no experimental data on compounds other
than ZnS available for the binary system, the data of the Fe-‐Zn-‐S system (ZnS-‐rich solid soluEon) indicates the existence of no more intermetallic compounds in the Zn-‐S system
Methodology
References Pelton, A. D., Degterov, S. A., Eriksson, G., Robelin, C. and Dessureault, Y., Metall. Mater. Trans. B 31B, 651-‐659 (2000).
Applica:on
S
SFe
Fe
Fe
SZn
Fundamental Equa0on: Gibbs Energy
GT = HT !TST
Solid Stoichiometric Compound: ZnS (α-‐ZnS=Sphalerite, β-‐ZnS = Wurtzite)
G°T = H°T !TS°T
H°T = !H298o + CpdT
298
T
"
gsol = (xZng°Zn+ xSg°S )!T"Sconfig + (xZnS / 2)"gZnS
,S°T = S298o +
CpTdT
298
T
!
Solid Solu0on: ZnS-‐rich Solu0on
gsol = (xZnSg°ZnS + xFeSg°FeS )+ RT (xZnS ln xZnS + xFeS ln xFeS )+ gex
where gex =!ZnSFeSxZnSxFeS!ZnSFeS = 0 à Ideal Solution Model
!gZnS = !g°ZnS + gZnSi0 (xZnZn )
i +i"1# gZnS
0 j (xSS )j
j"1#where
Where A= Zn, B=S B B A A B A ( ) + ( ) = 2( ) 0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.10.20.30.40.50.60.70.80.9
0.10.2
0.30.4
0.50.6
0.70.8
0.9
S
Fe Znmole fraction
Fe s.s. boundaryFeS s.s. boundaryBeta-ZnS (Sphalerite) s.s. boundary
Phase Boundaries at 1100K (Itoh 1999)
Zn(l) boundary
Zn - Fe - S1100 K, 1 atm
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.10.20.30.40.50.60.70.80.9
0.10.2
0.30.4
0.50.6
0.70.8
0.9
S
Fe Znmole fraction
Fe s.s. boundaryFeS s.s. boundarySphalerite s.s. boundary
Zn(l)
Phase Boundaries at 1200K (Itoh 1999)
Wurtzite s.s. boundary
Zn - S - Fe1200 K, 1 atm
Rubenstein 1977
Sysoev et al 1967
1718 ± 10 °C1830 ± 20 °C
Addamiano & Dell 1957
Liquid + Liquid#2
Liquid
Liquid + ZnS(s2)Liquid + Liquid#2
Liquid + ZnS(s2)
ZnS(s2) + ZnS2(s)
ZnS(s) + ZnS2(s)Liquid + ZnS2(s)
Liquid + ZnS2(s)ZnS2(s) + S(s2)
Zn(s) + ZnS(s)
Liquid + ZnS(s)
Liquid + ZnS(s2)
Liquid + ZnS(s2)
Optimized Zn-S Phase Diagram1 atm
S/(Zn+S) (mol/mol)
T(°C
)
0 0.2 0.4 0.6 0.8 10
500
1000
1500
2000
2500
wz + po + ironsp + po + ironsp + po + L2
sp + po + iron + wusp + po + pysp + po + py + mag
wz + po + melt
Sphalerite + Pyrite
Liquid Sulfur + Sphalerite Scott & Kissin 1973 boundary
Sphalertie + Pyrrhotite Scott & Barnes 1971
Lusk & Calder (2004)Chernyshev & Anfilogov (1968)Boorman 1967
sp+py+L2
Liquid S+Wurtzite
Sphalerite+Pyrrhotite+ BCC Fe
Sphalerite+Pyrrhotite+Fe(s)
Optimized ZnS - FeS - SS/(ZnS+FeS) (mol/mol) = 0.00001, 1 atm
FeS/(ZnS+FeS) (% mol)
T(°
C)
0 10 20 30 40 50 60 70 80 90 1000
200
400
600
800
1000
1200
1400
1600
1800
Liquid
Liquid + Liquid#2
Liquid + ZnS(s2)
Liquid + ZnS(s)
Zn(s) + ZnS(s)
Optimized Zn-S Phase Diagram (Zn-rich region)1 atm
8/13/2012C:\Documents and Settings\Youngeun Kim\Desktop\Joey\Figures\SURE poster2.emf
S/(Zn+S) (mol/mol)
T(°
C)
0 0.01 0.02 0.03 0.04 0.050
500
1000
1500
2000
2500
