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