Abstract
Cerium-sulfur equilibrium was studiel by melting Fe-S, Fe-C-S, or Fe-Mn-S alloys in high frequency furnace with subsequent addition of cerium under deoxidized argon. The possible reaction between Ce and crucible material was prevented by lining and sintering of CeS powder (3 mm thickness) on alumina crucible in which the melts were contained. Care was also taken to keep total oxygen in the melt to be less than 10 ppm by adding 0.1% aluminum prior to the addition of Ce.
The results obtained are:
1) Precipitates identified as CeS by EPMA indicate that the equilibrium is expressed by CeS (S) =Ce+S.
2) Equilibrium constant, K=acϑ·aS (a: Henrian activity), and interaction coefficients involved are determined to be
log K=-20600/T+6.39
e (Ce) S=-13.6 (1823°K), -9.1 (1873°K), -7.5 (1923°K)
for T=1823-1923°K and [%Ce] +4.37 [%S] ≤0.16, and
e (C) Ce=-0.077,
e (Mn) Ce=0.13
at 1873°K.
3) Standard free energy of solution, ΔG0, for Ce (1) =Ce is derived as
ΔGO=-4900-16.0T
Disagreement among the data previously reported for the solubility product, K′ = [%Ce] [%S], is interpretable by taking the given dependence of K′ on [%Ce] and [%S] into account.
