Thermodynamics of sulfur in the BaO-MnO-SiO 2 flux system
- PDF / 460,094 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 152 Views
I.
INTRODUCTION
where
T H E BaO-bearing fluxes are expected to be very effective for refining hot metals and steels since BaO is more basic than CaO. Therefore, thermodynamic properties of various BaO-bearing fluxes have been investigated. Recently, the BaO-MnO system has been developed for refining high manganese alloysv] and is reported to have extremely high refining ability.[ :] One purpose of this investigation, considering its application to the practical refining process, is to evaluate the effect of SiOz on the desulfurization ability of the BaO-MnO system. Another purpose is related to "oxide metallurgy," which is an attempt to make use of inclusions in steel. Namely, MnS precipitating on small oxide particles during solidification of steels acts as a nucleus of y-c~ transformation, and a higher MnS precipitation ratio, which is defined as (the number of oxide inclusions on which sulfide precipitates)/(the total number of oxide inclusions), was observed in the composition range of the MnO-SiO2 system whose liquidus temperature is low and whose sulfide capacity is high. [3J Therefore, by addition of BaO to the MnO-SiO2 system, the MnS precipitation ratio is expected to increase. For these reasons, the effect of BaO addition on the sulfide capacity of the MnO-SiO2 system has been investigated.
II.
EXPERIMENTAL
Sulfur dissolution from gas into a slag can be expressed by Eq. [1]. 1
1
$2 (g) + 0 2- (slag) = S2- (slag) + ~ 02 (g)
[1]
On the basis of Eq. [1], the sulfide capacity was defined by Fincham and Richardson. [41 Cs2 = (mass pct 52-) ~ P O ~ / 2
Ps'2'2
_
K I 9
ao 2-
[2]
A2-
TATSUO KOBAYASHI, formerly Graduate Student, Department of Metallurgy, The University of Tokyo, is with Sumitomo Metals, Wakayama 640, Japan. KAZUKI MORITA, Associate Professor, and NOBUO SANO, Professor, are with the Depamnent of Metallurgy, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. Manuscript submitted May 9, 1995. 652--VOLUME 27B, AUGUST 1996
(mass pct S-'-) ao2fs 2Pi K~
= = = = =
mass pct S in slag; activity of oxide ion in slag; activity coefficient of sulfide ion in slag; partial pressure of i; and equilibrium constant for Eq. [i].
In calculating sulfide capacities in the present work, the partial pressure of sulfur was calculated from the sulfur content of silver equilibrated with the slag by using Eq. [3]. 1
$2 (g) = S (mass pct Ag) A G ~ = -54,800 + 4.26T (J/mol)[5]
[3] [4]
By analogy to sulfide capacity, the carbonate capacity was defined on the basis of Eq. [5] by Wagner.t61 CO2 (g) + 02- (slag) = CO32- (slag) CCO32-
~-
(mass pct CO32-) = K 5 ~ ao2Pco2 fco32-
[5] [6]
where fco~-is the activity coefficient of carbonate ion in a slag. The experimental techniques and apparatus in the present investigation are almost identical to those described previously by Rachev et al. t7] Three grams of flux and five grams of silver were equilibrated in a nickel crucible in a flow of CO, CO2, and Ar mixture at 1573 K. The partial pressure of oxygen was controlled by a Pco/Pco~ ratio of the gas mixtur
Data Loading...
