| |
Behavoiur of manganese in iron-carbon melt:
- Mn is soluble in iron in any proportion
- Mn forms ideal solutions in iron
- Carbon lowers the activity of Mn in Fe-Mn-C system by forming
 .
Oxidation of Manganese:
Mn is oxidized readily at relatively low temperatures and can form oxides like  ,  ,  etc. But MnO is stable at high temperature.
 |
(1) |
 |
(2) |
The reaction 1 occurs with dissolved oxygen in metal, whereas reaction 2 is a slag/metal reaction. Both reactions are exothermic. Lower temperature favours oxidation of Mn from metal to slag; whereas higher temperature favours reduction of MnO of slag and there occurs reversal of Mn into steel. Reduction of MnO in slag is important; we consider reaction 2
 |
(3) |
Replacing activity by mole fraction and using  , we get,
 |
(4) |
Grouping all activity coefficient terms and putting 
We get,
 |
(5) |
Where  is an equilibrium quotient and it depends on composition of slag. Distribution of Mn between slag and metal can be written as
 |
(6) |
 |
(7) |
According to equation 7 increases with decrease in temperature(  and 20.33 at temperatures 1923K, 1873K and 1773K respectively)
Condition for oxidation of Mn according to equation 6
- High activity of
 in slag which means an oxidizing slag
- Decrease in temperature increases K* according to equation 7.
|
