1964 Volume 50 Issue 8 Pages 1161-1167
In an experiment related with the measurements of oxidation velocity of molten iron alloys by atmosphere, we studied the change in the rate of concentration of alloying elements by evaporation.The rate equations of evaporation of alloying elements were proposed by many investigators in various forms.Here, we measured the change of Mn concentration by evaporation in molten Fe-Mn alloys, and derived rate equations on the basis of 2-film theory. Results obtained here are as follows:
1) Under external pressures below 0.1 mmHg, the rate of concentration change is expressed by Eq.(10)_??_which is derived from the rate of evaporation in vacuum.As the external pressure increases, Eq.(10)_??_becomes meaningless because f k approaches to 0.
2) Under external pressures above 0.1 or 1 mmHg, Eq.(12a) derived from 2-film theory, _??_seems to be more suitable as the rate equation.At atmospheric pressure, assuming KG=Dm/σG approximately, σG, thickness of gas-side diffusion layer, was found to be 0'2 to 03 cm.Eq.(12 a) may be true independently of the external pressure and evaporative materials, and it can be transformed to a rate equation in vacuum by suitable approximations.
3) The rate is also expressed by Eq.(12 b)_?_ which has the same form as the rate equation of degassing from molten iron.
As the external pressure decreases, KL approaches to DL.σ/L.