表面活性成分を含む溶鉄の窒素吸収速度に関する研究

抄録

The rates of absorption of nitrogen in liquid iron containing surface active elements, such as oxygen.and sulphur, were measured at 1550°C and 1600°C.
The transfer of nitrogen across the gas-metal interface was remarkably disturbed by those surface.active elements, adsorbed on the surface of the metal. It was also recognized that the rates of absorption in those melts were proportional to the partial pressure of nitrogen, when the metal contained more than nearly 0.03% sulphur or oxygen. Furthermore, it was observed that the rates of absorption were inversely proportional to 2/3 power of sulphur(or oxygen) concentration in the bulk Contains higher than 0.03%S (or 0.02%O). These concentrations correspond to the coverage of the surface by sulphur or oxygen nearly as Fe S or Fe, calculated by the Gibbs' adsorption equation. It becomes
(dc/dt)_t=0=K·P_N2/(wt%S or wt%O)^2/3
Consequently, it seems reasonable to regard that in those melts the transfer of nitrogen from gas into liquid iron may be chemically controlled, namely it is mainly controlled by the rate of nitrogen adsorption. It is now accepted that oxygen or sulphur behaves as a poison on the metal surface. Behaviour of surface active elements at gas-metal interface could be explained, assuming that they were concentrated to the interface as ions, S^2- or 0^2-. The rate of reaction was also discussed from the stand--point of the absolute rates theory
There is a linear relation between apparent mass transfer coefficient of nitrogen and surface tension of liquid iron containing surface active elements, practically no different between sulphur and oxygen.
The activation energy for absorption of nitrogen should decrease as the surface coverage adsorbed by oxygen decreases, and is approximately 20kcal/mol at about 0.001% oxygen. This value corresponds nearly to the order of the activation energy for diffusion of oxygen in liquid iron.