プラズマ溶解における窒素の挙動

抄録

Nitrogen absorption in plasma jet melting of iron was studied by using A-N₂ and A-H₂-N₂ mixtures. The electric power supplied was 20kVA (DC), the total pressure inside a melting furnace was 30 Torr, and nitrogen partial pressure was less than 5×10^-2 Torr. Under these conditions nitrogen gas was almost completely dissociated in plasma jet. Little bublles were visually observed.
The obtained results were summarized as follows.
(1) Nitrogen solubility of liquid iron (nitrogen concentration in a steady state) is found to be approximately 100 times as great as the one expected from thermodynamical equilibrium at 2000°C. The solubility increases in proportion to the square root of nitrogen partial pressures. Sulfur increases the solubility.
(2) It may be concluded from these results that the solubility is determined by the rates of absorption and desorption reactions occurring on the melt surface; that is, N+??=N (ad) =N+?? at the are spot and 2N+2??=2N (ad) =N₂+2?? on the rest surface, where ?? is the vacant site on the surface and N (ad) the adsorbed nitrogen.
(3) Hydrogen in the mixture decreases the solubility of nitrogen. This effect of hydrogen can be explained by that in a boundary layer adjacent to the melt surface, nitrogen atom is converted to hydrogennitride such as NH, NH₂ or NH₃.