Kinetics of Nitrogen Desorption from Liquid Iron with Low Nitrogen Content under Reduced Pressures

Abstract

The kinetics of nitrogen desorption from liquid iron with less than 50 ppm nitrogen content under reduced pressure has been studied between 1520°C and 1 700°C.
The nitrogen desorption rate was described by 2nd order reaction with respect to [%N] under these conditions. The apparent activation energy for desorption rate was 35.4 kcal/mol.
The overall nitrogen desorption rate constant, k_ov, decreases with the increase in total pressure, [O] and [S] contents. The degree of harmful influence of oxygen in iron melt on k_ovwas about 2.5 times that of sulfur. But, k_ov in low oxygen and/or low sulfur concentration range was greater than those of previously published studies. The rate determining step of desorption in this concentration range tends to be mass transfer in diffusion layer at gas and/or metal.
Assuming the mixed control model, the chemical reaction rate constant, k_r, is estimated as follows,
k_r= 15.0{1/(1 +161[%O]+ 63.4[%S])} ² [cm/s·%]
The adsorption coefficients of oxygen, χ_O, and sulfur, χ_S, at 1600°C are given as follows,
χ_O=161, χ_S= 63.4