Abstract
A study was made on the rate of nitrogen desorption from molten iron by Ar gas injection together with blowing onto the melt surface. Two types of crucible (Al2O3, MgO) and two types of deoxidation method (Al addition, C addition) were used. The flow rate of injected gas was about 80 Ncm3/min and that of blown gas was 1 100 Ncm3/min. The immersion depth of the nozzle was 3.3 to 4.5 cm. During the experiment, the bubble formation time was measured by using a pressure pulse technique.
The kinetic data were compared with the calculations by a mixed control model of mass transfer of nitrogen and of interfacial chemical reaction. From the comparison between calculation and experiment, the interfacial resistance was quantitatively estimated. The interfacial resistance existed at the free surface while did not at the bubble-metal interface. Under the same deoxidation condition, the rate of nitrogen desorption with an Al2O3 crucible was lower than that with a MgO crucible. This comes from that the interfacial resistance exists at the free surface of the melt held in the Al2O3 crucible although the free surface appears clean. In the case of deoxidation with Al, Al2O3 layer behaves itself markedly as the interfacial resistance.
