Interfacial resistance to nitrogen desorption from molten iron.

Abstract

A study on the rate of nitrogen desorption from molten iron by Ar injection together with blowing onto the melt has been made by the use of Al2O3 and MgO crucibles, and with deoxidations by Al and C addition. The flow rates of gas injected into and blown onto the melt were about 80 and 11001Ncm3/min, respectively. The immersion depth of the nozzle was 3.3-4.5cm. During the experiment, the bubble formation time was measured by means of a pressure pulse technique.The rate data are compared with those calculated on the basis of a mixed control model. By comparison o f the calculated results with the experimental ones, the interfacial resistance to nitrogen desorption is quantitatively estimated. The interfacial resistance exists on the free surface while not on the bubble-metal interface. Under the same deoxidation condition, the rate of nitrogen desorption determined by the use of Al2O3 crucible is lower than that obtained by the use of MgO crucible. This comes from the fact that the interfacial resistance exists on the free surface of the melt contained in an Al2O3 crucible although the free surface looks clean. In the deoxidation with Al, the Al2O3 layer on the surface greatly retards the rate of desorption.