Interfacial Resistance to Nitrogen Desorption from Molten Iron.pdf

Interfacial Resistance to Nitrogen Desorption from Molten Iron* By Masamitsu TAKAHASHI,* * Ye-Tao HAN,* * * Masamichi Kaxum i MORI * * * * and Masahiro HIRASA WA* * * * SANO,**** Synopsis 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 o f A1203 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 11001Vcm3/min, respectively. The immersion depth of the nozzle was 3.3 -4.5 cm. 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 experi- mental 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 A1203 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 A1203 crucible although the free surface looks clean. In the deoxidation with Al, the A1203 layer on the surface greatly retards the rate of desorption. Key words: steelmaking; nitrogen desorption; interfacial resistance; A1203 crucible; oxide film. I. Introduction It is well-known that the existence of a very small amount of impurities (insoluble surface active ele- ments) in aqueous solutions at room temperature drastically reduces the rate of mass transfer through gas-liquid and liquid-liquid interfaces. Such a re- sistance to mass transfer is called the interfacial resist- ance. In metallurgical reactions at elevated tempera- tures, for example Fe-N2 reaction, it is found that the rate of