Surface Tension of Liquid Iron as Functions of Oxygen Activity and Temperature

Abstract

Surface tension of liquid iron is an important property for process simulations evaluating Marangoni flow in the melt. In this study, we succeeded to measure accurate surface tension of liquid iron under various oxygen activities and temperatures with overcoming experimental difficulties through the following attempts: (1) To prevent chemical contamination of sample, an oscillating droplet method using an electromagnetic levitator was employed. Surface oscillation frequencies were determined with taking into account sample rotation. (2) To control the oxygen activity of liquid iron, a gas-liquid equilibrium method using CO/CO2 containing gas mixtures was employed. This method enables precise control of oxygen activity with keeping carbon activity low, and therefore, oxygen activity dependence of surface tension was clarified without carbon effect. (3) To measure the surface tension for higher oxygen activities up to the Fe/FeO equilibrium, high-purity iron (99.9972 mass%) was used. Otherwise, minor reactive impurities in the melt such as aluminum are oxidized, which affects the surface tension measurement. Based on the experimental data, the surface tension of liquid iron was expressed as functions of oxygen activity and temperature using the Szyszkowski model. In addition, thermodynamic properties on the oxygen adsorption reaction and structure of the adsorbed oxygen layer on the melt surface were also discussed.

Influence of Oxygen Partial Pressure on Surface Tension of Molten Type 304 and 316 Stainless Steels Measured by Oscillating Droplet Method Using Electromagnetic Levitation

“…16) Even when the of atmospheric gas is high, the temperature coefficient is changed from a positive value to a negative value at a high temperature because the temperature elevation induces oxygen desorption through an adsorption equilibrium mechanism. [8][9][10][11][12][13][14][15] In this case, the thermocapillary convection flows from low temperature and high temperature regions to the temperature region, Tx, at which the surface tension shows maximum value as shown in Fig. 1(c).…”

“…Consequently it turns to a positive value as long as the molten metal is not oxidized under a comparatively high . [8][9][10][11][12][13][14][15] In this case, the thermocapillary convection flows radially inward in a weld pool. 16) Even when the of atmospheric gas is high, the temperature coefficient is changed from a positive value to a negative value at a high temperature because the temperature elevation induces oxygen desorption through an adsorption equilibrium mechanism.…”

“…Since oxygen can also exist in an atmosphere as a gas phase, the surface tension of molten stainless steel is expected to be affected by the oxygen partial pressure, , of atmospheric gas as in the case of other molten metals such as iron and nickel. [8][9][10][11][12][13][14][15] However little attention has been given to the influence of on the surface tension of molten stainless steel.…”

Surface Tension Measurements of 430 Stainless Steel

“…Among these, the electromagnetic levitation is the only method that can be applied under different oxygen partial pressures by controlling the gas mixture. [7][8][9][10] Since the levitation method prevents heterogeneous nucleation, it can be also used to investigate the surface tension of the undercooled liquid. 11) In the present study, the surface tension of SUS430 was investigated by means of the electromagnetic levitation (EML) method 12) in oder to prevent any possible contamination from a refractory ceramic material.…”

Dynamic Surface Tension Behavior of Liquid Iron during Carburization and Decarburization Processes

“…9,10) The equilibrium constant of the oxygen adsorption reaction at the liquid iron surface and surface excess of oxygen have been determined in previous studies. 9,10) In the present study, based on surface adsorption data, we propose a continuous technique for studying the carburization and decarburization processes by measuring the surface tension using the oscillating droplet method.…”