Influence of oxygen partial pressure on surface tension and its temperature coefficient of molten iron

Abstract

Influences of oxygen partial pressure, PO2, of ambient atmosphere and temperature on surface tension and its temperature coefficient for molten iron were experimentally investigated by an oscillating droplet method using an electromagnetic levitation furnace. We successfully measured the surface tension of molten iron over a very wide temperature range of 780 K including undercooling condition in a well controlled PO2 atmosphere. When PO2 is fixed at 10−2 Pa at the inlet of the chamber, a “boomerang shape” temperature dependence of surface tension was experimentally observed; surface tension increased and then decreased with increasing temperature. The pure surface tension of molten iron was deduced from the negative temperature coefficient in the boomerang shape temperature dependence. When the surface tension was measured under the H2-containing gas atmosphere, surface tension did not show a linear relationship against temperature. The temperature dependence of the surface tension shows anomalous kink at around 1850 K due to competition between the temperature dependence of PO2 and that of the equilibrium constant of oxygen adsorption.

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).…”

“…[9][10][11][12] It is also theoretically indicated for molten Fe-Ni-Cr system with respect to contents of sulfur and oxygen as a potential impurity. 7,8) However, the boomerang shape temperature dependence of surface tension has not yet been experimentally observed for molten stainless steels because conventional techniques for surface tension measurements such as the sessile drop method can only assure the measurement at a comparatively low temperature in order to prevent a chemical reaction between the sample and the measurement device.…”

“…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.…”