Temperature dependence of surface tension of molten iron under reducing gas atmosphere

Surface tension of molten iron was measured under Ar-He-5vol.%H₂ gas by oscillating droplet method using electromagnetic levitation furnace in consideration of the temperature dependence of oxygen partial pressure, Po ₂, of the gas. For comparison, the measurement was carried under Ar-He atmosphere to fix the Po₂ of the inlet gas at 10 ^-2Pa. The surface tension was successfully measured over a wide temperature range of about 780K including undercooling condition. When Po ₂ is fixed at 10^-2 Pa, the surface tension increased and then decreased with increasing temperature like a boomerang shape. When the measurement was carried out under the H₂-containing gas atmosphere, the temperature dependence of the surface tension shows unique kink at around 1810K instead of liner relationship due to competition between the temperature dependence of the Po₂ and that of the equilibrium constant of oxygen adsorption reaction. The relationship between the calculated lnK_ad with respect to inverse temperature using Szyszkowski model was different between the atmospheric gases.