Time Dependent Effects in Surface Tension Measurements of an Industrial Fe-alloy

The surface tension of an industrial FeC-alloy containing Si, Mn and S in the few atomic per cent range was measured by the oscillating drop method in ground based electromagnetic levitation and under reduced gravity conditions on board a parabolic flight. The results from the parabolic flight exhibited a large variation between different heating cycles and a discrepancy with the ground based experiments with regard to the value of the surface tension at the liquidus temperature and the temperature coefficient. The variation of the surface tension temperature coefficient is interpreted as resulting from the loss of volatile surface active components such as S and Si in subsequent heating cycles. The results demonstrate the importance of the time scale of the measurement and ambient atmosphere for surface tension measurements of industrial alloys containing volatile surface active components. For comparison with the experimental values the surface tension and segregation were modelled using different models. As a result of the analysis, the surface tension as a function of temperature best representing the starting industrial alloy is obtained as sigma(T) = 1.52-1.53 10(-4) (T-1752K) Nm(-1)