MEASUREMENTS OF SURFACE-TENSION ON LEVITATED OSCILLATING METALLIC DROPS

Metallic drops can be levitated and melted by inhomogeneous electromagnetic high-frequency fields. Also, oscillations about their equilibrium shape can be excited which can be detected by a suitably focused photodiode. The restoring force for these oscillations is the surface tension which therefore determines the frequencies of the oscillations. These can be obtained by Fourier transformation of the signal. In addition, the temperature was measured by a two-colour pyrometer. Using these data, the surface tension of nickel and nickel-iron alloys was determined at temperatures both above and below their melting points for a number of samples of different weight and concentration. We generally find slightly higher values than those reported in the literature and a decrease of surface tension with temperature.