Drop oscillation dynamics is a classical problem in hydrodynamics. The oscillations of the drop surface can be related to the surface tension by the formula ,
where, ю is the frequency of oscillations, l is the mode of oscillation, p is the density of the sample, R is the radius of the sample and r is the surface tension between sample and surrounding atmosphere. However, we are interested only in mode 2 oscillations frequency which is obtained by simplifying Eq. (1). Mode 2 oscillations frequency is simply given by Rayleigh’s formula,
A pure zirconium sample was tested using an electrostatic levitator at NASA MSFC. The levitated sample was excited an additional electrostatic field alternating near the natural frequency of the sample. A function generator was used to regulate the excitation frequency. Once enough excitation was achieved, the function generator was turned off and the sample was allowed to damp freely. The high speed video was taken at a frame rate of 1000 fps. The image processing was performed to extract the change in the projected area of the sample during damping as a function of time. An exponential decay function was fitted through the area-time plot to determine the oscillation frequency of the sample.
The experiments were performed in vacuum conditions of 10-7 torr. The mass of the sample is 43.288 mg . Mass loss f the sample due to evaporation is as low as 0.043% and the change in mass during processing was neglected. The sample went through one melt cycle to determine the density. Further, the sample went through twenty-four oscillation cycles at six different temperature holds between 1974 and 1600 °C. The change in projected area of each sample was captured using a LED back light and a high speed camera and the captured videos were analyzed to extract the oscillation frequency and thus surface tension.