Noncontact Measurement of Surface Tension of Molten Material

An improved method of noncontact measurement of the surface tension of a molten material has been developed, partly to overcome the disadvantages of contact measurement techniques as described in the preceding article, "Noncontact Measurement of Resistivity of Molten Material" (NPO-20369). This method also overcomes the primary disadvantage of an older noncontact method in which a nonrotating levitated sample is set into vibration, the frequencies of vibrational resonances are measured, and the surface tension is determined from the known relationship among the surface tension, frequencies, and other relevant quantities. The validity of the older method is limited to viscosities less than about 1 poise. The present method works over the full range of viscosities encountered in the thermal processing of metals, glasses, and metallic glasses.