High-temperature containerless viscosity measurement by gas-film levitation

The gas levitation process development program has, so far, been focused ma inly on contact-free manipulation, on molding and shaping of liquids, on hi gh-temperature contact-free treatment, and on shaping and solidification of interesting materials for scientific and technical purposes. Recently prop osed by Parayre for viscosity measurements, this process eliminates the per turbing effects of the container, in particular, that of crystallization wh en studying supercooled liquids. The method consists of extracting viscosit y values from the damped decay of perturbed liquid drops floating on a gas- film. An apparatus has been designed and developed for viscosity values hig her than 1 Pa . s and at temperatures up to 2000 degrees C. The method was applied to a silicate glass of industrial interest containing 70 wt % per c ent of SiO2, with viscosities ranging from 10(2) to 10(6) Pa s. Experimenta l results are compared with the Vogel-Fulcher-Tamann law for viscosity pred ictions. This paper demonstrates the industrial and scientific interest of this new method for viscosity determinations, which can be used for the wor king and softening points of any glass. These results may lead to a better understanding of network-forming or network-modifying behavior in oxide gla sses.