High-temperature containerless viscosity measurement by gas-film levitation

The gas levitation process development program has, so far, been focused mainly on contact-free manipulation, on molding and shaping of liquids, on high-temperature contact-free treatment, and on shaping and solidification of interesting materials for scientific and technical purposes. Recently proposed by Parayre for viscosity measurements, this process eliminates the perturbing effects of the container, in particular, that of crystallization when studying supercooled liquids. The method consists of extracting viscosity values from the damped decay of perturbed liquid drops floating on a gas-film. An apparatus has been designed and developed for viscosity values higher 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 cent of SiO2, with viscosities ranging from 10(2) to 10(6) Pa s. Experimental results are compared with the Vogel-Fulcher-Tamann law for viscosity predictions. This paper demonstrates the industrial and scientific interest of this new method for viscosity determinations, which can be used for the working and softening points of any glass. These results may lead to a better understanding of network-forming or network-modifying behavior in oxide glasses.