Effects of Gravity on ZBLAN Glass Crystallization

The effects of gravity on the crystallization of ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF glasses have been studied using the NASA KC-135 and a sounding rocket. Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.