Progress and Perspective of Processing Glass Forming Melts in Low Gravity

A review of the results from previous low-gravity experiments conducted on glass-forming melts is presented with particular emphasis on nucleation, crystallization, glass formation, and chemical homogeneity for high-temperature melts in low gravity. A review of this kind is important for 1) understanding the kinetics of glass formation (conversely, nucleation and crystallization) and the mechanism(s) of homogenization of high-temperature melts in low gravity, 2) avoiding duplication in future low-gravity experiments, and 3) properly utilizing low-gravity conditions for improving present-day glass processing techniques and, hence, the quality of glasses on Earth. It is consistently observed that glasses prepared in low gravity are more chemically homogeneous and more resistant to crystallization than those of the comparable glasses prepared on Earth, which is somewhat surprising. A hypothesis based on shear thinning of a melt is proposed as an explanation for these low-gravity results. A scheduled flight experiment, whose purpose is to acquire data on nucleation and crystal growth kinetics for Li 2 O.2SiO 2 glass prepared in low gravity, is discussed.