Phase and homogenization of lead borate glasses under low, normal or high gravity

The drop shaft experiments were conducted at Japan Microgravity Center, whose experimental facility allowed us to study the phase separation of glass for a few seconds either under low or high gravity. In these few seconds, it also allowed us to record the actual temperatures of samples during the melting and solidification of glasses; these temperatures are needed for the discussion of phase diagram. The glass with the composition of 3.5PbO·96.5B₂O₃ (mol%) was melted and solidified to explore the phase separation of glass under low, normal or high gravity through drop shaft experiments. The homogenization of elements in different samples (one sample melted under low gravity and solidified under high gravity, another melted under low and high gravity and solidified under normal gravity, and a third melted and solidified both under normal gravity) was compared through EDS analysis and the phase of each sample was determined through XRD. Results show that the samples all phase-separated into two different glass phases: Pb-rich phase and B-rich phase no matter under what gravity condition the particular glass was melted and solidified. For all the samples, the elements along the horizontal direction are homogenous while those along the gravity direction are heterogeneous, and the homogeneity of the sample whose phase separation occurred under high gravity is the worst.