Melting and phase-separation of lead borate glasses in low gravity drop shaft

A drop shaft experiment was conducted to melt and solidify a glass of 3.5PbO-96.5B₂O₃ (mol%) composition adhered to a small platinum heating coil (2-3 mm i.d., 5-6 mm long) at the Japan Microgravity Center (JAMIC). The temperature of glass melt recorded during the drop experiment indicates that the phase-separation of this glass mainly happened during the high gravity period of the experiment. A similar experiment was conducted on the ground to explore the effect of gravity level on the melting and phase-separation of lead borate glass. The homogeneity of different samples was compared through EDS analysis and the microstructure of the samples were observed by SEM. The lead borate glasses separated into two different glass phases, the separated phase (Pb-rich phase) and the continuous phase (B-rich phase), regardless of the gravity level the phase-separation happened. The size of separated Pb-rich phase in the top of sample from drop shaft experiment is much smaller than that in the bottom of sample, while the sizes of separated Pb-rich phase are almost the same in different locations in the ground sample. The homogeneity of the drop shaft sample is much worse than that of ground sample.