Melting and evaporating sodium tellurite melts in low gravity drop shaft

Glasses of Na₂O · xTeO₂(x=2,4, and 6) compositions were remelted and evaporated while supported by a platinum heater coil in the low gravity (approx. 10^-5 g) drop shaft at the Japan Microgravity Center (JAMIC). The evaporating species from all the melts, which formed a spherical cloud surrounding the melt during the few seconds low gravity time were identified to be amorphous particles of TeO₂. These particles were highly spherical, 5 to 10μm in diameter, and were, on the average, 6 to 8 times larger than the particles grown from similar experiments at 1-g. The melt remaining after evaporation was splattered on to a glass plate positioned at about 3.5 cm directly below the melt during the high-g (approx. 8 to 10 g) deceleration of the drop capsule and crystallized almost instantaneously. The chemical composition of the crystallized splatters was same as that of the starting glass. The crystallization tendency of these sodium tellurite splatters was estimated to be at least 1000 times greater than that of an identical melt at 1-g. No suitable explanation was found for the high crystallization tendency of the drop shaft splatters, but a sudden 5 orders of magnitude increase in the gravity level is suspected to be a contributing factor for this effect.