A novel quartz dendritic growth chamber for low temperature microgravity experimentation

Abstract

The material science community has demonstrated keen interest in performing a range of thermodiffusional dendritic growth studies in microgravity. While each of these experiments differ in the thermal-physical properties of the test fluid, the initial dendrite seeding configuration, and the resultant dendrite morphology, they are similar as each must be conducted within a growth chamber. Clearly, the growth chamber is the single most crucial experimental component because the ambience delivered by the chamber intrinsically effects the resultant dendritic growth. A unique sample chamber, comprised nearly entirely of precision machined quartz components, was developed for use in the microgravity experiment Isothermal Dendritic Growth Experiment (IDGE), which was conducted in the cargo bay of the Space Shuttle Columbia, as part of the Fourth United States Microgravity Payload (USMP-4), in November 1997. The growth chamber discussed is conventional in the selection of the construction materials, but is unique and unconventional from the standpoint of the quartz fabrication and microgravity operation. First, the selection of a fused quartz material was design enabling because the test fluid, pivalic acid, an organic material which melts at 35.975 °C, could be maintained ultrapure over the three-year duration of the complete experiment (assembling, ground test, shuttle integration, flight). Second, the quartz chamber has demonstrated large-scale fabrication of complicated fused quartz pieces, into a final monolithic structure. Third, the quartz chamber was successfully interfaced with ancillary hardware and was not damaged or operationally compromised through ground testing, shuttle launch, microgravity experimentation and shuttle return. Fourth and finally, the chamber has demonstrated a novel means to control, in a microgravity environment, a vapor bubble, which was included in the chamber to provide a volume dedicated to the expansion of the sample fluid during heating. The bubble was controlled by applying a Couette flow device to generate a transient, controlled cavitation of the test fluid. Overall, the critical technologies derived in the present study should lend themselves directly to the development of future microgravity dendritic growth experiments, thereby minimizing program risk and cost.