As depicted in Fig. 9.6, the thermocouple reading spikes to a much higher temperature than the controller reading does. Similar to findings with the pre-heat furnace characterization, the thermocouple read a few degrees higher than the controller. The thermocouple read an initial high of 310 C within 90 s of recording while the controller peaked at 301 C and leveled off within 60 s. The thermocouple leveled off at a higher temperature of 308 C. The 8 difference was also noticed in previous characterization testing. 9.3 Experimental Program The majority of the experimentation was completed on board the Zero-G Corporation’s parabolic aircraft sponsored by the Air Force Space Test Program (STP) and the National Aeronautics and Space Administration (NASA). The Zero-G Corporation stipulates a pristine 0.00 0.05 g environment of approximately 22 s. The transition between the microgravity portion of the flight puts the aircraft in a hyper-g environment of approximately 1.2–1.8 g. The hyper-g environment was also used as an experimental variable for testing. The in-flight Quencher operation requires two operators, one to load the samples and operate the controllers and the second to quench and store the samples. The operation consisted of the following steps, depending upon the desired temperature set point. Once the ampoule is loaded into the end of the pushrod the pushrod is manually translated to the center of preheat furnace for the duration of either the μ-g or the hyper-g section of the flight. After the sample has been pre-heated the pushrod is relocated to the center of the annealing furnace for the duration of the gravity level under testing. Lastly, the pushrod is extended out the end of the annealing furnace and the glass ampoule is grasped with a damp sponge and removed from the pushrod. This final process simultaneously quenches the sample as the operator removes the ampoule from the pushrod. This entire process will take place during the μ-g/hyper-g sections of the parabolic flight. The test matrix for both flights was developed based on a temperature scheme that spanned just below the glass transition temperature (270 C) to well above the crystallization temperature (650 C). Both the microgravity and hyper-g portions of the parabolas were used as variables in the experiment. Lower set point temperatures (270–350 C) were studied in the hyper-g section to determine if crystallization can be initiated below the recorded (1-g) crystallization temperature of 360 C. The second set of tests (360–650 C) were established to determine if crystallization can be suppressed in a μ-g environment and to determine at what temperature will crystallization occur regardless of the μ-g environment. 9.4 Analysis Optical microscopy was used as the primary investigation technique as the transmitting light through the sample will illuminate any transmission inclusions (crystals). A single temperature was selected to represent each technique. The temperature focused on was 360 C, in μ-g and 1-g, as this is the reported crystallization temperature of the ZBLAN 275 280 285 290 295 300 305 310 315 320 325 0 100 200 300 400 500 600 700 Temperature (C) Time (sec) Annealing Furnace Ramp from 280C to 300C Controller Thermocouple Fig. 9.6 Annealing furnace ramp time from 280 to 300 C 9 Characterization of a Heating and Quenching Apparatus for Microgravity Testing 71
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