Progress Report: Alloy C-103 Behavior in High Vacuum

1. Progress Report: Alloy C-103 Behavior in High Vacuum N. Jacobson, J. Horwath, D. Humphrey NASA Glenn Research Center

2. Alloy C-103 No oxygen P(O2) = 1 x 10-6 bar Behavior very sensitive to trace amounts of oxygen. Thermochemical modeling T = 1450C: ----------------------------------------------------------------------------------------------

3. Oxygen Active Metals at 1450C • Calculate minimum P(O2) to form oxide • Zr, Hf • Zr + O2(g) = ZrO2(s) P(O2) = 2.8 x 10-24 bar • Hf+ O2(g) = HfO2(s) P(O2) = 3.8 x 10-25 bar • Nb • Nb + 3/2 O2(g) = Nb2O5(s) P(O2) = 7.3 x 10-15 bar

4. Task to Support FIELDS Project • Evaluate behavior of candidate alloys in high vacuum with thermogravimetric analysis • Use heat schedule provided by SSL/UCB • All vacuum has some amount of oxygen • Control this with a getter • Characterize microstructure of post-exposure samples • Characterize optical properties of post-exposure samples (S. Miller)

6. Hot Zone and Placement of Getter 1. No getter—just W heat shields and W element. 2. Zr foil on top of bottom elements. 3. Zr foil on thermocouple, adjacent to sample.

7. Samples of C-103 Run

8. Results • 100 h runs according to UCB SSL Heat Schedule • Post-exposure characterization • X-ray diffraction (XRD) (in progress) • FE-SEM Field Emission Scanning Electron Microscopy • Optical properties (in progress)

9. No Getter

10. C-103 080112 No GetterPost Exposure to UCB SSL Heat Schedule

11. Getter at Bottom

12. C-103 072312 Getter at BottomPost Exposure to UCB SSL Heat Schedule

13. Alloy C-103 072312 Getter at BottomPost Exposure to UCB SSL Heat Schedule

14. Getter Near Sample on Thermocouple

15. C-103 080812 Getter on ThermocouplePost Exposure to UCB SSL Heat Schedule

16. Conclusions to Date C-103 consistently gains a few percent of its weight under these conditions Very sensitive to oxygen content in vacuum Appropriate placement of getter minimizers this weight gain Mechanism of weight gain appears to be related to Hf in alloy Changes in optical properties to be measured

17. Higher Temperature and Outlier Run