SYNTHESIS OF METAL HYDRIDES BY MECHANICAL ALLOYING IN AN ATTRITOR MILL: FY07 STATUS REPORT
The objective of this task was to demonstrate that metal hydrides could be produced by mechanical alloying in the quantities needed to support the tritium production facilities at the Savannah River Site. The objective for the FY07 portion of this task was to demonstrate the production of Zr-Fe getter materials by mechanical alloying and begin to optimize the milling parameters. Three starting compositions (ratios of elemental Zr and Fe powders) were selected and attritor milled under argon for times of 8 to 60 hours. Hexane and liquid nitrogen were used as process control agents. In general, milling times of at least 24 hours were required to form the desired Zr{sub 2}Fe and Zr{sub 3}Fe phases, although a considerable amount of unalloyed Zr and Fe remained. Milling in liquid nitrogen does not appear to provide any advantages over milling in hexane, particularly due to the formation of ZrN after longer milling times. Carbides of Zr formed during some of the milling experiments in hexane. Formation of carbides during milling appears to be much less of an issue than formation of nitrides, although some of the phases that were not able to be identified in the XRD results may also be carbides. Additional XRD experiments should be designed to improve signal to noise ratio (i.e., longer count times) and use a wider scan range to better identify phases that were not clear in the original data. Elemental Zr was present in the as-milled material but not detected after annealing for milling times of 48 and 60 hours. It may be that after intimate mixing of the powders in the attritor mill the annealing temperature was sufficient to allow for the formation of a Zr-Fe alloy. The phase diagram for the binary Zr-Fe system agrees with this proposition. If this is the case, then the annealing conditions should also be investigated and optimized to form as much of the Zr-Fe alloy as possible in the milled powder. Also, this finding would mean that milling times of more than 48 hours are not necessary. Further investigation of this conversion is necessary, and could provide an opportunity for reducing the amount of unreacted metal powder after milling. Elemental Fe remained in all of the powders after annealing for all of the milling times tested. This may indicate that the ratio of Zr to Fe needs to be increased in order to improve the yield of the desired Zr-Fe alloys. Particle size analysis data are presented to aid in the selection of filters for future hydrogen sorption testing. Based on the XRD results, four samples were suggested for further XRD analysis and hydrogen sorption testing: (1) Zr{sub 2}Fe, 24 hr milling, annealed; (2) Zr{sub 2}Fe, 24 hr milling in LN{sub 2}, annealed; (3) Zr{sub 3}Fe, 24 hr milling, annealed; and (4) Zr{sub 3}Fe, 48 hr milling, annealed. These four samples showed the largest volume (based on relative peak intensities) of the desired Zr{sub 2}Fe and Zr{sub 3}Fe alloys.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-96SR18500
- OSTI ID:
- 921679
- Report Number(s):
- WSRC-STI-2007-00596; TRN: US200806%%126
- Country of Publication:
- United States
- Language:
- English
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