Transcript Michael Woods REU poster (2)

Electrowinning DU from a KCl/LiCl Eutectic and Temperature-Dependent
Resistance Characterization
Michael Woods, Jorge Gonzalez, Amelia Estry, Anna Yannakopoulus, Amanda Chown, Dave Graf
Advisor: Stan Tozer
Department of Physics, Florida State University, Tallahassee, FL 32306
Completed at the National High Magnetic Field Laboratory, Tallahassee, FL 32310
Abstract
This project’s goal is to grow single crystals of depleted
uranium by means of electrorefining within a KCl/LiCl salt bath
at vacuum pressure. At vacuum, we used a molten KCl/LiCl
eutectic containing DU and applied a voltage across two
stainless steel electrodes. Uranium was electrowon and single
crystal x-ray diffraction performed. Temperature dependence of
the resistance was also measured, and from this CDW
transitions identified.
We used a quartz tube with inserts on top for electrodes and a K-type thermocouple.
On the bottom there was a path for the vacuum pump and argon. A stainless steel
crucible was used to house the salts, stainless steel electrodes and thermocouple. Our
eutectic was 44.3 mol% KCl – 55.7 mol% LiCl with a melting point of approximately 353
K [2]. Salts used were J.T. Baker granular LiCl (>= 99.0%) and G-Biosciences KCl
(>=99.0%). The DU was vacuum induction melted U238. We used an RF induction
heater to heat the crucible, which heated the elements inside. The eutectic was
maintained at 450±5°C and a voltage of -1.00±0.01 V applied for 24 hours. At the
end of the growth, the system was purged with Argon and transferred to an argon
glovebox for evaluation and extraction of crystals. Crystals were etched with HNO3,
then X-ray crystallography and resistance measurements were performed.
Depleted uranium (DU) is uranium which contains less of
the isoptope U-235 than natural uranium (0.71% U-235) and is
mostly made up of the isotope U-238. DU has uses in military
and civilian applications, primarily making use of its high density
for counterweights and armor-piercing munitions. There is still
much to be learned about DU’s Fermi surface. The Fermi
surface of a material is important in understanding the thermal,
electrical, magnetic, and optical properties of that material.
Recent experiments at NHMFL seeking knowledge of the Fermi
surface of uranium suggest that high purity uranium with a good
crystal lattice are needed. It is for the purpose of obtaining high
purity single crystals of uranium that we conducted this
experiment.
.
Scale:
1 div = 100 μm
XRD Indexing:
Avg. FWHM:
70.73 %
1.2
64.86 %
1.14
94.29 %
1.2
84.62 %
1.18
XRD was performed by Amanda Chown on
four of the single crystals using an OxfordDiffraction Xcalibur2 CCD system.
The
reflections of five peaks were indexed and
FWHM calculated. A percentage was
calculated describing the fit of the indexations
to known uranium lattice configurations.
Using a PPMS, and a 4-probe configuration, we measured a
crystal’s resistance while sweeping the temperature down to 2
K. Taking the derivative of the resistance with respect to
temperature, we found apparent CDW transitions (marked by
the green arrows) closely resembling those found in previous
experiments [1].
Crystal used for R vs. T
measurements.
Scale: 1 div = 100 μm
K-type thermocouple
Cathode
Anode, with DU
attached
Whole growth system set-up
The electrorefining process of uranium in a chloride-salt
system is done through electrotransport and an intermediate
UCl3 state. This electrometallurgical process was designed to
electrowin plutonium during the Manhatten project, and was
refined for uranium starting in the 1980’s [4]. Uranium is placed
into a crucible with molten KCl and LiCl and with an applied
voltage across two electrodes, uranium is deposited on the
cathode.
X-ray Diffraction and x-ray crystallography is a method
around 100 years old that can give information about the lattice
structure of a crystal. X-rays are directed at a crystal and
diffracted by atoms in the crystal lattice. Capturing the diffracted
and reflected x-rays from many different incident angles gives
an idea of the lattice configuration of the crystal.
Uranium undergoes a structural phase transition into
alpha-uranium near 660°C. Alpha-uranium goes through three
charge-density wave (CDW) phase tranisitons at low
temperatures [1]. By measuring the resistance of a uranium
crystal as it goes through this low temperature range (20 K to
50 K), we can observe the CDW transitions as peaks in the
graph of dR/dT.
Results and Discussion cont.
Experimental Set-up
Quartz tube housing the crucible
containing the electrolytic salts,
electrodes
and
thermocouple.
Copper induction coil is wrapped
around the quartz tube.
Electrodes (without crucible)
Results and Discussion
This experiment successfully grew uranium crystals by means of electrowinning from a molten
eutectic. The deposit of crystals in the crucible was much greater than expected, and likely due to a
combination of the voltage and the time duration of the applied voltage being greater than necessary. It
would be good to repeat this experiment with varying voltages and time durations to determine how these
affect the electrorefining process and resulting crystals.
XRD and resistance vs. temperature analysis suggest that the grown uranium crystals are of high
purity. Future experiments will be done with these crystals to study the Fermi surface of uranium.
Acknowledgements
There was a growth deposit on the cathode. It was tree-like as
expected, but quite condensed. The DU anode was eroded
considerably. There was a large quantity of DU crystals in the crucible.
These were not attached to either of the electrodes, but collected in
the crucible.
Anode (left) and cathode (right)
after growth
Thanks to Lee Marks and the Fabrication/Assembly crew for allowing us space to perform
our work, for lending us their RF heater, and many other appreciated accomodations
We would like to thank Robert (Red) Schwartz for machining much of the equipment used to
grow the crystals.
Thank you Jason Cooley for supplying the DU.
Jose Sanchez, Assistant Director, Center for Integrating Research & Learning (CIRL) for
directing the REU program.
This research is funded through DMR1157490
References
Cathode (left) and
deposits after growth
crucible
40 μm
1.2 mm
Close-up of cathode
Cluster from crucible, after
HNO3 etch.
Scale: 1 div = 100 μm
Close-up of crucible deposits
1. Schmiedeshoff, G. M. et al. (2004) “Magnetotransport and superconductivity of alpha-uranium” Philosophical Magazine,
84.19. pg. 2001-2022.
2. Sridharan, Kumar et al. (2012) “Thermal Properties of LiCl-KCl Molten Salt for Nuclear Waste Separation NEUP Final
Report”
3. Basin, A. S., Kaplun, A. B., Meshalkin, A. B. and Uvarov, N. F. (2008) “The LiCl-KCl binary system” Russian Journal of
Inorganic Chemistry, 53(9). pg. 1509-1511.
4. McPheeters, C. C., Gay, E. C., Karell, E. J., and Ackerman, J. P. (1997) “Electrometallurgically Treating Metal, Oxide, and
A! Alloy Spent Nuclear Fuel Types” JMetals, 49, 22.