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ANP QUARTERLY PROGRESS REPORT
chloride, TiCI,, and methylene blue, C, 6H1 ,N,SCI.
Of these reagents, methylene blue appears to be
the most promising reagent for a possible routine
method for the determination.
Cupric Chloride (CuCI,). Previous attempts to
oxidize UF, by Cu(ll) in H,SO, solution were unsuccessful.
Since the formal oxidation potential of
the [Cu(ll),Cu(l)] couple is increased in solutions
of high chloride concentration, experiments were
performed to ascertain whether quantitative oxidation
of trivalent uranium could be achieved by
adiusting the acidity and chloride concentration of
the CuCI, solvent solution.
Samples of UF, were dissolved under an atmoshere
of CO, in acidic solutions of NaCl which
contained a measured excess of a standard solution
of CuCI,. After dissolution of the samples,
nreduced CuCI, was determined iodometrically
and the trivalent uranium was calculated on the
ometry of the equation
u3+, cu+ + u4+
When the dissolution was carried out in a solu-
tion 1 M in HCI and 2 M in NaCI, the results were
in agreement with those obtained by the hydrogen
evolution method.2 Lower values were obtained
when either the chloride concentration or the
acidity was altered.
Samples of UF, which had been fused with NaF-
KF-LiF evolved hydrogen and subsequently
yielded low results when analyzed by the above-
described procedure. The method therefore appears
to be of limited applicability.
Titanium Tetrachloride (TiC14)o It was found that
UF, dissolved without evolution of hydrogen in
solutions of TiCI, in concentrated HCI to yield
dark-brown solutions of TiCI,. The color of these
solutions, when diluted, reverts to the rose tint
usually associated with Ti(lll) solution. When
these diluted solutions are titrated with a standard
solution of K,Cr,O, the equivalents which are
consumed at the first sharp change in potential
correspond to about 95% of the trivalent uranium
as determined by the hydrogen evolution method.
If the solutions are then heated to a temperature
of 90T, the total uranium can be determined by
U(VI) with further addition of
2D. L. Manning, W. K. Miller, and R. Rowan, Jr.,
Methods of Determination of Uranium Trifluoride, ORNL-
1279 (Apr, 25, 1952).
130
While this is the only method which has been
found to give a titration for trivalent uranium
without subsequent back-titration of excess
oxidant, it is not readily adaptable to routine
analysis because of the slow equilibrium of the
electrode potentials and the rapid oxidation of
titanous solution by air after the dilution of the
concentrated acid solutions. Experiments are now
being conducted to determine whether the TiCI,
can be titrated in the concentrated acid with
bromine which is generated coulometrically.
End points obtained potentiometrically in the
concentrated solutions were found to be poorly
defined, but sharp breaks with potential changes
of about 400 mv were obtained with polarized
platinum electrodes. Titrations between 5 and
10% in excess of the theoretical value were
obtained when UF, samples were titrated coulometrically.
This excess titration is probably a
result of diffusion of TiCI, from the cathode compartment.
Methylene Blue. A proposed method based on
the oxidation of trivalent uranium to the tetravalent
state by methylene blue was developed for the
determination of UF, in a fluoride fuel. In the
proposed procedure, the sample is dissolved in a
measured volume of 0.02 N methylene blue solution
in 3 to 6 N HCI under an atmosphere of CO, by
stirring for 2 hr at room temperature. The excess
methylene blue is then titrated to its reduced
state, methylene white, with 0.05 N chromous
sulfate solution. The equations involved in the
determination are as follows:
2U3+ + methylene blue + 2H++ 2U4+
+ methylene white
2Cr2' + methylene blue + 2 Ht4 2Cr3'
+ methylene white
Because of the intense color of the dye, the
visual end point, blue to green, is sharp and re-
producible even when the titrations are carried out
with 0.025 N chromous sulfate.
For the determination of trivalent uranium in
UF, the coefficient of variation is approximately
1%, and the results are in excellent agreement with
those obtained by the hydrogen evolution method.2
While somewhat poorer precision was obtained in
the analyses of NaF-LiF-KF-UF,-UF, samples,
the variations were probably a result of hetero-
geneous sampling, as is also indicated by the
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