The diffusion coefficient, D, of U (VI) in molten sodium metaphosphate at 694° C was determined by two independent methods. D was also determined at R values of 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5, where R is the molar M20 to P2O5 ratio and M is univalent. The relative amounts of various phosphate species present in the molten state were determined by thin layer chromatography after rapidly cooling the melt and dissolving the resultant glass in water. With the above information it was hoped to determine if D is independent of the experimental method of determination and then to relate the variation of D with R.
A three electrode system was employed for chronopotentiometry, a 1 cm2 platinum flag working electrode, a platinum flag counter electrode (>10 cm2 ), and a silver-silver metaphosphate reference electrode. Fused silica crucibles were used to contain the melts. The melts were allowed to equilibrate at 694° C for at least one hour prior to the taking of measurements.
There appeared to be no regular variation in D with increasing R. For R equals 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5, the diffusion coefficients were 1.30 x 10-7 cm2/sec, 6.29 x 10-8 cm2/sec, 1.67 x 10-7 cm2/sec, 2.24 x 10-7 cm2/sec, 1.48 x 10-7 cm2/sec, and 2.12 x 10-7 cm2/sec respectively. The diffusion coefficients were obtained from the slopes of iₒr ½ vs. C plots.
For chronoamperometry a two electrode system was employed A potential of 0.85 volts was selected after studying current-voltage curves for the melts.
Unlike chronopotentiometry, D values determined by chronoamperometry increased fairly regularly with R. For R values of 1. 0, 1. 1, 1. 2, 1. 3, 1. 4, and 1. 5 the corresponding D values were 1.16 x 10-7 cm2/sec, 1.47 x 10-7 cm2/sec, 1.62 x 10-7 cm2/sec, 1.96 x 10-7 cm2/sec, 2.12 x 10-7 cm2/sec and 2.45 x 10-7 cm2/sec.
The thin layer chromatography consisted of dissolving the glass in water and spotting the solution on to an Eastman cellulose chromatographic sheet. The solvent was a mixture of trichloroacetic acid, water, ammonia, and acetone. The spots were developed by an acid molybdate spray followed by exposure to ultraviolet light. The spots were then eluted off the sheet and the percent phosphorus determined colorimetrically. The results show that the uranium does change the amount of the various phosphate species present.
The application of the Stokes-Einstein equation indicates that the radius of the diffusing species, for an R = 1.0 melt, is the bare U (VI) ion. In light of the known chemistry of uranium, the existence of a bare U (VI) ion seems very improbable.
The Sandia Corporation, a prime contractor to the Atomic Energy Commission, provided financial support for a portion of this work. The author acknowledges the receipt of a N.A.S.A. Traineeship.
Level of Degree
Department of Chemistry and Chemical Biology
First Committee Member (Chair)
Roy Dudley Caton Jr.
Second Committee Member
Thomas Michael Niemczyk
Third Committee Member
William Fletcher Coleman
Fourth Committee Member
Guido Herman Daub
Fifth Committee Member
Albert Masakiyo Kudo
Miglio, John J.. "Chronopotentiometric And Chronoamperometric Investigations Of Uranium (VI) In Molten Condensed Phosphates.." (1974). https://digitalrepository.unm.edu/chem_etds/172