acid saturated with cerium(1V) sulfate did not result in appreciable bleaching or back extraction of the red complex. The red complex is rather easily reduced with excess tin(I1) sulfate. The yellow complex also shows no bleaching of the color on dilution by 60 volume % acetone-aqueous solution. ACKNOWLEDGMENT
The author expresses appreciation to
B. E. Hjelte, C. E. Johnson, and Matthew Laug for considerable work in
repeating and checking the procedures and many of the experiments. LITERATURE CITED
(1) Beeston, J. LI., Lewis, J. R., A x . 4 ~ . CHEII. 25, 651 (1953). (2) Crouthamel, C. E..Johnson. C. E.. Ibid., 26,'1284(1954). (3) Geilmann, K . , Wrigge, F. W., Weibke, F., 2. anorg. allgem. Chem. 208, 217 (1932). ( 4 ) Hindman, J. C., Wehner, P., J . Am. Chem. Soc. 75, 2869 (1953). (5) Hoffman, J. I., Lundell, G. E. F., J . Research S a t l . Bur. Standards 23, 508 (1939).
Malouf, E. E., White, iU.G., XSAL CHEM.23, 497 (1951). JIaun, E. K., Davidson, N., J . Am. Chem. SOC.72, 2254 (1950). Melaven, A. D., Whetsel, K. B., Axua~.CHEM.20, 1209 (1948). Taube, H., Chem. Revs. 50, 69 (1952). Tribalat. S.,Ann. chim., Ser. 12, 4, 289 (1949). Kahl. A. C.. Bonner. S . A , . "Radioactbitv Applied 'to Chemistry," p. 189, Wiley, Xew Tork, 1951. Wehner, P., Hindman, J. C., J . Am. Chern. Soc. 75, 2873 (1953). RECEIVED for review December 14, 1956. .%cceptedJuly 16,1957.
Precision of the Pyrohydrolytic Determination of Fluoride and Uranium in Uranyl Fluoride and Uranium Tetrafluoride JAMES 0. HlBBlTSl Union Carbide Nuclear Corp., Oak Ridge, Jenn. Although much has been published on use of the pyrohydrolysis technique, to date no study demonstrates the accuracy and precision obtainable b y this method in the determination of fluoride. The pyrohydrolysis of uranyl fluoride and uranium tetrafluoride was studied and the results were analyzed statistically. The maximum limits of error, at the 9570 confidence level, for the fluoride and uranium were k0.44 and j=o.17%, respectively.
A
REVIEW of early pyrohydrolytic experiments and later industrial and quantitative applications has been published by ST'arf, Cline, and Tevebaugh ( 5 ) . These authors divided the fluorides into rapidly and slowly hydrolyzable salts. Those rapidly hydrolyzed are : aluminum, bismuth, cerium, dysprosium, gadolinium, lanthanum, neodymium, samarium, and thorium fluorides, uranium tetrafluoride, uranyl fluoride, vanadium trduoride, magnesium fluoride, zinc fluoride, and zirconyl fluoride. Fluorides of the alkali and alkaline earth metals (except magnesium) are only s l o ~ d yhydrolyzed. The technique is raluable for some fluoride determinations, particularly to workers in the field of atomic energy (5-5), but is rarely used by workers in the industrial field, perhaps because of lack of knowledge of the reliability of the results that may be obtained. Be-
CONCISE
1 Present address, Aircraft Nuclear Propulsion Department, General Electric Co., Evendale 15, Ohio.
1760
ANALYTICAL CHEMISTRY
Table I.
Pyrohydrolysis of Uranyl Fluoride Av. Dev., Av. Dev.,
Sample
s o . of
3-0.
Detns.
%
1 2 3
3
0.2 0.2 0.2 0.1 0.1 0.2 0.3 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.1 0.1 0.3 0.15
%Fa 12.23 3 ii.26 3 12 27 :3 12.31 4 :3 12.24 5 0 12.27 6 -I :3 12.28 3 12.30 8 12.20 9 > :3 12.30 10 3 12.31 11 3 12,xo 12 3 12.31 13 3 12.32 14 3 12.32 15 :3 12 32 16 3 12.32 17 3 12.33 18 AV. 12.29 a Theoretical value 12.33%. * Theoretical value 77.2770. c Theoretical value 2.000.
cause no comprehensive study to date has demonstrated the accuracy and precision obtainable by this method, the follon-ing data are presented and critically analyzed. The data have been taken from the original project literature ( 2 ) . The pyrohydrolysis method consists essentially of passing superheated steam over the metallic halide (usually between 400" and 1000" C.), and condensing and titrating the volatile acid. Although pyrohydrolysis is usually performed in a platinum reaction tube, nickel has been used very succesqfully (1,3).
--70Ub .27 I I
77.00 77 03 76.93 76.91 77 92 -I I .0:3 7--7 .06 I I .07 -I , . ot5 -I I .0:3 77.08 -, I . 12 -#
1.15
77.78 -.15 I
I
77 17 7 7 .24 7 7 .08
F/UC 1 995 1 996 1 996 2 001 1 993 1 997 1 998 2 001 1 999 2 001 2 002 2 000 2 000 2 001 2 000 2 002 2 001 2 000 2 000
% 0.03 0.11 0.05 0.09 0.ox 0.10 0.11 0.03 0.01 0.03 0.03 0.01 0.02 0.02 0.03 0.01 0.02 0.02 0.04
The reactions for the two salts investigated can be represented as: 3
+ 3 HlO
+
Ui0s
+ 6 HF + 1/*02
3 UF4
+ G H20 +
0 2
12 HF
+
(1) L308
(2)
The oxide remaining in the reaction tube is n-eighed, either nithout further treatment, or after a short period of ignition, depending upon the salt used. -4s indicated by Reaction 2, a considerahle amount of oxygen is necessary for the conversion of uranium tetrafluoride to uranium oxide (UsOs); consequently,
the residuc from pyrohydrolysis must be ignited in air to achieve complete conversion to uranium oxide. REAGENTS
Sodiuni hydroxide, 0.1.l- (carbonatefree), standard solution. Phenolphthalein indicator solution, 0.57G in 50% ethyl alcohol. APPARATUS
The apparatus was identical t o t h a t shonn by U7arf (4), except that plastic beakers rather than a silver dish were used to collect the distillate. PROCEDURE
Determination of Uranyl Fluoride. Duplicate portions of 0.3 t o 0.4 gram each are weighcd t o 0.1 mg. into tared platinum boats. T h e water supply t o t h e condenser is turned on and a polyethylene receiver placed t o receive t h e distillate. T h e t,empcrature of t h e steam gcncrator is adjusted t o provide a steady flow of steam, and t h e preheater and rcact'ioii tube furnaces are heated to 650" t o 700" and 850" to 900" C., respect'ively. The sample is inserted into the platinum reaction tube and adjusted with a platinum nire to the place which will be hottest when heat is applied. The preheater and reaction tubes are connected, the furnaces are closed, and the distillate is collected for 15 minutes. The first receiver is then replaced n-it81ia second receiver of the same type. The hydrofluoric acid collected is titrat'ed ivith 0.1S sodium hydroxide to the phenolphthalein end point,. The second receiver is replaced with a third receiver and the second distillate is added t o the portion already titrated. If t,lie pink color does not fade when the second distillate is added, the titration is complete and t'lie volume of sodium hydroxide used is recorded. If the pink color fades, the hydrofluoric acid added must be titrated and anot'lier portion collected n.ith which to test for complete hydrolysis. W i e n the t'itration is complete, the tube furnaces are turned off, and the platinum tube is withdraxn from the apparatus and allowed to cool. The platinum boat is removed, allowed t o cool, and the net n-eight of the Us08 tletermined. Determination of Uranium Tetrafluoride. Fluorine in uranium tetrafluoride is determined b y t,he general p r o t d u r e for uranyl fluoride. T h e residue will contain a n excess of UOz (with respect to U308)because insufficient oxygen is present' during pyrohydrolysis; consequently the resiclue must be converted completely to ly,Os by ignition in air a t SOO" C. for 15 minut.es. Uranium may t.lieri be determined by weighing the oxide. RESULTS AND DISCUSSION
Uranyl Fluoride. T o determine t h e precision of t h e method, a nuniber of samples of uranyl fluoride were an-
alyzed. T h e average iesults arc rcported in Table I as per cent fluoride a n d per cent uranium; average deviations from t h e mean are given for each group of analyses t o shou t h e close agreement between individual samples. As this conipound \\as prepared for experimental use, values of t h e fluoride-uranium inolai ratio are also given. The statistical variation nitliin samples was calculated by the cvpression
nlicre 1. = value of an individual malysis, = total number of annlyses, S n = number of analyses on one sample, and m = total numbcr of samples. d t the 9570 confidence level. the standard tlwi:ition, s, and the limit of erior, L.C., for the data in Table I \\ere: &\-
Eleineiit
8,
%
F
1 2 3
3
4
3
5 G
I
8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24 25 2G
3 3 J
3 3 3 3 3 3 :< 3
SO.
%LYll
i0 17 io 35
1 1 1 2 2
76.79 76.76 76 81 77 -- 12
3 3 3 .3 3 3 3
3 3 3 5
3
3
4
4
3 3
5 L)
3 3 3
%P 76.73 76.74 76 79
.
li.05 77.12
I
.
.
%IJC
76.78
76.80 76.72
77 11 7 7 .02
2 ... 76,92 2 77.05 76.!)8 ... a Cnlculat,ed froin weight - of UaOs from pyrohydrolysis. 6 Calculated froin 11-eight of TT,O8 from pyrohydrolysis and igition in air a t 800' C. for 4 hours. c Calcnlsted from neight of L-308 after direct ignition at 800" C. for 4 hours.
Pyrohydrolysis of Uranium Tetrafluoride
3
3 3 3
II. Conversion of Uranyl Fluoride to Uranium Oxide
Sample
Thus, an individual fluoriuc tlctcrniination should lic n ithin 0.33'; of the mean of all futurc rcsults 95% of the time. Because neither a fluoi itlc, mrtliod nit11 high precibion nor a pGro standard reference compound is a v d a b l e , the accuracy of this method cannot be determiiicd. Hon-ever, the close correlation betwecn thc theorc+cal and
Table 111.
Table
L. 13; ,
70
1 0 os 1 0 17
u
observed fluoi ide-uranium molar ratios indicates that the precision may also be regarded as the accuracy. Complete conversion of uranyl fluoride to UaOs during pyrohydrolysis was tested by comparing the weights after pyrohydrolysis with those after ignition of the residue a t 800" C. for 4 hours. For further coniparison, the uranyl fluoride !vas ignited in air for 4 hours a t SOO" C. The data obtained, reported in Table 11, indicate that uranyl fluoride is stoichiometrically converted to U308. Uranium Tetrafluoride. The results for a number of uranium tetrafluoride samples are listed in Table 111. These samples n e r e taken from b:itchcis of uranium tetrafluoride in various stages of piotluction; con-
3
3 3 3 3 3 3
4
4
5
J
tJ
4
23 80 24 20 17 89 22 02 23 25 22 62 22 14 24 23 24.26 23.68 24.27 24.25 24.20 22.70 22.81 24. OS 23.65 24.41 24.24 22.82 23.85
24.11 24.16 24.16 24.32 21.28
0 17 0 08
0 13
0 4,i
0 22 0 17 0 00 0.08 0.17 0.26 0.03 0.21 0.03 0.09 0.27
0.08 0.03 0.05 0.21 0.23 0.13 0.13 0.04 0.13 0.13 0.13 ;iv. 0 . 14
76.02 -l a 65 79.01 76 89 76 23 76 61 76 75 75 7 2 7 5 78 76 08 7 5 ,70 -_ 13.76 -_ lJ.75
76.63
-_
76,60 ia.95 7 6 , 10 75.69 75,72 76.46 7 5 ,77
-- -_ 13.I I
76. i 7
i 5 . 83 -1 3 . IO -w
7 5 . 78
0 03
0 01
0.08 0 06 0 03
0 02
0.01
0 05 0 02 0 01
0.04 0.04 0.04 0.08 0.05 0.03 0.07 0.00 0.04 0.05 0.08 0.05 0.07 0.02 0.04 0.08 0.04
Theoretical value 24.277,. Theoretical value 7,5.7!%: Data in column obtained by igniting oxide from pyrohydrolysis a t 80b" C. for l a minutes.
VOL. 29, NO. 12, DECEMBER 1 9 5 7
1761
sequently, t h e fluoride-uranium molar ratios are not significant and are not given. Although t h e amounts of fluorinc and uranium v a r y greatly from sample to sample, good agreement was found between the uranium and fluorine precisions for uranium tetrafluoride and uranyl fluoride. A statistical analysis of the data in Table I11 b y means of the expression given previously yields the following results at the 95% confidence level. Elemerit U F
70
1.0.07
L.E., % 1 0 13
1 0 22
1.0.441
s,
ACKNOWLEDGMENT
The author wishes to express his appreciation to J. R. Day and T. H. Barton of the Y-12 Analytical Laboratory in Oak Ridge for their assistance in collecting the data. H e is also indebted to R. C. McIlhenny for his help in preparing the manuscript. LITERATURE CITED
(1) Gahler, A. R., Porter, G., ANAL. CHEX.29, 296 (1957). (2) Hibbits, J. O., U. S. Atomic Energy Commission. BEC Proiect ReDt. Y-883 ( J d v 2. 1952). (3) Susano, C. D.,’ White, J. C., Lee, J. E., ANAL.CHEAT. 27, 453 (1955).
(4) Warf, J. C., “Analytical Chemistry
of the Manhattan Project,” S a tional Xuclear Energy Series, 1st ed., Div. VIII, Vol. 1, pp. 728-30, McGraw-Hill, Yew Tork, 1950. ( 5 ) Warf, J. C., Cline, IT. D., Tevebaugh, R. D., A N A L . CHEhl. 26, 342 (1‘384); Manhattan Project Repts. CC-1981 (Oct. 10, 1944), CC-1983 ( S o v . 10, 1944), CC-2723 (June 30, 1945). RECEIVEDfor reviev May 15, 1957. Accepted July 22, 1957. 8th Annual Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. Based on work performed for the Atomic Energy Commission by Cnion Carbide h’uclmr Corp. at Oak Ridge, Tenn.
Determi nuti on of Ura nium Dioxide in Stainless Steel X-Ray Fluorescent Spectrographic Solution Technique LOUIS SILVERMAN, WILLIAM W. HOUK, and LAVADA MOUDY Atomics International, A Division of North American Aviation, Inc., Canoga Park, Calif.
b This paper outlines a rapid method for the determination of uranium dioxide in stainless steel b y direct fluorescent x-ray analysis after chemical solution of the sample in perchloric acid. A scintillation counter is used to detect the intensity of the radiation. Modifications in the apparatus are needed to ensure stabilization of the counter. Strontium is used as internal indicator. The determination o f uranium i s unaffected b y the presence o f large amounts o f iron, chromium, or nickel a t the dilutions described. The counting time for four pairs of counts (uranium and strontium) is about 12 minutes. A standard deviation corresponding to 0.5 to 1% of the uranium dioxide present was observed on synthetic samples ranging from 15 to 25% uranium dioxide.
I
fabrication of fuel elements for a n experimental reactor, uranium dioxide and powdered stainless steel (304) are mixed and then encased in stainless steel plates. The test for the homogeneity of uranium dioxide in the finished fuel elements presented a problem. Determination of the amount of uranium dioxide in the finished plates was complicated by the amount of stainless steel present. Gravimetric and volumetric procedures involved long and tedious separations. Direct colorimetric procedures were unsuccessful because of the interference of iron (5) and nickel (6). Fluorescent x-ray techniques were N THE
1762
ANALYTICAL CHEMISTRY
examined as a mpans of solving the problem. Direct radiation of the uranium in steel-encased sample by xrays \vas inapplicable, as the stainless steel case prevented the penetration of the x-rays to the uranium layer. Thus, the sample would have to be altered. The simplest procedure was to prepare an aqueous solution of the sample. Birks and Brooks ( 1 ) analyzed uranium in solution by x-ray fluorescence, but their technique required evaporation of aliquots of the solution and analysis of the dry residue. Pish and Huffman ( 2 ) determined uranium in aqueous and in organic solutions extracted from raw materials. Predominantly large amounts of iron, chromium, and nickel mere not present. This paper describes a rapid method for the determination of uranium dioxide in stainless steel by chemical solution of the sample and b y direct fluorescent x-ray analysis of the resulting perchloric acid solution, lvithout further separations or processing. APPARATUS AND REAGENTS
The apparatus consists of a Korth American Philips x-ray spectrograph Type 12049 and a milliampere stabilizer Type 52204 with a FA60 tungsten target x-ray tube and a lithium fluoride analyzing crystal. An additional voltage stabilizer was added to the equipment to regulate the po\ver to the electronic panel. The x-ray tube was operated off the original voltage stabilizer a t 50 kv. and 30 ma. This was necessary to prevent overloading the voltage stabilizer when all the circuits of the ap-
paratus were in operation. A s c i n t i l b tion counter and a scaler were used t o detect and record the counts. The solution cell (4) and the solution techniques (3) have been described. It is important that the space between the scintillation counter and the collimator be shielded with lead to p r e vent pickup of scattered radiation by the counter. Figure 1 shows a diagram of this shielding.
Figure 1.
Lead shielding of system
Reagent grades of hydrochloric, hydrofluoric, nitric, and perchloric acids were used to dissolve the samples. Chemically pure strontium nitrate was used to make the internal standard stock solution of 100 mg. per ml. of solution. EXPERIMENTAL PROCEDURE
Standard Working Curve. Perchloric acid solutions of synthetic mix’tures of uranium dioxide and stainless steel were prepared. T h e internal standard, strontium nitrate, was added t o t h e solutions to give a concentration of 2 mg. of strontium nitrate per ml. in the test solution. The
