this radiometric method cannot be less than 1 t o 2%, unless long counting times are acceptable. The second factor to be considered is the use of radioactivity per se. T P is not difficult to work with. It was not necessary to place, shielding around our short column containing 2 mc. of TlZO4, and no health hazard was associated with working with the analyzer. On the other hand, we were not careless with drippings and effluent solutions. Housekeeping with radioactive materials need not be more difficult than in other good analytical laboratory technique. All effluents were pooled, and T1I was precipitated
when convenient, and converted to TINOs. The Tlm4was thus ready for electrodepositing again. Tl204 can be obtained license-free from the AEC in 50-b~. quantities. By using this quantity of activity and a counter with larger active surface, a satisfactory oxygen analyzer could be constructed. It would be suitable only for oxygen concentrations above about 1 p.p.m. LITERATURE CITED
(1) Brown, 0. W., McGlynn, S. A., Trans. Am. Electrochem. SOC.53, 351 (1928). (2) Carritt, D. E., Kanwisher, J. W., ANAL.CHEM.31, 5 (1959).
(3) Clark, L. C., Jr., Wold, R., Granger,
D., Taylor, E., J. A p p l . Physiol. 6 , 189 (1953). (4) Furman, N. H., ed., “Scott’s Standard Methods of Chemical Analysis,” Vol. 11, p. 2079, Van Nostrand, New York, 1939. (5) Richards, T. W., Smyth, C . P., J. Am. Chem. SOC.44, 524 (1922). (6) Seidell, A., “Solubilities of Inorganic and Organic Compounds,” p. 471, Van Nostrand, New York, 1919. (7) Wright, J. M., Lindsay, W. T., Jr., Proceedings of Am. Power Conf., 21st Annual Meeting, 1959. RECEIVED for review January 29, 1962. Accepted May 23, 1962. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1962. Work carried out under Atomic Energy Commission, Division of Isotopes DeveIopment, Contract No. AT-(40-1)-2513.
Determination of Micro Amounts of Carbon in Uranium Tetrafluoride R. E. SIMMONS and M. H. RANDOLPH Paducah Planf, Union Carbide Nuclear Co.,Division of Union Carbide Corp., Paducah, Ky. A method for the determination of microgram amounts of carbon in uranium tetrafluoride is presented which offers considerable improvement over conventional methods. Standard methods of carbon analysis, whether gravimetric, volumetric, or by gas volume are handicapped by interference of fluorides and consequently are unreliable for determining carbon in uranium tetrafluoride. The proposed method depends upon the conversion of carbon to carbon dioxide b y igniting the sample, which is fluxed with silicon dioxide, in a high temperature combustion furnace with a flow of oxygen passing over the sample. The gases generated by igniting the sample are collected in an evacuated bulb and analyzed for carbon dioxide on an infrared spectrophotometer with no interference from the other gases present. The precision of the method for a single determination at the 95% confidence level is + 13% for uranium fetrafluoride containing 100 pap.m. carbon and =t3Oy0 for uranium tetrafluoride containing 50 p.p.m. carbon.
S
for determining carbon in organic compounds containing fluorine have been reported in the literature (8-6). Carbon was determined gravimetrically by absorption of carbon dioxide in Ascarite following ignition of the sample and separation from water, fluorine, and in some instances chlorine. I n these methods the samples analyzed contained from EVERAL METHODS
11 to 83% carbon with the weight ratio of fluorine t o carbon never greater than 6 to 1. Determination of micro amounts of carbon in uranium tetrafluoride presents a somewhat more difficult problem as the ratio of fluorine to carbon may be greater than 5000 to 1. A few methods for determining carbon in uranium tetrafluoride are reported in the Atomic Energy Commission project literature (1, 7, 8). These methods are basically the same in that the sample is ignited in a stream of oxygen and the carbon is determined gravimetrically by absorption of the carbon dioxide in Ascarite. In the method reported by Warf (8)magnesium oxide powder was blended with the sample to retain most of the fluorine, and lead dioxide was used for absorbing fluorine not reacted with the magnesium oxide. Bernhardt et d. (1) report two methods for determining carbon in uranium tetrafluoride. In one of the methods the sample is mixed with zinc oxide to retain most of the fluorine with the escaping fluorine compounds trapped by sodium fluoride pellets. This method requires that the pellets be conditioned after each determination by baking a t 200’ to 300” C. while under vacuum. Combustion of uranium tetrafluoride in the presence of water vapor was used in the second met,hod to convert the fluorine to hydrogen fluoride. The water and hydrogen fluoride were separated from the carbon dioxide by absorption in Anhydrone and sodium fluoride pellets, respectively. Van Kooten and Gardner (7) used an electrically fused, 40 to 80 mesh,
magnesium oxide sand to mix with uranium tetrafluoride for removing fluorine from the combustion gases. About 40 grams of the magnesium oxide was used to mix with and cover a 3-gram sample for the determination. Because of the necessity for determining carbon in uranium tetrafluoride a t a very low level, a method in which fluorine compounds did not interfere with the determination would be more desirable than those described where fluorine compounds must be removed. Of the methods described the size of the uranium tetrafluoride samples ignited varied from 0.5 to 3.0 grams. If the sample contained 50 p.p.m. carbon, the weight of carbon dioxide obtained would amount to only 0.1 to 0.5 mg. Problems of weighing in this order of magnitude, where essentially complete recovery and separation of carbon dioxide from fluorine compounds is necessary, are quite obvious. To overcome these problems, an investigation was made of the feasibility of determining carbon in uranium tetrafluoride by igniting the sample a t 1100” C. in a stream of oxygen, collecting the combustion gases in an evacuated cylinder, and subsequently analyzing the gases by infrared spectroscopy. Neither oxygen nor fluorine combustion products interfere with the infrared determination of carbon dioxide. EXPERIMENTAL
Apparatus. A schematic of the ignition apparatus is given in Figure 1. The combustion gases were analyzed VOL 34, NO. 9, AUGUST 1962
11 19
primary reaction which occurred may be exprewed by the following equation
3UF4
+ %io2+ O2
+
Us08
A. 0. C. D. E. F. G.
n.
1. 1. K. L.
M.
N. 0.
Apparatus for ignition of carbon in uranium tetrafluoride
Oxygen shut off valve Needle valve Flowmeter, 0-3 liters per minute Absorption bulb containing magnesium perchlorate and o r a r i t e Rubber tubing Glass tee Mercury monometer Aged rubber stopper with tubing and baffle Combustion boot High temperature combustion furnace McDanel combustion tube Aged rubber tubing Fluorothene tubing with hoke connector on bulb end Monel gas collecting bulb (56liter) with control valve and hoke connector Support stand for gas bulb
with a Perkin-Elmer Model 21 infrared spectrophotometer equipped with a 10-meter gas analysis cell. Procedure. Adjust the oxygen flow through the ignition apparatus to approximately 0.3 liter per minute. Raise the temperature of the combustion furnace to 1100' C. Weigh 5 grams of uranium tetrafluoride and blend with 2 grams of preignited (
