abundance, 7.42%, but are not out of line with results reported by Pupezin, eeric, and LozareviC. (IO). An obvious improvement of the method would be t h e counting of the alphas and tritons in coincidence to reduce the background. This would require a modified arrangement for holding the sample, perhaps on a “weightless“ zapon (35) film, mounted between the two required solid state detectors, all in a vacuum. The accuracy of the present method would further be improved in a reactor with a thermal column, as room would be available for needed gamma shielding to reduce the background spectrum. It is pleasant to consider a method which would determine both the lithium-6 and lithium-7. The lithium-7 absorbs a neutron and becomes lithium-8. This has a 0.85-second beta activity and becomes beryllium-8. The beryllium-8 disintegrates with a t1I2of 3 X 10-16 second to produce two alpha particles. Alpha, alpha coincidences would be counted for the lithium-7 and of the alpha, triton coincidences for lithium6. The low energy (47 keV) and the low cross section for formation of the lithium-8 present difficulties in our low flux, and the rather short useful life of existing solid state detectors in a higher flux would mitigate against working in such. With regard to analysis of the same sample by mass spectrometry and by the present method, such samples are listed in Tables I and 11, and the results are compiled in Table 111. If SS 5 is assumed correct, then HD 885 is so analyzed and is (35) L. Yaffe, Ann. Rec. Nucl. Sci., 12, 154 (1962).
in error by +0.67% ; or, if you assume HD 885, then SS 5 is 0.67x low. We believe that our present method requires very little in the way of special equipment, and simple wet chemistry. Our method provides adequate accuracy to sense reported geologic eLi/’Li variations of from 2 to 4.5%. It can easily be used for checking the atom ratios of depleted laboratory lithium compounds providing accurate molecular weights, A neutron flux suitable for this work may be found in many laboratories. The results are directly useful to the chemist utilizing lithium salts and presumably useful to students of the chemistry of the earth and of meteorites. Nuclear experimenters find the variation in the lithium-6 to lithium-7 ratios especially important because of the high thermal neutron cross section of lit hi um-6. ACKNOWLEDGMENT
We thank Ronald Macfarlane for suggesting that we study n, alpha reactions; Scott Smithson and Robert Houston with whom we discussed the geological possibilities of the reaction; and Jere Green and Jere Knight who read the manuscript most diligently and helpfully. RECEIVED for review August 7, 1967. Accepted January 6, 1968. Abstracted from Ph.D. Thesis, W. A. Sedlacek, University of Wyoming, 1965. Presented in part at the 153rd Meeting ACS, Miami Beach, April 1967. Work supported in part from the National Defense Education Act funds.
Remote Analysis of Radioactive Alloys for Carbon, Oxygen, Nitrogen, and Hydrogen Harvey T. Goodspeed, Ben D, Holt, John H. Marsh, Jr., and John E. Stoessel Chemistry Dicision, Argonne National Laboratory, Argonne, Ill. Combustion and inert as fusion methods are applied to the determination o carbon, oxygen, nitrogen, and hydrogen in alloys of high alpha, beta, and gamma radioactivity. The combustion and fusion furnaces are designed such that either can be used with a common shielding facility, energy supply, and analytical train. Sample addition, crucible replacement, and reaction tube exchange can be performed remotely using masterslave manipulators. Provisions are made to strip the carrier gas streams of radioactive and/or interfering gases before entering the measurement components of the analytical train. Advantages of the new furnace tubes, other than permitting remote handling, are noted.
9
VARIATIONS in the physical properties of the fuel and structural alloys that make up the cores of atomic energy reactors have led scientists t o look for correlations with changes in the concentration and distribution of impurities: carbon, oxygen, nitrogen, and hydrogen. Shifts in concentrations during power production have been suspected as being relatable to swelling of fuel materials and/or t o embrittlement, cracking, and dimensional changes in cladding alloys. This report deals with the determinatior? of these impurities in alloys characterized by strong alpha, beta, and gamma radioactivity. Samples were handled remotely in a n isolation box enclosed in a dense-walled cave cell. The combustion-
682
ANALYTICAL CHEMISTRY
manometric method was used for the microdetermination of carbon and the inert gas fusion method for oxygen, nitrogen, and hydrogen. The furnaces used in the combustion and fusion apparatus were chosen to meet the following requirements: a reaction chamber that could be opened remotely by mechanical hands (“master-slave” manipulators) for loading and disassembling; a replaceable crucible; a means of reaching the operating temperature rapidly without releasing excessive heat inside the box; a procedure for reducing the blank t o a low constant level while the crucible was heated in situ, prior t o sample addition and without exposure of the crucible to the containment atmosphere; provision that each sample should enter the crucible only after the blank was established, and several samples should be accumulable in each crucible; the same shielded box, induction heater, cooling water lines, and carrier gas lines should be usable for either the combustion or the fusion analyses; the portion of the analytical train confined to the hot cell should be minimal. EXPERIMENTAL
Carbon Analysis. APPARATUS.The combustion furnace used in the determination of carbon is shown in Figure 1. The envelope, crucible, and liners are made of fused quartz and are arranged such that the oxygen stream flows by the
-----------i--------
1
I A F2 c _
COOLI’NG
w
-
5
I I I I I
I I I
I -- J
19/22 GREASELESS O-RING JOINT
Figure 2. Schematic diagram of analytical train for carbon determination Copper oxide furnace Purification tube packed with Ascarite and Anhydrone GIand G2 Glass wool filters Sample furnace FZ Optical window W Mirror M RuO4 trap Ti Dry ice acetone cold trap TZ Oxidizing unit (CuO furnace or Schutze reagent) 0 Inlet stopcock Si C 0 2 analyzer (capillary manometer or gas chromaA tograph) Outlet stopcock SZ Vacuum system V Fi
P
CRUCIBLE, 13mm O.D. INNER LINER, 17mm D.D. PLATINUM CYLINDER OUTER LINER, 30mm 0.D
1 1
r T E F L O N GASKET
STAINLESS STEEL BASE -OXYGEN
liznikASH PIT
Figure 1. Combustion furnace for carbon analysis sample which is surrounded by the inductively-heated platinum cylinder (33/* inches long, ’is inch in diameter, 0.032inch wall thickness). The crucible rests on indentations in the inner liner, leaving channels for free gas flow at its base. The induction-heating work coil (13/4inches long by 2’/s inches i. d.) consists of 8 turns of flattened 3/*-inch copper tubing. The RF feed-through in the 28-inch cell wall, that connects t o a 20-kW Thermonic generator, Model 1070, is made of two parallel sections of 3/8-in~hcopper tubing encased inch apart in a solidified polyurethane foam plug that is encapsulated in a rigid polyester resin. Separate streams of recirculated cooling water flow through the work coil and the furnace assembly at 6 and 0.7 gal/min, respectively. Designs and protective features of the hot cell and of the isolation box within the cell have been described in the literature (1-4). ~~
(1) D. C. Stewart, “Technique of Inorganic Chemistry,” Vol. 111, John Wiley and Sons, New York, 1963, pp 188-231. (2) E. P. Horwitz, C. A. A. Bloomquist, H. W. Harvey, and J. C. Hoh, U.S.At. Energy Comm. Rept. ANL-7134 (1966). (3) E. P. Horwitz, C. A. A. Bloomquist, H. W. Harvey, D. Cohen, and L. J. Bade, U. S. A t . Energy Comm. Rept. ANL-6998
(1965). (4) C. H. Youngquist, J. F. Lindberg, W. C. Mohr, and R. B. Wehrle, U.S. A t . Energy Comm. Rept. TID-7599 (1960).
The overall arrangement of the analytical train is indicated by the schematic diagram in Figure 2. Both ends of the train, not contained in the hot cell, are mounted in a vacuum frame hood adjacent t o the cell. The hood ventilation is 300 cfm of air when the sliding transparent doors are completely closed. Glass wool filters, G1 and G2,in the oxygen stream before and after the combustion furnace confine radioactive dust particles t o the hot-cell area. The dry-ice cold trap, Tz, removes RuOl from the oxygen stream before reaching the COSanalyzer. Radioactive RuOc is a combustion product that accompanies ignition of fissium alloys. If it is not removed from the gas stream, part of it decomposes to R u 0 2 (a finely-divided, radioactive solid) which is deposited on surfaces throughout the train, while the remainder condenses as liquid RuOl in the capillary manometer, later to be counted as COSin the final measurement. Another and apparently better method of stripping most of the RuOl from a gas stream, as reported by the Idaho Chemical Processing Plant (Phillips Petroleum Co., Idaho Falls, Idaho), is to pass the gas through a bed of polyethylene pellets, ASTM Type 11 (5). At present, work is under way t o incorporate such a trap in the analytical line at T l , Figure 2. The type and level of radioactivity, as well as the concentration of fission-produced gaseous impurities such as xenon, krypton, and iodine, depend on the source and quantity of the material being analyzed. Iodine, if present, is trapped out with R u 0 4 . Xenon and krypton d o not interfere with the Conmeasurement. The oxidizing unit, 0, is included in the train to ensure the complete oxidation of traces of CO that may form in the combustion chamber. Either a copper oxide furnace a t 420” C or a bed of Schutze reagent (iodine pentoxide on silica gel) at room temperature can be used. The analyzer, A , shown in Figure 2 is a capillary trap manometer. Other sensitive devices for measuring micro(5) Denzel K. Jenson, “Health Physics,” Pergamon Press, Vol. 12,
1966, pp 923-26. VOL. 40, NO. 4, APRIL 1968
683
gram quantities of COZ can be used, such as gas chromatographic or conductimetric equipment. Procedure. The analytical procedure for the microdetermination of carbon in metals by combustion has been previously described (6, 7). Only the details that are related t o remote handling are considered here. With a helium flow rate of about 250 cc/min at 21 oz pressure, the inlet stopcock is closed t o A (Figure 2). The flatsided portion of the water-cooled standard taper joint is moved t o a nearby storage rack. A funnel is placed in the furnace opening and a weighed sample is dropped from a screw-cap vial into the crucible. The stream of purified helium emerging through the opening prevents exposure of the crucible and other furnace parts t o the ambient atmosphere that would otherwise contribute to high blanks, and also averts precombustion of sample if the crucible is warm from a previous analysis. The water-cooled standard taper joint is replaced on the furnace, and the inlet stopcock is adjusted at A such that the gas flow rate is 150 cc/min. Helium is switched t o oxygen. The temperature of the platinum susceptor is increased t o about 1240" C . In our apparatus this increase heats the quartz crucible t o about 1190" C. This temperature is sufficient t o readily ignite fissium alloys (95% uranium), or to adequately oxidize 0.3-gram stainless steel samples added with 0.7 gram of tin accelerator. Depending upon how readily the material is oxidized, the minimum lengths of the heating are established as well as flushing periods for complete combustion and for return to established low blank levels between sample runs. Our procedure has been t o heat fissium samples 15 min and stainless steel samples (with tin) 30 min. The temperature of the crucible was measured by a Leeds and Northrup optical pyrometer. The line of sight was oiu the 28-inch zinc bromide cave cell window, the 45" mirror, and the optical window in the cover joint. Correction was made for the transmissivity of the cell window. Procedure for Changing Crucibles. When a new crucible is to be installed, the water-cooled cover joint is removed as for adding a sample. The hex-nut flange clamp on the base is loosened and the envelope lifted. The upper section of the inner liner is withdrawn from the outer liner and the crucible and its oxides are dumped into an active waste container. The emptied inner liner is held at a 45" angle, while a new crucible is inserted sliding it gently down into position on the indented supports before reassembling in the furnace. It is apparent from Figure 1 that the platinum cylinder can be removed in a similar fashion by lifting the outer liner from the base. Oxygen, Nitrogen, and Hydrogen Analysis. APPARATUS. The apparatus used for the inert gas fusion determination of oxygen, nitrogen, and hydrogen is essentially the same as described in a previous publication (8), the chief exception being that the fusion furnace is designed t o accommodate remote handling. Figure 3 shows a diagram of the assembled furnace. Mounted in the same position with respect to the stationary, induction-heating work coil as the furnace tube of the carbon determination, the fusion furnace can be remotely assembled or disassembled. (Glass-wool filters in the carrier gas lines are remotely replaceable when changing furnace chambers from the combustion t o the fusion arrangement.) Greaseless, O-ring joints provided at the top and bottom with matching flange clamps are manipulatable with mechanical hands.
(6) B. D. Holt, ANAL.CHEM.,27, 1500 (1955). (7) W. G. Smiley, Ibid., p 1098. (8) B. D. Holt and H. T. Goodspeed, Ibid., 35, 1510 (1963).
684
ANALYTICAL CHEMISTRY
rl
m 3 5 / 2 5
O-RING
WA
T -12/5
O-RING B A L L JOINT
f
HELIUM
Figure 3. Fusion furnace for oxygen, nitrogen, and hydrogen analysis The chamber is positioned so that the lower section of the graphite crucible is centered in the middle of a 7-turn work coil Q3/*inches in diameter, 13/8 inches long). The thinwalled midsection of the crucible has three, equally-spaced, lengthwise slits 0.75 inch long by 0.025 inch wide. These conduct the carrier gas through the tube and prevent this section from suscepting R F energy from the coil. The enlarged diameter of the top section of the crucible permits support in the quartz chamber and serves as a funnel for incoming samples. The undercut lip near the top edge facilitates handling by appropriately designed forceps. The direct contact between the graphite crucible and the fused quartz chamber does not produce a detectable contribution to the oxygen blank. The temperature of the top section apparently does not become high enough to induce an appreciable carbon-Si02 reaction. Each crucible is precleaned of fabrication contaminants by inductively heating at about 2000" C for 10 min in a separate apparatus. In this preparative operation, the crucible is suspended o n a molybdenum wire in a stream of inert gas in a manner such that all parts of the crucible are thoroughly baked out. The chief advantage of the design of this crucible over that of the one previously used ( 7 , 8 ) lies in the elimination of alignment problems. In the older model considerable care had to be exercised, not only in directing the capillary stem of the crucible onto the tungsten wire support, but also in making sure that the top edge of the crucible was a t the proper distance from the wall of the fused quartz chamber. If it were too close, there was danger of carbon reduction of the S i 0 2 wall; if too far away, there was danger of losing samples by bouncing out of the crucible. The naked crucible
described here also has obvious manipulative advantage, especially in remote handling, over currently-used models that require graphite powder insulation for the production of adequate fusion temperatures when using 4 t o 5 kW induction heating generators. Other improvements t o the apparatus previously described (8) include: a diaphragm pressure regulator used instead of the liquid manostat; two vacuum thermocouple gauges used t o determine the degree of nitrogen removal from the charcoal traps; and two gas flowmeters employed t o detect gas linkage in the portion of the analytical train confined t o the hot cell. Procedure for Changing Crucibles. The procedure for remotely changing crucibles is not difficult. After removing the 45" viewing mirror and loosening the clamp on the 35/25 O-ring joint, the upper part of the joint is rotated out of the way, and, with forceps that engage the inner lip of the crucible, the latter is lifted out and placed in a n active waste container. A new crucible is inserted into the chamber. The chamber is closed and the train is again readied for use by adding 8 grams of platinum t o the crucible, followed by a sufficient number of heating cycles t o reduce the blanks of oxygen, nitrogen, and hydrogen t o low constant values. RESULTS AND DISCUSSION
Recovery data o n samples of known carbon content are shown in Table I. These data are presented not to prove the validity of this well-established method but to show that remote handling does not necessarily prevent the acquisition of useful results in the microgram range, Recovery results obtained o n oxygen, nitrogen, and hydrogen standards were essentially the same as reported previously (8). Some advantages of the modified equipment are not necessarily confined t o remote handling. The carbon furnace
Table I. Recovery Data on Samples of Known Carbon Content
c, PB Sample LECO Standard
BaC03
Added
Recovery,
x
Measured
90
89 88 88 83
190 210 215 20 1 188
188 208 214 200 186
99 98 98 92 Av 97 Std dev 1 3 98.9 99.0 99.5 99.5 98.9 Av 99.2 Std dev 1 0 . 3
chamber permits preheating a combustion crucible t o a constant low blank (in the microgram range) before the sample is added. Sample addition is made without exposure of the ignition vessel (crucible) to the atmosphere. The same degassed crucible can be used for several successive samples. Likewise, the modification of the fusion furnace chamber is generally advantageous in that it eliminates the problems of crucible alignment, of sample losses by missing the crucible, and of carbon-SiO9 interaction. RECEIVED for review September 27, 1967. Accepted January 15, 1968. This paper is based on work performed under the auspices of the U.S. Atomic Energy Commission.
~~~
Potentiometric Titration of Perchlorate with Tetraphenylarsonium Chloride and a Perchlorate Ion Specific Electrode R. J. Baczuk a n d R. J. DuBois Hercules Inc., Bacchus Works, Magna, Utah A number of organometallic salts have been used to measure the perchlorate anion. Both electrometric and gravimetric methods have been employed. This paper reports a potentiometric precipitation titration of perchlorate with tetraphenylarsonium chloride. The titration is followed with a perchlorate ion specific electrode and a double-junction calomel electrode. Best results are obtained with solutions between pH 4 and 7. The method is simple, rapid, and free from common interferences. However, extremely large amounts of some simple anions distort curve shapes and require adjustment in the titrant standardization. Accuracy and precision of the method for assaying simple perchlorate salts are equivalent to or better than available methods. Based on replicate analyses of three perchlorate samples, overall 95% confidence limits were 10.16%. In addition, the perchlorate electrode was found to respond linearly to permanganate, dichromate, and periodate ions over an appreciable concentration range.
THEAPPLICATION of organometallic salts such as tetraphenylarsonium chloride t o the measurement of perchlorate has been reported by many workers. Nezu ( I ) employed a n
amperometric titration with tetraphenylphosphonium chloride. Morris ( 2 ) described a n amperometric determination of perchlorate with tetraphenylstibonium sulfate. As early as 1939 Willard and Smith (3) proposed the use of tetraphenylarsonium chloride for perchlorate analysis, based o n a potentiometric back-titration with triodide ion. Recently, Baczuk and Bolleter (4) developed a conductometric precipitation titration of perchlorate with tetraphenylarsonium chloride, suitable for assay purposes and free from most common anionic interferences. However, there has been no published work employing any of these salts as titrants in conjunction with a n ion specific electrode for the determination of perchlorate. The availability of an ion specific electrode for perchlorate (Orion Research, Inc.) suggested the possibility of a direct (1) H. Nezu, Bunseki Kagaku, 10, 561 (1961); Chem. Absfr., 56, 26f ( 1962). (2) M. D. Morris, ANAL.CHEM., 37, 977 (1965). (3) H. H. Willard and G. M. Smith, IND. ENG. CHEM.,ANAL. ED., 11, 186 (1939). (4) R. J. Baczuk and W. T.Bolleter, ANAL.CHEM., 39, 93 (1967). VOL. 40, NO. 4, APRIL 1968
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