centration us. logarithm of the oxalate ion activity is shown in Figure 2. The points define a smooth curve having the shape expected from the theoretical prediction. The formation of the trioxalate complex with yttrium is somewhat surprising because Crouthamel and Martin found no evidence for the corresponding complex with >+,terbium or neodymium. This lack was ascribed to steric factors
because both these ions are smaller than cerous, which did form the trioxalate. Yttrium is smaller than the rare earth ions studied by Crouthamel and Martin ( I , 2) and in oxalate precipitations behaves as if it were smaller than all of the rare earth ions, yet the third complex is formed. LITERATURE CITED
(1) Crouthamel, C. E., Martin, D. S., J. Am. Chem. SOC.72, 1382 (1950).
(2) Zbid., 73, 569 (1951). (3) Freedman, -4. J., Hume, D. S . , Science 112, 461 (1950). (4) Kahn, B., Lvon, W. S., Phws. Rev. 98, 58 (1955).
(51 Korthincr. A. G.. Geffner. J.. “Treatment of -Experimental Data,’’ pp. 72-5, Kiley, Kew York, 1943. ~
RECEIVEDfor revieq- August 14, 1957. Accepted May 28, 1958. Research supported in part by the U s. Atomic Energy Commission.
Determination of Boron in Aluminum-Uranium Fuel Elements Application of the Carminic Acid Spectrophotometric Method KENNETH W. PUPHAL, JAMES A. MERRILL, GLENN L. BOOMAN, and JAMES E. REIN Atomic Energy Division, Phillips Petroleum Co., lduho Falls, lduho
b A rapid spectrophotometric method is described for the determination of boron in aluminum-uranium alloys, particularly in nonirradiated reactor fuel element samples. After dissolution of the sample in hydrochloric acid and hydrogen peroxide, the boron is determined without separation, by the carminic acid method. The complexes that uranium and aluminum form with carminic acid have weak absorbances a t the working wave length of 585 mp. Compensation is easily made by including uranium and aluminum in the blank. Under routine conditions, the precision is about 2% standard deviation for reactor fuel containing 0.1 weight boron. A sodium carbonate fusion pretreatment is described for boron analysis in an alloy of aluminum and boron carbide and in boronimpregnated polyethylene tape.
yo
I
fuel technology, the use of burnable poisons such as boron is gaining popularity. The range of reactivity over the life of the fuel is decreased and a more uniform flux distribution is obtained. The fuel of the Engineering Test Reactor (ETR), located a t the Kational Reactor Testing Station in Idaho, contains 83.6y0 aluminum metal and 16.4% uranium metal by weight, with about 1mg. of elemental boron per gram (4). The aluminum is grade 25 and the uranium is highly enriched (>goy0) in the 235 isotope. An alloy of aluminum and uranium metals and boron carbide, prepared by poq-der metallurgy techniciue, is being considered for the future. Satisfactory power output and neutron flux distribuN REACTOR
1612
ANALYTICAL CHEMISTRY
tion of the reactor requires control of both total boron content and boron distribution in the fuel. This requires that many samples be analyzed. Samples of polyethylene tape impregnated with boron are also submitted for boron analysis. This material is used experimentally t o measure reactivity of various fuel element arrays. This work was undertaken to find a rapid and precise method applicable to the three types of samples. One of the specifications for ETR fuel is a limit on the composition of the alloy. The allowable variation in uranium content is on the order of 2 relative %. This corresponds to absolute limits of 0.3 weight % in both the aluminum and uranium. With the ratio of both aluminum and uranium thus restricted, and the need for a rapid method, the choice was made to find a n existing method which could be adapted without preseparations. Spectrophotometric and emission spectrographic methods appeared most promising, The common volumetric method involving titration of a n invert sugar-boric acid complex with standard alkali does not tolerate aluminum and uranium. Spectrophotometric methods based on the chromogenic agents dianthramide ( 5 ) , diaminoanthrarufin (S), and carminic acid according to Hatcher and Wilcox ( 7 ) , were selected because aluminum and uranium were expected not to interfere. The latter method proved most applicable. Direct spark excitation of sample surfaces was not successful because boron n a s found to be segregated in many of the samples. Spark excitation of solutions after acid dissolution m s less pre-
cise and no faster than the spectrophotometric method finally adopted. APPARATUS
A Beckman Model B spectrophotometer was used with matched or calibrated I-cm. Corex cells. Low-boron, Corning 7280 glassware or quartzware was used for sample dissolutions. Dissolutions %-ere made under reflux to prevent loss of boron. Fusions were made in platinum crucibles with covers. Dissolved samples were stored in polyethylene bottles until analyzed. REAGENTS
Reagent grade chemicals were used unless otherwise stated. Distilled water, boron-free, was used throughout. An aluminum-uranium matrix, with the same aluminum and uranium concentration as dissolved and diluted E T R fuel samples, was prepared by dissolving 22.1 grams of a n 81.5% 2 s aluminum-18.5% uranium alloy (the individual metals can be used), and 2.9 grams of 2s aluminum in 600 ml. of 5 N hydrochloric acid. dfter dissolution was essentially complete, 50 ml. of 30% hydrogen peroxide was added. The excess hydrogen peroxide was removed by boiling, and after cooling, the solution was diluted with water to 1 liter. A standard 0.100 mg. per ml. boron solution n-as made by dissolving 0.5716 gram of orthoboric acid (H3B03). in distilled water and diluting to 1 liter ( 7 ) . Boron oxide, prepared by fusing boric acid, also can be used. The 0.05% (w./w.) carminic acid reagent was prepared by dissolving 0.920 gram of carminic acid in 1 liter
of 96yo sulfuric acid. The carminic acid was obtained from National Aniline Division, Allied Chemical and Dye Corp., 40 Rector St., Keiv York, a s C. I. Xo, 1239. PROCEDURE
Dissolution of Aluminum-Uranium Elemental Boron Samples. Dissolve a weighed 0.5- t o 2-gram sample under reflux, using 10 nil. of hydrochloric acid and 15 nil. of water per gram of sample ( 2 ) . After dissolution is essentially complete, add 2 nil. of 30% hydrogen peroside per gram of sample ( 2 ) . Boil (under reflux) to remove t'scess peroside. cool: and transfer to a graduated cj-linder. Dilute with distilled water to a volume equal to 40 times the weight of the sample in grams. Filter. and store in a polyethylene bottle. Small amounts of insoluble material obtained on some samples n-ere found by spectrographic :uialysis to be silicon and aluminum fwe of boron. An aluminum-silicon eutectic alloT- is used a,? a bonding matwin1 in fuel elements. Fusion of Boron Carbide-Containing Alloy and Polyethylene Tape Samples. Add ahout 1 gram of ashless cellulose 1):tp~rand dissolT-e a weighed sample of t h e alloy. (containing 1 t o 5 mg. of I ) o m i . in a covered quartz beaker with t h e came volumes of hydrochloric acid a n d \rater used above. Boron carhide quantitatively remains as a n irisoluble residue adsorbed on t,he paper. Filter with a fine grade of filter paper, surh as TTliatman S o . 42, and wash srvernl times with cold n-at,er. (Filtrntes spectrographically analyzed \vere ~:oiu~iletely free of boron.) Ash in a plntinuni crucible. Add 4 grams of fiiwly groiiiid sodium carbonate, cover tlrr rrucible. and fuse for 15 minutes a t 900" C. Dissolve the melt in water miti acidify n-ith 20 ml. of hydrochloric acid. Transfer to a 100-ml. volumetric flask and dilute to volume with water. Slowly burn a 11-eighed polyethylene tape sample containing 1 to 5 mg. of boron in a platinum crucible. Add 0.5 gram of finely ground sodium carhonate, cover. and quickly fuse over a flame. Continue as for boron carbide samples. Spectrophotometric Analysis. Pipet a n aliquot of a n y of t h e diluted samples, cont'ainiiig 0.01 t'o 0.07 mg. of boron. into a 25-nil. volumetric flask. Because color development must be made in strong sulfuric acid, the masiniuni aliyuot is 2 ml. If t h e aliquot is less than 2 nil., add water t o 2 nil. Add 2 drops of hydrochloric acid and mis. Place in an ice bath and add 10 nil. of cold sulfuric acid. Boric acid is volatilized from warm acid solutions. Shake until gas evolution ceases. Remove from the ice bath, and after room temperature is reached, add 10 mi. of the carminic acid reagent. Let st'and for 1 hour, dilute to volume with sulfuric acid, and measure absorbance a t 565 nip compared with a blank set' a t zero absorbance. The blank for aluminum-uranium elemental boron samples is an aliquot of
the aluminum-uranium matrix solution equal to the sample aliquot. Water serves a s the blank for sodium carbonate fused samples. Calibration. Add aliquots of t h e standard boron solution, ranging from 0.1 t o 0.7 ml., into 25-ni1. volumetric flasks. Add water t o give a total volume of 2.0 ml. a n d use 2 ml. of water as t h e blank. Continue with t h e spectrophotometric analysis. T h e method of least squares is reconimended for calculation of t h e calibration equation. EXPERIMENTAL AND DISCUSSION
Dianthramide and Diaminoanthrarufin Methods. Seither aluminum nor uranium formed optical absorbing complexes n i t h these reagents. H o n ever, aluminum sulfate is so slightly solublein concentratedsulfuric acid, t h e medium required for both methods, t h a t a prescparation n as necessary for t h e aluminum-uranium elemental boron samples. T h e aluniinum sulfate precipitate tended to be colloidal in nature and difficult to separate bv centrifugation or filtration. Satisfactory separation n'as obtained by vacuum filtration through glais mat filters but took mor? than an hoiir. Carminic Acid Method Studies. T h e spectra of t h e reagent and of the boron complexar egiven by Hatcherand TTi1co.i ( 7 ) . The wave length of masimum absorbance for the boron complex is 585 nip. The absorptivity of the boron complex a t this nave length, under the condition$ of the proposed procedure, is 385. EFFECT OF ALLXIXUIIA N D L-RAXIUX. Both these elements form weakly ab~ carminic acid. sorbing conipleses ' r ith A designed factorial experiment was made to establish the effect of a change in aluminum-uranium coniposition of the ETR alloy a t five times the specification limits on the proposed procedure. Uranium and aluminum concentrations were varied a t two levels corresponding to a l.670 absolute change from the normal composition of the alloy. The strength of the carminic acid reagent was varied a t t n o levels of 0.05 and 0.170 (w./w.) to establish whether uraniuni and,'or aluminum w r e reacting with the reagent in a manner to prevent complete reaction with boron. Boron concentration \?-as varied a t four levels t o establish linearity of alwrbance response as a function of boron concentration. The rrgression equation is: A
=
13.27 X-1
+ 0 0042% + 0 2181 + 4T.M XlXg - 0.01583 X2
x73
in 1% hich
A XI Xz X3
= = = =
absorbance boron concentration aluminum concentration carminic acid strength
Table I.
Effect of 2s Aluminum Impurities on Method
Impurity
__Copper Trnn -..
Manganese C hroniium Sickel Tit anium Zinc
Amount Added, Absorbance c-a /C Increase 1 0
0 2
0 1 0 05 0.05 0.05 0 05
0 000 0.004 0.002 0 001 0.000 0,001 0.000
a Impurities were added in amounts equivalent to those obtained in a sample processed according to the proposed procedure.
The boron aiid aluminunl conceiitrations are expressed in milligrams per 25 ml. of final volume. A statistical analysis of variaiiccl indicated the carminic acid strmgth to be significant-Le., the absorbance increased with increascd strcngth. The significant interaction of boron conccntration and carmiiiic acid strmgth means that the incrmsc of absorbance n ith increasing boron concentration (slope of the norking curve) n a - tlifferent for diffrrent levels of carniinic acid strength. For both carminic acid levels, the absorbance was linear T\ it11 boron concmtration over the range studied. Thii range n a b 0.01 to 0.07n mg. per 25-11-11. final x olunic. The change in absorbance as a fiinctlon of changing aluminum concentration 11:is small; that for uranium n a5 insignificant. A d e ~ i a t i o nof 1.6 absolntr % in aluminum content of E T R fuel changed the absorbancf only hr 0.001 a t the 0.04-mg. boron level. This shon ed t h a t the carminic acid method could be applied directly to dissolwd ETR fuel samples m-ith nobeparations required, merely by including sample levels of aluminum and uranium in the reference blank. Tlie efEFFECTOF D I T E R ~Iom. E fects of the impurity ions of 2s aluminum, the grade used for E T R fuel. n ere investigated. Specifications for this grade are minimum 99.2y0 aluniinmn, less than 1% iron aiid silicon, 0.2% copper, 0.17c manganese, and a maximum of 0.05% each but not greater than 0.15% combined of chromium, nichel. titanium, and zinc. The upper limit was tested for each impurity in the method, except silicon, by adding the chloride or snlfate salt to a boron-frce and aluminum-free blank and comparing the absorbance to the blank. Silicon is insoluble in hydrochloric arid, the d i q solution medium. The data are given in Table I. At the lm el> studitd, all t h r impurity elements give color, escept titanium ant1 zinc. Dissolved samples hai-e a l a a i s been free of impurity colors; hence the VOL. 30, NO. 10, OCTOBER 1958
1613
effects of 25 aluminum impurities were considered insignificant. Batches of 25 aluminum were spectrographically analyzed and found to contain less than the detection limit of 10 p.p.m. of boron. Boron in blanks is therefore less than 1% of the boron measured in samples. FUSIONCONDITIONS.Sodium carbonate fusion has been recommended (1, 6) for dissolving boron carbide. A factorial experiment was made t o establish effects of fusion variables. Levels of sodium carbonate were 2, 3, and 4 grams; fusion times were 15, 20, 25, and 30 minutes; amounts of boron carbide were 3.5 and 11 mg. Temperature of fusion was constant a t 900°C. in a muffle furnace. Covered platinum crucibles were used. Statistical interpretation of the data indicated no significant variables; any combination of amount of sodium carbonate and fusion time gave quantitative boron recovery a t both boron carbide levels. The minimum time was chosen for the proposed procedure. The maximum level of sodium carbonate was
selected to ensure adequate mixing by different analysts.
puted standard deviation n-as 1.8%. This agrees well with the predicted value of 1.4% from the calibration data.
PRECISION
An actual calibration equation based on nine standards for the proposed procedure is A = 15.62 B
+ 0.0103
in which A = absorbance B = mg. of boron in final 25 ml. The standard deviation of the intercept was 0.0057. A t test indicates the intercept not to be significantly different than zero. The standard deviation of the absorbance was 0.0079. This corresponds to 1.4y0standard deviation a t about the mid-point, 0.03 mg. of boron, of the calibration curve. Another estimate of the precision was calculated from a series of control samples submitted a t the rate of one per week over a 2-month period. These samples were analyzed by personnel trained under the laboratory’s Training and Testing Program (8). The com-
LITERATURE CITED
(1) American Society for Testing Ma-
terials, Philadelphia, “ASTJI Methods for Chemical Analysis of Metals,” 1950. (2) Churchill, H. V., “Chemical Analysis of Aluminum,” 3rd ed., p. 30, Aluminum Research Laboratories, X e r Kensington, Pa., 1950. (3) ‘Cogbill, E. C., Yoe, J. H., Anal. Chim. Acta 12, 455 (1955). (4) Dempsey, R. H., Jacobson, J. J., Levy, S., Wolfe, B., .Yudeonics 15, KO.3, 44 (1957). (5) Ellis, G. H., Zook, E. G., Baudisch, O., ANAL.CHEM.21, 1345 (1949). (6) Furman, iY. H., “Scott’s Standard Methods of Chemical iinalysis,” 5th ed., p. 181, Van Xostrand, Yew York, 1939. ~. -
( 7 ) Hatcher, J . T., Kilcox, L. V., A i i . 4 ~ . CHEM.22, 567 (1950). (8) Huff, G. B . , Tingey, F. H., Ibid., 29, 19A-22A (August 1957). RECEIVED for reviev December 16, 1957. Accepted June 9, 1958. Kork was done under Contract So. AT(10-1)-205 for the U. S. Atomic Energy Commission.
Volumetric Determination of Thorium in Uranium Alloys HOBART
H. WILLARD,’
ARTHUR W. MOSEN,2 and ROSS D. GARDNER
The University of California, 10s Alamos Scientific Laboratory, Los Alamos, N.
b Thorium is determined in uraniumthorium, uranium-tungsten-thorium, and uranium-titanium-thorium alloys by precipitation as the fluoride, using lanthanum as a carrier, followed by titration with EDTA. Eriochrome Cyanine RC is used as the indicator in the titration. In 161 determinations of known solutions simulating the above alloys with a thorium content of 0.1 to 3.0%, an average of 99.4% of the thorium was found. The relative standard deviation for individual values was 0.5670 with no significant difference in the various synthetic solutions.
T
investigation was initiated because of a need for a n analytical iiiethod t o determine 0.1 to 3y0thorium in uranium alloys which might also contain tungsten or titanium. N o s t of the older accepted methods for the determination of thorium are gravimetric (4, 6). A large number of insoluble compounds have been used in separations, but the element is usually HIS
1 Present address, University of Michigan, Ann Arbor, Mich. * Present address, General Atomic Corp., San Diego, Calif.
1614
ANALYTICAL CHEMISTRY
M.
weighed as the oxide after ignition. The oxalate method, which has been used in this laboratory for the determination of thorium in uranium alloys, has not been satisfactory for alloys containing less than 0.5% thorium because the loss due to solubility becomes significant (6). Increasing the size of the sample is impractical because of the limited solubility of uranyl oxalate. A spectrophotometric procedure ( 7 ) is available for very small amounts of thorium in uranium, but it lacks the precision required for the range under consideration. Furby ( 2 ) gives a procedure for determining larger amounts of thorium in uranium using a titration with E D T A [disodium (ethylenedinitrilo) tetracetic acid] after a separation as the benzoate. However, the benzoate precipitation involves a troublesome adjustment of p H and is an incomplete separation of thorium from a number of other metals. The precipitation of thorium fluoride in the presence of other metals has been described by Grinialdi and Fairchild (3). They showed that it was a good separation from uranium and certain other metals such as tantalum, niobium, titanium, zirconium, and iron. B y using
a carrier they obtained quantitative recoveries of less than milligram amounts. Fritz and Ford ( I ) investigated the titration of thorium Kith E D T A using Alizarin Red S as the indicator. A combination of these two processes, as described in this paper, has afforded a rapid and accurate procedure for the determination of thorium in uranium alloys. The thorium fluoride with a carrier of lanthanum fluoride is ignited to the oxide, dissolved in nitric acid, and evaporated with perchloric acid. The solution is adjusted to a p H of 2 and titrated with EDTA using Eriochrome Cyanine as indicator. APPARATUS A N D REAGENTS
Polyethylene beakers, funnels, and stirring rods were used where hydrofluoric acid solutions were involved. Other items were standard laboratory equipment. All chemicals used were analytical reagent grade. Ammonium Fluoride Solution. A 10% solution was kept in a polyethylene bottle. EDTA, Standard Solution. A 0.025M solution was prepared by dissolving 9.3088 grams of dry, reagent quality, disodium (dinitrilo) tetraacetate in water and diluting to 1
