I
i_;_
LITERATURE CITED
I
n
100
-
90
-
-
w 60
D:
W 0
2
40 30
-
20
IO
I
I
I
I
(1) Banks, C. V., Proc. U . A'. Intern. Conf. Peaceful Uses At. Energy, 2nd Geneva, AIConf. 28, 918 (1958). (2) Barnard, A. J., J r . , Broad, W. C., Flaschka, H., Chemtst Analyst 45, 86 (1956). (3) Ibzd., p. 111. ( 4 ) Ibid., 46, 18 (1957). ( 5 ) Zbid., p. 46. (6) Brown, W. B., Rogers, D. R,., Mershad, E. A., Amos, W. R., AXAL. CHEM.35, 1000 (1963). ( 7 ) Buddhaver, S., Anal. Chem. 4 c t a 19, 551 (1958). (8) Cabell, M.J., Analyst 1952, 859. (9) Datta, S. K., Z . Anal. Chem. 148,267 (1955). (10) Flaschka, H., Abdine, H., ( " h ~ n i i s t
ACKNOWLEDGMENT
25, 1640 (1953). (13) Fritz, J. S., Oliver, R. T., Pietrzyk, D. J., Zbid., 30, 1111 (1958). (14) Haar, K. ter., ilnalyst 77, 559 (1952). (15) Levine, H., Grimaldi, F. S., U. S. Atomic Energy Comm. Rept. AECD3186 (1940). (16) Peshkova, V. M., Gromova, M. I., Slexsandrova, K,AI.. Zh. Anal. Khzm. 17, 218 (1962). (17) Pribil, R., Koros, E., ilfagyar Kern. Folyoirate 64, 55 (1958). (18) Welcher, F. J., "The Analytical Wae of Ethylenediaminetetraacetic Acid," Van Sostrand, New York, (19.57).
The authors gratefully acknowledge the assistance of R. L. Deaton and E. 4. Mershad.
R~~~~~~~ for revien- April 19, 1963. hccepted May 20, 1963.
~
direct titrations must 3e performed in hot solutions (11). Fluoride Demasking. Fluoride masking is commonly used t o eliminate t h e interference of aluminum, zirconium, a n d thorium with direct EDTA titrations. In t h e indirect determination of thorium, ammonium fluoride is used as a dtmasking agent as represented by t h e reaction: Th(EDTA)
n ere treated
with various amount> of ammonium fluoride. The solutions mere heated to boiling and titrated with a standard copper solution to the PSN end point. The results of this study, summarized in Figure 2, indicate that the mole ratio of fluoride to thorium must exceed 10 before the demasking reaction is complete.
+ 4F- F?ThFI + (EDTA)-4
To dotermine the amount of fluoride necessary to demask E D T A stoichiometrically from the Th-EDTA compie.;, standard Th-EDTA solutions
Activation Analysis for Sodium in the Sodium Tungsten Bronzes ROBERT J. REULAND' cind ADOLF F. VOIGT Institute for Atomic Resecirch and Departmenf of Chemistry, Iowa State University, Ames, Iowa
b
The neutron activation method has been applied to the ssdium analysis of the sodium tungsten bronzes. The main obstacle was the large Wls5activity which was simulianeously produced with the N a Z 4activity and which interfered with the ccunting of the latter. Destructive activation analyses were investigated in which the two activities were radiochemically separated in reactions of the bronzes with either nitrosyl chloride or bromine trifluoride. Several types of measurements b y nondestructive testing were also tried, and one o f fhese, in which the two N o s 4gamma rays were counted in coincidence in a well crystal, was found to have sufficisent precision. The accuracyof the newtron activation
method was established b y analyzing cubic bronzes for which the sodium concentrations were accurately known from x-ray analysis.
s
discovery by Woh!er (6) in 1823, the sodium tungsten bronzes have been the object of many scientific investigations. Their electrical properties have received particular attention, especially in the last decade or so. However, most inveqtigstions of their physical properties have been restricted to those bronzes which crystallize in cubic symmetry (z in Na,WO3>O.4). This restriction has been dictated by the lack of a suitable method for determining the sodium IKCE THEIR
concentration of the noncubic bronzes. I n the cubic range, the 2 value can be accurately evaluated from x-ray powder photographs, according to Brown and Banks ( 1 ) . However, in the noncubic range, it has not been possible to establish a relationship betn.een the lattice contraction and the z value. Chemical analyses of the sodium tungsten bronzes are, at best, troublesome because of the difficulty of bringing the bronzes into soluble form. Thus, although interesting physical phenomena have been observed and are anticipated in this noncubic range of the bronzes, their interpretation in terms of the Present address, Texas Instruments, Inc., Dallae 22, Texas. VOL. 35, NO. 9, AUGUST 1963
1263
Table I.
Abundance
(“2)
iitomic absorption Activation cross cross section section (barns) (barns) 0 3
100 0 26 14 30 28
the case and even with high-resolution scintillation spectrometry, the W 8 7 Na24 activity ratio was too great to allow complete separation of the two groups of photopeaks. A large part of the S a 2 ‘ spectrum is superimposed upon the slope of the photopeaks of the highest energy Wa7gamma rays as illustrated in Figure 1, a gamma-ray spectrum of a tetragonal sodium tung0.1 sten bronze (S-2-4) lvith R: which vas observed after a 10-minute irradiation. Thus. \P7presents a major interference to the assay of the Eaz4activity. The possibility of self-shielding during the irradiation of Xa,KOJ and KazIT04 was considered because of the high cross section of tungsten. E s periments designed to detect and evaluate a self-shielding effect indicated that for samples of the size bonibarded in this investigation self-qhielding n as not a factor.
Nuclear Properties of the Bronze Constituents (3, 4 )
135 41 3 64 41
99 750 0 037 0 203Y
0.54
..
...
19 2
30 19 10.0 2.0 34
...
ten(Vl) oxide melt according to the method of Ellerbeck et al. (8). For the cubic bronzes, Debye-Scherrer x-ray p o der ~ photographs n ere obtained from n hich the lattice parameters n ere preciqcly interpreted. If the Brown and Bank- relation between the lattice pa1 ameter and the .odium concentration i. wcurate (Equation 5 ) , the x valu+ of th(.se cubic bronze, are knon-n to v( ithin ~t0.003. l h e s e bronzes n ere activated, together with suitahlc standard,. in the Iowa State University UTR10 Reactor, in each inqtance operated at 10 kw., and providing a thermal flux of 8 X 10lo n cm.? X second. 1 hree gamma-ray scintillation spectrometers n-ere used for the activity mea-urementq. A Suclear Chicago Llotlel 1520 single-channel analyzer n a\ used azs an energy discriminator in certain of the counting procedure-, in connection with a Kuclear Chicaqo AIodel 186 scaler. A Radigtion Counter 1,al)oratories (RCL) 256 channel analyzer, Model 20611 nas used exten4vely, the spectral information being read out either on a Hewlett Packard Model 560A digital recorder or a Moseley Model 2D-2 s-y plotter. A w o n d multichannel analyzer, Kuclear Data Model S D 102, was also used, with read-out on an 11311 electric typewriter. From the nuclear propertie.. of the bronze constituents, summarized in Table I, it can be seen that adequate activation of sodium is possible with a neutron source of moderate intensity and that Wa7is the only interference anticipated in a short-term irradiation. It happens, hon ever, that the magnitude and nature of the IT7187 interference present a serious obstacle to the an-
...
Product half life
-
15 0 hours 140 dajs 5 5 seconds
!table ( 4 days 23 0 hours Stable Stable
29 4seconds
alysis. For the case of a bronze with = 0.1 bombarded for 10 minutes in the thermal flux of a reactor, the ratio of IV1s7to KaZ4activity is calculated to be 110. I n the decay of Saz4, gamma rays of 1370 and 2i50 k.e.v. are emitted with equal intensity (4). Gamma rays of the following energies are associated with the decay of IY18i: i 2 , 136, 206, 226, 249, 482, 510, 552, 621, 627. 686, 775. and 866 k.e.v. ( 4 ) . I t would appear that the difference in energy betiwen the 866-k.e.v. WM7 gamma ray and the 13i0-k.e.v. S a j 4 gamma raj. a ould be sufficient to permit isolation of the ?;az4 activity 11y energy discrimination. Hon ever. thi- was not 5
DESTRUCTIVE NEUTRON ACTIVATION ANALYSIS
The problem of determining the Na?‘ activity was approached from both destructive and nondestructive vievipoints. Clearly, the difficulty in destructive methods of activation analysi. of these bronzes is just that encountered in conventional chemical analysis-the bronzes are extremely inert. However, several methods have been developed for the decomposition of the bronzes, and two of these were investigated. One involved a high tem-
r .
1264
ANALYTICAL CHEMISTRY
I
I
20
40
I
I
I
80 100 CHANNEL NUMBER 60
I
120
I 140
Figure 1, Gamma-ray spectrum of neutron-activated N a , W 0 3 ( x = O.l), positioned 1.5 inches from a 3.5X 3.5-inch Nal(TI) crystal
HELIUM CAPILLARY INLET /
HELIUM CAPILLARY OUTLET
'
VACUUM-PRESSURE
bronzes with bromine trifluoride, t h e tungsten is removed as t h e volatile tungsten hexafluoride leaving t h e sodium as t h e unstable, b u t nonvolatile, sodium bromofluoride. A somewhat more elaborate system is required and adequate precautions inust be taken in handling t h e broiiiine trifluoride. However, t h e fact t h a t t h e reaction i,- quantitative with rcspect t o sodium outweighs t h c inconveniences encountered. T h e rcact ion,
THERMOCOUPLE VACUUM GAUGE
A
4
f
~r F: TRANSFER TUBE
VACUUM
REAI2TION TUBE
\
/ ~LW;b-.'NiTRocEi
Figure 2. Na,W03
TRAPS
Apparatus for BrFs separation of radioactive
(1
] m a t u r e reaction of the bronze with nitrosyl chloride and required inverse isotopic dilution; in the other the rex t i o n of the bronze with bromine trifluoride was used (6). Nitrosyl Chloride Method. I n t h e wnetion of t h e so:liuni tungsten 1~r0112cs \\-ith nitro.;yl chloride, t h e tungstcm is removed as the volatile tungstt9n oxychloride ;rtnd thc aodiuni i.; converted to sodicni chloritic accmding to t h e equatioii, S:i,\TO3 (2 2 ) XOCl +
+ +
xSaCl (2
+ WC'ZC1* + + :Yo + 2)
1/2 0 2
(1)
Howevcr, a t the temperature required for the reaction, TOO" to 800" C., some of the S a c 1 is lost through volatilization. .is a re-ult, it was necessary to inrliidc the technique of inverse isotopic clilutioii in t h r post-i:~adiation treatment of t,hc bronzes. 70determine the amount,, y (mg,). of sc'diuni Iresent in the bronze whose .;pet fir activity as a rcsult of the irradiation \vas S o counts lier minute per nig. of Ya, z nig. of noni,atlioacti\-esodium as l-a2TT'04(dilricnt) \rere added to tlie bronze and a portion of this isotopic mixture of sodium v a s iwlated as S n C l by th. above reaction i1;quation 1 j . The spxific activity of tlic S a C l x i s S per minute per ing. of Sa. Sinw t,he 1 otal activity reiiiains constant, (y z ) S = ?/So or: on re:irranging,
+
irradiation S o . 3 two standards were used. Following the irradiations, the samples and standards were weighed into small porcelain combustion boats and inactive Sa?TY04was weighed int,o the boats containing the bronze samples. .I microbalance was employed for all post-irradiation n-eighings. The boats were placed in 7-mm. i.d. quartz tubes and heated in a tube furnace to 800" C. for 7 5 minutes in an atmosphere of SOC1. Gamma-ray spectra confirmed a complete radiochemical separation in each case. The S a g 4 activity of the samples and standards was assayed under identical geometry conditions with a 2- x 2-inch SaI(T1) c r p t a l detector and the Ringle channel analyzer, which was set to discriminate against all energiej less than 1.0 m.e.v. The statistical counting errors were less than 1%. The S a C l weights were determined by weighing the boats before and after the removal of the S a C l with nater and were used to calculate the .specific activitie;, SOand S , and the z values using Equations 2 and 3. The results of this analysis of the bronze S-2-.4 given in Table 11, shorn an average value of .T of 0.0991 10.0016. The standard dcvintioii of t h r individiial analyse? waq =0.0056, Bromine Trifluoride Method. I n the reaction of t h e sotliiini turigstcn
Table II.
'Hie -odium content n a - then coni erted to an .L' value, awmiing the t u n q t c n to oxygen ratio of the bronze to bc 1.3. using the relation,
Irradia-
tion 1 2
3
in which 10 is the weigllt of the Ixonze sample Ten samples of the bronze S-2-.1 were activated in five irradiations lasting from 3 t o 5 miiiuteq. -4 single S a 2 W 0 4standard mas irradiated in the same c a p u l e in each case, except that in
4 7
-4v*
+
z) Br2
+3
0 2
(4)
conducted under helium in the silicate glass system shown in Figure 2 . I n most instances, it was necessary to Ivarm the reaction tube tBo80" to 90" C. to cause the reaction to go to completion in a reasonable time. Following the reaction, the sodium lx-oniofluoride was isolated by pumping the volatile tungsten hexafluoride, liramine, and excess bromine trifluoride into the traps. This procedure could possilj!y hc used without activation by neighing tlie residual SaRrF4. However, the stoichiometry and stability of this compound are somewhat in doubt and such a method has not been shoxn to be quantitative. With activation analysis the exact formula of the residual material is immaterial as long as the ,sodium iij quantitatively retained. TKO irradiations lasting 5 and 10 minutes were performed on five sample. of the bronze S-2-.1 and four Xa2TT70, standards. The samples wertl then weighed into the reaction tubes and 0.05 ml. of hroinine brifluoride was added. Following the reaction, the gamma-my spectra which were obsen-ed confirmed a completc radicaration iii each caze. The \vas assaj-ed in a well-type the single channel analyzer to di~criniinate against cnergies < I .O
Analysis of Bronze N-2-A b y NOCl Method and Isotope Dilution
Kt. Xa,WO3, mg. ( E )
21.136 s ,852 9.519 2; ,338 26 ,949 21 ,739 24.908 2 6 , I39 29 ,099 24.650
4 715 4 IO6 4 414 4 022 3 863 4 264 4 0.30
6736" 12165 11643
313 0 423.1 302 . 4 657. 3 731.3 721.3 628.4
0 0'325 0 1117 0 0971 0 0939 0 0964 0 0985 0.0956
2304 2%53 2074 2298 0 2475 0 2816 0 231.5 0 0 0 0
0,0991 (h0.0016)
.kverage of two standard?.
VOL. 35, NO. 9, AUGUST 1963
1265
Analysis of Bronze N-2-A b y BrFl Method
Table 111.
Irradiation
Specific activities Sample, S' Standard, SO c.p.m./mg. Na,WOI c.p.m./mg. Na 574 557 565 390 389 393 391
1 AV
->
X
58497 58780 58640 f 140 41165 39421
1 4 8 8 4 5 2 3 0 i1 2
+
0 0982 i 0 0015
10290 f 870
0 0988 f 0 0022 0 0013
AV 0 0985
Table IV.
No. of Irrd. 1
2 3 1 3
samples 2 3
2 3 3
Standard K:nF
NaF NaF NatWO, XalWOr
+
Nondestructive Analysis of Bronze N-2-A KO. of standards
3
3
3 3 3
Specific activities Sample Standard 301 7 f 6 . 9
307.1 + 4.0
+ +
147.4 7 . 1 575.8 f 1 . 9 550.4 8.4
32140 f. 150 31060 i ii0 15310 =t130 58620 f 430 56080 == ! 520
4V.
m.e.v. and counting to a statistical error of
