1632
ANALYTICAL CHEMISTRY
vantage that the properties of such a chamber can be appreciably altered by small amounts of impurities in the gas filling. For example, the size of the plateau or its position as far as voltage is concerned varied with impurities. A t times the plateau was practically nonexistent. Often, trace amounts of impurities cannot be controlled without a considerable amount of effort. For this reason, the use of this approach was very limited. The third method, which was considered and used to an even more limited extent, was essentially one used by Walker ( 3 ) . It consisted of placing a cylindrical cell of boron-containing material in solution, suspension, or gas around a neutron counter and measuring the neutron attenuation produced by the boron. This approach has not been used very much for isotopic analysis, mainly because rather large samples are necessary if reasonable accuracy is desired. Therefore, comments in this discussion are confined to the scintillation method of analysis, Figure 1 gives the counting rate us. the pressure of the boron hydride in an earlier scintillation cell of 21-ml. volume. This variation is not linear, especially a t higher pressures. Spot checks showed that the newer cell of 7-ml. volume described above exhibited the same b e h a v i 8 presumably because of the absorption of the alpha particles by the gas in the cell. I n routine analyses, pressures of about 11 cm. for diborane and 4 em. for pentaborane have been used. -4plot of the counting rate us. boron-10 content is given in Figure 2. I n this calibration curve the isotopic content was taken from mass spectroscopic measurements. The plot is linear over the range of interest and, in many instances, if the counting rate was measured a t 18.8 and 96% boron-10, the straight line drawn through these points gave very satisfactory results for boron hydrides containing intermediate isotopic concentrations. I t appears from experience to date that the boron-10 content can be determined by this method to within 1%. The total amount
of boron required for the analysis was about 1 mg. I n checking the reproducibility of results a number of different fillings and measurements were made on penta- and diborane and all results checked to within 1%. Most of the measurements were routinely made on diborane and pentaborane; however, some have been made on dihydropentaborane and tetraborane. Although the results indicated that this method of analysis was also applicable to the latter gases, experience with these materials has not been sufficiently extensive to quote the data a t this time. ACKNOWLEDGMENT
This research was supported by the United States Air Force through the Office of Scientific Research, Air Research and Development Command. One of the authors (R.P.H.) wishes to acknowledge the support of the H. A. B. Dunning Fellowehip throughout the 4 years of his graduate research. The authors also wish to acknowledge their appreciation to Lewis Friedman, Brookhaven National Laboratory, and Harold C. Mattraw, Knolls Atomic Power Laboratory, for the mass spectroscopic measurements. LITERATURE CITED
(1) Koski, W. S., Maybury, P. C., Kaufman, J. J., ANAL.CREM.26, 1992 (1954). (2) Shapiro, I., Weiss, H. G., Skolnik, S., Smith, G. B., J. Am. Chem. Soc. 74, 901 (1952). (3) Walker, R., Manhattan District, Declassified Document, MDDC 362 (1940). RECEIVED for review March 22, 1956. Accepted M a y 22, 1956. Division of Physical and Inorganic Chemistry, 129th .Meeting, ACS, Dallas, Tex., April 195G.
Potassium Determination with the X-Ray Spectrograph L. B. GULBRANSEN Mechanical Engineering Department, Washington Universsity, St. Louis,
A procedure has been developed using the x-ray spectrograph, in which potassium K radiation is used for the quantitative analysis of potash concentrates and tailings. Two working curves were established by a series of standard samples over the ranges 0.8 to 18.2Yo and 57.8 to 60.5Yo potassium oxide. X-ray spectrographic results are in agreement with chloroplatinate chemical analyses to within 0.4% potassium oxide. The total time for analysis, after the samples have been ground, is 6 minutes for tailings samples and 3 minutes for concentrates.
D
ETERMINATIOS of potassium or potassium oxide in potash concentrates and tailings by chemical methods involves a number of separation steps, and these methods, although reliable, may not be suitable for control of plant processes because of the rather long analysis times involved. The x-ray spectrograph can be used to reduce the time of analysis of potash concentrates to about 3 minutes, and potash tailings to about 6 minutes, once a R-orking curve has been established. APPARATUS
A S o r t h American Philips x-ray spectrograph with a tungsten x-ray tube and sodium chloride analyzing crystal was used
Ma.
through the analytical work. The following operating conditions were used. Target Analyzing crystal X-ray tube operated at Operation of scaler Scale factor, potash tails Scale factor, potash concentrates Geiger tube operated at Analysis line
Tungsten Sodium chloride 50 kv., 40 ma. Fixed count 16 32 1500 volts
Potassium K , 83.07' (2 0 )
The long wave-length K radiation of potassium is strongly absorbed by air, so that the x-ray path had to be enclosed in a plastic bag and flooded with a gas of low atomic number. I n this work helium gas was used. In setting up the spectrograph for work in a helium atmosphere, it was found that the helium pressure, or rate of flow of helium through the system, had a marked effect on the counting rate for potassium K radiation. Higher pressures and more rapid rates of flow of helium in the chamber increased the counting rate appreciably. Because of the irregular shape of the Geiger tube, holder, and analyzing crystal, it was difficult to construct a soft plastic bag that was completely gas tight. However, it was simple to construct a soft plastic bag around the system, using a plastic tape, with a slight
VOLUME
NO. 10, O C T O B E R 1 9 5 6
28,
1633
52-
*
t
4 7 c
/. J
ul I-
z 32-
0 0
0 U
.
27r
t '
92
I /
/
82 1 57
171-
/a
-.
~ _ _ _ _ _ _ _ ~
-.
15
1 I 58 59 60 61 P E R C E N T POTASSIUM O X I D E
Figure 2.
I8
PER CENT POTASSIUM OXIDE
Figure 1.
Working
curie
I 62
Working curve for potash concentrates
for potash tailings .
Table I .
amount of leakage around the base of the ( h g e r the highest part of the enclosed path.
t i i b
holder
at
Potassirrm Chide %
1st day
~-
.
.
~-
Counting Rate Count8 per Second 3rd d a y
2nd day
-
.-
A V.
Standard Potash Tailings (Total Count, 6400)
IIelium gas was allowed to How from inlet) at tha samplr holder to outlet) a t the Geiger tube at, some constant rat'e. A constant flow of helium was maintained from day to day, using a Fischer and Porter Type TLK-19 Howmeter, and adjusting t h r rate of flow to 3700 cc. per minute. A rate of helium flow of 3700 cc. per minute was selected hecause a t this rat,e, for the chamber used, the rounting rate varied only slightly with slight increase or decrease in helium flow. This indicated that all or nearly all of the air was displaced from the chamher. With this type of chamber, reproducible counting rates were possible, once the spect,rograph had been aligned (1).
0.8 2.4 4 , .5 6.fi 14.0 18.2
18.6 19.8 25.4 28.3 42.0 50 9
16.1
22.8 2.5.3 29.8 43.0 50.6
18.1 22.8 27.0 29.8 42.8 50.3
17.6 21.8 25.9 29.3 42.6 50.6
Standard Potash Concentrates (Total Coiint 12,800) 57.8 .IS,5
60.0 fi0.4 61 .n 61.5
83.0 87.8 98.6 103.3 107.8 111.0
rs2.0 86.4 98. I
inz.1 1013.4
112.5
81.3 86.2 98.6 103.3 106.2 112.5
82.1 86.8 98.4 102.9 106. 8 112.0
METHOD
.i series of Hotation concentrates and tailings was used in constructing the working curves for the x-ray spectrograph. Both series, analyzed by the chloroplatinate method, were ohtained from the laboratories of the Southwest Potash Corp. a t Carlsbad, S . M. The matrixes of the samples were thoroughly dried and ground to -200 mesh in a disk-typc pulverizer. Because both sodium chloride and potassium chloride are relatively soft materials, the amount of iron contamination in grinding t o this particle size range was negligihlc A11 samples were ground in the same manner, so that any possible contamination was essentially constant throughout the samples. I n order t o reduce the probable statistical error in counting. four readings on each sample were taken consecutively vithoiit resetting the interval timer or scaler circuits.
Table 11. Comparison of Chemical and X-Ray Spectrographic Determination of Potassium Oxide Counts per Second 20.0 23.1 32.6 103.7 109.0
% Potsmiurn Oxide X-ray spectrograph Chloroplatinste 1.4 3.2 8.5 60.6 61.2
1.8 3.2 8.2 60.9 61.5
ANALYSIS OF POTASH SAMPLES F'ORKIXG CURVE
Two series of samples ranging in potassium oxide content from 0.8 to 18.2y0 and 57.8 to 61.5% were used in constructing the working curves. Counting rate readings were taken over a 3-day period and the results were averaged to obtain the final working curves. S o background correction was found necessary in the construction of the working curves, as absorption and scattering by the matrix material (primarily sodium chloride) were low and essentially constant. The presence of higher atomic numbered elements would be expected to alter the slope of the curves given in this paper ( 2 ) . The result? of t,his Pcries of data arc given in Table I and I'igrirc? I ant1 2.
Three tailings samples and two concentrates which had been analyzed by the chloroplatinate method were analyzed by the s-ray spectrograph. The results of this work are given in Table
11. CONCLUSIONS
The xvorking curves for both potash tailings and concentrates established on the x-ray spectrograph follow a straight line, and the results are reproducible to within statistical fluctuations in counting. Results based on the spectrographic method agree with chloroplatinate analyses to within 0.4y0 potassium oxide for tailings samples, and 0.3% potassium oxide for concentrates that could bc chpcked by this method. Using a larger scale factor for the
1634
ANALYTICAL CHEMISTRY
potash tailings samples might be expected to increase the accuracy of the spectrographic analysis for potash tailings, but also increase the total time of analysis per sample. Samples must be thoroughly dried before grinding, and preferably ground to -200 mesh. Early in the experimental work it was found that grinding to - 100 mesh resulted in a fairly wide scatter of points on the n-orking curve. By grinding thoroughly dried tailings and concentrates to -200 mesh, this scatter was practically eliminated. -4rate of helium flow was established a t 3700 cc. per minute for obtaining the working curves given in this paper. Different types of plastic or rubberized chambers, with rates of helium flow other than 3700 cc. per minute would be expected to give working curves with different slopes than those shown in Figures 1 and 2, but if a constant helium flow or constant helium pressure
can be maintained in the chamber, equally reproducible curves should be possible. Sample handling, after grinding, is at a minimum, the only handling required being to place the sample (approximately 15 grams) in the plastic sample holder. By keeping the surface of the samples a t the same level, and using the same surface area, samples of smaller size or liquids could also be counted. LITERATURE CITED
(1) North American Philips Co., Inc., ?;en. York, X . Y.,“Operating
Instructions for the X-Ray Spectrograph,” 1952.
(2) Shamsuaanian, N., “Effects of High -Atomic ?;umbered Elements
and Particle Size on Working Curves Established by the X-Ray Spectrograph,” .\I. S. graduate thesis, Department of Metallurgy, Colorado School of .\lines. 1954. RECEIVED for reiiew February 1’. 1956. .\ccepted June 11, 195G.
CRYSTALLOGRAPHIC DATA
136. Diammonium Diuranyl Trisulfate Pentahydrate, (NH4),(H0,),(S04),.5H20 EUGENE STARITZKY, DON T. CROMER, and D. 1. WALKER’, The University of California, Los Alamos Scientific Laboratory, Los Alarnos, N. M.
diuranyl trisiilfate pentahydrate crystallizes from Daqueous solutions of the component sulfates. .4ccording to IAMMONIUM
Colani (1) the stability range of this double salt at 25’ C. extends between molar ratios UOnS04:(XH4)2S04= 53 to 3.27. CRYSTAL MORPHOLOQY System and Class. Orthorhombic, dipyramidal. Axial Elements. a:b:c = 0.897: 1: 1,010 (derived from unit cell dimensions).
Partial Powder X-Ray Diffraction Pattern of
(NH~)z(U~Z)~(SO~)~.SH~O h kl
in1 o2n in2 201 210 022 122 221 03 1
103
z
301 222
311 230 123 132 040
d , A., Caled. 8.63 6.43
5.66 5.27 4.569 4,248
4.077’ 4.0711 4 . 0 5 4J
3.688 3.582 3.5451 3.4411 3.429L 3.4171 .’3 , 2 13
d . A.; Obsd.
,/I, h 10 100 20 25
8.54 6.39 5.64 5.26 4.5.5 4 , 23
10 40
LO5
:. ii
3 . 67 3.56
10
in
3,42
15
3.20 3.11 3.04
40
2.81
30 40
“0 10
2.81 2.62
2n
2.57
‘5
2.3fi 2.24
15 2.14 25 4 Philips 114.6-nim.-diameter powder camera, Strauinanis mounting; A ( c ~ K=~ 1.5418 ) A. b Relative Deak intensities abo7.e background froin densitometer measurements.
Orthographic projections on (100) and parallel to b of crystal of diarnnionium diuranyl trisiilfate pentahydrate
Habit. Tabular (100) with (101} and ( O l l } . Polar Angles. (lOO)A(lOl) = 41’37’; (OTl)A(Oll) = 90”34’.
X-RAYDIFFVAACTION DATA Diffraction Symbol. mmmPna-. Observed development of crystal forms and failure to detect a piezoelectric effect make it probable that the space group is Pnma (0::).
CellDimensions. al = 11.54A.: bo = 12.86A.; co = 0.897:l:l.OlO. Cell volume 1928 A?. Formula Weights per Cell. 4. Formula Weight. 954.50. Density. 3.29 grams per cc. (s-ray).
=
12.99A.;
a0:bo:co
OPTICAL PROPERTIES Refractive Indices (5893 A . ) . n x = 1.560; n y = 1.582; n z 1.583; geometric mean 1.575. llolecular refraction 95.9 cc.
=
1 Present addresa, Department of Chemistry, Unirwsity of Colorado Boulder, Colo.
