806
ANALYTICAL CHEMISTRY
50 Rockwell C. Occasionally the face deforms a t this hardness, but plugs which have been used for 50 or more runs a t 10,000 to 12,000 atm. are still in service. The face of the plug is surface ground and lapped on 0000 emery paper. I t is convenient to screw the plug into a lapping block 11/2 to 2 inches in diameter, which prevents curvature of the surface. iThen the window seats on the plug and cannot be blown off orally from underneath, or when the plug can be picked up by lifting the window, without separating window and plug, the seal is satisfactory for even the least viscous liquids. The brass cap is useful for holding the window in place during assembling and dissembling, and while applying pressure. The plugs can be sealed in the bomb using steel unsupported area rings as described by Bridgman (1). The window spacing can be varied from less than 1 mm. to 1 em. or more by varying the ring thickness. Linde synthetic sapphires make convenient windows. The standard mindow used for this work was l / 2 inch in diameter and ' / 2 inch thick. It is important that the C axis of the crystal be perpendicular to the window faces. If a flatness of a t least 0.0001 inch is specified, the sapphires lyill usually seal as purchased; otherwise, they must be lapped myth diamond paste. The major limitation on the use of sapphire windoim is that they cut off radiation of wave lengths longer than 5 microns. Preliminary information ( 2 ) on sodium chloride window indicates that they are satisfactory a t least to 1000 atm., and calcium fluoride windows may be useful at still higher pressures.
>MISCELLANEOUS FEATURES
I t is frequently convenient to have a plug (particularly the bottom plug) tighten flush n-ith the surface of the bomb. A convenient device for this purpose is shown in Figure 3. The square head of the plug is replaced by a removable hexagonal nut which pins to the plug with three a/8-inch diameter pins of SAE 4340 steel hardened to 50 Rockwell C. The nut can be made easily removable and lasts indefinitely. A modified design of apparatus involving three nindow plugs, one perpendicular to the ot,her two, can be used for light-scattering and light-absorption studies. ACKNOWLEDGMENT
The authors wish to acknowledge the skillful machine work and useful suggestions of W. W.Demlow. LITERATURE CITED
(1) Bridgman, P. W.,"Physics of High Pressure," pp. 34, 37, 39, G. Bell and Sons, London, 1947. (2) Parsons, R. W., private communication, U. of Illinois, Urbana, Ill. (3) Poulter, T. C . , Phgs. Rev. 35, 297 (1930). RECEIVED for review October 13, 1955. Accepted February 4 , 1956. Division of Industrial and Engineering Chemistry, Symposium on Processing under Extreme Conditions, 128th Meeting, ACS, .Minneapolis, Minn., September 1955. Other papers presented a t this symposium appear in Industrial and Engineering Chemistru, May 1956. Work was supported in part by t h e Atomic Energy Commission.
Spectrophotometric Determination of Zirconium in T h o r i m LOUIS SILVERMAN and DOROTHY W. HAWLEY Atomics International, Division o f North American Aviation, Inc., Canoge Park, Calif.
A t a controlled high acidity, zirconium, in the amount of 0.005 to 0.350q& can be determined colorimetrically using Alizarin Red S. As much as 200 mg. of thorium can be tolerated in the presence of 10 to 700 y of zirconium. Acetone and heat accelerate the rate of color development and increase the stability of the color. Small amounts of iron and other metals normally present in thorium do not interfere.
A
N INVESTIGATION of new techniques for the purification
of thorium presented a need for a method for the determination of small amounts of zirconium in thorium. -4number of organic reagents have been studied and recommended for the direct colorimetric determination of zirconium. These include p-dimethylaminophenylazobenzenearsonic acid (6))alizarin ( 2 , 8), Alizarin Red S ( 3 , 4,9-11, fd), purpurin, ( 2 , 8) quinalizarin ( 2 , 8 ) , thoron ( 6 ) ,and chloranilic acid (10,13). I n their present form, these methods are time-consuming or require the removal of thorium if present in large amounts. Alizarin Red S (sodium salt of 3-alizarinsulfonic acid) showed the most promise, because the colors ordinarily produced by interfering metals (other than hafnium) are vitiated in strong mineral acid solution. The various contributory factors were studied to obtain the maximum absorbance due to the zirconium-Alizarin Red S lake under conditions that result in minimum interferences from other sources. REAGENTS
Standard Zirconium. Dissolve 35.33 grams of C.P. zirconyl chloride octahydrate (ZrOC12.8H20)in an aqueous hydrochloric acid solution (pH 1.2) and dilute to 1 liter with the same acid
solution. Standardize using the p-bromomandelic acid method (7). This solution contains 10 mg. of zirconium per milliliter. Prepare solutions containing 0.100 and 0.010 mg. of zirconium per milliliter by properly diluting the stock solution with the aqueous hydrochloric acid solution. Standard Thorium. Dissolve and fume 29.74 grams of thorium nitrate tetrahydrate [Th(r\;03)4.4HzO] with 150 ml. of concentrated perchloric acid. Dilute to 1 liter w t h water, making certain that the pH is approximately 1. This solution contains 25 mg. of thorium per milliliter. Analyze by precipitating the thorium as oxalate and weighing the oxide ( 2 2 ) . Colorimetric Reagent. Dissolve 500 mg. of Alizarin Red S (National Aniline Division, Allied Chemical and Dye Corp., S e w York) in a 2 to 3 hydrochloric acid solution and dilute to 1 liter with the same solution. Let stand for 2 days and filter through Whatman S o . 40 paper. The solution is stable for a t least 1 month. Sample-Diluting Solution. Prepare a hydrochloric acid-water solution having a pH of 0.70. PROCEDURE
Sample Preparation. Weigh a sample (metal or compound) containing 0.800 gram of thorium into a latinum dish. Add 10 ml. of concentrated nitric acid and a g w drops of 2% hydrofluoric acid. Warm to initiate the reaction, then remove from the heat. If the reaction becomes too vigorous, it may be moderated by the addition of water. When the reaction subsides and solution is complete, add 5 ml. of concentrated erchloric acid. Eva orate to near dryness and cool. Add 2 ml. ornitric acid and 5 m! of perchloric acid and again evaporate almost to dryness. Dissolve the residue in 5 ml. of 1 to 1hydrochloric acid with heat. Transfer to a 100-ml. volumetric flask and adjust the volume with water. Transfer a 25-ml. aliquot (200-mg. sample) to a 50-ml. beaker. Add 4 ml. of acetone and adjust the volume to 32 =k 2 ml. with water. Determine the pH of the solution and adjust the sample to H 0 70 using 1 to 1 hydrochloric acid solution and water. 8ipet.10 ml. of Alizarin Red S reagent into a 50-ml. volumetric flask and then transfer the sample to the flask. URe the hydrochloric acid-water solution, pH 0.70, for all rinsings and any
807
V O L U M E 28, NO. 5, M A Y 1 9 5 6 volume adjustments. Heat in a water bath (70" to 90" C.) for 10 to 30 minutes to develop the zirconium color, then cool to room temperature. Measure the absorbance a t 540 mp within 3 hours after the start of heating. Absorbance is measured using 1-cm. cuvettes in a Beckman Model DU spectrophotometer, with water as a reference. Obtain the zirconium concentration from a standard curve showing absorbance us. zirconium content. The curve is prepared by using the same reagents and the standard solutions of zirconium and thorium. If the zirconium content is high, use a smaller aliquot and add the amount of thorium necessary to provide a total of 200 mg. per sample. RESULTS
When the recommended procedure is used on 200-mg. samples of thorium metal, it is possible to determine 0.005 to 0.350% zirconium in a 50-ml. volume solution. The standard curve is linear from 0.050 to 0.700 mg. of zirconium, but curves slightly a t lower zirconium contents. I n the linear portion of the curve, the change in absorbance per milligram of zirconium was 1.14 for the conditions recommended and for the solutions actually used in the authors' laboratory. The daily standard curves originated at 0.7 absorbance unit for 0.0 mg. of zirconium and 200 mg. of thorium; the absorbance for solutions containing 0.11 mg. of zirconium and 200 mg. of thorium ( a daily point) was 0.15. The entire curve is reproducible. Larger percentages of zirconium may be determined by using smaller samples and adding standard thorium to provide the necessary 200-mg. total. Compounds and solutions may be analyzed if the thorium content is known within lo%, if the thorium and zirconium content can be made soluble in water, and if the interfering complexforming ions are removable. Table I illustrates the reproducibility of the method as shown by a series of thorium-zirconium melts obtained from a zonemelting experiment. Similar reproducibility has been obtained from several other experiments. A thorium sample reported t o be 0.03% in zirconium by spectrographic analysis was found to contain 0.031,0.031, and 0.0337, zirconium. Two other thorium samples contained 0.021, 0.024, 0.025% and 0.027, 0.028, 0.028, and:0.028% zirconium, respectively.
Table I.
Zirconium in Thorium
(-4nalysis of a zone-melting run) Sample Number End 1
9
3 4 5
;
8 9 10
Thorium (unalloyed)
Zirconium,
% 0.092, 0.093, 0.106,0.106 0,150, 0.155, 0.062, 0,066 0.079, 0.079, 0.068, 0.069 0.074, 0,075, 0.081, 0.082, 0,089, 0.085. 0.079, 0,079, 0.005,0.005
Standard Deviation ( I ) , 8zu
0.093
0,001
0.155
0.001
0,080
0.001
0.077 0.083 0.090 0 . 0 7 5 , 0 081
0,002
0.001 0.001
0.002
0.000 0.000
DISCUSSION
Preliminary investigations showed that the absorbance of a solution containing Alizarin Red S, zirconium, and large concentrations of thorium is dependent on the wave length, conditions of color development, concentration of Alizarin Red S, acidity, and thorium content as well as the zirconium concentration. The effect of each variable was investigated in order to decrease the sensitivity of the method to all factors except zirconium content. Wave Length. Green ( 3 )showed that the effect of varying the necessary excess of Alizarin Red S on the absorbance of the zirconium-Alizarin Red S lake was least at 540 mp, under the
conditions of his experiments. At 510 mp and a t low pH, the absorbance caused by the excess Alizarin Red S is negligible and that resulting from the thorium-illizarin Red S compound decreases appreciably. The absorbance ascribed entirely to the zirconium compound is a t a maximum in the region from 520 to 530 mp and is only slightly lower a t 540 mp (Figure 1). Conditions of Color Development. It has been shown (3) that high ion content of the system decreases both the rate of color development and the stability of the zirconium-Alizarin Red S lake. Color development by preliminary (temporary) decrease in acidity ( 3 , 4,14) is negated by the presence of thorium, for under the usual conditions for the determination of zirconium in aqueous solution, the high thorium content causes clouding of the mixture before the zirconium-Alizarin Red S color has fully developed. 12
10
08 06 0.4
02 0 400
420
440 460 480 WAVE
500
520 540
560 580 600
LENGTH, m p
Figure 1. Absorbance spectra of Alizarin Red S complexes
-.-.-.-. ._. ._. _. _.~-
0 mg. of zirconium 0 mg. of thorium, water a s reference o mg. of zirconium: ZOO mg. of tliorium water as reference 0.293 mg. of zirconium, 200 mg. of thoridm, water a s reference 0.293 mg. of zirconium, 200 mg. of thorium, reference containing ZOO mg. of thorium and no zirconium
Of the stabilizing agents investigated, Carbitol (monoethyl ether of diethylene glycol) prolonged the period of stability but decreased the rate of color development and the over-all sensitivity of the method. An A41izarinRed S-Carbitol reagent was usable only during the second and third day after preparation. Acetone and heat increase the rate of color development; they have little or no adverse effect on the sensitivity of the system and produce a color stable for several hours. Variation of the acetone content causes no significant change in the color intensity. Four to 107, of acetone by volume is recommended to prevent precipitation. Reagent Concentration. Because the reaction of zirconium and Alizarin Red S attains equilibrium (8), a large excess of the reagent is desirable. Some of the excess is used by the thorium. Too high a concentration of the reagent, particularly in the presence of much thorium, favors the precipitation of the system as manifested by a general cloudiness. Five milligrams of Alizarin Red S per 50 ml. of final solution is a convenient reagent concentration. Acidity Control. At measurable pH, the absorbance of the Alizarin Red S-zirconium-thorium system is so sensitive to acid that reproducible results are not easily obtained. Simple additions of acid to systems of varying original acid content are unreliable, even though the sensitivity decreases a t the higher acidities. Consequently the sample solution should be adjusted to some reproducible pH at less volume and then the final acidity should be obtained by the addition of a prescribed amount of acid. Reproducible acid conditions are readily obtained by the addition of 10 ml. of ;Ilizarin Red S (which is prepared in 2 to 3 hydrochloric acid) t o 40 ml. of prepared test samples, which orig-
808
ANALYTICAL CHEMISTRY
inally were adjusted to pH 0.70. All rinsings and volume adjustments are made with a solution of pH 0.70. -2 variation of 2~0.20unit in the original pH adjustment results in an absorbance variation of ~k0.005unit. Thorium Content. Previously reported methods for zirconium using Alizarin Red S showed that the effects of the presence of large amounts of thorium include the tendency t o cause precipitation a t previously recommended p H values, delay in color development, and high absorbance caused by thorium-Alizarin Red S combination. The conditions recommended herein eliminate the first two effects and minimize the third. The absorbance attributed to the thorium-illizarin Red S is accounted for in the standard curve obtained by using 200 mg. of thorium with each synthetic standard. A variation in thorium content of as much as 10% (20 mg.) causes less than 27, error in results in the region from 0.3 to 0.4 mg. of zirconium. The error i. only slightly higher for loner zirconium contents.
Table 11. Effect of Diverse Ions on Determination of Zirconium in Presence of 200 3Ig. of Thorium Diverse Zirconium, y Ion RIg. Added Found Al(II1) 5 200 200 1 Be(I1) 178 175, 177 U as UOz(I1) 10 176 175, 176 Xi(I1) 176 176, 176 Fe(II1) 176 174, 180 Fe ( I 11) 10 176 177, 183 1 Ce(IV) 280, 280 280 5 Ce(IV) 200 182 110 as M o O P - 0 04 222 22% 222 110 as MoOa-0 08 222 110 as h$004-222 225 0 20 7.92 hfo as Mood-0.50 227 HaSOaa 176 0 HClOia 176 174 I/* i d . of acid included before P H adjustment.
:
_-
Diverse Ions. a-Hydro\j carljoxj lic acids, inorganic fluorides, and sulfates which form stable complexes with zirconium interfere in the determination. a - H j droxycarboxylic acids 2nd inorganic fluorides may be removed by repeated treatment !\ ith nitric and perchloric acids. The effect of sulfate may be eliminated by the addition of calcium, but not barium. Data in Table I1 indicate the effect of a number of diverse ions n hich might be present and interfere in the zirconium determination. Other ions, specifically reported to cause no interference a t lower acid concentrations, do not interfere a t the acidity used here, except in concentrations great enough to increase the ion concentration to the point of precipitation or delay of color development. Kitrates, equivalent to the thorium present, deciease the rate of color development Under the present condi-
tion, no reduction of iron is necessary for the quantities investigated. S o attempt was made to account for the presence of hafnium in any samples or standards, although this element undoubtedly causes an increase in absorbance when present (8). SUMMARY
The colorimetric determination of zirconium using *2lizarin Red S has been adapted to tolerate at least 200 mg. of thorium. The acidity should be controlled t o that of a 40-ml. solution with a p H of 0.70 plus 10 ml. of 2 to 3 hydrochloric acid. rlcetone and heat are used to develop and stabilize the color. The thorium content of the final samples should be 200 i 20 mg. per 50 nil. of final solution, corresponding to the content of the solutions used for the standard curve. The reproducibility of the determination of zirconium (0.01 to 0.7 mg.) in thoiium (200 mg.) is in the range of O.Olyczirconium; the standard deviation is 0.002yc. Higher percentages of zirconium may be determined ivith suitable sample and volume adjustment if the acid concentration is kept constant. ACHNOWLEDG\IEh-T
The authois wish t o express their graditude to Richard D. Burch for the preparation of the zirconium-thorium alloys used in this investigation. LITER.4TURE CITED
Dixon, W.J., Massey, F. J., “Introduction to Statistical h a l y sis,” RIcGraw-Hill, Sew York, 1951. Flagg, J. F., Liebhafsky. H. A . , Winslow, E. H., J . Am. Cheni. SOC. 71, 3630-2 (1949). (3) Green, D. E., . ~ N A L . CHEX.20, 370-4 (1948). (4) Guenther, R., Gale, R. H., U. 8. Department of Commerce, Office of Technical Services, Washington, D. C., KAPL-305, (March 10, 1950). ( 5 ) Hayes, \TT. G., Jones, E. W., IND.ESG. CHEX, ASAL. ED. 13, (1) (2)
603 (1941).
Horton, A. D., ~ N A L CHEJI. . 25, 1331-3 (1953). (7) Klingenberg, J. J., Papucci, R. A., Ibid.,24, 1861-2 (1952). (8) Liebhafsky, H. A , Winslow, E. H., J . A m . Chem. SOC.60, (6)
1776-84 (1938).
AIayer, A , Bradshaw, G., Analyst 77, 476-83 (1952). RIenis, O., U. S. Department of Commerce, Office of Technical Services, Washington, D. C., ORNL-1626 (April 7, 1954). (11) RIills, E. C., Hermon, S. E., ilfetallurgia 51, 157-8 (1955). (12) RIoeller, T., Sweitser, G. K., Starr, D. D., Chem. Revs. 4 2 , 85 (9) (10)
(1948). (13) (14)
Thamer, B. J., Voigt, A. F., J . Am. Chem. SOC.73, 3197 (1951). Wengert, G . B., dx.4~.CHEW24, 1449-51 (1952).
RECEIVLDf o r review August 1, 1955. .iccepted February 23, 1956. Based upon studies conducted for the -4tomic Energy Commission under Contract .iT-11-1-GEN-8.
