HYDROLYTIC CONSTANTS OF URANIUM (I\’)
Sept., 1950 H
H
I
I
I
I
H
+C-CHz:C-CH2-
OR
OR
H
I j C=CH2 I
I
+ +C-CHr-
OR
I
OR
etc.
Cessation:
I
IOR By this mechanism both monomer and low polymers are produced. The monomer which is known to be easily hydrolyzable can then split into alcohol and aldehyde. Thus, all products of degradation can be accounted for. The stabilizer acts on the carbonium ion in exactly the same fashion as in the cessation of a polymerization chain. The alkyl ether carbonium ion should behave sterically in a similar fashion to styrene. It is not surprising, therefore, that secondary amines are better stabilizers than primary amines. Finally, since benzoyl peroxide and light catalyze the aging, it may be that a radical depolymerization occurs side by side with the carbonium ion chain. Experimental OR
Nitrobenzene, carbon tetrachloride, styrene and the amines were purified as described in the preceding paper. a-Methylstyrene (Dow) was distilled under reduced pressure through an all-glass apparatus, b. p. 43” (2 mm.). Polymerizations were carried out as described in the preceding paper, bromine addition being used to determine both residual styrene and a-methylstyrene. Tetraethylammonium chloride was prepared as follows : Commercial triethylamine was purified by double
[CONTRIBUTION FROM
THE
AND PLUTONIUM (Iv)
3901
distillation. I t was refluxed in benzene with an equimolar amount of ethyl iodide for a period of thirty minutes. The mixture was then cooled and filtered. The solid was washed with benzene and ether, then dried in vacuum. N(GH6)J was dissolved in water and shaken for onehalf an hour with a slight excess of silver chloride. After filtering, the filtrate was distilled to dryness in vacuum. The solid residue was recrystallized twice from ethyl acetate to which a few drops of alcohol had been added, then filtered and dried in vacuum. The amount of chlorine was determined by dissolving part of the sample in water and titrating against standardized mercuric nitrate using sdiphenylcarbazone as an indicator; C1 found, 21.06; C1 calcd. 21.40. The quaternary chloride does not melt but, rather, decomposes slowly on heating.
Summary 1. Tin tetrachloride dibutylamine complex inhibits Friedel-Crafts polymerization as much as the amine itself. 2. Chloride ion inhibits the polymerization of styrene, thus adding weight to the proposed mechanism of polymerization of Polanyi and coworkers. Chloride ions, however, are not responsible for inhibition by tin tetrachlorideamine complexes. 3. The inhibiting efficiency of amines toward cumethylstyrene has been found to differ from styrene and to follow the order C4HgNHz < (CH&NC~HE,< (C4H&N < (GH9)zNH. This order is explained in accordance with the general mechanism of inhibition. 4. An explanation is offered for the relative efficiency of stabilizers in the aging of polyalkyl vinyl ethers by assuming a carbonium-ion mechanism of degradation. BROOKLYN 2, N. Y.
RECEIVED OCTOBER 7, 1949
CHEMISTRY DIVISION,OAK RIDGENATIONAL LABORATORY]
Hydrolytic Behavior of Metal Ions. I. The Acid Constants of Uranium(1V) and Plutonium(IV) BY KURTA. KRAUSAND FREDERICK NELSON I n the course of a study of the hydrolytic behavior of metal ions the existence of the species U+* was confirmed and the equilibrium constants (acid constants) for the reaction M+4
+ 2Hz0 J_ MOH+S+ HaO+
(1)
for uranium(1V) and plutonium(1V) were determined. In addition to reaction (1) which was found to be practically instantaneous, slow hydrolytic reactions were also observed. These are probably due to aggregation of hydrolysis products. The aggregates, which will be called “poly(1) This document is based on work performed under Contract No. W-7405 eng 26 for the Atomic Energy Commission at Oak Ridge National Laboratory. Part of this work has previously been published in the project reports CN-2289 (November, 19441, MonN870 (September 1847). CNL-87 (April 1848) and AECD-1888 (April 1948). Part of the material w u included in a paper presented at thm meeting of the American Chemical kdetr on April 81, 1848.
mers,” reach colloidal size, their composition approaches that of the hydroxide, and they greatly affect the chemistry of uranium(1V) and plutonium(1V) ~ y s t e m s . ~ JThey ~ ~ will be considered in some detail in later papers. The oxygenated species MO++ (M(OH)2++) were not observed. Experimental Uraniurn(1V) stock solutions were prepared by reduction of uranium(V1) chloride or perchlorate solutions with known amounts of zinc or by electrolytic reduction. The uranium (IV) concentration and completeness of reduc(2) K. A. Kraus, F.Nelson and G L. Johnson,THISJOURNAL, 71, 2510 (1949). (3) K. A. Kraus arid F. Nelson, ibid., 71, 2517 (1949). (4) For a summary of some observations on polymeric plutdnium(1V) see K.A. IGyaus, National Nuclear Energy Series (NNESY bivision IV, Vol. 14B 2.16, Mcbrea-Hill Book Co., Inc.. New York, 1949; EW E.A. Krsui and F. Nelaon, Report AECD-1888 (April, 1848).
3902
KURTA. KRAUSAND FREDERICK NELSON
tion was determined by cerate oxidimetry. A few stock solutions were prepared by dissolving uranium tetrachloride in oxygen-free acids of known strength. These were also polarographically analyzed for uranium (VI). The uranium(V1) solutions were prepared from spectroscopically pure6 uranyl nitrate hexahydrate, using several ammonia precipitations t o remove nitrate. Plutonium(1V) chloride solutions were prepared by dissolving the freshly precipitated hydroxide in strong hydrochloric acid and heating to remove possible small concentrations of polymeric plutonium(1V). Since each oxidation state has a characteristic spectrum, purity of the solutions was checked spectrophotometrically using a Beckmnn Model DU quartz spectrophotometer. Standard radiochemical techniques were used t o determine the ~ ~ ti/* = 24110 concentration of plutonium ( P Ua-emitter,
Vol. 72
erated on dissolving samples of anhydrous uranium tetrachloride. This salt was contained in small glass capsules (filled under nitrogen) which were broken in acids of known strength. From the ensuing potential change ( AV) of the glasselectrode assembly the change in acid concentration was calculated by the approximate equation Ab‘
= S log (mz/ml)
(2)
where ml and m2 are the initial and final molarities of acid, respectively, and where S is ideally 0.05915 v. a t 25’. This equation applies only if the changes in liquid junction potentials and activity Y6) coefficients are negligible, which was assumed Aliquots of the stock solutions were diluted with potas0.5) large since m2/m1 was close to unity and I.L (w. sium chloride, sodium chloride or sodium perchlorate of known ionic strength and acidity. These were analyzed compared with the final uranium concentration (ca. M ) . The slope S was determined exspectrophotometricaily. Readings were started less than one minute after mixing to permit extrapolation to zero perimentally and found to be dependent on acidity time (time of mixing). The acidity of the solution was and ionic strength, but a t most a few per cent. less measured with a vibrating reed electrometer assembly3e7 using a giass-calomel (satd. KCl) electrode system stand- than the theoretical value. It was found that less than 1 mole of acid was ardized with solutions of known acidity. The method used in confirming the species U + 4will be described below. liberated per mole of uranium dissolved. The Measur:ments were carried out in a thermostated room acid constants calculated from these experiments a t 25 * I . The toemperatwe of most solutions was maintained a t 25 * 0.2 . The experiments with uranium were were in reasonable agreement with those detercarried out under nitrogen (purified over copper shavings mined spectrophotometrically. While the speca t 500”). tral data only permit conclusions regarding changes in species, the agreement with these “abResults and Discussion solute” measurements establishes the existence Acidity of UC14Solutions-Identification of the of the species Uf4. Species U+4.-Although many data8 suggested The Acid Constant of U+4-Estimation of the that the species of uranium(1V) in acid solutions Activity Constant.-The absorption spectrum of is U+4(U(H20),+4 where n = 6 or 8 is most prob- uranium(1V) in acid solution (HCIO4 and HCI) is ableg) the existence of this ion was still controver- characterized by a number of sharp bands in the sial. Thus, the invariance of the potential of the visible region13 as shown in Fig. 1. Most of this uranium (III)/(IV) couple with aciditylOsllcan be work was carried out in the region 600-700 mp interpreted either by assuming that both ura- since the most prominent band is located near 648 nium(II1) and uranium(1V) are hydrolyzed to the same extentl0S1lor by assuming that both species mI.L. The spectrum is strongly dependent on the are the non-hydrolyzed U+3 and Uf4. Conclu- acidity of the solution and a t low acidities also sions from the potentials of the uranium (IV)/ dependent on time. To separate the instantane(VI) couple as a function of acidity are somewhat ous reactions from the (slow) polymerization remore decisive, since the species UOz++ for U(V1) actions the data were extrapolated to “zero time” is reasonably well established. The potentials of (time of mixing) whenever necessary. The obthis couple in chloride and perchlorate solutions served (extrapolated) extinction coefficient^'^ a t between pH 1 and 3 are consistent with the as- 648 mp (BO(648)) decrease with decreasing acidity sumption of the species U+4,UOH+3 and UOz++ and a plot of Eo (648) vs. log m2 has the characterand of equilibrium (l).3v12 istic “S’ shape of a simple hydrolytic reaction The existence of the species U+4was confirmed (13) The sharpness of these bands is reminiscent of rare earth through measurement of the amount of acid lib- spectra. This characteristic supports the assumption that uranium 9
( 5 ) We are indebted to Mr. C. Feldman of the Chemistry Division, Oak Ridge National Laboratory for the spectrographic analyses. ( 6 ) J. W. Stout and W. M. Jones, Phys. Rev., 71, 582 (1947). (7) K. A. Kraus, R. W. Holmberg and C. J. Borokowski, Anal. Chrm., 2’2, 341 (1950). (8) L. Brewer, L. A. Bromley, P. W. Gilles and N. L. Lofpen, Report BC-82 (April, 1947). (9) Although extrapolations from crystal structure data to structure of ions in solutions are of questionable validity, a coordination number of 8 is preferred since Pu(IV) has this coiirdination number with respect to oxygen in the dioxide (W. H Zachariasen, Report MDDC-67, June 1946). (10) I. M. Kolthoff and W. E. Harris, THISJOURNAL, 67, 1484 (1945). (11) H.G. Heal, Trans. For. SOL.,46, l(1949). (12) F. Nelson and K. A. Kraus, Report ORNL-286 (September, 1949).
(IV) contains two 5 f electrons, although the extinction coefficients of uranium(1V) as well as those of similar “actinides” are a t least an order of magnitude larger than those of the rare earths. The other members of the isoelectronic sequence U(IV), Np(V), Pu(V1) also have similar sharp bands, I n particular this series appears to have in common an infrared transition whose wave length decreases with increasing atomic number (U(IV), 1075 w ; Np(V), 985 w ; Pu(VI), 831 mp). If less than two “ f ” electrons were present, rare earth-like spectra would not be expected, (see e. g . , S. Freed, Phys. Res., 38, 2122 (1931), S. Freed and R. I. Mesirow, J . Chem. P h y s . , 6 , 22 (1937), and J . H. van Vleck, J. Phys. Chcm., 41, 67 (1937)) as corroborated by the absence of sharp absorption bands in uranium(V) and neptunium(V1) both of which could have only one “ f ” electron. (14) The extinction coefficient (E) is defined by the equation E (log Io/I)/rn, where rn is the molarity, 1 the cell length and I Q / I the ratio of intensity of incident to transmitted light.
-
HYDROLYTIC CONSTANTS OF URANIUM(IV) AND PLUTONIUM(IV)
Sept., 1950
3003
10 0
700 800 900 1000 1100 Wave length, millimicrons. Fig. 1.-Absorption spectra of U+' and Pu": A: U+4: 1 M HClOI-1 M NaClO4, 8.86 X lo-' M U(IV), corrected M Pu(IV), corrected for hydrolysis asfor hydrolysis, 10 cm. cell. B: Pu+4: 0.50 M HC104-0.015 M HCl, 7.3 X suming negligible absorption of the hydrolysis product, 10-cm. cell. 400
500
600
(see Fig. 2). At high acidity (above ca. 1 M ) the observed extinction coefficients (Eo) approach asymptotically that of U+4(El) and a t low acidity that of the hydrolysis product (E2 of UOH+3).
where E1 and E2 are the extinction coefficients of the species X+4and UOH+3JM I and M2 their respective molarities and Mt the total concentration of uranium (IV). If El and E2 are known and M2 = Mt the acid constant (moassuming Ml larity constant) K , can be calculated from the equation Km = [H80+][XOH'31/[X+41 = ma(& - &)/(EO &)
+
-
(4)
where brackets indicate molar concentration and m2 the final acidity of the solution. Actually El, E2 and K , were obtained by trial and error, using first preliminary values of K , and the data a t high and low acidities.
0.001
Fig. 2.-Change
0.01 0.10 1.00 10.0 Molarity of HC1. of extinction coefficient maximum with acidity.
The probable spectrum of UOH+3Jcalculated from low acidity data and the acid constant, is shown in Fig. 3. I n the pertinent concentration range (using minimal slit-widths) the absorption bands of U+4 obey Beer's law. Since the bands of UOH+3probably also obey this law, i t may be assumed that the observed extinction coefficients (EO)are a linear function of the concentrations of U+4 and UOH+3, i. e. Eo EiMiIMt &&/MI (3)
+
350 400 450
500 550 600 650 700 Wave length, millimicrons. Fig. 3.-Absorption spectrum of U(OH)+J, 8.80 X lo-' M U(IV), 2 M C104-, calculated from spectrum in 8.2 X MHCIO4.
The results of the experiments are summarized in Table I. It was found that a t constant 1.1, K , adequately describes the data over a considerable hydrolysis range and that it is practically independent of uranium(1V) concentration, thus confirming the assumed hydrolysis reaction (1).
KURTA. KRAUSAND FREDERICK NELSON
3004
Vol. 72
(where Zi is the charge of the ion and di the “mean T A B ~IaE and assuming that an ACID CONSTANTOF URANIUM(IV)IN PERCHLORATEdistance of approach’’15~16p17 average value d can be used instead of the different values di, equation (5) yields
SOLUTIONS /I
= 0.519, 8.868 X lo-‘ MoU(IV), temperature
25
* 0.2 .
Final H30+
Eo(648)
%UOH+*
0,0096 .0204 .0323 ,0680 .128 .250
17.1 27.0 32.8 43.1 49.5 54.0
79.9 61.4 50.6 31.5 19.5 11.2
K m X 1OB (3.73) 3.24 3.33 3.12 3.10 3.16
TABLEIb OF URANIUM(IV) IN PERCHLORATE AND ACID CONSTANT CHLORIDE SOLUTIONS MU(1V) Acidity %UOH+s K, No. p
X 103
range(M) range Perchlorate solutions
2.004 1.014 0.503 ,520 ,519 .55 ,272 ,116 ,115 ,112 .lo8 ,0634 ,0452 .0349 .0328 ,0173
0.886 0.0082-0.105 ,886 ,032 - ,056 ,183 ,0107- ,304 ,725 ,0143- ,305
2.004 1.014 0.67 ,519
1.00 0.0032-0.253 0.948 .0065- .250 ,0535- ,130 9.23 0.932 ,0064- ,0550 ,0181- ,109 1.34 0.679 .0057- .201 ,932 ,0113- ,0561 ,932 ,0165- ,104 1.225 .0160- .lo6 1.222 .0431 1.228 .OS5 1.228 .0352 1.222 ,0305 1.228 ,0253 0.616 ,0282 1.228 ,0163 0.616 ,0155
,886
3.55 0.886 1.228 1.222 0.662
,616 ,890 ,890 ,890
,616 .616
19.5-73.6 33.5-46.0 7.2-76.0 8.8-68.4 ,0204- ,250 11.2-61.4 .025 - ,240 12.1-61.4 ,0146- ,131 23.3-75.7 ,0555- ,105 33.4-47.8 ,0190 75.5 ,0110- ,0900 40.8-84.6 ,0160 76.8 .0469 61.0 ,0288 73.6 .Ol9 84.6 75.0 .0285 ,0134 89.9
X 1Ozexpts.
2.36 2.78 2.9 3.12 3.19 3.55 4.33 5.17 5.85 6.03 5.30 7.2 7.9 10 8.6 12
5 2 6 6 5 7
1.53 1.88 2.59 2.62 2.33 2.57 3.25 4.38 4.44 4.56 6.1 6.8 7.9 7.5 7.3 9.6 9.8
8 7 2 4 4 6 4 4 7 1 1 1 1 1 1 1 1
5 2 1
5 1 1
1 1 1 1
ua
0.09 (.05)b .33 .09 .09 .33 .19 (.09)
.. . . .14
....
.... .... .... .... ....
log Ka = log K , -0.509A(Zi2)
-
/.&I/%
1 f 0.3286d p ’ / ~
~
(7)
where A ( 2 i ’ ) = -6. Using d = 7.5 A., the perchlorate data can be fitted to equation (7) within the rather wide limits of experimental error (cu. * 10%) up to p = 2. The agreement is illustrated in Fig. 4 where log K , has been plotted as a function of p’/z/(l 2.465 P I / ? ) . The solid line is drawn with the theoretical slope -6 X 0.509 = - 3.054. By extrapolation to p = 0, K a = 0.21 * 0.02 is found. The choice of it = 7.5 d. appears reasonable since even for 2-1 electrolytes (i. e., for electrolytes of considerable lower valence type than occur here) values of d = 6 A. have been used.15 Furthermore, it was found that d = 7.5 8.permits a reasonable fit of the activity coefficients for 3-1 electrolytes a t low molarity. The activity coefficient ratios YUOH +v/yu+d and Y U O H X ~ / Y U X ~ (where X denotes Clod- or other non-complexing anions) were calculated assuming YFI,O+ = y t ~ a . a n dY * H C I = Y ~ H C I O respectively, and using the values y *HCI given by Harned and Hamerl8 for 0.01 M HCI solutions in
+
TABLEI1 IN THE U +‘-UOH ACTIVITY COEFFICIENTS
+3
SYSTEM
Chloride: solutions
.529
.506 .272 ,123 .115 108 .0654 .0449 .0395 ,0345 .0327 ,0250 ,0235
5.7-84.1 7.3-76.1 17.0-32. O 31.4-81.9 17.4-57.7 11.6-80.6 36.5-73.9 26.8-74.0 32.2-72.5 51.4 52.5 65.8 72.1 74.8 72.2 85.4 86.3
0.08 .ll ( . 07) .17 .ll .15 .06 .29 .29
....
.... .... ....
.... .... .... ....
5The standard deviation u was calculated with the equation u = d Z ( x - X)2/n where x is the observed value, 5 arithmetic mean and n the number of observations. Values in parentheses indicate deviations from the mean.
From the ionic strength dependence of K, an attempt was made to evaluate the activity constant Ka which is given by the equation K S = K, Y H ~ o +Y u o ~ + ~ / Y u + ‘
(5)
where y is the activity coefficient of the ion indicated as subscript. Assuming that the activity coefficients follow a Debye-Huckel limiting law of the form ..
1.94 2.15 0.75 0.68 1.76 0,904 2.39 2.74 2.09 ,873 .69 .61 3.07 2.56 .836 3.67 .63 .53 3.59 4.41 .815 .58 .48 2.93 ,790 4.42 .10 3 . 4 9 5.60 .54 .43 .20 4 . 4 6 .752 5.93 7.90 .47 .36 .706 8 . 6 7 12.30 .50 6.13 .44l .29 1.00 7.61 .719 10.58 14.73 .36 .26 Calculated using equation (7). * From Harned and Hamer, ref. 18. Y,HCI = Y,HCIO~ is assumed. Calculated from column (2) assuming = Y ~ H C I . Calculated from column (2) by diving by Y,HCI, “X” indicates a non-complexing negative ion, particularly ClOca Cal0.01 .02 .04 .06
/II/Z
d a t e d from log Y* = -0.509 ZZj + 0.3286 Calculated from columns (5) and (6). using & = 7.5.
’
~
(15) R. A. Robinson and H. S. Harned, Chem. Reu., 18, 419 (1941). (16) Equation (6) differs from the Debye limiting law in that yi has been substituted forfi, the activity coefficient on a mole fraction basis (see ref. (15)),and Zit for ZiZj, the product of the charges of the positive and negative ions. I n view of the limited precision of the data no distinction will be made betweenfi, yi and yi, the activity coefficients on a mole fraction, molality and molarity basis since the error introduced is small (less than 10% even at an ionic strength of 2). For the relationship betweenfiyi and yi, see ref. (15). (17) For values of the constants in equation (6) see 0.G . Manov,
~ ~
HYDROLYTIC CONSTANTS OF URANIUM( 1V) AND PLUTONIUM( IV)
Sept., 1950
KC1. These values are given in Table I1 together which were obtained from with estimates of y Y U O H X ~ ( Y U X , by estimating YUOHX,. This was done with the Debye limiting law since UOHX3 can be considered a 3-1 electrolyte and since the activity coefficients of most 3-1 electrolytes differ only by a few per cent. for values of p = 1 and appear to obey this law for d = 7.5. Estimate of the Stability Constant of the Uranium(1V)-Chloride Complex.-The values of K , for chloride solutions are generally lower than for perchlorate solutions, which is probably due to chloride complexing of uranium(1V) according to the equation Uf4
+ c1-
UClfS
3905
t i 0.1 U
9
U
c“
8
a
8
(8)
To evaluate the stability constant Kc for this reaction (KO,a t p : 0) i t was assumed that equation (7) with A(Ziz) = -8 is applicable. Through A trial and error K,O = 7.0 was found to bring the acid constants for chloride solutions in line with those for perchlorate solutions (see Fig. 4). From 0.01 I I I I I the precision of the data it is questionable that 0 0.1 0.2 0.3 0.4 0.5 this value of KO, is better than * 30%. Complexp1/’/(1 + 2 . 4 6 5 ~ ’ / ~ ) . ing in 2 M C1- can be estimated to be ca. 42%. It is surprising that this large amount of complex- Fig. 4.-Estimation of acid (activity) constant of U ( I V ) , ing hardly affects the absorption spectrum. Assignment of the Species P u + ~lg-The . evi- is of interest, particularly since i t extends to a dence for the assignment of the formula P u + ~ number of details and confirms the assumption ( P U ( H ~ O ) ~ for + ~ )plutonium(1V) ~ is similar to that these elements are members of a “second that for uranium(1V). Thus the potential of the rare earth series.” The similarity is so great as to plutonium(III)/(IV) couple was found to be suggest that P u + ~only has two 5 f electrons inpractically independent of acidityz0 (from 0.2-1 stead of the expected four. The prominent absorption band located near :lI H 3 0 + ) and the acid dependence of the plutonium(IV)/(VI) couple is in fairly close agree- 470 mp was chosen (&(470) = 56) for analysis. ment with the assignment of the species P u f 4 and Deviations of this maximum from Beer’s law are P u O Z + + . ~In~ addition, Pu(II1) was found to hy- negligible in the concentration range of interest drolyze near pH 7 as predicted by analogy with if the slit width used is small (cu. 0.04 mm.). the rare earth^.^^^^^ Since during this hydrolysis There is no indication for an absorption maximum more than two hydroxide ions are picked up, the of the hydrolysis product in the wave length range assignment Puf3 for acid solutions can be made studied (ca. 450-500 mp) although absorption due with fair certainty and hence the assigiiriient Puf4. to it is by no means negligible (&(470) = cu. 17). The results of two series of experiments for perThe Acid Constant of p~+~.--The method and calculations for the evaluation of the acid chlorate and chloride solutions are summarized constant K,,, (molarity constant) of Pu+‘ were in Table 111. At p = 0.5, KIn = 0.025 was very similar to those used for uraniuni(1V). found for perchlorate solutions and K , = 0,022 However, plutonium(1V) polymerizes more readTABLEI11 ily than uranium(1V) and undergoes disproporACID CONSTANT OF PLUTONIUM(IV) IN PERCHLORATE AND tionation into plutonium(II1) and plutonium(V1) CHLORIDE SOLUTIOXS (with rate increasing with decreasing acidity). Ionic strength p = 0:5, 7.2 X lo-‘ X Pu(IV) Thus extrapolation of the data to “zero-time” is considerably more difficult, particularly under conditions where more than ca. 50y0of the Pu+4 are hydrolyzed. 0.011 2 5 . 8 7 6 . 8 ( 3 . 6 4 ) 0.011 2 5 . 3 7 8 . 0 ( 3 . 9 ) The absorption spectrum of unhydrolyzed P u + ~ ,021 3 3 . 4 5 6 . 8 2 . 7 6 ,031 38.9 4 2 . 3 2 . 2 7 is shown as curve B in Fig. 1. The striking sirni,031 3 8 . 0 4 4 . 5 2 . 4 9 .051 4 3 . 4 3 0 . 3 2 . 2 2 larity of the absorption curves for U+‘ and P u + ~ ,051 4 2 . 7 3 2 . 2 2 . 4 2 .091 4 7 . 3 2 0 . 2 2 . 3 0 (19) For il tnorr detailed discussion regarding the evidence for this assiynnirnt see ref. 4a. (20) J. C.Hindman, Report CN-2289 (November 1944). (21) K. A. Kraus and J. R. Dam, National Nuclear Energy Series, I V , 14B no. 4.14, McGraw-Hill Book Co.,Inc., New York, N. Y., 1949.
,091 ,131 ,211 ,500
46.9 21.2 48.8 16.1 51.3 9 . 6 53.2 4 . 7 Av.
2.45 2.51 2.24 2.47 2.49
,131 49.8 .500 53.3
13.6 4.5 Av.
2.06 2.35 2.24
R. W. GURRYAND L. S. DARKEN
3906
for chloride solutions. K , was found to be independent of Pu(1V) concentration in the range 3.6 X to 2.9 X M Pu(1V). Since K , is smaller for chloride solutions than for perchlorate solutions, weak chloride complexing of Pu+4 is indicated. However, the precision of the experiments is not sufficient to warrant calculation of a stability constant. A persistence of properties with changing atomic number would be expected for a “rare-earth-like” series (actinide, thoride or uranide) of the same oxidation number. The qualitative and quantitative similarity in the hydrolytic properties thus supports the assumption that uranium and Plutonium are members of such a series. The similarity of the absorption spectra with each other and with the rare earths (see footnote 13) is further confirmation as is the weakness of the chloride complexes of these elements (strong chloride complexes would be expected if they were transition elements). Uranium(1V) ( K , = 0.032, p = 0.5) is slightly more acidic than plutonium(1V) ( K , = 0.025, p = 0.5). This difference is barely outside the experimental error but appears to be significant. On the basis of simple “coulombic arguments” the reverse would be expected, since uranium(1V) is larger than plutonium(1V) as indicated by the metal-oxygen distances of the dioxides (U-0,2.363 8.; Pu-0, 2.332 8 . 2 2 ) . A similar but considerably more pronounced anomalous trend was ~ ~the case found for the MOz+and M O z + + i o n ~ .In of the M f 4 ions, however, this trend is too small (22) W. H. Zachariasen, Report MDDC-67 (June 1946). (23) K. A. Kraus and F. Nelson, Report AECD-1864 (March 1948).
[CONTRIBUTION FROM
RESEARCH LABORATORY,
VOl. 72
to provide an adequate basis for extensive interpretation, Acknowledgment.-We are indebted to the Chemical Development Division of the Research Laboratory of Y-12 (Electromagnetic Plant), and particularly Mr. Albert Clark and Mr. G. H. Clewett for their helpful cooperation in connection with this problem.
Summary 1. Through pH measurements of UC14 solutions, U+4was established to be the species of uranium(1V) in acidic solutions. 2. The acid constant of U+4 was determined as a function of ionic strength for chloride and perchlorate solutions through a spectrophotometric method. The molarity constants could be fitted approximately to a Debye-Huckel limiting law and the activity constant Ka = 0.21 * 0.02 was 2H20 F! estimated for the equilibrium U+4 UOH+~ H~o+. 3. The stability constant for the reaction U+4 C1UCl+a was estimated to be K , = ca. 0.63 ( p = 0.5) andK,O = 7.0 ( p = 0). 4. The acid constant of F’u+~ ( K , = 0.025, p = 0.5) was found to be almost identical with though slightly smaller than that of U f 4 (Km = 0.032, p = 0.5). 5 . The spectral data, the quantitative hydrolytic data and the observation that the chloride complexes of uranium( IV) and plutonium( IV) are weak, are confirmatory evidence of the hypothesis that these elements are members of a “rare-earth-like’’ series.
+
+
+
OAK RIDGE,TENNESSEERECEIVED NOVEMBER 25, 1949
UNITED STATES STEEL CORPORATION OF DELAWARE]
The Composition of CaO-FeO-Fe,O, and MnO-FeO-Fe,O, Melts at Several Oxygen Pressures in the Vicinity of 1600’ BY R. W. GURRY AND L. S. DARKEN
As a step in the extension of the work on the to steel-making slags i t was iron-oxygen thought desirable t o investigate near 1600” the several ternary systems formed by the addition t o iron oxides of each of the other important elements to be found in such slags. The investigations of Chipman and co-workers3*don the activity of FeO in slags of the system CaO(Mg0)-SiOzFeO furnish a basis for o w knowledge of slags in equilibrium with liquid iron, that is, a t partial atmospressures of oxygen in the vicinity of pheres at 1600O. This paper reports the results of some determinations of the composition of the (1) Darken and Gurry, Tms JOURNAL, 67, 1398 (1945). (2) Darken and Gurry, ibid., 68, 798 (1946). (3) Fetters and Chipman, Trans. A m . Insl. Min. Mcl. Eng., 146, 95 (1941). (4) Taylor and Chipman, i b i d . , 164, 228 (1943).
liquid oxides in the systems Ca-Fe-0 and MnFe-0 in the vicinity of 1600’ at oxygen pressures up to one atmosphere. Similar data from the literature on the system Si-Fe-0 have been included and tentative phase diagrams a t 1600’ for all three systems have been constructed. Some of the data here reported were accumulated several years ago when i t was intended t o make a more complete investigation; some are the recent byproduct of another investigation. This partial report based on such fragmentary data is made now, since the more complete investigation is no longer planned for the immediate future. The experimental technique including the method of analysis was substantially that reported in our earlier investigations. The vertically mounted tubular globar furnace was used
