W. G. WITTEMAN, A. L. GIORGIAND D. T. VIER
434
Vol. 64
where I is the moment of inertia and W is the energy of the state. In order for the left-hand side of equation 4 to agree with the ratio of experimental t’s on the right-hand side it was necessary to take Vu
=
460 cal./mole
The rotational energy levels W J , ~ then I were deS‘O.g(H2) termined using Stern’s paper where the subscript so that J is the total angular momentum quantum number of the state when the hindering potential vanishes a p - H H Z = 1.0 and RI is the quantum number which specifies ao-liz = 0.53 the component of angular momentum along the Similarly we find Z-axis. -4 few of the lowest rotational energy CW-D~ = 0.55 levels for both hydrogen and deuterium are found CYO-D? = 0.97 to be We note that the condensation coefficients of h ydrogcn deuterium both parahydrogen and orthodeuterium are at or IB,,, = 260 cnl./molc It’c,~ = 260 cal./mole q = 480 T I 1 c = 340 near their maximum value. This is not surprising W’l 1 520 W1,] = 670 since neither species is rotating (except a few in TV,., = 1230 W;.a = 760 excited states) in the vapor phase, and so all of T P 2 . 1 = 1200 W?,, = 750 these molecules which evaporate from the surface T t i ? , p .= 1350 TV, 2 = 910 have essentially the gas phase distribution of rowhere IT‘I 11= J I 7 , , - ~ ~ . S o w , if we assume that there is no activation tational states giving rise to the maximum rate of energy needed for condensation, the condensation evaporation. The molecules of orthohydrogen coefficient a is the ratio of the internal partition and paradeuterium do not have the same distrifunction for the surface molecules to the internal bution of rotational states on the surface as in the partition function for the molecules in the vapor vapor phase, and so upon evaporation these molephase.? Since the vibrational partition function cules do not go over into the same distribution as for the molecules on the surface and in the vapor found in the vapor phase. As a result these moleis expected to be the same, the ratio of the inter- cules do not evaporate a t the maximum rate. nal partition functions just becomes the ratio of The reason that the condensation coefficient of orthodeuterium is not unity is because there are rotation3 1 partition functions. Since the energies of the rotational partition an appreciable number of molecules in excited function- for the burface are referred to a state rotational states and these behave in a similar having no rotation rather than to the zero point manner to the molecules in the rotational states of energy, the abow rotational partition functions orthohydrogen and paradeuterium. I n parahymust be buitably corrected. The zero point energy drogen the number of molecules in excited rofor the para qttLte of hydrogen is just Woo, and tational states is negligible. Acknowledgment.-The authors wish to exfor the ortho state T V l o - E , where El is the rotational energy for a molecule in the vapor phase press their appreciation to Dr. George Stewart with J = 1. The condenwtion Coefficients for for discussions on certain phases of this work and to Professor Paul Harteck for helpful suggestions. hydrogei~then are given by FT’j
THE I’KEPA€UTIO?; ASD IDENTIFICATIOI.\; OF SOME INTERMETALLIC COllPOUKD S OF POLOSIUM1 BY IT. G. WITTEMAS,A. L. GIORGI.4ND D. T. T’IER C‘ontrzbiition f r o m the Cniverszty of California, Los Alamos Scientific Laboratory, Los Alamos, Sex Mexzco Receaoed September 1 I 1,969 ~
A micro technique for the preparation of intermetallic polonium compounds is descrihed. Several compounds were prepared by this technique, and their composition and crystal structure were investigated by X-ray powder diffraction. The diffraction results obtained are summarized in Table 11. Similar investigations indicated that (1) nickel and polonium apparently farm compounds with a composition and a crystal structure which vary continuously between S i P o and S i P o r and between SiAs and C t l ( 0 H ) ~ structures, respectively; ( 2 ) gold and polonium form solid solutions over a wide range of composition; (3) tantalum, tungsten, molybdenum and carbon do not react with polonium; and (4) copper and silver formed coinpoiinds with polonium, but good X-ray data were not obtained.
Introduction Little is knolvrl collcerlling high temperature reaction? of poloniunl metal \vith other metals. The early literature on this phase of polonium (1) Work performed under t h e auspices of the .4tomic Energy Corn-
mission.
chemistry contains only fragmentary information of doubtful significance. More recently, in an inr.estigation of the action of molten polonium on gold, platinum, nickel and tantalum surfaces, Or formation the first three metals was evident. but no reaction with tan-
INTERMETALLIC COMPOUNDS OF POLONIUM
April, 1960
talum mas observed.2 In addition, the preparation and identification of zinc polonide (ZnPo), lead polonide (PbPo), sodium polonide (h'a2Po), platinum polonide (PtPoz), and nickel polonide (KiPo) have been reported by L. G. Fauble, R. E. Brockelhurst, L. F. Yassamillet, A. W. Martin, J. SI. Goode, D. L. Timma and L. K. L a i ~ t z . ~ Since such information is useful for an understanding of the chemistry aiid metallurgy of polonium, an iiivestigation of the high temperature reactions or' polonium with other metals appeared desirable. This paper summarizes all results that have been obtained in this investigation. A few of these results have been reported p r e v i ~ u s l y . ~ Severe limitations are imposed on experimental procedures that can be considered for an investigation of high temperature reactions involving polonium metal. The known ~ o l a t i l i t y ~and ,~ oxide forming properties7$*of polonium metal require the reaction to be carried out in a closed system and either in an inert atmosphere or in vacuo. The small quailtities of polonium available, as rx-ell as the high specific a-activity of polonium (:;2 curies of polonium weigh 7 mg. and produce 1 watt of heat), exclude macro techniques. Finally, the radioactive decay of polonium to form lead a t the rate of 0.5% per d?yg-ll requires both a purification of the polonium immediately before use and a short period of investigation with a particular sample. Because of these limitations, a method for studying these reactions was developed which takes advalitage of the high vapor pressure of polonium metal. The method offers a general micro technique for studying the reactions of any element which has a sufficiently high vapor pressure.
Experimental The intermetallic compounds of polonium were prepared by two separate techniques: (1) a differential furnace technique for compounds of relatively low vapor pressure, and (2) a selective distillation technique for compounds of higher vapor pressure. In both techniques, the reaction chamber consisted of an evacuated and sealed quartz capillary of sufficient length to allow the section of the capillary containing the product to be flame-sealed and separated for subsequent X-ray diffraction analysis and calorimetric assay.*Jl In the first method, the metal to be investigated was placed in one end of the capillary, and a relatively large excess of freshly purified polonium metal was distilled into the other. The distillation technique is illustrated in Fig. 1. Up to 18 hours at 400" were required for the distillation. The c:ipillary thrn w:as sealed, separated, and po(2) W. G . Witteman, G . N. Spillert a n d D. T. Vier, Los Alamos Scientific Laboratory Report LA-1546, 1953 (classified). (3) H. V. Moyer. editor, "Polonium," TID-5221, Office of Technical Services, Department of Cominerce, Washington 2 5 , D. C.. 1950. (4) \f'. G. Witternan, -1.L. Giorgi and D. T. Vier, Loa .4lamos Scientific Laboratory Reports LA-1502, 1953, a n d LA-1890, 1955. ( 5 ) L. S.Brooks, J . A m . Cham. Soc., 77, 3211 (1955). ( 6 ) A . I,. Giorgi, recent investigation in this Lsboratory, to be reliorted in a separatc article. (7) C,. 1-1. AIoulton, .I. I>. Varr and 11. T. Viinr. I,os Alniuos Scientific Lahoratorj- Kcport L.4-I X:$, 19.53, is) K. \V. Bocrnall, " ~ l i ~ ~ i n i s ot fr yttic Rare Rndiot~leiiicnts," Academic Press, Inc., New l-orli, a n d Ratterwortlis Scientifir Publications, London, 1 9 i 7 . ( 0 ) R-,€1. B(3:inier itnrl \\-. E. Enston, .I. C h c n l . l'hys., 1'7, 1298 ( 1! I 19). (10) 11. C. C:,nnin~s, A . V. Bail :ind I ) . T. Tiel, J . Itcsrarch S a f L Bur. Standards, 50, 75 (1953). (11) J. F. Eirlielberger, IC. C. Jordon, S. R. Orr and J. R. Parks. P h y s . Her.. 96, 719 11954).
435
Po COATED To FOIL Po D I S T I L L A T E METAL
FURNACE
Fig. 1.
Fig. 2 . sitioned within a differential furnace that maintained the metal end of the capillary at a higher temperature than the polonium end. Thus, the metal was e-iposed to polonium vapor a t a pressure corresponding to the vapor pressure of polonium a t the temperature of the colder end of the furnace and was free of excess polonium. The rate of reartion was conveniently followed by counting the y-rays originating a t the metal end of the capillary. For this purpose, a stilbene-type scintillation y-counter was used with a lead slit system ( 3 / 4 inch wide, 6 inch long hole) which permitted the crystal to "see" only the base metal end of the capillary. Completion of the reartion was assumed when the y-count reached a constant maximum value. The experimental arrangement is i1lustratt.d in Fig. 2 . The furnace was constructed from stainless-steel rod and wa5 and (B). A capillary well (D) made up of two sections, (-4) extended into both sertions and was aligned in assembly by three studs (C). Two thermocouple wells ( F ) were included in each section. The temprrature of the polonium section (B) was controlled by a tube furnace (E). The metal sertion ( A ) contained an insulated heater winding (G) which kept this section a t a fixed higher temperaturc,. Tpmperatnres were maintained within +IO". In the second method, the capillary was first prepared ab described above. The capillary then was placed in a horizontal tube furnace. The reartion, a t increasingly higher temperatures, was followed conveniently b j periodically removing the capillary for visual inspection. Completion or partial completion of the reaction was assumed when the kmse metal deposit fluoresced in a darkened room. Vpon pxtial completion of the reaction, the position of the capilh r y was changed to expose a section outside the furnace so that selective distillations of the excess metals and the reartion product could be achieved. Ailthoughattempts were made to determine the formula of the compounds by using weighed quantities of metal and by determining the polonium content of the compound by calorimetry, these attempts were not fruitful. Accordingly. formulas are assigned on the basis of X-ray data alone, and
W. G. WITTEMAN, A. L. GIORGI AND D. T. VIER
436
Vol. G i
TABLE I POLONIDE PREPARATION Metal temp.,
hletal
Source of metal
Be Mg Ca Sr Ba Zn Cd Hg Pb
Brush Be Brawn hlerck NacKay King Labs. K.B.S. Baker Quick Silver Prod. Gen. Chem.
OC.
600 450 550 500 525 550 550 200 350
Po
Po
teomp.,
pressure, mm.
575 425 525 500 525 535 550 200 350
7 0.3 3 1 3 3
C.
4 17 0.02
Reaction time, hr.
Remarks
7 5 7 24 5 5 16 4 3
Po was distilled off a t 400' Po was distilled off a t 400' ZnPo condensed in center of capillary Metals were distilled off a t 475". CdPo distilled a t 525" Hg was distilled off a t 200". HgPo distilled a t 400' Metals were distilled off a t 665'. PbPo distilled a t 700"
surh questions as the solubility of the metal or polonium in the polonide are left unanswered. However, analogy with the sulfides, tellurides and selenides, including comparison of calculated covalent radii, would indicate that the compounds are near stoichiometric. The polonium was obtained as a metallic deposit on platinum gauze. It contained varying amounts of lead and, possibly, bismuth. The polonium purification procedure consisted of the following steps. (a) The polonium was distilled from the platinum gauze onto a glass surface where i t was deposited as a polonium mirror. ( b ) The polonium mirror was dissolved in 15 ml. of 7.8 A' "03, and diluted to 78 ml. volume and the polonium electroplated on a tantalum foill2 (0.010 inch thick). (e) The polonium metal was distilled from the tantalum foil into 1he quartz reaction chamber to give 99+% pure Po. All exposures were taken on Eastman Type-A X-ray film in a North American Philips 114.59 mm. diameter powder camera. Copper radiation from a General Electric CA-6 X-ray diffraction tube was used in a General Electric XRD-1 unit. The films were measured without magnification with a pointer attached to a slide. A vernier scale permitted measurements of any one sharp line to within a possible error of h O . 1 mm. A4nickel foil (0.001 em. thick) was used over the zamera pinhole assembly to filter out the K-p radiation from the copDer. Since the high a-activitv of uolonium caused the auartz capillary to fluoreke strongl;, i t ;vas necessary to cover the film in the camera with a sheet of black photographic paper (0.001 em. thick). This procedure proved t,o be completely effect,ive in eliminating any fogging from the fluorescence and had no effect on the normal exposure time of 18 to 20 hours used in all runs. The samples were contained in quartz capillary tubes of approximately 0.5 mm. diameter and 0.15 mm. mall thickness. The relative intensities of the powder lines were calculated from the expression 1 COS^ 28 'oalc sin2 e cos e P F 2
the corresponding sulfide, sclenide and telluride of the metal. Examination of calculated covalent radii (and R-X distances) supported this assignment. In the case of MgPo, the unit cell was smaller than that of MgTe as reported by Zachariasen.l3 Since the radius of the polonium atom is larger than that of the tellurium atom, the unit cell would be expected to be larger if the two compounds were isomorphous. It would appear, therefore, that the magnesium polonide cell is not the same type (ZnO) as that of RIgTe. A similar situation existed in the case of mercury polonide, which indicated that this compound did not have the same type of structure (ZnS) as that reported for HgTe.14 The assignment of the structure type and formula in these two cases is discussed below. The results of the X-ray diffraction analysis are shown in Table 11. Also included are a description of the physiral appearance of the polonide and the total amount of polonium in the X-ray sample. The latter is the maximum size of the sample since i t was not always possible to completelv eliminate polonium from the extremity of the X-ray capillary. Nickel Po1onide.-Kickel wire (0.0015 inch diameter, Grade A, W. B. Driver Co.) was used in the preparation of nickel polonide samples by the differential furnace method. Several reactions were carried out in which known weights of wire were heated between 300 and 600°, in polonium vapor. A crystalline metal product resulted in each case. From the amount of polonium contained in each sample, the experimental mole ratios of polonium to nickel were calculated. Mole ratios consistent with the X-r'ty lattice parameters and heating temperature were not obtained, but in most cases the ratio P o / X was between 1 and 2 . The calculated experimental mole ratios assumed that none of the nickel was lost by volatilization of the polonide. This assumption was not valid since the nickel polonide was quite volatile and tended to distil tonmrd the cold end of the capillary, particularly a t temperatures above 500". At these temperatures crystal plates of the polonide were formed whose surfaces exhibited a high metallic luster. The X-ray diffraction patterns indicatd a hryagonal, close-packed structuie for the nickel polonide with lattice with no corrections for the absorption and temperature facno S 3.95 A . and CQ = 5.68 8. tors being made. It was impossible to determine accurat>ely constants Tungsten, Molybdenum, Tantalum and Carbon Polonides the temperat,ure of the diffraction samples a t exposure time experiments were performed using tungsten, molyhsince the decay of polonium caused a small temperature rise -Similar denum, tantalum and carbon bathed in polonium vapor at in the sample which varied with the size and configuration of temperatures up to liOO", but no reaction occurred. the sample. Gold, Copper and Silver Po1onides.-Gold as found to dissolve polonium vapor a t temperaturcs above 650", the Preparation of Samples and X-Ray Diffraction solubility depending both on the temperature of the gold Results and the relative temperature of the gold and polonium ends Group I1 Polonides and Lead Po1onide.-The experi- of the capillary. However, no compound was observed. mental conditions used in the preparation of these polonides Copper and silver both formed compounds (see ref. 3, are shown in Table I. All polonides were prepared from also), but good X-rav data were not ohtained. Copper high purity, commercially available metals. Except for polonide was both unstable and volatile a t about 400". liquid mercury, the metals were used in the form of 150Volatility of Po1onides.-In the prep:wation of these mesh powder or filings. polonides, the volatility of the polonidc often dictated its K i t h the exception of l\lgPo and HpPo, each rompound method of preparation Also, the volatility of polonidcs is had the same rrystal structure as the corresponding siilfidc, of general intrrest in high temperature U ~ Uof poloniiim defielenitle and telluride, as evidenced by the agreement be- posits. Accordingly, ordrr-of-magnitudc ( stimntrs ot vola tween calculated and observed X-ray line intensities. Accordingly, the polonide was assigned the same formula as
-
+
(12) M G. Bowman and N. H. Krikorian, Los Alamos Scientific Report LA-1402, 1953 (classified).
(13) W. H. Zachariasen, 7. physik. Ckem., 124, 277 (l92G). ( 1 4 ) R. W. G. Wyckoff, "Crystal Structures," Vol. I. Interscience Publishers, Inc., New Yorlc. N. l-.,1931.
INTERMETALLIC COMPOUNDS OF POLOXIUM
April, 19GO
437
TABLE I1 POWDER DIFFRACTION RESULTS Formmila
wt. of
of polonllle
PO,
Description
mg.
Symmetry
IkPo NgP0
Black powder Black
202 86
f.c.c. h.c.p.
ZnS
CaPo SrPo BaPo ZnPo CdPo HgPo PbPo
Grey, non-metallic Grey, metallic Grey, metallic Metallic crystalline Grey, metallic, crystalline Metallic Metallic, crystalline
294 63 47 20 16 12 12
f.c.c. f.c.c. f.c.c. f.c.c. f.c.c. f.c.c. f.c.c.
NaCl
tility as o1)t:iincd from this investigation are given in Table 111.
TABLE I11 TEMPERATURE AT WHICHTHE SUBLIMATION (OR VAPOR) PRESSURE OF POLONIDE IS ESTIMATED TO BE 0.1 MM.
.
Volatile
7 . -
-Nan-volatile-
Polonide Temp.,
Hg
(Po), Cu
Zn,Cd, Ni
Pb
Mg
Be, Ca
Sr, B a
OC.
300
400
500
700
>500
>600
2650
The high volatility of HgPo and its ease of formation a t 200" (or below) are of special interest. For instance, this indirates that precautionary measures must be taken when poloniiim is handled in a vacuum system to avoid contamination of the polonium by HgPo. X-Ray Powder Diffraction Data.-Comparisons of the calculated and observed intensities for the polonides are shown in Tnblcs IT through XII. TABLE
Iv
BERYLLIUM POLONIDE Indices hkl
----Sin2 Obsd.
8---
Calcd.4
Relative intensities 0bsd.b Calcd. (ZnS)
0.0522 VS 1.00 ,0696 RIS 0.49 MS ,1393 .42 MS ,1915 .49 IT' .2089 .13 F ,2785 .07 R.I IT ,3307 .19 3IST ,3482 .17 \v ,4178 .I4 iv ,4700 .16 Nil ,5571 .... .05 .6107 .6093 iWT .18 6200 .6267 .ll . . .e863 Nil .09 . .. 7485 Xi1 .OB 7076 ,7659 V\t' . lo 444 .835G Xi1 .04 71 1-551 8889 8878 IV 30 a Sin2 e v.tlws ralrulated for aa = 5 838 A . bT'S = very strong, R = strong, X S = moderately strong, >I = faint, wcxnlL,IF- = ivpak, F moderate, ~ 1 1mocjpratclv ~ I T = cry faint, T3 = broad. 0.0524 ,0699 ,1395 .1912 ,2097 ,2781 ,3303 ,3480 ,4171 .-4700
111 200 220 311 222 400 331 420 422 511-333 440 531 442-600 620 533 622
w
TABLE V M.IGXS~IUM POLOXIDE Indices hhl
100 002 101
102
----Sin? Obsd
0 0418 .0474 .0539 .0897
--Relati> W--
Calcd
0 0419 0474 .0538 0893
Obsd.
e intensitiesCalcd. WnO)
INIA~
o
?*IS
12 0 20
VS MW, B
0 27
?*IS
100
o
35 0 31 1 00 0.21
Type
NiAs
Sac1 XaC1 ZnS ZnS XaC1 NaCl
110 103 112 20 1 004 202 203 210 211 114 105 212 j 300 213
1
0.1255 ,1481 ,1733 ,1797 .1894 .2161 .2743 .2934 .3051 ,3151 .3405 .3765 .3995 .4244
006 '05} 106
.4643
220 222 116 311 304
,5044
E
Unit cell dimensions,
1
.5531 ,5679
.5903 206 313 .6520 224 .6954 0 Sin: e values 7.077 A .
X-Ray density, g./cc.
6.
7.3
5.838 f 0.006 4.345 f ,010 7.077 f ,020 6.514 f ,006 6.796 f ,003 7.119 f .003 6.309 -I. ,004 6.665 f .004 6.250 f .003 6.590 f .003 0.1257 ,1486 .1731 .1795 .1896 ,2150 .2743 .2933 .3052 .3153 .3382 .3407 .3771 .4000 *4245 .4266 .4639 .4685
S 31, B S
hI
W W JLW VW
6.7 6.0 6.3 6.3 7.2 7.2 11.1 9.6 0.27 .25 .20 .10 .05 .07 .09
0.32 .35 .32 .19 .04 .06
.13 .04 .I6 .09
.04
M
.I5 .12
11
\v, MW
.05
.04 .I0
hfW
.I4
mv, P
,5028 F ,5502 f .5523 LV, B .5566 ,5667 W ,5896 \I7, B .5921 .5942 .6511 VW ,6924 VW (dculated for a. = 4.345
.03 .04
I
.04 .05
1 :I; { ::; .05
.04
.OF
.01 .09 .04
.05 A . , and co =
Discussion Magnesium Po1onide.-The X-ray diffraction pattern for the magnesium polonide sample conformed to the hexagonal system. The cell dimensions give an axial ratio of 1 629 which favors a ZnO structure type. However, the unit cell of MgPo is smaller than the unit cell of MgTe. Since the radius of the polonium atom is larger than that of the tellurium atom, the unit cell would be expected to be larger if the two compounds were isomorphous. It would appeal, therefore, that the magnesium polonide cell is not of the ZnO type. A KiAs arrangement is suggested as this would more conveniently accommodate the atoms. For purposes of comparison, relative line intensities were computed for a magnesium polonide structure of the ZnO type (MgTe type) and of a NiAs type. I n the calculations for the NiAs arrangement, the polonium parameter was varied
W. G. WITTEMAN,A. L. GIORGIAND D. T. VIER
438
TABLE VI CALCICM POLONIDE Indices h kl
111 200 2'20 311 222 400 33 1 420 422 511-333 440 53 1 442-600 620
533 622 Sin*B
--_-_
s i n * e--
Obsd.
Calcd.5
Relative intensities Calcd. Obsd. (NaCl)
0.0425 0,0419 S 0563 .0559 VS ,1129 .1118 S hlS 1546 ,1538 31 ,1684 ,1678 M \T ,2248 ,2237 2660 ,2656 Sl .2805 ,2796 hIS 3361 3355 hIS 3774 .3775 hZ 4474 ,4474 vn4895 ,4893 SI ,5035 5033 hI ,5592 .5592 IT 6014 6012 VW 6150 ,6151 w va~ticqranlculoted for a" = 6.514
K.
0.81 1.00 0.77 .44 .28 .13 .19 .37 .2F .14 .09 .15 .18 .13 .06 .I3
TABLE VI1 STRONTIUM POLOXIDE Indices hkl
111 200 220 311 222 400 331 420 422 511-333 440 531 600-442 620 533 622 444 7 11-551 640 642 731-553 800
,---sin* Obsd.
6
-___Ca1cd.a
0.0385 ,0509 ,1030 ,1413 ,1543 .2060 .24448 ,2574 ,3085 ,3474 ,4117 ,4480 ,4630 ,5143
Relative intensities Calcd. Obsd. (NaC1)
0.0385 h1 ,0514 vs .lo28 S ,1413 ,1541 11 ,2055 ,2441 F ,2569 I1 ,3083 M .3468 F .4111 P .4496 F .4624 3f ,5138 .... .5524 Xi1 ,5660 ,5652 I1 ,6187 ,6166 F .... ,6551 Nil ,6677 ,6680 \v ,7184 .7194 M ,7595 .7579 F .... .8221 Nil 733 .... ,8607 Nil 820-644 .8727 '8735 M 660-822 ,9261 ,9249 ;\I Sin20 values calciilat~edfor a. = 6.7961.
w w
w
0.30 1.00 0.78 .17 .29 .14 .08 .37 .27 .06 .09 .06 .I8 .13 .02 .12 .04 .05 .11 .24 .08 .04
.03 .35 .34
TABLE VI11 BARIUM POLONIDE Indices hkl
200 220 222 400 420 422 440 600-442 620
7 -
Obsd.
0.0472 ,0941 .1414 .1884 ,2351 .2816 ,3750 ,4222 .4688
Sin* e----. Ca1cd.a
0.0468 ,0937 .1405 ,1873 ,2341 .2810 .3746 .4214 ,4683
Relative intensities Calcd. Obsd. (NaC1)
VS
w
1.00 0.80 .30 .14 I39 .29 .09
1cz
.19
AT W
.13
vs M
w S M
622 444 640 642 800 820-644 822-660 662 840
Tol. 64 \I7
0.5151
0.5158 ,5621 ,6091 .6557
,5621 F .6087 m .6556 s .... ,7492 Si1 ,7951 .7960 5 ,8418 .8420 P ,8885 ,8897 Jr ,9344 .9365 r )-I a Sin*8vnlucs c:ilciilnted for a0 = 7.119 Ai.
0.12 .04
.10 .21 .03 .24
.21 .17 .11
TABLEIX Z I N C POLONIDE
Indices hkl
--Sin? Obsd.
6
-
Relative intensities Obsd. Cslcd. (ZnS)
7
Ca1cd.a
I11 0,0449 0,0447 200 ,0597 ,0596 220 .ll95 .1192 311 .1638 .1640 222 .l793 ,1789 400 .2393 .2385 331 ,2840 ,2832 420 .2990 .2981 422 .3588 ,3577 511-333 .4038 .4024 440 .4778 ,4770 53 1 .5214 ,5217 600-422 ,5268 ,5366 620 .5963 .5962 533 ,6404 .6409 622 ,6550 ,6558 444 .7150 ,7155 711-551 .7606 ,7602 G40 .... .7751 642 ,8339 ,8347 731-553 ,8802 ,8784 Sin*8 values cnlciihted for no = 6.309 (I
1%
?\I
1.00 0.21
ITS
.64
8 Tt'
.50 .06
w AZ w 31 b4 VF M F 1%F VF VF Xi1 kl
11
K.
.ll ,21 .09 .21
.15 .07 .17 .05 .12 .07 .03 .04 .16 .04
.:HI .34
TABLE S CADMIUM POLOSIDE Indices hkl
-Sin2 Obsd.
-e
Ca1cd.a
Relative intensities Obsd. Calcd. (ZnS)
111 0.0404 0.0401 vs 200 ,6534 Nil 220 .IO77 .lo68 d 311 ,1477 ,1469 11s 222 .... .1603 Xi1 400 .2146 ,2137 \v 331 .2545 ,2538 Sl 420 ,2671 Si1 422 .3208 .3205 11s 511-333 .3610 ,3606 51 440 .4292 .4274 F 531 ,4674 .a74 it' 600-442 .... .4808 Xi1 620 ,5336 .5342 \v 533 ,5735 ,5743 VF 622 .... ,5876 Si1 444 .... ,6411 Si1 711-551 .... .6811 w 640 .... ,6945 Si1 642 .749(3 .7479 SI 731-553 ,7872 ,7880 51 a Sin2 8 values calcidated for nu = 6.665 A.
1.00 0.08
.eI D.52 .03 .13 .22 .04 .26 .16 .08 .16 .02 .13 . 07 .01 .04 .13 .01 .2G .23
from 0.22 to 0.28. The most satisfactory agreement between calculated and observed line intensities was obtained for a polonium parameter of 0.250. The latter are the values listed in Table V.
INTERMETALLIC COMPOUNDS OF POLOSIUM
April, 1960
439
Mercury Po1onide.-Consideration of the rehtive scattering factors of the two atoms, and the observation that only those reflections were found Relative intensities -----Sing 8 - - 7 Calcd. Indices on the pattern where h, k and 1 were even, sughkl Obsd. Calcd.0 Obsd. (NaC1) gested that the cell was of the NaCl type. Close 200 0.0612 0 0608 VS 1.00 agreement between the observed and calculated 220 .1217 .1215 S 0.77 intensities based on a KaC1 f.c.c. cell indicates that ,1825 ,1823 M 222 .28 mercury polonide is of the KaC1 type and has the ,2431 .2430 MTS’ 400 .13 formula HgPo. 420 ,304I ,3038 MS .36 Nickel Po1onide.-The first sample of nickel 422 .3650 ,3645 M .27 polonide was in the form of rather large crystals and .4871 ,4860 F 440 .09 yielded an X-ray pattern comprised of a large .5474 .5468 M 600-442 .20 number of spots rather than the usual diffraction .6076 ,6075 W 620 .15 lines. The X-ray sample was heated above the 622 .6680 .6683 W .15 melting point of the polonide (-625”) and then .... ,7290 Nil 444 .05 cooled rapidly in an attempt to decrease crystal .is88 ,7898 w 640 .17 size. This treatment not only decreased the .84960li 8505~ 111 642 .41 size of the crystals (as evidenced by lines in the .8537ap ,8548~~2 diffraction pattern), but also induced changes: Sin2 e Td u e calculated for a0 = 6.250 1. (a) Polonium lines were found in the mttern. TABLE XI1 indicating a lower P o / X ratio in the cokpound LEAD POLONIDE than existing before heating. Relative intensities (b) The lattice constants increased from a? E -------Sins 0 - 7 Indices Calcd. Obsd. (NaC1) 3.96 and eo i 2 5.70 A. Obsd. Calcd. 3.95 and co E 5.68 to a0 hkl (e) The order of the relative intensity of difVS 1.oo 200 0.0548 0.0546 fraction lines had changed, suggesting a change in VS 0.79 .lo93 ,1093 220 the structure of the unit cell. MS ,1637 .1639 222 .29 As a result of this experience, several additional M .14 ,2194 .2185 400 samples of nickel polonide were prepared under S 420 .38 ,2738 ,2731 various experimental conditions. T‘ariations in ,3285 ,3278 MS .27 422 the lattice constants for the hexagonal cell were ,4370 IS’ .09 .4385 440 observed between the limits C L ~ 3.95 and cG = ,4925 ,4917 M .19 600-442 5.68 to a. = 3.98 and eo = 5.71 A. Correlation of M .14 ,5473 ,5463 620 mole ratios with lattice constants mas not achieved. ,6008 ,6009 M .13 622 However, the variations in the lattice constants VF .... ,6555 .04 444 suggest the formation of nickel-polonium comMW ,7102 .7102 .14 640 pounds of varying composition. These observa,7649 .7648 M .29 642 tions indicate that the Xi-Po system may be very .Si31 ,8741 F .05 800 similar to the Xi-Te system. Klemm and FratiniI6 MS .9278ai ,9287~~1 820- 644 .53 have established that nickel and tellurium form . 9 3 2 7 ~ .9333a2 compounds of continuously varying composition ,9822 ,9833 BI S .82 822-660 between KiTe and XiTe, and that the lattice cona Sin2 6 values calculated for a0 = 6.590 1. stants for the hexagonal cell increase with a deExcept for the reflections from the 102 and 103 crease in the Te,/Iii mole ratio. A change in strucplanes, the observed line intensities are in good ture of the unit cell ( S i h s type for KiTe and Cdagreement with the values calculated for the NiAs structure. Of special interest are the sharp re- (OH), type for the NiTe,) also was ohserved. Summary flections from the 211 and 114 planes. Here one 1. Nine compounds of polonium-BePo, Mgwould expect approximately equal intensities from the NAs-type structure and a difference of Po, CaPo, SrPo, BaPo, ZnPo, CdPo, HgI’o, been prepared on a microgram almost a factor of 2 between the intensities of the PbPo-have two lines from a ZnO-type structure. A NiAs-type scale and identified by analysis of their X-ray structure is suggested since the two lines are diffraction data. 2 . With the exception of IfgPo and HgPo, all actually of about equal intensity. Although the lines from the 102 and 103 planes are less intense compounds that have been identified appear to be than expected for a NiAs-type structure, one may isomorphous with the corresponding compounds of still accept this structure for magnesium polonide sulfur, selenium and tellurium. 3. The lattice dimensions, crystal systems, sin2 since the lines are rather broad and diffuse and, hence, may be expected to appear less intense. 6 values, ahd relative line intensities of the poloFurther, consideration of either the ionic or atomic nium compounds are given. 4. Reactions of polonium with nickel, copper, radii of magnesium and polonium atoms, together with the interatomic distances calculated for the silver, gold, carbon, molybdenum, tantalum and two structures, renders the ZnO structure in- tungsten are described. Acknowledgment.-The authors are deeply herently unlikely and suggests that magnesium polonide has a NiAs-type of structure. On this grateful to W. H. Zxhariasen for his assistance basis, the formula of magnesium polonide is pre(15) W. Iilemm and N. Fratini, Z. U ~ O T Q allgem. . Chem., 251, 222 sumed to he IJIgPo. (1913). TABLE XI MERCURY POLONIDE
0
0
A. G. WILLIAMSON AND R. L. SCOTT
Vol. 64
in determining the crystal structure of magnesium Treiman and R. B. Bevan for the purification and polonide, and to N. H. Krikoriaii, R. Krohn, 1,.H. calorimetry of the polonium.
€€EATS OF RIIXISG OF KON-ELECTROLYTE SOLUTIONS. I. ETHASOL + BENZEh’E AND METHANOL + BESZEKE’-2 BY A. G. WILLIAMSON AND R. L. SCOTT Department of Chemistry, University of California, Los Angeles, California Received September 21, 1959
+
-4 calorimeter suitable for measuring heats of mixing of fluorocarbon hydrocarbon mixtures is described. The calorimeter is similar to that of Adcock and McGlashan but uses a thermistor as the temperature sensitive element. In the course of testing the calorimeter a discrepancy between our measurements and the published data for the system ethanol benzene a t 45’ \vas observed; our new results have since been confirmed by new measurements by the original workers. The new data on ethanol benzene a t 45” and methanol benzene a t 25 and 45” correlate well with the available data for other alcohol benzene systems.
+
+
+
+
Apparatus.-The calorimeter is essentially one-half of the twin instrument described by Adcock and hlcGlashan3 with the thermopile replaced by a thermistor. The thermistor ( a “Veco” type 31A2, R2p1000Q) is made one arm of a Wheatstone bridge which is brought to balance a t the beginning of each experiment. Temperature changes in the calorimeter during the measurement are recorded in terms of the “off balance” current in the detector arm of the bridge. In about half of the experiments recorded here the detection was by means of a galvanometer (Leeds and Northrup type 2385-G). Galvanometer readings were taken every 30 seconds during the course of the experiment and were used to construct a temperature us. time curve for the experiment. In the remainder of the experiments the detector arm of the bridge was connected to the input circuit of L: Liston-Becker model 14 breaker amplifier. The output of the amplifier was then used to drive a 10 my. span Varian strip chart recorder. I n both cases the current through the thermistor was kept to about 25 pamp. The sensitivity of the galvanometer detector was about 15 mm. deflection pcr joule. With the amplifier-recorder arrangement and the amplification adjusted so that the noise level did not evceed division a sensitivity of about 30-40 chart divisions per joule was obtained. Obviously with either system of detection a higher sensitivity could be obtained with higher thermistor currents. However this was considered undesirable because of the possibility of thermal inhomogeneity in the calorimeter arising from heat dissipation by the thermistor. Heat is supplied to the calorimeter from a 50Q resistance heater wound non-inductively on the outer bell of the calorimeter. The resistance of this heater was measured accurately after it had been mounted. The current in the heater was ascertained by measuring the potential drop across an accurately calibrated loa resistance placed in series with the heater. The current flow was timed with a Standard Electric Time Company clock which could he read to 0.01 sec. The mercury pool switches operating the heater and the clock m r e coupled (see ref. 3) so that they could be switched on and off simultaneously. Test of the switching equipment showed that the error in timing was not more than =k0.04 sec. The method of operating the calorimeter was that described by Adcock and hfcGlashan3 (i.e., for endothermic processes the heat of mixing -nas estimated to within about 5% and compensating heat was supplied to the calorimeter simulaneously with the mixing process). I n this way temperature changes in the calorimeter were reduced to a minimum. Following each experiment a calibration was made by supplying a known amount of heat to the calorimeter and noting the galvanometer or recorder deflection. Since the calibration is required only to corrert (1) This work ia supported b y t h e U. 9. Atomic Energy Comfor the differenre between the heat of mixing and the electrimission under Project 13 of Contract AT(ll-1)-34 with the University cal heating in the first part of the experiment it need not be of California. known to better than 1t3-457,. (2) Presented a t the 135th National Meeting of t h e American Measurements were made with the calorimeter immersed Chemical Society, Boston. ?Jess., April 9, 1959. (3) D. S. Adcock and hl. L. JIcGlashan, Proc. Roy. Soc. (London), in a water filled thermostat in which temperature fluctuations did not exceed =k0.002”. 8326, 266 (1954). (4) G. 11. Cheesman and A. B. M. Whitaker. %bid., A312, 406 Trial Measurements.-The system ethanol benzene a t (1952). 45’ was chosen initially as a test system because the heat effect in the calorimeter was about the same as that expected ( 5 ) I. Brown s n d W. Fock, Aust. J . Chem., 8 , 361 (1955).
Introduction I n recent years there has been a considerable interest in the thermodynamic properties of mixing of fluorocarbon hydrocarbon mixtures. Vaporliquid equilibrium measurements have been made and the excess Gibbs free energies of mixing have been derived for several such systems. However even very good excess Gibbs free energy data may not lead to values of the excess entropy and heat of mixing of useful accuracy. It has been our aim therefore to construct a calorimeter suitable for measuring the heats of mixing directly. Since the fluorocarbons are not readily available in high purity and since the fluorocarbon hydrocarbon mixtures have large volumes of mixing our criteria in selecting a calorimeter for this work have been that it should require only a small quantity of material for each measurement and that it should be one in which volume changes on mixing are not restricted so as to produce pressure changes during the mixing process. I n addition to these requirements the vapw space in the calorimeter should he as small as possible to prevent errors arising from evaporation or condensation in the calorimeter. Of the calorimeter designs published during the last few years3+ that of Adcock and l\lcGlaqhan3 seems the most suitable for our purpoqes. The apparatus described by these workers uses only 1-2 ml. of each component per measurement, has virtually no vapor space and imposes no restrictions on volume changes. We have therefore used a modified version of their design. I n the course of the trial measurements a large discrepancy was obvrved between our measurements and those of Brown and Fock5 and this paper is concerned with the resolution of the discrepancy. Measurements on fluorocarbon hydrocarbon mixtures will be published in a later paper.
+
+
+
+
