DESSITIES O F ~ I . ~ G S E S I U ~ ~ - C r l D h I I U ,ALLOYS \i
J. &I. SISGI->\\.ere obtained from the Sational Lead Company and the ;Inacoiida Copper 3Iining C'ompt~ny. respectively, and n-ere stated to be of tlie highest purit'y ohtainahle commercially, Spectrographic analysis of the material confirmed the absenw of nictallir impivities Ivithin 0.014.02 per cent, and grarimetric analysis of the pure materials indicated completely pure materials irithin the error of tlie determination. The alloys \\-ere prepared in steel crucibles provided 11-it21a thin graphite lining machined from a graphite electrode of the t8ypeused in spectrographic anal The crucihle was provided 113th a stirrer consisting of a steel rod tipped \\.it11 graphite so that t'he only niaterial coming in contact ivith the melt was s p t ~ ~ t r o scopically pure graphite. The crucible ivas contained in a Pyrcs tube ivhich could be evacuated and refilled Tvith an inert atmosphere,--in thia case :wgoii, ~vhichhad been purified by condensing oTTer actiI-:tted charcoal at liquid-air temperatures. The stirrer roiild lie operated externully hy :i bellows ariangement, and the melt Tvas stirred T-igorouslj- t o insure complete mixing. llelt'ing ivas 1 This ivork \vas supported hy :t hasics rcscarch g r a n t f r n i n t he Officr (if Saw1 Ilrse:~rc~l! of the L-nited States 1 - a ~ )lIep:irt!iie~it~ ('ontract S 6 0 r i 13,Task Order 2. 2 This paper is bawd upon H thesis suhmittetl by J. 31. Sirigcr t o t h c Facult!- of t h e
Graduatc School of tlie Piiiversity of I'ittshurgh i n Ixirtiiil fulfillnient of I hc rc~quiremcrits for tlic degree of l l a s t e r of Science, FebruarJ-, 1047.
1000
J. 11. SIKGER AKD TI-. E. TY.-\LL.-\CX
accomplished by use of an induction fuinace n hich surrounded the Pyres tube. The samples so prepaied XI ere practically free of oxidation. Kevertlieleis, the surface 11as machined away prior to determining the densities. After its density had been measured, the alloy 11 as analyzed for its cadmium content by the electrodeposition method. The compositions are believed to he reliable to slightly better than 0.1 per cent. Densities were measured using the method of -\rchimedes with redistilled C.P. grade carbon tetrachloride as the confining liquid. The density of the carbon tetrachloride used in these experiments I\ as determined over the temperature range required. Differences between our 1 esults and published values vere insignificant for the present purpose. The technique employed by Egerton and Lee (2) for eliminating surface tension effects on the supporting TI ire was used in these determinations. The precision with I\ hich duplicate determinations on the same specimen agreed was approximately 0.1 per cent. S o attempt mas made to measure the density at exactly 25'C. In all cases the actual temperature- nere measured, and since they fell betneen 20°C. and 30°C., no correction was necehsary. 11. THE PHYSICAL STATE O F THE ALLOYS A S D FACTORS LIJIITISG I'RECISIOS O F THC DESS1TII~:S
A. Cacitatio?i The principal systematic error associated with measurements of density by the method of Xrchimedes wises from the existence of carities ivithin a sample which nppears upon extemil examination to be sound. I t is possible that our samples were imperfect in t'his respect, but it is felt that the error due to cnvities is small sind is probably ove don-cd by possiblc vffects of varying degrees of order in the alloys. The in ce of the lattci, ivill be referred to belo\\.. The case against' appreciable cavitation is based upon t v o lines of evidence. First, we have compared o u r results ivitli those c:ilciilated from the httice parameters obtained from x - r ~ diffraction y studies. Hume-Ilothery and Raynor (4, 9) have made an extremely careful investigation of this system. Trnfortunately, much of the ~vork as at an elevated temperature (310"('.1 and in the absence of reliable thermal expansion data is not s:uit#ablefor comparison n-ith the results of t'his study. Hon-ever, some of the data are of use and the results, t,oget#Iternith the value for pure cadmium calculated from the data of Jette and Foote (G)! are shown in table I . Since densities computed from lattice parameters are imaffect>edhy the presence of cavities in the alloys subjected t'o diffract,ion study, t,he csistence of cavities in our alloys should he revealed by consistent,ly smaller den~it'ies.~ The lncal; of siwh differeilces can be taken as evidence against cavitation. w u r w \v('rr uiisouiid. ('svities iverc observed prior t o prpimriiig alloys. .ilso, t h e densities were low. Cpon renwitiiig, stiriitig, :tiid in a l l n-ays 1i:iritlIitlp i h c r n n t c l , i d iis if i t n ~ r a11 e ullo>-. the tlrrisity ii!crr:ised t t i t Iic v:iluc givcti i r i t n l ~ l rI .
iietals
11
:IS oI)t:iiiircI f i , o i i i t
i 1 - i ~iixirhiiicd ~
Second, Stockdalc (12) has showi in a very careful study of the tlensities of alloys of silver and zinc that certain otherwise unexplained variations in density can be attributed to cavitation and the sample can be made sound and the densitie5 reproducible by subjecting the specimens to pressure of the order of 10,000 atni. Ailthoughour densities were quite reproducible and gave a smooth curve when plotted against composition, IT e thought it advisable t o test for possible cavitation by a procedure similar to that of Stockdale. After iuhjevting eight samples covering the entire composition iange to approximately 10,000 atm. pressure, the densities were remeasured and found to have increaiccl on the average 0.11 per cent. The maximum increase noted was 0.25 per cent. It may be concluded, therefore, that if the alloys were unsound, the extent must have been small, probably insufficient to affect the density by more than 0.2-0.3 per cent. Possibly, those density increments arc due t o ordering of the alloy rather than t o n filling in of cavities, since orderetl ctriictiires are more tlen,c 13).
11. -~-on-ho))ioyerLeilyof the solid solutions
'l'hc mutual solid solubility of magnesium and cadmium has hcwi (>>t~ ~ l ~ l i s h e d t o he very extensive, if not complete (3, 4,5). It, is ivell Itno\vn tliat the cooling of melts of siibstances exhibiting appreciable solid solubility prodiic~snon-lioinogerieous solid phases because of t'he initial pimeferential crystallizing out. of the higher melting component. Homogeneous solid solutions arc obtuinctl hy subsequent annealing at temperatures close to the melting pont. Til ronncction with other phases of the ~ v o r kIvith this system ~ v ve w e interestetl i n lmth lioniogcrieous and non-homogeneous samples, so that, IYP have meamircd (lensit-ies of sonic of the alloys in t.he annealccl arid uiixnnealctl state. As lye shall int1ic:ttP lwlou-, the effect, of annealing on the tlensity is practically ncgligihlc. ('.
Order-disorder traizsforiiiatioiL
€'erkiaps tlic least satisfactory fcatiu,e of this 1\-0rk u-its oiir ignoiari(Ar 11i the extent t o xhich the order-tlisoi,tlci, tixnd'ormation in the d l u y lint1 t:ilicq~ 11I:tce. It is our opinion that the densities i,eporttcl refer t o the almost cwmplctelg disordered alloy. V7ebase this opinion upon the tlctnilccl studies of the oi~ile~~clisortlc~. transformat'ioii made by Grube and Sehietlt (3) at Stuttgwt and by Stepanol- a11cl coworkers i i , S, 10, 11) at Leningrad.
1002
J. M. SINGER AXD TV. E. WALLACE
Transformations based upon the compositions ?\lg,Cd, lIgCd, and lIgCda occur at the approximate temperatures 150", 250", and 90°C., respectively. The rate studies of Stepanov indicate that, except for compositions in the region of IlgCda, the ordered structure is formed rather slo~vly,if at all, at room temperature. Special low-temperature annealing (100-200"C.) Tvas required to develop the superlattice. However, for compositions between 72 and 78 atomic per cent cadmium, ordering n-as observed t o proceed with an appreciable rate at 0°C. (8). The thermal treatment given our alloys was such as to suppress superlattice formation. They were brought immediately from the temperature of solidification or annealing to room temperature and the density determined within a fern hours. The single alloy (72.37 atomic per cent cadmium) which might have become appreciably ordered fell on the smooth curve of density versus compo-
sition! TABLE 2 Densities of magnesium-cadmium alloys COXPOSITION: ATOMIC P E R C E X T CADDYIUU
I
1-
g./cc.
0 6.65 17.02 35.3s 39.43 52.87 60.36 63.21
'
I
COMPOSITION: ATOXIC P E R CEKT C4DDYIITU
DENSITY
66.57
1.737 2.192 2,902 -1,248 4.511 5.51s 6.048 6.270
69.19 72.37 S i . SO 90.67 96.32 100
I
I
DE\bITk
g./cc.
6.488 6,591 6 800 7.727 7.905 8 ,300 S 642
~-
Cslculations based upon the thermal expansion data determined by Grube and Schiedt (3) indicate that the order-disorder transformation may be accompanied by changes in the density amounting to as much as 0.5 per cent in some instances. The uncertainties in the densities due to an undetermined extent of ordering probably do not amount to more than 0.2-0.3 per cent. However, the actual effect is difficult to assess exactly and this factor would undoubtedly prevent one from ascertaining densities for this system to better than 0.1 per cent unless the degree of order were controlled. 111. CXPERIMESTAL D.1T.i
AKD DISCUSSIOS O F RESULTS
The measured densities are given in tables 2 and 3 . The results given in table 2 are presented in graphical form in figure 1. Values at rounded concentrations taken from a large-scale plot of the data in table 2 are shown in table 4. In table 3 the effect of annealing is summarized. Annealing was carried out for periods of 3 4 weeks a t temperatures within 50" of the melting point of the particular alloy 4 It may be that the lion-homogeneity of this sample retarded formation of the superlattice.
1003
CHASLL
___Per cclil
-0.2 0.0 0.0 +o. 1 -0.2 0.0 0.0
1
80
3
ATOMIC % Cd FIG. 1. Graph showing the variation of density \vith compositioii for magnesiumcadniiuni alloys (solid solutionsi.
after tlic -amplcs hat1 bcen :,euled into evacuated Pyres tubes. The effect of annealing on the densities i:, been to be practically negligible.
COMPOSITIOS: ATOMIC PER CLXT C.4DXIUY
DLXSITY
1'
COILPOSITIOX: .\TOXIC I'ER CEZT C.AU11IU)I
DESSIT1
g.icc
6.035 G.6i0 7.250 7.850
0 10 20 30 10
8.642
50
3 ATOMIC %
Cd
FIG.2. (;Iuph slio\viiig t h e volume cluiiigc accompanying the formation of 1 mol(' of alloy (solid solution! a s it futictioii of composition. 0 , calculated from the d a t a i n table 2 ;
- - _, ca1c~ul:itrtlfroin Iiayrior's x-ray d a t a a t 2 5 T . ; - - -,
cxlculated f r o i o EIuInc-Rothery
a n d Ilnyiior's :.-r:iy tlxta at SIOY'.
The curmture in the density-composition curve apparent in figure 1 is probably real, since it is in general accord n-ith other thermodynamic information :~vailnblefor this system. If the solutions were ideal, thc density-composition curve would be concave upn-arc1 for the entire composition range. Biltz and
Holiorst (1) determined the heat of formation of an alloy of compobition MgC'tl and demonstrated that for this composition the solid solution exhibited a strong negative deviation from ideal behavior. Such deviations woultl modify the ideitl density curve and, if sufficiently pronounced, lead to the t n o point5 of inflcction apparent in figure 1. T-olume changes accompanying the formation of the alloy f i om its components are shown in figure 2. The negative values ere more or less expected, as tlicy are consistent with the general chemical tendencies which lead t o the formation of ordered structures. The positire deviations at high cadmium concentrations u cre not anticipated and may possibly be attributed to unsuqpected syqteniatic errors in the densities of O.4LO.G per ccnt, although these errors are somenhat larger than had been asbigned to the measurements. Included in figure 2 are values of the volume changes computed from the x-ray data of Raynor (9) a t 25°C. and Hume-Rothery and Raynor (4) a t 310°C. The general similarity of the three curves is evident. There seems little doubt that alloys of compositions 0-80 atomic per cent caclmium are formed from their components with a decrease in volume. The incrcments in volume noted at high cadmium concentrations perhaps bhould not be regarded as definitely established. I t is perhaps v orth pointing out in this connection, however, that the x-ray data a t 310°C. indicate a behavior at tlie c:dmium end unlike that in solutions less rich in cadmium. Conceivably, tlie region of zero slope at 310°C. might bc modified in the direction of positive deviations as the temperature is loivered. Returning to the question of using the cleii,ity-coniposition curve a b an analytical tool, by examination of the slope of the curve one finds that a density precise to 0.3 per cent will establish composition to 0.36 unit on the atomic per cent wale in the region of pure cadmiurn and 0.09 unit at thc magne4um end, if the curve is asaumed to be exact. Aillovingfor lack of precision in both the curve and the density measurement, it seems that one could definitely establish compo5ition within limits of 0.5 unit on the atomic per cent scale for all caws and I\ itliin narrower limits, perhaps 0.1-0.2 unit, for magnesium-rich alloys. This method is obviously inferior in precision to conventional chemical analysis but has it distinct advantage in the time required for cases where high precision i5 not ezsential. IT. 5U11MARY
I he densities of thirteen uiiannealecl magnesium-cadmium alloys, ranging in composition from 6.65 to 96.32 atomic per cent cadmium, have been determined x i t h an estimated precision of 0.1 per cent. The densities of seven additional alloys, ranging in composition from 21.7 to 84.0 atomic per cent cadmium, have been determiiied before and after annealing. The influence of annealing on the density is practically negligible in comparison with the stated precision of the measurements. Computations of volume changes accompanying formation of the alloys show that betn-een 0 and 85 atomic per cent cadmium there is an appreciable decrease in volume. .Above 85 per cent slight increments in volume are observed. 7
7
The effectiveness of the density-composition curve as an analytical tool is sufficient to establish composition to about 0.3 unit or better on the atomic per cent scale. IlEFERENCIiS (1) BILTZ,JY.,ASI) HoaoRsr, ( ; . : %. aiiory. allgern. C h r n i . 127, 1 (1923). LEE,W. B . : Proc. Roy. SOC.(London) A103, 487 (1923). (31 GRCBE,'2.)AN IEDT, 1 1 . : % . anorg. allgern. Chem. 194, 190 (1930). (4j ~ I n f E - R o T I m z TW., , A X U RAYXOR, G . I-.:Proc. Roy. 6oc. (Idondon)A174, 471 (1940). (5) HcafE-RorrrmRi-,IT.,ASI) ROWELL, 9. i V . : J. Inst. bIetals 38, 137 (1927). (6) JETTE,E. R., .&XU F o o m , F . ; J. Chem. Phys. 3, 605 (1935). ( 7 ) KORKILOV? I. I.: Bull. acad. sci. 1_'.11.S.S., C'lasse sci. math. nat., Ser. chim. 1937,313. ( 8 ) KORNILOV, I. I . : Compt. rend.a c a d . sei. IT.R.S.S.19, 1.57 (1938).
(9) RAYNOH, G . V.:Proc. Roy. Soc. (Loridon) A174, 457 (1940). (10) STEPANOV, S . 1.: AST) BVI..WH,S. A , : Cornpt. rend. acad. sci. L-.lt. 147 (1936). (11) STEPASOV, S . I., ..\si)KORXILOV, I. I . : . \ J I I ~ . s r c t e u r aiial. pliys.-chim.. Inst. chini. g6n. (L.S.6.R.)10, 7 8 , 97 (1938). (121 STOCKDALE, D.: .J. Iiist. .\IrtaIs 66, 287 (1940).
lteceiccd Junitai IJ 26, 19@
In continuation of btudie- on the solvent estraction of thorium started by two of us (G), we hare determined the distribution of thorium nitrate at room temperature between water and each of the following solvents: isoamyl alcohol, n-hexyl alcohol, methyl isobutyl ketone, methyl n-amyl ketone, and methyl n-hexyl ketone. These five organic solvents appear to be the most promising for the liquid-liquid estraction of thorium nitrate from aqueous solutions also containing the nitrate5 of the rare earths and zirconium. The effect of added nitric acid has been ascertained on the systems containing 7%-hexylalcohol and methyl n-hexyl ketone. Some preliminary extractions with methyl n-hexyl ketone haye been described to show the applicability of the conclusions drawn from these distribiition data. DETERJIIS.iTIOS
O F DISTRIBUTIOS DATA
The experimental technique was that used in the earlier solubility work (G). Each system was composed of 5 ml. of the organic solvent (Eastman Kodak Company, practical grade) and 3 ml. of an aqueous phase brought t o the proper
