996
ARSOLDREISMAN AND JOAN MINEO
Vol. 65
CORIPOUXD REPETITIOX IS OXIDE-OXIDE IKTERACTIONS. THE SYSTEM C s ~ O - N b ~ O ~ BYARNOLDREISMAN AND JOAN MINEO Watson Laboratory of International Business Machines, Yorktown Heights, N . Y . Received December 16, 1960
In order to test the predictions made in a previous paper,’ the mixed oxide system Csz0-Nbz05 mas investigated using differential thermal, X-ray and density analyses. Five compounds were identified in the region 0-66 mole 70CSZO. Except for a compound melting congruently a t approximately 27.7 mole % CSZO(5CszO.l3Nb$&) and 1415’, the remaining compounds, 2Cs~O.15Nb~06, Csz0.2Nb205, 2Cs~0.3Kb20sand Cs~O.Nb205melt incongruently a t 1403, 1153, and 972 and 857“, respectively. The 2: 15 and 5:13 compounds are isomorphic with the analogous rubidium compounds and the remainder are not. The trends observed in the lower weight members of the series have been found to continue. Thus, the barely emerged cornpound Rbz0.4Nb2Oahas no cesium analog, and the greatly submerged 4Rbz0.3Pu’b2O5composition also fails to repeat. thermal recrystallizations from water, and the final prodIntroduction uct was of the order 99.8% Cs2C03. an attempt has been made I n previous Sample Preparations.-Samples for cooling, heating, to test the va,lidity of the Goldschmidt hypothesis5 density and X-ray analyses were prepared in the same except for reaction temperatures. concerning model behavior, and to gather informa- manner as These were as usual some 20’ below solidus or incongruent tion concerniag compound repetition in a series of transformation temperatures determined by preliminary congener interactions. Since the latter objective cooling analysis from the melt. DBerential Thermal. Density and X-Ray Analysis.has been approached primarily via a study of the were utilized without series al.kali o:xide-Nb.,Os, it is evident that generali- The methods preciously modification. For obvious reasons, liquidus data were zations based on these systems require independent acquired from cooling curve analyses. Data for four phase verification obtainable by investigations of similar equilibria were gathered from both heating and cooling series of ini;eractions. Such studies involving, studies. Since most of the compositions were markedy for example, the alkali oxides and the compound moisture sensitive, tending to hydrolyze, solid state reacted samples were protected from moisture, and density V~OS,whose structural and chemical attributes studies were conducted in trichloroethylene. differ appreciably from those of NbzOa, have been Discussion of Experimental Results initiated and will be reported upon a t a later date. Tables I and I1 list the composite results of As a first stage, however, partial verification of the ideas previously expressed depends on success thermal, density and X-Ray studies. Figures 1 a t predicting the diagram of state for an unknown and 2 show the proposed construction of the thermal and density diagrams. Meaningful liquidus data system in the series now under investigation. Based on observations of progressive submer- could not be collected for alkali oxide compositions gence of repeated compound fields with increasing greater than 66 mole % for several possibly related ionicity of thle alkali metal in the sequence lithium reasons. I n melts containing greater quantities through rubidium, speculations were entertained of the alkali component, both platinum and goldconcerning the composition of compounds to be 20% palladium crucibles were severely attacked expected in the system CssO-SbkOs.l These spec- in the time interval necessary to melt the samples ulations led to predictions t,hat two compound ratios and take them through their liquidus crystallizapresent in the rubidium interaction would not re- tions. Appreciable volatilization of the alkali peat in the cesium system and that a third ratio component also was observed in this region and the might or might not recur. Relat’ed to the question data were found to scatter much more than of compound repetition is the question of whether normally. In addition to the above, the latent compound ratios, not detected in the lower weight heats associated with primary crystallizations interactions, would appear. This phenomenon diminished rapidly, even at differential sensitivities appears to depend on marked changes in interocta- of 5 pv./inch, although one would expect an increase hedral coordinat,ion which appear to be coincident in such anomalies as a compound peak is apwith the introduction of the potassium ion into the proac hed. Attempts a t resolving the diagram in this region lattice. Consequently, new ratios were not exusing X-Ray techniques were not definitive. The pected in the cesium system. problem of contamination by the container maExperimental Procedure terials plus difficulties encountered in carrying reReagents.-Trona Cs2COI and Fansteel “High Purity” Nb205 wrved :is the starting materials for all reactions. actions to completion in the solid state, and even Pretreatment of the pentoxide has been described prev- slightly above the eutectic temperature, coupled ious1y.l The c:trbonate was found to contain small quanti- with rather diffuse and inconsistent X-Ray patterns ties of iron, 0.5-1.0% by weight, but was esscntially free of made iiiterpretation difficult. Thcmnal and X-Ray other impuritirs. The iron was removed by several isodata do, however, indicate the existeiice of one other ________ compound to the right of 66 mole 9; Cs?O. Since (1) A . Reisman a n d F. Holtzberg, J . Phys. Chem., 64, 748 (1960). the present system shows a continuation of the (2) A. Reismail and F. Holtzberg, J . Am. Chem. SOC.,80, 6503 (1958). behavior observed in the rubidium systcm in all (3) A . Reisman, F. Holtzberg a n d E. Banks. ibid., 80, 37 (1958). other regions, it is assumed that the unresolved (4) A . .Reisman and F. Holtzberg, ibid., 7 7 , 2115 (1955). region includes a 4CszO.Kbz06 compound. ( 5 ) V. RI. Golaschmidt, Skrift Norski V i d . Oslo. Mat. N a t . KL,8 , 7 (1926). I n the pentoxide rich portions of the diagram,
COMPOUND REPETITION IN OXIDE-OXIDE INTERACTIONS
*June, 1961
997
TABLE I THERMAL DATAFOR THE SYSTEM Csz0-Nb206 NblO6. mole
CSZO.
mole
%
0 2 4 6 8 10 12 14 16
% Liquidus Solidus
IC0 0
97 96 94 92 90
5 0 0 0 0 88 0 86 0 84 0
5 0 0 0 0 0 0 0
18.0
1491 1176 1460 1441 1437 1413 1400 1392 1386
1491 1309 1402 1399 1404 1406 1372
Nhz06 NbOa NbsOs Sbz05 Nb205 NbsOs
I I I
80.0 78.0 76.0 74.0 72.0 70.0 68.0 66.0 62.0 60.0 59.0 58.0 56.0 54.0 52.0 50.0 49.0 48.0 46.0 44.0 42.0 40.0 38.0
62.0
1395 1403 1412 1414 1411 1410 1403 1381 1331 1294 1245 1197 115-1
1097 1010 950 870 848 813 767 748
1367 1363 1357 1131 1154 1146 965" 1155 071" 1154 968" 1158 849" 973" 859" 1151 873" 857" 975" 854" 974" 854" 974" 859" 973" 740" 752" 857" 747" 856" 752" 748" 748" 748
1300 -
I+E
Nb205+I
1200 -
1
W
+ I1 I + I1
1377
8 2 . 0 1377 1371
20.0 22 0 24.0 26.0 28.0 30.0 32.0 34.0 38.0 40.0 41.0 42.0 44.0 46.0 48.0 50.0 51.0 52.0 54.0 56.0 58.0 60.0
Primary phase
Transitions
I1 I1 I1 I1 I1 I1 I1 I1 I1 IT1 I11 I11 I11 I11 111 I11 111 IV IV V V V V
I
eutectic lies in this interval
s5
IIOO
-
IU+LlQ
w n.
E 1000 -
I-
900
-
5 cu
800 -
*
7000
M% c s 2 0 .
Fig. 1.-Thermal 4.830 4.810
diagram of the system Cs20-Sh20,.
-
4.770 -
4.790
4.750 4.720
-
Q .
+
? eutertic lies here
?:
64.0 36.0 801 746 66.0 34.0 826 738 a Heating curve data only.
?
TABLEI1 DENSITY DATAFOR THE SYSTEM Cs20-Nbz05AT 25' hiole %
Mole % NbzOj
0 2 4 6 8
100 08 96 94 92 !)0 89 88
CaaO
10 11 12 14 16 18 20 22 24 25 26 28 30 32
8G 84 82
80 78 76 75 74 72 70 68
Density, g . / c o . a t 25'
4.540 4.580 4.612 4.651 4.692 4.734 4.747 4.763 4.766 4.779 4.786 4.795 4.805 4.813 4.815 4.828 4.824 4.805 4.787
4.758 4.763 4.774
4.815 4.819 4.817 4.825 4.824 4.822 4.806 4.783
Av.
4.540 4.580 4.612 4.651 4.692 4.734 4.747 4.761 4 765 4.777 4.786 4.795 4.805 4.814 4.817 4.827 4.823 4.806 4.785
M% CszO.
Fig. 2.-Partial
density diagram of the system CszO-r\'b20a.
density measurements were employed to fix the composition of the niobium richest compound Within the limits of experimental error, the intersection of density arms occurs a t 11.6 mole yo CszO and 4.755 g . / ~ ma. t~25'. As in the ru'nidium system, the smallest whole number ratio corresponding to this value is 2:15 (11.76 mole %). X-Ray examination of this compound which melts incongruently a t 1402' showed it to be isomorphic with its rubidium analog. As expected, the 1 : 4 compound, seen in the rubidium system, as a congruently melting compound just intersecting the liquidus arms on either side, does not occur heterogeneously. The liquidus field for the 2:15 compound terminates in a eutectic at 17.5 mole yoCszOand 1372'.
In the rubidium interaction, it was pointed out that the location of the 4 : 11 compound was effected via heating curve analyses, and was assigned a composition of 26.67 mole % Rb20 based on these data. The concern a t that time was whether this seemingly odid ratio was reasonable. Since the only volatile component is the alkali oxide, loss of this material would result in a displacement of the compound's apparent composition to higher pentoxide values rather than to the observed lower one. In the present study, the combining ratio for this compound was established using the density techaique. Within the limits of error, the intersection of the arms is a t 27.4 mole yo and 4.831 g./cm.3 a t 25'. as compared to the more approximate value of 27 mole % given in the rubidium paper. Assuming that if anything, the mole fraction indicated by the density data lies to the left of the true point, a small number value of 5:13 was assigned to this compound. This ratio corresponds to 27.7 mole % CspO, and is assumed to be more representative than the 4 : 11 value previously assigned. The $5 : 13 compound melts a t 1415' and is isomorphic with its rubidium analog. The 1:2 compound melting at 1155' and 46 mole %? Cs20 was readily located with X-ray and heating curve analyses. X-Ray analysis indicated that this compound is not isomorphic with its rubidium analog. As expected, a compound having a base to acid ratio of 2 :3 was resolved using X-ray and thermal techniques. This material melts incongruently a t 975' and 51 mole %, and its liquidus field is appreciably submerged. It is not improbable that a similar ratio would fail to reappear in the next higher interaction. The 2:3 analogs are not isomorphic with one another. The meta compound which is slightly submerged in the rubidium interaction is now almost completely submerged. It melts incongruently a t 850' and 56 mole % and its field of primary crystallization terminates in a eutectic a t 748' and 62 mole %. This compound is not isomorphic with its rubidium counterpart. As expected, the highly submerged 4 : 3 rubidium compound fails to have a stable analog in the cesium system lending some further support to the ideas previously expressed.
While in general the present system shows a continuation of compound submergences with increasing atomic weight in a given congener series, there are two apparent inconsistencies for which no explanation suffices.-These involve the 2: 15 and 1 : 2 compounds both of whose liquidus curves do not appear indicative of greater dissociation. While one cannot derive absolute data on the heat of fusion of a compound solely from solubility data, one can in certain cases make approximations which are indicative of the level of dissociation in the liquid phases. If the state of unit activity for a liquid compound is taken as that of the pure undissociated liquid, one can derive a freezing point equation where the activity term represents that of an ideal solution whose apparent activity and mole fraction difference is due to a dissociation process. Without going into the details of such a treatment, one can demonstrate that the effect of dissociation is t o decrease the solubility of the material in question. This approach can be employed qualitatively in comparing the rubidium and cesium systems for the case of Xb205 and consequently for the 2 : 15 analogs. If we assume that differences between the solubility curves of the Nbz05 in the two interactions are due to the differences in its idealized activity caused by different degrees of dissociation of the next adjacent compound, one would expect the Kb205 solubility to decrease in the cesium system. In other words, the Nb20, liquidus curve should be displaced to the right. 9 comparison of the curves, however, shows an apparent increase in solubility, indicating that the 2 : 15 cesium compound is less dissociated. In the case of the 1:2 compound whose disposition was unclear, two effects are observed. The temperature interval for its liquidus field is two to three times that in the rubidium system while its liquidus slope is almost coincident with that of the 5:13 compound. It is expected that plausible explanations for these possible inconsistencies will become evident from a study of the vanadium series where the pentoxide portion of the diagram is expected to exhibit less compound formation. Acknowledgment.-The authors wish to express thanks to B. Agule for performing the density analyses.
