Vol. 77
value for the compound is only O.GVb greater than TABLE 11 for the constituents. This difference becomes progressively larger a t lower temperatures, reaching 3.1% at 100'K. and an indicated 15.7% a t 50OK. Although the designation of this substance as a compound (rather than as a solid solution of calcium oxide in calcium metatitanate) is justified by the work of Coughanour, Koth and DeProsse," the present results offer further support in that Zinc-titanium spinel requires further considerathese lower temperature differences appear too large tion. This substance is a spinel of the variate to be ascribed to a solid solution. Entropies at 298.16"K.-The entropies were cal- class.1b One-half of the zinc atoms occupy metal culated in the usual manner. The measured por- sites that are tetrahedrally coordinated with tions, between 51 and 298.16"K., were obtained by oxygen. The other half of the zinc atoms and the Simpson rule integrations of plots of Cp against titanium atoms occupy metal sites that are octalog T. The extrapolated portions, between 0 and hedrally coordinated with oxygen, being irregu.Jl'K., were obtained from the following empirical larly arranged among these sites. The disorder of sums of Debye and Einstein functions, which fit arrangement of the zinc and titanium atoms should the measured heat capacities between 31 and lead to a zero-point entropy. However, the degree 29% 1Ci'K. to within the inaximutn deviations indi- of disorder is not known and is not ascertainable by X-ray diffraction. If the arrangement is comcated in parentheses. pletely random, then the addition of 2R In 2 = AI ?TiOi L.73 cal. deg. mole to the Sn,98 Is-value in Table I1 would be required, making Sn29816 = 33.6, which is the maximum possible value. .Is there is a CasTizO; tendency for localized electrical neutralization in D + 5E + 5E +E (0.5%) crystals, it may well be, for example, that each Zn04+ group is neutralized. This would require I,i,TiOs an equal number of Ti+4and Zn+2 nearest neighbors, and calculation gives an entropy increment of R In 3'9 = 0.S1, making so,,,], = 33.6, which Zri2Ti01 probably is about the minimum possible value. A more definite entropy assignment is not feasible a t this time. (16) I< \k' G Wyckoff, "Crystal Structures," \'ol 11, Interscience The results of the entropy calculations are in Table TI. It is noted t h a t the measured portions Publishers, I n c , New York, N 'I,1981, p 43 constitute 93.7 to 96.9% of the totals for 298.16'K. BERKELEY 4, CALIFORYIA
(LF)
(??)
(6i.2)
[CONTRIBUTION FROM THE hf1NERAI.S
(TF)
THERMODYXAMICS BRANCH,REGION111, BUREAUO F DEPARTMEST O F THE ISTERIOK]
M I X E S , LTXITED STATES
High Temperature Heat Contents of Some Titanates of Aluminum, Iron and Zinc BY K. R. BONXICKSON RECEIVED NOVEMBER 29, 1954 Measurements of heat contents above 298 OR.were conducted for aluminum titanate, ferric titanate, titanomagnetite and zinc-titanium spinel to temperatures of 1803, 1739, 1513 and 1798"K., respectively. Sormal behavior was observed, except for titanomagnetite which shows an unusual upward trend in heat content beginning about 1200'K. A table of smooth matching values of heat content and entropy increments was constructed arid heat conterit equations were derived.
Introduction (ZnsTiO4). No previous similar data for any of Investigation of high temperature heat contents these substances have appeared in the literature. o f interoxidic compounds of titanium has been a Materials.-The ferric titanate and titanomagnetite used part of the recent program of thermodynamic in this work are portions of the samples described b y Todd and King.5 Likewise, the aluminum titanate and zincmeasurements of this Laboratory. Previous papers titanium spinel are portions of the samples described by dealt with the sodium titanates,' metatitanates of King.8 Their papers include the methods of preparation, calcium, iron and magnesium,2 titanates of mag- the chemical analyses and the results of X-ray diffractions. ~ i e s i u m ,and ~ titanates of barium and ~ t r o n t i u m . ~ Measurements and Results This paper reports results for aluminum titanate (Al2TiO6),ferric titanate (FeaTiOb), titanomagnetite The measurements were conducted with previ(a spinel, FezTiOl), and zinc-titanium spinel ously described apparatus.I The samples were (1) B. I;. S a y l o r , THISJ O U R N A L , 67, 2120 (1945). (2) B. F. Naylor a n d 0. A. Cook, i b i d . , 6 8 , 1003 (1946). (3) R. L. Orr a n d J. P. Coughlin, ibid.,'14, 3186 (1952) 14) J. P.Coughlin a n d R. L. Orr, i b i d . . 7 5 , 630 (1953).
( 5 ) S. S. T o d d a n d E. G. King, ibid , 7 6 , 4547 (1953). ( 6 ) E . G. King, ibid., 7 7 , 2150 (1955).
(7) K. K. Kelley, B. I;. Naylor a n d C. H. Shomate, E.S. Bur. Mines Tech. P a p e r 686 (1946).
TIT,IN.\TES O F ALUMINUM,
April 20, 1935
enclosed in platinum-rhodium capsules, the heat contents of which were determined by separate experiments. The capsule containing the titanomagnetite was evacuated, filled with helium, and sealed by platinum welding, The necks of the other capsules were merely pinched shut. In all instances careful account was taken of the weights of the capsules and contents during the measurements to assure that no losses occurred. The furnace thermocouple was checked frequently against the melting point of pure gold. The experimental heat content results are listed in Table I and plotted in Fig. 1. They are expressed in defined calories (1 cal. = 4.1840 abs. joules) per mole. Molecular weights are in accord with the 1953 International Atomic Weights8 TABLE I EXPERIMENTAL HEAT CONTENTSABOVE 298.16 OK. (CAI,./ MOLE)
-
HT Hzss. i o
T. OK.
Hzsa.ia
HT
o$,
HT
-
H298.16
411.0 509.9 594.7 608.7 708.8 724.1 806.8 847.1 848.4
AlrTiOa (mol. wt.,181.863 1517.3 1006.1 30,680 4,030 1527,5 8,050 1030.1 31,880 1553.5 11 ,660 1176.7 39,020 1610.7 12,360 1249.1 42,600 1703.1 16,800 1269.1 43,640 1736.8 17,560 1319.6 46,100 1744.1 21,260 1399.2 50,230 23,220 1406.1 50,530 1803.2 23,280 1,502.9 55,480
56,190 *56,760 58,070 60,870 66,110 67,340 67,700 71,:mo
410.2 513.2 620.0 716.9 836.0
FesTi05 (mol. wt., 239.60) 4,650 908.6 28,470 1430.7 9,320 1017.8 33,780 1516.9 14,290 1122.8 39,410 1627.9 18,800 1232.5 44,890 1739.0 24,780 1322.6 49,720
55,410 60,000 65,910 72,170
423.7 517.6 626.0 730.0 837.8 935.7
4,630 8,150 12,790 17,160 21,910 26,410
402.2 513.5 596.4 716.3 793.8 925.0
ZnnTiO? (mol. wt., 242.66) i 0 4 ~ 5 . 0 30,730 1507.9 1119.2 34,070 1610.4 1214.1 38,590 1701.6 1303.0 42,710 1759.6 19,470 1417.2 47,970 1798.2 25,250
FezTiOa (mol. wt., 223.60) 959.9 994.3 1041.0 1130.7 1213.9
27,570 29,140 31,330 36,850 39,940
1279.7 1305.3 1378.5 1406.9 1513.3
3,660 7,740 11,120 16,120
43,140 44,530 48,280 50,260 5~,65o
52,320 57,210 61,520 64,300 66,490
Aluminum titanate has been reported as being unstable below 1570°K.9 In the range 1000 to 1570'K. decomposition may occur a t an appreciable rate. Consequently, in making the measurements care was taken to minimize the time in the furnace in this range, and to thoroughly heat the sample above 1570'K. between measurements to recombine any possible dissociated material. This procedure appears to have been effective as the results (8) E. Wichers, THISJ O U R N A L , 76, 2033 (1954). (9) S. M. Lang, C. I,. Fillmore and L. H. Maxwell, J. Reseavch
No(1. Bur. Standards. 48, 298 (1952).
I R O N AND Z I K C
21 53
80 70
s
2 60
-
>
3 50
4
10
'
30
G
20 in 0
300
a n
700
900 1100 1300 i500 i7oo 1900
T , "K. Fig. 1,-High temperature heat contents: curve A , FenTi06; curve B, AlzTiOs; curve C, FetTiOa; curve D, ZnzTi04. (Scale at left is for FesTi04 and Zn?Ti04; scale at right is for FezTiOj and AlzTiOs.)
in Table I show no evidence of decomposition. Likewise, zinc-titanium spinel has been reported as unstable with respect to decomposition into a solid solution and free zinc oxide a t temperatures below 1270'K. la The similar procedure of minimizing the furnacing time and thoroughly heating above 1270'K. between runs was adopted. Again, the heat content data show no evidence of decomposition of the sample. The ferric and aluminum titanates give similar, very regular heat content curves. The heat content of ferric titanate averages about 11% higher than that of aluminum titanate a t all temperatures between 500 and 1700OK. Both titanomagnetite and zinc-titanium spinel belong to the variate class of spinels.'' The titanium atoms and half of the iron atoms in the first instance, and the titanium atoms and half of the zinc atoms in the second, are irregularly arranged among the octahedral lattice sites. The remaining iron or zinc atoms are regularly arranged in tetrahedral sites. The heat content of the zinc compound follows a regular course throughout the temperature range studied. That of titanomagnetite follows a similar course to about 1200'K., but a t higher temperatures the slope of the heat content curve increases in a rather unusual manner. The reason for this is not known. One possibility is that it may be related to increasing randomness in the arrangement of iron and titanium atoms in the crystal. Another possibility is that it is merely the result of additional electronic energy levels of the iron atoms (or preferably ions) coming into play a t the higher temperatures. Magnetite itself does not show this behavior,12 but does have a (10) S. S. Cole and W. K. Nelson, J . Phys. Chcm., 42, 245 (1938). (11) R. W. G. Wyckoff, "Crystal Structures," Vol. 11, Interscience Publishers, Inc., New York, h'. Y., 1951, pp. 42-43. (12) J. P. Coughlin, E. G. King and K. R , Bonnickson, THIS JOURN A L , 73, 3891 (1951).
215 1 11
'r.4ULE
I I EAT CONTENTS (CAL./MOLE)A N D ENTROPIES (CAI,./DEG.MOLE)A B O V E 298.16 "I.;. I . "E;.
$00
>(io 600 700 800 !)Oil 1000 1 l!)O
12011 1;3! 10 1400 I500 l6On 1700 1800
AIzTiOh
HT - 11z.a.~S'r - S?SS.IS HT -
3,600 7,620 11,930 16,420 21,020 25,700 :30,450 :15,2m 40,180 45,150 50,180 55,260 60 ,370 65,490 70,620
10.35 19.30 27.16 34.07 40.22 45.73 50.78 .55,33 59.59 63.57 67.30 70.80 74.10 77.21 80.14
FezTiOs HZS.16
4,330 8,740 13,300 18,010 22,870 27,860 32,9G!) 38, 1:10 43,3:10 48, 550 53,800 59,080 64,400 69,760
ST
-
(13) K. K. Kelley, U. S. Bur. Mines Bull. 470 (1949).
LOW
FIT
-
ZnzTiO4
FerTiOd H2~8.16
ST -
.hS.I6
IO. 80 19 40 2fj. 74 33 . 2'3 39.06 44.28 49.29
3,750 7,610 11,640 15,850 20,220 24,740 29, 400 34,210 39,180 34,350 49,160
