K. R. BONNICKSON
220
Vol. 59
HIGH TEMPERATURE HEAT CONTENTS OF ALUMINATES OF CALCIUM AND MAGNESIUM BY K. R. BONNICKSON Contribution .froin the Minerals Thermodynamics Branch, Region 111, Bureau of Mines, United States Department of the Interior, Berkeley, Calif. Received August 20, 1064
Heat contents of the compounds, 3CaO,&O3, 12Ca0.7Al~03,Ca0.A1203, CaO.2AI2O3and MgO.Al203, were measured in the temperature range 298 to 1808°K. Regular behavior was observed except for 12Ca0.7A1208 which has an anomaly (heat capacity peak) a t 1310'K. Heat content and entropy increments above 298.16"K. are tabulated, and representative beat content equations are derived.
Introduction A recent paper' from this Laboratory reported low-temperature heat capacities and entropies at 298.16 OK. for magnesium aluminate (Mg0.A1203spinel) and the more important of the calcium aluminates (3Ca0.A1203,l2Ca0.7Al2O3,Ca0.A1203 and Ca0.2Alz0,). The present paper records the results of heat content measurements for the same substances in the temperature range 298 to 1808°K. The only previous similar measurements are those of von Gronow and Schwiete2 for 3Ca0.A1203 (293-1573°K.) and Ca0.Al2o3(293-1673°K.). Materials and Method.-The substances investigated are ortions of the samples used by King1 in low temperature [eat capacity measurements. His paper describes the methods of preparation and gives the results of chemical analyses and X-ray diffractions, so that repetition here is unnecessary. The indicated purity is 99.5% or better in each instance. The heat content measurements were conducted with previously described* apparatus and methods. The samples were held in platinum-rhodium capsules, the heat contents of which were determined by separate experiments. The
furnace thermocouple was checked frequently against the melting point of pure gold.
Results The measured heat contents, expressed in defined calories (1 cal. = 4.1840 abs. joules) per mole, appear in Table I and Fig. 1. Molecular weights conform with the 1953 International Atomic weight^.^ The estimated uncertainty in the measured heat contents is about +0.2%. TABLE I HEATCONTENTS ABOVE298.16"K. T O I L
HT
-
Hze8.16
T, OK.
HT h'2cS.lS
(CAL./MOLE)
T,
ox.
HT
-
HZ..l6
3CaO.AlzOa (mol. wt., 270.20) 373.6 381.3 383.8 413.2 482.6 495.7 501.9 502.6 592.7 598.6 601.6 684.9 713.3
3,980 4,280 4,380 6,070 10,120 10,920 11,320 11,440 16,880 17,090 17,390 22,630 24,220
394,4 506.1 622.0 637.8 753.7 845.4 908.6 924.9 930.3 954.7
26,250 60,160 98,480 103,540 142,610 174,390 196,640 202,020 204,170 212,300
402.6 498.2 611.4 710.9 817.4 922.6
3,250 6,570 10,820 14,560 18,710 22,930
403.7 494.5 578.0 704.7 797.0 910.8
5,570 10,800 16,070 24,230 30,700 38,530
421 .O 485.7 584.5 767.4 814.4
3,830 6,070 9,760 16,870 18,720
742.4 796.9 811.3 812.7 845.9 909.0 944.9 997.4 1010.2 1031.1 1050.0 1093.1 1099.7
26,290 29,530 30,520 30,410 32,950 36,680 39,190 42,410 43,610 45,230 46,640 48,710 49,480
1127.4 1196.5 1215.5 1253.3 1292.1 1361.4 1449.8 1527.8 1632.6 1731.3 1757.4 1780.8 1807.9
51,430 56,310 56,770 60,070 62,770 67,300 73,210 78,540 85,550 92,470 94.160 95,890 97.910
12Ca0.7A1~03 (mol. wt., 1386.68)
3
8 120
2
$100
Y
6
j
80
983.0 1016.5 1027.9 1029.0 1140.3 1221.3 1290.4 1306.2 1310.3
222,480 235,610 238,600 239,810 279,350 309,230 336,550 342,730 344,930
1322.3 1341.5 1358.0 1378.6 1412.1 1534.4 1632.6 1651.1 1672.6
348.900 355,220 361.240 368,870 381,320 427,590 465,050 472,180 482,030
Ca0.A120s(mol. wt., 158.04)
40 20
300
1000.1 1109.8 1204.8 1307.9 1342.5
26,340 30,780 34,820 39,220 40,430
1443.7 1510.7 1623.2 1721.1 1800.2
44,980 48,090 53,230 57,610 61,130
Ca0.2A120a (mol. wt., 260.00) 500
700
900 1100 1300 1500 1700 1900 T, OK. Fig. 1.-Heat contents above 298.16"K.: A, 12Ca0. 7A1203 ( I / $ mole is plotted); B, CaO.2Alz03; C, 3CaO.ALOa; D, Mg0.A1203; E, CaO.Al203. (1) E.G. King, THISJOURNAL,69, 218 (1955). (2) H.E. yon Gronow and H. E. Schwiete, Z . anow. Chem., 216, 185 (1933). (3) K. K. Kelley, B. F. Naylor and C. H. Shomate, U. S. Bur. Mines Tech. Paper 686 (1946).
1013.9 1108.1 1207.7 1306.4 1392.4
45,760 52,440 59,470 66,890 73,040
1518.7 1608.3 1714.6 1773.8 1801.5
82,190 88,670 96,620 100,600 102,860
MgO.Al203(mol. wt., 142.28) 909.0 1020.9 1109.9 1212.2 1325.5
22,570 27,230 31,150 35,690 40,710
1388.4 1508.2 1610.1 1695.0 1805.5
(4) E.Wichers, J . A m . Chem. Soc., 1 6 , 2033 (1954).
43,630 49,060 53,590 57,770 62,690
HEATCONTENTS O F ALUMINATES O F CaLCIUM AND MAGNESIUM
Mar., 1955
22 1
TABLE I1 HEATCONTENTS (CALJMOLE)A N D ENTROPIES (CALJDEG.MOLE)ABOVE298.16"K. T, OK.
400 500 600 700 800 900 1000 1100 1200 1300 1310 1310 1400 1500 1600 1700 1800
--3CaO.AhOs---
-
HT " m e
ST
-
S288.18
5,380 11,180 17,280 23,570 29,990 36,510 43,110 49,770 56,460 63,170
15.48 28.41 39.52 49.22 57.79 65.47 72.42 78.77 84.59 89.96
...
...
69,900 76,660 83,460 90,310 97,220
94.95 99.61 104.00 108.15 112.10
--12Ca0.7AlzOr-H HT z ms
27,800 58,250 90,850 124,650 158,900 193,600 228,750 264,500 301,150 340,250 344,50O(oc) 344,500 (0) 376,700 414,400 452,600 491,400
...
ST
-
S288.18
80.0 147.8 207.2 259.3 305.0 345.9 382.9 417.0 448.9 480.2 483.4 483.4 507.2 533.2 557.9 581.4
...
-CaO.AlzOs-
2s.;
ST
-
HZBS.16
Sass.18
3,140 6,610 10,320 14,130 18,030 22,020 26,100 30,260 34,500 38,810
9.03 16.76 23.52 29.39 34.60 39.30 43.59 47.56 51.25 54.70
5,340 11,200 17,480 24,050 30,830 37,760 44,800 51,920 59,100 66,320
15.34 28.40 39.84 49.97 59.02 67.18 74.60 81.38 87.63 93.41
...
...
...
.. ...
43,180 47,610 52,090 56,610 61,160
57.93 (30.99 63.88 66.62 69.22
73,570 80,830 88,100 95,400 102,750
98.78 103.79 108.48 112.91 117.11
No transformations, isothermal or otherwise, were observed, except in the case of 12Ca0.7A1203. This substance has a heat capacity peak a t 1310°K. The heat capacity increases from 259.3 cal./deg. mole a t 298.16"K. to about 391 at 1310"K., then falls abruptly to about 357.5, and finally again increases to about 396 cal./deg. mole a t 1700°K. The heat content of Mg0.A1203is higher than that of Ca0,A120aby amounts ranging from
