NOTES
xov., 1959
1975
TABLEI11 INDEXED POWDER PATTERN OF LiThLFe I
Obsd.
VW M
0.0096 .0193 ,0376 .0465 .0579 .0674 .0748 .0774 .0839 .0937 ,1329 .1420 .I491 .1542 .1670
vs S
W M M M-
vw M
S S S S M
sin2 e
hkl
I
Obad.
0.0093 .0186 .0373 .0466 .0580 .0673 .0746 .0766 .0839 .0932 .1326 .1419 .1491 .1538 .1678
110 220 220 3 10 002 112 400 202 330 420 402 332 440 213 600
M W W+ W W
0.1864 .1912 .2048 .2237 .2327 ,2643 .2690 .2789 .2900 .2979 .3156 .3271 .3802 .3848 .4070
S S
M M M M-
vw W VW W+
TABLEIV INDEXED POWDER PATTERN OF LiTh+F1? I W M
vw S vs S W
vs S M
vw W S
vs S
sin’ e Obsd. Calcd. 0.0141 0.0141 .0181 .0181 .0283 ,0282 .0324 .0322 .0400 .0398 ,0469 .0463 .0567 .0565 .0710 ,0700 .0755 .0751 ,0885 .OS3 .096l .0963 ,1039 .lo38 .1314 .1311 .1413 .1412 .1442 .1443
hkl 220 002 220 202,221 003,311 222 400 420 421,313 500,422 511 304 442,601 620 305,540
I S S S 9S VS M W VW W M VW W M W M
W
sin2 e Obsd. Calcd. hkl 0.1468 0.1478 315 612 .1487 ,1486 .I586 .1588 630,325 ,1615 ,1620 000 .1809 711 .I810 .1872 .1871 720 .2005 .2008 505 .2029 .2025 614 731 .2089 ,2092 .2121 .2132 624 .2150 .2153 650,525 65 1 .2197 .a198 .2262 .2259 800 .2313 .2308 634 ,2358 ,2346 207 .2434 .2430 615 .2483 .2487 227,714
LisThF7 Li,ThaFsl LiThlFe LiTh4F17
Symmetry
Tetragonal Tetragonal Tetragonal Tetragonal
THE
6.206 f 0.006 15.10 I .002 11.307 =k ,009 12.984 =k .004
hkl
620 323 541 631 710,004 523 224 314 712 800 334 732 444 ‘ 215 305
SYSTEMLiF-Thf
Lattice parameters (A.) a0
Calcd.
0.1864 .1911 .2056 .2242 0.2330,O.2320 0.2656 .2693 .2786 .2910 .2982 .3159 .3283 .3811 .3858 .4044
were tentatively indexed (Table IV) and found to best fit a tetragonal unit cell whose lattice parameters are a,, = 12.984 f 0.004 A. and co = 11.46 f 0.02 A. The absence of single-crystal data allows for the possibility of error due to pseudosymmetry. The data assembled from the X-ray analyses of the four crystalline phases in the system LiF-ThF4 are summarized in Table V. Future detailed structure determinations are planned for all four compounds. Acknowledgment.-The authors wish to thank H. L. Yakel, Jr., and R. M. Steele for their aid with the single-crystal determinations. Our thanks are also due to M. P. Haydon for density calculations. In addition, we are grateful for the support of other members of the Ceramic Laboratory.
TABLEV CRYSTALLOGRAPHIC DATA8s4s6 FOR PHASES IN Phase
sin2 e
Calcd.
EO
6.470 f 0.002 6.60 I .02 6.399 f .008 11.46 =k .02
Space group
P4/nmm or P4/n 14~a
Body-centered (1)
.......... . .
Density, g./cc;
5.143 4.387
... ...
HEAT AND ENTROPY OF FUSION OF MERCURIC BROMIDE’
LiThzFg.--The phase LiTh2Fg, which was reported to be optically uniaxial,2 gave reflections which were indexed (Table 111) from DebyeScherrer film and single-crystal data. The unit cell is tetragonal with lattice parameters a,, = 11.307 I 0.009 A. and co = 6.399 0.008 A. From the Weissenberg photographs the only systematic extinctions observed were those that arise from a body-centered cell. LiThiFI,.-This phase was reported to be optically biaxial with a variable optic angle (2V).2 The data obtained from the DebyeScherrer films
To study the constitution of molten salt mixtures with mercuric bromide as solvent, an accurate value of the cryoscopic constant, based preferably on a calorimetrically determined heat of fusion, is essential. Beckmann,2 Olivari,8 and Jander and
(3) C. J. Barton, W. R. Grimes, H. Insley. R. E. Moore and R. E. Thoma, THIEJOURNAL, 62, 605 (1958). (4) C. J. Barton, H. A. Friedman, W. R. Grimes, H. Insley. R. E. Moore and R. E. Thoma, J . A m . Ceram. SOL, 41, 63 (1958). (5) R. E. Thoma, H. Insley. B. 8. Landau, E. A. Friedman and W. R. Grimea, ibid.. 41, 538 (1958).
(1) Part I1 in the series: “Structure of Molten Mercuric Halides.” Thin work was made posaible in part by support reaeived from the U.8. Air Force, Air Research and Development Command,Office of Saientifia Research, under Contraot No. AF-49(638)-50. (2) E. Beckmann, 2.anoro. Chem., 06, 175 (1909). (a) F. Olivari, Atti Accod. Lincei, a l l , 718 (1912).
*
BY GEORQE J. JANZAND JEROMEGOODKIN Department of Chemistry. Reneeelaer Polytechnic Imtitute, T r o y , N . Y . Received April 8, 1969
1976
Vol. 63
NOTES TABLE I HEATEVOLVED BY MERCURIC BROMIDEIN COOLING FROM INITIAL TEMPERATURE TO 300°K.
Temp. rise calorimeter
Total
2.11 1141.81 2.00 1082.28 1.48 800.80 1.99 1076.87 1.00 541.14 1.04 562.79 1.00 541.14 0.93 503.26 2.03 1098.51 2.16 1168.86 a 40.2528 g. HgBrz.
Heat evolved (cal.) Capsule Sam le” alone onPy
124.59 116.86 111.11 112.83 106.24 108.92 102.43 98.13 120.82 129.27
1017.22 965.42 689.71 964.04 434.90 453.87 438.71 405.13 977.61 1039.57
HgBrr (1 mole)
9106.71 8642.97 6174.66 8630.62 3893.46 4063.29 3927.57 3626.95 8752.82 9306.80
Brodersen4 reported values of 5010, 4617, and 5010 cal./mole, respectively, for the heat of fusion derived cryoscopically. KelleySa derived a value of 4020 cal./mole from the available phase diagram data in the literature. A second value, from an analysis of the available vapor pressure data, 3960 cal./mole, was recommended by Kelley6b as the best value for the heat of fusion. One value for mercuric bromide obtained calorimetrically,6 4614 cal./mole, differs from the above best value but insufficient information is given in this early study to account for the discrepancy. The present note reports a redetermination of the heat of fusion by the method of drop calorimetry. Experimental Heat of Fusion Apparatus and Accessories.-The calorimetric assembly designed to yield results with an accuracy of 2 ~ 2 %for heats of fusion in the range 2-4 kcal./mole, and the recording differential potentiometer for the temperature-time measurements were the same as described elsewhere in detail.’,* For salts for which the vapor pressure is appreciable at the fusion temperature, e.g., HgBrz, 105 mm., some modification of the platinum capsule design is necessary so that the sample can be hermetically sealed in the capsule without loss due to volatilization. It was found that a small latinum tube, 5 cm. long X 3 mm. diameter, welded to tge lid of the crucible to serve as a filling tube, proved adequate. With the modified lid soldered to the empty crucible, the sample was loaded conveniently through the platinum chimney tube, after which the upper end of the “chimney” was crimped shut and welded to give the sealed system required for the calorimetric measurements. Sample evaporation in the latter operation was prevented by cooling the “chimney” with wet cotton wool. Mercuric Bromide.-The mercuric bromide (reagent grade) was purified by vacuum drying and resublimations as described elsewhere.9 The reproducibility and sharpness of the melting point, 238.1 f 0.lo, were taken as criteria of purity.
Results The procedure for calibration of the calorimeter and measurement of the heat of fusion have been adequately described elsewhere.’,* The data and results for a series of 10 determinations over the temperature range 210-360’ to establish the en(4) G. Jander and K. Brodersen, 2. anorg. allgem. Cham., 264, 57 (1951). (5) (a) K.K. Kelley, U. 8. Bur. Mines Bull. 393, Washington, 1936; (b) ibid., 383, Washington, 1935. ( 6 ) M. Guinchant, Comp. rend., 149, 479 (1909). (7) J. Goodkin, C. Solomons and G. J. Janz, Rev. Sci. Inatr., 29, 105 (1958). (8) C. Solomons and G. J. Janz, Anal. Cham., 80, 623 (1959). (9) G. J. Janz and J. D. E. McIntyre, Proc. N. Y.Acad, Sci., Conference on Molten Salts (1959).
Final temp.
E n t h a l ~ ychange, (caKlmole) Cor. to 300’K. HT - Ham
Initial
9083.30 8672.24 6250.75 8695.00 3922.97 4114.02 3974.39 3656.22 8729.41 9312.65
533.4 522.3 513.9 516.6 502.5 507.4 496.3 487.4 526.8 544.1
~
(OK.)
298.8 301.5 303.9 303.4 301.5 302.6 302.4 301.5 298.6 300.3
-23.41 29.27 76.09 64.38 29.27 50.73 46.82 29.27 -23.41 5.85
“CY
