A. G.
PINKUS,
J. s. KIM, J. L.
hICATEE, JR., AND
C. R.COSCILIO
Yol. s1
the estimated energies of transition and temperatures of the maxima in the heat capacity measure1 1 1 en ts. I t is o f interest to note that thc hcat capacities o f the R P and H C P forms are identical within the limits of our experimental error (rather large, 5 1-27;) below the transition temperature. h'othing is observed in this temperature range that can be associated with the conversion of one form to the other; presumably both change to the H T F a t the transition temperature. From the X-ray data on quenched samples it appears possible to change the R P form to the H C P structure b y prolonged heat20 40 60 ing; this transition occurs more readily a t temperatures in the vicinity of 300' when small amounts of Fig. 3.--ll)ifferential cooling curves water vapor are in the system, which may be related to the observation t h a t the transition to the that the effect of water is reversible. A final ex- HTF also then occurs a t a lower temperature; the periment was conducted in which twice as much H T F may provide the mechanism for the converwater was added, Fig. 3d. The temperature halt sion by reverting to the H C P form on cooling. The then was observed nearly 50' lower than for the transition from R P to H C P appears quite slow ill degassed samples. The monohydrate of FeBr? samples thoroughly degassed prior to annealing, is not stable a t these temperatures (decomposition surprisingly so even a t 500' where 2 hr. annealing pressure of H2O estimated to be 10 atm. at was apparently insufficient. This observation may %SOo). Previous experiments in this temperature actually be a matter of lack of detection of ordered range also have shown no interaction of water va- lines on the powder pattern because of the small por with FeBr? of such a nature to cause a pressure particle size of the original dehydrated (RP) samchange detectable on a diaphragm gauge.? ple. -4. longer annealing interval allows larger crysThe marked effect of small amounts of water va- tallites to grow by vaporization. por on the transition temperature again suggests The calorimeter is currently being redesigned to the transition is of the cooperative type. Small permit measurement of heat capacities a t higher amounts of impurities have been shown to have a temperature to give better definition of the transipronounced effect on second-order type transitions tion. It is also planned to investigate other subin certain metal systems.g-'O n'ater vapor ap- stances having similar structural characteristics to pears to interact with the FeBrl lattice reversibly in those of iron(I1) bromide to see whether they unsome way which markedly affects the transition. dergo similar transitions. Slightly varying amounts of water vapor could be Acknowledgment.-\Ye are pleased to acknowlresponsible for some of the differences observed in edge financial support received for this work from (8) P W Selwood, "lIagnetochemistry," 2nd Ed., Interscience the Office of Ordnance Research, U. S. ;\rmy. Publishers. Inc., A-ew York, S . Y., 1955, p. 204.
I
i
-
(9) J Uorin, P h y s . Rev., 78, 819 (19.50) (10) V Xlarian, r l i i i z . P h y s . , 7 , 4.59 ( 1 0 3 7 ) .
/CO\TRIRUTIOU
FROM T H E
SEATTLE, M:ASHIXCTON
DEPARTMENT O F C H E X I S T R Y , BAYLOR l - \ I V E R S I rY, A Y D BAROIDDIVISIOY, N A T I O Y A L LEADC O ]
X-Ray Diffraction Pattern for Monoclinic Sulfur BY A. G. PINKUS, J. S. KIM,J. L. LIc~ATEE, J R . , ' AND C. R. CONCILIO' RECEIVED JULY 2.5. 1958 The X-ray diffraction pattern of rnonoclinic sulfur has been determined by making use of a special heated sample holder
I n connection with some X-ray diffraction studies2 on orthorhombic and carbon disulfideinsoluble sulfur, we were surprised to find t h a t an X-ray diffraction pattern for nionoclinic sulfur I t is noteworthy that alhad not been r e p ~ r t e d . ~ (1) Baroid Dirision, Houston, Texas. (2) A. G. Pinkus, J. S. Kim, J. L. Mchtee, Jr., and C. B. Concilio, Tins J O U R N A L , 79, 4566 (1957). (3) After our work was complete (J. S.Kim, thesis, Baylor Univers i t y , 1957) a notice of a preliminary report of the diffraction pattern of monoclinic sulfur came t o our attention [C.A , , 51, 10965 (195711 T h e abstract of t h e paper presented a t a meeting of the American Physical Society, Southeastern Section a t the University of Florida, Gainesville, Florida [J. E. hliller, N. S. Rendrick, Jr., and G XV. Crawford, P h y s . Reo., 99, 163 (1955)1, however, does not present any data for comparison with our results.
though the crystal structure of orthorhombic sulfur is w e l l - e ~ t a b l i s h e d only , ~ ~ ~ a preliminary report on the unit cell and space group of monoclinic sulfur has been published using single crystal data.6 The reasonable assumption has been made4 t h a t monoclinic sulfur consists of a cyclic ring of eight sulfur atoms. Das7 recently enumerated the difficulties encountered in his unsuccessful attempts to obtain a powder X-ray pattern of monoclinic (4) B. E. Warren and J . T. Burwell, J . Chem. P h y s . , 3 , 6 (1935). ( 5 ) S. C. r2brahams. A d a C v y s l . , 8 , 661 (1955). (6) J . T.Burwell, 11, Z . Krzsl., 97, 123 (1937).
(7) S.R.Das in "I U P A C Colloquium Munster, on Silicon-SulphurPhosphates," Verlag Chemie, 0 m , b . H . ,Wcinheim!Bergstrasse 1955, p. 103.
X-RAYDIFFRACTION PATTERN FOR MONOCLINIC SULFUR
June 5, 1959
2653
TABLE I X-RAYDIFFRACTION DATAON MONOCLINIC SULFUR dobd
6.65 6.32 4.41 3.79 3.74 3.29 3.10 3.04 3.00 2.60 2.49 2.46 2.44 2.18 2.10 1.932 1.894 1.872 1.857 1.786 1.708 1.679 1.635 1.599 1.567 1.452 1.432
(11)
Q0b.d
26 4
0.0226 ,0250 ,0514 ,0696 .0714 ,0924 .lo40 ,1082 ,1111 .1479 ,1613 ,1652 ,1679 ,2104 ,2267 .2678 ,2787 .2853 .2900 ,3135 ,3427 .3546 .3741 .3910 .4072 ,4743 ,4876
5 13 20 100 9 12 4 2 7 6 4 3 2 1 2 3 6 3 2 1 5 2 3 17 3
111
221,122 222 (213?) 032 123 141 412,214 042 323,240,124 340,143 234,502 144,343,252
0.0718,0.0i12 ,0928 ( .1056) ,1083 ,1110 .1481 ,1622, ,1601 .1666 ,1673, .1673,0.1675 ,2100, ,2109 ,2267, .2267 ,2678, ,2672, .2678 .2850 ,2890 ,3131, .3422, ,3562 .3749, ,3917, ,4080 .4748 .4875
.3144, .3137 ,3419, .3419,0.3421,0.3424,0.3416 .3750 .3915
sulfur. He obtained only lines characteristic of orthorhombic sulfur and postulated t h a t the transition from monoclinic to orthorhombic must have occurred during the process of powdering and/or the time of exposure to X-radiation. In another experiment only the orthorhombic pattern was obtained for sulfur particles imbedded in celluloid film a t temperatures from SO to 114’. In the present work, using a recent device for heating the sample holder,* a sample of purified orthorhombic sulfur was heated and the diffraction pattern determined immediately on solidification. The data are shown in Table I. Calculated and observed Q values along with the corresponding hkl indices are also in Table I. The Q-values were calculated on the basis of the cell constants reported by BurwelL6 Four of the observed d-lines do not correspond to calculated Q values. On the basis of further experiments, i t seems reasonable that the 3.79 line in the monoclinic pattern represents the appearance of the 3.85 line of orthorhombic sulfur, this being the strongest line in the orthorhombic pattern. Since the calculated and observed Qvalues for the 3.10 line do not check closely, it is possible t h a t a similar explanation may hold here, this line possibly representing the 3.11 or one of the neighboring lines of the orthorhombic pattern. It is evident from a comparison with the orthorhombic diffraction pattern in Table I1 t h a t the remaining three lines a t 6.32, 4.41 and 1.894 cannot be explained similarly. A reasonable explanation of these lines is t h a t they stem from some substance intermediate in the transformation from monoclinic to orthorhombic sulfur. It may be t h a t this (8) R. .4. Roland and E.
h,k,l
ocalod
0.0232
J. Weiss, Am. Mineralogist, 41, 117 (1956).
350 325 434,601,415 353,261,054,045,154,306 245 326,063 543,632 070 346 463
is the ?-(or “nacreous”)-sulfur first discovered by Muthmanng and more recently investigated by Briske and Hartshorne’O in their studies on transformations of y-sulfur to orthorhombic and monoclinic sulfur. Evidence that the extra lines are not due to impurities in the sulfur are (1) the use of highly purified sulfur, (2) the fact that the same sample after standing for 24 hr. gave a diffraction pattern with no extraneous lines being present. The diffraction data for this sample after standing for 24 hr. are listed in Table 11. Thus, although the diffraction pattern of the 24-hr. sample shows only 19 lines, all of these lines correspond1I to 19 of the 45 lines in the orthorhombic pattern. The lesser number of lines in the 24 hr. sample is due to the difference in the methods of obtaining the diffraction patterns. Thus, for the orthorhombic sulfur, a rotating sample holder1* was used. This makes possible the obtaining of a more nearly complete and accurate diffraction pattern since i t minimizes orientational effects in powdered samples. Orientational effects, however, might be expected to be present for the monoclinic patterns since the sample is in the form of a thin film. This would tend to decrease the number of observed lines. Furthermore, an exact matching of intensities would (9) W.Muthmann, 2. K r i s f . ,11, 336 (1890). (10) C. Briske and N. H. Hartshorne, Disc. F a r a d a y Soc., 23, 196 (1957). (11) One of the referees has pointed out that the d-values for the material after 24 hr. are consistently larger than the corresponding data for pure orthorhombic sulfur and that a definite pattern seems to emerge since Ad varies regularly from 0.05 a t the lowest scattering angle t o 0.002-0.003 a t the highest scattering angle. Thus, this would appear to be the result of systematic error in measurement rather than orientation. We thank the referee for pointing this out. (12) J. L. McAtee, Jr., Am. M i n e t d o g i s t , 41, 942 (1956).
2654
RICHARD D. D E ~ ~ AAND R S IRVINGSHAIN TABLE I1 X-RAYDIFFRACTION DATAON SULFUR SAMPLES
Monoclinic after 24 hr.
n
4.11 3.90 3.48 3.36 3.24 3.14
(I/Zl)
14 100 37 38 i6 59
2.63
8
2.43 2.39
54 10
2.15 2.13 1.996
8 16 35
Pure orthorhombic2 d
7.62 5.75 4. t i 4.06 3.85 3.56 3.45 3.34 3.22 3.11 3.09 2.85 2.68 2.62 2.57 2.50 2.43 2.38 2.29 2.14 2.11 1.988
(I/II)
Monoclinic after 24 hr. d (I/Ii)
6 10 1 16 100
.. I
19 31 39 21 15 15 3 11 5 9 10 9
1.906 1.829
25 6
1.760 1.i26
i 2
1.649
8
1.607
2
1.531
8
4 3 14 3
Pure orthorhombic2 d (I/Zl)
1.959 1.901 1.823 1.783 1.757 1.725 1.696 1.668 1.649 1.622 1.604 1.561 1.535 1.529 1.499 1.4i4 1.457 1,437 1.418 1.388 1.351 1.305 1,279
5 8
8 3 n
13 6 1 3 8 5 2 3 2 1 3 2
4 4 2 3 2 2
not be expected for the two samples for the same reason. In view of the recent experiments of Hartshorne and co-workers on the rate of transformation of monoclinic to rhombic sulfur,13 i t would appear certain t h a t the conversion to orthorhombic sulfur should be complete in 24 hr. It would seem possible t h a t the rate of this conversion may be increased by the X-ray irradiation. It has been shown that this is the case for the transformation (13) N. H. Hartshorne and hl. Thackray, J. Chrm. Soc., 2122 (1957), and earlier papers.
[CONTRIBUTION FROM
THE
Yol. SI
of plastic sulfur to the rhombic formI4 and more recently i t has been reported t h a t rhombohedral sulfur (SB) is converted to a mixture of plastic aiid orthorhombic sulfur on exposure to X-rays.’j In some further experiments in which crpstallization of the melted sample was induced by various methods (touching with a spatula, tapping the side of the holder, etc.) various anomalous patterns were obtained which could not be indexed as completely, using the nionoclinic cell constants. l y e have not yet been able to assess completely the significance of these results. JThenever the sample was allowed to crystallize undisturbed, however, reproducible patterns were obtained. Acknowledgment.-The authors express their appreciation to the Texas Gulf Sulphur Co., Newgulf, Texas for a fellowship to J. s. I
