NOTES
Feb., 1955 deviate from ideality less than was previously assumed. Also, the solubility curves for chlorine in carbon tetrachloride and in ethylene bromide, shown in Fig. 1, are parallel instead of crossing as shown earlier.4 SOLUBILITY
Temp., OC.
40
OF
TABLE I CHLORINE IN CARBON
TETRdCHLORIDE
Total Moles Clr/ pressure (atm.) (kg. soln.)/(atm. Clz)
NCW Atm. Ch
0.797
2.02 2.36
0.789 Av. 0.793
0.115
50
2.02 2.36
0.590 0.602 Av. 0.596
60
2.02 2.36
0.522 0.522 Av. 0.522
0.0771
70
2.36 2.36
0.417 0.433 Av. 0.425
0.0632
0.340 0.329 Av. 0.335
0.0502
0.0875
~
80
2.36 2.70
90
2.70
0.296
0.0444
Experimental.-The solubilities were determined using a two-bulb glass apparatus with a pressure stopcock and a spherical joint between the upper and lower bulbs. The upper bulb was partially filled with distilled carbon tetrachloride and heated for several minutes in a hot bath (130-140") in order to degas the solvent and sweep the air out of the bulb. A 20% solution of potassium iodide was added to the lower bulb which was then weighed and attached to the upper bulb. The apparatus was connected to a cylinder of chlorine (The Matheson C2mpany) and immersed in a therAfter flushing the connecting mostat regulated to f O . l tubing with chlorine several times, the apparatus was agitated by hand until the total pressure in the system, measured with a calibrated Bourdon gage, remained constant. The stopcock was then turned, allowing a sample of saturated chlorine solution to flow into the potassium iodide solution. The lower bulb was detached and weighed. The amount of iodine liberated by the chlorine was determined by titrating with standard sodium thiosulfate solution using starch solution as the end-point indicator.
189
quently the chlorine-carbon tetrachloride solutions show less deviation from ideality above 40" than predicted by an extrapolation of the earlier data.
EXCHANGE BETWEEN HEAVY WATER AND CLAY MINERALS* BY JOSEPH A. FAUCHER~ A N D HENRY C. THOMAS Deportment 01Chemistry, Yale University, New Haven, Conn. Received September BO, 1064
Water associated with a clay mineral may either be an integral part of the crystal lattice, as OH groups, or bound more or less loosely to the clay in a variety of ways. We report here experiments of a somewhat preliminary nature on exchanges between the water of clays and added deuterium oxide done in the hope of adding to our knowledge on the nature of clay water and the intimacy of its contact with the structural hydroxyl groups. The exchange of deuterium oxide directly with the hydroxyl groups of two clay minerals has been studied by McAuliffe, Hall, Dean and Hendricks3 who found with kaolinite and halloysite complete and rapid H-D exchange with surface OH groups and a slow diffusion into the lattice a t elevated temperatures. These workers used clay intensively dried in vacuo. The present work was done with air-dried material, Le., with material containing much free water, and the exchange results correlated with weight-loss curves done a t temperatures up to 800". Experimental
The procedure for most of the exchanges was as follows. About 0.5 g. of clay of known water content was accurately weighed into a small glass centrifuge tube, heavy water added, and the tube again weighed. The tube was tightly closed, shaken vigorously and allowed to stand overnight. After more shaking the tube was centrifuged and the supernatant liquid (about 0.5 g.) removed. The water mixture was distilled in a short-path molecular type still, used merely for ease in handling the small samples, closed to the outer atmosphere through a drying tube. The distillates were analyzed by means of a Zeiss dipping refractometer equipped with the auxiliary prism for small samples. Temperature control for the refractometer was provided by a water-bath at Discussion.-The results of the solubility meas- 30.00 f 0.03'. The instrument was set against water, urements are given in Table I. The total pres- taking n = 1.33196 a t 30". Our stock of 9935% DzOgave sures a t which the measurements were made are a reading corresponding to n = 1.32754 for pure D20. gives 1.32760 for pure DzO a t 30". Compositions given along with chlorine solubilities expressed both Luten4 of mixtures were computed taking the refractive index as a as moles of chlorine/1000 grams of solution/atmos- linear function of mole fractions, according to Luten an esphere chlorine partial pressure and as mole frac- cellent approximation. Two synthetic mixtures of H 2 0 tion of chlorine/atmosphere chlorine partial pres- and D20 gave results within the error of reading the instrument, about 0.00002 in m. This instrumental uncertainty sure. The partial pressures of carbon tetrachlo- entails gross errors in the analysis of mixtures of low H 2 0 ride were calculated from the vapor pressure of car- content, hence our experiments were done with as large a bon tetrachloride5 assuming Raoults law, and the ratio of clay to added DzO as could be conveniently handled. partial pressures of chlorine were obtained by dif- Even so, the determination of small exchanges is subject to large error. ference. Weight loss curves on the minerals were obtained simply Figure 1 shows our solubility data along with the by heating samples in platinum crucibles in a regulated solubility data of Taylor and Hildebrand3 for chlo- muffle furnace for periods of 12-24 hours at each temperarine in carbon tetrachloride and in ethylene bro- ture. Temperatures were measured on a thermocouple mide. Also shown are the ideal solubilities, f/j'J,placed near the crucibles.
.
calculated previously. * It appears that the two solubility lines do not intersect, as previously r e p o r t e ~ l , ~and , ~ conse(5) J. Timinermans, "Pliysico-C1i~111ical Constants of Pure Organic Compounds," Elsevier Publisliirig Co., New York, N. Y., 1950, p. 225.
(1) Contribution No. 1248 from the Sterling Chemistry Laboratory of Yale University, New Haven, Connectiout. (2) 22 Hamilton Place, Garden City, N. Y. (3) C. D. McAuliffe, N. S. Hall, L. A. Dean and S. B. Hendricks, Proc. Soil Sci. Soc. Amer., 12. 119 (1947). (4) D. B. Luten, Phus. Rev.. 45, 11.31 (193.4).
190
NOTES
Results and Discussion Kaolinite.-American Petroleum Institute Reference Clay No. 4, Macon, Georgia. The clay lost 1.3% a t 60", 2% a t 400", 3% a t 450°, 13% at 500°, and a total of 14.7% on ignition, the curve showing the familiar sharp rise corresponding to the destruction of the mineral. With heavy water no exchange outside the error of our determination was found. The surface moisture and exposed OH groups undoubtedly exchanged, but according to McAuliffe, et uZ.,~ the magnitude of this effect corresponds to our experimental error in this region. We also observed no significant exchange on heating the clay-DzO mixture a t 200" for a day in a Parr bomb. Hal1oysite.-A.P.I. No. 13, Eureka, Utah. The heating curve was similar to that obtained by Ross and Kerr6 and showed an initial rapid loss of 6% up to 60", a gentle rise to 9.5y0 a t 400", a steep rise to 19% at 500", followed by a gentle rise to 20.iy0 a t ignition temperature. The exchange results on this material show points of considerable interest. (In the following discussion results of the exchange experiments will be given in terms of the percentage of water in the mineral apparently coming to equilibrium with the added D20, designated % E.W. Thus complete exchange on the halloysite would give 20.7% E.W.) At room temperature the average of eight experiments gave 12.5y0 E.W., the range of the experiments being 11.8-13.3%. Experiments done in the Parr bomb at 200" gave 17.0% E.W. (six determinations between 15.8 and 18.6yq). At room temperature no significant difference in the extent of exchange was observed on increasing the time of contact to 48 hours. At 200" contact for 24 hours gave 15.8 and 16.070; contact for 96 hours gave 18.0 and 18.6%. These results may be explained if we suppose, as appears reasonable from the structure of the mineral, that in halloysite, in addition to the relatively small amount of surface hydroxyl, all interlayer water together with three-quarters of the water of constitution (Le., those hydroxyl groups in contact with the interlayer water) are exchangeable. We suppose further, in analogy with the results on kaolinite, thltt in completely dehydrated metahalloysite no water of constitution is exchangeable. Assuming ideal formulas, we compute from the weight loss data that our clay can be considered as a mixture of 39.3% completely dehydrated metahalloysite and the remainder completely hydrated halloysite. We are thus led to a calculated value of 13.7y0 E.W., to be compared with the average experimental value of 12.5y0. If in addition we suppose that under pressure a t 200 " metahalloysite is rehydrated, we compute for the high temperature limit 17.5% E.W., in agreement with the experimental finding. This discussion must be considered as tentative only, particularly as regards the assumed rehydration of metahalloysite. Attapu1gite.-A.P.1. No. 26, Quincy, Florida. The heating curve obtained is entirely different in character from those of the other clays, being always convex upward. It shows an initial sharp ( 5 ) Ross and Kerr, U. S. Geological Survey, Professional Pager 165-E,1931.
VOl. 59
rise to 6% a t BO", followed by a nearly linear increase to 15.5y0 a t 500", finally reaching l6.iY0 a t ignition temperature. The shape of this curve allows no differentiation between various "kinds" of water in the mineral. This is borne out, although somewhat roughly, by the exchange results, which gave 14.0, 14.9, 17.2, 18.9 % E.W. These results are consistent with the structure assigned t o attapulgite by Bradleye which implies an intimate contact between the hydroxyl groups and the water present in the channels of the crystal. Chabazite.-For comparison with the results on attapulgite similar experiments were done with a sample of finely ground chabazite. The heating curve is very similar to that of attapulgite and showed a total water content of 21.870. After 24-hour contact with D20at room temperature two experiments showed complete exchange, again indicative of the intimate contact between OH groups and intra-lattice H20. Montmorillonite. A.P.I. No. 23, Chambers, Arizona.-The weight loss curve showed the characteristic two-step form, the first step corresponding to a loss of 17%, followed by a relatively sharp rise to 21.1% on ignition. Five exchange experiments a t room temperature with contact times from 24 to 120 hours gave 19.7% E.W. (range 19.4-20.0%). A single experiment with contact time 5 min. gave l8.9%, indicating that the exchange is very rapid, as was to be expected. These results imply that only 93% of the total water of the mineral exchanges with added DzO. To confirm this result in a less ambiguous manner the following experiment was done. About 8 g. of clay was washed four successive times with 99% DzO over a period of two days. The final wash liquid, after centrifuging and distilling, showed 1.5 mole % HzO. The wet clay was quickly transferred to a large nickel boat and placed together with a thermocouple in a long combustion tube. Dry nitrogen (from a sulfuric acid bubbler and two magnesium perchlorate tubes) was passed slowly over the clay as it was gradually heated in a furnace. Water was condensed from the efffuent gas in a cooled U-tube, protected from the outside air by magnesium perchlorate. During the first stage the tube was gradually heated to 150", a t which point the U-tube was emptied. This water also contained 1.5 mole % H20. A second sample was collected between 150 and 180°, which showed 7.3% H20. At this point a clay sample was removed from the boat which on ignition showed 5.5% of volatile matter remaining. From the heating curve this is seen to be largely OH water. A dry Utube was put in place, and the clay heated rapidly to 800". About 0.4 ml. more water was collected which contained 52 mole % HzO. These experiments are best interpreted in terms of the now generally accepted structure of montmorillonite in which no OH groups are exposed to interlayer water. The heating experiment alone does not rule out a modified Edelmann-Favajee structure in which part of the OH water is exchnngeable. Although the data are not of sufficient precision to permit of a definite conclusion, it appears (6) W. F. Bradley, A m . ~ V i n .26, , 405 (lQ40).
NOTES
Feb., 1955 reasonable that the increase in the HzO content of the water evolved up to 180" is due to an increased rate of diffusion through the lattice. The final water collected up to 800" now necessarily contains much exchanged DzO. For an excellent summary, with references, of present ideas on montmorillonite structure and with important confirmatory evidence see Karsulin and Stubican.' A single experiment a t room temperature on a sample of bentonite from Clay Spur, Wyo., showed the E.W. to be 94% of the total water in agreement with the above experiments. This work was done under the auspices of Brookhaven National Laboratory, Upt,on, New York, to which it is a pleasure to acknowledge our indebtedness. (7) M. Karsulin and VI. Stubican, Monateh., 86, 343 (1954).
191
determined fixed value below the melting point. Measurements of scattered light were made with the photometer a t 4 and 16" with respect to the primary beam. Since the refractive index of the amorphous polymer was found to be 1.427 these angles correspond to scattering angles of 2.80 and 11.13" within the sample. The scattered light from the melted sheet was subtracted from that of the crystallizing sheet to correct for the small scattering from foreign particles in the matrix. The light from the melted sheet was never more than few per cent. of that from the crystallizing tiheet, and the hot stage itself showed no variation in scattered light with changing temperature.
Results and Discussion If one considers a block of material composed of small well separated regions of one refractive index imbedded in a matrix of different index of refraction, then from the theory of light scattering4 it is possible to define an average square distance, p2, within the small regions as
LIGHT SCATTERING FROM CRYSTALLIZING POLYMERS '
BY FRASER P. PRICE
General Electric Research Laboratory, The Knolls, Schenectady, N . Y . Received September 24, 1.964
Crystallizable high polymers when cooled from above the melting point frequently developed crystalline regions in the form of spherulites. While the nature of these structures is still not completely elucidated, and therefore is still the subject of much investigation, 1 ~ 2almost certainly they are not single crystals in the usual crystallographic sense. The investigations of spherulite structure have, thus far, been confined to examination with light or electron microscopes. Both these techniques are incapable of examining the crystals in the very early stages of their formation. This note describes a brief and very cursory light scattering investigation of crystal development in polychlorotrifluoroethylene. This technique affords a means of examining the crystalline regions very close to their beginning. The results were somewhat unexpected and hence, in spite of their brevity, are deemed worthy of presentation. Experimental Polychlorotrifluoroethylene was obtained from M. W. Kellogg Company of Jersey City, N.J., under the trade name Kel-F. The material was from the same batch on which previous investigations of spherulite formation had been made.s Measurements were carried out in a light scattering app:tratus which permitted observation of scattered light down to within about 2' of the primary beam. Light of wave length 4358 A. was used. The polymer sample, a 0.012 in. thick pressed sheet, was clamped to an electrically heated hot stage of low heat capacity mounted normal to the light beam. The low heat capacity of the hot stage made it possible to heat and cool the polymer very rapidly (250 to 150" in 30 sec.). The temperature was controlled to &3" by a thermocouple-actuated relay system. I t was necessary to clean the polymer sheet very carefully to eliminate bubbles from decomposing lint at the elevated temperatures. After the polymer sheet had been placed in the apparatus, the temperature was raised to 250" for five minutes. The temperature was then allowed to drop rapidly to a pre(1) A. Keller, et al., Nature, 169,913 (1952); 171, 170 (1953); J . Polymer Sci., 11, 215, 5G7 (1953). (2) G . Schuur, ibid., 11, 325 (1953). (3) F. P.Price, J . A m . Chem. Soc., 7 4 , 311 (1962).
where -
p 2 = mean square radius of the scattering regions ni = no. of particles of ith kind Vi = vol. of particles of ith kind ~ i = 2 mean square distance from center of gravity in scattering particles of ith kind h = wave length of light in the matrix light scattered a t 4" D light scattered at 16" XI = 2 sin 1.40' Sz = 2sin 5 . 5 7 "
=(
Equation 1 was derived assuming no secondary scattering. If a Lambert type law is assumed for diminution of the scattered light due to secondary scattering, then since the path lengths for the 16 and 4' scattered light differ by only 4% only a negligible change in D would result. The inclusion of this correction will affect the quantitative but not the qualitative aspects of the conclusions presented below. Figure 1 shows D as a function of time for the sample of polychlorotrifluoroethylene quenched from 250 O to various crystallization temperatures. Even though the light scattered a t a given angle increased with time, these results show that D and hence the root mean square radius decreased with increasing time. It is surprising that the average size decreased as crystallization proceeded. This might result from any one of three causes; first the average shape of the scattering regions might change in such a way as to produce a decrease in the radius; second the crystallites might actually break up under the stress induced by volume changes resulting from crystallization; third, and most probable, the crystallites might be nucleated faster than they can grow. It is reasonable to expect that large crystallites would appear rapidly from the liquid magma because, in this state, the long chains are relatively free to move about and to line up with each other. As the crystallization proceeds, however, because (4) P. Debye, THISJOURNAL, 61, 18 (1947).
