NOTES
2782 coordinated aluminum from zeolite Y effects a marked improvement in thermal and hydrothermal stability. The removal of aluminum is accompanied by a contraction of the unit cell which is not surprising since new Si-0-Si bonds are probably formed where Si-0-A10-Si sites existed in the original zeolite.'^' These findings support the conjecture of McDaniel and Maher, who assumed that “stabilization of the structure is a direct result of cell ~hrinkage.”~It now seems quite clear that the ultrastable faujasite of MeDaniel and Maher is an aluminum-deficient material with regard to the tetrahedral framework. These workers stated that their ultrastable faujasite had a significantly lower cation exchange capacity than normal faujasites. The aluminum removed from the framework not only reduces the number of anionic sites but also occupies cation sites as previously described.6 To simplify nomenclature, it is suggested that aluminum-deficient zeolite Y be referred to in the future as simply zeolite Y’.
Acknowledgment. The help of Dr. D. H. Olson in measuring lattice parameters is gratefully acknowledged. Mr. Arthur Julian rendered valuable assistance in the experimental work.
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(7) The formation of these Si-0-Si bonds involves a dehydroxylation reaction distinct from that involving simple hydrogen zeolites. Dr. E. Dempsey, using zeolite models, demonstrated to the author that Si atoms, adjacent t o aluminum-deficient sites, could be geometrically oriented to form new Si-0-Si bonds without disrupting the remainder of the faujasite structure.
Ionic Diffusion under High Pressure in Porous Solid Materials Permeated with Aqueous, Electrolytic Solution
by R. A. Horne,l A. F. Day, and R. P. Young Arthur D . Little, Incorporated, Cambridge, Massachusetts (Received December 5, 1968)
Richardson, Bergsteinsson, Getz, Peters, and Sprague2 studied ionic diffusion in aqueous solutions of seawater constituents under high pressure using a fritted glass diaphragm. Unfortunately, the experiment proved t o be a difficult one and although the “approximate average of data scatter limits” of the integral binary diffusion coefficient appeared to increase from about 1.48 X low5cm2/sec to about 1.6 X lo5em2/ see in going from 1 atm to 1000 bars (dashed curve in Figure 1) for a 3.5 w t % NaCl solution a t 28”, the experimental scatter was so great that the authors concluded that “the influence of the pressure on the ordinary diffusion coefficient. . . was found to be negligible” over that pressure range. The Jozirnal of Physical Chemktry
Pressure kg/cm2
Figure 1. Pressure dependence of various solution properties. Curve 1, viscosity of pure water a t 20’; R. A. Horne and D. S. Johnson, J . Phys. Chem., 70, 2182 (1966). Curve 2, electrical conductivity of 0.100 m KC1 a t 25’; R. A. Horne and R. A. Courant, J. Chem SOC.,3548 (1964). Curve 3, specific volume of pure water a t 20’; E. H. Amagat, Ann. Chim. Phys., 29, 68, 505 (1893). Curve 4, dielectric constant of pure water a t 20”; 5. Kyropoulos, 2. Physik, 40, 507 (1926). Curve 5, dielectric constant of pure water a t 20’; B. B. Owen, R. C. Miller, C. E. Milner, and H. L. Cogen, J . Phys. Chem., 61, 2068 (1961). Curve 6, self-diffusion of pure water a t 30”; G. B. Benedek and E. M. Purcell, J . Chem. Phys., 22, 2603 (1954). Curve 7, proton relaxation time a t 30’; G. B. Benedek and E. M, Purcell, ibid., 22, 2603 (1954). Curve 8, diffusion of THO in HzO a t 25’; R. B. Cuddeback, R. C., Koeller, and H. G. Drickamer, ibid., 21, 589 (1953). Curve 9, transference number of K + in 0.1 N KC1 a t 25’; F. T.Wall and J. Berkowitz, J . Phys. Chem., 62, 87 (1958); F. T. Wall and S. J. Gill, ibid., 59, 278 (1958).
We have examined the relative rates of diffusion of aqueous electrolytic solutions through 06 Selas microporous porcelain disks (capillary radius less than 0.2 X cm) into pure water, without stirring and a t (1) Woods Hole Oceanographic Institution, Woods Hole, Mass. (2) J. L. Richardson, P. Bergsteinsson, R. J. Gets, D. L. Peters,
and R. W. Sprague, “Sea Water Mass Diffusion Coefficient Studies,” Philco Corporation Aeronutronic Division of Applied Research Laboratories Publication No. U-3021 (Dec 1964), Office of Naval Research Contract No. Nonr-4061(00). (3) L. Devel, Acta Chem. Scand., 16, 2177 (1962). (4) (a) R. A. Horne and D. 5. Johnson, J . Phys. Chem., 70, 2182 (1966); (b) R. A. Horne, Sur. Progr. Chem., 4, 1 (1968). (5) R. A. Horne in “Advances in High Pressure Research,” Vol. 2, R. S. Bradley, Ed., Academic Press, London, 1969, in press.
NOTES
2783
different hydrostatic pressures, by following the decay of the electrical resistance of the system. The results are shown in Figures 2 and 3. Although we could
20
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40
30 Time, Minuter
50
60
Figure 2. Resistance decay (diffusion rates) for 3.0 M KC1 under pressure.
readily observe the increased rate of diffusion with increased temperatures a t 1 atm over the range 15 to 4 5 O , the parallel slopes in these figures lead to the conclusion that, in agreement with Richardson, et U Z . , ~ hydrostatic
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KC1 solutions, in ethanol-water systems (Figure 3), and 0.1 A4 MgS04 solutions with comparable results. I n the latter case, more gentle slopes reflected the slower diffusion of this strong structure-maker.a This conclusion may be surprising in view of the profound influence of hydrostatic pressure on the structure of pure liquid water and aqueous electrolytic solutions in the bulk phase;4"*bi6however, it should be noted that the pressure dependence of various water and solution properties in general exhibit virtually no correlations with one another (Figure 1). Unfortunately, because of their relative nature and the experimental and interpretation uncertainties, the present results are compatible with and cannot distinguish between two quite different descriptions of the diffusion process: (1) the traditional point of view that absolute ionic diffusion coefficients in aqueous solution in porous media do not differ appreciably from the corresponding values in free solution, and a t 2000 kg/cm2, like viscous flow, diffusion is facilitated by a few per cent; or (2) in contrast to the structurebreaking effect of pressure on the bulk phase mentioned above, that " . . .solid and liquid surfaces can modify the intermolecular structure of water and that these structural effects can be of a long-range nature and cannot be accounted for on the basis of monolayer or, indeed, multilayer adsorption."6 Soviet scientists have suggested that the properties of this specially structured interfacial water is quite different from that of "normal" bulk water.' Its density is 1.2 to 1.3 times greater and accordingly it appears to be much more stable than the Frank-Wen clusters with respect to hydrostatic pressure8--& possible explanation for the absence of pressure effects in the present experiments. It tends to exclude selectively certain solutesgand its viscosity may be as much as 10 to 15 times greater than that of normal water, which would be expected to result in a general retardation of transport process in the porous mediuma retardation which appears in ionic conduction in memb r a n e ~but ~ which the present experiments fail to confirm because of their relative nature. That is to say the present results are also not incompatible with highly structured water in the microporous disk resulting in a diminution of the ionic diffusion coefficient by a factor as great as 10 to 15, and little dependence of diffusion on hydrostatic pressure. Acknowledgment. This work was supported in part by the Office of Naval Research.
Time, Minutes
Figure 3. Resistance decay (diffusion rates) for 0.1 M KCl in ethanol-water under pressure.
pressure up to 3000 kg/cm2 has little effect (less than lo%, dashed curve in Figure 2) on diffusion rates. Experiments were also made on more dilute (0.3 M )
(6) F. Franks, Chem. I n d . (London), No. 18, 560 (1968). (7) B. V. Rerjaguin, Discussions Faraday Sac., 42, 109 (1966), and the references cited therein. (8) R. A. Horne, A. F. Ray, R. P. Young, and N-T. Y u , Electrochim. Acta, 13, 397 (1968). (9) J. H. B. George, R. A. Horne, and C. R. Schlaikjer, "An Investigation of the Transport Properties of Ion Exchange Membranes," Arthur D. Little, Inc., Final Report (Dec., 1967), Office of Saline Water Contract No. 14-01-0001-962. Volume 78, Number 8 August 1969
