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THE SWELLING OF CA‐MONTMORILLONITE DUE TO WATER ABSORPTION
Author(s) -
EMERSON W. W.
Publication year - 1962
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1962.tb00678.x
Subject(s) - swelling , montmorillonite , absorption of water , bentonite , flake , absorption (acoustics) , volume (thermodynamics) , mineralogy , perpendicular , materials science , chemistry , analytical chemistry (journal) , composite material , geology , chromatography , geometry , physics , quantum mechanics , paleontology , mathematics
Summary The increase in thickness of dry orientated flakes of Ca‐montmorillonite about 0·2 mm. thick, prepared from Wyoming bentonite, when brought into vapour equilibrium with solutions of increasing relative vapour pressure has been measured with a travelling microscope. The three solutions used were sat. NH 4 H 2 PO 4 ( P/P 0 = 0·92), sat. Ba(NO 3 ) 2 ( p/p 0 = 0·985), and water ( p/p 0 = 1·0). X‐ray and water‐absorption measurements were also made on separate portions of the flakes at these values of p/p 0 . The density of the dry clay and the apparent density of the dry flake were determined. As the lateral swelling of the flakes was found to be very small compared with the swelling perpendicular to the general plane of orientation of the crystals, the distribution of air and water in the flakes could then be calculated at each value of p/p 0 . Up to p/p 0 = 0·985, 80 per cent. of the water absorbed by the flake was accounted for by the increase in the thickness of the water films on the clay crystals, the remaining water filling about half the pore space. On the basis of the total volume of the flakes, the total pore space was reduced by 12 per cent. at p/p 0 = 0·92 compared with the dry flake, due to expansion of the crystals, but then remained the same up to p/p 0 = 0·985. Between p/p 0 = 0·985 and 1·0, the pore space in the flake was filled and a further small expansion of the flake occurred, but the (001) spacing did not increase beyond 18·9 Å. Swelling in the vapour phase was unaffected by addition of I per cent. CTAB to the clay. The relation between macroscopic swelling and increase in water‐film thickness is consistent with the crystals being in the form of a tactoid. The swelling as p/p 0 → 1·0 was much lower than that of a flake immersed in liquid water (see Part 2). It is suggested that this arises from the formation of polymolecular layers of water on the surfaces of the clay crystals, due to the influence of the exchangeable‐Ca ions which differ in structure from that of bulk water.