Abstract
IN a recent discussion on clay–water relationships1, it was reported that Prof. U. Hofmann had prepared dry clay-gels by a freeze-drying technique. I have also made a number of samples of montmorillonite in 20–30 gm. batches by a similar method. A 20 per cent aqueous dispersion of the clay, after purification and saturation with the required base, was frozen so as to form a layer about 5 mm. thick over the inner surface of a 2-litre bolt-head flask, which was then rapidly evacuated to a pressure of less than 1 mm. mercury, the evaporated water being trapped by calcium chloride towers. The final product was a curved sheet of pith-like material of fibrous structure which tended to fracture normally to the surface and had properties similar to those of Prof. Hofmann's product. The bulk density was 0.12 gm. per c.c. as compared with a density of 0.82 for the original powdered bentonite. Attempts to prepare similar gels of kaolin and a soil clay fraction failed since the dry products fell to a fine powder.
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References
Nature, 171, 682 (1953).
J. Amer. Chem. Soc., 62, 1457 (1940).
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CALL, F. Preparation of Dry Clay-Gels by Freeze-drying. Nature 172, 126 (1953). https://doi.org/10.1038/172126a0
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DOI: https://doi.org/10.1038/172126a0
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