768
.4RTHUR A. VERNON
COLLOIDAL i l L U M I N J M OXIDE ARTHUR A. VERNON Department of Chemistry, Northeastern University, Boslon, Massachusetts Received July 16,1946
d considerable body of literature exists describing methods of preparation of colloidal aluminum oxide hydrates ; the available information has been well summarized by Weiser (3) and Weiser and Milligan (4,5 ) . Bohm and Niclassen (1) reported that evaporation of a dialyzed colloidal aluminum oxide sol t o remove the dispersion medium gave a glass-like solid which was redispersible in water. d patent (2) on the formation of such material mas obtained in 1937. Neither of the articles gives details of the properties and formation of the reversible solid; as part, of a larger program it was necessary to investigate this reversible hydrate or “soluble alumina.” EXPERIMESTAL
Yalerials: In all the experiments aluminum chloride, ammonium hydroxide, and hydrochloric acid of C.P. grade were used. Procedure: A slurry was first made by adding 5 N ammonium hydroxide to 5 N aluminum chloride a t 25°C.; it was then centrifuged with successive addition of distilled water until the mother liquor gave only a faint test for chloride ion with silver nitrate. The centrifuged solid was then transferred to a beaker, the peptizing agent was added, and the suspension was evaporated t o dryness on a steam bath. Since the prepared hydrates were dispersible up to gel formation, an arbitrary comparison method \vas used to determine the concentration at the gel point. The hydrate was added to water in a test tube having an inside diameter of 3 in. until a gel mas formed which would not flow when the tube was put in a horizontal position. The gel \vas then removed, v-eighed, dried, and re-iveighecl. RESULTS
Preliminary work: Table 1 gives the method of preparation of some typical sols which were selected from a large number of experiments. Since t,he preliminary experiments indicated that a small amount of hydrochloric acid was necessary for reversible sol formation, further work was done to determine the minimum amount necessary. The results are summarized in table 2. DISCUSSIOS
Particle size seems to determine t o some extent whether a gel is clear or opaque; for example; in table 1 the only difference betiyeen samples 202 and 203 is that the latter \vas dried before the peptizing agent Tvas added. The added heating operation apparently caused agglomeration to larger particles to produce a cloudy gel. Experimental proof of the composition of the product is not available, but the literature \~-ouldindicate that the hydrate is -,-Al~Oa.H20.
COLLOIDAL ALUMIWUM OXIDE
e
769
770
ARTHUR A. VERSON
The minimum amount of hydrochloric acid necessary for redispersion was 0.11 g. per 6.52 g. of A.1903.H~0.This corresponds to 0.060 mole of chloride per mole of aluminum oxide.
cc.
per CMI
5
No gel
6
27 27 25 23 22
8
10 15 20
Suspensionwith about 4 per cent solid
SUMMARY
1. A peptized hydrated alumina has been prepared which can be dried and redispersed in water. 2. The material forms a gel in water when the solid content is between 20 and 25 per cent. 3. The composition of the sol was 0.06 mole of chloride per mole of aluminum oxide. REFERENCES BoHaf AND NICLAISEX: Z. anorg. Chem. 152, 1 (1924). U. S. patent 2,085,129 (June 29, 1927). WEISER:J. Phys. Chem. 24, 521 (1920). WEISERAND MILLIGAX: Chem. Rev. 25, 1-30 (1939). (5) WEIIER AND MILLIG.4N: Advances in Colloid Soi. 1, 227-46 (1942).
(1) (2) (3) (4)
