The surface properties of precipitated alumina II ageing at room temperature

Abstract

AbstractAlumina precipitates were prepared by mixing solutions of aluminium chloride and sodium hydroxide under conditions of constant concentration and pH, dried and stored under various conditions at room temperature. Adsorption isotherms of nitrogen, determined at −196° on the outgassed samples, were all of reversible S‐type. Surface areas were calculated from the isotherms by the usual Brunauer, Emmett and Teller (B.E.T.) method.Storage produced a change in surface area of all samples. With those containing more than about 100 parts of H2O per 100 parts Al2C3, an increase in surface area was produced over the first few days followed by a very gradual decrease. Samples stored after more thorough drying gave a marked fall in area, with no initial increase. Storage in vacuo produced little change, but admission of water vapour caused rapid ageing. Prolonged outgassing at room temperature of all samples reduced the composition to Al2O3,3H2O, but no hydrate structure could be detected by X‐ray analysis.