Abstract: A highly active superdry silica aerogel free of adsorbed water and hydrogen-bonded silanol groups the infrared spectrum of which is characterized by a single narrow intense band at about 3700 cm.sup..sup.-1 within the range between 4000 and 2000 cm.sup..sup.-1 indicating the presence of free silanol groups and which spectrum is further characterized by the absence of bonds indicating the presence of adsorbed water and hydrogen-bonded silanol groups, the said silica aerogel having been produced by subjecting a pyrolytically produced silica aerogel containing adsorbed water and both free and hydrogen-bonded silanol groups to treatment in a fluidized bed at a temperature between about 700.degree. and 1000.degree. C and at a pressure between 2 torrs and atmospheric pressure for a period between 1 second and a few minutes through which fluidized bed a stream of a dried gas that had been preheated to a temperature between 100.degree. and 300.degree. C was passed.

Abstract: An apparatus for making particulate materials hydrophobic has means for activating the material, means for charging the material with a substance capable of imparting hydrophobic characteristics thereto, means for causing reaction between the material and the substance with which it is charged and means for treating the material subsequent to the reaction so as to remove excess of the substance therefrom.