Silicon dioxide has been used in various applications in which it is preferred that the surface have hydrophobic properties. One method which has been used to impart hydrophobic properties to silicon dioxide is described in U.S. Pat. No. 3,132,961 to Pierpoint et al., in which silicon dioxide having a surface area of more than 50 m.sup.2 /g is treated with for example octamethylcyclotetrasiloxane and an acid. Compared to the process described in this patent, the process of this invention has the advantage that the inherent dangers of corrosion caused by the use of an acid is avoided. Moreover, the silicon dioxide obtained from the process of this invention exhibits a higher degree of hydrophobicity.
Therefore, it is an object of this invention to provide a process for preparing silicon dioxide having hydrophobic properties. Another object of this invention is to provide a process for preparing hydrophobic silicon dioxide in the absence of a corrosive acid. A further object of this invention is to provide a process for preparing silicon dioxide having a higher degree of hydrophobicity.