Fumed silica having a BET surface area

Fumed silica having a BET surface area of 200±15 m2/g, a goniometer value of less than 30 μm, and a median value by PCS of 65 to 85 nm are prepared by grinding a fumed silica having a surface area of 200±25 m2/g, and silicone rubber containing this silica. This application is a continuation of Ser. No. 12/095,840 filed Jun. 2, 2008, a U.S. National Stage Filing of international No. PCT/EP2006/068889 filed Nov. 24, 2006, which claims priority from EP 051125334 filed Dec. 20, 2005, which all are being incorporated herein by reference. The invention relates to fumed silica, preparing it, and its use. Fumed silica (pyrogenic ally-prepared silicon dioxide) is known from Ullmanns Enzyklopädie der Technischen Chemie, Volume 21, page 464 (1982). It is prepared by burning a vaporizable silicon compound, such as silicon tetrachloride, in a mixture of hydrogen and oxygen. The comminution of materials to form coarse powders (50-500 μm), fine powders (5-50 μm), and even greater finenesses (less than five μm) is a widespread practice. For all comminution tasks, there is an assortment of technical and industrial equipment offered and operated; all adapted to the particular circumstances of the specific tasks. A good overview of the comminution problems and the diverse machines is given in Ullmanns Enzyklopädie der Technischen Chemie, 3rd Edition, Volume 1, pages 616 to 638. For fumed silica, the average primary particle diameters are notably lower (5-50 nm) than can be obtained by mechanical comminution. The primary particles and aggregates of the fumed silica with a surface area of 200 m2/g can be visualized in the electron microscope. If you are looking for high quality, high purity, and cost-effective Fumed silica, or if you require the latest price of Fumed silica, please feel free to email contact mis-asia.