C CHEMISTRY; METALLURGY
C01 INORGANIC CHEMISTRY
C01B NON-METALLIC ELEMENTS; COMPOUNDS THEREOF;; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
C01B33/00 Silicon; Compounds thereof
C01B33/113 Silicon oxides; Hydrates thereof
C01B33/12 Silica; Hydrates thereof, e.g. lepidoic silicic acid