. . "For example, pores can be formed easily by mixing in advance 50 mol % or less of alkyl group such as CH3, C2 H5, C3 H7 in a basic oxide or an acidic oxide, and then removing the alkyl group by subjecting the product to a heat treatment of 300???-500 ??? C. The heat treatment in this case will become effective by carrying it out in a vacuum of equal to or smaller than 10 Torr in an atmosphere with" . .