PORE-STRUCTURE STABILITY OF NANOSTRUCTURED RUTILE TITANIA CONTAINING A STRUCTURE-DIRECTING 2ND-PHASE STABILIZER

Metastable-to-stable transformation in oxides is always associated wit h a drastic reduction in surface area and/or porosity. Because of this , all earlier efforts to stabilize the pore-structure of oxides underg oing a metastable-to-stable phase transformation have been directed to retarding or preventing the transformation. Here we report the pore-s tructure stabilization of nanostructured titania by promoting the anat ase-to-rutile transformation using a ''structure-directing second-phas e stabilizer.'' In the present study pure titania transformed to more than 95% rutile and became completely dense at 800 degrees C (near zer o porosity), whereas titania containing 2.4 mol% tin oxide transformed to about 70% rutile already at 750 degrees C, but retained a surface area as high as 16 m(2)/g. At 800 degrees C it transformed to 100% rut ile and still retained a surface area of about 8 m(2)/g. (C) 1998 Else vier Science Ltd.