PROPERTIES OF THE TIO2 MEMBRANES PREPARED BY CVD OF TITANIUM TETRAISOPROPOXIDE

Thin films of TiO2 were deposited on the inner surface of porous Vycor glass tubes by atmospheric pressure chemical vapor deposition (APCVD) at temperatures ranging from 200 to 400 degrees C using titanium isop ropoxide as a precursor. Dense and hydrogen-permselective membranes we re formed only in the temperature range between 230 and 300 degrees C. Gas permeation through the dense membrane was governed by an activate d diffusion mechanism and the H-2:N-2 permeation ratio was far beyond the range of Knudsen diffusion. At 200 and 400 degrees C, however, hig hly porous films were formed and the permselectivity of the membrane w as not improved at all, because gas permeation through the porous memb rane was in the Knudsen diffusion regime. Selectivity (H-2:N-2 permeat ion ratio) profile showed a maximum value of 57 at a deposition temper ature of 250 degrees C. The oxygen added to the reaction environment a ppeared to have some effects on the stability and the permselectivity of the membrane formed. The permeation properties of the TiO2 membrane s were not so appreciable and the stability of the membrane was poor w hen compared with dense SiO2 membranes. The characterization of the Ti O2 films by SEM and TEM reveals that phase change from amorphous to cr ystalline state occurs at a temperature about 300 degrees C.