Processing of biomorphic porous TiO_2 ceramics by chemical vapor infiltration and reaction (CVI-R) technique

摘要

Porous biomorphic TiO_2 ceramics were manufactured from paper preforms by chemical vapor infiltration and reaction (CVI-R) in a three-steps process. First, the cellulose fibers of the paper were converted into carbon (C_b) by pyrolysis in an inert atmosphere. Then, C_b,-template was infiltrated with a precursor system consisting of TiCl_4, CH_4 and H_2 to produce porous TiC ceramics, which were oxidized in a final step with air at temperatures in the range of 400-1200 deg C. Depending on the conversion degree, TiC/TiO_2 or TiO_2 ceramics were obtained. The kinetics of the oxidation process was studied by thermal gravimetric analysis (TGA) and activation energies of 63 and 174 kJ mol~(-1) were estimated for the lower (400-800 deg C) and higher (950-1200 deg C) temperature regions, respectively. The TiO_2 ceramics were characterized by Raman spectroscopy . anatase/rutile ratio), SEM/EDX (morphology, composition) and nitrogen gas adsorption (pore structure). It was shown, that the anatase/rutile ratio as well as the pore structure of the resulting TiO_2 ceramics could be controlled varying the oxidation temperature. The TiO_2 samples obtained by oxidation of TiC biomorphic porous ceramics are lightweight but nevertheless have very good mechanical performances. Their bending strength varies between 30 and 40 MPa at a porosity of 65-70 percent. These structures have many potential applications, e.g. light structured materials, implants because of their bio-compatibility, catalyst support or catalyst for photo catalytic applications.