Porosity reduction, packing, pore-size distribution, and anatase to rutile phase transformation behavior of nanostructured titania ceramics prepared from both peptized and unpeptized sols were studied and compared using XRD, DSC, and nitrogen-gas physisorption techniques. Precursor gels prepared from the peptized sol had a green density of about 70% after drying at 4 0 T , whereas the samples prepared from the unpeptized sol had a green density of only 50%. Samples prepared from the peptized sol showed higher sintering and phase transformation rates compared to the unpeptized sols.
Textural evolution in sol-gel derived nanostructured unsupported titania membranes has been studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermal gravimetry (TG), X-ray diffraction (XRD) and N, adsorption. The anatase-to-rutile phase transformation kinetics were studied using the Avrami model. The precursor gel had a surface area of ca. 165 m2 g-', which after heat treatment at 600 "C for 8 h reduced to zero. Undoped titania-gel layers transformed to more than 95% rutile after calcination at 600 "C for 8 h. The causes of surface-area reduction and pore growth were anatase crystallite growth and the enhanced sintering of rutile during transformation. Lanthanum oxide was identified as a suitable dopant for shifting the transformation temperature to ca. 850 "C. Lanthanum oxide doped titania showed an improved stability of porous texture compared to that of the undoped titania membranes.
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