Thermal Stability of Ceramic Membranes

In comparison with pure j alumina, mixing the precursor boehmite sol with 3% LaNOs or impregnation of calcined y-alumina with LaNOs solution stabilised the unsupported membrane. After 120 h at 800°C the La doped system had a pore diameter of about 5 nm compared with about 9 nm for the pure y-alumina. 

PVA addition to zirconia precursor solutions resulted in an increase of the membrane pore volume and the pore size compared to samples without PVA. Similar effects were found for titania membranes but at lower temperatures indicating a relatively small thermal stability of these titania membranes. This can be improved by doping with alumina [39,40]. 

Kumar [39] reports a considerably larger thermal stability for titania membranes in the rutile phase instead of the usual anatase form. The effect of the support on thermal stability has been reported by Kumar et al. [40,41]. Pure, non-supported titania (anatase) membranes lose their porosity completely when calcined at 600°C for 8 h, where as the supported titania membrane retained ca 30% porosity at 900°C (8 h). Unsupported titania-(50 wt%)alumina composite membranes retained a porosity of ca 40% at 700°C (8 h), supported ones retained porosity even at 900°C. 

Finally, other examples of thermal behaviour of zirconia and titania membranes have been reported by Larbot et al. in a series of papers, e.g. Ref. [33]. 

Mesoporous membranes with high thermal stabilities to 1100°C have been reported by Chai et al. [65], These membranes were obtained by dip coating an alumina-silica support (a 20-step process) into a mixed sol consisting of an alumina sol to which about 11 wt% Ba or La was added in the form of salts. 

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