Ultrafiltration conducting membranes and coatings from redispersable, nanoscaled, crystalline SnO2:Sb particles

Inorganic membranes prepared by the sol-gel method are promising candidates for use as filters in separation processes. Conducting supported membranes and coatings have been produced from redispersable nanoscaled crystalline Sb-doped SnO2 powders with Sb contents up to 10 mol%. The crystalline particles (ca. 4 nm) are fully redispersable in aqueous solution at pH greater than or equal to 8 with a solid content up to 37 vol.% and are monosized. After thermal treatment at different temperatures and times, the pore size diameter of such a powder can be adjusted from 4-20 nm with a very narrow pore size distribution (ca. +/-1 nm) and a total porosity of 63%, practically independent of the sintering parameters. Uniaxial compacted substrates (unsupported membranes) present similar characteristics but with a larger pore size distribution (+/-5 nm) and 80% total porosity. Their electrical resistance decreases with sintering temperature and rime to 4 Ohm (800 degrees C, 8 h). Crack free transparent conducting coatings on glasses and ceramics have been obtained by spin-coating using fully dispersed aqueous solutions of the powder with volume content up to 7.8%. After thermal treatment (1 h at 550 degrees C) single layers 200 nm thick are still porous and exhibit specific electrical resistivity as low as rho = 2.5 x 10(-2) Ohm cm with 90% transmission in the visible range.