Perovskite-type B-site Bi-doped ceramic membranes for oxygen separation

Novel mixed conducting oxides, B-site Bi-doped perovskites were exploited and synthesized. Cubic perovskite structures were formed for BaBi0.2COyFe0.8-yO3-delta (y less than or equal to 0.4) and BaBixCo0.2Fe0.8-xP3-delta (x=0.1-0.5) The materials exhibited considerable high oxygen permeability at high temperature. The oxygen permeation flux of BaBi0.2Co0.35Fe0.45O3-delta membrane reached about 0.77 x 10(-6) mol/cm(2) s under an air/helium oxygen partial pressure gradient at 900 degrees C, which was much higher than that of other bismuth-contained mixed conducting membranes. The permeation fluxes of the materials increased with the increase of cobalt content, but no apparent simple relationship was found with the bismuth content. The materials also demonstrated excellent reversibility of oxygen adsorption and desorption. Stable time-related oxygen permeation fluxes were found for BaBi0.2CO0.35Fe0.45O3-delta and BaBi0.3Co0.2Fe0.5O3-delta a membranes at 875 degrees C.

Titanium-based perovskite-type mixed conducting ceramic membranes for oxygen permeation

A titanium-based perovskite-type oxide was synthesized by an improved method of combining EDTA acid and citric acid complexes. High structural stability, good sintering ability, and relatively high oxygen permeation flux were obtained simultaneously for disks synthesized from this ceramic oxide. (C) 2002 Elsevier Science B.V All rights reserved.

Mesoporous spinel MgAl2O4 prepared by in situ modification of boehmite sol particle surface: I Synthesis and characterization of the unsupported membranes

Mesoporous spinel membranes as ultrafiltration membranes were prepared through a novel sol-gel technique. By in situ modification of the sol particle surface during the sol-gel process, control of the material structure on a nanometer scale from the earliest stages of processing was realized. Nano-particles with a chocolate-nut-like morphology, i.e. spinel MgAl2O4 as a shell and gamma -Al2O3 as a core, were first revealed by HRTEM results. The formation of the spinel phase was confirmed by X-ray diffraction (XRD). N-2 adsorption-desorption results showed that the mesoporous membranes had a narrow pore size distribution. (C) 2001 Elsevier Science B.V. All rights reserved.

Synthesis of NaA zeolite membranes from clear solution

NaA zeolite membranes were successfully synthesized on a porous alpha -Al2O3 support from clear solution. The synthesis parameters, such as surface seeding, synthesis time, synthesis stages, etc. were investigated. Surface seeding can not only accelerate the formation of NaA zeolite on the support surface, but can also inhibit the transformation of NaA zeolite into other types of zeolites. A continuous NaA zeolite membrane formed on the seeded support after 2 h of synthesis. Gas permeation results showed that a synthesis time of 3 h produced the best NaA zeolite membrane. When the synthesis time was longer than 4 h, the NaA zeolite on the support surface began to transform into other types of zeolites, and the quality of the NaA zeolite membrane decreased. The quality of the NaA zeolite membrane can be improved by employing the multi-stage synthesis method. The NaA zeolite membrane with a synthesis time of 2 h after a two-stage synthesis showed the best gas permeation performance. The permeances of H-2, O-2, N-2, and n-C4H10 decreased as the molecular kinetic diameter of the gases increased. which showed the molecular sieving effect of the NaA zeolite membrane. The permselectivities of H-2/n-C4H10 and O-2/N-2 were 19.1 and 1.8, respectively. These values are higher than the Knudsen diffusion ratios of 5.39 and 0.94. However, the permeation of n-C4H10 also indicated that the NaA zeolite membrane had certain defects with diameters larger than the pore size of NaA zeolite. A synthesis model was proposed to clarify the effect of surface seeding. (C) 2001 Elsevier Science B.V. All rights reserved.