Mesoporous glass films supported on α-Al_2O_3

Glass–alumina composites were developed for possible use as membrane supports. Preparation involved dip-coating of α-Al_2O_3 tubes with a suspension of borosilicate glass particles (9.1% Na_2O–29.7% B_2O_3–61.2% SiO_2), sintering to convert the particle layer into a nonporous layer of phase separated glass, and leaching the glass with a strong acid to remove the soluble phase and obtain the final porous layer of about 10 μm thickness. In some preparations a 10% α-Al_2O_3 powder was added to the initial suspension. The composite supports were characterized by SEM, EDAX and EPMA for elemental composition, XRD for crystalline phase content, nitrogen adsorption for surface area and pore size distribution, and by permeation measurements with single gases and mixtures. After leaching the glass layers had pore size 1–4 nm, and contained varying amounts of boron, sodium, and aluminum oxides, in addition to silica. The nitrogen permeance of the composite supports was 10–100 times higher than that of standard porous Vycor tubing.