Patent ID: 7588628

Claim:
A microporous ceramic substrate of a gas separation membrane, the substrate comprising primarily alpha-silicon nitride; containing essentially no needle-like beta-silicon nitride; having a maximum of micropore size distribution at or an average micropore size of 0.5 μm or greater, but less than 2 μm; and having a porosity of 30% or greater, but less than 40%, and wherein the substrate is produced by a manufacturing process comprising the steps of: (A) preparing a starting material containing silicon nitride power and metal silicon powder at a mass ratio of 100 parts of silicon nitride to between 10 and 100 parts of metal silicon; and further containing yttrium oxide powder and aluminum oxide powder at a molar fraction of yttrium oxide to aluminum oxide (Y 2 O 3 /Al 2 O 3 ) in a range from 0.9 to 1.1 and each at 2% by mass or greater, but less than 250% by mass of the amount of metal silicon powder, and yet not exceeding 20% by mass of the total amount of the starting material, (B) molding the starting material into a prescribed shape; and (C) subjecting the molded product of the prescribed shape to reaction sintering at a temperature from 1200° C. to 1500° C. in an atmosphere that allows nitrization.