Process for the production of exhaust gas filters

In a method for the production of exhaust gas filters comprising aluminum oxide produced by the decomposition of alumina hydrate deposited on a substrate contained within a metal casing, in which said alumina hydrate is deposited from an alkali metal aluminate solution, by mounting a plurality of said substrates upon a stand therefor, immersing said stand in said alkali metal aluminate solution, and depositing alumina hydrate on said substrate, the improvement which comprises subjecting said stand to vertical or horizontal reciprocating motion or rotating motion or a vector combination of said motions through said alkali metal aluminate solution whereby said alkali metal aluminate solution is caused to flow over and through said substrates while alumina hydrate is deposited on said substrates.

A method for the production of exhaust gas filters comprising aluminum oxide produced by the decomposition of alumina hydrate deposited on a substrate contained within a metal casing, in which said alumina hydrate is deposited, at a temperature of from about 60 to about 95.degree. C., from a sodium aluminate solution having a free soda strength (as Na.sub.2 O) of from about 60 to about 300 grams per liter, an Al.sub.2 O.sub.3 concentration of from about 78 to about 500 grams per liter, and an initial weight ratio of from about 1.3:1 to about 1.67:1, said sodium aluminate solution being obtained by dissolving an aluminum source selected from aluminum metal at least about 99% pure, alumina hydrate, bauxite and bauxitic clay in a sodium hydroxide solution, which method comprises mounting a plurality of said substrates upon a stand therefore, immersing said stand in said sodium aluminate solution, and vertically reciprocating said stand through said alkali metal aluminate solution whereby said sodium aluminate solution is caused to flow over and through said substrates while alumina hydrate is deposited on said substrates.