Process for producing a porous diffusion membrane

A diffusion membrane having a sandwich construction, the pore diameter of which is 1,000A or less, is provided for the separation and enrichment of, for example, U-235F from U-238F. Flexibility, corrosion resistance and separation efficiency of the barrier are improved by a process which comprises the steps of filling powders of metallic or inorganic materials into a mesh or grid-like support, superimposing onto the filled support a fluorine resin sheet consisting of a fluorine resin and a liquid foaming agent so that the outermost layers are the fluorine resin sheets, adhering them by applying a pressure of 30 to 30,000kg/cm2, and removing the foaming agent. Particle size of the powders may be 0.3 microns or less, but preferably 0.1 microns or less. Gold, silver, copper, platinum, nickel, monel metal, stainless steel, alumina and the like can be used with or without fluorine treatment. The powders are filled in the support by slip casting, rolling or electrophoresis. In one example, 100 parts by weight of polytetrafluoroethylene mixed with 50 parts of perfluoroalkane were compressed in a metallic die under a pressure of 25kg/cm3 and were rolled to a thickness of 0.05m. A 250 mesh nickel wire filled with alumina particles having a diameter of 0.05 microns were compressed under 10 tons/cm2. The above sheets were laminated onto the nickel support on opposite surfaces, and thereafter pressed under a pressure of 100kg/cm2. The perfluoroalkane was removed. Argon isotope permeability of the product was 1.60 x 10-5 mol/cm2.min.cmHg. The separation efficiency was 78%. (Iwakiri, K.)