Method of making microporous asbestos diaphragms/cathodes for electrolytic cells

A process for the production of a microporous diaphragm which comprises a sintered, fluoropolymer microconsolidated asbestos-based microporous fibrous sheet material, said sheet material comprising from 3% to 35% by weight of fluoropolymer binder, from 1% to 50% by weight of a uniformly distributed gel of an oxohydroxide of at least one metal of Groups IVA, IVB, VB and VIB of the Periodic Table or of the lanthanide or actinide series thereof, and from 20% to 95% by weight of fibers, at least 1% by weight of said fibers being asbestos fibers, comprising (a) formulating an essentially aqueous dispersion of said fibers, particulates of said fluoropolymer binder and particulates of at least one precursor of an oxohydroxide of at least one metal of Groups IVA, IVB, VB and VIB of the Periodic Table or of the lanthanide or actinide series thereof, (b) depositing a sheet material by vacuum filtering said dispersion through a porous support substrate, (c) removing the liquid material therefrom and optionally drying the sheet material thus formed, (d) sintering said sheet material, (e) formulating a gel from the oxohydroxide precursor of step (a), and (f) treating said sintered sheet material with an aqueous solution of alkali metal hydroxide.