DIAPHRAGMS FOR ELECTROLYTIC CELLS

摘要

1498733 Asbestos coated cathode HOOKER CHEMICALS & PLASTICS CORP 20 May 1975 [9 April 1975] 21594/75 Heading C7B [Also in Division B2] A diaphragm-coated cathode for an electrolytic cell, comprising a foraminous cathode bearing on the cathodically active surfaces thereof an adherent and coherent dimensionally stable diaphragm consisting essentially of asbestos fibres bound together with a discontinuous polymer coating, the concentration of polymer decreasing from the outer surface of the diaphragm to the cathode-diaphragm interface, is produced by placing a foraminous cathode member in a slurry of asbestos fibres and drawing a layer of asbestos on to the cathode by suction through the cathode, removing the coated cathode from the slurry while maintaining suction to abstract slurry liquid from the asbestos layer, placing the coated cathode in a slurry of thermoplastic polymer particles ranging in size between 0À2 and 100 microns, drawing polymer particles into the asbestos layer by suction through the coated cathode, removing the cathode from the polymer slurry and heating it to a temperature sufficient to soften the polymer particles and thus join adjacent asbestos fibres together, and then cooling the coated cathode. The cathode member may be in the form of a can or box of wire mesh, foraminous sheet metal, expanded metal or woven metal. The asbestos slurry may be in water or solutions of brine or other cell liquor, and suitably is applied at a thickness of 25-125 mms, i.e. 0À18-0À3, preferably 0À22-0À26 pounds per square foot. Preferred polymers are fluorine-containing polymers having a softening point between 105‹C and 400‹C, e.g. polytetrafluoroethylene, polyhexafluoropropylene, polychlorotrifluoroethylene, polyvinylidene fluoride, alone or as copolymers with each other or with ethylene vinyl chloride or other hydrocarbon monomers. The preferred polymer is polyvinylidene fluoride or a 1:1 copolymer of ethylene and chlorotrifluoroethylene. The polymer slurry may contain a wetting agent, preferably non-ionic, and is drawn into the asbestos layer until a polymer concentration of 1-20% of the weight of asbestos is reached. The coated cathodes may be used in chlor-alkali cells for electrolysis of brine.