GB1389007A - Catalytic coating - Google Patents

Abstract

1389007 Catalytic coating IMPERIAL CHEMICAL INDUSTRIES Ltd 24 April 1972 [23 April 1971] 11009/71 Heading C1M [Also in Division F4] A substrate bears a self-cleaning oven coating which contains enamel and one or more oxidation catalysts and comprises adherent porous aggregates each porous aggregate particle comprising adherent catalyst particles and enamel particles. The coating preferably has a porosity of 30-60% by volume and an overall thickness of 200-800 microns. The oxidation catalyst may be an oxide or a metal. The metal of the oxide or the metal may be Cu, V, Bi, Mo, Mn, Fe, Ni, Pt-group metals Sn, Nb, Cr, W, Rh, Co or Ce. The oxidation catalyst particles may be at least 2 microns in size. Compounded oxidation catalyst particles containing cement or alumina may also be used, and may also contain a minor proportion of alumina. The catalyst may be in the form of hard particles made by grinding cylindrical shapes having an end-on crushing strength of 1500-10,000 p.s.i.g. The coated substrate may be made by making a mixture of oxidation catalyst particles and enamel particles, forming the mixture into porous aggregates smaller than the intended coating thickness, applying the aggregates to the substrate and heating to cause adhesion of the aggregates to each other and to the substrate. The porous aggregates may be applied to the surface to be coated by spreading them dry (pre-calcined), the surface preferably having been pre-treated with a viscous liquid to facilitate preliminary adhesion of the aggregates. The aggregate may also be made up into a slip and applied by flow-coating, brushing or spraying. Conveniently a viscous slurry of the particles of oxidation catalyst and vitreous enamel is sprayed from a spray-gun to form porous aggregate particles. Preferably the substrate is at 50-150‹ C. when the coating is applied. In the specific example the catalyst comprises a mixture of copper oxide/cobalt oxide/manganese oxide in the atomic ratio 20 : 20 : 60 and a slurry of this with a vitreous enamel frit comprising, in per cent by weight, 43À9 SiO 2 , 2À8 Al 2 O 3 , 14À9 Na 2 O, 1À1 K 2 O, 9À9 ZnO, 26À0 CaO, and 1À4 B 2 O 3 , is applied to mild steel which is at 100‹ C. The coating is sintered at 775‹ C.