GB901649A - A method for coating the surface of solid materials - Google Patents

Abstract

The surface of a solid material is coated with a film of a coating material which is crystalline in solid form by contacting the surface in the absence of oxygen with a drop or drops of molten coating material, the said surface being at a temperature sufficiently below that of the drop(s) such that the coating material of the drop(s) is supercooled instantaneously on contact with the surface whereby the coating material exhibits superfluid properties and spreads over the surface. Coating may be effected under vacuum, in an inert atmosphere such as nitrogen, or with the surface immersed in a molten flux or in oil. The drops of coating material may be produced by passing an electric discharge between two electrodes, at least one of which is of the material required, or by placing the coating material in the arc generated between a pair of non-consumable electrodes: the production of the drops is preferably effected in the absence of oxygen, e.g. the arc may be struck in an inert atmosphere or the electrodes may be immersed in molten flux or oil. The drops thus formed may be allowed to fall on to the substrate or may be sprayed thereon. The following processes are disclosed in the Examples: (a) coating plates of cast iron or steel with SiO2 by immersing the plates in molten borax or KF/KCl and producing drops by spark discharge or by melting the coating material between carbon electrodes, (b) coating a steel plate in molten 80% Na2 SiO3/20% NaF with alternate layers of Cr and Al2O3 and then removing the steel to leave a Cr/Al2O3 laminate, (c) coating Mo wires in molten 51,7% CaF2/27,8% NaF/20,5% AlF3 with SiO2, (d) coating bricks with Al2O3, MgO or ZrO2, and (e) producing a magnet by placing an Fe plate in an oil bath, subjecting it to a magnetic field and alternately coating with barium ferrite powder and an alloy consisting of Co 20%, Ni 18%, Al 6%, Ti 6%, Cu 3%, Fe balance. Reference is also made to coating with Fe3O4, Cr2O3, S and mica.ALSO:The surface of a solid material is coated with a film of coating material which is crystalline in solid form by contacting the surface in the absence of oxygen with a drop or drops of molten coating material, the said surface being at a temperature sufficiently below that of the drop(s) such that the coating material of the drop(s) is supercooled instantaneously on contact with the surface whereby the coating material exhibits superfluid properties and spreads over the surface. Coating may be effected under vacuum, in an inert atmosphere such as nitrogen, or with the surface immersed in a molten flux or in oil. The drops of coating material may be produced by passing an electric discharge between two electrodes, at least one of which is of the material required, or by placing the coating material in the arc generated between a pair of non-consumable electrodes: the production of the drops is preferably effected in the absence of oxygen, e.g. the arc may be struck in an inert atmosphere or the electrodes may be immersed in molten flux or oil. The drops thus formed may be allowed to fall on to the substrate or may be sprayed thereon. The following processes are disclosed in the examples: (I) coating plates of cast iron or steel with Mo, W, Ti, stainless steel, Cu, Si, Pt, Cr, WC, Pb, Zn or Al by immersing the plates in molten borax or KF/KCl and producing drops by spark discharge or by melting the coating material between carbon electrodes; (II) coating powdered WC in molten borax with Co; (III) coating a steel rail in molten borax with a hard alloy composed of W 34%, C 4%, Fe balance; (IV) coating an Al plate in molten B2O3/Na2 B4O7 with Pb, Sn, Zn, Cd, Cu, brass or Be; (V) coating a steel plate in molten 80% Na2 SiO3/20% NaF with alternate layers of Cr and Al2O3 and then removing the steel to leave a Cr/Al2O3 laminate; (VI) coating Mo wires in molten 51.7% CaF2/27.8% NaF/20.5% AlF3 with SiO2; (VII) coating a bronze valve in molten B2O3/Na2B4O7 with "Monel" (Registered Trade Mark) metal; (VIII) producing a photo-cell by coating an Fe plate in molten B2O3 first with Si and then with Ag; (IX) producing a self-lubricating bearing by pressing phosphor-bronze wire scrap into a bar, and coating with phosphor-bronze in molten B2O3/Na2B4O7; (X) coating glazed porcelain in molten borax with Pb, Al, Zn, Sn and Fe; (XI) coating an iron plate in blast furnace slag with 89% W-11% Mo by alternately arcing between the iron plate and W and Mo electrodes; (XII) producing a magnet by placing an Fe plate in an oil bath, subjecting it to a magnetic field and alternately coating with barium ferrite powder and an alloy consisting of Co 20%, Ni 18%, Al 6%, Ti 6%, Cu 3%, Fe balance, and (XIII) coating a steel plate in molten borax with Si and optionally heating in H2 at 600 DEG C. to diffuse the Si into the interior of the plate. Reference is also made to coating with Ni and Au.