COATING PROCESS AND COATED MATERIALS

Abstract

The present invention relates to a method and an apparatus for coating large area solid substrates with metal based alloys or compounds by contacting the substrate surface with an unoxidised metal powders formed by in situ reaction of a metal halide and a reducing agent. The method is suitable for coating large area substrates such as flakes, powder, beads, and fibres with metal based alloys or compounds starting from low-cost chemicals such as metal chlorides. The method is particularly suited for production of substrates coated with metals, alloys and compounds based on Zn, Sn, Ag, Co, V, Ni, Cr, Fe, Cu, Pt, Pd, Ta, Nb, Rh, Ru, Mo, Os, Re and W.

Claims

1. A method for depositing metal-based coatings on a particulate substrate, including: a) mixing the particulate substrate with an uncoated metal-based powder to form a mixture; the metal-based powder being formed by exothermically reducing a precursor powder comprising a chloride or sub-chloride of one or more of Zn, Sn, Ag, Co, V, Ni, Cr, Fe, Cu, Pt, Pd, Ta, Nb, Rh, Ru, Mo, Os, Re and W by contacting with a reducing agent; and b) heating the mixture to produce a coating on said particulate substrate.

2. The method according to claim 1, wherein said mixing occurs concurrently with the formation of the uncoated metal-based powder

3. The method according to claim 1, wherein the reducing agent is selected from one or more of Na, K, Ca, Mg, or Al.

4. The method according to claim 1, wherein the metal chloride is selected from chlorides, fluorides, bromides or iodides.

5. The method for forming a coating on a substrate according to claim 1, comprising: immersing a substrate powder in a reactant mixture comprising an uncoated metallic powder and metal chlorides and a reducing agent and optionally any coating additives, and heating the resulting mixture at temperatures between 400 C. and 800 C. to induce reactions between the substrate surface and the said mixture and form a coating on the substrate; and wherein the uncoated metal powder is formed by exothermically reducing a metal chloride precursor with a reducing agent; and wherein the reducing agent includes Na, K, Ca, Mg, or Al; and condensing by-products away from a reaction zone, where the reducing alloy and precursor materials are reacting; and condensing unreacted metal chlorides and returning them to the reaction zone; and separating the coated substrate from residual un-reacted materials.

6. The method according to claim 1 for coating a particulate substrate wherein the metal chlorides comprise one or more metal chlorides and the reducing agent includes an Al alloy.

7. The method according to claim 6 for coating particulate substrates comprising: reducing one or more metal chlorides with Al powder in the presence of a particulate substrate at temperatures between T.sub.0 above 160 C. and T.sub.max to produce intermediates comprising metallic M.sub.c-based species in a nanopowder form; continuing heating and stirring of the reactants to induce physical or chemical reactions between the M.sub.c-Al species and the substrate and cause a coating to form on the surface of the substrate; and T.sub.max is below 900 C.; and condensing by-products including aluminium chlorides away from the reactants; and separating the coated substrate from residual un-reacted materials.

8. The method according to claim 6 for coating particulate substrates, wherein an uncoated metallic powder is reacted with the substrate to produce a coating on the substrate surface, and wherein the method is conducted stepwise: in a first step, one or more metal chlorides is reduced with Al powder at temperatures between T.sub.0 above 160 C. and T.sub.1 below 500 C. to form a mixture comprising metallic M.sub.c-Al species in a fine powder; and in a second step, a mixture comprising the resulting metallic M.sub.c-Al species and the substrate is heated at temperatures between T.sub.2 above 400 C. and T.sub.max below 900 C. to induce physical or chemical reactions between the M.sub.c-Al species and the substrate and cause a coating to form on the surface of the substrate.

9. The method according to claim 8, wherein an amount of submicron particles in the said powder is more than 1 wt %.

10. The method according to claim 6 for coating a particulate substrate comprising: reacting metal chlorides with the substrate at temperatures below T.sub.max to form a coating on the substrate surface; and the coating comprises a metallic coating deposited on the substrate surface or a metallic skin obtained by chemically incorporating metallic elements into the substrate surface; and T.sub.max is below 900 C.; and condensing by-products away from the reactants.

11. (canceled)

12. The method as claimed in claim 1, wherein processing is carried out under inert gas.

13. The method as claimed in claim 1, wherein the coating metal includes one or more of Zn, Sn, Ag, Co, V, Ni, Cr, Fe, Cu, Pt, Pd, Ta, Nb, Rh, Ru, Mo, Os, Re and W, the coating metal chloride includes one or more of ZnCl.sub.2, SnCl.sub.2, AgCl, CoCl.sub.2, VCl.sub.(2,3), NiCl.sub.2, CrCl.sub.(2,3), FeCl.sub.(2,3), CuCl.sub.(1,2), PtCl.sub.(4,3,2), PdCl.sub.2, TaCl.sub.(4,5), NbCl.sub.5, RhCl.sub.3, RuCl.sub.3, MOCl.sub.5, OSCl.sub.(2,3,4), ReCl.sub.3 and WCl.sub.(4,5,6); wherein the reducing agent comprises Al, and wherein reactions between the coating metal chlorides and Al are exothermic.

14. The method according to claim 13, wherein the coating metal chlorides are mixed with AlCl.sub.3 before reacting with the substrate, and wherein the volume of AlCl.sub.3 is between 10 wt % and 500 wt % of the volume of the substrate.

15. The method according to claim 1, wherein the reducing Al alloy is mixed with AlCl.sub.3 before mixing with the substrate and the metal chlorides, and wherein the volume of AlCl.sub.3 is between 10 wt % and 500 wt % of the volume of the substrate.

16. The method as claimed in claim 1, wherein the substrate is in the form of a powder, flakes, beads, fibres, or particulates comprising: itransition metal alloys and compounds including oxides, nitrides, carbides, and borides, iiglass, glass flakes, glass beads, quartz, borosilicate, soda-glass, silicon nitride, mica flakes, talc powder, iiigraphite powder, graphite flakes, carbon fibre or a mixture thereof.

17. The method according to claim 16, wherein the weight ratio of solid metal chlorides to substrate is between 0.01 and 0.5.

18. The method according to claim 16, wherein the substrate include silicon based chemicals and the coating includes metal silicides.

19. The method according to claim 18, wherein the substrate includes a borosilicate substrate and where T.sub.max is below 650 C.

20. The method according to claim 18, wherein the substrate includes a soda-glass substrate and where T.sub.max is below 650 C.

21. The method according to claim 16, wherein the substrate is made of powder, beads, flakes or fibre based on carbon and the coating includes metal carbides.

22. The method according to claim 1, wherein the method is carried out at a pressure between 0.0001 bar and 1.1 bar.

23. The method according to claim 2, wherein precursor materials which escape the reaction zone are condensed and returned to the reaction zone for recycling.

24. The method according to claim 13, wherein the method includes the additional step of reacting the coated substrates with a reactive gas.

25. The method according to claim 5, wherein the coating additives include boron, carbon, oxygen or nitrogen and the products comprise a substrate coated with metal borides, metal carbide, metal oxide or metal nitride.

26. The method according to claim 16, wherein the coating on the coated substrate products include Al at levels between 0 wt % and 50 wt %.

27. The method according to claim 24, wherein the reactive gas includes a reactive element from the group of oxygen, nitrogen, carbon and boron.

28. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0129] Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings, in which:

[0130] FIG. 1 shows a block diagram for one embodiment illustrating steps for coating a substrate.

[0131] FIG. 2 shows an XRD trace for a sample of glass flakes coated with Cu.

[0132] FIG. 3 shows an XRD trace for a sample of glass flakes coated with CuZn.

[0133] FIG. 4 shows an XRD trace for a sample of glass flakes coated with FeMoW.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0134] FIG. 1 is a schematic diagram illustrating processing steps for one preferred embodiment for production of coated glass flakes.

[0135] In a first step (101), a fine Al alloy powder is mixed together with an AlCl.sub.3 to produce a large volume AlAlCl.sub.3 mixture. Other coating additives may be added to the AlAlCl.sub.3 if required.

[0136] The substrate (102) is mixed with the coating metal chloride (103) together with other compatible coating additives (104) leading to a first mixture (Mix1) (105). The remaining coating additive precursors (104) are prepared into several mixtures (106). Mixing and preparation of the precursor materials is carried out under an inert atmosphere (107).

[0137] The reducing Al alloy (101) and mixtures (105) and (106) are fed into a premixer (not shown) and then into a reaction zone where they are mixed, stirred and reacted at temperatures between 160 C. and 800 C. (108), depending on the substrate materials and coating.

[0138] The resulting by-products (109), including aluminium chlorides, are condensed away from the solid reactants, and collected in a dedicated vessel (110). A part of the aluminium chlorides may be recycled through (101). All processing steps are preferably carried out under inert gas (e.g. Ar) and the exit of the by-product collection step, the gas is cleaned in a scrubber (111) before discharging into the atmosphere or recycling (112).

[0139] At the end of the reaction cycle (108), the solid products are discharged or moved into another reaction zone (113). If required, the products can then be reacted further with gaseous reactant for example before separating the coated substrate from residual undesired compounds and then substrate may be washed and dried (114) leading to end products (115).

[0140] Residual waste (116) is stored separately for further processing or disposal.

[0141] Materials produced using the invention described here have unique characteristics that may not be obtained using prior art methods.

[0142] The invention extends to materials made using the invention and use of the materials, without being limited by the examples provided herein by way of illustration. Specific properties include the ability to produce nanostructured coating for large area substrate of complex composition usually unachievable with conventional physical vapour deposition or chemical vapour deposition.

[0143] For example, the coating process described here can be used to produce a composite material of cobalt borides supported on graphite (or on glass flakes) where the carbon is encapsulated inside the coating. The composite graphite-Cobalt boride can then be consolidated into porous structure using conventional binding techniques. Such materials are useful for use as catalysts for several chemical processes. Other examples of materials that can be produced using the current invention include supported catalysts of Mo on alumina, Rh on activated carbon, Pt on activated carbon/dielectric powder and V.sub.2O.sub.3 supported on TiO.sub.2.

[0144] A second example of the quality and use of materials produced using the current technology is in production of luxury metallic pigment for use in the automotive paint industry and in the wider pigment industry in general. There are various techniques capable of producing a limited number of metal flake pigments; however, these techniques are limited to common metals such as aluminium, and for a number of other metals, the cost can be prohibitive. For example, the present method allows for production of low cost pigment with various hues, optical properties and functional characteristics that cannot be manufactured using existing technologies. Such metallic pigments can be attractive for use in the plastics industry, automotive paint, and in general paint and architectural applications. Such pigments and their use are claimed as a part of the present invention.

[0145] The following are examples of preparation of various coating compounds in accordance with an embodiment of the present invention.

Example 1: Ni on Glass Flakes

[0146] 200 mg of NiCl.sub.2 powder mixed with 2.5 g of AlCl.sub.3 powder.

[0147] 60 mg of Ecka Al powder (4 microns) mixed with 2.5 g of AlCl.sub.3.

[0148] 5 g of glass flakes (average diameter of 200 microns and a thickness of 1.6 microns).

[0149] The three materials are mixed together thoroughly.

[0150] The mixture was then heated in a rotating quartz tube under argon at temperature ramping from room temperature to 600 C. in batches of 4 g for 30 minutes. The powder was then sieved to remove un-deposited products and the remaining coated flakes washed water and dried. The coated flakes have metallic appearance. Examination under an SEM and EDX shows that the surface is thoroughly coated with metallic Ni but with the presence of lumps of metallic Ni.

Example 2: Cu on Mica Flakes

[0151] 1.2 g of CuCl.sub.2 powder was thoroughly mixed with 3 g of AlCl.sub.3 powder.

[0152] 410 mg of Ecka Al powder (4 microns) was mixed with 3 g of AlCl.sub.3 powder.

[0153] The CuCl.sub.2AlCl.sub.3 was mixed with 5 g of Mica flakes (size 0.5-0.8 mm) and then the resulting mixture was thoroughly mixed with the AlAlCl.sub.3. The resulting reactant mixture was then heated in a rotating quartz tube at 700 C. in batches of 5.5 g for 30 minutes. Products were then sieved to eliminate fine powder and the coated flakes was then washed and dried. The end products have a shiny metallic colour.

Example 3: Won Glass Flakes

[0154] 1.22 g of WCl.sub.6 powder was milled with 2.5 g of AlCl.sub.3 powder.

[0155] 180 mg of Ecka Al powder (4 microns) was mixed with 2.5 g of AlCl.sub.3 powder.

[0156] The WCl.sub.6AlCl.sub.3 was mixed with 5 g of glass flakes (average diameter of 200 microns and a thickness of 1.6 microns) and then the resulting mixture was thoroughly mixed with the AlAlCl.sub.3. The resulting reactant mixture was heated in a rotating quartz tube at 575 C. in batches of 2.2 g for 30 minutes. The resulting product was then discharged, washed and dried. The flakes have a shiny deep dark grey appearance.

Example 4: Cu on Glass Flakes

[0157] 1 g of CuCl.sub.2 powder was milled with 2 g of AlCl.sub.3 powder.

[0158] 200 mg of Al powder (4 microns) was mixed with 1 g of AlCl.sub.3 powder.

[0159] The starting reactants were mixed with 5 g of glass flakes (average diameter of 200 microns and a thickness of 1.6 microns) and then the resulting mixture was thoroughly mixed with the AlAlCl.sub.3 mixture. The resulting reactant mixture was heated in a rotating quartz tube at 575 C. in batches of 4 g for 20 minutes. The resulting product was then discharged, washed and dried. The flakes acquire the brown-reddish appearance copper. XRD trace for the resulting product is in FIG. 2.

Example 5: CuZn on Glass Flakes

[0160] 104 mg of ZnCl.sub.2+318 mg of CuCl.sub.2 powder was mixed with 1 g AlCl.sub.3 powder.

[0161] 168 mg of Ecka Al powder (4 microns) mixed with 1 g AlCl.sub.3 powder.

[0162] The starting reactants were mixed with 2 g of glass flakes (average diameter of 200 microns and a thickness of 1.6 microns). The resulting mixture was heated in a rotating quartz tube at 575 C. for 30 minutes. The resulting product was then discharged, and then washed and dried. The powder has a shiny appearance. SEM analysis shows complete coverage and some occasional lumps on the surface. XRD trace for the product is in FIG. 3.

Example 6: Fe on Glass Flakes

[0163] 1.3 g of FeCl.sub.3 was first reduced with Al to FeCl.sub.2 powder.

[0164] 1 g FeCl2 was mixed with 2.5 g AlCl.sub.3 powder.

[0165] 200 mg of Al powder (4 microns) were mixed with 2.5 g of AlCl.sub.3 powder.

[0166] The FeCl.sub.3AlCl.sub.3 was mixed with 5 g of glass flakes (average diameter of 200 microns and a thickness of 1.6 microns) and then the resulting mixture was thoroughly mixed with the AlAlCl.sub.3. The resulting reactant mixture was then heated in a rotating quartz tube at 575 C. in batches of 3.5 g for 30 minutes. The resulting product was then discharged, washed and dried. The flakes have a metallic grey appearance and are stable in air, water and mild HCl. They are also highly magnetic. EDS analysis of the flakes suggest the presence of Al and Si in the mainly Fe coating matrix.

Example 7: FeMoW on Glass Flakes

[0167] Fe 18 wt %, Mo74 wt % and W 8 wt %.

[0168] FeCl.sub.3: 183 mg, MoCl.sub.5: 791 mg and WCl.sub.6: 65 mg mixed with 1 g AlCl.sub.3.

[0169] 200 mg of Ecka Al powder (4 microns) mixed with 1 g AlCl.sub.3.

[0170] The starting reactants were mixed with 5 g of glass flakes (average diameter of 200 microns and a thickness of 1.6 microns). The resulting mixture was heated in a rotating quartz tube at 575 C. in batches of 2 g for 20 minutes. The resulting product was discharged, and then washed and dried. The powder has a dark metallic appearance. XRD trace for the product is in FIG. 4.

Example 8: FeMoW on Carbon Fibres

[0171] Fe 18 wt %, Mo74 wt % and W 8 wt %.

[0172] FeCl.sub.3: 183 mg, MoCl.sub.5: 791 mg and WCl.sub.6: 65 mg mixed with 1 g AlCl.sub.3.

[0173] 200 mg of Ecka Al powder (4 microns) mixed with 1 g AlCl.sub.3.

[0174] The starting reactants were mixed with 2.5 g of carbon fibres cut to 1 cm length. The resulting mixture was heated in a rotating quartz tube at 800 C. 30 minutes. The resulting product was discharged, and then washed and dried.

Example 9: CuZn on Coarse Iron Powder

[0175] 104 mg of ZnCl.sub.2+318 mg of CuCl.sub.3 mixed with 1 g AlCl.sub.3.

[0176] 168 mg of Ecka A/powder (4 microns) mixed with 1 g AlCl.sub.3.

[0177] The starting reactants were mixed with 5 g of stainless steel powder (mean particle size 210 microns). The resulting mixture was heated in a rotating quartz tube at 600 C. for 20 minutes. The resulting product was discharged, and then washed and dried. SEM analysis suggests the powder is thoroughly coated with CuZn.

[0178] The present method may be used for production of coating or compounds of various compositions based on Zn, Sn, Ag, Co, V, Ni, Cr, Fe, Cu, Pt, Pd, Ta, Nb, Rh, Ru, Mo, Os, Re and W including compounds of pure metal, oxides, nitrides of other non-inert elements as described above. Modifications, variations, products and use of said products as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

[0179] In the claims which follow and in the preceding description of embodiments, except where the context requires otherwise due to express language or necessary implication, the word comprise and variations such as comprises or comprising are used in an inclusive sense, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[0180] It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention, in particular it will be apparent that certain features of embodiments of the invention can be employed to form further embodiments.