Thermochemical synthesis of metallic pigments

Abstract

A method for depositing a metal-based coating on a particulate substrate, including: i) preparing a mixture comprising the particulate substrate, a powder comprising a coating metal oxide of one or more of Ti, Al, Zn, Sn, In, Sb, Ag, Co, V, Ni, Cr, Mn, Fe, Cu, Pt, Pd, Ta, Zr, Nb, Rh, Ru, Mo, Os, Re and W, a reducing agent powder of Al metal or Al alloy, and a powder of aluminium chloride; and ii) mixing and heating the mixture to form a coating on the particulate substrate, to produce a coated substrate product.

Claims

1. A method for depositing a metal-based coating on a particulate substrate, including: a) preparing a mixture comprising the particulate substrate; and a powder comprising a coating metal oxide of one or more of Ti, Al, Zn, In, Sb, Ag, Co, V, Ni, Cr, Mn, Fe, Cu, Pt, Pd, Ta, Zr, Nb, Rh, Ru, Mo, Os, Re and W; and a reducing agent powder of Al metal or Al alloy, and a powder of aluminium chloride; and b) mixing and heating the mixture to form a coating on the particulate substrate, to produce a coated substrate product.

2. A method according to claim 1, comprising the steps of: immersing a substrate powder in a reactant mixture comprising the coating metal oxide and the reducing agent powder and aluminium chloride and optionally one or more coating additives, and heating and mixing the reactant mixture at temperatures between 100° C. and 900° C. to induce reactions between a particulate substrate surface and the reactant mixture and form a coating on the particulate substrate; and condensing by-products away from a reaction zone where the reducing agent and reactant mixture are reacting; and separating the coated particulate substrate from residual un-reacted materials.

3. A method according to claim 2, wherein the coating additives include boron, carbon, oxygen or nitrogen and the coated substrate products comprises a substrate coated with metal borides, metal carbide, metal oxide or metal nitride.

4. A method according to claim 2, wherein the reducing agent is mixed or co-milled with AlCl.sub.3 or the reducing agent is mixed or co-milled with the particulate substrate or a part of the particulate substrate.

5. A method according to claim 1, wherein the method includes the steps of condensing volatile by-products away from the mixture; and separating the coated substrate from residual un-reacted materials.

6. A method according to claim 1, wherein the method comprises the steps of: reacting the mixture including the coating metal oxide and the aluminium chloride with the particulate substrate at temperatures below Tmax to form a coating on the particulate substrate surface; the coating comprising a metallic coating deposited on the particulate substrate surface and/or a metallic skin obtained by chemically incorporating metallic elements into the particulate substrate surface; and Tmax is below 900° C.; and condensing by-products away from the mixture.

7. A method as claimed in claim 1, wherein reactions between the coating metal oxide and the reducing agent are exothermic.

8. A method as claimed in claim 1, wherein the particulate substrate is mixed and reacted with the aluminium chloride before mixing and heating with the coating metal oxide and the reducing agent powder.

9. A method as claimed in claim 1, wherein the particulate substrate is in the form of a powder, flakes, beads, or fibres comprising: i.—pure metals or alloys and compounds based on metals and transition metals including one or more of alloys, oxides, nitrides, carbides, silicides and borides; or ii.—silica, glass, quartz, silicates, borosilicate, soda glass, silicon nitride, mica, talc, graphite carbon fibre or a mixture thereof.

10. A method according to claim 9, wherein the weight ratio of the coating metal oxide to the particulate substrate is between 0.01 and 5.

11. A method according to claim 9, wherein the particulate substrate includes silicon and the coating includes metal silicides.

12. A method according to claim 11, wherein the particulate substrate includes a borosilicate substrate or a soda-lime glass substrate and where Tmax is below 650° C.

13. A method according to claim 9, wherein the particulate substrate comprises one or more of carbon powder, carbon beads, carbon flakes, or carbon fibres.

14. A method according to claim 9, wherein the coating on the coated substrate product includes Al at levels between 0 wt % and 50 wt % and unreacted coating metal oxide.

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

16. A method according to claim 1, wherein the method includes an additional step of reacting the coated substrate product with a reactive gas including oxygen, nitrogen, carbon or boron.

17. A method according to claim 16, wherein the reactive gas includes a reactive element from the group of oxygen, nitrogen, carbon, and boron, and wherein a flow of the reactive gas is controlled to produce a coating with a controlled amount of the reactive element.

18. A method according to claim 1, wherein an amount of the coating metal oxide reduced by the reducing agent is between 5 wt % and 100 wt % of the coating metal oxide.

19. A method for depositing a metal-based coating on a particulate substrate, including: a) heating a mixture comprising a particulate substrate and a mixture of a powder of aluminium chloride and a powder of aluminium; b) adding to the heated mixture a powder comprising a coating metal oxide of one or more of Ti, Al, Zn, Sn, In, Sb, Ag, Co, V, Ni, Cr, Mn, Fe, Cu, Pt, Pd, Ta, Zr, Nb, Rh, Ru, Mo, Os, Re and W; and c) mixing and further heating to form a coating on said particulate substrate.

20. A method for producing a metallic coating on a particulate substrate surface, and wherein the method is conducted stepwise: in a first step, a coating metal oxide of one or more of Ti, Al, Zn, Sn, In, Sb, Ag, Co, V, Ni, Cr, Mn, Fe, Cu, Pt, Pd, Ta, Zr, Nb, Rh, Ru, Mo, Os, Re and W is reacted with other reactants comprising a powder of aluminium chloride at temperatures between 100° C. and 500° C. to form intermediates in a powder form; and in a second step, a mixture comprising the intermediates, a reducing agent powder of Al metal or Al alloy and the particulate substrate is heated at temperatures between T2, above 300° C., and Tmax, below 900° C., to induce physical or chemical reactions between reactants in the mixture and cause a coating to form on the particulate substrate surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 shows a process schematic for one example embodiment illustrating steps for coating a substrate using an Al reducing agent; and

(3) FIG. 2 shows a process schematic illustrating processing steps for a further example embodiment for two-step production of a coated substrate starting from metal oxides and Al.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) FIG. 1 is a schematic diagram illustrating processing steps for one preferred embodiment for production of a coated substrate starting from metal oxides and Al.

(5) In a first step (101), a fine powder of the reducing agent (e.g. Al) is prepared. The powder can be introduced separately or together with other reactants depending on compatibility with other precursor chemicals.

(6) The substrate (102) (e.g. glass flakes or powder) is mixed with the coating metal oxide(s) (103) together with other compatible coating additives (104) leading to a first mixture (105). The remaining coating additive precursors (104) (e.g. borax, graphite powder) are prepared into several mixtures (106). Mixing and preparation of the precursor materials is carried out under a protective atmosphere (107).

(7) The substrate (102) and/or the reducing Al (101) may be mixed with AlCl.sub.3 (110-A) before processing through the reaction zone.

(8) Reactants are arranged in separate streams depending on chemical compatibility. For example, it is preferred not to premix reactants which have the potential to react exothermically leading to the release of excessive amounts of heat.

(9) The reducing Al agent (101) and mixtures (105) and (106) are fed into a pre-mixer (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.

(10) The resulting by-products (109), including aluminium chlorides, are condensed away from the solid reactants, and collected in a dedicated vessel (110). A part or all of the aluminium chlorides may be recycled through (101). All processing steps are preferably carried out under an inert gas or a non-fully reactive gas (e.g. Ar, CO.sub.2, N.sub.2, Ar—O.sub.2 . . . ) 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).

(11) 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).

(12) FIG. 2 is a schematic diagram illustrating processing steps for one preferred embodiment for production of a coated substrate starting from metal oxides and Al but with processing carried out through two processing stages. This arrangement is suitable for a number of metals (e.g. Cu and Zn) Here, the reactants such as the mixture substrate-metal oxides-Al—AlCl.sub.3 or some constituents of the reactants (e.g. a mixture of metal oxides-Al—AlCl.sub.3 or a mixture substrate-metal oxides-AlCl.sub.3) are first processed in Stage 1 (108-A) to carry out some of the chemical reactions such as converting a part of the metal oxides to metal chlorides, and then, the reactants are further heated in Stage 2 (108-B) to complete processing and produce the coated end-products.

(13) Residual waste (116) is stored separately for further processing or disposal.

(14) Materials produced by preferred forms of the invention described here may have unique characteristics that may not be obtained using prior art methods.

(15) 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 example properties may 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.

(16) Another important aspect of preferred forms of the present invention is to provide coated substrates with coatings having predetermined chemical compositions and phases present in the coating, enabling control over the physical and optical properties of the coated substrate. In one form of this aspect, the coating constituents are made to react with the substrate surface allowing chemicals from the substrate to enter the coating compositions and therefore to have influence over the chemical and physical properties of the end products.

(17) One example of the quality and use of example 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 currently limited to common metals such as aluminium, and for a number of other metals, the cost can be prohibitive. For example, the example forms of the present method allow 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.

(18) The following are examples of preparation of various coating compounds in accordance with an embodiment of the present invention.

EXAMPLE 1

Ti on Glass Flakes

(19) 200 g of borosilicate glass flakes are mixed together with 20 g of TiO.sub.2 powder, 10 g of Al and 20 g of AlCl.sub.3 powder.

(20) The mixture was then fed and reacted in a continuous reactor at temperatures ramping from room temperature to 600° C. The coated flakes were then washed in water and dried. The coated flakes have metallic appearance. Examination under an SEM and EDX shows the presence of metallic Ti, TiO— Ti—Al and Ti—Si species including the presence of lumps of metallic Ti. Al was also detected in the sample.

EXAMPLE 2

Ti on Glass Flakes

(21) 200 g of soda-lime glass flakes are mixed together with 20 g of TiO.sub.2 powder and 10 g of Al powder (4 microns).

(22) The mixture was then fed and reacted in a continuous reactor at a temperature ramping from room temperature to 600° C. with a residence time of 20 minutes. The coated flakes were then washed in water and dried. The coated flakes have metallic appearance. Examination under an SEM and EDX shows that the surface is coated with metallic Ti but with the presence of Ti-based metallic lumps. Al was also detected in the sample. XRD analysis of the sample indicates the presence of residual TiO.sub.2.

EXAMPLE 3

Cu on Glass Flakes

(23) 200 g of borosilicate glass flakes.

(24) 20 g CuO.

(25) 18 g of Al—AlCl.sub.3 mixture (1 wt part Al to 2 part AlCl.sub.3 per weight). Al is 4 microns.

(26) The CuO—Al—AlCl.sub.3 were mixed with the flakes (6 microns) and then the resulting reactant mixture was heated in a continuous reactor at 600° C. (residence time=30 minutes). The coated flakes were then washed and dried. The end products have a deep marron colour consisting of a mixture of Cu, Cu.sub.2O and CuO.

(27) EXAMPLE 4

Cu on Borosilicate Glass Flakes

(28) 150 g borosilicate glass flakes.

(29) 30 g of a CuO.

(30) 30 g of AlCl.sub.3.

(31) 7 g of Al powder (4 microns).

(32) The flakes, the AlCl.sub.3 and CuO are first mixed together, and then fed together with the Al into a first reactor set at 180° C. for a residence time of 15 min. The resulting intermediates are then transferred into a second reactor at a temperature 600° C. for another 15 min. In both reactors, the reactants are continuously mixed.

(33) The products are then discharged and processed. The product has a maroon colour.

EXAMPLE 5

Cu on Borosilicate Glass Powder (10 Microns)

(34) 150 g borosilicate glass powder.

(35) 30 g of a CuO.

(36) 10 g of AlCl.sub.3.

(37) 7 g of Al powder (4 microns).

(38) The substrate powder, the AlCl.sub.3 and CuO are first mixed together and then fed together with the Al into a first reactor set at 180° C. for a residence time of 15 min. The resulting intermediates are then transferred into a second reactor at a temperature 600° C. for another 15 min. In both reactors, the reactants are continuously mixed.

(39) The products are then discharged and processed. The product has a yellow-gold colour.

EXAMPLE 6

Cu—Zn on Glass Flakes

(40) 150 g of soda-lime glass flakes (100 microns).

(41) 7.5 g of CuO+7.5 g of ZnO.

(42) 4.5 g of Al powder (4 microns) milled with 9 g AlCl.sub.3 powder.

(43) The reactants were mixed, and the resulting mixture was heated in a continuous reactor for a residence time for 30 minutes. The resulting product was then discharged, and then washed and dried. The powder has a shiny appearance. SEM analysis shows occasional lumps on the coated surface.

EXAMPLE 7

Zn on Silica Powder (10 Microns)

(44) 200 g silica powder (average particle size=10 microns).

(45) 50 g of ZnO.

(46) 10 g of AlCl.sub.3.

(47) 20 g of Al powder (4 microns).

(48) The silica powder, the ZnO and the AlCl.sub.3 are first mixed together and then the Al is added, and the reactants are heated and continuously mixed in a batch reactor at temperatures of 600° C. for one hour.

(49) The products are then discharged and processed. The product has a grey colour. Various analyses including XRD, SEM and EDS suggest a ZnO-to-Zn conversion efficiency of the order of 75%.

EXAMPLE 8

Zn on Fumed Silica Powder (400 Nm)

(50) 100 g fumed silica powder (average particle size=300-400 nm).

(51) 100 g of ZnO.

(52) 20 g of AlCl.sub.3.

(53) 40 g of Al powder (4 microns).

(54) The reactants are first mixed together. The reactor is brought to a temperature of 600° C. The materials are then fed gradually while monitoring reactant temperature and reaction rate. At the end of the feeding process, the materials are further processed for 30 min at 600° C. During processing the reactants are continuously mixed.

(55) The products are then discharged and washed. The products have a grey-brownish colour. Various analyses including XRD, SEM and EDS suggest a ZnO-to-Zn conversion efficiency of the order of 70%.

EXAMPLE 9

Zn on Silica Nanopowder (<100 Nm)

(56) 100 g silica nanopowder (<100 nm).

(57) 100 g of ZnO.

(58) 20 g of AlCl.sub.3.

(59) 40 g of Al powder (4 microns).

(60) The powder is first dried and then mixed with the rest of the reactants. The reactor is brought to a temperature of 600° C. The materials are then fed gradually while monitoring reactant temperature and reaction rate. At the end of the feeding process, the materials are further processed for 30 min at 600° C. During processing the reactants are continuously mixed.

(61) The products are then discharged and washed. The products have a greyish colour. Various analyses including XRD, SEM and EDS suggest a ZnO-to-Zn conversion efficiency of the order of 67%.

EXAMPLE 10

Zn on Glass Flakes

(62) 100 g borosilicate glass flakes (particle size less than 50 microns and 1 micron thick).

(63) 25 g of ZnO.

(64) 2.5 g of AlCl.sub.3.

(65) 10 g of Al powder (milled Al flakes).

(66) The reactants are first mixed together. The reactor is brought to a temperature of 600° C. The materials are then fed gradually while monitoring reactant temperature and reaction rate. At the end of the feeding process, the materials are further processed for 30 min at 600° C. During processing the reactants are continuously mixed.

(67) The products are then discharged and washed. The products have a metallic appearance. ZnO-to-Zn conversion efficiency of the order of 75%.

EXAMPLE 11

Zn on Silica Powder (10 Microns)

(68) 200 g silica powder (average particle size=10 microns).

(69) 100 g of ZnO.

(70) 20 g of AlCl.sub.3.

(71) 40 g of Al powder (4 microns).

(72) The silica powder, the ZnO and the AlCl.sub.3 are first mixed together and then the Al is added, and the reactants are heated and continuously mixed in a batch reactor at temperatures of 600° C. for one hour.

(73) The products are then discharged and processed. The product has a grey colour. Various analyses including XRD, SEM and EDS suggest a ZnO-to-Zn conversion efficiency of the order of 75%.

EXAMPLE 12

Sn—Cu on Silica Powder (−600 Mesh)

(74) 150 g silica powder (−600 mesh).

(75) 15 g of a SnO.sub.2.

(76) 20 g of AlCl.sub.3.

(77) 2.5 g of Al powder (4 microns).

(78) The substrate powder, the AlCl.sub.3 and SnO.sub.2 are first mixed together and then processed together with the Al at temperatures up to 700° C. The resulting powder is then used as a substrate to deposit Cu as follows:

(79) 30 g of a CuO.

(80) 30 g of AlCl.sub.3.

(81) 7 g of Al powder (4 microns).

(82) The substrate powder, the AlCl.sub.3 and CuO are first mixed together and then fed together with the Al into a first reactor set at 180° C. for a residence time of 15 min. The resulting intermediates are then transferred into a second reactor at a temperature 600° C. for another 15 min. In both reactors, the reactants are continuously mixed.

(83) The products are then discharged and processed.

EXAMPLE 13

Cr on Borosilicate Glass Flakes

(84) 100 g borosilicate glass flakes (particle size less than 50 microns and 1 micron thick).

(85) 50 g of Cr.sub.2O.sub.3.

(86) 10 g of AlCl.sub.3.

(87) 15 g of Al powder (4 microns).

(88) The flakes, the Cr.sub.2O.sub.3 and the AlCl.sub.3 are first mixed together and then the Al is added. The reactor is brought to a temperature of 600° C. The materials are then fed gradually while monitoring reactant temperature and reaction rate. At the end of the feeding process, the materials are further processed for 30 min at 600° C. During processing the reactants are continuously mixed.

(89) The products are then discharged and processed. The product has a dark metallic colour colour.

(90) A part of the materials was then heated in air at a temperature of 600° C. resulting in a powder with a green colour.

EXAMPLE 14

Fe on Glass Flakes

(91) 150 g of borosilicate glass flakes.

(92) 10 g of Fe2O.sub.3 powder was milled with 10 g of AlCl.sub.3 powder.

(93) 3.5 g of Al powder (4 microns) was milled with 10 g of AlCl.sub.3 powder.

(94) The reactants were all mixed and then the resulting mixture was processed in a continuous reactor at 600° C. for a residence time of 30 minutes. The resulting product was then discharged, washed, and dried. The flakes have a shiny deep dark greyish appearance.

(95) A part of the materials was then heated in a stream of oxygen at a temperature of 600° C. resulting in a powder with a orange-red colour. XRD analysis indicates the presence of Fe.sub.2O.sub.3.

EXAMPLE 15

Stainless Steel on Borosilicate Glass Flakes (50 Microns)

(96) 150 g borosilicate glass flakes (particle size less than 50 nm and 1 micron thick).

(97) 7.5 g of a mixture of oxides: Fe.sub.2O.sub.3, Cr.sub.2O.sub.3, NiO and MoO.sub.3.

(98) 10 g of AlCl.sub.3.

(99) 5 g of a milled mixture of Al powder and AlCl.sub.3 ratio 1 to 2.

(100) The flakes and the reactants are all mixed together. The reactor is brought to a temperature of 600° C. The materials are then fed gradually while monitoring reactant temperature and reaction rate. At the end of the feeding process, the materials are further processed for 30 min at 600° C. During processing the reactants are continuously mixed.

(101) The products are then discharged and processed. The product has a dark metallic colour.

EXAMPLE 16

Ta on Silica Powder (10 Microns)

(102) 150 g glass powder (−600 mesh).

(103) 15 g of a Ta.sub.2O.sub.5.

(104) 15 g of AlCl.sub.3.

(105) 2 g of a powder (4 microns).

(106) The substrate powder, the AlCl.sub.3 and Ta.sub.2O.sub.5 are first mixed together and then fed together with the Al into a reactor set at 700° C. for a residence time of 15 min. The reactants are continuously mixed during processing.

(107) The products are then discharged and processed.

EXAMPLE 17

Iron Oxide on Mica Powder

(108) 150 g glass powder (−600 mesh).

(109) 30 g of a Fe.sub.2O.sub.3.

(110) 50 g of AlCl.sub.3.

(111) 7.5 g of Al powder (4 microns).

(112) The substrate powder, the AlCl.sub.3 and Fe.sub.2O.sub.3 are first mixed together and then fed together with the Al into a reactor set at 700° C. for a residence time of 15 min. The reactants are continuously mixed during processing.

(113) The products are then discharged and processed.

EXAMPLE 18

Titanium on Synthetic Mica Powder

(114) 150 g on borosilicate glass powder (10 microns).

(115) 30 g of a TiO.sub.2.

(116) 30 g of AlCl.sub.3.

(117) 10 g of Al powder (4 microns).

(118) The substrate powder, the AlCl.sub.3 and TiO.sub.2 are first mixed together and then fed together with the Al into a reactor set at 700° C. for a residence time of 15 min. The reactants are continuously mixed during processing.

(119) The products are then discharged and processed.

EXAMPLE 19

Zn on Silica Powder (10 Microns)

(120) 200 g silica powder (average particle size=10 microns).

(121) 100 g of ZnO.

(122) 20 g of AlCl.sub.3.

(123) 40 g of Al powder (4 microns).

(124) The silica powder is loaded into a reactor at a temperature of 600° C.

(125) The Al is mixed with the AlCl.sub.3.

(126) The ZnO and the Al—AlCl.sub.3 are fed gradually into the reactor at 600° C. and mixed and heated with the silica powder for 30 minutes.

(127) The products are then discharged and processed. The product has a grey colour. Various analyses including XRD, SEM and EDS suggest a ZnO-to-Zn conversion efficiency of the order of 75%.

(128) For all embodiments and examples provided above, the Al reducing agent can be replaced with Mg and the AlCl.sub.3 reducing metal chloride can be replaced with magnesium chloride without any significant change in the processing conditions. Then, only minor variations would be required to handle the by-products including magnesium chloride when magnesium chloride is used as a part of the starting reactants.

(129) The present method may be used for production of coating or compounds of various compositions based on Ti, Al, Zn, Sn, In, Sb, Ag, Co, V, Ni, Cr, Mn, Fe, Cu, Pt, Pd, Ta, Zr, 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.

(130) 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.

(131) Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

(132) It will be understood to persons skilled in the art of the invention that 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.