POWDERS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63/187,601, filed May 12, 2021, the entirety of which is incorporated into this application by reference.

BACKGROUND

[0002] Composite and coated metal powders are increasingly being used in thermal spray and high-velocity spray applications to maintain elemental ratios and to help prevent segregation due to differences in particle morphology and densities between the different metal components.

[0003] Copper-chromium metal composites are typically made by physically mixing the individual metal powders followed by pressing and sintering. Due to the differences between copper and chromium, inhomogeneities in the resulting composite are the result. Making the composite material from coated metal powders can vastly improve the homogeneity of the final material.

[0004] Chromium metal powder is difficult to use as a substrate for electroless deposition due to its passivating oxide coating. There is a need in the art for a process in which electroless, or autocatalytic copper or any other metal coatings can be deposited on chromium metal powder. These needs and other needs are satisfied by the methods of the present disclosure.

SUMMARY

[0005] In accordance with the purpose(s) of the invention, as embodied and broadly described herein, this disclosure, in one aspect, relates to an electroless copper coating process for chromium metal powders, chromium metal powders prepared by the disclosed process, and uses thereof.

[0006] In one aspect, disclosed is a method for electrolessly coating copper onto a chromium metal powder, the method comprising adding a nickel-coated chromium powder to an aqueous electroless copper plating bath comprising a source of copper cations, a copper-

1 cation complexing agent, a copper-cation reducing agent, and a first base, thereby forming a copper-coated chromium metal powder.

[0007] In a further aspect, disclosed are copper-coated chromium metal powder prepared by a disclosed method.

BRIEF DESCRIPTION OF THE FIGURES

[0008] The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects and together with the description serve to explain the principles of the invention.

[0009] FIG. 1 is an SEM image of 0.44 wt.% nickel coated chromium metal powder.

[0010] FIG. 2 is an SEM image of 37 wt.% Cu coated chromium metal powder.

[0011] FIG. 3 is a cross-sectional SEM image of 8% Ni, 37% Cu coated chromium metal powder showing conformal Ni/Cu coating of chromium metal particles.

[0012] Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DESCRIPTION

[0013] The present invention can be understood more readily by reference to the following detailed description of the invention and the Examples.

A. Definitions

[0014] When the term “about” precedes a numerical value, the numerical value can vary within ±10% unless specified otherwise.

2 [0015] As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or can not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0016] As used herein, the term “by weight,” when used in conjunction with a component, unless specially stated to the contrary is based on the total weight of the formulation or composition in which the component is included. For example, if a particular element or component in a composition or article is said to have 8% by weight, it is understood that this percentage is in relation to a total compositional percentage of 100%.

[0017] “Chromium powder” refers to a powder having at least 95% Cr metal, the balance weight of the powder being any trace metals. In some aspects, the “chromium powder” has at least 99% (e.g., at least 99.95%) Cr metal. “Chromium powder” does not refer to any non- metallic particles such as diamond that have been coated with chromium, such as described in Niazi et al., “Parameters optimization of electroless deposition of Cu on Cr-coated diamond,” Trans. Nonferrous Met. Soc. China 24, 136-145 (2014). In further aspects, “chromium powder” refers to a powder that is free of chromium carbide (Cr ₃ C ₂ ) and in some aspects, free of any chromium ion In some aspects, the “chromium powder” has an average particle size as measured according to techniques known in the art ranging from 10-150 microns.

[0018] A “roughening treatment” refers to any known method of roughening the surface of a metal powder, including a roughening treatment with acid (e.g., nitric acid, sulfuric acid, hydrofluoric acid, combinations of these acids) optionally in combination with other agents such as hydrogen peroxide. The “roughening treatment” can include any those methods described in US 2019/0240729, which is incorporated by reference for its teaching of roughening treatments. “Roughening treatment” also includes methods described in Luo, et al., “Preparation and characterization of Ni-coated CT ₃ C ₂ powder by room temperature ultrasonic-assisted electroless plating,” Ceramics International 36, 1989-1992 (2010), including coarsening treatement prior to plating by immersing a metal powder into an aqueous solution of hydrofluoric acid, nitric acid, and ammonium fluoride. An unexpected advantage of the disclosed methods is that in some aspects, the method does not require any roughening treatment prior to either metal coating step.

3 B. Electroless Plating Method

[0019] The disclosed method enables the electroless deposition of copper onto a substrate, e.g., chromium, that is not active towards electroless copper deposition. Additionally, an advantage of the disclosed method is that the amount of nickel required to initiate the copper plating is relatively small, so as not to affect the conductivity of the final copper coated chromium.

[0020] In one aspect, the method for electrolessly coating copper onto a chromium metal powder comprises adding a nickel-coated chromium powder to an aqueous electroless copper plating bath comprising a source of copper cations, a copper-cation complexing agent, a copper-cation reducing agent, and a first base, to thereby form a copper-coated chromium metal powder.

[0021] According to one aspect, the source of copper cations can be a cupric (Cu(II)) salt. In some aspects, the cupric (Cu(II)) salt can be copper sulfate (CuSCri), copper chloride (CuCh), copper nitrate (Cu(NC>3)2), copper acetate (Cu(OAc)2), copper flouride (C11F2), copper bromide (CuBr2), copper carbonate (CuCCh), copper chlorate (Cu(C103)2), copper phosphate (Cu3(PC>4)2), copper perchlorate (Cu(C104)2), copper sulfide (CuS), copper tetrafluroborate (CU(BF4)2), or a combination thereof.

[0022] In one aspect, the copper-cation complexing agent can be a tartrate salt, an alkanol amine, a glycolic acid, ethylenediaminetetraacetic acid (EDTA), or a combination thereof. The alkanol amine, for example, when present, can be a C1-C14 alkanol amine. Non-limiting examples of suitable alkanol amines are ethanolamine, diethanolamine, triethanolamine, N,N,N’,N’-tetrakis(2-hydroxypropyl)ethylenediamine), or a combination thereof.

[0023] According to one aspect, the first base can be sodium hydroxide, lithium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, lime, or a combination thereof.

[0024] In one aspect, the copper-cation reducing agent can be glyoxylic acid, formaldehyde, dimethylamine borane, borohydride, hypophosphite, hydrazine, sucrose, glucose, dithionite, or a combination thereof.

[0025] The method generally involves first preparing the nickel-coated chromium powder. The nickel-coated chromium powder can be prepared by a method comprising adding

4 chromium powder to an aqueous electroless nickel plating bath comprising a source of nickel cations, a nickel-cation complexing agent, a nickel-cation reducing agent, and a second base, to thereby coat the chromium powder with nickel.

[0026] According to one aspect, the source of nickel cations for coating the chromium powder with nickel can be a nickel(II) salt. Non-limiting examples of suitable nickel(II) salts include nickel sulfate (NiSCri), nickel chloride (NiCh), nickel flouride (N1F2), nickel iodide (N1I2), nickel bromide (NiB^), nickel formate (Ni(CH02)2), nickel acetate (Ni(CH3C02)2), nickel ammonium sulfate (NiCNFUMSCriK nickel sulfamate (Ni(S03NH2)2, nickel fluoborate (Ni(BF4)2), nickel borate (Ni3(B03)2), or a hydrate or combination thereof.

[0027] In one aspect, the nickel-cation complexing agent can be sodium pyrophosphate. The second base can be a suitable base for maintaining an adequate pH, e.g., ammonium hydroxide. The nickel-cation reducing agent can be sodium hypophosphite.

[0028] The chromium powder can be coated with nickel in an electroless nickel plating bath. The plating bath can comprise water, e.g., deionized water, a suitable nickel-cation complexing agent such as sodium pyrophosphate. The bath can further comprise the nickel(II) salt, such as nickel sulfate. Additionally, the bath can comprise a suitable nickel-cation reducing agent such as sodium pryophosphate and a suitable base such as ammonium hydroxide.

[0029] The nickel plating bath can then be heated to a suitable temperature, e.g., from 50°C to 80°C. According to one aspect, the nickel plating bath can be heated to a temperature ranging from 60°C to 70°C, e.g., 65°C. Once the nickel plating bath is heated to a suitable temperature, the bath can be agitated, and chromium metal powder can be added with agitation. The resulting bath can be agitated for a suitable time, e.g., from 60 to 120 minutes. According to one aspect, the bath can be agitated for about 90 minutes.

[0030] After a suitable agitation period, the resulting powder can be dried in an inert atmosphere such as argon. Drying can be accomplished at a suitable temperature, e.g., from 90°C to about 120°C. According to one aspect, the powder can be dried in an oven at a temperature of about 110°C. Drying can be accomplished over a suitable time, e.g., 8-15 hours. According to one aspect, sufficient drying can be accomplished in about 12 hours.

5 [0031] By varying the amount of chromium metal powder added to the bath, the nickel percentage in the powder can be altered. For example, nickel coatings having from about 0.1% by weight to about 20% by weight of nickel can be prepared. According to one aspect, nickel coatings having from about 0.2% by weight to about 10% by weight of nickel can be prepared using the disclosed method. For example, powders comprising 0.2%, 0.3%, 0.4%, 0.44%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 10% by weight of nickel can be prepared. An example SEM image of a nickel-coating chromium powder comprising 0.44% by weight of nickel is shown in FIG. 1.

[0032] The method generally does not require stabilizing either electroless bath, e.g., by adjusting the pH to prevent accumulation of a salt onto the metal powder. This can be accomplished in some aspects by consuming the entire source of nickel in the first plating step and/or the entire source of copper in the second plating step. In addition, in some aspects, neither the first electroless plating bath nor the second electroless plating bath are re-used, i.e., some aspects of the method are batch as opposing to continuous process or methods in which one or more baths is re-used for a subsequent plating method.

[0033] To prepare the copper-coat on the nickel-coated chromium powder, an electroless copper plating method can be used. An electroless copper plating bath can be prepared in a suitable bath. The bath can comprise water, e.g., deionized water heated to a temperature of from about 35°C to about 45°C. A suitable second base such as sodium hydroxide can be added, along with a suitable copper-cation complexing agent such as EDTA. A suitable source of copper cations such as a cupric (Cu(II)) salt, e.g., copper sulfate, can be added to the bath, along with the copper-cation reducing agent such as glyoxylic acid.

[0034] Agitation of the electroless copper bath can then be increased, after which a suitable amount of the nickel-coating chromium powder can be added. After a suitable agitation time, e.g., 15 minutes to 45 minutes, an additional amount of the source of copper cations can be added, e.g., copper sulfate. An additional amount of the second based, e.g., sodium hydroxide, and the copper-cation reducing agent, e.g., glyoxylic acid, can be added. The resulting mixture can be allowed to react for a suitable time, e.g., 15 minutes to 45 minutes. According to one aspect, the reaction time can be about 25 minutes. This process can be repeated as desired, e.g., two additional times.

6 [0035] Once the electroless copper coating process has occurred, the plating bath can be filtered and washed with deionized water. Washing with deionized water can dissolve any byproducts resulting from the copper-cation reducing agent. For example, when the copper- cation reducing agent is glyoxylic acid, washing with deionized water suffices to removed oxalic acid byproduct. An exemplary powder produced according to this method is shown in the SEM image of FIG. 2. FIG. 3 shows a cross-sectional SEM image of a similar copper- coated chromium metal powdering comprising 8% by weight nickel.

C. Copper-Coated Chromium Metal Powders

[0036] Also disclosed are copper-coated chromium metal powders prepared by a disclosed method. According to one aspect, the chromium metal powder can comprise from 1% to 50% by weight of copper. According to a further aspect, the chromium metal powder can comprise from 10% to 40% by weight of copper. In a still further aspect, the chromium metal powder can comprise from 30% to 40% by weight of copper. In yet a further aspect, the chromium metal powder can comprise from 35% to 40% by weight of copper. Additionally, in some aspect, the chromium metal powder can comprise from 0.2% to 10% by weight of nickel.

D. Aspects

[0037] The present invention can be described in various non-limiting aspects, such as the following.

[0038] Aspect 1: A method for electrolessly coating copper onto a chromium metal powder, the method comprising adding a nickel-coated chromium powder to an aqueous electroless copper plating bath comprising a source of copper cations, a copper-cation complexing agent, a copper-cation reducing agent, and a first base, thereby forming a copper-coated chromium metal powder.

[0039] Aspect 2: The method of Aspect 1, wherein the source of copper cations is a cupric (Cu(II)) salt.

[0040] Aspect 3: The method of Aspect 1 or 2, wherein the cupric (Cu(II)) salt is copper sulfate (CuSCri), copper chloride (CuCh), copper nitrate (Cu(NC>3)2), copper acetate (CU(OAC)2), copper flouride (CuF2), copper bromide (CuBr2), copper carbonate (CuCCE),

7 copper chlorate (Cu(C103)2), copper phosphate (Cu3(P04)2), copper perchlorate (Cu(C104)2), copper sulfide (CuS), copper tetrafluroborate (Cu(BF4)2), or a combination thereof.

[0041] Aspect 4: The method of any of Aspects 1-3, wherein the copper-cation complexing agent is a tartrate salt, an alkanol amine, a glycolic acid, ethylenediaminetetraacetic acid (EDTA), or a combination thereof.

[0042] Aspect 5: The method of any of Aspects 1-4, wherein the alkanol amine, when present, is a CI-CM alkanol amine.

[0043] Aspect 6: The method of any of Aspects 1-5, wherein the alkanol amine, when present, is ethanolamine, diethanolamine, triethanolamine, N,N,N’,N’-tetrakis(2- hydroxypropyl)ethylenediamine), or a combination thereof.

[0044] Aspect 7: The method of any of Aspects 1-6, wherein the first base is sodium hydroxide, lithium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, lime, or a combination thereof.

[0045] Aspect 8: The method of any of Aspects 1-7, wherein the copper-cation reducing agent is glyoxylic acid, formaldehyde, dimethylamine borane, borohydride, hypophosphite, hydrazine, sucrose, glucose, dithionite, or a combination thereof.

[0046] Aspect 9: The method of any of Aspects 1-8, wherein the nickel-coated chromium powder is prepared by a method comprising adding chromium powder to an aqueous electroless nickel plating bath comprising a source of nickel cations, a nickel-cation complexing agent, a nickel-cation reducing agent, and a second base, thereby coating the chromium powder with nickel.

[0047] Aspect 10: The method of Aspect 9, wherein the source of nickel cations is a nickel(II) salt.

[0048] Aspect 11: The method of any of Aspects 9 or 10, wherein the nickel(II) salt is nickel sulfate (NiSCri), nickel chloride (NiCh), nickel flouride (N1F2), nickel iodide (N1I2), nickel bromide (NiB^), nickel formate (Ni(CH02)2), nickel acetate (Ni(CFbC02)2), nickel ammonium sulfate (Ni(NH4)2(S04)2, nickel sulfamate (Ni(S03NH2)2, nickel fluoborate (Ni(BF4)2), nickel borate (Ni3(B03)2), or a hydrate or combination thereof.

8 [0049] Aspect 12: The method of any of Aspects 9-11, wherein the nickel-cation complexing agent is sodium pyrophosphate.

[0050] Aspect 13: The method of any of Aspects 9-12, wherein the second base is ammonium hydroxide.

[0051] Aspect 14: The method of any of Aspects 9-13, wherein the nickel-cation reducing agent is sodium hypophosphite.

[0052] Aspect 15: A copper-coated chromium metal powder prepared by the process of any of Aspects 1-14.

[0053] Aspect 16: The metal powder of Aspect 15, comprising from 1% to 50% by weight of copper.

[0054] Aspect 17: The metal powder of Aspect 15 or 16, comprising from 10% to 40% by weight of copper.

[0055] Aspect 18: The metal powder of any of Aspects 15-17, comprising from 30% to 40% by weight of copper.

[0056] Aspect 19: The metal powder of any of Aspects 15-18, comprising from 35% to 40% by weight of copper.

[0057] Aspect 20: The metal powder of any of Aspects 15-19, comprising from 0.2% to 10% by weight of nickel.

E. Examples

[0058] The examples described herein are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the methods claimed herein are made and evaluated, and are intended to be purely exemplary of the invention and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric.

9 [0059] Electroless coatings of copper on chromium metal powder was achieved by first depositing a small amount of electroless nickel on the surface of the chromium metal powder. An example follows for making a 35-40 wt.% copper coated chromium metal powder.

[0060] An electroless nickel plating bath was made in a 20L glass cell containing four baffles and equipped with an overhead stirrer and nitrogen sparging. The plating bath contained 10L deionized water, 132.5g sodium pyrophosphate (Na ₂ P207-10H ₂ 0), 67g Nickel sulfate (NiSCfi- 6H2O), 185.6g sodium hypophosphite (NaH2P02-l- 120), and 600mL ammonium hydroxide (NH ₄ OH). After the bath was heated to 65°C, the agitation was increased to 420RPM and 3kg of chromium metal powder (45pm) was added. After 90 minutes the bath was filtered, and the powder washed with water. The powder was dried in an argon atmosphere oven at 110°C for 12 hours.

[0061] ICP analysis of the resulting powder is shown in Table 1 and its SEM analysis is shown in FIG 1. By varying the amount of chromium metal powder added to the bath, the nickel percentage can be altered. Nickel coatings from 0.2 wt.% to 10 wt.% can be prepared, for example.

Table 1: ICP Analysis of Nickel-Coated Chromium Metal Powder

[0062] This nickel coated chromium metal powder was then coated with copper by first preparing an electroless copper plating bath in the same 20L cell, though without nitrogen sparging. The electroless copper plating bath contained 10L hot deionized water (35-45°C), 450g sodium hydroxide (NaOH), 400g ethylenediamine tetraacetic acid (EDTA), 17 lg copper sulfate (CUSO4-5H2O), and 350mL glyoxylic acid (50%).

[0063] The agitation was increased to 500RPM, after which 260g of the nickel coated chromium metal powder was added. After 25 minutes an additional 170g copper sulfate (CUSO4-5H2O), 140g sodium hydroxide, and 170mL glyoxylic acid were added and allowed to react for 25 minutes. This was repeated two additional times, after which the bath was filtered and washed with copious amounts of deionized water to dissolve the oxalic acid byproduct and wash the copper coated nickel chromium metal powder.

10 [0064] ICP analysis of the coated powder is shown in Table 2. SEM analysis of the powder is shown in FIG 2. FIG 3 shows a cross-sectional SEM image of a similar copper coated chromium metal powder containing 8 wt.% nickel.

Table 2: ICP Analysis of Copper-Coated Nickel Chromium Metal Powder

[0065] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

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