Graphene-copper coated electrical contacts

Abstract

The present disclosure relates to an electric contact (1), which comprises a substrate (5) of a conductive material and a graphene-copper composite coating (6) located on the substrate. The graphene content in the coating is in the range of 0.1 to 2 weight %.

Description

Technical Field

[0001] The present disclosure relates to an electrical contact including a substrate and a coating on the substrate. Background Art

[0002] Silver (Ag)-plated copper (Cu) is used as an electrical contact material for a range of arcing contacts (e.g. in LV (low voltage) disconnectors) and non-arcing contact applications (e.g. power connectors). Ag is an excellent contact material with low contact resistance and oxidation resistance. However, Ag material is expensive and sensitive to sulfur-containing atmospheres. Summary of the invention

[0003] An object of the present invention is to provide an improved electrical contact.

[0004] The inventors have now realized that by using graphene composites, the corrosion resistance of copper can be greatly improved, which is why cheaper graphene-copper composite coatings can be used instead of silver. Also at relatively low graphene concentrations, the composite coating provides oxidation protection for the substrate material and prevents the substrate material from diffusing through the coating. By maintaining a low graphene concentration in the composite coating, electrical conductivity is substantially unimpeded, which is why the composite coating can be advantageously used in electrical contacts, such as in power connectors or disconnectors. The use of graphene in contacts can also reduce their friction, increase their conductivity, increase their wear resistance (e.g., arc resistance), and extend their service life.

[0005] According to one aspect of the present invention, an electric contact is provided, comprising a conductive material substrate and a graphene-copper composite coating on the substrate, wherein the graphene content in the coating is in the range of 0.1 to 2 weight %.

[0006] According to another aspect of the present invention, a contact device is provided. The contact device includes an embodiment of the electric contact disclosed herein.

[0007] According to another aspect of the present invention, a method for coating a substrate for an electrical contact is provided. The method includes providing a graphene-copper electrolyte comprising graphene and copper ions. The method also includes coating the substrate by electrodeposition, whereby the graphene and copper ions are co-deposited to form a graphene-copper composite coating on the substrate. The graphene content in the solution is in the range of 0.01-1.5 g / L.

[0008] It should be noted that any of the features of any aspect may be applicable to any other aspect (if applicable). Similarly, any advantages of any aspect may be applicable to any other aspect. Other objects, features and advantages of the attached embodiments will become apparent from the following detailed disclosure, the attached dependent claims and the accompanying drawings.

[0009] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the technical field, unless otherwise explicitly defined herein. Unless otherwise explicitly stated, all references to "a / an / the element, device, component, equipment, step, etc." should be publicly interpreted as referring to at least one instance of an element, device, component, equipment, step, etc. Unless explicitly stated, the steps of any method disclosed herein do not have to be performed in the exact order disclosed. The use of "first", "second", etc. for different features / components of the present disclosure is intended only to distinguish these features / components from other similar features / components, rather than to give these features / components any order or ranking. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments will be described by way of example with reference to the accompanying drawings, in which:

[0011] Figure 1 is a schematic circuit diagram of a contact device according to some embodiments of the present invention.

[0012] Figure 2 is a schematic side view of an electrical contact according to some embodiments of the present invention.

[0013] Figure 3 is a graph illustrating the evolution of the contact resistance of a Cu reference contact (of the present invention), an Ag reference contact and a Cu-graphene contact during aging exposed to a temperature of 130° C. for 30 days in a hot air oven.

[0014] Figure 4 is a schematic cross-sectional side view of an electrodeposition cell according to some embodiments of the present invention.

[0015] Figure 5 is a schematic flow chart of some embodiments of the method of the present invention. DETAILED DESCRIPTION

[0016] Embodiments will be described more fully below with reference to the accompanying drawings, in which certain embodiments are shown. However, within the scope of the present disclosure, many different forms of other embodiments are possible. On the contrary, the following embodiments are provided by way of example so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Throughout the specification, the same numbers refer to the same elements.

[0017] Herein, the term graphene (G) refers to carbon atoms in a 2D honeycomb lattice in the form of a single layer, a double layer, a few (3-5) layers, or a nanoplatelet with a thickness of up to 50 nm (e.g., in the range of 1-50 nm). In addition, when graphene is discussed herein, it should be understood that some graphene may be in the form of graphene oxide (GO) or reduced GO (rGO). Therefore, graphene may include only pure graphene or a mixture of pure graphene and GO and / or rGO.

[0018] Figure 1 A contact device 10 is shown, which is used to conduct and / or switch a current I, alternating current (AC) or direct current (DC) with a voltage U, and includes a contact pair 2, and the contact pair 2 includes a contact 1. The contact device can be, for example, or include a power connector (a type of fixed contact), and the contact device is configured to carry the current I, for example, when the contact device is connected to a load, or is a switching device (such as a disconnector), the contact device is configured to switch and / or disconnect the current I, in which case the contact 1 can be an arc contact. It can be seen that the contact device 10 and thus its contact pair 2 and contact 1 can be configured to be conductive and arc-free (such as in a power connector), or configured to be conductive and arc-free (such as in a disconnector).

[0019] Silver-plated copper is used as an electrical contact material for both a range of arcing contacts (e.g., in LV disconnect switches) and non-arcing fixed contact applications (e.g., power connectors). Some embodiments of the present invention using a G-Cu composite coating instead of silver plating can be used in the same applications as silver-plated Cu contacts.

[0020] The contact device 10 is preferably used for low voltage (LV) applications having a rated AC voltage of at most 1 kV, for example in the range of 0.1-1 kV, or a rated DC voltage of at most 1.5 kV, for example in the range of 0.1-1.5 kV, or for applications with higher rated voltages, for example up to 70 kV, such as a rated AC or DC voltage in the range of 1-70 kV.

[0021] Figure 2 An electrical contact 1 is illustrated, comprising a substrate 5 of a conductive material and a G-Cu composite coating 6 located on the substrate, typically on the surface of the substrate, such that the composite coating is in direct contact with the conductive material of the substrate without any intermediate layer. The thickness of the composite coating 6 may be at most 100 μm, for example in the range of 0.1-100 μm or 1-50 μm.

[0022] The conductive material of the substrate 5 may be metal, for example comprising or consisting of (usually consisting of) copper or aluminum. Cu may be advantageously used because using Cu in both the substrate 5 and the composite coating 6 may improve the adhesion of the coating to the substrate.

[0023] The G content in the composite coating 6 is in the range of 0.1 to 2 weight percent (wt%), for example in the range of 0.3 to 1 weight percent, so that its concentration is low enough to not substantially hinder the conductivity of the contact 1. The G content is still high enough to reduce the friction of the contact 1 at the surface of the composite coating 6, thereby avoiding the need to use grease or other non-solid lubricants, for example, when the contact is used in a disconnector. Preferably, the composite coating 6 does not contain silver. For example, the composite coating can consist only of G and Cu.

[0024] G is preferably present as several layers of graphene sheets 7 (also referred to herein as nanoplatelets) in the coating 6, preferably with a thickness in the range of 1-50 nm. The G sheets 7 each have a lateral size, discussed herein as the longest diameter, which is several times larger than the thickness, thereby forming a platelet form (thin sheet or sheet form). In some embodiments, the sheets 7 each have a longest diameter in the range of 5-80 μm. The G in the composite coating 6 greatly improves corrosion resistance. It is believed that the G sheets 7 can naturally align themselves with the substrate surface (e.g., as a result of electrodeposition discussed below) so that the platelets are generally arranged parallel to the coated surface. The G sheets 7 can prevent atoms of the substrate 5 (e.g., Cu) from diffusing through the coating 6, which is a known problem when using, for example, a pure Ag coating, thereby additionally preventing oxide growth on the surface of the coated contact 1. The G sheets 7 can also effectively provide a conductive path from the contact surface to the bulk, thereby limiting the impact of the oxide layer resistance.

[0025] Thus, embodiments of the present invention, by using a G-Cu composite coating, can combine the following advantageous properties even with relatively low graphene content in the contact 1: 1) low friction under dry conditions, at a level similar to that of a greased system, due to the lubricating properties of the graphene; 2) low contact resistance, which may be similar to that of pure silver rather than pure copper, due at least in part to the low resistivity of the graphene; and 3) high corrosion resistance in air at elevated temperatures, also resulting in maintenance of low contact resistance over time, due at least in part to hindering the formation of an electrically insulating oxide surface layer on the contact and providing a conductive path to the substrate 5.

[0026] Figure 3The evolution of the contact resistance of a Cu reference contact (of the present invention), an Ag reference contact and a Cu-graphene contact during aging at 130°C for 30 days in a hot air oven is shown. The contact resistance was measured at different mechanical contact loads (10 and 30 Newtons, N, respectively) relative to a silver counter electrode. It can be seen that the resistance for the Cu reference increases rapidly with exposure time, while the Cu-graphene coated Cu contact shows a limited increase, very similar to the increase in contact resistance for the Ag reference.

[0027] Reference again Figure 2 , a thinner coating 8 of pure Cu may be applied on top of the composite coating in order to encapsulate the composite coating 6. The thickness of the pure Cu coating may be at most 20 μm, for example in the range of 0.1-20 μm or 1-10 μm. The combined thickness of the composite coating 6 and the pure Cu coating may be at most 100 μm, for example in the range of 0.1-100 μm or 1-20 μm.

[0028] Figure 4 An electrodeposition apparatus or electrodeposition cell 30 is illustrated for electrodeposition (also referred to as electroplating) of the composite coating 6 (and, where applicable, also in connection with electrodeposition of a pure Cu coating 8, if used).

[0029] The G-Cu electrolytic solution 33 (usually aqueous) includes graphene 7 (usually in the form of nanoplatelets) and copper ions 34. The substrate 5 serves as a cathode and is connected to a voltage source 31 similar to a corresponding anode 32 (e.g., a Cu anode). By applying a voltage between the substrate 5 and the anode 32 by the voltage source 31, the graphene nanoplatelets 7 and the Cu ions 34 are co-deposited onto the surface of the substrate 5 to form a composite coating 6. Similarly, if desired, for a pure Cu coating 8, an electrolytic solution 33 including copper ions 34 but not including G7 is used.

[0030] Copper ions 34 are typically provided by dissolving a copper salt in the electrolyte solution 33. Examples of copper salts that can be used include CuSO4 and / or CuCl2. In some embodiments, the copper salt content in the solution 33 is in the range of 50-250 grams per liter (g / L). The graphene content in the solution 33 is typically in the range of 0.01-1.5 g / L.

[0031] Figure 5 is a flow chart illustrating some embodiments of the method of the present invention. The method is used to coat a substrate 5 for an electrical contact 1, such as the contact 1 discussed herein. A graphene-copper electrolytic solution 33 including copper ions 34 and graphene 7 is provided at S1. Then, the substrate 5 is coated by electrodeposition at S2, whereby the graphene 7 and the copper ions 34 are co-deposited to form a graphene-copper composite coating 6 on the substrate 5.

[0032] In some embodiments, the method further comprises forming a pure copper coating 8 on top of the composite coating 6, typically in direct contact with the composite coating without any intermediate layer. Thus, the method may comprise providing a copper electrolytic solution comprising copper ions 34 at S3, and then, coating the graphene-copper composite coating 6 by electrodeposition at S4, whereby the copper ions 34 are deposited to form a pure copper coating 8 on top of the composite coating 6.

[0033] The present disclosure has mainly been described above with reference to a few embodiments. However, as readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.

Claims

1. An electrical contact (1), comprising: a substrate (5) of a conductive material; as well as A graphene-copper composite coating (6) located on the substrate (5); The graphene content in the coating is in the range of 0.1 to 2 weight %.

2. The contact according to claim 1, wherein the coating (6) is free of silver.

3. Contact according to any of the preceding claims, wherein the substrate (5) material comprises copper and / or aluminium. The contact of claim 3 , wherein the substrate material is copper.

5. The contact according to claim 1, wherein the graphene is in the form of a sheet (7), the sheet (7) having a thickness in the range of 1-50 nm.

6. The contact according to claim 5, wherein the sheet (7) has a longest diameter in the range of 5-80 μm.

7. The contact according to claim 1, further comprising: A pure copper coating (8) is located on top of the composite coating (6).

8. A contact device (10) comprising at least one electrical contact (1) according to any one of the preceding claims.

9. The contact arrangement according to claim 8, wherein the contact arrangement (10) is configured for a rated voltage of at most 70 kV.

10. The contact device according to any one of claims 8-9, wherein the contact device (10) is a power connector.

11. The contact device according to any one of claims 8-9, wherein the contact device (10) is a disconnector.

12. A method for coating a substrate (5) for an electrical contact (1) according to any one of claims 1 to 7, the method comprising: Providing (S1) a graphene-copper electrolytic solution (33) comprising graphene (7) and copper ions (34); as well as coating (S2) the substrate (5) by electrodeposition, whereby the graphene (7) and the copper ions (34) are co-deposited to form a graphene-copper composite coating (6) on the substrate (5); The graphene content in the solution (33) is in the range of 0.01-1.5 g / L.

13. The method according to claim 12, wherein the copper ions (34) are provided by a copper salt dissolved in the electrolytic solution (33), the salt comprising CuSO4 and / or CuCl2.

14. The method according to claim 13, wherein the copper salt content in the solution (33) is in the range of 50-250 g / L.

15. The method according to any one of claims 12 to 14, further comprising: Providing (S3) a copper electrolytic solution including copper ions (34); as well as The graphene-copper composite coating (6) is applied (S4) by electrodeposition, whereby the copper ions (34) are deposited to form a pure copper coating (8) on top of the composite coating (6).

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