EP3971928A1 - Contact électrique comprenant une couche composite métal-graphène - Google Patents

Contact électrique comprenant une couche composite métal-graphène Download PDF

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Publication number
EP3971928A1
EP3971928A1 EP20197503.4A EP20197503A EP3971928A1 EP 3971928 A1 EP3971928 A1 EP 3971928A1 EP 20197503 A EP20197503 A EP 20197503A EP 3971928 A1 EP3971928 A1 EP 3971928A1
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EP
European Patent Office
Prior art keywords
metal
graphene
composite layer
electric contact
graphene composite
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20197503.4A
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German (de)
English (en)
Inventor
Andreas FRIBERG
Anna Andersson
Erik Johansson
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ABB Schweiz AG
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ABB Schweiz AG
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Publication date
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Priority to EP20197503.4A priority Critical patent/EP3971928A1/fr
Priority to EP21770279.4A priority patent/EP4218038A1/fr
Priority to PCT/EP2021/075892 priority patent/WO2022063757A1/fr
Publication of EP3971928A1 publication Critical patent/EP3971928A1/fr
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/02—Contacts characterised by the material thereof
    • H01H1/021—Composite material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0545—Dispersions or suspensions of nanosized particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
    • B22F7/06—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools
    • B22F7/08—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools with one or more parts not made from powder
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/10—Alloys containing non-metals
    • C22C1/1026—Alloys containing non-metals starting from a solution or a suspension of (a) compound(s) of at least one of the alloy constituents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/02—Contacts characterised by the material thereof
    • H01H1/0203—Contacts characterised by the material thereof specially adapted for vacuum switches
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/02—Contacts characterised by the material thereof
    • H01H1/021—Composite material
    • H01H1/023—Composite material having a noble metal as the basic material
    • H01H1/0237—Composite material having a noble metal as the basic material and containing oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/02—Contacts characterised by the material thereof
    • H01H1/021—Composite material
    • H01H1/027—Composite material containing carbon particles or fibres
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H11/00—Apparatus or processes specially adapted for the manufacture of electric switches
    • H01H11/04—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts
    • H01H11/048—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts by powder-metallurgical processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2300/00—Orthogonal indexing scheme relating to electric switches, relays, selectors or emergency protective devices covered by H01H
    • H01H2300/036—Application nanoparticles, e.g. nanotubes, integrated in switch components, e.g. contacts, the switch itself being clearly of a different scale, e.g. greater than nanoscale

Definitions

  • the present disclosure relates generally to an electric contact configured to repeatedly closing and opening a conducting path by breaking and connecting an electrical circuit, and in particular to a metal-graphene composite layer used the electric contact, and a method of producing the metal-graphene composite layer.
  • Silver (Ag)-based contact materials are commonly used in various electrical power switching devices, where low losses and stable contact performance over life are of key importance.
  • Ag is for example used as base material in arcing contact systems in which the electric contact is configured to repeatedly close and open a conducting path by breaking and connecting an electrical circuit, owing to its electrical properties.
  • the mechanical and tribological properties of Ag are not spectacular. It is soft and prone to cladding onto counter surfaces. For arcing contacts this usually means high wear rate and high contact welding.
  • Ag is still used in many applications, owing to its electrical properties.
  • Ag is used as a matrix with an array of possible fractional additives, e.g. graphite (C), tin oxide (SnO2) and tungsten (W).
  • C graphite
  • SnO2 tin oxide
  • W tungsten
  • C graphite
  • SiO2 tin oxide
  • W tungsten
  • the hardness and density of such a composite is however limited owing to a low adhesion of the carbon surface to the Ag-matrix. This gives a high arc erosion rate for Ag-graphite components.
  • graphene is still very expensive, which is disadvantageous from an industrial point-of-view.
  • An object of the present invention is to overcome at least some of the above problems, and to provide a metal-graphene composite material or layer with improved properties for an arcing contact of an electrical power switch.
  • the invention relates to a metal-graphene composite material or layer with unusually good properties, especially as arcing. This, and other objectives, which will become apparent in the following are accomplished by means of an electric contact and a method of producing a metal-graphene composite layer.
  • an electric contact configured to repeatedly closing and opening a conducting path by breaking and connecting an electrical circuit.
  • the electric contact comprises a metal-graphene composite layer in which functionalized graphene is dispersed in a matrix of the metal, wherein the functionalized graphene is present in an amount within the range of from 0.05 wt% to 3 wt%.
  • the functionalized graphene is typically in the form of flakes, having a thickness from a single graphene layer (Angstrom range thickness) to graphene nano-sheets (NS) having a nano-range thickness.
  • Functionalized graphene is here referring to graphene comprising functional groups.
  • the functional groups are typically based on the addition of atoms or molecules other than carbon.
  • graphene oxide (GO) is considered a functionalized graphene with this definition as it comprises various oxygen containing functional groups.
  • oxygen functionalities at GO surface provide reactive sites for chemical modification.
  • GO is advantageous because of its easier production and dispersion as well as simple chemical functionalization compared to graphene.
  • the presence of the oxygen functional groups at GO surface is believed to cause its hydrophilicity, on contrary to graphene which hydrophobic.
  • an aqueous solution of GO is typically stable for a longer period of time compared to pure graphene.
  • a wash process, or cleaning method, of GO that provides clean, metal- and ion-free GO flakes with uniform size distribution (small particles removed), may be used to obtain good dispersion of the GO flakes in the metal matrix. Improved dispersing of GO in the metal matrix reduces the amount of GO needed and hence limits the effect of the GO on the electrical properties.
  • any type of functionalized graphene e.g. fluorinated graphene, or any mixture of functionalized graphene and graphene, may be used.
  • the functionalized graphene is graphene oxide or fluorinated graphene.
  • the term functionalized graphene is changed to "graphene oxide or fluorinated graphene". Additionally or alternatively, reduced graphene oxide, may be used.
  • Careful sintering of a green body of the composite which allows gaseous species to be released from the GO flakes and escape the composite, may lead to reduction of at least some of the GO to graphene (also denoted rGO herein).
  • the electric contact configured to repeatedly closing and opening a conducting path by breaking and connecting an electrical circuit may be an arcing contact.
  • the electric contact of the present invention is typically not a sliding contact, in which the contacting surface slides in relation to each other, but instead an arcing contact in which the contacting surfaces are repeatedly brought into contact with each other (closing) and brought apart (opening), the latter state indicating the contacting surfaces are not in contact with each other.
  • sliding contacts are excluded from the present invention.
  • the inventors have realized that by providing a metal-graphene composite layer in which functionalized graphene is dispersed in a matrix of the metal, wherein the functionalized graphene is present in an amount within the range of from 0.05 wt% to 3 wt%, an advantageous combinations of material properties, electric contact effects and low cost is achieved.
  • the metal-graphene composite layer exhibits improved anti-weld properties, with the result of reduced contact welding in the electric contact without sacrificing the good electrical properties of the pure metal.
  • the hardness of the material for metal-graphene composite layer is improved in relation to pure Ag, and the wear in terms of average weight loss is reduced compared to a corresponding material without the functionalized graphene.
  • the electric contact of the invention exhibits low contact erosion as compared to an electric contact comprise pure Ag.
  • the metal-graphene composite layer is a contact layer for establishing contact when closing the electric circuit.
  • the electric contact comprises a set of arcing contact elements or arcing contact legs, e.g. a first arcing contact element comprising the metal-graphene composite layer having a first external surface, and comprises a second contact element comprising the metal-graphene composite layer having a second external surface, which first and second external surfaces are used to be brought into contact with each other for closing the circuit, and brought apart for opening the circuit.
  • a first arcing contact element comprising the metal-graphene composite layer having a first external surface
  • a second contact element comprising the metal-graphene composite layer having a second external surface
  • the metal is silver, copper, gold or nickel.
  • the metal is aluminum (Al), platina (Pt), Indium (In) or tin (Sn).
  • the metal is a mixture of at least two of the following: Ag, Cu, Au, Ni, Al, Pt, In and Sn.
  • the functionalized graphene is present in an amount within the range of from 0.05 wt% or 0.1 wt% to 0.95 wt% or 1 wt%, or within the range of from 0.05 wt% or 0.10 wt%, to 0.45 wt% or 0.5 wt%.
  • the advantageous effects may be achieved already at relatively low amounts, further reducing the costs.
  • functionalized graphene present in an amount as low as between 0.05 wt% and 0.5 wt%, both hardness of the metal-graphene composite layer, and anti-welding properties of the electric contact is sufficient.
  • the metal-graphene composite layer is a sintered or extruded metal-graphene composite layer.
  • sintering in which the metal particles are diffused together to form a more solid product, similar to a cast metal product, may (e.g. for Ag) be performed at a temperature within the range of 300-500°C, e.g. at about 400°C, for a prolonged time period, e.g. at least 10 h or at least 15 h.
  • the density of the metal-graphene composite layer may come close to a cast metal product, e.g. metallic silver, e.g. at least 90% or at least 95% of cast metal density.
  • Sintering may also reduce some of the GO to graphene, i.e. rGO.
  • the metal-graphene composite layer is produced by additive manufacturing, thermal spraying, cold spraying or infiltration.
  • the metal-graphene composite layer has a hardness at 0.3 kg load of at least 70 HV, preferably at least 80 HV.
  • the hardness here is thus referring to the Vickers hardness (HV) at 0.3 kg constant load.
  • the electric contact has a weld force below 40 N.
  • the metal-graphene composite layer has a friction coefficient of 0.08-0.10.
  • the metal-graphene composite layer comprises a metal oxide, such as e.g. tin oxide and/or zinc oxide, and/or a secondary metal, such as e.g. tungsten or chromium, and/or a carbide such as tungsten carbide.
  • a metal oxide such as e.g. tin oxide and/or zinc oxide
  • a secondary metal such as e.g. tungsten or chromium
  • a carbide such as tungsten carbide.
  • Such additives may further improve the material properties of the metal-graphene composite layer.
  • the functionalized graphene is homogenous distributed in the metal matrix such that the largest diameter of a metal island having no graphene oxide particles in the surface of the metal-graphene composite layer is ⁇ 2 ⁇ m.
  • the electric contact is a low voltage switchgear or a medium voltage vacuum breaker.
  • the operating range for the low voltage application may be between 0 and 1000 V (AC) or between 0 and 1500 V (DC).
  • the medium voltage vacuum breaker voltages up to 38kV is possible.
  • a method for producing a metal-graphene composite layer for an electric contact configured to repeatedly closing and opening a conducting path by breaking and connecting an electrical circuit. The method comprising:
  • metal-graphene composite powder wherein the functionalized graphene is well-dispersed in the matrix of the metal is provided.
  • Such metal-graphene composite powder may be utilized when forming a metal-graphene composite layer used in the electric contact of the first aspect of the invention, with the same advantageous combinations of material properties, electric contact effects and low cost.
  • the method comprises:
  • the density of the metal-graphene composite powder can be formed into a body having a relatively high density.
  • the method comprises:
  • a metal-graphene composite layer having a high density may be achieved.
  • the method comprises:
  • the wash process results in clean, metal- and ion-free GO flakes with uniform size distribution (small particles removed), which may be used to obtain good dispersion of the GO flakes in the metal matrix.
  • Improved dispersing of GO in the metal matrix reduces the amount of GO needed and hence limits the effect of the GO on the electrical properties.
  • the solvent is ethanol.
  • Ethanol is readily available, relatively economical, and an adequate solvent.
  • the mixing comprises sonication.
  • the flakes are graphene oxide nano sheets.
  • Figs. 1A and 1B conceptually illustrates an arcing contact arrangement 100 (which may simply be referred to as an arcing contact) for an electrical switching device such as low voltage switchgears, low voltage contactors, low voltage circuit breakers, low voltage switch disconnectors, manual motor starters, although other devices are also conceivable, e.g. medium voltage vacuum breakers.
  • an electrical switching device such as low voltage switchgears, low voltage contactors, low voltage circuit breakers, low voltage switch disconnectors, manual motor starters, although other devices are also conceivable, e.g. medium voltage vacuum breakers.
  • the arcing contact arrangement 100 comprises a set of arcing contact elements or arcing contact legs, a first arcing contact element 102, a second arcing contact element 104, and a third arcing contact element 106.
  • Each of the arcing contact elements 102, 104, 106 comprises a substrate 102a, 104a, 106a.
  • a first substrate 102a comprises a metal-graphene composite layer 102b forming an electric contact
  • a second substrate 104a comprises two metal-graphene composite layer 104b, 104c, forming a respective electric contact
  • a third substrate 106a comprises a metal-graphene composite layer 106b forming an electric contact.
  • the metal-graphene composite layer used as metal-graphene composite layers 102b, 104b, 104c, 106b in Figs. 1A-1B , is a layer in which functionalized graphene is dispersed in a matrix of the metal, wherein the functionalized graphene is present in an amount within the range of from 0.05 wt% to 3 wt%.
  • the metal, and corresponding matrix of metal is preferably Ag. Although Ag is preferred and used as an example of the base metal of the metal-graphene composite layer discussed herein, any other suitable electrically conducting metal, or combination thereof, such as Cu, Au or Ni, may be used instead.
  • the functionalized graphene is preferably graphene oxide. However, the functionalized graphene may be functionalized with another substance, e.g. flour, F, and thus be fluorinated graphene.
  • the substrates 102a, 104a, 106a and the corresponding metal-graphene composite layers 102b, 104b, 104c, 106b are arranged such that two arcing contacts 110a, 110b are formed, a first arcing contact 110a between the metal-graphene composite layer 102b of the first arcing contact element 102 and a first metal-graphene composite layer 104b of the second arcing contact element 104, and a second arcing contact 110b between the metal-graphene composite layer 106b of the third arcing contact element 106 and a second metal-graphene composite layer 104c of the second arcing contact element 104.
  • Fig. 1A illustrates the conceptual arcing contact arrangement 100 in the open state in which no electrical current flows through the arcing contact 100.
  • the metal-graphene composite layers 102b, 104b of the first and second arcing contact elements 102, 104 in the first arcing contact 110a, as well as the metal-graphene composite layers 106b, 104c of the third and second arcing contact elements 106, 104, in the second arcing contact 110b are brought apart.
  • a closed state shown in Fig.
  • the external surfaces of the metal-graphene composite layers 102b, 104b of the first and second arcing contact elements 102, 104 in the first arcing contact 110a, as well as the external surfaces of the metal-graphene composite layers 106b, 104c of the third and second arcing contact elements 106, 104, in the second arcing contact 110b are brought into contact with each other, whereby an electrical current / may flow from a current inlet at the first arcing contact element 102 and via the first arcing contact 110a to the second arcing contact 110b, subsequently to the third arcing contact element 106.
  • the metal-graphene composite layers 102b, 104b, 104c, 106b are contact layers for establishing contact when closing the electric circuit.
  • the second arcing contact element 104 may be e.g. spring loaded in order to maintain the arcing contact arrangement in the closed state as shown in Fig. 1B .
  • metal-graphene composite layers 102b, 104b, 104c, 106b are exchanged with e.g. pure metal layers (e.g. pure Ag or Cu)
  • arcs between the contacting arcing elements 102, 104, 106 may occur, as well as contact welding between first and second arcing contacts 110a, 110b.
  • the first substrate 102a may comprise an electric contact different to the metal-graphene composite layer, while the second substrate 104a and its first electric contact 104b is formed by the metal-graphene composite layer.
  • the arcing contact 100 is configured to repeatedly closing and opening a conducting path (i.e. by means of the first arcing contact 110a, and/or the second arcing contact 110b) by breaking and connecting an electrical circuit (i.e. a circuit from the first arcing contact element 102 to the third arcing contact element 106).
  • an electrical circuit i.e. a circuit from the first arcing contact element 102 to the third arcing contact element 106.
  • Fig. 2 illustrates embodiments of a method of producing the metal-graphene composite powder, used for the metal-graphene composite layer.
  • the metal is Ag
  • Ag particles 1 or Ag nanoparticles, AG NP, 1 are suspended in a solvent 3 to form a metal suspension 5.
  • the solvent 3 may be any suitable solvent, e.g. water or ethanol, or a mixture thereof, preferably polar and environmentally friendly solvent options.
  • graphene oxide nano flakes, GO NS, 2 are suspended in a solvent 3, e.g. the same or similar solvent as in the metal suspension, to form a graphene suspension 7.
  • a solvent 3 e.g. the same or similar solvent as in the metal suspension
  • graphene flakes, e.g. graphene NS may be present in solvent 3.
  • the GO flakes, or graphene flakes preferably have an average longest axis as measured within the range of from 100 nm to 50 ⁇ m, 30 ⁇ m, 10 ⁇ m 1 ⁇ m or 500 nm, e.g. within a range of from 1 or 10 to 20 ⁇ m, and an average thickness of at most ten graphene layers.
  • the graphene suspension 7 may be sonicated to prevent agglomeration of the flakes in the suspension.
  • flakes e.g. NS
  • rGO reduced graphene oxide
  • the metal suspension 5 and the graphene suspension 7 are mixed, e.g. by adding the graphene suspension 7 to the metal suspension 5, to form a mixture to form a metal-graphene mixture 9 or metal-graphene suspension 9.
  • the metal-graphene mixture 9 is sonicated to further improve the mixing and dispersion of the GO flakes 2 with the Ag particles 1 and to prevent agglomeration of the flakes in the suspension.
  • the mixing is for obtaining good dispersion of the GO flakes 2.
  • Such dispersion results in that the GO is homogenous distributed in the metal matrix.
  • the largest diameter of a metal island having no graphene oxide particles in the surface may be ⁇ 2 ⁇ m.
  • the GO flakes 2 are preferably present in an amount of less than 1, 0.95, 0.5, 0.45, 0.2 or 0.1 wt% of the combination of the GO flakes 2 and the Ag particles 1 in the suspension, such as within the range of from 0.05 wt% to 0.5, or 0.45 wt%.
  • a suspension of 0,005 g GO flakes 2 e.g. in 100 mL ethanol
  • a suspension of 10 g Ag particles NP e.g. in 500 mL ethanol.
  • Drop mixing may be preferred in order to make sure that the GO flakes 2 are properly dispersed in the mixture, avoiding agglomeration.
  • the graphene suspension 5 may be drop mixed into the metal suspension 3 during at least 20 or 30 minutes to obtain a metal-graphene suspension 9 having a dry weight of about 10 g.
  • the solvent is evaporated from the metal-graphene suspension 9 to form a metal-graphene composite powder, e.g. an Ag-GO composite powder in this case.
  • a relatively volatile solvent may be preferred, e.g. ethanol, which may be recycled to save cost and the environment.
  • the evaporation of the solvent may be followed by drying of the metal-graphene composite powder at an elevated temperature of e.g. at least 80°C such as at about 100°C to remove traces of solvent and/or water.
  • the GO flakes 2 are preferably washed and centrifuged before mixing with the Ag particles 1.
  • the GO flakes 2 prior to obtaining the graphene suspension 7, are subjected to a plurality of sequential wash cycles, wherein each of the wash cycles comprises suspension of the GO flakes 2, centrifugation of the suspension and removal of the supernatant.
  • an objective of the wash process is to purify GO
  • the process reduces the amount of inorganic impurities, increases the pH of aqueous purified GO solutions towards neutral, and decrease the proportion of small, highly oxidized carbonaceous components.
  • the new process may involve ultra-sonication and (ultra-)centrifugation-assisted sedimentation.
  • the process is efficient, limits aggregation of the purified GO flakes and allows a change of solvent for the GO solution/suspension/paste from water to water-miscible organic solvents such as low-boiling alcohols, e.g. ethanol.
  • the suspension of GO in water may be mixed with the same volume of ethanol (e.g. 99% pure) with bath sonication for at least 10 minutes, after which the mixture is transferred to appropriate centrifugation flasks. Centrifugation at medium speed (5000-6000 g) for 4-8 hours sediments the GO, leaving the most soluble impurities in the supernatant. Removal of the supernatant, without disturbing the sediment material, leaves a concentrated water-ethanol suspension of GO of higher purity.
  • ethanol e.g. 99% pure
  • Fresh ethanol is added, followed by sonication, centrifugation and supernatant removal, this sequence may be repeated 2-4 times with centrifugation speed increasing and centrifugation time decreasing for each wash cycle.
  • the supernatant is colourless and the sedimented GO, after removal of the supernatant, has a gel-like appearance and a GO concentration of 30-40 mg/mL.
  • This concentrated GO gel may be dissolved/suspended in water and in water-miscible organic solvents.
  • Well-dispersed GO flakes in an Ag matrix enhances tribological properties and performance without sacrificing the electrical properties of pure Ag.
  • a well dispersed Ag-GO nanocomposite product may be obtained. This improves the anti-welding properties of the material. It has also been shown that with well-dispersed GO flakes, very small amounts of GO (e.g.
  • 0.01 wt%) is enough to dramatically reduce the friction coefficient compared with using pure Ag in dry conditions (from about 1.4-1.5 for pure Ag to about 0.08-0.09 for the Ag-GO (0.01 wt%) composite layer) and increase wear resistance without sacrificing the electrical properties of Ag.
  • An objective of the wash process is to separate GO into, preferably, monolayer sheets and disperse them as evenly possible in a metal matrix.
  • the method includes a wet mixing process, suspending both metal nanoparticles, as Ag NP 1, and cleaned GO flakes 2 as discussed in relation to Fig. 2 , first separately in ethanol suspensions and then mixing together the two suspensions and evaporating the solvent 3 to get a well-dispersed e.g. Ag-GO mixture. This mixture may then be pressed and sintered into the final contact material and the metal-graphene composite layer.
  • the obtained metal-graphene composite powder may be compacted to a green body e.g. at room temperature and a pressure of at least 400 MPa or 500 MPa, e.g. within the range of 400-600 MPa, which may be preferred for Ag NP 1.
  • a green body e.g. at room temperature and a pressure of at least 400 MPa or 500 MPa, e.g. within the range of 400-600 MPa, which may be preferred for Ag NP 1.
  • the density of the metal-graphene composite product may come closer to a cast metal product, e.g. metallic silver, e.g. at least 70% or at least 80% or at least 85% of cast metal density.
  • the green body may be used for the arcing contact, or the green body may be sintered, and the sintered product be used for the arcing contact.
  • Sintering in which the metal particles are diffused together to form a more solid product, similar to a cast metal product, may (e.g. for silver) be performed at a temperature within the range of 300-500°C, e.g. at about 400°C, for a prolonged time period, e.g. at least 10 h or at least 15 h.
  • the density of the metal-graphene composite layer may come close to a cast metal layer, e.g. metallic silver, e.g. at least 90% or at least 95% of cast metal density.
  • Sintering may also reduce some of the GO to graphene, i.e. rGO.
  • the metal-graphene composite layer may be a sintered metal-graphene composite layer.
  • the metal-graphene composite material or metal-graphene composite layer in at least one of the electric contacts in an arcing contact (i.e. at least one of the contacts in a contact pair) of an electric power application, an advantageous combinations of material properties, electric contact effects and low cost is achieved.
  • the metal-graphene composite layer exhibits improved anti-weld properties, with the result of reduced contact welding in the electric contact without sacrificing the good electrical properties of the pure metal since the amount of GO dispersed in the metal matrix can be kept low thanks to embodiments of the method of producing the metal-graphene composite layer of the present invention.
  • the hardness of the material for metal-graphene composite layer is improved in relation to pure Ag, and the wear in terms of average weight loss is reduced compared to a corresponding material without the functionalized graphene.
  • the weld force vs arc energy were measured for pure Ag layers and metal-graphene composite layers in the form of Ag-GO composite layer by an electric circuit using a mechanical switch, somewhat simplified compared to the arcing contact arrangement 100 of Fig. 1 .
  • an arcing contact arrangement comprising a first and second arcing contact element, each comprising a circular copper rod with a corresponding contact tip/layer comprising the material to be compared (i.e. Ag, and Ag-GO composites) was used.
  • the first and second arcing contact elements were brought together for closing the arcing contact arrangement (to form an Ag/Ag interface, or Ag-GO/Ag-GO interface), the closing being performed during an arc, and were subsequently brought apart when opening the arcing contact arrangement.
  • an electric pulse was allowed to flow through the circuit, where after a tensiometer was used to measure the force needed to bring the mechanical switch into an open state.
  • Two different Ag-GO composite layers sintered green bodies
  • the pure Ag reference show significantly higher weld forces for corresponding arc energies compared to the two Ag-GO composite layers.
  • the weld force drops significantly compared with the pure Ag reference.
  • the weld force is always below 30 N and in a majority of the measurements, below 20 N, while for the Ag reference, almost all registered measurements are above 30 N, often as high as about 60 - 120 N.
  • the Vickers hardness at 0.3 kg were measured for pure Ag layers and metal-graphene composite layers in the form of Ag-GO composite layer by a Vickers hardness measurement at 0.3 kg load (i.e. a Vickers-impression is made with a diamond in the form of a square-based pyramid at the specified load of 0.3 kg, where after the area of the impression is measured and compared with the load.
  • Two different Ag-GO composite layers (sintered green bodies) were formed, one with 0.05 wt % GO and Ag nano particles, and one with 0.05 wt% GO with Ag micro particles, and two different Ag layers, one with a density of 100 % and one with density of 96.3 % (the density here being related to the theoretical density of the respective material in the layers, and is thus a measure of the effectiveness of the sintering process).
  • the hardness increases significantly compared with the pure Ag reference.
  • the hardness is above 70 HV, even when Ag micro particle are used, and as high as 80 HV when Ag nano particles are used.
  • tribological pin-on-disc measurements were carried out on pure Ag, and an Ag-GO composite layers with 0.01 wt% GO, respectively, at a constant contact load of 5 N and with a counter contact being an Ag-coated Cu pin.
  • the wear of a pure Ag contact is difficult to measure as the Ag is soft and tend to clad and re-clad back and forth between the two interacting external (contacting) surfaces. Ploughing also occurs. An uneven wear track is formed, due to the cladding behavior.
  • the Ag-GO composite layer with 0.01 wt% GO arranged on corresponding interacting external (contacting) surfaces and exposed to 10 000 operations i.e.
  • the Ag-GO composite layer had a significantly lower wear rate than the pure Ag reference, as shown in Fig. 4 .
  • the Ag-GO composite layer with 0.01 wt% GO as analyzed by light-optical microscopy (LOM), revealed an even distribution of large graphene oxide sheets in the Ag matrix.
  • LOM light-optical microscopy
  • Scanning electron microscopy showed thin, transparent GO sheets with dispersed Ag nanoparticles above and below the sheets. This suggests well-separated GO and Ag particles.
  • the transparency of the GO sheets indicates that they contain mono-layers or few layers of GO stacked on top of each other.
  • Fig. 5 is a flow-chart comprising the steps of a method for producing a metal-graphene composite layer for an electric contact configured to repeatedly closing and opening a conducting path by breaking and connecting an electrical circuit. The method is partly overlapping with the method described with reference to Fig. 2 .
  • flakes of functionalized graphene such as e.g. graphene oxide, are suspended in a solvent to obtain a graphene-solvent suspension.
  • the flakes typically has an average longest axis within the range of from 100 to 50 ⁇ m.
  • metal nanoparticles such as Ag nanoparticles, are suspended in a solvent to obtain a metal-solvent suspension.
  • a step S5 the metal-solvent suspension and the graphene-solvent suspension are mixed with each other, forming a mixture.
  • a step S7 the solvent is evaporated from the mixture to obtain a metal-graphene composite powder having a functionalized graphene content within the range of from 0.05 wt% to 3 wt%.
  • steps S1, S3, S5 and S7 are corresponding to the method described with reference to Fig. 2 .
  • the method may comprise the following steps: In a step S9, the metal-graphene composite powder is pressed to obtain a compacted composite green body.
  • the composite green body is sintered at elevated temperature to obtain a sintered metal-graphene composite product, such as e.g. a metal-graphene composite layer.
  • a step S0 occurring prior to the step S1, the flakes are subjected to a plurality of sequential wash cycles, wherein each of the wash cycles comprises suspension of the flakes, centrifugation of the suspension and removal of the supernatant.

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EP20197503.4A 2020-09-22 2020-09-22 Contact électrique comprenant une couche composite métal-graphène Withdrawn EP3971928A1 (fr)

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EP20197503.4A EP3971928A1 (fr) 2020-09-22 2020-09-22 Contact électrique comprenant une couche composite métal-graphène
EP21770279.4A EP4218038A1 (fr) 2020-09-22 2021-09-21 Contact électrique comprenant une couche composite métal-graphène
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WO2018189146A1 (fr) * 2017-04-12 2018-10-18 Abb Schweiz Ag Matériau composite de graphène pour contact coulissant
CN110484803A (zh) * 2019-03-20 2019-11-22 河南科技大学 一种混合弥散增强型铜钨铬电触头材料及其制备方法

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Publication number Priority date Publication date Assignee Title
WO2018189146A1 (fr) * 2017-04-12 2018-10-18 Abb Schweiz Ag Matériau composite de graphène pour contact coulissant
CN110484803A (zh) * 2019-03-20 2019-11-22 河南科技大学 一种混合弥散增强型铜钨铬电触头材料及其制备方法

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