WO2014141071A1

WO2014141071A1 - Electrodeposition on metal foams

Info

Publication number: WO2014141071A1
Application number: PCT/IB2014/059634
Authority: WO
Inventors: Nadia UCCIARDELLO; Stefano GUARINO; Vincenzo Tagliaferri; Francesco BERTOCCHI
Original assignee: Jaber Innovation S.R.L.
Priority date: 2013-03-12
Filing date: 2014-03-11
Publication date: 2014-09-18
Also published as: EP2971268A1; ITRM20130146A1

Abstract

The present invention refers to a method for the preparation of metal foams with coating of metal matrix and graphene by an electrodeposition process and to the high-performance metal foams obtainable with said method.

Description

ELECTRODEPOSITION ON METAL FOAMS

DESCRIPTION

The present invention refers to a method for the preparation of metal foams with a coating of metal matrix and graphene by an electrodeposition process, and to high-performance metal foams obtainable with said method.

STATE OF THE PRIOR ART

Metal foams are known materials, described e.g. in Patent Application US2012/0175534. Metal foams are porous materials with open-cell structures, having an external surface that can essentially consist in one or more metal coatings deposited, e.g., by electrodeposition.

Suchlike metal foams have many fields of application and can be used for the production of electrodes for electrical accumulators or batteries, as well as for electrodes for fuel cells.

Moreover, suchlike materials can be employed as support materials for catalysts that are used in plants for chemical processes and also in catalytic devices of motor vehicles. Moreover, metal foams can be used for acoustic insulation.

It has now surprisingly been discovered that some properties of metal foams known in the state of the art can be remarkably improved by modifying their metal coating.

Object of the present invention is to provide novel coated metal foams and methods for their preparation, with improved physical and/or chemical properties compared to metal foams obtained with known methods.

SUMMARY OF THE INVENTION

The solution proposed in the following invention is a method for the preparation of metal foams with a coating of metal (or alloys thereof) and graphene capable of giving to metal foams better mechanical properties (e.g. compression strength, energy absorption capacity, flexibility and/or traction strength) compared to metal foams without this type of coating. The present invention is based on the observation that by varying the amount of graphene used in the preparation method, possibly in combination with other parameters of the method such as metal foam porosity, coating thickness and/or metal, it is possible to modulate the mechanical properties of open-cell metal foams, remarkably improving them. In fact, coated metal foams with a thermal conductivity improved by up to 150% and a yield strength improved by up to 50%, compared to non-coated metal foams, were obtained.

Therefore, a first object of the present invention is a method for the preparation of open-cell metal foams with a coating of metal or an alloy thereof and graphene, comprising the following steps: a) electrodeposition of a first layer of metal or an alloy thereof and graphene on said metal foam;

b) electrodeposition of a second layer of metal of an alloy thereof on said metal foam.

A second object of the invention is a method for the preparation of open-cell metal foams with a coating of metal or an alloy thereof and graphene comprising the following steps:

a') electrodeposition of a first layer of metal or an alloy thereof on said metal foam;

b') electrodeposition of a second layer of metal of an alloy thereof and graphene on said metal foam;

c') electrodeposition of a third layer of metal of an alloy thereof on said metal foam.

A third object of the invention is a coated open-cell metal foam, wherein said coating comprises a first layer of metal or an alloy thereof and graphene, a second layer of metal or an alloy thereof.

A fourth object of the invention is a coated open-cell metal foam, wherein said coating comprises a first layer of metal or an alloy thereof, a second layer of metal or an alloy thereof and graphene, a third layer of metal or an alloy thereof.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1. In Fig. 1 , a diagram of the cell utilized in one embodiment of the method of the present invention is reported. It may be observed that the cathode is comprised of an open-cell foam of aluminium, surrounded by the anode of metal material.

Figure 2. In Fig. 2, images of microscopic analyses, highlighting the layer of graphene and of metals deposited on a detail of metal foam, are reported.

Figure 3. In Fig. 3, microscope-magnified images of the individual stages of deposition on metal foams are reported.

Figure 4. In Fig. 4, a diagram of the system for measuring the thermal conductivity of an open-cell foam sample with a coating of metal and graphene is reported.

DETAILED DESCRIPTION OF THE INVENTION

As previously indicated, the present invention relates to a method for the preparation of open-cell metal foams with a coating of metal (or an alloy thereof) and graphene, comprising the following steps of electrodeposition:

a) electrodeposition of a first layer of metal or an alloy thereof and graphene on said metal foam; b) electrodeposition of a second layer of metal or an alloy thereof on said metal foam, such that said metal foam obtained from step b) has a coating comprising a first layer of metal or an alloy thereof and graphene and a second layer of metal or an alloy thereof overlapped with said first layer.

Preferably, said second layer will be substantially without graphene and/or graphite. In the method of the present invention, preferably metal foams selected from metal foams of aluminium, copper, nickel, iron, titanium, magnesium, lead and alloys based on the abovementioned metals could be used, while the size of the pores of the open- cell structure will generally be in the range of from micrometers to centimeters, or, when expressed as size of pores per inch, of between 3 and 30 ppi.

Current density of the step of electrodeposition a) could vary, e.g., from 0.02 to 0.2 mA/cm², while current density of the step of electrodeposition b) could vary, e.g., in a range of 0.2-40 mA/cm².

The method of the present invention could comprise another step of electrodeposition of a layer of metal of an alloy thereof before step a).

The addition of a step of electrodeposition of a metal or an alloy thereof before step a) allows to obtain a metal foam having a coating comprising, besides said first and second layer, also a third inner layer on which said first and second layer are overlapped. Preferably said third layer will be substantially without graphene and/or graphite.

The electrodeposition of a metal layer on the metal foam before steps a) and b) further improves the thermal conductivity and the mechanical strength of the coated foam, and could be conducted, e.g., at a current density of between 0.2-40 mA/cm², The temperature of the method is generally in a range of 20-100°C. The overall duration of the method will clearly depend on the value of the current density and can range, e.g., from 5 minutes to 3 hours. The selection of parameters of the various steps of the method, such as current density, temperature and duration of the electrodeposition, affect coating properties, like thickness, hardness, ductility and homogeneity.

The metals used in the electrodeposition step are, e.g., nickel, zinc, tin, chrome, iron, copper, titanium, silver, gold, platinum and other elements of the platinum group, like Ru, Os, Rh, Pd and ir and alloys thereof, like e.g. brass, bronze, monel, iron-chrome alloys, and combinations thereof. For certain applications, like heat exchangers, radiators, fuel cells, copper, copper alloys, nickel and nickel alloys are particularly preferred. Preferably, yet not necessarily, the same metal could be used in the various steps of electrodeposition of the method.

The electrolytic baths of the various steps of electrodeposition can contain the same reagents used in the conventional electrodeposition of metals, metal alloys or metal matrix composites; for instance, they could be CuS0₄ and CuCI. The electrolytic bath of the second step b) of electrodeposition will preferably be basic and contain graphene, preferably in a concentration by weight of between 1 and 5%. Graphene will preferably be selected between graphene oxide (GO), graphene nanoplatelets (GNP), and GO or GNP functionalized with metal particles.

Graphene oxide is a stratified product from graphite oxidation by strong acid and oxidizing treatments. The basic unit of GO is the oxidized graphene plane, bearing hydroxyl and epoxy groups thereon, besides carbonyl and carboxyl groups at the edges.

The presence of these functional groups makes GO strongly hydrophilic and, unlike graphite, a bad electrical conductor (sp2 to sp3 hybridisation). With a chemical or thermal reduction it is possible to nearly totally restore the original hybridisation of graphite, making the GO (GOr) a good electrical and thermal conductor.

Graphene nanoplatelets (GNP) appear in the form of a partially volatile grey-black powder. The estimated average particle thickness preferable for the application varies from 0.3 nanometers (Graphene and few-layer Graphene) up to about 100 nanometers, preferably up to about 30 nanometers.

The surface size of such nanoplatelets is from 5 to 200 microns, preferably from 20 to 30 microns. Calculated Carbon content is higher than 98%, whereas bulk density ranges from a minimum of 0.010 g/cm³ to 0.050 g/cm³.

The electrolytic baths during the various steps of electrodeposition could advantageously be placed under magnetic stirring in order to foster uniformity of the end coating obtained.

By the term "graphene nanoplatelets", packets of graphene layers of from 0.3 nm to 100 nm are meant; typically, materials commonly defined as graphene nanoplatelets have thicknesses below 25-30 nm.

Within the scope of documents issued by the European Commission of the Seventh Framework Programme, in particular in documents OUTLINE WORK PROGRAMME OF THE GRAPHENE FLAGSHIP CORE PROJECT" and "COMPETITIVE CALL FOR CONSORTIUM EXTENSION CALL CONTENT", reference is made to terms "graphite nanoplatelets" and GRMs (Graphene and related materials).

The present description refers to the use of GRMs, among which graphene (monoatomic layer), graphene nanoplatelets, meant as bundles of nanolamellas of variable average thickness lower than 14 nm) and graphene oxide (meant as oxide obtained from oxidation of the abovementioned graphene nanoplatelets).

According to one embodiment, in the steps of electrodeposition the metal foam acts as cathode. The cathode will be surrounded on all sides by a sacrificial anode. The anode forms a cubic cage around the foam (see, e.g., FIG. 1). The distance of the anode from the external surface of the foam to be coated could be, for instance, of about 2 cm.

According to one embodiment, before performing the steps of electrodeposition the method could comprise a step wherein the metal foam is subjected to a sandblasting process (e.g. with glass beads); the surface of the foams will thus be advantageously activated.

According to one embodiment of the method, the electrolytic bath of step a) comprises CuS0₄ and graphene nanoplatelets, the electrolytic bath of step b) comprises H₂S0₄, CuS0₄ and CuCI, and the electrolytic bath in the step before step a) comprises H₂S0₄, CuS0₄ and CuCI.

According to one embodiment, the metal foam coating obtained by electrodeposition of the various layers as described above covers at least 70% of the external surface of the metal foam, preferably at least 90%, even more preferably it covers 100% thereof.

A further object of the present invention are coated open-cell metal foams wherein said coating comprises a first layer of metal (or an alloy thereof) and graphene and a second layer of metal or an alloy thereof, preferably without graphene and/or graphite, overlapped with the first layer. In one embodiment, the coating will also comprise another layer of metal (or an alloy thereof), preferably without graphene or graphite, placed between the metal foam and said first layer of metal and graphene.

The metals used in the coating of said metal foams are, e.g., nickel, zinc, tin, chrome, iron, copper, titanium, silver, gold, platinum and other elements of the platinum group, like Ru, Os, Rh, Pd and Ir and alloys thereof, like, e.g., brass, bronze, monel, iron- chrome alloys and combinations thereof. The metal foams will preferably be selected from metal foams of aluminium, copper, nickel, iron, titanium, magnesium, lead and the alloys based on the aforementioned metals.

According to one embodiment, the thickness of the coating is substantially uniform, meaning that deviation from standard thickness is no greater than about 20%. Generally, the thickness will be in a range of 1-1000 microns, preferably 20 to 500 μηι. The thickness of the layer of metal and graphite will preferably be at most 100 microns.

According to one embodiment, the metal foam coating of the various layers covers at least 70% of the external surface of the metal foam, preferably at least 90%, even more preferably it covers 100% thereof.

According to one embodiment, the coated open-cell metal foams as described above will be obtained with the electrodeposition method of the present description.

A further object of the present invention are manufactured articles comprising the metal foams of the present description in the form of grids for batteries, components for heat exchangers for chemical and industrial systems, heat exchangers for electrical household appliances, for high-power current transformers, for heat exchangers for the automotive, aeronautical and aerospace fields, fuel cells, power electronic systems, energy production systems with small thermal drops, heat exchangers for chimney stacks in aggressive environments, integrated componentry with thermal and structural exchange properties of the industrial, transportation and aerospace fields.

Hereinafter, examples aimed at better illustrating the present invention and some specific embodiments are reported hereinafter; such examples are in no way to be construed as a limitation of the present description and of the appended claims.

EXAMPLES

Methods for assessing the properties of metal foams with and without coating

To assess the mechanical behaviour of foams with and without coating, in terms of yield strength and deformation energy, compression tests were performed, using a 10-KN load cell. Compression rate was set at 10 mm/min, in order to best highlight the broad plateau zone that can be related to energy absorption capability by the foams. Instead, to perform the thermal tests a small experimental apparatus was set up, the diagram of which is reported in Figure 4.

Two Peltier cells were used, resting on the bases of the foams, placed between two finned plates. Each cell, electrically connected to a power supplier, enabled to set a one-way bottom-to-top thermal flow which involved the foam and created a thermal gradient therein. The foam was insulated to contain heat dispersion in a lateral direction. To measure temperature at foam bases, two "J-type" Iron-Constantan thermocouples were used. Exchanged thermal flow proved to be:

Q = V ^■ i

Where V and i represent voltage and current set by the power suppliers to the Peltier cells. Knowledge of this value and of the test piece height h enabled calculation of the product between the foam conductivity and the surface into contact with the cell:

Q -

A. ' S — — —

AT

Graphene oxide preparation

Graphene oxide (GO) was synthesized from a byproduct of graphite flakes chemically treated with sulfuric acid, nitric acid and potassium permanganate (modified Hummers method). The obtained product is strongly hydrophilic and therefore easily dispersable in water. In solution, it has the typical yellow/brown colour, indicating a good degree of graphene oxidation (C/O ratio = 2: 1). Analyses confirmed the presence of hydroxyl, carbonyl, carbonyl functional groups on the planes and along the edges of graphene. Average surface size was from 1 to 6 microns. Average thickness of water-dissolved GO lamellas was lower than 1 nm. GO solutions in water at different concentrations were tested. The material was then reduced by thermal annealing.

Graphene nanoplatelets preparation

Graphene nanoplatelets (GNP) were prepared from graphite intercalated with sulfuric acid (Expandable Graphite). The graphite used may be natural graphite (NG) or synthetic graphite (SG) of different grain sizes, from micrographites (10 microns) to graphite flakes (500 microns) and of different degrees of purity (98 - 99.9% C).

Intercalation comprises the preparation of mixtures of sulfuric acid and nitric acid in different ratios (from 9-1 to 4-1). Graphite was added in the mixture and the whole was kept under mechanical stirring for times ranging from 2 to 120 hours. To help mechanical stirring, also sonication systems such as ultrasound vats or probes were used.

In a next stage, intercalated graphite was filtered to separate it from the mixture of acids and washed and purified with deionized water until reaching a neutral pH of the wash waters.

By providing energy, in the form of heat or microwaves, to expandable graphite, it expands forming granules of worm-like morphology with a very low apparent density (~ 0.005 g/cm³). This material was wetted with a solvent and treated with ultrasounds to attain complete exfoliation of the graphene packets. Then, the material was dried and desiccated in a vacuum oven. The sizes of graphene packets vary, based on the parameters used in the stage of expansion and sonication. Thicknesses can range from a few nanometers (few layers) to more than 30 nm. Surface sizes instead were from 5 μηι to ~ 200 μηι. The material appeared in the form of powder, partly volatile, of an apparent density ranging from 0.05 to 0.01 g/cm³.

Example 1

An aluminium foam with a porosity of 10 ppi was used as starting material.

Electrodeposition was subdivided into three stages. The bath of the first and third stages was comprised of: 60g/l H₂S0₄, 190 g/l CuS04 and 100 ppm of CuCI. The bath of the second stage was comprised of: 250 g/l CuS0₄ and 1 g/l GNP.

For all stages, the anode consisted of a hollow copper cube.

Electrodeposition parameters for the first and third stage were:

Current = 2.3 A; time = 50 minutes, and stirring = 3.5 rpm.

The parameters of the second stage were:

Current = 0,02 A; time = 30 minutes, and stirring = 3.5 rpm. Temperature was kept constant at 25°C.

A foam with a coating of copper and nanoplatelets of uniformly distributed graphene was produced. The coated foam thus obtained exhibited, compared to the starting aluminium one, a 100% improvement of thermal conductivity and a 50% improvement of yield strength.

Example 2

The aluminium foam had a porosity of 10 ppi. Electrodeposition was subdivided into three stages.

The bath of the first and third stages was comprised of: 60g/l H₂S0₄, 190 g/l CuS0₄ and 100 ppm CuCI.

The bath of the second stage was comprised of: 250 g/l CuS04 and 2g/l GNP.

For all stages, the anode consisted of a hollow copper cube.

Electrodeposition parameters for the first and third stage were: Current = 2.3 A ; time = 50 minutes, and stirring = 3.5 rpm.

The parameters of the second stage were: Current = 0.02 A; time = 60 minutes, and stirring = 3.5 rpm.

Temperature was kept constant at 25°C.

A foam with a coating of copper and nanoplatelets of uniformly distributed graphene was produced. The coated foam thus obtained exhibited, compared to the starting aluminium one, a 130% improvement of thermal conductivity and a 60% improvement of yield strength.

Example 3

The bath of the first and third stage was comprised of: 225 g/l NiS0₄, 30 g/l NiCI₂ and

The bath of the second stage was comprised of: 250 g/l CuS0₄ and 2g/l GNP.

The anode consisted of a hollow nickel cube for the first and third stages, and of a hollow copper cube for the second stage.

Electrodeposition parameters for the first and third stages were: Current = 1.5 A; time = 60 minutes, and stirring = 3.5 rpm.

Foam with a coating comprised of nickel, copper and nanoplatelets of uniformly distributed graphene was produced. The coated foam thus obtained exhibited, compared to the starting aluminium one, a 70% improvement of thermal conductivity and a 50% improvement of yield strength.

Example 4

A copper foam with a porosity of 10 ppi was used as starting material.

Electrodeposition was subdivided into two stages. The bath of the first stage was comprised of: 250 g/l CuS0₄ and 1 g/l GNP. The bath of the second stage was comprised of: 60g/l H₂S0₄, 190 g/l CuS0₄ and 100 ppm CuCI.

For all stages, the anode consisted of a hollow copper cube.

The parameters of the first stage were:

Current = 0.01 A; time = 60 minutes, and stirring = 3.5 rpm.

Electrodeposition parameters for the second stage were:

Current = 2.3 A; time = 90 minutes, and stirring = 3.5 rpm.

Temperature was kept constant at 25°C.

A foam with a coating of copper and nanoplatelets of uniformly distributed graphene was produced. The coated foam thus obtained exhibited, compared to the starting one, a 150% improvement of thermal conductivity and a 50% improvement of yield strength. Example 5

An aluminium foam with a porosity of 20 ppi was used as starting material.

Electrodeposition was subdivided into three stages. The bath of the first stage was comprised of: 60g/l H₂S0₄, 190 g/l CuS0₄ and 100 ppm CuCI. The bath of the second stage was comprised of: 250 g/l CuS0₄ and 1 g/l GNP. The bath of the third stage was comprised of: 225 g/l nickel sulfate, 30 g/l nickel chloride, 30 g/l boric acid:

The anode of the second stage consisted of a hollow copper cube. The anode of the third stage consisted of a hollow nickel cube.

Electrodeposition parameters for the first stage were:

Current = 2.3 A; time = 50 minutes, and stirring = 3.5 rpm.

The parameters of the second stage were:

Current = 0.02 A; time = 30 minutes, and stirring = 3.5 rpm.

The parameters of the third stage were:

Current = 1.5 A; time = 30 minutes, and stirring = 3.5 rpm.

Temperature was kept constant at 25°C.

A foam with a coating of copper, nanoplatelets of uniformly distributed graphene and nickel was produced. The coated foam thus obtained exhibited, compared to the starting aluminium one, an 80% improvement of thermal conductivity and a 70% improvement of yield strength. Exam le 6

The aluminium foam had a porosity of 5 ppi. Electrodeposition was subdivided into three stages.

The bath of the first and third stage was comprised of: 60g/l H₂S0₄, 190 g/l CuS0₄ and 100 ppm CuCI.

The bath of the second stage was comprised of: 250 g/l CuS0₄ and 2g/l GNP.

For all stages, the anode consisted of a hollow copper cube.

Electrodeposition parameters for the first and third stage were: Current = 2 A ; time = 60 minutes, and stirring = 3.5 rpm.

The parameters of the second stage were: Current = 0.01 A; time = 60 minutes, and stirring = 3.5 rpm.

Temperature was kept constant at 25°C.

A foam with a coating of copper and nanoplatelets of uniformly distributed graphene was produced. The coated foam thus obtained exhibited, compared to the starting aluminium one, a 100% improvement of thermal conductivity and a 70% improvement of yield strength.

Claims

1. A method for the preparation of open-cell metal foams with a coating of metal or an alloy thereof and graphene comprising the following steps:

a) electrodeposition of a first layer of metal or an alloy thereof and graphene on said metal foam;

b) electrodeposition of a second layer of metal or an alloy thereof on said metal foam,

such that said metal foam obtained from step b) has a coating comprising a first layer of metal or an alloy thereof and graphene and a second layer of metal or an alloy thereof overlapped with said first layer.

2. The method according to claim 1 , wherein said metal foam is of aluminium, copper, nickel, iron, titanium, magnesium, lead or an alloy based on said metals.

3. The method according to claim 1 or 2, wherein in said step of electrodeposition a) the graphene in the electrolytic bath is in a concentration of between 1 and 5% by weight.

4. The method according to any one of claims 1 to 3, wherein said graphene is selected from graphene oxide (GO), graphene nanoplatelets (GNP), graphene oxide (GO) functionalized with metal particles, graphene nanoplatelets (GNP) functionalized with metal particles, wherein said graphene nanoplatelets have a thickness between 0.3 and 100 nm.

5. The method according to any one of claims 1 to 4, comprising another step of electrodeposition of metal or an alloy thereof on said metal foam before step a), such that said metal foam obtained from step b) has an external coating comprising a third layer of metal of an alloy thereof on which said first and second layer are overlapped.

6. The method according to any one of claims 1 to 5, wherein in said steps of electrodeposition said metal is selected from nickel, zinc, tin, chrome, iron, copper, titanium, silver, gold, platinum, osmium, ruthenium, rhodium and palladium.

7. The method according to any one of claims 1 to 6, wherein said metal foam before being subjected to electrodeposition is subjected to sandblasting.

8. The method according to any one of claims 1 to 7, wherein the pores of said metal foam have a size between 3 and 30 pores per inch, preferably between 5 and 20 pores per inch.

9. The method according to any one of claims 1 to 8, wherein said coating covers at least 70% of the external surface of said metal foam, preferably covers at least 90%, even more preferably it covers 100% thereof.

10. The method according to claim 5, wherein:

-the electrolytic bath of step a) comprises CuS0₄ and graphene nanoplatelets.

- the electrolytic bath of step b) comprises H₂S0₄, CuS0₄ and CuCI;

-the electrolytic bath in the step before step a) comprises H₂S0₄, CuS0₄ and CuCI.

1 1. A coated open-cell metal foam, wherein said coating comprises:

-a first layer of metal or an alloy thereof and graphene;

-a second layer of metal or an alloy thereof.

12. The metal foam according to the preceding claim, wherein said coating comprises a further layer of metal of an alloy thereof placed between said metal foam and said first layer.

13. The metal foam according to claim 1 1 or 12, wherein said coating is substantially uniform with a thickness between 1 and 1000 microns.

14. The metal foam according to any one of claims 1 1 to 13, wherein said metal is selected from nickel, zinc, tin, chrome, iron, copper, titanium, silver, gold, platinum, osmium, ruthenium, rhodium and palladium.

15. The metal foam according to any one of claims 1 1 to 14, obtainable by electrodeposition.

16. The metal foam according to any one of claims 1 1 to 15, wherein said graphene is selected from graphene oxide (GO), graphene nanoplatelets (GNP), graphene oxide (GO) functionalized with metal particles, graphene nanoplatelets (GNP) functionalized with metal particles, wherein said graphene nanoplatelets have a thickness between 0.3 and 100 nm.

17. The metal foam according to any one of claims 1 1 to 16, wherein said graphene is present only in said first layer.

18. The metal foam according to any one of claims 1 1 to 17, wherein said coating covers at least 70% of the external surface of said metal foam, preferably covers at least 90%, even more preferably it covers 100% thereof.

19. A manufactured article comprising a metal foam according to any one of claims 1 1 to 18 in the form of grid for batteries, heat exchangers, high-power current transformers, fuel cells, power electronic systems, energy production systems.