WO2007121659A1

WO2007121659A1 - Porous metal materials with elliptic type pores and their manufacturing process

Info

Publication number: WO2007121659A1
Application number: PCT/CN2007/001107
Authority: WO
Inventors: Qing Yu; Entao Zheng; Yumin Wang; Bin Shao; Fen He; Wei Li
Original assignee: Inco Advanced Technology Materials (Dalian) Co., Ltd; Inco Advanced Technology Materials (Shenyang) Co., Ltd.
Priority date: 2006-04-18
Filing date: 2007-04-04
Publication date: 2007-11-01
Also published as: CN1847196A; CN100372808C

Abstract

A porous metal with elliptic/quasi-elliptic pores, in which the aspect ratio, i.e., the ratio of longitudinal axial to transverse axial, is 1.5-10. The porous metal has excellent directional characteristics, significantly higher tensile strength and electric conductivity in longitudinal direction than that of the porous metal with equi-axial pores and with the same aerial metal density. A process for manufacturing the porous metal comprises the following steps: heating a polymeric foam sheet to the temperature at which the sheet becomes plastic; stretching the foam sheet; cooling the foam sheet to a temperature below the plastic point thereof; making the stretched sheet electric conductive; and electroplating the foam sheet with a desired metal.

Description

Porous metal materials with elliptic type pores and their manufacturing process

Technical field

The present invention relates to porous metal materials, particularly to porous metal foams with elliptic type or quasi-elliptic pores and their manufacturing process. The main technique of the manufacturing process for producing porous metal materials is electrodeposition. The key technique to obtain improved porous metal materials according to the present invention is to improve the pore structure of substrate by elongating the pores in one direction and to retain the improved pore structure in the final porous metal product.

Technical background

It is known in the art that the technique for manufacturing porous metal materials by electrodeposition attempts to keep the elastic porous substrate under "zero" or low tensile stress condition, to retain equi-axial pore structure and isotropic functional properties. For example, this point is especially emphasized in CN patent 9710443.5 . However it is sometimes required that the porous metal material has directional characteristics to meet the functional direction requirement for the product. For example in the rechargeable battery field, output power can be improved by reducing resistance of the electrodes in the direction of electric current. One object of the present invention is to meet this requirement by using "nickel foam with elliptic type pores" according to the present invention, whose typical characteristics lie in controllable and higher long axis/short axis ratio than available by conventional process, namely in the range of 1.5-10.0. Some nickel-foam products on the market have slightly elliptic pores due to unavoidable tension required to keep the foam strip straight during the plating process. Elongation of material achieved during the plating process is, however, very limited (usually around 1.1-1.2). It is also undesirable as the stretching is not uniform causing non-uniform plating. The foam strip produced by rotary peeling contains periodically repeating weaker zones and stronger zones. The weaker zones stretch preferentially creating periodic variation of width and, as a consequence, variation of areal metal density, i.e. amount of metal plated per unit of sheet area. Stretching during electrodeposition will also compromise the integrity of the conductive film produced by vacuum deposition (PVD), by electroless plating or by carbon ink. This will cause subsequent electrolytic plating to be non-uniform, making this approach unsuitable for significant improvement of directional properties of porous metal strips such as metal foam.

Description of the Invention

The object of the present invention is to provide a process for manufacturing porous metal materials such as metal foam with elongated (elliptic type or quasi-elliptic) pores, having controlled directional characteristics. In longitudinal direction of the elliptic pores, the tensile strength and electric conductivity of the material obtained according to the present invention are significantly higher than those of porous metal with the same surface density, but with equi-axial or nearly equi-axial pores produced by conventional process. These characteristics are especially suited for manufacturing products, which can benefit from improved characteristics in desired directions. Nickel foam with elliptic type pores can, for example, be used to manufacture electrodes for high performance rechargeable batteries such as high power nickel-metal hydride cells, industrial electrochemical electrodes etc.. The technical basis of the present invention is: a porous metal material with three dimensional structure pore of elliptic type or quasi-elliptic pores, having, the pore in surface or any section parallel to the surface being elliptic or quasi-elliptic, the long/short axis ratio of elliptic or quasi-elliptic pore, that is the ratio of the pore diameter in longitudinal direction to that in transverse direction, in the range of 1.5~10, pore number per square inch(PPI, JIS6400 standard) in the range of 10~200, the apparent density (surface density) being 100~4000g/m². In the cross- section perpendicular to longitudinal direction, the number of metal framework elements (struts or fibres) per unit of area, is significantly higher than that in the other sections. Therefore, the tensile strength and electric conductivity in this direction is significantly higher than those of porous metal materials with the same areal metal density, but with equi-axial pores. The tensile strength in longitudinal direction is above 1.3MPa (generally about IMPa) and the electric conductivity is above 330 Siemens (generally about 260 Siemens), both are improved by more than 25% compared to the reference materials with equi-axial pores.

The shape of porous metal materials mentioned above can be sheet or strip, the thickness of sheet in the range of 0.3-10mm and the thickness of strip in the range of 0.3-5mm.

The technical basis of the manufacturing process according to the present invention is: the elongated substrate with required long/short axis ratio elliptic pore is produced first in an operation involving heating the substrate to temperature required to soften the organic polymer, followed by cooling the substrate to stabilize the elongated pore structure. The elongated substrate can be made conductive by vacuum sputtering, electroless plating or by coating with conductive slurry in a separate operation. Alternatively the substrate elongation by heating and cooling can be made part of the vacuum sputtering process. The electrochemical plating to the desired density is the final operation.

There is a plurality of methods for obtaining the substrate with elliptic pores:

Firstly ,in one aspect of the present invention, the strip of thermoplastic polymeric porous foam with equi-axial pores (for example polyurethane foam etc.) is fed at a controlled speed through a device provided with a) means for controlled heating of defined zone of the said moving strip, b) means for controlled cooling of the said moving strip and c) means for uniform stretching the said moving strip while passing through the hot zone. The said device allows the temperature in the hot zone to be controlled, at about 100~400°C, so that the moving polymeric porous strip can be made sufficiently plastic, while the temperature of the cooling zone is controlled at sufficiently low temperature to cool the moving strip to below the plastic point and to stabilize the shape of elongated pores. The desired degree of stretching is achieved by controlling the substrate feed velocity in the range of 3~100m/h, and by controlling the load on the moving strip or by controlling the uptake velocity relative to the feed velocity of the strip according to the required long/short axis ratio of pore structure. The elongated and stabilized strip is then made conductive by applying a conductive layer by electroless plating, coating with conductive slurry or by vacuum deposition.

In order to prevent porous polymeric foam strip from high temperature oxidization, the heating and cooling operation can be made under inert gas , such as nitrogen, argon, carbon dioxide etc.

Finally the produced substrate with elongated pores and made conductive by applying a conductive layer is subjected to electroplating using the said strip as a cathode. .

Secondly, in another aspect of the invention, the controlled stretching of the porous plastic substrate with equi-axial pores into the substrate with the desired elongated pore structure can be achieved during the vacuum deposition process. The metallized substrate with the desired pore structure can then be used as cathode in electroplating process producing porous metal with elliptic pores. In the PVD equipment, the foam plastic substrate can be stretched by applying a controlled tensile force or by controlling the differential between the winding and unwinding speeds, according to the desired long/short axis aspect ratio of pore structure. The temperature in the hot zone can be controlled at about 100~400°C, and processing speed in the range of 3-300m/h., Finally, electroplating process is carried out by using the conductive polymeric substrate strip with elliptic pores as cathode, producing the porous metal product with the desired long/short axis aspect ratio of the pore structure.

To reduce the variation of areal density during electroplating, the elongated strip can be trimmed to constant width before electroplating.

The anode materials in the present invention include various metals or alloys, which can be electrodeposited in a suitable electrolyte. Alternatively insoluble anodes can also be used to electro-deposit the desired metal onto the conductive substrate with elongated pores.

The porous metal and its corresponding anode include nickel, copper, iron, tin, lead, chromium, cobalt, tungsten, sliver, gold, platinum, palladium and nickel-copper, nickel-cobalt, nickel-iron, iron-nickel-chromium, lead-tin, copper-sliver, copper-zinc, nickel-tungsten, copper-tungsten, copper-tin, nickel-palladium alloys etc.

The beneficial effects of the present invention are: 1. The long/short axis aspect ratio of elliptic pore contained in porous metal material according to the invention can be designed and controlled, in the range of 1.5~10 to make characteristics of these porous metal materials highly directional. The properties in longitudinal direction, such as tensile strength and electric conductivity can be significantly increased compared to porous metal materials with equi-axial pores. This characteristics are especially suited to manufacture products which can benefit from such improved directional characteristics.

2. Compared to conventional product, the porous metal material according to this invention is especially suitable for manufacturing high-power and, high-energy density nickel metal hydride batteries. The discharging current density and output power density can be improved at least 10% due to increased electric conductivity in the desired direction.

Brief description of the drawings

Fig 1, Fig 2, Fig 3 and Fig 4 are comparisons of SEM micrographs of nickel foam manufactured according to the invention and prior art respectively.

Fig 1 shows the SEM micrograph of elliptic-pore metal foam. The long/short axis aspect ratio is 1.6, the tensile strength and conductivity in longitudinal direction are increased by about 25% over similar foam manufactured according to prior art.

Fig 2 shows the SEM micrograph and characteristic parameters of product with equi- axial pores.

Fig 3 shows the SEM micrographs and characteristic parameters according to example 2, long/short axis aspect ratio is 1.5, the tensile strength and conductivity in longitudinal direction are increased by about 25% over the same density foam manufactured according to prior art.

Fig 4 shows the SEM micrograph and characteristic parameters of product with equi- axial pores manufactured according to prior art.

Fig 5 shows the SEM micrograph and characteristic parameters according to example 3, long/short axis aspect ratio is 4.0, the tensile strength and conductivity in longitudinal direction are increased by about 40% over the same density foam manufactured according to prior art.

Embodiments:

The following porous foam plastics are used as the substrates of the present invention products:

1. species: various organic polymer foams with thermoplastic properties, including polyurethane, polyester polyurethane, polyether polyurethane, polyethylene, polystyrene or polypropylene foams etc.

2. The thickness of organic foam used in the invention is in the range of 1-30 mm. 3. The PPI (pore number pre inch, JIS 6400) of organic foam substrate used in the invention is between 10-200.

Example 1: Nickel foam with elliptic pores

The technical requirement for product is: HOppi, thickness 1.7mm, areal density 400g/m², the long/short axis aspect ratio of elliptic pore Y/X=1.6, the tensile strength and conductivity in longitudinal direction to be significantly improved (by more than 20%), compared to product with equi-axial pores, of the same areal density

The polyurethane foam strip with equi-axial pores was uniformly heated and stretched, temperature controlled at 250°C and elongation controlled according to the required aspect ratio of pores. Then, in a separate operation the substrate strip was made conductive by PVD sputtering of nickel under no tensile force. Electrodepositing process was finally carried out under no tensile force using the conductive substrate strip with elliptic pores as cathode, nickel as anode; the electrodepositing nickel used Watts solution as electrolyte. The SEM appearance micrograph and characteristic parameters are shown in Fig 1. The characteristic parameters of foam nickel with elliptic pores according to the invention are: llOppi, thickness 1.7mm, surface density 400g/m², in figure 1, Y is longitudinal axis, X is transverse axis, the electric conductivity in longitudinal direction is 330 Siemens, the tensile strength was increased by 25% compared to conventional product. In Fig. 2, the characteristic parameters of nickel foam product manufactured by prior art are llOppi, thickness 1.7mm, areal density 400g/m², long/short axis aspect ratio 1.0, electric conductivity in longitudinal direction 265 Siemens.

Example 2: Nickel foam with elliptic pores

Differences from example 1 are:

The technical requirement for product: 94ppi, thickness 1.8mm, areal density 400g/m², the long/short axis aspect ratio of elliptic pore Y/X=1.5, the tensile strength and electric conductivity in longitudinal direction are to be significantly higher (by more than 20%) than those of product with equi-axial pores and the same surface density.

The polyurethane foam substrate strip with equi-axial pores was processed through the PVD apparatus modified to permit controlled stretching of the substrate during the PVD operation. In the modified PVD equipment the plastic foam substrate can be loaded with controlled tensile stress in longitudinal direction in the range of 2- 10kg (detailed description can be seen in CN 0112840.9). In current example the load of 5.4kg was used, the plasma radiant intensity and quantity of deposited nickel in magnetically controlled sputtering process were controlled, the moving velocity of substrate of uniform traction in longitudinal direction was lm/min, and the strip after stretching in the hot zone was naturally cooled down to 5O⁰C. The elongation was controlled according to give the required long/short axis aspect ratio of pore structure. As in example 1, electrodeposition process was carried out under no tensile force, using the conductive substrate strip with elliptic pores as cathode, nickel as anode, and Watts solution as electrolyte. The SEM micrograph and characteristic parameters are shown in Fig 3. The characteristic parameters of nickel foam with elliptic pores produced in this example are 94ppi, thickness 1.8mm, areal density 400g/m², long/short axis aspect ratio 1.5, electric conductivity in longitudinal direction 350 Siemens, the tensile strength increased by 25% compared to foam produced by conventional process and shown in Fig 4 (94ppi, thickness 1.8mm, surface density 400g/m², long/short axis aspect ratio 1.0, electric conductivity in longitudinal direction is 275 Siemens).

Example 3: copper foam with highly elongated elliptic pores

The differences from example 1 are: product to be used as filtration material, requiring acid resistance and high tensile strength in longitudinal direction;

The technical requirements for product are: 60ppi, thickness (after rolling) 0.5mm, areal density 200g/m², the long/short axis aspect ratio of elliptic pore Y/X=4.0, the tensile strength and electric conductivity in longitudinal direction to be significantly improved (by more than 40%) over the product with equi-axial pores and same areal metal density.

The strip of polypropylene foam with equi-axial pores was uniformly heated with temperature controlled at 165±5 °C in nitrogen gas to prevent oxidation of PP .The elongation was controlled to produce pores with long/short axis aspect ratio of 4. The substrate strip was uniformly moved at 5m/h and quickly cooled to room temperature by using liquid nitrogen. The elongated substrate strip was then made conductive by electroless deposition of copper under no tensile force. Finally electroplating process was carried out under no tensile force by using the conductive substrate strip with elliptic pores as cathode, copper as anode and ordinary acidic CuSO₄ plating bath as electrolyte. The characteristic parameters of the product were: 60ppi, final thickness 1.7mm, areal density 200g/m², pore aspect ratio Y/X=4.0. The tensile strength in longitudinal direction (after thickness reduction to 0.5 mm by rolling) was improved, by more than 40%.

Claims

1. Porous three-dimensional foam-like metal structure with sheet thickness between 0.3 and 10 mm, aerial density of 100 - 5000g/m², porosity <99.5% containing elongated ellipsoid or quasi-ellipsoid pores which give in any cross- section parallel with the axis of elongation elliptic or quasi-elliptic pores with aspect ratio, i.e. of the ratio of the long axis to the short axis, of 1.5 - 5, and with pore numbers per inch (PPI, JIS6400 standard) of 10~200.

2. Porous three-dimensional metal structure according to claim 1, where the conductivity and tensile strength in the longitudinal direction is increased by >20%, compared to otherwise similar structure with aspect ratio 1.0

3. Porous three-dimensional foam-like metal structure with sheet thickness between 0.3 and 10 mm, aerial density of 100 - 5000g/m², porosity <99.5% containing elongated ellipsoid or quasi-ellipsoid pores which give in any cross- section parallel with the axis of elongation elliptic or quasi-elliptic pores with aspect ratio, i.e. of the ratio of the long axis to the short axis, of 1.9 - 4, and pore numbers per inch (PPI, JIS6400 standard) of 10~200

4. Porous three-dimensional metal structure according to claim 3, where the conductivity and tensile strength in the longitudinal direction is increased by >30%, compared to otherwise similar structure with aspect ratio 1.0.

5. Porous three-dimensional foam-like metal structure with sheet thickness between 0.3 and 10 mm, aerial density of 100 - 5000g/m², porosity <99.5% containing elongated ellipsoid or quasi-ellipsoid pores which give in any cross- section parallel with the axis of elongation elliptic or quasi-elliptic pores with aspect ratio, i.e. of the ratio of the long axis to the short axis, of 2.0 - 3.0, and pore numbers per inch (PPI, JIS6400 standard) of 10~200,

6. Porous three-dimensional metal structure according to claim 1, which was produced from polymeric foam previously stretched at temperature over 14O⁰C and cooled to ambient temperature before electroplating.

7. Porous three-dimensional metal structure according to claim 3, which was produced from polymeric foam previously stretched at temperature over 14O⁰C and cooled to ambient temperature before electroplating.

8. A manufacturing process for producing porous three-dimensional foam-like metal structures with elongated pores, which includes controlled pre- stretching of starting polymeric foam using heating and cooling to ambient temperature before electroplating with the desired metal.

9. A manufacturing process for producing porous three-dimensional foam-like metal structures with elongated pores comprising the following steps a) Producing a sheet of reticulated polymeric foam sheet with thickness of 0.3 -5mm pore numbers per inch (PPI, JIS6400 standard) of 10~200, porosity >95% and length of >10m b) Introducing the said sheet continuously into a device equipped with heat source, control of temperature and degree of stretching c) Heating the foam sheet to temperature where the sheet in the hot zone becomes plastic d) Stretching the foam by 10-400% by applying load and /or controlling unwinding and rewinding speeds e) Cooling the foam to a temperature below plastic point to stabilize the structure f) Electrify the stabilized stretched foam with a desired material before electroplating g) Electroplating the stabilized stretched foam with the desired metal

10. A manufacturing process for producing porous three-dimensional foam-like metal structures with elongated pores according to claim 8 wherein the foam stretching and stabilizing is accomplished inside the vacuum-sputtering (PVD) device.

11. A manufacturing process for producing porous three-dimensional foam-like metal structures with elongated pores according to claim 8 wherein the stretched and stabilized foam is trimmed to constant width before electroplating.

12. A manufacturing process of ellipse-pore type porous metal material according to claim 6,7, it is characterized in: in order to prevent porous foam plastic from high temperature oxidization, the porous foam plastic is heated in inert gases protection, such as nitrogen, argon, carbon dioxide, and quickly cooled down to room temperature for sizing in inert gases protection.

13. A manufacturing process of ellipse-pore type porous metal material according to claim 9, it is characterized in: the term "electric-conductive process" including vacuum coating metal film, chemically coating metal film, coating conductive film etc., involved metals be selected from the metal or alloy groups: nickel, copper, iron, tin, lead, titanium, chromium, cobalt, tungsten, sliver, gold, platinum, palladium and nickel-copper, nickel-cobalt, nickel-iron, iron-nickel-chromium, lead-tin, copper-sliver, copper-zinc, nickel-tungsten, copper-tungsten, copper-tin, nickel-palladium alloys etc.

14. A manufacturing process of ellipse-pore type porous metal material according to claim 9, it is characterized in: the desired materials selected from metals which are suitable for electrodepositing and their alloys, or using non- dissolvable anode and its corresponding electrolyte with the same metal ions.

15. A manufacturing process of ellipse-pore type porous metal material according to claim 9, it is characterized in: the required porous metal and its corresponding anode selected from metal or alloys group: nickel, copper, iron, tin, lead, chromium, cobalt, tungsten, sliver, gold, platinum, palladium and nickel-copper, nickel-cobalt, nickel-iron, iron-nickel-chromium, lead-tin, copper-sliver, copper-zinc, nickel-tungsten, copper-tungsten, copper-tin, nickel-palladium alloys etc.

16.A manufacturing process of ellipse-pore type porous metal material according to claim 1,3 and 5 , it is characterized in: the said foam plastics selected from various thermoplastic foaming members, including: polyester polyurethane, poly ether polyurethane, polyethylene, polystyrene or polypropylene foaming member.