CA1216823A - Reusable electrolysis cathode for electrodeposition of metals - Google Patents

Abstract

REUSABLE ELECTROLYSIS CATHODE FOR ELECTRODEPOSITION
OF METALS

ABSTRACT OF THE DISCLOSURE

The surface of an elongated strip of electrically conductive metal is coated with an electrically non-conductive material such that the conductive metal is exposed at intervals along the edge sides in the longitudinal direction of the strip. Two strips of electrically conductive metal may be joined to provide a combination strip having an X-shaped cross section. Prederably, a plurality of these strips may be assembled into a single unit acting as a cathode between anodes in an electrolytic cell. The assembly is capable of producing near-spherical electrodeposited metals that can be immediately used without further processing in a plating plant.

Description

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- BACKGROUND OF T~E INVENTION

Field of the Invention:
The present invention relates to a reusable electrolysis cathode for electrodeposition of metals, and more specifically, to a reusable electrolysis cathode suitable for obtaining an electrodeposited metal in a near-spherical form.
Description of the Prior Art:
In electrolytic refining of nickel, nickel is electro-deposited on a cathode usually in the form of a flat sheet havinga thickness of about 10 mm. Typically, this flat nickel sheet is used as an anode for nickel plating after it has been cut into small pieces and subsequently placed in a titanium basket.
For commercial applications, the electrodeposited nickel sheet is cut into small pieces having sides 25 mm long. Such pieces are sharply angular and may become stuck in the lath of the titanium basket during use at a plating plant when the titanium basket is filled with the angular pieces or while the titanium basket is used as an anode. The resulting unfilled spaces caused by the stuck pieces reduce the filling density and prevent the uniform passage of electric current through the plating bath. In consequence, the current distribution is upset resulting in a non-uniform plating formed on the substrate. Therefore, many proposals have been made for producing an electrodeposited material that is not angular and needs no cutting~
US Patent 3,577,330 describes methods wherein small pieces of metal are electrodeposited on electrically insulated areas of a permanent metal cathode mandrel and are then stripped from the mandrel. US~. 4,040,915, US. 4,082,641 US. 4,139,430 disclose methods wherein disks or hemispheres of metal are ~216823 electrodeposited on electrically conductive metal surfaces of corresponding shapes exposed through an electrically insulating sheet. However, the shape of the product obtained by these methods is far from being spherical and the corresponding fluidity in the basket is not adequately high. Completely spherical nickel balls can be produced by casting electrodeposited nickel that has been melted in an electric furnace or the like, but because of high pro-duction cost, they are suitable only for very limited uses.
SUMMARY OF TXE INVENTION
Therefore, a general object of the present invention is to provide a reusable electrolysis cathode capable of producing near-spherical electrodeposited metal, particularly nickel, at a cost almost equal to that for producing generally square, disk-shaped or hemispherical shaped pieces of nickel.
This ob]ect can be achieved by a reusable electrolysis cathode including an elongated strip of electrically conductive metal, the surface of which is coated with an electrically non-conductive material having the conductive metal exposed at longitudinally spaced intervals. In a preferred embodiment, a plur-ality of these cathodes having various shapes are assembled into a single set of cathodes and disposed between anodes in an electrolytic cell for causing spherical nickel metals to be electrodeposited on the exposed areas of the conductive metal in the set of cathodes.
Thus, according to one aspect of the invention there is provided a reusable electrolysis cathode for ~a6823 metal electrodeposition upon immersion in an electro-lyte in an electrolytic cell, said cathode comprising:
at least one elongated metal strip comprising at least two generally flat faces and at least one narrow side edge located between said faces; and a coating of an electrically non-conductive material provided on said strip and covaering at least those surfaces of the strip which are immersed in said electrolyte when elec-trodeposition is taking place, said coating having a plurality of perforations in a part thereof covering said at least one side edge so as to expose areas of the metal of said strip to said electrolyte through said perforations.
According to another aspect of the invention there is provided an apparatus for forming spherical electrodeposited metal comprising: a plurality of electrically conductive metal strips spaced-apart at predetermined intervals and connected so as to ~orm a set of cathodes; and a coating of an electrically non-conductive material provided on each of said strips and having a plurality of perforations formed therein for exposing areas of said metal through said perfora-tions at spaced intervals.
BRIEF DESCRIPTION OF THE DRAWINGS
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, in which like reference characters designate like or corres-ponding parts through the several views and wherein:

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~216~Z3 Fig. 1 is a partial perspective view showing one embodiment of the reusable electrolysis cathode of the present invention;
Fig. 2 is a side elevation view of Fig. l;
Fig. 3 is a partial side view showing another embodiment of the reusable electrolysis cathode of the present invention, with the coating being partially removed;
Fig. 4 is a partial perspective view showing still another embodiment of the reusable electrolysis cathode of the present invention;
Fig. 5 is a side view showing how metal is electrodeposited on the reusable electrolysis cathode of the present invention;
Fig. 6 is a perspective view of a further em-bodiment of the reusable electrolysis cathode of the present invention; and Figs. 7 to 12 are plan views that show schematically various arrangements of the reusable electrolysis cathode of the present invention.
ETAILED DESCRIPTION OF THE INVENTION
Figs. 1 and 2 show an embodiment of the reusable electrolysis cathode of the present invention, wherein an elongated strip of electrically conductive metal 1 is provided with a coating of electrically non-conductive material 2 having the conductive metal exposed in areas 3 formed by making holes at suitable intervals along the side edges in the longitudinal direction. A hook 4 is electrically connected to the top of the strip and is hung on a cross bar in an electrolytic cell. By passing L6~Z3 an electric current through the reusable electrolysis cathode, metal is deposited on the exposed areas 3. The exposed areas 3 are formed along the side edges of the conductive metal strip l and may extend to the contiguous lateral faces so as to "straddle" them. The unfolded shapes of the exposed areas 3 may be circular, ellip--tical, rectangular or of any other form when initially formed through the non-conducting coating 2. When the strip of conductive metal l is adequately thick t the exposed areas 3 may be formed on only the side edges of strip l without straddling the contiguous lateral faces.
The conductive strip l is usually made of stainless steel or titanium to facilitate the subse-quent stripping of the electrodeposited metal. The non-conductive coating is usually made of plastics in view of its ease of molding, but any non-conductive material may be used if it is inert in the electrolyte, has high wear resistance and does not cause exfoliation.
Suitable plastics include organic polymeric materials,

2- e.g. epoxy, polyurethane, polypropylene, polyethylene, acrylic, vinyl chloride and polyester resins.
If the exposed areas 3 are too small, no large deposit is obtained and frequent stripping is required.
If the exposed areas 3 are too large, a near-spherical deposit is not produced and the large increased area of contact between the deposit and the conductive strip l makes the subsequent stripping step difficult. There-fore, ~ the exposed areas are circular, they should preferably have a diameter between about 2 and 15 mm.
Such dimensions should be used as a guide for cases ~ ,,,~ .

~12~6823 where the exposed areas 3 have other shapes.
The thickness of the conductive strip 1 is preferably at least a third of the horizontal length of the unfolded plane of each exposed area 3 when the conducting strip is in a suspended sondition, and the thickness of the non-conductive coating 2 is preferably not more than 5 mm. As shown in Fig. 3, the exposed areas 3 may be extended outwardly to make their sur-faces flush with the surfaces of the coating 20 There is no particular limitation on the posi-tion and number of the exposed areas 3 so long as they are arranged in such a manner as to perform the most effective electrodeposition. Preferably, their number should be as large as possible and they should be arranged as close to each other as possible without the exposed areas being so close that the individual metal deposits make contact with each other. In the embodiments of Figs. 1 and 2, the ex-posed areas 3 are formed on each side edge of strip 1 at equal intervals with the exposed areas 3 along one side edge of the strip 1 being staggered with respect with those formed along the other side edge. This staggering arrangement is effective to prevent contact of the depos-ited metal on either side edge. IE the exposed areas 3 are too small, the initial current density cannot be made higner than a certain value without reducing the amount of the initial deposition. If the initial current density is increased to provide higher production, a mis-shapen deposit is formed resulting in an unsightly product. If the exposed areas 3 are too large, a near-spherical de-posit cannot be ob~ained, and difficulty is encountered ~2~6~23 in stripping the deposit.
Fig. 4 shows another embodiment of the reusab~eelectrolysis cathode of the present invention, which in-cludes two strips of conductive metal 1 joined to provide an X-shaped horizontal cross section. ~s in the embodi-ments of Figs. 1, 2 and 3, the surface of each strip 1 is provided with an electrically non-conductive material 2.
Each strip is exposed in areas 3 along its side edges in the longitudinal direction, and a hook 4 is electrically connected to the top of one strip 1 The horizontal cross section of the side edges of each strip 1 may be semi-circular or triangular, and this also applies to the case where two or more strips 1 are joined to provide cross sections other than an X-shape, such as a Y-shape, star shape or an asterisk shape.
When electrolysis is conducted with the reusable electrolysis cathode of the present invention, metal is first deposited on exposed areas 3. Another layer of the metal is then deposited over the initial layer. Then, the metal deposition extends to the non-conductive coating to give a final product whose shape, as shown in Fig. 5, is much more similar to a sphere than conventional products.
After a suitable period, the strip 1 now having a plurality of near-spherical metal deposits formed thereon is taken out from the electrolyte, and given a light blow whereupon the metal deposits are easily dislodged from the cathode.
The initial current density is preferably 2 to 50 A/dm2 per unit area of the exposed conductive metal strip 1.
An excessively great current density produces an unsightly mis-shapen nodule of deposited metal.

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i~2~ 23 A plurality of the reusable electrolysis cathodes of the presen-t invention may be placed at suitable inter-vals and suspended on a cross bar by hooks between anodes.
By using the reusable electrolysis cathode and applying an electric current through the electrolyte, spherical elec-trodeposited metals can be obtained. Alternatively, to perform a smoo~h electrolytic operation, a plurality of the cathodes may be arranged to meet predetermined re-quirements and be elec~rically connected to each other to form an integral cathode. Modifications of this em-bodiment are hereunder described by reference to Figs.
6 to 12.
~n Fig. 6, elongated reusable electrolysis cathodes 5 are arranged along a straight line in a side-by-side relation with one another and in a per-pendicular relation with respect to the anodes. When the gap between each exposed area 3 is designed to be at a minimum to the extent that the deposited metal areas on adjacent exposed areas do not contact each other, the adjacent reusable electrolysis cathodes are spaced a distance equal to or greater than the gap be-tween each exposed area. As further shown in Fig. 6, each strip of conductive metal 1 is bent into an inverted U~shape in the middle, and the center 6 of each U-shaped strip is secured to a linking metal bar 7 to permit the entire set of the cathodes to be hung on a cross bar~ The lower parts of the cathodes 5 are ~onnected by a polyvinyl chloride tube which passes through the cathodes. The tube is provided with a polyvinyl chloride ring 10 as a spacer and is bolted to the cathodes 5 at both ends. Contact between deposits on individual exposed areas 3 can be prevented by spacing two adjacent cathodes by the dis-tance specified above.
Fig. 7 is a plan view that shows schematically the arrangement of the reusable electrolysis cathode 5 shown in Fig. 6. In Fig. 8, the cathodes 5 are arranged on a straight line parallel to the anodes and as in Fig.
7, the spacing between adjacent cathodes is equal to or larger than the gap between each exposed area 3. In Fig.
9, two sets of the cathodes shown in Fig. 8 are arranged parallel to the anodes in the same positional relation with respect to the widthwise direction of the anodes, with the distance between each set being equal to or greater than the gap between adjacent exposed areas.
In Fig. 10, two sets of the cathodes shown in Fig. 8 are also arranged parallel to the anodes but in a staggered relation with respect to the widthwise direc-tion of the anodes, with the distance between each set being equal to or greater than the gap between adjacent exposed areas. In Fig. 11, the cathodes are arranged at an angle o~ ~5 degrees with respect to the anodes. The individual cathodes should not be parallel to each other if the smallest distance between the edge sides of two adjacent cathodes is equal to or greater than the gap between adjacent exposed areas.
In Fig. 12, two strips of conductive metal 1 are joined to provide an X-shaped cross section. Such combi-nations of the cathodes are connected electrically at an angle of about 45 degrees with respect to the anodes~ with the distance between the edges of adjacent cathodes being _ g _ f~

:~LZ16~;23 equal to or greater than the gap between adjacent exposed areas. However, the X-shaped combinations of cathodes should not be arranged exactly at an angle of 45 degrees with respect to the anodes. In each of the embodiments shown above, ad3acent cathodes need not be spaced by a distance equal to the gap between adjacent exposed areas if the latter spacing is adequately great. The only requirement is that electrodeposited metals should not contact each other.
By using the reusable electrolysis cathode of the present invention, nickel or copper deposited metal spheres each weighing up to 60 to 120 gm can be obtained.
The cathode can be used for electrodeposition of not only nickel but also other metals such as copper and zinc.
The present invention is now described in greater detail by reference to the following non-limiting examples.
Example 1 Twenty-four elongated strips of 5US 316 stainless steel 1 m long, 3 mm thick and 30 mm wide were arranged at intervals of 35 mm. The strips were coated with A poly-vinyl chloride layer 0.5 mm thick to form reusable elec-trolysis cathode which were assembled as shown in Fig.
6. The stainless steel substrate was exposed in areas at intervals of 35 mm and, when unfolded, the exposed areas assumed a circular shape having a diameter of 5 mm. The reusable electrolysis cathodes were disposed in a cathode box which was placed between two nickel matte 975 mm long, 755 mm wide and 49 mm thick, with an anode-to-cathode spacing of 200 mm. Using an electrolytic cell having this arrangement, nickel electrodeposition was conducted ~,~}~
~- i 12161~23 with an electrolyte of the following composition provided within the cathode box:
Ni: 80 (g/l), SO4: 125, Cl: 65, Na: 40, H3BO3; 10, pH: 2.75, temp.: 50 - 70~C
The waste electrolyte was purified and circulated to the electrolytic cell. For the first 5 days, current was applied at a density of 5 A/dm2 per unit exposed area, about 0.2 cm2 of stainless steel. For the following 7 days, the current density was controlled so that it did not exceed 10 A/dm2 of the deposited metal. On the 12th day, the reusable electrolysis cathodes were taken out from the cathode box and on stripping gave rise to near-spherical nickel pellets having diameters ranging between 15 and 20 mm and weighing between 45 and 50 gm.
Example 2 Two strips of ~US 316 stainless steel 1 m long, 2 mm thick and 25 mm wide were joined to form a strip having an X-shaped cross section. The combination strip was coated with a FRP resin layer 2 mm thick. The stain-less substrate strip was exposed in areas 5 mm long atintervals of 30 mm. Each exposed area was 0.1 cm2. Ten more combinations of reusable electrolysis cathode were prepared in the same manner, and a total of eleven combin-ations were electrically connected and arranged with the intersections of the crosses of each strip being spaced at an interval of 75 mm and the strips of each combination being positioned at an angle of 45 degrees with respect to the anodes. Using this arrangement as a set of cath-odes, nickel electrodeposition was conducted, with the dimensions of the anodes, the anode-to-cathode spacing and r.t;
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~Z~6~3%3 the composition of the electrolyte being the same as in Example 1. For the first day, current was applied at a density of 45 A/dm2 per unit exposed area. For the following two days, the current density was 120 A/dm2 for the exposed area, and for the following three days, the density was 218 A/dm2 of the deposited metal. On the slxth day, the reusable electrolysis cathode assembly was taken out from the cathode box and on stripping gave rise to spherical or ellipsoidal nickel pellets having diameters ranging between about 20 and 25 mm and weighing between 50 and 55 gm.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A reusable electrolysis cathode for metal electrodeposition upon immersion in an electrolyte in an electrolytic cell, said cathode comprising:
at least one elongated metal strip compris-ing at least two generally flat faces and at least one narrow side edge located between said faces; and a coating of an electrically non-conductive material provided on said strip and covering at least those surfaces of the strip which are immersed in said electrolyte when electrodeposition is taking place, said coating having a plurality of perforations in a part thereof covering said at least one side edge so as to expose areas of the metal of said strip to said electrolyte through said perforations.

2. The reusable electrolysis cathode of claim 1 wherein said at least one elongated strip comprises a first strip and a second strip joined so as to form a strip assembly having an X-shaped cross section.

3. The reusable electrolysis cathode of claim 1 further comprising connecting means provided on an end portion of said at least one elongated strip for con-nection of the cathode to an electrical supply.

4. The reusable electrolysis cathode of claim 1 wherein said perforations are disposed at fixed inter-vals along said part of said coating overlying said at least one side edge.

5. The reusable electrolysis cathode of claim 1 wherein said metal cathode comprises titanium.

6. The reusable electrolysis cathode of claim 1 wherein said metal cathode comprises stainless steel.

7. The reusable electrolysis cathode of claim 1 wherein said electrically non-conductive material comprises an organic polymeric material.

8. The reusable electrolysis cathode of claim 1 wherein said perforations comprise circular perforations each having a diameter within the range of two to fif-teen mm.

9. The reusable electrolysis cathode of claim 1 wherein said at least one side edge has a predetermined thickness and wherein each of said plurality of perfor-ations comprises a predetermined width such that said predetermined thickness is at least one third of said predetermined width.

10. The reusable electrolysis cathode of claim 1 wherein said electrically non-conductive coating has a thickness not greater than 5 mm.

11. The reusable electrolysis cathode of claim 1 wherein said perforations are laterally extended to straddle the adjacent flat faces of the strip.

12. The reusable electrolysis cathode of claim 1 wherein said exposed areas are circular when visualized as folded into a flat plane, if not already planar.

13. The reusable electrolysis cathode of claim 1 wherein the exposed areas of the strip have outer sur-faces which are flush with the adjacent outer surfaces of the coating.

14. An apparatus for forming spherical electro-deposited metal comprising:
a plurality of electrically conductive metal strips spaced-apart at predetermined intervals and connected so as to form a set of cathodes; and a coating of an electrically non-conductive material provided on each of said strips and having a plurality of perforations formed therein for exposing areas of said metal through said perforations at spaced intervals.

15. The apparatus of claim 14 wherein each of said predetermined intervals is greater than or equal to each of said spaced intervals.

16. The apparatus of claim 14 wherein said strips each have narrow side edges located between generally flat faces, said perforations being located on said side edges and straddling said adjacent flat faces.

17. The apparatus of claim 14 wherein said exposed areas are circular when visualized as folded into a flat plane, if not already planar.

18. The apparatus of claim 14 wherein said exposed areas have outer surfaces which are flush with the ad-jacent outer surfaces of the coating.