GB2291070A

GB2291070A - Fixing electrode to electrode substrate by welding metal filled in a plurality of holes in the electrode to the electrode and the substrate

Info

Publication number: GB2291070A
Application number: GB9514006A
Authority: GB
Inventors: Shigeharu Akatsuka; Akihiro Suitsu; Kenichi Ozaki
Original assignee: Permelec Electrode Ltd
Current assignee: De Nora Permelec Ltd
Priority date: 1994-07-14
Filing date: 1995-07-10
Publication date: 1996-01-17
Also published as: FR2722512B1; JPH0827598A; GB9514006D0; FR2722512A1

Abstract

An electrode structure for electrolysis eg. electroplating or electroforming copper foil comprises an electrically conductive electrode substrate eg. Ti having fitted to the surface thereof an electrode eg. Ti coated with an electrode substance eg. iridium oxide the electrode being fixed to the electrode substrate by welding a metal eg. granules filled in a plurality of holes formed in the electrode to the electrode and the electrode substrate. In the electrode structure, the electrode can be easily fitted to the electrode substrate or easily removed from the electrode substrate and also the electrode can be changed while equipping the electrode structure to an electrolytic bath. The voltage drop at the electric current supplying portion is reduced and electric current can be uniformly supplied to the entire surface of the electrode.

Description

ELECTRODE STRUCTURE AND PROCESS FOR PRODUCING THE SAME FIELD OF THE INVENTION The present invention relates to an electrolytic electrode, and particularly to an electrode structure comprising an insoluble metal electrode equipped with an electrode formed by coating an electrode material on an electrode substrate which is used for the electrolysis of an acidic aqueous solution under a high electric current density.

The present invention also relates to a process for producing the electrode structure.

BACKGROUND OF THE INVENTION In the electrolysis of an acidic aqueous solution, such as an electrolytic collection of a metal, electroplating, etc., a lead electrode has mainly been used as the anode, but recently an insoluble metal electrode, formed by coating a solution of an electrode material, including a platinum group metal, on the surface of a corrosion resistant valve metal, such as titanium, etc., and thermally decomposing the coated layer in an oxidative atmosphere at a temperature of from 4000C to 6000C to form an oxide coating, has been used in place of the lead electrode. Recently, the utilization of these insoluble metal electrodes as electrolytic electrodes at a large-scale high current density, such as high-speed zinc plating, the production of copper foils, etc., has increased due to the durability, the dimensional stability, and the ease of shaping.

For example, in high-speed zinc plating, a large electrode having an area of one anode of about 2 m2 is sometimes used, and where the maximum current density is 20 kA/m2, it sometimes happens that an electric current of about 40 kA passes through one anode. Also, even in the case of an anode for producing electrolytic copper foils, attempts have been made to increase the current density by enlarging the area of the anode. Furthermore, in these electric platings, since the non-uniformity of the electric current distribution greatly influences the quality of the products, it has been required to make the electric current distribution particularly uniform.

Thus, for passing a large electric current, even when using a metal having a good electric conductivity, such as titanium, etc., as an electrode substrate, it is necessary to insure that the thickness of the electrode substrate is at least 10 mm and, as the case may be, the electrode substrate having a thickness of at least 40 mm is used.

On the other hand, coating an electrode substance on an electrode substrate is generally carried out by thermally decomposing a liquid containing the electrode substance coated on the electrode substrate. Also, in the case of an electrode substrate having a large thickness for passing a large electric current, a time of from 30 minutes to one hour is required for raising the temperature to the thermal decomposition temperature of from 450"C to 6000C and also after carrying out the thermal decomposition for from 10 to 15 minutes, a time of at least 2 hours is required for keeping the electrode substrate warm and allowing the electrode substrate to cool down.Furthermore, for making the coating thickness of the electrode substance a desired thickness, the above operation is repeatedly carried out from 10 to several tens of times and thus, a period of from one week to two weeks, or a longer period, is required to coat the electrode substance to a desired thickness.

For solving these problems, it has been proposed to prepare an electrode structure by separately making an electrode substrate portion and an electrode portion having formed thereon a coated layer of an electrode substance and fitting the electrode to the electrode substrate by screws or fitting stud bolts to the electrode. However, in this method, since it is required to form tapped holes in the electrode and/or equip other connecting means to the electrode, it is necessary for the thickness of the electrode to be from about 3 to 10 mm. Only a method of heating such an electrode is far easier when compared with a conventional method of heattreating a whole electrode structure, but it cannot sufficiently shorten the heating time and the cooling time.

Also, there is a problem that since various kinds of fitting means for fitting the electrode to the electrode substrate are formed on or in the electrode plate, the thermal environment around the fitting means is slightly different from that of other portions, which results in a change in the characteristics of the electrode. Furthermore, since in a conventional electrode structure, fitting of the electrode to the electrode substrate is carried out at the back surface of the electrode, it is difficult to exchange the electrode when it is attached to the electrolytic apparatus.

Thus, the present inventors have previously proposed a method of fitting a thin electrode to the surface of an electrode substrate by welding or screwing as disclosed in JP A-5-171486 and JP-A-5-202498 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").

According to the method in JP-A-5-171486 and JP-A-5202498, the exchange of the electrode becomes possible when the electrode structure is equipped in the electrolytic bath, the coating on the electrode can be easily formed, and the electrode structure can be used without any troubles up to the current density of about 100 A/dm2. Since in the method the supply of the electric current from the electrode substrate to the electrode plate is mainly carried out through the contact surface where the electrode substrate and electrode plate are clamped together by fitting screws, a voltage drop occurs at the contact surface by the contact resistance.Since the contact resistance is several hundred times larger than the resistance of the conductor itself, there is a limitation on the amount of electric current that can be passed for meeting the passing of an electric current having of a large current density, it is required to increase the fitting portions and increase the thickness of the electrode.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrode structure comprising an insoluble metal electrode in which the electrode substrate and the electrode used as an anode for an electrolytic collection of a metal or plating at a large current density are separately produced, wherein the electrode can be easily fitted to the electrode substrate, and the voltage drop at the electric current supplying portion is reduced and an electric current can be uniformly supplied to the entire surface of the electrode.

Another object of the present invention is to provide a process for producing the electrode structure.

A first embodiment of the present invention is an electrode structure comprising an electrically conductive electrode substrate having fitted to the surface thereof an electrode coated with an electrode substance, wherein the electrode is fixed to the electrode substrate by at least one connected portion formed by welding a metal which is filled in a hole which is formed in the electrode.

A second embodiment of the present invention is a process for producing the electrode structure comprising an electrically conductive electrode substrate having fitted to the surface thereof an electrode coated with an electrode substance, which comprises placing the electrode, having formed therein at least one hole, on the electrode substrate, filling a metal in the hole(s) in the electrode, and melting the metal filled in the hole(s) in the electrode to weld the electrode to the electrode substrate.

In a preferred embodiment of the electrode structure of the present invention, the metal which is used to fill in the hole(s) in the electrode is a granular metal, such as a granular metal having a spherical form.

In another preferred embodiment of the electrode structure of the present invention, the granular metal which is used to fill in the hole(s) in the electrode is the same kind of metal as the metal which constitutes the electrode substrate.

In another preferred embodiment of the electrode structure of the present invention, the electrode is formed by coating an electrode substance, containing iridium oxide, on the surface of titanium or a titanium alloy, the electrode being usable as an anode in an acidic aqueous solution.

BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 (A) and (B) are views of an embodiment of the electrode structure of the present invention, and Fig. 2 (A) to (D) are views explaining the production process of the electrode structure of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is explained in detail below by referring to the accompanying drawings.

Fig. 1 is a view showing one example of the electrode structure of the present invention, wherein Fig. 1 (A) is a plain view of the electrode structure, and Fig. 1 (B) is a cross-sectional view cut along the A-A line of the electrode structure shown in Fig. 1 (A).

At least the surface of an electrode substrate 1 is formed by a corrosion resistant metal such as titanium, tantalum, and the alloy of each of them. It is preferred that the surface of the electrode substrate is formed by an electrically conductive corrosion resistant coating. The electrically conductive corrosion resistant coating may be formed as an oxide layer of the metal or the alloy described above on the surface of the electrode substrate by heating the coated layer on the surface in air at a temperature of from 5000C to 6500C for from 1 to 3 hours or may be formed as a protective layer by coating an aqueous solution of a salt of titanium or tantalum on the surface of the electrode substrate and oxidatively decomposing the coated layer by heating the coated layer in air at a temperature of from 4000C to 6000C.

Furthermore, by forming the coating while adding a compound of a platinum-group metal such as platinum, ruthenium, etc., to titanium or tantalum, the electric conductivity and the corrosion resistance of the coating can be increased.

An electrode 2 is formed by forming a coated layer 3 of an electrode substance on an electrically conductive substrate 1 comprising a corrosion resistant metal such as a thin layer forming metal of titanium and tantalum or an alloy thereof.

The electrode substance forming the electrode is preferably an oxide formed by thermally decomposing in air a coated layer of an aqueous solution of a compound of a platinum-group metal. The electrode having a coating formed by coating a coating liquid formed by dissolving iridium chloride and tantalum chloride in butyl alcohol such that the ratio of iridium chloride/tantalum chloride becomes 70/30 mole% is preferable as an anode for generating oxygen in an acidic electrolyte although the function of the electrode differs according to the material to be electrolyzed or the composition of the electrolyte.

The electrode substrate 1 is connected to the electrode 2 by welding a metal which has been filled into a plurality of holes 4 which are formed in the electrode.

Fig. 2 is the cross sectional view explaining the production process of the electrode structure of the present invention.

Holes 4 are formed in an electrode 2 at a plurality weld-connecting portions, as shown in Fig. 2 (A). The form of the hole may be a circle or a polygon in the cross-sectional form and when the form of the hole is a circle, the holes can be easily formed by a drill. Also, the diameter of the hole is preferably from 0.3 to 5 mm, and more preferably from 0.5 to 3 mm. The number of holes can be appropriately selected according to the amount of electric current which is to be passed. When the amount of electric current is large, the current passing resistance can be lowered by decreasing the spacing between the holes and increasing the number of holes.

The corrosion resistant coating 6 of the electrode substrate 1 is removed at the weld-connecting portions 5 to expose the metal surface of the electrode substrate at the weld-connecting portions 5 as shown in Fig. 1 (B).

The electrode 2 is disposed on the electrode substrate 1 in such a manner that the positions of the holes 4 in the electrode coincide with the positions of the removed portions 5 of the corrosion resistant coating. Thereafter, a granular material 7, such as spheres of a metal of the same kind as the metal which constitutes the electrode substrate, is filled into the holes 4 in the electrode as shown in Fig. 2 (C). As the granular material which is used to fill in the holes in the electrode, materials having an optional form, such as a sphere, a square pillar, a column, etc., can be used.In the case that the electrode substrate is formed by, for example, titanium or a titanium alloy, when using a sphere of metallic titanium having a diameter which is the same as or slightly larger than the diameter of the hole, only one sphere of the metal is placed into the hole under pressure, such that a sufficient connecting strength can be obtained by melting the spherical metal. Also, by previously disposing each of the titanium spheres in all the holes of the electrode under pressure, the working time for connecting the electrode to the electrode substrate can be shortened.

An electrode tip of spot welding is pushed to each metal filled in each of the welding holes and by passing a welding electric current through the filled metal to weld the filled metal to the substrate and to the inside surface or wall of the hole in the electrode as shown in Fig. 2 (D).

In another method, by putting the granular material in each welding hole under pressure or by supplying a filling metal material (filler) in the welding hole, the metal is welded to the electrode substrate and the electrode by TIG welding.

In the electrode structure of the present invention, since the resistance of the connected portions is almost the same as the resistance of the metal by welding of the metal, the area of the connected portions can be reduced. Further, since the molten amount of the metal in each welded portion is small, the problem of causing thermal deformation, etc., of the electrode or the electrode substrate when connecting the electrode substrate and the electrode by welding the metal does not occur. Also, since the area of each welded portion is small, each welded portion can be removed without need of a large force, and thus when it is necessary to remove the electrode from the electrode substrate when deterioration of the electrode substance occurs, the electrode can be easily removed even when there are many welded portions.Moreover, after removing the electrode by grinding, etc., protruding portions remain on the electrode substrate where the electrode substrate and the electrode are once connected. Because the protruding portions remain on the electrode substrate, another electrode can be easily placed on and connected to the electrode substrate.

As described above, in the electrode structure, the granular material of a metal of the same kind of metal which constitutes the electrode substrate is filled in a plurality of holes formed in the electrode from the electrolytically acting surface side, the electrode is fixed to the electrode substrate by TIG welding or spot welding of the filled granular material, and the electrode can be easily removed from the electrode substrate by cutting the fixed/welded portions, whereby the electrode can be exchanged when the electrode structure is equipped in an electrolytic bath. Also, even when a large electrode is used, the electrode can be easily prepared by assembling plurally split electrode parts and an electrode structure having an excellent dimensional accuracy can be obtained.

Furthermore, by increasing the number of connected portions, the electrode structure having a low electric resistance, a uniform current distribution through the whole electrode, a low electrode voltage, and a long life is obtained.

The present invention is further described practically by the following examples.

Example 1 After heating an electrode substrate, composed of titanium and having a length of 300 mm, a width of 300 mm, and a thickness of 1 mm, and an electrode substrate material, composed of titanium and having the same area as above and a thickness of 10 mm, in air at 5309C to form a coating of the oxide on each member, a coating solution obtained by dissolving iridium chloride and tantalum chloride in butyl alcohol such that the ratio of iridium oxide to tantalum oxide in the oxides became 70 to 30 (mole%) was coated on both surfaces of the electrode substrate and heated in air to 5300C for 10 minutes to thermally decompose the chlorides.In this case, the electrode substrate side of the electrode substrate was treated only once and the treatment steps from coating to thermal decomposition were repeatedly applied 12 times to the electrolytically acting surface side.

Holes each having a diameter of 1.2 mm were formed in the electrode with an interval of 50 mm between the holes and also the coating of the oxide was removed from the surface of the electrode substrate at the portions matching to the positions of the holes of the electrode to expose the metallic titanium surface of the electrode substrate at these positions.

The electrode and the electrode substrate were put together such that the positions of the holes of the electrode coincided with the exposed portions of the electrode substrate, titanium spheres having a diameter of 1.5 mm were put in each hole of the electrode from the surface side of the electrode and the titanium spheres were connected to both members by spot welding.

In the electrode structure thus obtained, the ohm loss of each fixed portion at passing an electric current at a current density of 100 A/dm2 was 0.9 mV.

Example 2 Titanium spheres were placed in the holes of the electrode disposed on the electrode substrate produced as in Example 1, and the titanium sphere portions were welded to both members in an argon inert atmosphere by TIG welding. As a result thereof, the titanium sphere portions were strongly welded to both members at a low electric current value.

Example 3 The electrode and the electrode substrate produced in Example 1 were used except that the diameter of each hole formed in the electrode was changed to 2.5 mm. The electrode and electrode substrate were put together such that the positions of the holes of the electrode coincided with the positions of the exposed portions of the electrode substrate and fillers each composed of rod-form titanium having a diameter of 1 mm were supplied from the electrode surface side.

First, the fillers and the electrode substrate were welded, then the inside surface of titanium of each of the holes of the electrode and the fillers were welded, and they were welded by TIG welding such that the fillers were filled in each hole, whereby a strong connection was obtained by spot welding.

Comparative Example 1 The electrode substrate made of titanium and the electrode made of titanium each having the same size as in Example 1 and having tapped holes with an interval of 50 mm were fixed to each other by screws each having a head diameter of 18 mm. In the electrode structure, when the electric current was passed at a current density of 100 A/dm2, the electric current was concentrated to the screw portions, whereby the ohm loss of the fixed portion was 2.5 mV in average.

In the electrode structure of the present invention, when a large-sized insoluble metal electrode is used for a large continuous iron or steel surface treatment apparatus or a large copper foil production apparatus, or for the use at a high current density, the connection of the electrode to the electrode substrate and the removal of the electrode from the latter can be easily carried out, the electrode can be exchanged in the state of equipping the electrode structure to an electrolytic bath, the voltage loss is small even at passing a large electric current, and the electrode structure of a large area can be easily obtained by using many electrodes each having a small area.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

Claims:

1. An electrode structure comprising an electrically conductive electrode substrate having fitted to the surface thereof an electrode coated with an electrode substance, wherein the electrode comprises at least one hole, and wherein the electrode is fixed to the electrode substrate by at least one connecting portion formed by welding a metal which has been filled into the at least one hole in the electrode.

2. The electrode structure of claim 1, wherein the metal filled in the at least one hole of the electrode is a granular metal.

3. The electrode structure of claim 2, wherein the granular metal is a spherical metal.

4. The electrode structure of claim 1, wherein the metal filled in the at least one hole in the electrode is the same kind of metal as the metal comprising the electrode structure.

5. A process for producing an electrode structure comprising an electrically conductive substrate having fitted to the surface thereof an electrode coated with an electrode substance, which comprises disposing the electrode, having formed therein at least one hole, on the electrode substrate, filling a metal in the at least one hole, and melting the metal filled in the at least one hole to weld the electrode and the electrode substrate together.

6. The electrode structure of claim 1, wherein the at least one hole in the electrode has a diameter of 0.3 to 5 mm.

7. The electrode structure of claim 1, wherein the electrode substance is an oxide of a platinum-group metal.

8. The process according to claim 5, wherein the electrode and the electrode substrate are welded together by TIG welding or spot welding.

9. The process according to claim 5, wherein the electrode can be removed from the electrode substrate.