JPH0681198A - Insoluble electrode and its production - Google Patents

Abstract

PURPOSE:To provide an insoluble electrode excellent in corrosion resistance even though electrolysis is performed in high current density and enabling to tolerate use of a long time and the production method therefor. CONSTITUTION:This insoluble electrode has an electrically conductive layer consisting of a dense IrO2 layer >=90% in the relative density as a first layer on an electrode mother material made of on electrically conductive metal and a secondary layer thereon essentially consisting of IrO2 being 50-90% in the relative density and is produced by forming the IrO2 layer of the first layer by an ion plating method. Thus, the formation of an oxidized film on the electrode mother material is prevented and the product superior in durability in high current density of >=150A/dm<2> in a sulfuric acid bath is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insoluble electrode and a method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, when electroplating a metal material, an insoluble electrode is used in an electroplating bath to electroplate a metal such as Zn, Sn, Ni or Cr on the surface of a metal material to be plated which is a cathode. Has been done. When electrorefining metal, an insoluble electrode is used in the refining bath to remove Mn, Zn
Electric refining of metal such as is performed.

The most commonly used insoluble electrode at this time is a Pb-based alloy.
In this electrode, PbO ₂ is produced on the surface of the electrode in the electroplating bath, the electrorefining bath, particularly in the sulfuric acid solution during the electric current treatment. Although PbO ₂ exhibits the function of an insoluble electrode, the generated PbO ₂ and Pb have a weak adhesive force and are mixed in the electrolytic solution to cause defective plating or refined metal containing impurities.

Therefore, as a countermeasure, an electroplating bath, an electric smelting bath, especially IrO ₂ which is a platinum group oxide which is the most electrochemically stable in a sulfuric acid solution, is used as a valve metal (Ti, Ta) which is an electrode base material. Japanese Patent Publication No. Sho 48-3954 discloses an electrode coated with a metal such as Zr, Zr or the like, which forms an insulating oxide layer on the surface and stops the energization when energized.

Further, in order to suppress the oxidation of the valve metal or to improve the adhesion of IrO ₂ , Ta is used as the intermediate layer.
_{A method} of forming a coating film to which ₂ O ₅ or the like is added and using an insoluble electrode having an IrO ₂ layer formed thereon is disclosed in Japanese Examined Patent Publication No. 46-21.
No. 884 and Japanese Patent Application Laid-Open No. 63-235493. FIG. 2 shows the electrode structure. 1 is an electrode base material made of SUS, 2 is a valve metal layer, 3 is IrO ₂ —Ta ₂ O
Layers ₅ and 4 are IrO ₂ layers. The layers 3 and 4 are applied by applying a solution containing an Ir compound precursor and a Ta compound precursor on the electrode base material and performing heat treatment in an oxidizing atmosphere.
This is a so-called coating and baking method in which a conductive layer made of O ₂ and Ta ₂ O ₅ is formed.

[0006]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 46-2188
No. 4, JP-A-63-235493, the insoluble electrode having a layer mainly composed of IrO ₂ by the coating and baking method can be used for a long time at a low current density (up to 50 A / dm ² ). However, when a galvanic corrosion test was carried out at a high current density, especially in a sulfuric acid solution at 150 A / dm ² , it was 3000.
After about 4000 hours, a sharp voltage rise occurs and the electrode becomes unusable.

The corrosion mechanism of this electrode will be described with reference to FIG. Since the layers 3 and 4 containing IrO ₂ are produced by heat treatment of the solution, pores due to volatilization of the solution components, and a hexagonal crack 5 in the coating film due to the difference in thermal expansion between the valve metal layer 2 and the IrO ₂ layer. It has occurred.

For this reason, the porosity of the coating is as large as 10 to 30%, and the direct conduction with the valve metal layer 2 occurs due to the pores and the cracks, and the insulating oxide coating 6 is formed on the surface of the valve metal layer.
Is formed, and further, the oxidation of the valve metal proceeds along the interface between the valve metal layer and the IrO ₂ layer, causing an increase in voltage and losing the function as an electrode.

As a countermeasure against this, it is necessary to prepare a homogeneous coating film having no pores or cracks. Conventionally, there are reactive sputtering method and reactive vapor deposition method as a method for obtaining a coating film which is homogeneous and has few cracks and pores.

However, the IrO ₂ film (hereinafter referred to as IrO ₂ reactive sputter film, IrO ₂ reactive vapor deposition film) produced by this reactive sputtering method or reactive evaporation method is 10
There is a drawback that the energization is stopped in a short time due to the energization at a low current density of 0 A / dm ² .

The reason for this is that the IrO ₂ reactive sputter coating and the IrO ₂ reactive vapor deposition coating are easily peeled off due to the increase in film thickness, and the optimum film thickness for production is several hundred to several thousand Å, which is very thin and the melting loss speed is fast. is there.

The present invention provides an insoluble electrode having excellent corrosion resistance even when electrolysis is performed at a high current density of 150 A / dm ² or more, and capable of withstanding the longest use, and a method for producing the same.

[0013]

The insoluble electrode of the present invention has a relative density of 9 as a first layer on an electrode base material made of a conductive metal.
0% or more dense IrO ₂ layer, relative density 9 as second layer
It is characterized by having a conductive layer of which the main component is 0 to 50% of IrO ₂ . Still the production method of the present invention electrode, in a closed container the IrO ₂ layer of the first layer is an oxygen atmosphere, dissolve the Ir, evaporated, the IrO ₂ to the electrode base metal surface was applied a bias by ion plating A method for producing an insoluble electrode, which comprises forming a film.

Since the electrode of the present invention has a relative density of 90% or more, that is, a dense IrO ₂ film as the first layer on the electrode base material, cracks existing in the conductive layer whose main component of the electrode second layer is IrO ₂ The pores do not penetrate into the electrode base material, and the electrode base material is not exposed on the electrolyte surface. For this reason, the oxidation of the electrode base material can be suppressed, and even if electrolysis is carried out at a high current density of 150 A / dm ² or more, the corrosion resistance is excellent and it can be used for a long time.

Next, the insoluble electrode of the present invention will be described. The electrode base material used in the present invention may be any conductive metal. However, the valve metal (metal such as Ti, Ta, Zr which hardly melts in a sulfuric acid bath) itself, or the valve metal on a base metal such as SUS Those provided with a metal layer are preferable. The reason for this is that the valve metal has excellent corrosion resistance in a sulfuric acid bath,
This is because it has a high breakdown voltage.

The coating property of IrO ₂ of the first layer of the electrode of the present invention is characterized in that the relative density is 90% or more. However, the film thickness is preferably 0.01 μm or more. This is because the IrO ₂ film is dense, that is, the relative density is 90%.
In the above case, the plating solution hardly reaches the electrode base material with almost no pores or cracks, and the effect of preventing the corrosion of the electrode base material and the formation of the insulating oxide film is obtained, whereas it is less than 90%. Corrosion of the electrode base material starting from pores and cracks causes the electrode life to be drastically reduced. Also, when the film thickness is less than 0.01 μm, when a coating film is formed as a second layer on the upper part by a coating baking method. This is also because the coating thickness is too thin to exert the effect of preventing corrosion of the electrode base material by the first layer.

The first layer of the electrode of the present invention can be formed by a so-called PVD method such as a reactive vapor deposition method, a reactive sputtering method and an ion plating method.

The coating characteristics of the second layer of the electrode of the present invention are characterized in that the relative density is between 50 and 90%, that is, it is porous and that it is a conductive layer whose main component is IrO ₂ . The conductive layer containing IrO _{2 as a} main component means that IrO ₂ is between 50 and 100% by volume and the balance is Ta, Ti, Pt,
Si, Nb, Ru, Os, Rh, Pd, Zr, Mo,
W, Fe, Co, Ni, Mn, Pb, Sn, Sb, B
It contains at least one metal selected from i, In, Tl, and Al, or an oxide of the metal.

A so-called coating and baking method can be adopted as a method for forming this layer. The coating and baking method is a method in which a solution containing a Ir compound precursor as a main component is applied, dried, and then heat-treated in an oxidizing atmosphere to form a coating film one or more times.

A solution whose main component is an Ir compound precursor is disclosed in JP-A-62-240780 and JP-A-63-2.
35493, JP-A-3-193889, and JP-A-59-150091, for example, an alcohol solution containing a compound precursor such as iridium chloride, tantalum alkoxide, and chloroplatinic acid, which is heat treated. Thus, IrO ₂ is mixed in a volume ratio of 50 to 100%, and the balance is Ta ₂ O ₅ , Pt, or the like.

The above solution is applied on the first layer of the electrode of the present invention by means such as brush coating, spraying, dipping, etc., and then dried at 150 to 200 ° C. for several tens of minutes to evaporate the solvent and then oxidized. 300 to 70 in a natural atmosphere, for example in the atmosphere
Heat treatment at 0 ° C. The second layer of the electrode of the present invention is formed by repeating the operation from this application to the heat treatment once or a plurality of times.

[0022] In the present invention, reasons for adopting such arrangement the IrO ₂ coating, reactive deposition method, IrO ₂ film is formed by such as reactive sputtering in the case of the use of a single layer, but dense but thin Due to high current density (150A / dm
² ) In contrast to the short durability when energized, a coating formed by the coating and baking method and having a small relative density of 90 to 50% can be thickened, and the corrosion of the electrode base material and insulation When the formation of oxide film is prevented (that is, when the lower layer has a dense IrO ₂ film with a relative density of 90% or more), the durability at high current density (150 A / dm ² ) is long. This is because

Further, for energization at a high current density, Ir
A coating with 100% component has excellent durability, and Ta, T as a binder for the Ir component for energization at low current density.
i, Pt, Si, Nb, Ru, Os, Rh, Pd, Z
r, Mo, W, Fe, Co, Ni, Mn, Pb, Sn,
It has been found that a coating film to which a metal selected from Sb, Bi, In, Tl and Al or one or more kinds of oxides of the metal is added has excellent durability.

As a method for forming the dense IrO ₂ film as the first layer of the electrode of the present invention, as a result of various studies on the film forming method by the ion plating method, it was found that the adhesion was excellent and a film thickness of up to 20 μm was possible. It was found that a highly durable electrode can be prepared by applying this coating to the electrode first layer of the present invention. However, if the coating film is thickened to 20 μm, peeling easily occurs, and the optimum film thickness is between 0.1 and 5 μm.

As the ion plating method, an arc discharge type ion plating, which can dissolve Ir having a high melting point and a high boiling point and has a high ionization rate, is most preferable.

Details of this film forming method will be described below. First, Ir is used as an evaporation source installed in a closed container.
This is because when IrO ₂ is dissolved, oxygen and Ir are generated at 1100 ° C.
This is because there is a possibility that it will be decomposed into particles and volume contraction will occur, and the evaporation source will be reduced, resulting in damage to the crucible, which will cause difficulties in the process. Therefore, Ir is melted by an electron gun, made into an ionic state by an ionization electrode, and applied to the electrode base material in an oxygen atmosphere while applying a bias to the electrode base material. However, there is no problem as long as the shape of the electrode base material fits within the closed container.

At this time, the oxygen atmosphere in the closed container is preferably in the range of 1 × 10 ⁻⁴ to 1 × 10 ⁻³ Torr. This is because if it is less than 1 × 10 ⁻⁴ Torr, Ir is less likely to be oxidized, and if the pressure is more than 1 × 10 ⁻³ Torr, the ionization reaction of Ir is less likely to be promoted during film formation.
The electrode base material temperature at the time of film formation needs to be 300 to 700 ° C. This is Ir below 300 ° C.
This is because the adhesion between the O ₂ coating and the electrode base material is weak. Then, when the temperature exceeds 700 ° C., Ir diffuses into the electrode base material, and it becomes difficult for the coating film to show the composition of IrO ₂ .

[0028]

The structure of the electrode of the present invention is shown in FIG. Since the electrode of the present invention has the thin film dense IrO ₂ layer 7 formed on the valve metal layer by the reactive sputtering method, preferably the ion plating method, the oxidation progress of the valve metal layer is suppressed. In addition, since it has a porous coating film formed by coating and baking as an upper layer of the coating film, the current density per area is low and the melting loss of the coating film is small. Therefore, even if electrolysis is carried out at a high current density of 150 A / dm ² or more, the corrosion resistance is excellent, and it has a feature that it can be used for a longer time than the electrode of FIG.

[0029]

EXAMPLES The production method, evaluation method and results of the electrode of the present invention will be described in detail below. 1) Electrode base material 100 x 100 x 20 m using a Ti plate as the electrode base material
The surface of the electrode base material of m is washed with oxalic acid and then roughened by blasting. 2) First layer of the electrode of the present invention The first layer of the electrode of the present invention was formed by a reactive sputtering method and an ion plating method.

Reactive Sputtering Method A base material Ti plate was placed in vacuum (8 × 10 ⁻⁴ Torr) so as to face the Ir plate. Ar pressure 1 × 10 ^-1 to 2 in the vacuum chamber
The pressure is set to × 10 ^-2 Torr, a potential of 1 kV is applied to the target, Ar ions are discharged, Ir atoms are struck out on the Ir plate, and O ₂ gas is ejected at a gas pressure of 4.5 × 10 ^-4 Torr to form a base metal Ti plate. An IrO ₂ reactive sputtered coating of 0.005 to 1 micron was formed on the surface of the Ti base material by spraying a film onto the Ti base material at a deposition rate of 2Å / sec.

Ion Plating Method Ir was inserted into the crucible, melted by an electron beam and evaporated,
Further, it was ionized under the conditions of 40 V · 10 A by the ionization electrode on the crucible. Then, the titanium base material is installed so as to face Ir, the bias voltage is 500 V, and the film formation rate is 10Å.
IrO2 was coated at 0.1 to 20 μm for 1 _second / sec.
At this time, the oxygen atmosphere was 5 to 10 ⁻⁴ Torr and the film forming temperature was 250 ° C. to 750 ° C.

A Ta ₂ O ₅ [0032] 3) The present invention second layer (coating baking method) the IrO ₂ by thermal decomposition H ₂ IrCl ₆ per se, and the H ₂ IrCl ₆ and pyrolysis of the IrO ₂ by pyrolysis A solution of Ta (OC ₂ H ₅ ) ₃ mixed in a volume ratio of 7: 3 dissolved in butanol was applied with a brush, dried, placed in an electric furnace and baked at 450 ° C. multiple times to make a thickness of about 10 μm. A film was formed.

The durability of the produced electrode was evaluated by the following method. The electrodes of the present invention 1 to 5, conventional products 6 and 7 and comparative products 8 to 11 were used as the anode, and a platinum plate was used as the cathode.
Current density 200 A / dm ² , 400 in wt% sulfuric acid solution
An energization test was performed at A / dm ² and the time until the voltage increased by 10 V was measured. In Table 1, ◯ indicates a current density of 200 A / d
Life of 1500 hr or more at m ² , life of 400 A / dm ² at 8
It is an insoluble electrode having a durability of 00 hr or more. Table 1
It can be seen from the results that the electrode of the present invention has excellent durability.

Incidentally, this time, the outermost layer of the electrode was IrO ₂ and Ta _2.
The results of durability evaluation of an insoluble electrode having a volume ratio of O ₅ to 7: 3 are shown. The outermost layer of the electrode is IrO.
_{When 2} is 50 to 100 vol% in volume ratio, similar durability is exhibited.

[0035]

[Table 1]

[0036]

The insoluble electrode of the present invention is 150 A / dm
^It has excellent corrosion resistance even when electrolysis is performed at a high current density of ² or more, and can withstand long-term use, and is extremely useful as an electrode for other applications such as electric refining as well as an electrode for electroplating.

[Brief description of drawings]

FIG. 1 shows an electrode structure of the present invention.

FIG. 2 shows a conventional electrode structure.

FIG. 3 is an explanatory diagram of a conventional electrode corrosion mechanism.

[Explanation of symbols]

1 ... SUS-made electrode base material 2 ... valve metal layer 3 ... IrO ₂ -Ta ₂ O ₅ coating baking coating 4 ... IrO ₂ coating baking coating 5 ... crack 6 ... insulating oxide 7 ... dense IrO ₂ film

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C25B 11/08 A 9046-4K

Claims (3)

[Claims] 1. A dense layer IrO ₂ layer having a relative density of 90% or more as a first layer and an IrO ₂ main component having a relative density of 90 to 50% as a second layer on an electrode base material made of a conductive metal. An insoluble electrode having a conductive layer. 2. A first IrO ₂ layer is formed on a surface of an electrode base material to which a bias is applied by an ion plating method by dissolving and evaporating metallic Ir in a closed container in an oxygen atmosphere. The method for producing an insoluble electrode according to claim 1, which is characterized in that. 3. The pressure of oxygen in the closed container is set to 1 × 10 ^-4 .
3. The method for producing an insoluble electrode according to claim 2, wherein the first IrO ₂ layer is formed at 300 to 700 ° C. at 1 × 10 ⁻³ Torr.