JPH062194A - Electroplating method - Google Patents

Abstract

PURPOSE:To restrain the dissolution and wear of an anode to lengthen its useful life when giving electroplating to a metal in a plating bath contg. organic substances by using an oxygen generating anode which a Ti thermally sprayed layer and an electrode catalytic layer consisting of IrO2-Ta2O5 are laminated on a Ti substrate to form. CONSTITUTION:A plating bath (acidic water electrolyte in which tin or zinc is dissolved) contg. organic substances (sodium acetate, etc.) is used to give electroplating to a metal (particularly ferrous metal). In this case, as an oxygen generating anode, an electrode is used which is constituted by providing a Ti thermally sprayed layer (5-500mu thick, 05-15% porosity) on a Ti substrate by arc melt-spraying, etc., and providing an electrode catalytic layer (converted to about 10g/m<2> IrO2) contg. >=30mol% (preferably 40-90mol%) IrO2 and having Ta2O5 as the balance on the former layer. As a result, an electrode which excels in durability and is industrially useful is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electroplating a metal, particularly an iron-based metal, using a plating bath containing an organic substance.

[0002]

2. Description of the Related Art Steel sheet plating of tin, zinc or the like is usually carried out at a high temperature of 50 to 60 ° C. or higher using an aqueous acidic electrolytic solution, and a very large current density, for example, 100 A / d.
The anode current density is about m ² . As described above, the steel plate plating is performed under extremely severe conditions, and it is considered difficult to economically find a material having a long life desired at the high anode current density as the anode used for the plating. ing.

At present, as the above-mentioned anode for plating a steel plate,
Lead or lead alloys are used, but lead is relatively rapidly consumed, and there are problems such as contamination of the plating bath by the eluted lead and deterioration of the plating film. Platinum-plated anodes and platinum foil clad anodes have been studied as alternative anodes, but platinum also has the drawback of being considerably worn out, and as a result, there is little consumption of precious metals and their oxides as the electrode catalyst for oxygen generation. Have been proposed.

However, in an electrode in which titanium or its alloy, which is widely used from the viewpoint of economy and workability, is simply coated with an electrode active substance, an electrode coating layer is formed by oxygen generated in the anode during use. An oxide having no conductivity is formed between the substrate and the electrode catalyst, even if the remaining amount of the electrode catalyst is sufficient, loses its function as an electrode, and eventually the electrode coating layer peels off, rendering it unusable. Inconvenience (Kenichiro Ota et al., Electrical Science 57, No1, P71-
75). Therefore, many improvement means have been proposed for providing an intermediate layer of various substances between the substrate and the electrode coating to protect the substrate and improve the durability of the electrode.

As such an oxygen generating anode, an electrode in which tantalum or niobium metal or an oxide thereof is used as an intermediate layer, and an oxide of mainly iridium or its alloy is coated as an electrode catalyst is durable and economical. Has been attracting attention. On the other hand, as the electroplating bath, a technique of incorporating an organic substance in the bath is industrially carried out for the purpose of uniformity of the plating film. Typical of such organic compounds are sodium acetate and phenol sulfonic acid. However, the electrode potential for oxygen generation increases in the plating bath to which organic substances are added, and the dissolution loss of the electrode catalyst increases (Masao Takahashi, “Soda and Chlorine” 39, P531-54).
0 (1988)). As described above, in the plating bath containing an organic substance, the electroplating conditions are more severe than in the case where an organic substance is not contained, and no electrode using iridium oxide or its alloy as an electrode catalyst layer has been developed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to use, as an anode, an electrode having a highly durable and industrially useful electrode mainly composed of iridium oxide having a high electrode activity in a plating bath containing an organic substance. An object is to provide an electroplating method.

[0007]

The present inventors have found that one of the causes of loss of the electrode catalyst layer in a plating bath containing an organic substance is that the adhesion between the intermediate layer and the catalyst layer is insufficient. It was examined that the intermediate layer is made porous to make these deposits firm and increase the electrode surface area. A thermal spraying method is suitable for forming such a porous intermediate layer, but a metal sprayed layer of tantalum or niobium is extremely weak to heat, and a catalyst layer is formed thereon by thermal decomposition of the catalytic metal compound. It was found that when it was formed, it was oxidized and became extremely fragile, failing to achieve its purpose.

The present invention has been made on the basis of the above-mentioned investigations, that is, in electroplating a metal using a plating bath containing an organic substance, a titanium sprayed layer is formed on a titanium substrate as an oxygen generating anode. The electroplating method is characterized by using an electrode provided with an electrode catalyst layer comprising iridium oxide in an amount of 30 mol% or more and the rest being tantalum oxide on the sprayed layer.

The titanium substrate used in the present invention may have various shapes such as a plate shape, a rod shape, an expanded shape and a perforated plate shape. The sprayed layer formed on the titanium substrate takes in some oxygen and becomes a sprayed layer of titanium metal and its oxide.
The thermal spraying methods include flame spraying, plasma spraying, arc spraying, explosive spraying, and the like, and stable coating can be obtained especially by performing arc spraying or plasma spraying.

The substrate surface is subjected to grit blasting, shot blasting or sand blasting as a pretreatment for thermal spraying. Alumina, silicon carbide, sand or the like is used as the blasting material, and the particle size is preferably about 200 to 1000 μm.

In the arc spraying used in the present invention, a voltage is applied between two metal wires to generate an electric arc between the metal wires at the tip of the spray gun, and the arc melts the metal wires. Then, the molten metal is deposited on the metal substrate with a high-speed compressed gas. In plasma spraying, an inert gas such as nitrogen or argon is heated to a high temperature by an electric arc, and when passing through the electric arc, it is ionized to form a plasma jet stream and is ejected from a nozzle. The thermal spraying powder is supplied thereto, and the thermal spraying powder is heated and melted by the plasma jet, and is accelerated and collides with the surface of the base material to form a film.

The thickness of the titanium coating sprayed by these methods is preferably about 5 to 500 μm. Since this coating is formed by thermal spraying, it has many pinholes and a porosity of 0.
It is in the range of 5 to 15%.

The electrode catalyst layer formed on the surface of the sprayed layer is composed of a mixture of iridium oxide and tantalum oxide, and the iridium oxide content is 30 mol% or more, preferably 40 to 90 mol%. If only iridium oxide is used, it tends to dissolve and drop during electroplating, resulting in a shorter electrode life.

For the electrode catalyst layer, an alcohol-soluble metal salt such as iridium chloride, iridium trichloride or tantalum pentachloride is dissolved in a solvent such as ethyl alcohol, butyl alcohol or propyl alcohol to prepare a mixed solution having a predetermined composition, Apply by brushing, roll coating, spray coating or dipping. After application, the solvent is dried at 100 to 150 ° C. for about 10 to 20 minutes to evaporate the solvent, and subjected to thermal decomposition treatment at 360 to 600 ° C., preferably 380 to 550 ° C. for 10 to 30 minutes in an electric furnace in an air or oxygen atmosphere. To do. If the heat treatment temperature is less than the above range, thermal decomposition does not occur completely, and if it exceeds the above range, the titanium substrate and the titanium sprayed layer are oxidized and damaged. When the amount of the electrode catalyst layer coated in this manner is 10 g / m ² (calculated as iridium oxide) or more, both the catalytic ability and the life are improved when oxygen is generated.

The anode used in the present invention preferably has a current density of 10 A / dm ² or more during electroplating, and can be used up to 300 A / dm ² .

[0016]

The function of the electrode composed of the above electrode catalyst layer formed on the titanium sprayed layer in the present invention is long when used as an anode of an electroplating bath containing an organic substance, but it is not clear as follows. There are many possible factors. That is, the electrode catalyst provided by the thermal decomposition method is considerably impregnated in the porous titanium sprayed layer, and the shape of the electrode catalyst layer is also influenced by the shape of the titanium sprayed layer. When the relative surface area of the electrode catalyst layer is determined by the voltammetry method, it is several times to several tens of times larger than in the case where the thermal spray layer is not provided or in the case where the intermediate layer is formed by a method other than the thermal spray method. This has the effect of lowering the electrode potential for oxygen generation, and is believed to lead to an increase in electrode life. Then, the electrode potential is lowered even in an electroplating bath containing an organic substance such as sodium acetate or phenolsulfonic acid. This is considered to make it possible to prevent the abnormal consumption of iridium oxide in organic substances to a considerable extent and to contribute to the extension of the life of the electrode. It is considered that the fact that the sprayed layer is the same metal as the substrate and is appropriately porous also increases the adhesion between the substrate and the electrode catalyst layer.

[0017]

The present invention will be described in detail below with reference to Examples and Comparative Examples.

Example 1, Comparative Example 1 A commercially available titanium plate (1 × 10 × 0.1 cm) was degreased with acetone and then blasted with alumina grit (# 30) at a pressure of 4 kg / cm ^2. It was Next, wire diameter 1.
Perform spraying with an arc sprayer using a 6 mm titanium wire,
A sprayed layer having a thickness of 50 μm was obtained. A solution having the following composition was applied to the surface. Tantalum pentachloride 0.32 g Iridium chloride 1.00 g Hydrochloric acid 0.5 ml Butyl alcohol 10 ml This was dried at 120 ° C. for 20 minutes and then pyrolyzed in an electric furnace at 450 ° C. for 20 minutes to produce Ta ₂ O.
An electrode having a film made of a mixed oxide of ₅ (30 mol%) and IrO ₂ (70 mol%) was obtained. This operation was repeated to obtain an electrode catalyst layer containing 12 g / m ^{2 of} iridium oxide. The adhesion between the electrode catalyst layer and the sprayed layer was very good.

This electrode was mounted in the electroplating tank as an anode at a position 2 cm away from the cathode of the steel plate. 300 g /
1 Synthetic aqueous zinc plating solution containing zinc sulfate (ZnSO ₄ .7H ₂ O), 100 g / l sodium sulfate (pH = 1.2), and 20 g / l sodium acetate was placed in a battery case and the anode current density was 200 A / dm. ^2. Electroplated at 50 ° C. The plating solution was taken out every 7 days and a new plating solution was placed in the battery case. The time until the cell voltage increased by 5 V was determined as the electrode life. With this, the available time is 720
It was time. On the other hand, as a comparison, the sprayed layer was omitted, an electrode catalyst layer was formed on the substrate in the same manner as above, and the same electroplating test was performed. The life of the anode was 350 hours.

Examples 2-5, Comparative Examples 2 and 3 Iridium oxide was formed by forming a thermal sprayed layer on the same titanium substrate as in Example 1 and changing the composition of the electrode catalyst layer as shown in Table 1. As a result, an electrode containing 12 g / cm ² was prepared and the same electroplating test as in Example 1 was conducted. The results shown in Table 1 were obtained.

[0021]

[Table 1]

Example 6 A commercially available titanium plate (1 × 10 × 0.1 cm) was blasted in the same manner as in Example 1, and titanium powder (particle size 20) was used.
˜50 μm) was plasma sprayed using argon gas as the plasma gas to obtain a sprayed layer having a thickness of 25 μm.
An electrode catalyst layer of 12 g / m ² (IrO ₂ : Ta ₂ O ₅ = 70: 30 molar ratio) as iridium oxide was obtained thereon by the same method as in Example 1. When the same electroplating test as in Example 1 was performed, the life of the anode was 740 hours.

[0023]

In the oxygen generating anode used in the method of the present invention, the electrocatalyst layer, which is formed by thermal spraying titanium and is thermally decomposed and coated, has good adhesion to the thermal spray layer and contains an organic substance. Shows excellent durability in electroplating baths. Therefore, when this electrode is used for electroplating a metal using a plating bath containing an organic substance, the excellent effect that the wear due to the dissolution or dropping of the electrode is reduced and the life is prolonged can be obtained.

Claims (4)

[Claims] 1. When electroplating a metal using a plating bath containing an organic substance, a titanium sprayed layer is provided on a titanium substrate as an oxygen generating anode, and the sprayed layer contains 30 mol% or more of iridium oxide. An electroplating method comprising using an electrode provided with an electrode catalyst layer, the balance of which is made of tantalum oxide. 2. The electroplating method according to claim 1, wherein the organic substance is sodium acetate or phenolsulfonic acid. 3. The electroplating method according to claim 1, wherein the plating bath is an acidic aqueous electrolytic solution containing tin or zinc dissolved therein. 4. The electroplating method according to claim 1, wherein the electrode catalyst layer is formed by thermal decomposition of a compound that becomes a catalyst metal.