JPH03260097A - Method of chromium plating using insoluble anode - Google Patents

Abstract

PURPOSE:To reduce production of sludge and to obtain chromium plating films stable for a long time by using such an insoluble anode as the anode that has specified oxygen generation potential and is coated with a film containing platinum group metal. CONSTITUTION:In a plating method using a chromium plating liquid, the anode to be used is such an insoluble anode comprising a corrosion-resistant base body and an electrode coating provided thereon containing platinum group metal and its oxide. The oxygen generation potential of the insoluble anode is specified to 2.2-2.8 volt under standard conditions. Thereby, chromium plating is performed while maintaining 6-8g/l trivalent chromium. Contamination of the plating liquid due to lead sludge in a conventional method using a lead insoluble electrode can be prevented by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a chromium plating method, and more particularly to a method for industrial chromium plating using an insoluble anode.

(Prior art) The plating bath used for chromium plating consists of chromic anhydride as a main component and a small amount of sulfuric acid or sulfate added thereto, or a sergeant bath, or ammonium fluoride, hydrofluoric acid, fluoroboric acid, sodium silicofluoride, etc. A fluoride-containing bath replaced with a fluorine compound of ) etc.

Although the plating method using a Sargent bath allows easy handling of the solution, it has the disadvantage of low current efficiency. Plating methods that use fluoride-containing baths are characterized by a good finish and relatively high current efficiency, but they are difficult to control due to poor bath stability, and also have low current due to the presence of fluoride ions. Density operation has the drawback of causing corrosion of the plated material.

In contrast to these plating methods, the plating method using a HEEF bath does not corrode the plated object at low current densities and exhibits high current efficiency over a wide range of current densities, so it emphasizes electrodeposition speed and improves productivity. It has come to be widely used in the chrome plating industry, where improving the quality is paramount.

(Problems to be Solved by the Invention) On the other hand, as electrodes used for chromium plating, electrodes such as lead alloy electrodes and lead dioxide coated electrodes are known.

In particular, electrodes in which lead dioxide is coated on a conductive substrate such as titanium through an intermediate layer of platinum group metals and their oxides have less electrolytic consumption and generate less sludge than lead alloy electrodes. This makes it widely used in the plating industry.

However, these lead alloy electrodes or lead dioxide coated electrodes are heavy and have poor workability when replacing the electrodes.In particular, in the case of lead alloy electrodes, lead chromate, the main component of the generated sludge, cannot be safely disposed of as waste fluid in accordance with pollution regulations. It has drawbacks such as the need to

On the other hand, the surface of a conductive metal substrate such as titanium containing one or more platinum group metals such as platinum, iridium, and rhodium and their oxides, or oxides such as titanium and tin, can be prepared by thermal decomposition. Noble metal coated electrode (
It is known that noble metal electrodes (hereinafter simply referred to as noble metal electrodes) exhibit an extremely lower polarization potential than lead electrodes such as lead alloy electrodes and lead dioxide-coated electrodes when plated with chrome. However, this electrode has a low ability to oxidize trivalent chromium to hexavalent chromium;
Although sufficient plating is possible in the initial stage, it is not possible to perform ROM plating continuously.

Generally, when electrodepositing chromium, it is important to include a small amount of trivalent chromium in the chromium plating bath, and it is necessary to adjust the concentration of trivalent chromium in order to achieve high-quality plating. When plating is performed in a chromium plating bath, trivalent chromium is generated at the cathode (the object to be plated), and is oxidized at the anode to become hexavalent chromium, that is, chromic acid. This reduction and oxidation effect is not uniform depending on the electrode material used.
Trivalent chromium reaches equilibrium at a certain concentration. As mentioned above, noble metal electrodes have a low ability to oxidize trivalent chromium, and if plating continues, the trivalent chromium concentration in the electrode will increase, resulting in poor plating, and the sliding voltage will increase, reducing current efficiency. There's a problem.

In chromium plating using Sargent bath, it is possible to solve the above problems, consume less electricity, generate less sludge, and perform stable chromium plating for a long time without frequently adjusting the trivalent chromium concentration. As a method for achieving this, a method has been proposed in which a lead dioxide-coated electrode and an iridium dioxide electrode are used in combination, and plating is performed by effectively utilizing the characteristics of the picture electrode (Japanese Patent Laid-Open No. 63-270490).
) However, when this method is carried out in a HEEF bath, etc.
Unsubstituted alkyl sulfonic acid salts, boric acid, and the like are adsorbed to the electrode surface and increase the electrode potential, resulting in severe wear and a short lifespan.

In addition, this method has the disadvantage that the oxygen generation potentials of the lead dioxide electrode and the iridium dioxide electrode are different, so unless the arrangement of both electrodes is carefully arranged, the current flow to the electrodes will be uneven, resulting in uneven plating. Ta.

Other methods of chrome plating have also been proposed. This method uses an electrode in which a platinum coating is formed on a substrate such as titanium, a base metal oxide is coated on the base metal oxide as an intermediate layer, and lead dioxide is further coated on the base metal oxide (Japanese Patent Application Laid-Open No. 1999-1-1992). 184299). In this method, lead dioxide is consumed during the chrome plating process, so a lead component is added to the plating process. According to this method, chromium plating can be performed using one type of electrode, but due to poor adhesion between the platinum coating and the base metal oxide in the intermediate layer, the intermediate layer falls off and the platinum coating is exposed in a few months. This has the disadvantage that trivalent chromium increases, making it unusable.

(Means for Solving the Problems) As a result of various studies, the present inventors have found that in plating operations using a chromium plating bath, the oxygen evolution potential under standard conditions is 2.2 to 2.8 volts as an anode, and corrosion resistance. It has been discovered that a chromium plating method using an insoluble anode in which an electrode coating containing a platinum group metal and/or an oxide thereof is provided on a substrate solves the above problems, and the present invention has been completed.

If the oxygen evolution potential of the insoluble anode used in the present invention is lower than 2.2 volts, the ability to oxidize trivalent chromium to hexavalent chromium is low, which is undesirable. This is undesirable because the voltage becomes high and may exceed the capacity of the rectifier being used.

In the present invention, the oxygen evolution potential under standard conditions refers to the oxygen evolution potential at a current density of 30 A/dm2 in a 1 molar sulfuric acid solution at 25 DEG C. with reference to a silver-silver chloride electrode.

The present invention will be explained in detail below.

The corrosion-resistant substrate in the present invention is not limited in any way as long as it has corrosion resistance during anodic polarization during plating and has electrical conductivity. For example, titanium or titanium alloys are best suited for use in Sargent baths or HEEF baths. In fluoride-containing baths, titanium is not corrosion resistant, so
Materials that are resistant to corrosion by fluorides, such as JP-A-57-79
Titanium lower oxide (TxOs: 1.5
An electrically conductive sintered body having the following relationship (5≦X≦1,9) can be used. The shape of the base may be a flat plate, an expanded mesh, or a perforated plate.

Next, the platinum group metals and their oxides in the present invention will be explained.

Conventional electrodes coated with platinum group metals and/or their oxides have a low oxygen evolution potential. Even the highest platinum plated titanium electrode is 2.0 volts under standard conditions. Iridium oxide and rhodium oxide have a lower oxygen evolution potential than platinum.

Therefore, in order to increase the oxygen generation potential, a base metal oxide is included in the coating of platinum group metals and/or their oxides.

The platinum group metal is preferably platinum, and the platinum group metal oxide is preferably iridium oxide or rhodium oxide. Ruthenium and palladium have poor durability against oxygen generation, so
Even if it is used, it is only in a small proportion, and it is preferable not to use it. As the base metal oxide, oxides of titanium, tantalum, niobium, zirconium, bismuth, antimony, tungsten, tin, etc. are preferable.

As a method for forming a coating containing a platinum group metal or the like and a base metal oxide, known methods such as a thermal decomposition method, a vacuum evaporation method, and a plasma spraying method can be applied. Industrially, thermal decomposition is widely used as a method for producing insoluble anodes. The method will be described below.

A coating solution is prepared by adding hydrochloric acid, if necessary, to a salt of a platinum group metal such as chloroplatinic acid, iridium chloride, or rhodium chloride, and mixing a base metal chloride or alkoxide with alcohol. This coating solution was applied onto a corrosion-resistant substrate, and
Decomposes by heating at 0-600°C. This operation can be repeated several times to obtain a coating of any desired thickness.

The base metal content to obtain an electrode coating exhibiting an oxygen evolution potential of 2.2 to 2.8 volts under standard conditions varies considerably depending on the combination of platinum group metals and/or their oxides and base metal elements used; -Cannot be generalized.

Furthermore, in the plating method of the present invention, by making lead ions present in the plating solution, a thin film of lead dioxide can be formed on the surface of the electrode, thereby protecting the electrode.

(Examples) The present invention will be explained in detail below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Iridium chloride and pentanormal butoxytantalum were added in a molar ratio of I to a titanium substrate whose surface was roughened by sandblasting a titanium plate between 15+aa+X 200mm
They were weighed and mixed so that r02: Ta20s=3:7, a coating solution containing a small amount of hydrochloric acid and butanol was applied, and after drying, it was heated at 500° C. for 1 hour. This operation was repeated until IrO2 reached 10 g/m2. The oxygen evolution potential of this electrode under standard conditions was 2.3 volts.

Example 2 Iridium chloride and pentanormal butoxytantalum were added in a molar ratio of I to a titanium substrate obtained by etching a titanium plate of 15 m + a x 200 mm x 1 am with hot oxalic acid.
They were weighed and mixed so that r02:Ta203=2:8, a coating solution containing a small amount of hydrochloric acid and butanol was applied, and after drying, it was heated at 500° C. for 1 hour. This operation was repeated until IrO2 reached 8 g/m2. The oxygen evolution potential of this electrode under standard conditions was 2.6 volts.

Example 3 Chloroplatinic acid, chloroiridic acid, pentanormal butoxytantalum, and stannic chloride were added to a titanium substrate obtained by etching a 15m Peng x 200 mm x 1 Pengyuan titanium plate with 5% hydrofluoric acid in a molar ratio of pt:IrO2. :Ta20
Weigh and mix so that the ratio is 5:5n02 = 1:2:6:1, and apply a coating solution containing a small amount of hydrochloric acid and butanol.
After drying, it was heated at 500°C for 1 hour. This operation was repeated until IrO2+Pt reached 15 g/m2. The oxygen evolution potential of this electrode under standard conditions was 2.3 volts.

Example 4 Chloroplatinic acid, iridium chloride, pentanormal butoxytantalum, and butyl orthotitanate were weighed onto a titanium substrate prepared by etching a 15 mm x 200 m x 1-hole titanium plate with hot oxalic acid, and the molar ratio of Pt:IrO2: T
They were weighed and mixed so that a205:Ti02=2+2:5:1, a coating solution containing a small amount of hydrochloric acid and butanol was applied, and after drying, it was heated at 500° C. for 1 hour. IrO2+
This operation was repeated until the amount of Pt was 15 g/m2.

The oxygen evolution potential of this electrode under standard conditions was 2.4 volts.

Example 5 A titanium plate of 15 x 200 x 1 mm was etched with 5% hydrofluoric acid as a titanium substrate, and tantalum chloroplatinate and stannic chloride were added in a molar ratio of I.
They were weighed and mixed so that r02: Ta205: 5n02 = 1:6:3, a coating solution containing a small amount of hydrochloric acid and butanol was applied, and after drying, it was heated at 500° C. for 1 hour. 15 as I r02+Ta205+ S n 02
This operation was repeated until it reached g/m2. The oxygen evolution potential of this electrode under standard conditions was 2.5 volts.

Example 6 Under the same conditions as Example 5, I r 02: T a2o5
:5nO2=1:7:2 An electrode having a coating was prepared. The oxygen evolution potential of this electrode under standard conditions was 2.4 volts.

Example 7 A 15 mm x 200 mm x 1 am titanium plate was etched with hot oxalic acid to form a titanium substrate, and chloroplatinic acid, iridium chloride, and pentanormal butoxy tantalum were added in a molar ratio of P t : I r02 : Ta20s=1
A coating solution containing a small amount of hydrochloric acid and butanol was applied, dried, and then heated at 450° C. for 1 hour. Ta205+ I r020pt as 1
This operation was repeated until it reached 5 g/m2. The oxygen evolution potential of this electrode under standard conditions was 2.4 volts.

Comparative Example 1 On a titanium substrate etched in the same manner as in Example 2, iridium chloride and pentanormal butoxytantalum were weighed and mixed in a molar ratio of I r Q2: Ta203 = 4:6, and a small amount of hydrochloric acid and butanol were added. Apply a coating solution containing IrO2, dry it, and heat it at 500℃ for 1 hour.
This operation was repeated until Log/Sono 2 was obtained.

The oxygen evolution potential of this electrode under standard conditions was 2.1 volts.

Comparative Example 2 A titanium substrate etched in the same manner as in Example 3 was coated with chloroplatinic acid, chloroiridic acid, pentanormal butoxytantalum, and stannic chloride in a molar ratio of Pt:I r02:
Ta205: 5n02=1:4:4:1
A coating solution containing a small amount of hydrochloric acid and butanol was applied, and after drying, it was heated at 500° C. for 1 hour. This operation was repeated until IrO2+pt was 15 g/m2. The oxygen evolution potential of this electrode under standard conditions was 2.0 volts.

Comparative Example 3 Iridium chloride and butyl orthotitanate were added to a titanium plate etched in the same manner as in Example 4 in a molar ratio of IrO2:T.
Weigh and mix so that i02 = 5:5, apply a coating solution containing a small amount of hydrochloric acid and butanol, dry, heat at 500°C for 1 hour, and repeat this operation until IrO2 is 10 g/plate 2. Ta. The oxygen evolution potential under standard conditions was 1.9 volts.

Comparative Example 4 Under the same conditions as Example 7, Pt:IrO2:Ta20s=
Electrodes with a coating of 80:11:9 were prepared. The oxygen evolution potential of this electrode under standard conditions was 2.0 volts.

Plating operation experiment Using a high-speed chrome plating bath manufactured by Japan M&T Co., Ltd., the anode area and cathode area were both 30e112,
24 at 30A/d+s2 using 5US304 for the cathode
Under the conditions of time continuous electrolysis, Examples 1 to 7, Comparative Examples 1 to 4,
Chrome plating was performed using a commercially available platinum-plated titanium electrode (Pt/TI) as an anode.

Table 1 shows the amount of trivalent chromium in the plating after 24 hours.

(Effects of the invention) In chromium plating operations where lead alloys were conventionally used, trivalent chromium can be coated with 6 to 8 volts of trivalent chromium using a non-lead insoluble electrode with an oxygen evolution potential of 2.2 volts or more under standard conditions.
The present invention makes it possible to carry out chromium plating while maintaining g/I, thereby making it possible to prevent liquid contamination by lead sludge.

Claims (1)

[Claims] 1. In a plating operation using a chromium plating bath, as an anode, the oxygen evolution potential under standard conditions is 2.2 to 2.
A chromium plating method characterized in that it is 8 volts and uses an insoluble anode having an electrode coating containing platinum group metals and/or their oxides on a corrosion-resistant substrate.