JPH0220709B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a hydrazine-type plating bath for electroless plating of iridium onto the surface of metal or non-metallic materials.

Purpose of the invention The purpose of the present invention is to provide extremely excellent stability of the bath liquid.
It is an object of the present invention to provide a novel electroless plating bath for iridium which has a high plating speed and a high utilization rate of iridium.

Prior Art Thermal decomposition method, molten salt plating method, etc. are known as methods for coating metal surfaces with iridium.

The former is a method of applying a mixed solution of iridium chloride, alcohol, etc. to the metal surface and then thermally decomposing it to obtain an iridium film.The latter is a method of obtaining an iridium film by electroplating from a molten salt bath using KIr(CN) ₄ . This method is used to obtain an iridium coating.

However, these methods are not sufficient when the shape of the object to be coated is complex, and it is extremely difficult to apply them to polymeric materials with low heat resistance.

Therefore, there is a need for the development of an iridium coating method, especially a chemical plating method, that can be applied to metals with complex shapes or polymeric materials with low heat resistance, but there are very few reports on this to date. .

Furthermore, there is no chemical plating method for platinum group metals other than iridium that can be directly applied to iridium.

The present inventor has previously shown that a bath solution consisting of iridium chloride and dialkylamine borane can be used (Japanese Patent Application Laid-Open No. 134586/1986).

However, as will be described later, in the dialkylamine borane type bath liquid, the plating speed is slow because the alkylamine, which is a decomposition product of dialkylamine borane, acts as a control agent, and the stability of the bath liquid is insufficient. The utilization rate of iridium was also unsatisfactory in that it was not necessarily sufficient.

Solution The present inventor has conducted detailed research on the electroless plating method for iridium in comparison with other platinum group metals such as platinum, rhodium, palladium, ruthenium, etc.
It was found that the precipitation rate of iridium is strongly influenced by the composition of the bath solution, especially the coexisting ions, and its behavior is significantly different from that of other platinum group metals.

That is, in the case of iridium, unlike other platinum group metals, ammonium ions, alkyl amines, etc. act as inhibitors that significantly slow down the precipitation rate. For this reason, bath solutions containing ammine complex ions, ammonium ions, alkyl amines, etc. used in electroless plating baths of platinum, palladium, rhodium, ruthenium, etc., or nitro complex salts that generate ammonium ions during the reaction process. ,
It has also been found that bath solutions in which nitroso complexes, nitrates, etc. are present are also undesirable.

Therefore, the inventor of the present invention has continued to conduct further intensive research, and in particular, has investigated ring-forming agents that can replace dialkylamine borane.As a result, the inventors have found that when using an iridium halide, especially in combination with hydrazine as a reducing agent, the bath is extremely stable at pH 3 to 10. These plating baths have a high plating speed and can be suitably used not only for metals but also for a wide range of non-metallic materials. Because the bath solution is stable, it can be stored at room temperature for several weeks without adding hydroxylamine salts, and for two to three times as long in cases with added hydroxylamine salts, without self-decomposition (precipitation, etc.); It was discovered that the utilization rate of iridium was also sufficiently high, and the present invention was completed.

Structure of the Invention The present invention contains an iridium electroless plating bath characterized by containing an iridium halide and hydrazine and having a pH of 3 to 10, and an iridium electroless plating bath containing an iridium halide, hydrazine and a hydroxylamine salt and having a pH of 3 to 10. The present invention relates to an iridium electroless plating bath characterized in that the iridium is 10 to 10.

Examples of iridium halides used in the present invention include iridium halides (), iridium halides (), hydrates thereof, halogenated iridic acids, potassium halogenated iridium () acids, and halogenated iridium () acids. Sodium, iridium halide ()
Examples include alkali metal salts of halogenated iridic acid such as potassium acid and sodium halogenated iridium() acid, and at least one of these is used. As the halogen, chlorine or bromine is preferred. Particularly preferred among the above are potassium chloroiridate () (K ₃ IrC ₆ ), which has a constant chemical composition and has a relatively slow hydrolysis rate in an aqueous solution, and potassium chloride () () (K ₂ IrC ). ₆ ) etc.

As the hydrazine in the present invention, hydrazine that becomes hydrazine in an aqueous solution state, such as hydrazine hydrate, hydrochloride, sulfate, etc., can be suitably used.In addition, in the present invention, in order to further stabilize the bath liquid, The hydroxylamine salt used is preferably a water-soluble salt such as a hydrochloride or a sulfate.

The bath solution composition of the present invention is 2.5×10 ^-3 to 5× iridium chloride as an iridium concentration.
10 ^-2 M/(0.1~10g/) preferably 2.5×
10 ^-3 to 2.5×10 ^-2 M/(0.1 to 5 g/), and hydrazine 0.003 to 1.5 M/(in the case of hydrate,
0.15~75g/) preferably 0.003~0.3M/
(0.15 to 15 g/in the case of hydrates). Also,
When using a hydroxylamine salt, the concentration is 0.0014 to 0.7 M/(in the case of hydrochloride, 0.1 to 50 g/) as hydroxylamine, preferably 0.0014
~0.14M/(for hydrochloride, 0.1~10g/)
It is.

In the present invention, the bath solution having the above composition is prepared using an acid such as hydrochloric acid, an alkali such as sodium hydroxide, a PH buffer solution, etc., as necessary, to a pH of 3 to 10, preferably 4.
Use by keeping it within the range of ~9.5.

In the present invention, the pH during plating is an important factor related to the stability of the bath liquid and the plating speed, and the pH
is larger than 10, hydrolysis progresses in the bath solution, and [IrC
₄ (OH) ₃ ] ^2- , [IrC ₂ (OH) ₄ ] ^2- , Ir(OH) ₃ C, IrO ₂ .nH ₂ O, etc. are generated, and as a colloidal precipitate, iridium grows. If the pH is less than 3, the plating speed becomes very slow, which is not preferable.

The plating temperature is about 50~100℃, preferably 60~
Performed at 90°C.

At temperatures below 50°C, the growth rate of pine wood slows down,
At temperatures above 100°C, the amount of evaporation of the bath liquid tends to increase, which is unfavorable from an operational point of view.

As the plating temperature increases, self-decomposition of the bath liquid becomes more likely to occur, but when a hydroxylamine salt is used, it exhibits an effect as a stabilizing agent.

When an object to be plated whose surface has been activated in advance is immersed in the plating bath of the present invention thus prepared, iridium selectively grows on the surface and does not precipitate in the bath liquid or on the walls of the plating tank.

The objects to which the plating bath of the present invention can be applied include metals such as copper, nickel, iron, alloys thereof, electronic parts such as steel titanium and tantalum, and industrial materials such as electrode materials. Also, acrylonitrile-butadiene-styrene copolymer (ABS)
It can be applied to materials that can be conventionally electroless plated, such as resins, synthetic resins such as polyamide resins and carbonate resins, glass, and ceramics. Further, the plating bath of the present invention is particularly suitable as a bath solution for bonding iridium to the membrane surface of a polymer membrane such as an ion exchange membrane. Such a bonded body is used in water electrolysis, halogen acid electrolysis, halide electrolysis, etc. as solid polymer electrolyte electrolysis methods.

In either case, it is preferable that the object to be plated be subjected to a surface activation treatment in advance.

In the case of metal, after surface cleaning, it is immersed in an aqueous salt solution of palladium, platinum, rhodium, ruthenium, gold, silver, etc., and if necessary, it is subsequently activated by immersion in a boron hydride salt aqueous solution, etc. Immerse in the plating bath of the present invention.

In the case of polymer materials, glass, and ceramics,
Normally, these surfaces are subjected to surface hydrophilicization, sensitization treatment, and activation treatment similar to those for the above metals, which are used when chemically plating copper, nickel, etc., and then applied to the plating bath of the present invention. Soak.

In addition, in the case of polymer membranes such as ion exchange membranes,
After the surface is roughened, a solution of metal salts (for example, salts of platinum, palladium, rhodium, iridium, ruthenium, etc.) is adsorbed, and then cyclized with a sodium borohydride solution, hydrazine solution, etc.
After forming a first layer of about 1 μm, it is immersed in the plating bath of the present invention to grow an iridium layer.

Effects of the Invention According to the present invention, the following particularly remarkable effects can be obtained.

(1) The plating bath is extremely stable. That is, the novel electroless plating bath of the present invention exhibits extremely excellent stability without self-decomposition even when stored at room temperature for several weeks or more when the object to be plated is not immersed. In addition, when hydroxylamine salt is added, the stability is further increased, and under the above conditions, the above 2 to 3
It will not self-decompose for three times as long.

(2) The plating speed is extremely high. For example, if the plating temperature is 80 DEG C., only 2 to 3 hours is sufficient to complete iridium plating with a thickness of 2 .mu.m.

(3) The utilization rate of iridium is sufficiently high. Moreover, it can be suitably used not only for metals but also for non-metallic materials.

Examples Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A solution having the following composition was prepared using potassium hexachloroiridate().

K ₂ IrC ₆ (Ir content, 39.7%) 250 mg NH ₂ OH・HC (5% aqueous solution) 20 ml N ₂ H ₄・H ₂ O (20% aqueous solution) 8 ml Water Total volume 200 ml Nickel sample (5 x 5 x 0.1 cm) was degreased with alkali, immersed in a solution consisting of 2 g of PHC ₃ , 10 ml of HC, and 1 part of water, then washed with water, and then immersed in a 0.5% NaBH ₄ aqueous solution for activation treatment.

This activated sample was immersed in the above iridium plating bath and plated at 75° C. for 3 hours while adjusting the pH to 7.7±0.1 with 0.1N HC to obtain an iridium plating layer of about 0.5 μm.

Example 2 A solution having the following composition was prepared using potassium hexachloroiridate().

K ₃ IrC ₆・3H ₂ O 300mg (Ir content, 33.3%) NH ₂ OH・HC (5% aqueous solution) 20ml N ₂ H ₄・H ₂ O (20% aqueous solution) 10ml Water Total amount 200ml ABS resin (Japanese synthetic rubber The surface of a plate-like sample (3 x 4 cm) with a thickness of 2 mm (manufactured by Co., Ltd.) was activated using known chromic acid etching, a catalyst bath, and an activation bath.

Then, it was immersed in a bath solution with the above composition at 70°C for 3 hours,
During this time, the pH was maintained at 6.8 using 0.1N HC. As a result, an iridium layer with a thickness of approximately 1 μm was obtained.

Example 3 A solution having the following composition was prepared using hexachloroiridic acid.

H ₂ IrC ₆・6H ₂ O 272 mg (Ir content, 36.8%) N ₂ H ₄・H ₂ O (20% aqueous solution) 8 ml Water Total volume 200 ml PH (adjusted with 0.1N HC) 6.5 Alumina ceramic plate (3 cm x 3cm x 0.2cm)
was activated according to the following procedure.

Acetone cleaning → water washing → immersion in 0.5% ammonia aqueous solution of tetraamminepalladium chloride [Pd(NH ₃ ) ₄ ]C ₂ → water washing → immersion in 11% NaBH ₄ aqueous solution → water washing.

Then, soak it in the above iridium plating solution for 80 minutes.
It was kept at ℃ for 2.5 hours. As a result, an approximately 1 μm iridium layer was obtained on the ceramic surface.

Example 4 A solution having the following composition was prepared using sodium hexachloroiridate().

Na ₂ IrC ₆・6H ₂ O 600mg (Ir content, 34.2%) NH ₂ OH・HC (10% aqueous solution) 20ml N ₂ H ₄・H ₂ O (20% aqueous solution) 15ml Water Total volume 400ml PH (0.1N HC) 8.0 Perfluorocarbon sulfonic acid type cation exchange membrane [manufactured by Dupont, "Nafion 117", film thickness 7
Iridium was bonded to both sides of a circular part (approximately 50 cm ² ) with a diameter of 80 mm using a mill (approximately 0.175 mm).

The surface of the membrane was first roughened by sandblasting, then boiled with 4N HC and then washed with hot water.

The pretreated membrane was sandwiched between acrylic resin Metxel, and a tetraammineplatinum () salt solution [Pt(NH ₃ ) ₄ )] ²⁺ , (50mg/Pt) was added to both sides of the membrane.
100ml) and left it for 2 hours to absorb.

Then, after washing with water, ammonia NaBH ₄ 0.05%
An aqueous solution was added thereto, and the mixture was cyclized at 40 to 60° C. for 2 hours to deposit a platinum layer of about 0.5 μm on the surface of the membrane.

Next, an iridium plating solution having the above composition was circulated through the Metxel, and during this time the temperature and pH were maintained at 80°C and 8.0±0.1. After 3 hours, an iridium layer of about 0.7 μm was obtained.

Example 5 A solution having the following composition was prepared using potassium hexachloroiridate().

K ₃ IrC ₆・3H ₂ O 900mg (Ir content, 33.5%) NH ₂ OH・HC (10% aqueous solution) 20ml N ₂ H ₄・H ₂ O (20% aqueous solution) 20ml Water Total volume 400ml PH (0.1N HC) 8.0 Perfluorocarbon sulfonic acid membrane [manufactured by Dupont, "Nafion 125", membrane thickness 5 mil (approx. 0.127 mm)]
Iridium was bonded to the 80mm diameter part using a .

The membrane was pretreated in the same manner as in Example 4, sandwiched between Metxel, and an ammoniacal aqueous solution of pentaammine rhodium () salt [Rh(NH ₃ ) ₅ C]C ₂ (50 mg as Rh) was added to the chambers on both sides of the membrane. /100ml) was added for adsorption.

Then, in the same manner as in Example 4, ring formation was performed with an aqueous sodium borohydride solution, and about 1 μm of rhodium was bonded to the membrane surface.

Next, a bath solution having the above composition was sent to Metxel and reacted at 80°C while being circulated. After 3 hours, a bonded body with an iridium layer of about 1 μm was obtained.

Claims (1)

[Scope of Claims] 1. An iridium electroless plating bath containing an iridium halide and hydrazine and having a pH of 3 to 10. 2. An iridium electroless plating bath containing an iridium halide, hydrazine and hydroxylamine salt, and having a pH of 3 to 10.