JPH0421794A - Composition having low melting point and aluminum electroplating method - Google Patents

Abstract

PURPOSE:To facilitate the handling of a plating bath and to enable efficient Al electroplating by using a compsn. having a low m.p. prepd. by mixing Al halide with specified tetraalkylphosphonium halide as the plating bath. CONSTITUTION:Al halide is mixed with tetraalkylphosphonium halide represented by the formula, wherein each of R<1> to R<4> is 1-12C alkyl and X is halogen, to prepare a compsn. having a low m.p. and Al electroplating is carried out with the compsn. as a plating bath. The compsn. becomes an easily handleable liq. at ordinary temp. and has high ionic conductivity in a molten state. Since tetraalkylphosphonium cations are electrochemically stable, plating can be carried out at a higher temp. and high current density.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a novel low-melting, aluminum-containing composition containing aluminum and a method for efficiently electroplating aluminum using this composition.

(Prior Art) It is difficult to perform electroplating of aluminum in a liquid-based plating bath because aluminum has a large affinity for oxygen and has a lower potential than hydrogen. For this reason, aluminum electroplating has traditionally been non-aqueous liquid plating.
Studies are currently being conducted on plating baths, especially those using Ariiso beach medium.

Examples of the organic sanding medium-based plating resin include aluminum chloride and LiAj2H4 or LiH dissolved in ether, and 4 to ffc12. and LiAffH.

A typical example is a dropwise solution of
trochem, 999(6), p. 234). However, all of these plating layers are exposed to highly active Li.
Because it contains AffH or L-H, if oxygen or moisture is present, it reacts with them and decomposes, reducing the current efficiency and shortening the lifespan of the battery. The organic solvent used has a low boiling point, which poses a problem in that there is a high risk of explosion or combustion.

Furthermore, as another example, triethylaluminum and N
A plating method in which aF is dissolved in toluene has also been proposed (
R, 5uchentrunkZ, Werkstofft
ech, Vol. 12, p. 190) However, in this case as well, the handling of triethylaluminum, which is highly dangerous, is extremely problematic, and it is considered difficult to put it into practical use.

(Problem to be solved by the invention) Although the above-mentioned conventional technology has succeeded in the problem of electroplating aluminum, it cannot be widely used as a practical technology due to the difficulty in handling the chemical substances used. It's hard to call it a thing.

(Means for Solving the Problems) The present invention provides a low melting point composition that is easy to handle and can be efficiently used for aluminum electroplating, and an electroplating method using the bath.

The present invention provides an aluminum halide and a tetraalkylphosphonium represented by the following formula (wherein R', R'', R3 and R4 each represent an alkyl group having 1 to 12 carbon atoms, and X represents a halogen atom). The present invention is a low melting point composition characterized by being mixed with a halide, and an electrolytic aluminum plating method using this low melting point composition as a plating bath.

Specific examples of the tetraalkylphosphonium halides used in the present invention include tetramethylphosphonium bromide, tetraethylphosphonium chloride, tetrapropylphosphonium bromide, methyltriethylphosphonium chloride, diethyldimethylphosphonium bromide, ethyltrimethylphosphonium bromide, and hexyltrimethylphosphonium bromide. , phthyltribrovirphosphonium chloride, and the like.

Also, aluminum halide is 1, = lX3 (
(X represents a halogen atom), specific examples include 61F, Aj2C13, AffBrxP, and A 12 Ia.

The composition of the present invention can be made into a low melting point composition by mixing 20 to 80 mol% of aluminum halide and 80 to 20 mol% of tetraalkylphosphonium halide.

In particular, in order to efficiently carry out electrolytic aluminum plating using the above composition as a plating bath, the preferred composition ratio is 50 to 75 mol% of aluminum halide and 25 to 50 mol% of tetraalkylphosphonium halide.
, more preferably the aluminum halide is 55-7
0 mole % and 30-45 mole % of tetraalkylphosphonium halide. A system containing too little aluminum halide may cause a reaction in which the tetraalkylphosphonium cation decomposes, while a system containing too much aluminum halide tends to increase the viscosity of the plating bath, which is not preferred.

For example, a composition of aluminum chloride and ethyltoptylphosphonium bromide is liquid at room temperature and has a fairly low viscosity in the aluminum chloride concentration range of 60 to 75 mol%.

The novel composition of the present invention is prepared by mixing and melting an aluminum halide and a tetraalkylphosphonium halide.

- It can be carried out by a method consisting of 22 steps described below.

As the first step, the alkyl halide and trialkyl phosphine are charged into an autoclave equipped with a stirrer together with a reaction solvent, and heated to a temperature of 20 to 200°C, preferably 50 to 150°C.
After the reaction is carried out at 0.degree. C. for quaternization, the solvent and unreacted substances are removed to obtain a tetraalkylphosphonium halide. As the reaction solvent in this case, hydrocarbon solvents such as benzene, toluene, and hexane, polar solvents such as water, methanol, ethanol, tetrahydrofuran, dimethylformamide, and dimethyl sulfoxide, etc. can be used.

In the second step, the tetraalkylphosphonium halide and aluminum halide produced in the first step are mixed in a predetermined amount and heated in an inert gas atmosphere, or
The desired composition can be produced by heating and mixing both in a state in which they are suspended in an appropriate solvent, and then removing the solvent.

In either case, considerable heat is generated during mixing, so
Care must be taken to ensure that the reaction temperature does not run out of control.

Electroaluminum plating is generally performed in a dry, oxygen-free atmosphere from the viewpoint of maintaining the stability of the plating bath and the plating properties. Plating conditions include bath temperature of 0 to 300°C and current density of 0.01 to 5.
When carried out at 0 A/dm2, uniform plating can be achieved with good current efficiency. If the bath temperature is too low, uniform plating will not be achieved, and if the bath temperature is too high or the current E degree is too high, the quaternary phosphonium cations will decompose, the plating layer will become uneven, and the current efficiency will decrease. occurs and is not desirable.

When uniformly and continuously plating strips, etc., it is necessary to replenish the plating bath with AJ2 ions to maintain the Aff ion concentration within a certain range. AI2 ions are automatically replenished, without depending on aluminum halide replenishment! The ion concentration can be maintained within a certain range.

When plating efficiently at low temperatures, it is effective to add an organic solvent to the plating bath in order to reduce the viscosity of the plating valleys. In this case, the organic solvent is preferably an inert solvent such as benzene, toluene, xylene, or chlorobenzene, and is usually used in an amount of 5 to 95Vo1%.

Furthermore, in order to increase the conductivity of the plating bath or to make the aluminum plating layer uniform, it is also effective to add an alkali metal or alkaline earth metal halide. In this case, examples of alkali metal or alkaline earth metal halides include LiCff, N
Examples include aCff, NaF, CaCff2, etc., and these compounds are usually added to the plating bath in an amount of 0.1 to 30 mol%.

(Example 1) 1.0 mol (202.3 g) of tributylphosphine, 11 mol (1199 g) of ethyl bromide, and 100 g of methanol as a solvent were charged into a glass reactor and reacted at 60°C for 5 hours with stirring. The solvent and unreacted substances were distilled off from the 0 reaction product using a rotary evaporator to obtain 308.1 g of a solid. This solid substance was ethyltributylphosphonium bromide, and the reaction yield based on tributylphosphine was 99 mol%.

Next, 31.1 g (0.10 mol) of the obtained ethyltributylphosphonium bromide was placed in a glass reactor under a nitrogen atmosphere, and 26.6 g (0.10 mol) of aluminum chloride was added to the glass reactor.
, 20 mol) were gradually mixed. By introducing aluminum chloride, a reaction occurs at the solid interface with ethyltributylphosphonium bromide, and liquefaction gradually progresses. However, this reaction is accompanied by heat generation, so be careful not to let the reaction temperature exceed 70°C. All aluminum was added. This mixture is liquid at room temperature and has an electrical conductivity of 25°C.
It showed 1.3 mS/cm.

In addition, in this system, the molar ratio of aluminum chloride and ethyltributylphosphonium bromide was changed from 1.5 to 2.
Table 1 shows the relationship between temperature and conductivity when the temperature is changed up to 0. As is clear from Table 1, this composition exhibits high electrical conductivity and is excellent as an electrolytic aluminum plating bath.

Table 1 Relationship between temperature and conductive ring Molar ratio 1.50 1.75 2.00 Temperature 25 ("C) 0.5 1.1 1.3
30 0.7 1.4 1
．． 540 1.6 2.0
2.150 2.3 2.7
2.960 3.4 3.7
3.9 (Example 2) Tetrapropylphosphonium bromide was synthesized from tripropylphosphine and propyl bromide by the same reaction method as in Example 1.

The obtained tetrapropylphosphonium bromide was mixed with aluminum chloride in the same manner as in Example 1.

In this system, Table 2 shows the relationship between temperature and conductive ring when the molar ratio of aluminum chloride and tetrapropylphosphonium bromide was varied from 1.5 to 20.

Table 2 Relationship between temperature and conductive ring Molar ratio 1.50 1.75 2.00 Temperature 40 ("C) 2.1 3.0 3.6
50 3.0 4.4 4
．． 860 4.9 5.9
6.370 6.8 7.6
8.1 (Example 3) A cold-rolled steel plate with a thickness of 0.5 mm was subjected to solvent vapor cleaning by a conventional method.
Immediately after drying the product which had been subjected to alkaline degreasing and pickling, it was immersed in an electrolytic aluminum plating bath using the composition shown in the above example, which had been previously kept in a nitrogen atmosphere.

After that, a cold-rolled steel plate was used as a cathode, and an aluminum plate (purity 99.
99%, plate thickness 1.0 mm) was used as an anode, and aluminum plating was performed on a cold rolled steel plate by direct current.

The plating bath of Example 1 having a composition in which the molar ratio of aluminum chloride and ethyltributylphosphonium bromide was 20 was used as the plating bath, and the electrolytic conditions were a temperature of 50°C and a current density of IA/dm2. When plating was performed for 30 minutes, a dense aluminum plating with a plating layer thickness of 10 microns was obtained with a current efficiency of 95% or more.

(Example 4) Aluminum plating was performed on a cold rolled steel sheet in the same manner as in Example 3 using the plating bath having a composition in which the molar ratio of aluminum chloride and tetrapropylphosphonium bromide was 20 as described in Example 2.

The electrolytic conditions were a bath temperature of 150°C and a flow degree of 48/dm2. When plating was performed for %i electrolysis time of 10 minutes, aluminum plating with a current efficiency of 95% or more and a plating layer thickness of 10 microns was obtained.

(Example 5) The molar ratio of aluminum chloride and tetrapropylphosphonium bromide described in Example 4 was 2. A plating solution was prepared by mixing the composition of No. 0 and toluene as an organic medium at a ratio of 1+1 (volume ratio). This plating bath is 7.5 at 25°C.
It shows a conductive ring of mS/cm.

Using this plating bath, aluminum plating was performed on a copper plate (plate thickness: 0.5 mm) in the same manner as in Example 3.

When plating was carried out under the electrolytic conditions of bath temperature 25°C, current density IA/dm'', and electrolysis time 30 minutes, a dense and glossy aluminum plating with a plating layer thickness of 10 microns was obtained with a current efficiency of 95% or more. Ta.

(Effects of the Invention) The novel composition according to the present invention is characterized in that it forms a low melting point compound and becomes a liquid that is easy to handle even at room temperature. Additionally, this new composition has significantly higher ionic conductivity in the molten state, and because the tetraalkylphosphonium cation is electrochemically stable, it can be used at higher temperatures and at higher current densities. In other words, these characteristics are important basic characteristics of an excellent plating bath, and according to the present invention, aluminum plating can be performed with high current efficiency and high current variation with good productivity. It is possible.

Furthermore, in the electrolytic aluminum plating method using the composition of the present invention, when aluminum is used in the anode, the A! Ions are AI2 from the anode
Since the bath water is metered and automatically replenished, bath management is simple, and in this respect it is also more convenient than other methods.

Claims (2)

[Claims] (1) Aluminum halide and the following formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R^1, R^2, R^3 and R^4 each represent an alkyl group having 1 to 12 carbon atoms. A low melting point composition characterized by being mixed with a tetraalkylphosphonium halide represented by the following formula (wherein X represents a halogen atom). (2) An electrolytic aluminum plating method using the low melting point composition according to claim 1 as a plating bath.