JP2806116B2 - Molten salt electroplating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten salt electroplating apparatus, in particular, for electroplating aluminum or an aluminum alloy (hereinafter sometimes collectively referred to as Al) on a base metal such as a steel plate in order to improve corrosion resistance and heat resistance. To a molten salt electrolytic Al plating apparatus.

[0002]

2. Description of the Related Art Aluminum plating products have excellent corrosion resistance, beautifulness,
Although it has many advantages such as non-toxicity, it cannot be electrodeposited from an aqueous solution, and is currently mainly produced by a hot metal immersion plating method. However, thin plating is difficult with this molten metal immersion plating method, and since the operating temperature exceeds 700 ° C, an alloy layer is formed between the base material and the plating film, or the base material is adversely affected. ,
There are many problems.

[0003] Therefore, recently, research and development have been advanced to solve the above-mentioned problems by electroplating instead of the molten metal immersion plating and to open the way to industrialization of Al electroplating. As described above, since electric Al plating cannot be simply electrodeposited from an aqueous solution, an electroplating method using a molten salt bath capable of electrodeposition is conceivable, and many electric Al plating methods based on this have been proposed. Practical application is underway.

A molten salt bath such as AlCl _{3-is used} for electroplating of Al.
The method using a binary or ternary molten salt bath of XCl (X: alkali metal) has an operating temperature of 150 to 200 ° C, which is much lower than that of the molten metal immersion method. Since there is no adverse effect on the material and thin plating is possible, the above problem has been solved for the time being.

[0005]

However, the aluminum chloride-based molten salt is characterized by extremely strong hygroscopicity, and the water mixed in the bath causes extremely severe corrosion of the metal material. This results in shortening of the equipment life due to wall thinning wear and stress corrosion cracking of structural materials, and these metal ions eluted in the molten salt bath, which is a plating bath, inhibit the formation of good plating films as impurities. Will be.

It is considered that such a problem is basically solved if the mixing of water can be completely suppressed. However, the incorporation of moisture is unavoidable due to the ingress and egress of the plating base material, the maintenance of the equipment, and the like, and even if the seals and the like are improved, it is considered that complete suppression is not possible with practical equipment.

Therefore, given the fact that water is mixed in to some extent, there is a need for a device that can minimize the adverse effects of water even if mixed. Thus,
An object of the present invention is to provide an apparatus for performing electroplating of Al or an Al alloy using a molten salt bath, which has excellent durability as an apparatus, and is capable of producing a good plating material. It is in.

[0008]

With respect to the corrosion of metallic materials, measures such as lining rubber or the like can be considered as seen in, for example, an aqueous plating system. However, in this aluminum chloride-based molten salt, general organic materials such as rubber, vinyl chloride, and bakelite have no durability. It has been found that even with a fluororesin known for its excellent heat resistance and chemical resistance, sufficient durability cannot be obtained by the inventors' attempts.

In addition, materials having excellent durability such as ceramics, glass, and polyimide resin have been studied. However, it is not possible to line such a brittle material on the entire plating apparatus having a complicated shape or to constitute the entire apparatus with such a material. The technical problem of being extremely difficult remains. Therefore, in this molten salt electroplating apparatus, it was concluded that a metal material had to be used at least in a part in contact with the molten salt bath. Therefore, the present inventors first studied steel materials and high alloy steel materials that are commonly used for aqueous plating facilities.

As a result, most of the materials were severely corroded, causing stress corrosion cracking or pitting. Materials that cause cracking or pitting corrosion are not suitable as device materials. Among these, the only material that did not crack and had small pitting corrosion was a Ni-Cr-Mo alloy (for example, a high alloy material such as Inconel or Hastelloy) or a steel material containing 1% or less of Ni. In consideration of economy and welding / workability, the latter material is optimal, but the amount of corrosion is greater than the former. Either way, it is still not enough from a comprehensive perspective.

For this reason, the present inventors have taken an electrochemical viewpoint to reduce the amount of corrosion, and have conducted intensive studies on metals that protect the material by sacrificial corrosion protection. As a result, the metal material constituting the device itself is coated with Al. Alternatively, it has been found that the amount of corrosion of the metal material can be effectively suppressed by contact.

[0012] The molten salt plating bath, which has absorbed moisture, generates hydrogen gas and alumina by being brought into contact with Al and is dehydrated. Even if steel components are eluted, their metal ions undergo a substitution reaction with Al. It was also found out that it can be removed by precipitation.

As a result of a more detailed study, it has been clarified that this effect of Al is due to the cathodic protection effect of the metal material due to the preferential dissolution of Al in the molten salt bath over other metal materials. In addition to being necessarily applied as a coating material or a structural material, it may be installed in a molten salt bath in a block shape and electrically connected to a metal material constituting the device itself, that is, also installed as a sacrificial anode. It turned out to be effective. Therefore, it is also possible to use Mn, Ti, Mg or the like as the sacrificial anode. It has also been found that the object can be achieved by applying a voltage to the metal material using an external power supply instead of the sacrificial anode.

Further, a more detailed study revealed that it is most effective for the steel material to have the cathodic protection potential in the range of -0.2 to +0.5 V. It has also been found that when strictly suppressing the elution of iron ions, it is more effective to use Cr-containing steel as the metal material instead of ordinary steel. In this case, it is important that the Cr-containing steel is ferritic, and SUS304 and SUS3
In the case of an austenitic system such as 16, it was also evident that stress corrosion cracking occurred.

[0015]

Next, the operation of the present invention will be described more specifically with reference to the accompanying drawings. FIG. 1 is an explanatory view of a molten salt electrolytic plating apparatus according to the present invention. When passing through this apparatus, a steel strip is continuously electroplated with Al.

That is, the steel strip 1 to be subjected to Al plating first enters the drying preheating tank 2, is dried and preheated, and first enters the pre-electrolysis tank 6 in a region set in the inert atmosphere 4 via the seal roll 3. In this pre-electrolysis tank 6, primary plating is performed with the molten salt 8 for pre-electrolysis while traveling between the cathodes 7. 5a, 5b
Is an energizing roll for pre-electrolysis, and the pre-electrolysis bath is continually circulated and renewed through a circulation path having a pre-electrolysis bath circulation tank 20 attached thereto.

The steel strip 1 'thus subjected to the pre-electrolysis treatment
Then, the plating tank 12a continuous through the compartment roll 10
And enter 12b. In the plating tank 12, plating of a predetermined thickness is performed by the molten salt for plating 14, 14 'while traveling between the cathodes 13 in the same manner as described above.
Through the plating apparatus. 11a, 11b, 11c
Denotes a plating energizing roll.

In this plating tank 12, molten salt for plating is also used.
14 and 14 'circulate through the circulation path to the plating bath circulation tank 25 and are constantly updated. Plated steel plate
1 ″ is subjected to a washing process by a washing nozzle 17 and then dried and wound up as appropriate.

The molten salt bath used in the present invention is a commonly used two-component or multi-component mixed molten salt anhydrous bath of AlCl ₃ -XCl (X: alkali metal). In this case, the bath temperature is 150-250 ° C.
_{The present} invention can be similarly applied to a molten salt bath such as pyridinium salt (e.g., ethyl pyridinium chloride) or imidazolium salt (e.g., 1-ethyl-3-methylimidazolium chloride) which is an organic salt. Still further, these plating baths may be added with an organic amine, a fluoride, a bromide, an iodide, an alkaline earth salt, or the like, if necessary.

The plating performed by the apparatus of the present invention is pure Al or Al alloy plating, and the Al alloy is Al-Mn, Al-T
i, Al-Li, Al-Ta, Al-Cr, Al-Sn, Al-Pb, etc., but there is no particular limitation on the alloy type. It may be. The base metal as the material to be plated is generally a continuous form such as a steel plate or a steel wire, but there is no problem even with a batch type, and the shape is not limited to a plate, a rod, a tube, or the like. The type of the base metal may be any type, such as iron, steel, stainless steel, copper, aluminum, and titanium, as long as Al plating is possible.

The present invention is characterized in that Al or an Al alloy for the purpose of cathodic protection is applied to a metal material which comes into contact with an extremely corrosive aluminum chloride-based molten salt. It widely refers to those parts which must be brought into contact with the above-mentioned molten salt plating bath, such as cell structural materials, piping, lining materials, and the like.

The plating apparatus is not limited to a part to be plated, but may be, for example, a molten salt bath in a plating pretreatment activation step using a molten salt bath proposed by the present inventors in Japanese Patent Application Laid-Open No. 63-143282. , Means all facilities related to molten salt associated with the plating tank.

When a metal material constituting these devices is required to have particularly high strength, a so-called steel material is used, and Al or an Al alloy may be lined or connected as a sacrificial anode. In this case, Al dissolves preferentially in other metal materials such as steel. However, Al is a constituent ion of the molten salt system, and is preferable because it does not contaminate the bath as an impurity. In addition, for example, Al
For the purpose of plating alloys such as -Mn, Al-Ti, and Al-Mg, Mn, Ti, and Mg do not become impurities in the bath.
It is also possible to use n, Ti and Mg as sacrificial anodes.

The shape of the sacrificial anode may be plate, block, rod, etc.
Although not particularly limited, in order to make it work more effectively, it is preferable that the area is large, and from the viewpoint of the corrosion prevention range, it is preferable that the distance from the metal material to be protected is short.
The most preferable example is to cover the entire area with a sacrificial anticorrosive material such as Al. However, such a complete coating is not always easy with pumps, valves, piping, etc. It is preferable that the portion has a distance within the range of the sacrificial corrosion prevention distance and an area 0.1% or more of the exposed area (referred to as a surface pole ratio). This arrangement according to the invention
FIGS. 3A to 3C show specific examples of sacrificial corrosion protection of pipes.
You. Fig. 3 (a) shows Al installed as a block in the middle of piping
Fig. 3 (b) shows an example in which an Al rod was placed in the middle of the pipe (melting).
If the flow rate of the molten salt is large, some fixing means may be provided.
Good), and FIG. 3 (c) shows a plate with Al in the piping, especially a cylindrical plate.
An example of installation is shown below.

It is needless to say that the metal material and the sacrificial anticorrosion material need to be electrically connected in view of the operation principle. Further, it is also possible to perform cathodic protection for the same purpose by using an external power supply such as a constant potential power supply or a constant current power supply. In this case, the anode of the external power supply may be one that is controlled and dissolved using the sacrificial anode material, or an insoluble anode such as carbon or tungsten may be used. However, when an insoluble anode is used, chlorine is generated in the aluminum chloride-based molten salt, so that consideration must be given to means for removing the generated chlorine.

In the present invention in which cathodic protection is the principle, the potential set for the metal material is an important factor. That is, in this bath containing aluminum chloride as a main component, pure
This is because precipitation of Al occurs on the base side (minus side) from the reference potential of Al, dissolution of Al on the noble side (plus side), and dissolution of steel further on the noble side.

According to the study results of the present inventors, when the set potential is lower than -0.2 V, a large amount of Al precipitates and hinders the function of the apparatus. ,
It has been found that corrosion, pitting and cracking of steel cannot be sufficiently prevented. Therefore, the potential is preferably set between -0.2 V and +0.5 V with respect to the potential of pure Al in the molten salt bath.

Incidentally, the potential of this pure Al is an absolute potential.
(For example, the potential of the hydrogen electrode at 1 atm and 25 ° C.). This is because, in this molten salt bath, the potential of pure Al greatly changes depending on conditions such as bath composition and temperature. However, the other components constituting the aluminum chloride-based molten salt are alkali metal salts such as NaCl, KCl, and LiCl, and pyridinium-based organic salts. Precipitation of Na metal with a high potential cannot usually occur except under extreme electrolysis conditions. Therefore, in the present invention, precipitation of aluminum,
The potential is based on the potential at which dissolution occurs. Specifically, it is sufficient that the potential measured by the reference electrode in the molten salt plating bath is within the above range. It is considered that the absolute potential rather complicates the setting conditions.

This potential is automatically set in the range of approximately 0 to +0.2 V when the Al material is used as the sacrificial anode.
1 to + 0.3V. The same applies to Ti and Mg, and so does their alloy systems. However, care must be taken when using an external power supply. In both the case of applying a constant voltage and the case of applying a constant current, the reference electrode constantly or irregularly monitors that the potential is in the range of -0.2 to + 0.5V. Need to be done.

According to another embodiment of the present invention, a ferritic Cr-containing steel is used as the metal material to be cathodic protected.
The effect of cathodic protection in the present invention is most remarkable in the case of such Cr-containing steel. When the cathodic protection is not performed, the corrosion rate of the Cr-free ordinary steel and the Cr-containing steel is similar in the molten salt, and the effect of the Cr content can hardly be expected. However, when performing the cathodic protection of the present invention, corrosion elution is extremely reduced. this is,
This is effective when the amount of impurity Fe ions in the plating bath due to elution of the cell structural material needs to be suppressed to the lowest possible level.

The Cr content of such a Cr-containing steel is 1
%, But mass-produced materials such as SUS410 containing about 12% Cr and SUS430 containing about 17% can also be used. SUS304 and SUS316 containing Ni and Cr are also useful as mass-produced materials, but austenitic stainless steels may generate stress corrosion cracking in this aluminum chloride-based molten salt. In this regard, in the case of ferritic stainless steel, the occurrence of stress corrosion cracking is not observed by performing the cathodic protection of the present invention. Next, the present invention will be described in more detail with reference to examples thereof, but this is merely an example, and the present invention is not unduly limited thereby.

[0032]

【Example】

(Example 1) Using a device shown in FIG. 1, a steel plate was subjected to molten salt electrolytic Al-Mn electroplating under the following conditions. The plating conditions in this example were as follows.

Plating bath: AlCl ₃ -NaCl (molar ratio 61: 26: 1)
3) Add 5000 ppm of MnCl ₂ , 200 ° C, bath volume 200 liter Pre-electrolysis bath: AlCl ₃ -NaCl-KCl (molar ratio 52:32:16) 200
° C, bath volume 100 liters Plating conditions: Pre-electrolysis, Al-
Mn plating was performed.

Test period: 2 years Test: 5 mm thick on the entire inner surface of mild steel plating tank 12a
Was lined with a pure Al plate. Test: An Al-1% Mn alloy square bar having a width of 30 mm and a thickness of 20 mm was installed at a pitch of 250 mm inside the mild steel plating tank 12b by bolting. Test: A 10 mmφ tungsten rod anode was installed inside the SUS410 pre-electrolyzer 6, and a constant current of 10 A was flowed between the anode and the wall. At this time, the potential distribution of each part of the tank wall based on pure Al was measured, and the corrosion measurement points were -0.3 V (6a), -0.2 V
(6b), -0.05V (6c), + 0.2V (6d), + 0.5V (6e), + 0.7V
I scored 6 points (6f). Test: 100 mm inside mild steel plating solution circulation tank 25
A corner Mn block was provided and electrically connected to the cell with a 1 mmφ molybdenum wire. Test: No cathodic protection was performed on the pre-electrolysis bath circulation tank 20 made of SUS430.

Results after two years of use: Test: The Al plate corroded 1 mm on average and 4 mm at most, but the mild steel of the tank body was not damaged at all. Test: The Al-1% Mn square bar corroded 7 mm on average and 10 mm at maximum, but the damage to the tank body was 0.1 mm on average and 0.7 mm at maximum.

Test: −0.3V point (6a): 70% of Al deposits
mm. -0.2V point (6b): Al deposits were attached at a height of 5 mm, but there was no damage to the tank wall. −0.05V point (6c): No deposits were observed at all, and damage to the tank wall was 0.03 mm on average and 0.1 mm at maximum. + 0.2V point (6d): No deposits, average damage 0.05mm, maximum 0.
Stayed at 1 mm. + 0.5V point (6e): No deposits, damage 0.1 mm on average, maximum 0.
Stayed at 2 mm. + 0.7V point (6f): Damage is seen, average 1.3mm, maximum 4.8mm
Met.

Test: Mn block average 5mm, maximum
Despite the corrosion of 20 mm, the mild steel material in the tank body was 0.1 mm on average and 0.8 mm at maximum. Test: obvious damage, average 2.3 mm, max
5.6 mm. After two years of use, the concentration of impurities such as Fe ions in the bath was kept at 5 ppm or less, and a plating film of excellent plating quality was continuously formed.

(Example 2) The plating bath circulation tank of Example 1
U-bend samples of various materials were immersed in the inside of the sample 25 as shown in FIG. 2, and the corrosion amount of the sample 28 after one year was measured. That is, the U-bend sample 28 is prepared as follows: width 15 mm × length 70 mm × thickness 2
The mm plate was fixed with bolts 29 so that the inner bending dimension became 10 mm (5 t bending). This was electrically connected to the anticorrosion counter electrode 30 with a lead wire 31 and immersed in a molten salt plating bath 32 with an area of 20 cm.
^The electrodes were immersed and opposed to each other with a gap 33 between the electrodes.
After one year, corrosion weight loss was weighed, and SCC cracking was visually inspected. The results are summarized in Table 1. It can be seen that according to the present invention, the corrosion weight loss is greatly reduced.

[0039]

[Table 1]

[0040]

As described above, according to the present invention, Al
Alternatively, the production of Al alloy electroplating has become practical, and in particular, it has been significant that the durability of the apparatus, which has been a problem in the past, can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a plating apparatus to which the present invention is applied.

FIG. 2 is a schematic diagram of an experimental method for evaluating the effect of the present invention.

3 (a) to 3 (c) are explanatory views showing an example of sacrificial corrosion protection of a pipe according to the present invention.

[Explanation of symbols]

1,1 ', 1 ": Steel strip 16: Sink roll 2: Drying preheating tank 17: Rinse nozzle 3: Seal roll 20: Pre-electrolysis bath circulation tank 4: Inert atmosphere 25: Plating bath circulation tank 5a, 5b: Front Electrolytic energizing roll 28: U-bend sample 6: Pre-electrolyzer 29: U-bend fixing bolt 7: Cathode 30: Counter electrode 8,8 ': Pre-electrolysis molten salt 31: Lead wire 9: Sink roll 32: Molten salt plating bath 10: Compartment roll 33: Distance between poles 11a, 11b, 11c: Plating energizing roll 12a, 12b: Plating tank 13: Anode 14,14 ': Molten salt for plating 15a, 15b: Sink roll

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuaki Tsuda 4-5-33 Kitahama, Chuo-ku, Osaka City Inside Sumitomo Metal Industries, Ltd. (72) Inventor Yasuhiro Yamamoto 4-5-33 Kitahama, Chuo-ku, Osaka Sumitomo Inside Metal Industry Co., Ltd. (72) Inventor Hirohisa Seto 4-5-33 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries Co., Ltd. (72) Inventor Kunihiro Fukui 4-5-33 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries Incorporated (72) Inventor Ken Abe 4-5-33 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries, Ltd. (72) Inventor Yoshio Tarutani 4-5-33, Kitahama, Chuo-ku, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Junkichi Yoneda 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City Inside the Hiroshima Works of Mitsubishi Heavy Industries, Ltd. (72) Inventor Norio Hashimoto Nishihiroshima 4-6-22 Kannon Shinmachi, Ward, Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Toshio Taguchi 4-622, Kannon Shinmachi, Nishi Ward, Hiroshima City, Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (56) References JP Hei 1-127971 (JP, A)

Claims (3)

(57) [Claims] 1. An apparatus for electroplating aluminum or an aluminum alloy on a base metal using a molten salt plating bath containing aluminum chloride as a component, wherein at least one of the devices is in contact with a molten salt plating bath of steel constituting the apparatus. Some parts are coated or contacted with aluminum or aluminum alloy in the form of cathodic protection to reduce wear on the steel.
A molten salt electrolytic plating apparatus characterized in that the metal salt is controlled and impurity metal ions are precipitated and removed . 2. An apparatus for electroplating Al-Mn or Al-Ti or Al-Mg alloy on a base metal by using a molten salt plating bath containing aluminum chloride as one component, which constitutes the apparatus. At least a portion of the steel material in contact with the molten salt plating bath is formed with M
It is contacted with n or Ti or Mg, the wear of the steel material
Suppresses, molten salt electroplating device comprising an this <br/> precipitating remove impurity metal ions. The method according to claim 3 wherein at least part of further external power source in contact with the molten salt plating bath of a metal material the device to configure, is cathodic protection, and the potential of the metal material, pure aluminum of the molten salt plating bath −
The molten salt electrolytic plating apparatus according to claim 1, wherein the molten salt electrolytic plating apparatus is maintained in a range of 0.2 to +0.5 V. 4.