JPS5959890A - Method for preventing deterioration in activity of ferrous cathode of electrolytic cell - Google Patents

Abstract

PURPOSE:To prevent inexpensively and easily the deterioration in the activity of a cathode, by electroless plating Ni on the inside surface of a cathode chamber consisting of a ferrous material and a cathode base material and further forming a porous Ni layer on the cathode by electroplating and leaching. CONSTITUTION:Ni is electrolessly plated in the presence of a reducing agent on the inside surface of a cathode chamber consisting of a ferrous material and the surface of a cathode base material to form a uniform Ni coating layer and to prevent the deterioration of the activity of the cathode owing to the elution and deposition of iron, in an electrolytic cell used for electrolyzing an aq. soln. of alkali metal halides, etc. A metallic coating layer of an alloy of Ni and a sacrificial metal such as Zn is further provided by electroplating on the Ni coating layer coated on the above-mentioned cathode base material; thereafter, the cathode base material is subjected to a leaching treatment by using alkali such as caustic soda to elute away at least a part of the sacrificial metal and to form a porous Ni layer, whereby the activity of the cathode is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing a decrease in the activity of a cathode in an electrolytic cell suitable for use in the electrolysis of an aqueous alkali metal halide solution or an aqueous alkaline solution, and particularly relates to a method for preventing a decrease in the activity of a cathode in an electrolytic cell suitable for electrolysis of an aqueous alkali metal halide solution or an aqueous alkaline solution, and is particularly concerned with The present invention relates to a method for preventing a decrease in activity of a cathode having a shape.

Conventionally, iron, mild steel, stainless steel, etc. have been used as cathodes for electrolysis of aqueous solutions of alkali metal halides, etc. However, since the hydrogen overvoltage of these materials is not very low, a material such as nickel is used on the surface of iron, etc. However, when using this shade V8 to electrolyze sodium chloride/kasa, it is necessary to form a porous layer of metal with a low hydrogen overvoltage. Because iron is not coated, iron is eluted and deposited on the cathode surface by the sodium hydroxide, etc. that is produced, reducing the activity. There is a drawback that iron is eluted through the coating layer and precipitated on the coating layer, resulting in a decrease in activity.

The latter drawback can be overcome if a uniform coating layer can be formed on a cathode substrate such as iron, but the conventional thermal spraying or electroplating methods do not produce complicated coatings, especially in the case of a covering mesh. However, it was not possible to form a uniform coating layer on the cathode base material, which had a similar shape.

In other words, according to the thermal spraying method, the coating due to thermal spraying will be different unless the shadow (heel) faces in a certain direction, and the coating will not be formed depending on the location. Depending on the distance, the thickness of the coating layer becomes non-uniform.Furthermore, thermal spraying and electroplating are relatively expensive and complicated, and are not preferred from the economical and workability standpoints.

The present inventors formed a uniform coating layer on the inner surface of the cathode chamber made of iron-based material and on the cathode base layer by applying nickel without any heat treatment. It was found that the cathode activity could be reduced by forming a porous nickel layer on the covering layer formed on the cathode substrate by electrolysis and leaching, while also preventing the activity from decreasing. In particular, the present invention
This is advantageous when applied to electrolytic cells with complex structures.

In other words, in the present invention, a coating layer is formed on the inner surface of the cathode chamber made of an iron-based material and on the surface of the cathode group I in the presence of a reducing agent without using IKM.
After providing an alloy coating layer of p-nickel and a sacrificial metal on the surface of the nickel coating layer by electric plating, the cathode base material is subjected to a leaching treatment to elute and remove at least a part of the sacrificial metal. In the method for preventing a decrease in the activity of an iron-based cathode in a 4% tank, t,;2, mild steel, stainless steel, etc. can be used as the iron-based conductive substrate.

The nickel layer coated on the inside of the cathode chamber and on the cathode base plate is effective in preventing corrosion of the cathode chamber and cathode base material.
The thickness is 3 to 200μ, preferably 5p to 100μ. To form this nickel coating layer, nitrogen chloride,
The cathode chamber and cathode base material are immersed in a plating solution consisting of an aqueous solution of a nickel compound such as nickel nitrate and a reducing agent such as hypophosphite. And an electroless plating method is adopted in which the material is deposited on the cathode substrate. This 7115-free plating method is extremely simple in that it involves immersing the cathode chamber and cathode base material in the plating solution, and even if the cathode chamber or cathode base material has a complicated shape, it can be applied evenly to the plating solution. In order to contact
The coating layer can be coated with a uniform thickness, shielding the inner surface of the cathode chamber and the cathode substrate from the outside, and completely preventing iron and the like from being leached during electrolysis. In addition, before forming the nickel Oi scrap, it is desirable to perform surface treatments such as degreasing, derusting, pickling, and plasting on the cathode chamber and cathode substrate to make it easier to plate with nickel. . Note that as the electrolytic cell, both a diaphragm type electrolytic cell and a filter press type electrolytic cell can be used.

Next, on the surface of the nickel coating layer coated on the cathode substrate,
Electroplating forms a nickel and an alloy layer on the sacrificial gold. Here, it refers to metals that can be eluted and removed by leaching, such as I-associated metals. During this electroplating &:t,
, nickel compounds such as nickel chloride and nickel nitrate,
A cathode electrolessly plated with nickel is immersed in a mixed aqueous solution of zinc compounds such as zinc chloride and zinc nitrate to serve as a cathode for electroplating, and platinum, nickel, etc. are used as an anode.
Electroplating is carried out under acidic conditions at a flow rate of about 1 to 10 A/dm''.

The thickness of the alloy layer should be 30 μm or more, preferably 50 μm to 300 μm, in order to maintain its activity as a cathode.

The weight ratio of nickel to zinc, etc. should be 90:10 or more, because if there is too little zinc, the effect of forming a porous nickel coating will be reduced, and if it is too much, the coating layer will be brittle and the life of the cathode will be shortened. 50:50 is 94 preferable.

After coating the metallurgical layer with an alloy layer consisting of nickeled zinc and the like as described above, zinc and the like are leached and removed from the metallurgical layer. This elution is carried out by immersing it in an alkali such as caustic soda. Elution condition e, alloy layer (varies depending on the V component, but for example 5~
in a 20% by weight aqueous caustic soda solution at 40 to 80°C,
It is appropriate to soak for 2 to 5 hours.

In the present invention, nickel is electrolessly plated on the inside of the cathode chamber and on the surface of the cathode base material2, an alloy layer of nickel and a sacrificial metal is formed on the nickel coating layer of the cathode base material, and then a mixed layer is formed. The sacrificial metal is eluted by leagueing, and by providing a nickel entrained layer, it is possible to prevent iron from corroding and dissolving from the cathode chamber and cathode substrate, and prevent iron from depositing on the cathode surface. It does not have any stains and can maintain its activity over a long period of time when it is cathode bound. In addition, in this case, the nickel coating layer is coated by electroless plating, so even if the cathode substrate has a complicated shape such as a bag-like mesh, it can be coated uniformly, and it can be coated using thermal spraying or Differences occur in the coating layer depending on the distance from the anode. Unlike the plating method, it is possible to reliably prevent the dissolution of -j(, Therefore, 1. It is useful for quantitative applications.

Example: A bag-shaped mesocye cathode substrate made of mild steel and a diaphragm tank made of mild steel were subjected to UrR treatment in a 5-fold diluted solution of 1-Den 5X manufactured by Murakami Kyoto Co., Ltd. at 8[]°C for 4 hours. Then, in the next plating process, an alloy layer of nickel and zinc was formed on the cathode substrate that had been coated with a nickel coating layer.Bath composition NiC1x250V/ 1ZnC1,45
y/l pH, 4,5 (adjusted with ILCl) Current density: 3 A/dm' Temperature: 45°C Time: 2 hours The cathode substrate coated with the alloy layer was treated with 10 wt.
The mixed layer was immersed for 8 hours at 40x for 8 hours, and the zinc in the mixed layer was eluted and removed to produce a cathode.

Using the cathode and cathode chamber manufactured as described above, salt electrolysis was carried out under the following conditions.

Supply saline water P degree 300? /1 Sodium hydroxide Concentration 52q4 ion exchange membrane Du Pant I'J Nd1on 901 Current Density 30 A/dm' Electrolytic bath temperature 85℃ After 6 months elution amount of iron is 0.02 ppm or less in,
No change in hydrogen overvoltage was observed during the 6-month operation period [+, IV.

Comparative Example Using a cathode chamber and a cathode on which no nickel coating layer was formed, salt type M was carried out under the same conditions as in the example, and the amount of iron eluted after 6 months was 3 ppm. two.

Claims (1)

[Claims] A nickel coating layer is formed on the inner surface of the cathode chamber made of an iron-based material and on the surface of the cathode base material by applying electroless M-Megging with nickel in the presence of a sifting agent, and at least on the surface of the nickel coating layer on the cathode base material, Activation of an iron-based cathode of an electrolytic cell characterized in that after providing an alloy coating layer of nickel and a sacrificial metal by electroplating, the cathode base material is subjected to a leading treatment to elute and remove at least a part of the sacrificial metal. How to prevent decline.