JPS6015712B2 - Cathode for producing caustic soda and its production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode for electrolyzing an aqueous alkali metal halide solution and a method for producing the same.

More specifically, the object of the present invention is to provide a new cathode that can significantly lower the hydrogen overvoltage in this electrolysis than conventional ones, and a method for manufacturing the cathode.

The new cathode referred to herein means a cathode having a plating layer containing a powder containing a Raney nickel component on a base metal. When an electrolytic cell is used to electrolyze a saline solution for producing hydrogen, chlorine, and caustic soda, for example.

Power efficiency loss caused by hydrogen overvoltage at the cathode is a serious problem.

It is known that the hydrogen overvoltage at the cathode varies significantly depending on the material, surface material, or surface condition of the cathode. In other words, if iron, stainless steel, nickel, platinum group metals, etc. are used as the substrate, the hydrogen overvoltage will be lower.
It is also known that the more similar the surface state is, the lower the hydrogen overvoltage will be.

Based on these findings, various methods have been proposed for attaching powder of materials with low hydrogen overvoltage to the cathode surface. For example, a cathode coated with nickel powder or Raney nickel powder by the Akatsuki method, a cathode in which a powdered metal such as nickel, cobalt, platinum, iron, etc. is adhered to the base metal by a thermal spraying method (Tokukan Sho 52-32832), A cathode for alkali metal halide aqueous solution electrolysis made of particulate cobalt and particulate zirconia is coated with a molten mist mixture.
In addition to 2), there is also an electrolytic cathode having a coating in which aluminum is removed from a coating that is sprayed during melting of particulate nickel, cobalt, or a mixture of both of these and particulate aluminum (Japanese Patent Laid-Open No. 52-36 This includes spots 3). However, with these cathode manufacturing methods, it is difficult to uniformly coat a cathode substrate with a complicated surface shape, such as a wire mesh plate or a box-shaped wire mesh, and there is also a large loss of metal powder, making it expensive. There are many problems such as. As a result of intensive research into a cathode that is effective in reducing hydrogen overvoltage and can be easily applied to cathode substrates of various shapes, we have developed a composite nickel plating layer containing Raney nickel powder or at least a partially expanded Raney nickel alloy powder. It has been found that a cathode having a plating layer on its surface which does not contain these powders is suitable for this purpose, and that iron, stainless steel, or nickel can be used as the cathode base metal.

Furthermore, methods for producing such a cathode include a method in which a composite nickel plating bath containing Raney nickel powder is used on the cathode base metal, a method in which after the plating is performed, plating not containing Raney nickel powder is overlaid, and at least A method of performing plating using a composite nickel plating grade containing partially unexpanded Raney nickel alloy powder to remove the contained aluminum, and after removing the aluminum,
It has been found that a method of plating using a plating material that does not contain the at least partially powdered Raney nickel alloy powder is effective, and that the aluminum contained can be removed using an alkaline aqueous solution.

Next, the cathode and its manufacturing method according to the present invention will be explained in detail. The cathode substrate may be any electrically conductive material as long as it has the mechanical properties necessary for a cathode and the chemical resistance commonly used in salt electrolysis, and iron, stainless steel, nickel, etc. are suitable base materials.

Plating may be performed by electroplating or electroless plating, but electroplating is superior in that it allows a large amount of powder to be uniformly contained in the plating layer.

Pre-treatment of the substrate for plating is done by conventional means, such as degreasing,
It is sufficient to perform etching, blasting, etc. alone or in combination as appropriate. Powders used suspended in the plating solution include Raney nickel powder and at least partially expanded Raney nickel alloy powder. The smaller the size of the powder used here, the more effective it is and the easier it is to suspend. Powder with a diameter of 500 peaks or more requires elutriation and is not practical. It is preferably around 100 peaks or less. The plating grade can be nickel plating grade, ordinary electroplating such as iron plating bath, or electroless plating. Generally, the above-mentioned Raney nickel powder or a suspension of at least partially undeveloped Raney nickel alloy powder can be used. The content is 10,500 g/sleeve, preferably 10 to 10,000 g/sleeve from the viewpoints of adhesion amount, maintenance of suspension, uniformity of adhesion, economical efficiency, etc.
It has 200 long sleeves.

As the above-mentioned final nickel plating grade, Watt bath, nickel borofluoride plating grade, nickel sulfamate plating grade, etc. can be used, but in view of the reactivity of Raney nickel, the bath pH is 4 or higher, preferably 5. The above is preferred. In the case of plating, addition of surfactants such as polyoxyethylene alkylamine, alkylimidazolium chloride, etc. is effective for smoothing the surface, as in the case of ordinary electroplating and electroless plating.

On the other hand, the amount of plating and the amount of powder adhesion are influenced by the current density, and the higher the current density, the larger the amount of plating and the amount of powder adhesion. Practically speaking, Hiroshi/d is preferred. The plating temperature may be a normal plating temperature (400-70:00) and is not particularly limited.

As a method for suspending powder such as Funehnickel powder or at least partially expanded Raney nickel alloy powder in plating, methods such as mechanical lighting, gas bubble lighting, liquid circulation rope, etc. can be applied. Composite plating is achieved under the above conditions, but the adhesion strength of the cathode surface containing the powder is greater when the powder concentration is lower than when the powder concentration is high. If the adhesion strength is low, add more layers,
It is possible to increase the adhesion strength by forming a nickel plating layer of preferably 10 mm (thickness) or less using a normal plating method in which no powder such as Raney nickel powder is suspended. Next, the aluminum component of the cathode surface, which has been composite plated with the partially expanded or partially expanded Raney nickel alloy powder, is removed using an alkaline solution.

There are no particular restrictions on the type, composition, concentration, temperature, soaking time, etc. of this alkaline solution, but it is typically 10 to 25% by weight of sodium or potassium hydroxide.
Practically suitable conditions include an aqueous solution at a temperature of 25 to 8,000 ℃ and a leaching time of 1 hour or more. It goes without saying that the longer the leaching time is, the less residual aluminum is left, and the less aluminum is mixed into the electrolytic product during the electrolytic operation, which is preferable. Examples 1 and 2 Asbestos was deposited on a cathode wire mesh prepared under the conditions shown in Table 1 to form an asbestos diaphragm cathode, which was placed opposite to an anode coated with ruthenium oxide on a titanium slope at a temperature of 50:00.
As a result of electrolysis of saturated saline solution at a current density of 17 Amp/d, the maximum total cell voltage was 0.15 V (Example 1) and 0.12 V (Example 2) compared to when an unplated cathode was used. I knew I was going down.

Mild steel polished with #80 abrasive paper was used as the funa bran or ferrite-plated cathode.

Claims (1)

[Scope of Claims] 1. A cathode for producing caustic soda, characterized in that it has a composite nickel plating layer containing at least partially expanded Raney nickel alloy powder on at least a portion of a base metal. 2. The cathode for producing caustic soda according to claim 1, wherein the base metal is iron, stainless steel, or nickel. 3. A method for producing a cathode for producing caustic soda, which comprises plating at least a portion of the base metal using a composite nickel plating bath containing Raney nickel powder. 4. The method for producing a cathode for producing caustic soda according to claim 3, wherein iron, stainless steel, or nickel is used as the base metal. 5. A cathode for producing caustic soda, characterized in that at least a portion of the base metal is plated using a composite nickel plating bath containing at least partially undeveloped Raney nickel alloy powder, and then at least a portion of the aluminum contained therein is removed. manufacturing method. 6. The method for producing a cathode for producing caustic soda according to claim 5, wherein iron, stainless steel, or nickel is used as the base metal. 7. A method for producing a cathode for producing caustic soda according to claim 5 or 6, characterized in that an alkaline solution is used to remove aluminum.