JPS6018758B2 - Manufacturing method of cathode for alkali metal halide aqueous solution electrolysis - Google Patents

Description

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

More specifically, the present invention provides a new method for producing a cathode that can significantly lower the hydrogen overvoltage in this electrolysis than conventional methods.

The new cathode referred to herein means a cathode having a plating layer on the surface of which powder containing a Raney nickel component is held on a base metal made of titanium or a titanium alloy. When electrolyzers are used to electrolyze, for example, hydrogen, chlorine, and aqueous saline solutions for the production of caustic soda, the loss of power efficiency 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. That is, the base material is titanium, titanium alloy,
The hydrogen overvoltage will be lower if iron, stainless steel, nickel, platinum group metals, etc. are used, and the rougher the surface condition, the lower the hydrogen overvoltage will be.
It is known that hydrogen overvoltage is low.

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 in which an iron plate or the like is coated with nickel powder or Raney nickel powder by a sintering method, or a cathode in which a powdered metal such as nickel, cobalt, platinum, or iron is adhered to the base metal by a thermal spraying method (Japanese Unexamined Patent Application Publication No. 52-118) 32832), a cathode for aqueous alkali metal halide electrolysis having a coating of a molten mist mixture of particulate cobalt and particulate zirconia on an iron plate (Samurai Seki 52-36 Ball 2), particulate nickel,
An electrolytic cathode having a coating obtained by removing aluminum from a molten atomized coating of a mixture of cobalt or both of these and particulate aluminum
This includes spots 3).

However, with these cathode manufacturing methods, it is difficult to uniformly coat cathode substrates with complex surface shapes such as wire mesh plates or box-shaped wire meshes, and there is a large loss of metal powder, making them expensive. There are many problems such as becoming.

Therefore, as a result of intensive research into a method for manufacturing a cathode that is effective in reducing hydrogen overvoltage and can be easily applied to cathode substrates of various shapes, we have found that at least a portion of the substrate metal made of titanium or titanium alloy is A method of plating using a composite nickel plating bath containing a Raney nickel alloy powder and removing aluminum contained in the powder before or after plating with a nickel plating bath that does not contain the alloy powder. was found to be effective.

Next, a method for manufacturing a cathode according to the present invention will be explained in detail. As the cathode substrate, titanium or a titanium alloy, which is an electrically conductive material and has mechanical properties necessary for a cathode and chemical resistance at a salt electrolyte level, is used.

Here, the titanium alloy used is an alloy of titanium and zirconium, tantalum, niobium, molybdenum, chromium, iron, vanadium, manganese, or the like. Generally, components other than titanium are suitably contained in several weight percent. 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 preferable to carry out surface roughening or cleaning treatment such as etching or blasting treatment alone or in combination as appropriate. The at least partially undeveloped Raney nickel alloy powder used suspended in the plating chamber is an at least partially undeveloped Raney nickel alloy of aluminum and nickel.

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 mm or more is difficult to maintain in a suspended state and is not practical. It is preferably around 100 or less. As the plating grade, a suspension of the above-mentioned at least partially undeveloped Raney nickel alloy powder in ordinary electroplating such as nickel plating, iron plating, or electroless plating can be used, but the powder content is as follows: 1 in terms of adhesion amount, maintenance of suspension, uniformity of adhesion, economic efficiency, etc.
~500 sleeves/sleeve, preferably 10-200 sleeves.

As the nickel plating grade mentioned above, Watt grade, nickel borophide plating bath, nickel sulfamate plating bath, etc. can be used. The pH value is 4 or more, preferably 5 or more. 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, I/d's is preferable. The plating bath temperature may be the usual plating temperature (40 to 70 qo) and is not particularly limited.

As a method for suspending the at least partially unexpanded Raney nickel alloy powder in the finishing bath, methods such as mechanical lighting, gas bubble lighting, and liquid circulation can be used. Although composite plating is achieved under the above conditions, the adhesion strength of the cathode surface having the powder is greater when the plating grade is low in powder concentration than when it is high.

If the adhesion strength is low, it is possible to increase the adhesion strength by further layering and forming a nickel plating layer with a thickness of preferably 10 mm or less using normal plating without suspending the powder. It is. Next, the aluminum component is removed from the composite plated surface containing the unexpanded or partially expanded Raney nickel alloy powder using an alkaline solution, regardless of whether or not the surface is plated without the powder.

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. In addition to being used as a single electrode, the cathode manufactured by this manufacturing method has characteristics such as chemical resistance and oxidation resistance that allow it to be used as a bipolar electrode.

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 an anode made of a titanium wire mesh coated with ruthenium oxide at a temperature of 50q.
oAs a result of electrolysis of saturated saline solution at a current density of 17Amp/d, the total cell voltage was 0.14 to 0.15V (Example 1) 0.14V (compared to the case where a European steel wire mesh cathode was used)
Example 2) It was found that the

Table 1 Also, the mild steel wire mesh cathode was polished with a wire brush before use.

Claims (1)

[Scope of Claims] 1 At least a portion of a base metal made of titanium or a titanium alloy is plated using a composite nickel plating bath containing at least a portion of undeveloped Raney nickel alloy powder, and then at least a portion of the aluminum contained therein is plated. 1. A method for producing a cathode for alkali metal halide aqueous solution electrolysis, characterized by removing. 2. Plating at least a portion of a base metal substrate made of titanium or a titanium alloy using a composite nickel plating bath containing at least a portion of undeveloped Raney nickel alloy powder, and then further using a nickel plating bath that does not contain the above powder. A method for producing a cathode for aqueous alkali metal halide electrolysis, which comprises removing at least a portion of aluminum contained in the powder before or after plating.