JPS62240778A - Metallic electrode coated with carbonaceous substance and its production - Google Patents

Abstract

PURPOSE:To obtain an electrode having characteristics of both of metallic and carbon electrodes by forming a coating layer of a carbonaceous substance contg. a prescribed percentage of graphite on a corrosion resistant metallic substrate. CONSTITUTION:A carbonaceous substance contg. 50-95wt% graphite is prepd. A corrosion resistant metallic substrate is coated with the carbonaceous substance by application or extrusion molding and the substance is dried and heated. Thus, a metallic electrode coated with a carbonaceous substance and having characteristics of both metallic and carbon electrodes is obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is useful for surface treatment such as electrolytic etching of metals, for energization in corrosive liquids such as organic electrolysis, or for electrolysis through direct current or alternating current in these liquids. This invention relates to corrosion-resistant electrodes used in the process.

(Prior Art and its Problems) Carbon electrodes have conventionally been used as corrosion-resistant conductive members and electrodes for electrolysis in corrosive liquids. Carbon electrodes have high electrical conductivity for a non-metal and extremely good corrosion resistance.
It functions effectively as both a cathode and an anode. However, in response to the recent high current densities in electrolysis, they have lower electrical conductivity than metals, so if you try to use them forcibly, they will have to be extremely thick and large to ensure conductivity. In addition, the electrodes are generally brittle and inconvenient to handle, and their surfaces tend to collapse during electrolysis.

To solve these problems, so-called metal electrodes, which have a coating layer mainly composed of platinum group metals or their oxides on a valve metal substrate (core) typically made of titanium, have been developed and are now widely used. (For example, Japanese Patent Publication No. 48-3954).

However, such metal electrodes have the disadvantage that valve metal is extremely stable when used as an anode, but when used as a cathode, hydrogenation and corrosion of the base material occur, resulting in a short lifespan. When used as an anode, stainless steel, nickel, etc. will corrode in a short period of time, depending on the electrolyte. Therefore, when these metal electrodes are used as either negative or negative electrodes, they can be used by selecting the appropriate material, but in the case of alternating current that carries both negative and negative charges, such as alternating current, they can be used in a short period of time. It has the disadvantage of being corroded.

In addition to these, ceramic electrodes typified by ferrite are known, but they have insufficient conductivity and have the same drawbacks as carbon electrodes. There is also less freedom in shape.

(Objective of the Invention) The object of the present invention is to provide an electrode that has both the characteristics of conventional metal electrodes and carbon electrodes, which can be used particularly for current conduction in corrosive liquids and as electrodes for electrolysis in such liquids. An object of the present invention is to provide a carbonaceous-coated metal electrode capable of passing a yin-yang alternating current, and a method for manufacturing the same.

(Means for Solving the Problems) The present invention provides, firstly, an electrode formed by forming a coating layer on a corrosion-resistant metal substrate, characterized in that the main component of the coating layer is a carbonaceous material. Second, in an electrode formed by forming a coating layer on a metal substrate, a composition containing a carbonaceous substance is coated on the metal substrate by coating or extrusion molding, and then heated after drying. This is a method for manufacturing a carbonaceous electrode characterized by forming a coating layer containing a carbonaceous material as a main component.

The present invention will be explained in more detail below.

As the metal base of the electrode of the present invention, it is preferable to use valve metals such as tungsten, molybdenum, titanium, zirconium, and niobium, or alloys thereof, and depending on the use, stainless steel, Inconel (trade name), Hastelloy (trade name) are used. It is also possible to use corrosion-resistant alloys such as iron-nickel-chromium based alloys, which are appropriately selected depending on the electrolytic conditions such as the electrolytic solution used. The reason for using such corrosion-resistant metals and alloys is that even if the coating layer is dense, it cannot completely prevent the electrolyte and the ions in the electrolyte from penetrating into the coating layer. This is to make it happen.

Before coating the coating layer on the metal substrate, the surface of the metal substrate is roughened by blasting or surface activated by chemical treatment such as etching in order to improve the adhesion resistance between the coating layer and the metal substrate. It can be performed.

The coating layer is mainly composed of carbonaceous material, and its chemical composition can be changed depending on the purpose of use.

The carbonaceous material of the coating layer is made of graphite or amorphous carbon, and preferably contains 50 to 95% graphite, and the particle size of the graphite raw material particles is preferably 94 mesh or less. The amount of graphite in the carbonaceous material is 50%
If it is below, the conductivity and corrosion resistance of the carbonaceous material itself will deteriorate, making it difficult to use it stably for a long period of time, and furthermore, the shrinkage during formation of the coating layer will be too large, making it difficult to form a high-quality coating layer. Also, if the amount of graphite is greater than 95%, the shrinkage during coating layer formation will be reduced, but the coating layer will become brittle.
When heated further, the coating layer itself becomes less compact.

In addition, in the present invention, in order to improve the conductivity of the coating layer, the coating layer can contain tungsten and/or a tungsten compound such as tungsten carbide, and the content thereof is about 0 to 40 mol% of the entire coating layer. It is preferable to do so.

In addition, the coating layer contains carbonaceous substances such as graphite, as well as residues from the heat treatment of the organic binder or binder described later, and since these residues cannot be identified, the molarity of tungsten in a strict sense cannot be determined. % cannot be calculated. Here, the mole percent of tungsten was calculated assuming that the residue was entirely carbonaceous material. When converting this “0 to 40 mol%” to weight percent, it is “0 to 95% by weight”.
% by weight," and it seems as if tungsten is the main component of the coating layer, but this is because the atomic weight of carbonaceous material is 1.
2. The atomic weight of tungsten is 184, which is because the difference in atomic weight between the two greatly affects the weight percent, and the carbonaceous material is still the main component according to mole percent or volume percent.

If the tungsten content exceeds 40 mol%, the coating layer becomes brittle and its strength decreases. Adding a tungsten component to the coating layer improves the conductivity of the coating layer, and since it does not absorb any hydrogen generated during cathodic polarization, stability does not decrease, the cathode overvoltage is extremely small, and it also functions as a valve metal during anodic polarization. This results in better corrosion resistance.

In addition to these components, the coating layer also includes carbonaceous material residues formed by heat treatment of the organic binder or binder contained in the coating composition described below.

A coating layer made of a dense carbonaceous material is formed on the metal substrate, for example, by the following procedure.

First, if necessary, tungsten and/or
Alternatively, a tungsten compound, phenolic resin, organic binder or binder such as polyvinyl alcohol or carboxymethyl cellulose (CMC) is added and kneaded to form a slurry-like coating composition.

The coating composition may be applied to an appropriately shaped metal substrate with a brush or the like and baked, but preferably, the kneaded coating composition is extruded around a rod-shaped metal substrate to form a dense and strong coating layer. do. The thickness of the coating layer is usually about 0.2 to 51 mm.

Subsequently, heat treatment is performed to remove the solvent remaining in the coating layer, stabilize the coating layer, and improve the adhesion resistance between the metal substrate and the coating layer. This heat treatment varies depending on the composition of the coating layer, etc., but is usually at 100 to 1,800°C for 30 minutes to 10 hours, especially at 100 to 680°C when the amount of residual hydrogen is not a problem.
Preferably, the reaction is carried out at 0.degree. C. in vacuum or in an inert atmosphere.

This allows a sufficiently dense coating layer to be formed, but
Furthermore, if a coating layer is not completely formed on the entire surface of the metal substrate and only a small portion of the coating layer is exposed, the metal substrate may be impregnated by being immersed in the coating composition, for example, as necessary.

(Examples) Examples of the present invention will be described below, but these Examples do not limit the present invention.

Example 1 Graphite powder of 100 to 200 mesh, graphite powder of 325 mesh or less, amorphous carbon powder of 325 mesh or less, polyvinyl alcohol, and phenol resin in a weight ratio of 25:25:15:5:60 (percentage ratio of approx. 19.2:19.2:11.6:3.8246
．． After blending in step 2), kneading is carried out, and the kneaded product is vacuum extruded around a tungsten base wire (diameter 3 mm, length 200 mm) with a purity of 99% or more that has been subjected to mechanical polishing after drawing.
A carbonaceous material coating layer No. 4 was formed and then dried at 120°C. Further, heat treatment was performed at 400° C. for 3 hours in a non-oxidizing atmosphere. The composition of this coating layer, measured by X-ray diffraction, was 57.4% (Graphai) and 42.6% amorphous carbon.
(by weight and moles).

The periphery of the carbonaceous coated electrode, in which the tungsten base wire produced in this way was coated with a carbonaceous substance, was covered with a sealing tape made of fluororesin, leaving 20 fins in the length direction, and was used as a sample for electrolysis (the area of the n-crest part was is 0.0314d+*2). Two of these electrolytic samples were placed in parallel in hydrochloric acid with a liquid temperature of 60°C and a concentration of 200 g/A' so that the distance between the electrodes was ioam,
100 A/d while reversing the direction of current every second
Electrolysis was carried out at a current density of m''.

For comparison, an electrolytic test was conducted under the same conditions by covering the circumference of a rod-shaped graphite electrode of the same shape, that is, diameter 5 mm, with a sealing tape leaving a length of 2 cm.

As a result, stable electrolysis continued for more than 2,000 hours with the electrode of this example, whereas with the graphite rod-shaped electrode, it was difficult to keep the liquid temperature constant due to heat generation.
After about 0 hours, the electrolytic surface of the electrode started to collapse, and 3
After 0 hours, the thickness was reduced to about half, and after 35 hours, it became impossible to apply electricity.

Weight ratio of graphite powder, amorphous carbon powder, thickener, phenolic resin, and tungsten powder is 75:25, respectively.
=4260:20 (percentage ratio approximately 40.8:13.6:2
．． 17:32. (3:10.9), then kneaded, and the kneaded material was drawn around a molybdenum base wire (diameter: 3 fins, length: 200 fins) with a purity of 99.9% or higher, which was mechanically polished. A carbonaceous material coating layer containing tungsten powder was formed by vacuum extrusion molding, and was further dried at 110° C. and heat treated at 600° C. for 2 hours in a non-oxidizing atmosphere. When the composition of the carbonaceous material coating layer was measured by X-ray diffraction method and fluorescent X-ray method, it was found that 53.1% by weight of graphite and 3% by weight of amorphous carbon.
2.8% by weight and 14.1% by weight of tungsten.

Two carbonaceous electrodes coated with a carbonaceous substance on the molybdenum base wire obtained in this manner were heated at 200 g/200 g/m at a liquid temperature of 70″C.
1 of hydrochloric acid, the distance between electrodes is 10 mm, and the electrolytic area is 0.1 mm.
An electrolytic test was conducted while arranging the electrodes in parallel so that the current was 0.0314 dm'' and supplying 5011z alternating current of 100 A/dm'' from the molybdenum base wire. The specific resistance of this carbonaceous coating layer is 0.13 Ω, and the current is 100 A/dm.
A layer thickness of 1 fl only causes a voltage drop of 0.0L3V. Cell voltage shows 0.94-1.02V 2000
No changes were observed over time. At this point, the electrolysis was stopped and the cut surface of the electrode was analyzed using an XMA (XvA microanalyzer), but no voids were formed between the molybdenum base wire and the carbonaceous coating layer, and no compound layer was observed.

On the other hand, when a carbonaceous electrode containing tungsten powder was prepared in the same manner as the above method except that the molybdenum base wire was not used and subjected to an electrolytic test, heat generation was significant and the liquid boiled (the electrode shape was 5 am in diameter and 200 m in length). Yes, the length from the current supply part to the electrolytic part is 100mm, and the specific resistance is 0.13Ω・
If the value and supply current are 3.14A, the ohmic loss is 6.6
65W of heat will be generated at 2Ω).

Also, a diameter of 3fl and a length of 2 without a carbonaceous coating layer formed.
When a 00 mm molybdenum wire was similarly subjected to an electrolytic test, the molybdenum wire was violently eluted.

The ratio of tungsten in the coating layer composition was 0.10, 30, 50, 70, and 90 (wt%) in the same manner as in Example 2.
Carbonaceous coated metal electrodes were fabricated by coating six types of molybdenum wires with carbonaceous substances.

The cathode potential of this electrode was measured under the following conditions. The results are shown below, and it can be seen from the results that the addition of tungsten further lowers the cathode potential and improves the electrode activity.

Measurement method: Intermittent current method Solution: 150g/j! Hydrochloric acid aqueous solution temperature: 28-29°C Current density: 20 A/ds+” Electrolytic area: 0.0314 dm” Anode Titanium electrode whose surface is coated with a thin film containing ruthenium dioxide as the electrode active material Reference electrode: 5CE (saturated calomel electrode) Tungsten cathode potential [νvsSCE) ratio in raw materials (wt%) 0 -1.13 10 -0.83 30 -0.78 50 -0.74 70 -0.7490
-0. 69 husband" 1 Tsuji ethangestene, molybdenum, titanium, zirconium, tantalum, niobium, copper, nickel, aluminum, Ti-
Carbonaceous electrodes were prepared in the same manner as in Example 2 using 12 types of metals and alloys as metal substrates: 5Ta, stainless steel 316L, and 30% cupronickel (Cu-30%Ni-0.5%Fe) (purity was All commercially available purity).

These electrodes were subjected to an electrolytic test in the same manner as in Example 2. Tungsten, molybdenum, and
Titanium, zirconium, tantalum, niobium, Ti-5T
A and stainless steel 316 were used, and copper, nickel, aluminum, and 30% cupronickel were severely dissolved in about 20 to 150 hours, making it impossible to electrolyze them.

(Effects of the Invention) Firstly, the present invention uses a corrosion-resistant metal as the metal base for the electrode, so the metal base has corrosion resistance and conductivity and can be formed into any shape. It becomes possible to make it more compact.

Second, since the carbonaceous coating layer is mainly made of a dense carbonaceous material, it can withstand use in alternating currents of negative and yang, which was difficult to do with conventional metal single-layers.

Thirdly, carbonaceous materials have high corrosion resistance, and when they contain tungsten or tungsten compounds, conductivity and electrode activity are further improved, allowing operation at low electrode potentials that are stable for long periods of time with good durability. It can be performed.

Claims (9)

[Claims] (1) A carbonaceous coated metal electrode comprising a coating layer formed on a corrosion-resistant metal substrate, characterized in that the main component of the coating layer is a carbonaceous substance. (2) The electrode according to claim (1), wherein 50 to 95% by weight of the carbonaceous material is graphite. (3) The electrode according to claim (1) or (2), wherein the coating layer contains 95% by weight or less of tungsten and/or a tungsten compound in addition to the carbonaceous material. (4) The electrode according to claim (3), wherein the tungsten compound is tungsten carbide powder. (5) The metal base is tungsten, molybdenum, titanium,
The electrode according to any one of claims (1) to (4), which is a valve metal such as zirconium, tantalum, niobium, or an alloy thereof. (6) The electrode according to any one of claims (1) to (4), wherein the metal substrate is an iron-nickel-chromium alloy such as stainless steel. (7) In an electrode formed by forming a coating layer on a metal substrate, a composition containing a carbonaceous substance is coated on the metal substrate by coating or extrusion molding, and then heated after drying to form a composition containing a carbonaceous substance as the main component. A method for producing a carbonaceous electrode, the method comprising forming a coating layer. (8) The method according to claim (7), wherein the surface of the metal substrate is pretreated to roughen or activate it. (9) The method according to claim (7) or (8), wherein the coating layer is formed by repeating coating or extrusion multiple times.