JPH0768626B2 - Carbonaceous coated metal electrode and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to electrolysis in corrosive liquids such as surface treatments such as electrolytic etching of metals and organic electrolysis, or electrolysis through direct current or alternating current in these liquids. The present invention relates to a corrosion-resistant electrode used when performing.

(Prior art and its problems) A carbon electrode has been conventionally used as an electrode for electrolysis in a corrosion-resistant conductive member or a corrosive liquid. As a non-metal, the carbon electrode has a large electric conductivity and excellent corrosion resistance,
It effectively functions as both a cathode and an anode. However, as in recent years, in order to increase the current density in electrolysis, if it is forcibly used because of its low electric conductivity as compared with metal, it becomes extremely thick and large in order to secure conductivity. Further, the electrode is generally fragile and inconvenient to handle, and the surface thereof is easily broken during electrolysis.

In order to solve such a problem, a so-called metal electrode has been developed and widely used in which a coating layer containing a platinum group metal or its oxide as a main component is provided on a valve metal substrate (core) typified by titanium. (For example, Japanese Patent Publication No. 48-3954). However, such a metal electrode has a drawback that when a valve metal is used as an anode, it is extremely stable, but when it is used as a cathode, hydrogenation or corrosion of the base material occurs and the life is short. Used as stainless steel,
When nickel or the like is used as the anode, it corrodes in a short time depending on the electrolytic solution. Therefore, these metal electrodes can be used by selecting the material when they are used as either of the positive and negative electrodes, but in the case of alternating current such as alternating current, which has both positive and negative charges, it takes a short time. It has the drawback of corrosion.

Other than these, ceramic electrodes typified by ferrite are known, but they have insufficient conductivity and have the same drawbacks as carbon electrodes. In addition, there is little freedom in shape.

(Object of the invention) The object of the present invention is useful as an electrode having the characteristics of conventional metal electrodes and carbon electrodes, especially as an electrode for energizing in a corrosive liquid and as an electrode for electrolysis in such a liquid. An object of the present invention is to provide a carbonaceous coated metal electrode capable of passing an alternating current of Yin and Yang and a method for producing the same.

(Means for Solving the Problems) First, the present invention relates to an electrode formed by forming a coating layer on a corrosion-resistant metal substrate, wherein the coating layer comprises a carbonaceous material composed of graphite and amorphous carbon, and 0-40. A carbonaceous coated metal electrode comprising a mol% of tungsten and / or a tungsten compound. Secondly, in the electrode formed by forming a coating layer on a metal substrate, carbon is formed on the metal substrate. Characterized in that a composition containing a carbonaceous material is applied or extrusion-molded to be coated, dried and then heated to form a coating layer comprising a carbonaceous material and 0 to 40 mol% of tungsten and / or a tungsten compound. It is a manufacturing method of a carbonaceous electrode.

The present invention will be described in more detail below.

As the metal substrate of the electrode of the present invention, it is preferable to use a valve metal such as tungsten, molybdenum, titanium, zirconium, niobium or an alloy thereof, and depending on the application, stainless steel, Inconel (trade name), Hastelloy (trade name). Corrosion-resistant alloys such as iron-nickel-chromium based alloys can also be used, and they are appropriately selected depending on the electrolysis conditions such as the electrolytic solution used. The reason for using such a corrosion-resistant metal or alloy is that even if the coating layer is dense, it is not possible to completely prevent the electrolytic solution or ions in the electrolytic solution from penetrating into the coating layer, and improve the resistance to these. This is to allow it.

Before coating the metal substrate with the coating layer, in order to improve the adhesiveness between the coating layer and the metal substrate, the surface of the metal substrate is roughened by blasting or surface activated by chemical treatment such as etching. It can be carried out.

The coating layer contains a carbonaceous substance as a main component, and its chemical composition can be changed depending on its intended use.

The carbonaceous material of the coating layer is preferably made of graphite or amorphous carbon, usually contains 50 to 95% of graphite, and the particle size of the graphite raw material particles is preferably 94 mesh or less. If the amount of graphite in the carbonaceous material is 50% or less, the electrical conductivity and corrosion resistance of the carbonaceous material itself deteriorate, making stable use difficult for a long period of time, and the shrinkage during the formation of the coating layer is too large, resulting in a good quality coating. It becomes difficult to form layers. On the other hand, if the amount of graphite is more than 95%, the shrinkage at the time of forming the coating layer becomes small, but the coating layer becomes brittle, and the heating of the coating layer itself becomes poor when heated.

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

In addition to carbonaceous substances such as graphite, the coating layer contains residues due to the heat treatment of the organic binder or binder described later, and these residues cannot be specified. % Cannot be calculated. Here, the mol% of tungsten was calculated assuming that all the residues were carbonaceous materials. When this "0-40 mol%" is converted to wt%, it becomes "0-95 wt%", and it seems as if tungsten is the main component of the coating layer. This is because the difference between the atomic weights of 184, which has an atomic weight of 184, has a large effect on the weight%.

If the content of tungsten exceeds 40 mol%, the coating layer becomes brittle and the strength decreases. Addition of a tungsten component to the coating layer improves the conductivity of the coating layer, and does not absorb the hydrogen generated during negative polarization at all, so the stability does not decrease, the cathode overvoltage is extremely small, and it functions as a valve metal during positive polarization. Good corrosion resistance.

In addition to these, the components of the coating layer include the residue of the carbonaceous substance formed by the heat treatment of the organic binder or the binder contained in the coating composition described below.

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

First, if necessary, tungsten and / or
Alternatively, an organic binder or a binder such as a tungsten compound, a phenol resin, polyvinyl alcohol or carboxymethyl cellulose (CMC) is added and kneaded to obtain a muddy coating composition. The coating composition may be applied to a metal substrate having an appropriate shape 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. To do. The thickness of the coating layer is usually about 0.2-5 mm.

Subsequently, heat treatment is performed to remove the solvent remaining in the coating layer, stabilize the coating layer, and improve the adhesiveness between the metal substrate and the coating layer. Although this heat treatment varies depending on the composition of the coating layer, etc., it is usually carried out at 100 to 1800 ° C for 30 minutes to 10 hours, and particularly at 100 to 680 ° C when the residual hydrogen amount does not matter, in a vacuum or an inert atmosphere. desirable. With this, a sufficiently dense coating layer can be formed, but if the coating layer is not completely formed on the entire surface of the metal substrate and only a very small portion thereof is exposed, for example, the above-mentioned It is also possible to carry out the impregnation treatment by immersing it in the coating composition.

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

Example 1 100 to 200 mesh graphite powder, 325 mesh or less graphite powder, 325 mesh or less amorphous carbon powder,
Polyvinyl alcohol and phenolic resin in weight ratio of 25: 25: 15: 5: 60, respectively (percentage ratio about 19.2: 19.2: 11.6: 3.8:
46.2) and then kneading the mixture, and subjecting the kneaded product to drawing mechanical polishing to obtain a tungsten substrate wire having a purity of 99% or more (diameter: 3 m).
m, length 200 mm) by vacuum extrusion to form a 1 mm thick carbonaceous material coating layer and then dried at 120 ° C. Furthermore, heat treatment was performed at 400 ° C. for 3 hours in a non-oxidizing atmosphere. The composition of this coating layer was determined by X-ray diffractometry and found to consist of 57.4% graphite and 42.6% amorphous carbon (weight and moles).

The tungsten substrate wire thus produced was coated with a carbonaceous substance, and the periphery of the carbonaceous coated electrode was covered with a fluororesin seal tape leaving 20 mm in the lengthwise direction to obtain a sample for electrolysis (the exposed area is 0.0314dm ² ). Two samples for this electrolysis
The distance between the electrodes is 10 mm in a hydrochloric acid solution with a temperature of 60 ° C and a concentration of 200 g /
The cells were arranged in parallel with each other so as to be electrolyzed at a current density of 100 A / dm ² while reversing the direction of current every one second.

For comparison, a graphite rod having the same shape, that is, a graphite rod having a diameter of 5 mm was similarly covered with a sealing tape, leaving a length of 2 cm, and an electrolytic test was performed under the same conditions.

As a result, in the electrode of this example, stable electrolysis continued for 2000 hours or more, whereas it was difficult to keep the liquid temperature constant due to heat generation in the graphite rod electrode, and after about 10 hours, The electrolytic surface of the electrode began to collapse, and after 30 hours, the thickness was reduced to about half, and after 35 hours, current flow became impossible.

Example 2 Graphite powder, amorphous carbon powder, thickening agent, phenol resin and tungsten powder in a weight ratio of 75: 25: 4: 6, respectively.
0:20 (percentage ratio about 40.8: 13.6: 2.17: 32.6: 10.9) was blended and then kneaded, and the kneaded product was drawn and mechanically polished
99.9% or more molybdenum base wire (diameter 3 mm, length 200 mm)
Was vacuum extruded to form a carbonaceous material coating layer containing 1 mm thick tungsten powder, 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 an X-ray diffraction method and a fluorescent X-ray method, it was 53.1% by weight of graphite, 32.8% by weight of amorphous carbon and 14.1% by weight of tungsten.

Two carbonaceous electrodes coated with a carbonaceous substance on the thus obtained molybdenum base wire were placed in parallel in 200 g / hydrochloric acid at a liquid temperature of 70 ° C. so that the distance between the electrodes was 10 mm and the electrolytic area was 0.0314 dm ^2. An electrolytic test was performed while supplying 100 A / dm ² of 50 Hz alternating current from the molybdenum substrate wire. The specific resistance of this carbonaceous coating layer is 0.13 Ωcm, current 100 A / dm ² , layer thickness 1 mm.
Causes only 0.013V drop. Cell voltage is
No change was observed even after 2000 hours showing 0.94 to 1.02V. At this point, the electrolysis was stopped and the cut surface of the electrode was analyzed by XMA (X-ray microanalyzer), but no void was generated between the molybdenum substrate wire and the carbonaceous coating layer, and no compound layer was observed.

On the other hand, except that the molybdenum base wire was not used, a carbonaceous electrode containing tungsten powder was prepared in the same manner as in the above method and subjected to an electrolytic test. , Length from current supply part to electrolysis part is 100mm, specific resistance is 0.13Ω ・ cm, supply current is 3.1
If it is 4A, the ohmic loss is 6.62Ω and 65W of heat is generated).

In addition, the carbonaceous coating layer is not formed diameter 3mm, length 200mm
When the molybdenum wire of No. 1 was similarly subjected to the electrolytic test, the molybdenum wire was severely eluted.

Example 3 Six kinds of molybdenum wires with the ratio of tungsten in the coating layer composition changed to 0, 10, 30, 50, 70 and 90 (% by weight) were coated with a carbonaceous material in the same manner as in Example 2. A carbonaceous coated metal electrode was prepared.

The cathode potential of this electrode was measured under the following conditions. The results are shown below. From this result, it is understood that the addition of tungsten further lowers the cathode potential and improves the electrode activity.

Measurement method: Current interruption method Solution: 150 g / hydrochloric acid aqueous solution Temperature: 28-29 ° C Current density: 20 A / dm ² Electrolytic area: 0.0314 dm ² Anode: Titanium electrode whose surface is coated with a thin film of ruthenium oxide as an electrode active substance. Reference electrode: SCE (saturated calomel electrode) Example 4 Tungsten, molybdenum, titanium, zirconium, tantalum, niobium, copper, nickel, aluminum, Ti-5T
a, Stainless steel 316L, 30% cupro nickel (Cu-30% N
A carbonaceous electrode was produced in the same manner as in Example 2 using 12 kinds of metals or alloys of i-0.5% Fe) as the metal substrate (purity is all commercially available purity).

These electrodes were subjected to an electrolytic test in the same manner as in Example 2. After 2000 hours, the cell voltage, and no abnormalities were observed in the cut surface were tungsten, molybdenum, titanium, zirconium, tantalum, niobium, Ti-5Ta and stainless 316L, and copper, nickel, aluminum,
30% cupronickel was so strongly dissolved in 20 to 150 hours that electrolysis became impossible.

(Effects of the Invention) In the present invention, firstly, since a corrosion-resistant metal is used as the metal substrate for electrodes, the metal substrate has corrosion resistance and conductivity, and can be formed into any shape. Can be made compact.

Secondly, since the carbonaceous coating layer is mainly composed of a dense carbonaceous material, it can withstand use in an alternating current of the cathode, which has been difficult with conventional metal electrodes.

Thirdly, the carbonaceous material has a high corrosion resistance, and when it contains tungsten or a tungsten compound, the conductivity and the electrode activity are further improved, and it is operated at a low electrode potential which is stable for a long period of time with good durability. It can be performed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisaaki Yokota 3-5-21 Hamatake, Chigasaki City, Kanagawa Prefecture (72) Inventor Shingo Yoshida 1 731 Tehiro, Kamakura City, Kanagawa Nishigaya Shinko Dormitory (56) References 59-6388 (JP, A)

Claims (8)

[Claims] 1. An electrode comprising a coating layer formed on a corrosion-resistant metal substrate, the coating layer comprising a carbonaceous material consisting of graphite and amorphous carbon and 0-40 mol% of tungsten and / or a tungsten compound. A carbonaceous-coated metal electrode characterized by being dense. 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, wherein the tungsten compound is a tungsten carbide powder. 4. The metal substrate according to claim 1, which is a valve metal such as tungsten, molybdenum, titanium, zirconium, tantalum, niobium or an alloy thereof. Electrodes. 5. The electrode according to any one of claims (1) to (3), wherein the metal substrate is an iron-nickel-chromium alloy such as stainless steel. 6. An electrode formed by forming a coating layer on a metal substrate, coating or extruding a composition containing a carbonaceous substance on the metal substrate to coat, drying and heating the mixture to remove the carbonaceous substance and the carbonaceous substance.
A method for producing a carbonaceous electrode, which comprises forming a dense coating layer composed of -40 mol% of tungsten and / or a tungsten compound. 7. The method according to claim 6, wherein the surface of the metal substrate is pretreated to roughen or activate it. 8. A coating layer is formed by repeating coating or extrusion molding a plurality of times to form a coating layer.
Item or the method according to Item (7).