JPH10310892A - Electrode plate for electrolysis of water or aqueous solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrode plate for electrolysis less liable to pollute electrolyzed water and not generating black turbidity or causing cracking by specifying the impurity content, total porosity and bending strength of an electrode plate consisting of a carbonaceous material and a resin cured body. SOLUTION: The impurity ash content of graphite powder is reduced to <=1% by screening, acid washing and ash removal treatment after graphitization. A blend of 50-90 mass % of the resultant graphite powder with 10-50 mass % resin cured body is kneaded, pulverized, charged into a preheated metallic mold and subjected to hot press compacting at about 190 deg.C under about 200MPa pressure. Pores are filled with the resin and hardening is carried out to obtain the objective electrode plate for electrolysis having <=1% impurity ash content, <=5% total porosity and <=10MPa bending strength and suitable for use as an anode capable of smoothly and efficiently generating O2 or CO2 by electrolysis of water or an aq. soln.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode plate for electrolysis of water or an aqueous solution (hereinafter sometimes simply referred to as an electrode plate). More specifically, the present invention relates to water or water which generates oxygen or carbon dioxide as a solvent. The present invention relates to an electrode plate suitable for use as an anode for electrolysis of an aqueous solution of an electrolyte.

[0002]

2. Description of the Related Art In recent years, attention has been paid to water or an aqueous solution in which carbon dioxide is dissolved using a carbon electrode in order to promote the growth of plants. In order to obtain such water or an aqueous solution, a petroleum or coal coke is used as a filler, and coal tar pitch or the like is used as a binder, molded, calcined, and an electrode made of a graphite material obtained by graphitization is used as an anode in an aqueous electrolytic bath. When electrolysis (electrolysis) is performed, anodic oxidation occurs not only on the electrode surface but also in the pores, a large amount of graphite particles are dropped, and finally the electrolytic bath becomes black. In addition, when electrolysis is performed using vitreous carbon prepared from a thermosetting resin and having almost no pores as an anode, local oxidative anodic oxidation occurs, peeling occurs on the electrode surface, and finally, the electrode breaks and becomes unable to electrolyze. I fall.

Accordingly, the present applicant has solved the above-mentioned disadvantages of the prior art and used the anode as an anode for electrolysis of water or an aqueous solution of an electrolyte using water with the generation of oxygen or carbon dioxide. We have developed an electrode for electrolysis in which the carbon powder is less likely to fall off and no breakage of the electrode occurs, and filed this application earlier (see JP-A-7-34280).

[0004] The invention of the prior application is an electrode for electrolysis comprising a composition of 50 to 90% by mass of a carbonaceous substance and 10 to 50% by mass of a cured resin, wherein the carbonaceous substance and the cured resin are in the above-mentioned range. In this case, the specific resistance of the electrode can be reduced and the generation efficiency of carbon dioxide can be increased. In addition, electrolysis of water or an aqueous solution can be performed without causing carbon powder to fall off and without causing breakage of the electrode. This electrode is prepared by mixing a carbonaceous material and resin in the above range at a temperature of around 180 ° C and pressure.
Because it is manufactured by hot pressing at around 20 MPa,
The carbonaceous substance (carbon powder) is in a form held and bound by the cured resin, which makes it difficult for the carbon powder to separate from the cured resin even when used for electrolysis, so that the carbon powder is less likely to fall off. It is considered something. In addition, it is considered that since the cured resin is hardly consumed by electrolysis, breakage and collapse of the electrode were prevented.

[0005]

By the way, the electrode for electrolysis according to the invention of the prior application reduces the falling off of the carbon powder by limiting the mixing ratio of the carbonaceous substance and the cured resin, thereby reducing the general carbon electrode and the like. Although the performance as an electrode for electrolysis of water or an aqueous solution was made superior to that of a graphite electrode, a factor that has a particularly large effect on the performance of an electrode plate for electrolysis of water or an aqueous solution is a carbonaceous material and a resin. In addition to the compounding, impurities, pores, and strength may be mentioned. For example, if there are many impurities, the electrolyzed water is contaminated with impurities dissolved from the anode during electrolysis and cannot be used depending on the application. If there are many pores, carbon is consumed from the inside on the anode side, and the life of the electrode plate is shortened. On the cathode side, a precipitate is formed inside, and when the polarity is switched, the precipitate is hard to separate from the electrode plate. If the strength is low, cracks are likely to occur due to expansion due to water absorption, and the life of the electrode plate is shortened. And so on.

The present invention has been made on the basis of the above circumstances, and has as its object to minimize contamination of electrolyzed water and to prevent black turbidity or cracking, and to comprise a carbonaceous material and a resin. An electrode plate for electrolysis of water or an aqueous solution is provided.

[0007]

In order to achieve the above object, an electrode plate for electrolysis of water or aqueous solution according to the present invention comprises an electrode plate for electrolysis of water or aqueous solution comprising a carbonaceous substance and a resin as a composition. In this method, impurities are formed with ash content of 1% or less, total porosity of 5% or less, and bending strength of 10MPa or more.

In the electrode plate for electrolysis of water or aqueous solution according to the present invention, the resin may be heated to form a cured resin.

Further, in the electrode plate for electrolysis of water or aqueous solution according to the present invention, even if the carbonaceous substance is composed of 50 to 90% by mass and the cured resin is composed of 10 to 50% by mass. Good.

Hereinafter, the structure and operation of the present invention will be described in detail. The impurities in the carbon electrode are derived from the raw materials,
There are Fe, Ca, Mg, Al, B, Ni, Si, Ti, V and the like. If these impurities are present mainly in the carbonaceous material of the anode-side electrode, the electrode will be consumed as the water is electrolyzed, and the impurities contained will be eluted as ions, thus contaminating the electrolyzed water. Not all impurities are toxic to plants, but see "Plant Environment and Arrangement" AHFitter, RK
As described by M. Hay (Society Press Center), Chapter 6 "Toxicity of ion components", Al and Ni are unnecessary and toxic to plants, and other ions are also plant properties. More toxic to soil and soil. That is, as water to be sprayed on plants, electrolyzed water containing a large amount of impurities is not preferable, and sometimes becomes harmful. In particular, the water sprayed on the leaf surface of the plant may evaporate and concentrate on the leaf surface, and the effect of electrolyzed water is considered to be greater than the water described in the literature. The harmlessness of the impurities in the electrolyzed water cannot be determined unconditionally due to the resistance to the toxicity of plant species and ions, the properties of soil, and the like. However, from the results of tests on various plants up to now, if the total impurities in the carbon electrode plate are 1% or less in ash content, no toxicity to the plants that may be caused by the impurities has appeared, so the electrolytic It was considered preferable as an electrode for generating water.
For this reason, in the present invention, impurities are reduced to 1% or less in ash content. In addition, the measurement method of JIS R 7221 is used for the measurement of ash content.

By the way, as for the ash content in the electrode plate, the ash content of the electrode plate is almost determined by the type of the carbon material as the raw material, since there is almost no ash content in the resin or pitch used for the binder. For example, natural graphite has many impurities. But,
Deashing treatments such as sorting, acid washing, and graphitization can reduce ash content. The acid washing is a method in which metals in graphite are changed into metal salts that can be easily dissolved, and washed out of the graphite with water. When a high temperature treatment of about 3000 ° C called graphitization is performed, impurities are vaporized and ash can be reduced to a low concentration of 1% or less.

On the other hand, breakage or cracking of the carbon electrode plate generated during electrolysis of water or an aqueous solution is related to the strength of the carbon electrode plate. The breakage of the electrode plate near the water interface depends on the strength of the remaining portion of the carbon electrode plate consumed by electrolysis, and is not affected by the mixing ratio of carbon and resin. The vertical cracks appearing at the end of the life of the electrode plate are considered to be caused by the stress caused by the resin absorbing water and expanding. Therefore, it is considered that it is necessary to increase the strength to prevent the vertical crack. Therefore, in the present invention, the bending strength is set to 10 MPa.
This is what has been described above. In addition, the measurement method of the carbon society standard (JCAS-10-1968) is used for the measurement of the bending strength.

In addition, pores can be cited as a cause of shortening the life of the electrode plate. When there are many pores, it is considered that carbon is consumed from the inside on the anode side, and the strength is affected by electrolysis. From such a thing,
In the present invention, the total porosity is set to 5% or less. The total porosity (%) is obtained by (true specific gravity−bulk specific gravity) × 100 / true specific gravity, and the measurement of the true specific gravity uses a measuring method of JIS R 7221.

That is, in the carbon electrode plate of the present invention, the ash content of impurities is 1% or less, the total porosity is 5% or less, and the bending strength is 10 MPa or more.
Electrolytic water contamination by the carbonaceous material constituting the electrode plate can be reduced, and the carbonaceous material can be uniformly consumed to reduce turbidity and cracks, thereby extending the life of the electrode plate itself.

[0015]

Embodiments of the present invention will be described below. Demineralize in advance and use graphite powder with an ash content of 1% or less as raw material. The graphite powder and the resin are mixed and pulverized, then placed in a preheated mold, and hot-pressed at a predetermined temperature (about 190 ° C.) under pressure (about 20 MPa). From the molded body obtained in this way, impurities are less than 1% in ash content, and the resin is filled and hardened by the hot-press molding,
An electrode plate for electrolysis with a total porosity of 5% or less and a bending strength of 10 MPa or more can be obtained. That is, when the mixture of the artificial graphite and the resin is molded while applying heat, a mixture having almost no pores is obtained. Also, if the mixing ratio of the resin is large,
As the bonding strength between graphite particles increases, the
It may be adjusted within 10 to 50% by mass.

[0016] The carbon material obtained by mixing the carbonaceous material with the pitch, pulverizing, forming and firing is heated at a high temperature of about 3,000 ° C to be graphitized, and the resulting graphite material (bending strength of about 10 MPa) is added to a plate. Alternatively, the graphite plate may be impregnated with a resin to fill the pores. The molded body obtained in this way also has impurities of 1% or less in ash content and a total porosity of less than 1%.
Electrode plates for electrolysis with 5% or less and a bending strength of 10 MPa or more can be obtained. In this case, not all the pores are filled by the volatile components and shrinkage of the resin, but the pores are almost eliminated by repeating this impregnation operation. Although the strength is slightly increased by the impregnation operation, the influence of the strength of the substrate is large. Hereinafter, Examples and Comparative Examples will be described with other manufacturing means.

[0017]

【Example】

[Example 1] Demineralization was performed in advance, and the amount of impurities was 1
% Of artificial graphite of 70% by mass or less, mixed with 30% by mass of a resin, crushed, placed in a preheated mold, and hot-pressed on a steel plate at a temperature of 190 ° C. at a pressure of 20 MPa for 30 minutes. The properties of the obtained molded product were as follows: ash content: 0.2%, porosity: 1% or less (0.005 cc / g in pores), and flexural strength: 90 MPa.

[Example 2] A graphite material (flexural strength of about 38 MPa) formed by applying a high temperature of about 3000 ° C to a carbon material to form a plate is formed into a plate shape, and the graphite plate has a pore of 5% or less. Until the resin was impregnated. The properties of the obtained molded body are as follows: ash content: 0.1%, porosity: 3%, bending strength: 40 MPa
Met.

Example 3 A mixture of 75% by mass of natural graphite having an ash content of 1% or less and 25% by mass of a pitch binder, pulverized, molded, and calcined has a pore of 5% or less. The resin was impregnated and molded until it became thin. The properties of the obtained molded product were as follows: ash content: 1%, porosity: 5%, bending strength: 10MP
a. In this example, the strength is lower than that of Examples 1 and 2 because a fired substrate is used. In addition, it is necessary to repeat the process to fill many pores with resin. The ash
Since about 1% of natural graphite was used as raw material, the ash content was also high.

Comparative Example 1 Natural graphite 85 different from that of Example 3
The mixture was crushed, molded, and fired by mixing 15% by mass of the pitch binder with 15% by mass. The properties of the obtained molded body are ashes: 3
%, Porosity: 20%, flexural strength: 8 MPa. In this example, the firing was performed with less pitch binder than in Example 3, so that the strength was lower than that in Example 3. Further, since the base material was not fired but impregnated with resin, the pores increased. The ash content was also high because natural graphite with an ash content of about 3% was used as a raw material.

Next, the compacts obtained in Examples 1 to 3 and Comparative Example 1 were made into an electrode plate having a length of 200 mm, a width of 50 mm and a thickness of 5 mm, and immersed in 2 liters of water to a length of 150 mm. 1
Electrolysis was performed by passing a current of 00 mA. The polarity was switched every four hours. As a result, the electrode plates of Examples 2 and 3 were found to be more opaque than the electrode plates of Example 1, but could be used satisfactorily. On the other hand, in the electrode plate of Comparative Example 1, a phenomenon was observed in which the precipitate on the cathode surface was not sufficiently separated during the polarity switching several times and remained on the surface. The cloudiness was also much higher than that of Example 3, and it broke and collapsed after 5 days. In Comparative Example 1, inorganic substances (eg, Fe,
Al, Si, etc.) eluted much, and the composition of the electrolyte in the water changed.

[0022]

As described above, according to the electrode for electrolyzing water or an aqueous solution according to the present invention, the contamination of electrolyzed water by impurities harmful to plants can be minimized, and black turbidity and cracks can be prevented. Without causing this, it is possible to prolong the life and to produce carbon dioxide smoothly and efficiently.

Claims (3)

[Claims] In an electrode plate for electrolysis of water or an aqueous solution comprising a carbonaceous substance and a resin as a composition, impurities are ash content.
% Or less, a total porosity of 5% or less, and a bending strength of 10 MPa or more. 2. The electrode plate according to claim 1, wherein the resin is a cured resin. 3. The electrode plate for electrolysis of water or an aqueous solution according to claim 1, wherein the composition comprises 50 to 90% by mass of the carbonaceous substance and 10 to 50% by mass of the cured resin.