JPH03135494A - Carbonaceous electrode base material - Google Patents

Abstract

PURPOSE:To obtain an electrode base material having a long service life, high strength, and superior electric conductivity by regulating the half-width of the <002> plane of carbon determined by a wide-angle X-ray to a specific value and also regulating the relative integrated intensity of oxygen element / carbon element determined by surface analysis by an X-ray photoelectron spectroscopic method to a specific value. CONSTITUTION:This electrode base material is the one usable for cathode as well as for anode for D.C. electrification, capable of being used by converting polarity at every prescribed amount of electrification, and consisting of carbonaceous material, and further, the half-width of the <002> plane of carbon determined by a wide-angle X-ray is regulated to 5.5-8.0 deg. and also the relative integrated intensity of oxygen element / carbon element determined by surface analysis by ESCA (X-ray photoelectron spectroscopic method) is regulated to 0.18-0.60. Since the consumption of electrification can be extremely reduced and high physical strength can be provided in this carbonaceous electrode base material, this carbonaceous electrode base material can produce useful effects for electrolysis and electroosmosis and dehydration.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to electrolyzing seawater or an aqueous solution containing salt in order to prevent biofouling or sterilization in a cooling water system, or to electrolyze sludge with electricity. The present invention relates to a long-life, high-strength carbonaceous electrode base material that can be used as both an anode and a cathode in cases such as dehydration by osmosis.

(Prior art) As a polar base material for an electrode for current electrolysis of an aqueous solution containing salt,
The carbonaceous electrode base material is advantageous in that it can be used as either an anode or a cathode. Among these, a graphite electrode base material whose heat treatment temperature is close to 3000°C is preferably used. This is because graphite has less oxidative consumption due to oxygen generated from the anode during electrolysis than carbon.

However, if only the anode is selectively consumed, the lifespan of the anode and cathode will differ and this is not desirable for stable operation. Therefore, since the same electrode base material is used for the anode and cathode, the polarity is changed to the opposite polarity during DC current flow. A method of operation will be adopted.

When a graphite electrode is used for electrolysis of seawater, calcium ions contained in the seawater form an insulating layer of calcium carbonate on the cathode surface, which inhibits current flow. Therefore, the formation of an insulating layer is prevented by making the two electrodes have opposite polarities before it becomes difficult to conduct electricity.

However, even with the above-mentioned graphitic carbon electrode, in addition to oxidative consumption,
Since it is subject to various electrochemical corrosion effects, its lifespan is not permanent. For example, in graphitic carbon sintered plates, binder coke is selectively eroded, causing graphite particles to fall off, which is a problem. Furthermore, when a graphitic carbon material electrode is used in an aqueous solution containing sulfate ions, there is a problem in that the sulfate ions enter between the graphite crystal layers and destroy and consume the graphite.

Furthermore, there is a problem in that graphitic carbon requires heat treatment at a very high temperature and consumes a large amount of energy to produce.

Carbonaceous electrodes used for electroosmotic dehydration of sewage and water sludge require not only low wear and tear on the electrodes, but also physical strength to withstand the squeezing force as the current is applied while applying squeezing force. Moreover, since the sludge contains miscellaneous electrolytes, current flow is inhibited by a complex electrochemical mechanism, making the conditions even more severe. The earlier application, JP-A-64-30613, provides an electrode configuration adapted to this condition, and JP-A-64-30,614 provides a standard for converting the electrodes to the opposite polarity in this case.

However, since the above-mentioned problems still remain in graphite bridges, there is a need for a pole base material that can be produced at low cost, has a long lifespan, and has high strength.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the polar base material of the prior art, and has a long life useful as an electrode for electrolysis of an aqueous solution system containing salt such as seawater or an electrode for electroosmotic dehydration. The object of the present invention is to provide a polar base material with high strength and good conductivity.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a material that can be used as either an anode or a cathode for electrolytic and electroosmotic dehydration, and that changes polarity at every fixed amount of current. The half-width of the <002> plane of carbon determined by wide-angle X-ray is 5.5'~
8.0'' and a relative integrated intensity of oxygen element/carbon element determined by surface analysis using ESCA (X'!a photoelectron spectroscopy) of 0.18 to 0.60. This is achieved by using a polar base material.

In the present invention, on the premise that the polarity is changed every predetermined amount of DC current, the half-value of carbon determined by wide-angle X-rays of the carbonaceous electrode base material is set to be 5.5° or more. The half width of the <002> plane becomes smaller, for example, 2 degrees or less, as the carbon material becomes more graphitic. However, in the present invention, in order to make the carbon material as far away from the graphite structure as possible, the <002>
>The half width of the surface should be large, 5.5' to 8.0
up to °. However, if this half width is larger than 8@, the conductivity of the carbon material deteriorates rapidly, making it difficult to conduct electricity. On the other hand, if this half width is smaller than 5.5°, the consumption of the carbonaceous electrode base material becomes large.

The reason is not clear.

Furthermore, in the present invention, the relative integrated intensity of oxygen element/carbon element determined by ESCA surface analysis of the carbonaceous electrode base material is set to 0.18 or more. The larger the half width of the <002> plane of the carbonaceous electrode base material, the larger the relative integrated intensity of oxygen element/carbon element.

A suitable range is from 0.18 to 0.60. If this characteristic value ratio is smaller than 0.18, the amount of consumption of the carbonaceous electrode base material becomes large, and if it is larger than 0.60, it becomes difficult to conduct electricity.

(Function) As a polar base material for the above applications, it is fundamentally important to reduce the amount of wear and improve the lifespan, and in this regard, the half width of the <002> plane of carbon determined by wide-angle X-rays and the ESCA surface analysis. Since the determined relative integrated intensities of oxygen element/carbon element are related as described above, it is not clear which is the important factor that acts preferentially, but as in the present invention, it is possible to If conversion is assumed, the latter is considered to be important. In other words, since the oxygen element on the surface of the carbonaceous electrode base material bonds with the carbon element to form functional groups such as galvonyl groups, carboxyl groups, or hydroxyl groups, when the polarity is changed, some of these functional groups undergo reversible oxidation and As a reduction reaction occurs, the amount of electrolyzed water is reduced, and the oxidative consumption of the electrode base material by the generated oxygen is reduced, so the relative integrated intensity of oxygen element/carbon element, which is closely related to this electrochemical mechanism, is directly affected. It seems to have an impact.

Note that the amount of current applied until polarity change related to electrode consumption due to this mechanism is 500 coulombs/unit area of the electrode.
It is preferably less than c+fi, more preferably less than 400 coulombs/ctA. When the amount of continuous energization of the same polarity is 500 coulombs/- or more, the effect of reducing the amount of electrode consumption due to polarity conversion is not significant.

Next, as for the carbonaceous electrode base material, increasing the physical strength is as important as reducing wear and tear. Preferably, it is made of a material. The carbon fibers may be polyacrylonitrile-based, pitch-based, rayon-based, etc., but polyacrylonitrile-based carbon fibers are preferred because of their superior strength. As a carbonaceous polar base material containing carbon fibers, 10 to 50% by weight of the carbonaceous material is short carbon fibers with a fiber length of 2 to 20 cm, and is substantially dispersed in random directions within a two-dimensional plane. Such a polar base material, which is preferably laminated and has a carbonaceous structure in which carbon fibers are bonded to each other by binder carbon, is made of, for example, a polyacrylonitrile single yarn with a diameter of 4 to 15 μm and a length of 2 ~20mm short carbon fibers are mixed with a papermaking medium prepared by diluting a papermaking binder such as polyvinyl alcohol with water, stirred to form a sheet or plate, and dried to remove the solvent to create an intermediate base material. This is obtained by impregnating this with a solution of a carbonizable resin such as a phenol resin, hardening the resin by hot press molding, and then heat-treating in an inert gas atmosphere to carbonize the impregnated resin.

Alternatively, felt-like carbon fiber, which is a nonwoven fabric, may be impregnated with the phenolic resin and the resin may be carbonized. Furthermore, flame-resistant fibers or white threads, which are precursors of carbon fibers, may be used and carbonized simultaneously with the resin. Alternatively, it may be molded by a bulk molding compound method in which a mixture of carbon fibers and solid phenol resin is filled into a mold and hot pressed, and then carbonized.

Even when the carbonaceous polar base material is made by any of the above methods to have a structure mainly composed of carbon fibers that can obtain sufficient physical strength, the <002> of carbon determined by wide-angle X cotton as in the present invention is used. Set the half width of the surface to 5.5” to 8.0° and ESC
In order to set the relative integrated intensity of oxygen element/carbon element determined by A surface analysis to 0.18 to 0.60, the temperature at which the phenol resin is carbonized has an important relationship. That is, the heat treatment temperature that satisfies the above requirements of the present invention is 1200°C or less,
Preferably it is in the low temperature range of 1000°C to 650°C. When the heat treatment temperature is higher than 1200'C, the oxygen element/carbon element ratio on the surface of the carbonaceous electrode base material becomes small, and the amount of consumption of the electrode base material due to energization becomes large.

Further, if the temperature is below 650°C, a problem arises in that the carbonized resin has low conductivity.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples to clarify its characteristics. In addition, throughout each example, E S
CA (Electron Spectrograph
Hyfor Chemical Analysis:
The relative integrated intensity of oxygen element/carbon element on the surface of the carbonaceous electrode base material by X-ray photoelectron spectroscopy) is determined by ■ Shimadzu Corporation, ESCA
750, and Mg Kα1.2 ray (h
ν=1253.6 eV). Further, as an energy correction, the binding energy (B, E,) value of the main peak of C10 was adjusted to 284.6 eV.

Further, the half-width of the peak obtained from the <002> plane of the carbon crystal by wide-angle X-ray diffraction was measured by a transmission method using Model 4032A2 manufactured by Rigaku Denki Co., Ltd. and using Cukα rays as the X-ray source. The output is 35KV and 15mA.

(1) Example A Polyacrylonitrile carbon fiber manufactured by Toshi ■, trading card T-
300 was cut into a length of 12 mm, dispersed in an aqueous solution of polyvinyl alcohol, and made into paper.

Next, the paper was impregnated with a phenol resin and dried, and then the resin was cured by hot pressing. The phenol resin was then heat treated at 800°C in a nitrogen atmosphere to carbonize it to a thickness of approximately 511II11 and an apparent specific gravity of 1.05g.
/cnllO A carbonaceous electrode base material of the present invention was obtained.

<002> of carbon determined by wide-angle X-ray of this carbonaceous electrode base material
The half width of the surface was 6.6°, and the relative integrated intensity ratio of oxygen element/carbon element by ESCA surface analysis was 0.25.

As shown in FIG. 1, the electrode base material of the present invention was used as an anode (1) and a cathode (2), and a DC power source (4) and a voltmeter (5) were connected in an aqueous solution (3) containing 4 g/l of CaClt. Use 0
．． When we investigated the current consumption by changing the polarity at 20 minute intervals at a current density of 0.02A/cii, we found that the horizontal axis in Figure 2 shows the current application time (Hr) and the vertical axis shows the remaining weight (%). Line above (
A). Now the electrode consumption is 0.01g
/AH or less.

(n) Example B The carbonization heat treatment temperature of the phenol resin in Example (1) was changed to 1
The temperature was set at 000°C and all other conditions were the same as in Example (I) to obtain the carbonaceous electrode base material of the present invention. That wide angle
The half width of the <002> plane of carbon determined from cotton was 6.5°, and the characteristic value of oxygen element/carbon element determined by ESCA surface analysis was about 0.25. As in Example (1), the first
When the amount of electrode consumption was investigated using the method shown in the figure, the results shown by line (B) in FIG. 2 were obtained.

(III) Comparative Example C The phenol resin carbonization heat treatment temperature in Example (1) was set to 25
00°C and all other conditions were the same as in Example (1) to obtain a carbonaceous electrode base material of a comparative example. The half value of the <002> plane of carbon determined by wide-angle X-rays of this polar base material is approximately 2'', and the characteristic value of oxygen element/carbon element in ESCA surface analysis is 0.1 or less, which is outside the scope of the present invention. When the amount of current consumption was investigated, it was shown as line (C) in FIG. 2, and the amount of consumption was much larger than that of Examples (1) and (n).

(Effect of the invention) As described above, the half value of the <002> plane of carbon obtained by wide-angle X-ray of the carbonaceous electrode base material which is energized together with polarity conversion is 5.5.
°~8.0°, and the relative integrated intensity ratio of oxygen element/carbon element determined by ESCA surface analysis is 0.18~0.60.
The carbonaceous electrode base material of the present invention exhibits a significantly small amount of current consumption and high physical strength, and therefore exhibits useful effects for electrolysis and electroosmotic dehydration.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the outline of the apparatus used for the current consumption test of the carbonaceous electrode substrate, and Fig. 2 shows the carbonaceous electrode substrate of the embodiment of the present invention, with the horizontal axis representing the energization time and the vertical axis representing the remaining weight. It is a chart showing the results of an energization consumption test of the material in comparison with that of a comparative example. (])... Anode, (2)... Cathode, (3)... Aqueous solution, (4)... DC power supply, (5)... Voltmeter. 500 1000 Current application time (1-Tr)

Claims (1)

[Claims] An electrode base material made of carbonaceous material that can be used as either an anode or a cathode for direct current flow for electrolysis and electroosmotic dehydration, and is used by changing the polarity at each given amount of current. The base material has a carbon <002> plane half-width of 5.5° to 8.0° as determined by wide-angle X-ray, and an ESCA (
Oxygen element determined by surface analysis using X-ray photoelectron spectroscopy
A carbonaceous electrode base material characterized in that the relative integrated intensity of carbon element is 0.18 to 0.60.