JP2002143859A - Anti-fouling method and device for underwater structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means exhibiting satisfactory sterilization effect and capable of suppressing the corrosion of a corrosion resistant metal in the electrochemical control for microorganism on the surface of underwater structure made of the corrosion resistant metal. SOLUTION: The anti-fouling method of the surface of the underwater structure is performed by forming the anti-fouling surface of the underwater structure from the corrosion resistant metallic material and applying alternately and periodically positive potential and negative potential on the anti-fouling surface. The applying time of negative potential applied on the anti-fouling surface is controlled to be longer than that of the positive potential, that is, to be 2-20 times of that of the positive potential. The positive potential applied on the anti-fouling surface is controlled to be <=+1.5 V vs. SCE and the negative potential is controlled to be -0.1 to -1.0 V vs. SCE. The cycle of applying the positive potential and the negative potential on the anti-fouling surface is controlled to be <=60 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antifouling method and an antifouling apparatus for an underwater structure, which electrochemically controls the attachment of aquatic organisms to the surface of the structure in water.

[0002]

2. Description of the Related Art Attachment of marine organisms to the surface of marine structures such as marine stations, piers, cooling pipes of power plants, and ship bottoms causes blockage of pipes, lowers navigation speed, lowers energy efficiency, and causes corrosion. This is a problem because it also causes

[0003] Conventionally, in order to prevent such marine organisms from adhering, a bactericidal chlorine compound is injected into water,
A method of applying a paint containing an organotin compound to a surface where the adhesion is to be prevented (antifouling surface) has been often used.
However, since these methods are concerned with environmental pollution and influence on ecosystems, various methods for preventing marine organisms from adhering without such environmental problems have been studied.

The mechanism of adhesion of aquatic organisms is as follows. Gram-negative bacteria are first adsorbed on the surface of an underwater structure and proliferate, and a biofilm is formed by microorganisms using the gram-negative bacteria as a nutrient source. Large aquatic organisms are formed on the film. It is known that algae, shellfish and barnacles adhere.

Therefore, the present inventors have focused on the fact that it is possible to prevent the adhesion of marine organisms by sterilizing the antifouling surface, and apply a positive or negative potential of several volts or less to the conductive antifouling surface. A method for controlling microbes in water was previously proposed (Japanese Unexamined Patent Publication No.
-341392).

In applying this method to an actual underwater structure, what kind of material is to be selected as a conductive material constituting the stainproof surface is a problem. Therefore, the present inventors have already made a conductive composition (for example, JP-A-8-302247) comprising a binder resin and a conductive filler, or a metal nitride, a metal carbide, a metal boride, a metal silicide (For example, Japanese Patent Application Laid-Open No. H10-158863).

Further, the present inventors have proposed an antifouling member having a sprayed coating made of a metal nitride formed on a water-contacting surface (Japanese Patent Application Laid-Open No.
No. 1-61373) and an antifouling member whose water contact surface is made of valve metal (Japanese Patent Application Laid-Open No. 10-195682).

[0008]

The materials constituting the above-described various antifouling surfaces are expensive in themselves, and the production and construction thereof are troublesome. is there. In particular, when the area of the antifouling surface is large, how to form the antifouling surface at low cost is an important issue.

In general, the surface of an underwater structure is often made of a corrosion-resistant metal or coated with a corrosion-resistant metal for the purpose of corrosion protection. Therefore, if an electric potential can be applied to the corrosion-resistant metal itself to control the above-mentioned underwater microorganisms, the cost required for preventing the adhesion of aquatic organisms can be greatly reduced.

However, according to the findings of the present inventors, it is necessary to apply a positive potential to kill bacteria in water such as Gram-negative bacteria. Excluding the consequence of accelerating the corrosion of the metallic material.

Therefore, the present invention provides a method for electrochemically controlling microorganisms on the surface of an underwater structure made of a corrosion-resistant metal.
It is an object of the present invention to provide a means which has a sufficient sterilizing effect and can suppress corrosion of a corrosion-resistant metal by selecting an appropriate potential application condition.

[0012]

According to the present invention, there is provided an antifouling method for an underwater structure, wherein the antifouling surface of the underwater structure is made of a corrosion-resistant metal material, and a 0 V vs. .
This is an antifouling method for underwater structures, characterized by alternately and periodically applying a positive potential of SCE or more and a negative potential of 0 V vs. less than SCE.

In the above antifouling method, it is preferable that the application time of the negative potential applied to the antifouling surface is longer than the application time of the positive potential. Further, it is preferable that the application time of the negative potential is set to 2 to 20 times the application time of the positive potential.

In the antifouling method described above, it is preferable that the positive potential applied to the antifouling surface is +1.5 V vs. SCE or less, and the negative potential is -0.1 to -1.0 V vs. SCE. .

Further, in the above antifouling method, the period of the positive potential and the negative potential applied to the antifouling surface is preferably 60 minutes or less. In the above antifouling method, the corrosion-resistant metal material may be stainless steel.

The antifouling apparatus for an underwater structure according to the present invention is an apparatus used in any of the above antifouling methods, wherein an electric potential is applied between an antifouling surface made of a corrosion-resistant metal material and a counter electrode immersed in water. And a potential control device for controlling the potential applied to the antifouling surface in a predetermined periodic pattern of alternating positive and negative.

An underwater structure characterized by further providing a reference electrode in the above-described antifouling device and controlling a potential between the reference electrode and the antifouling surface in a predetermined periodic pattern of alternating positive and negative. An antifouling device for objects.

[0018]

1 and 2 are schematic diagrams showing an example of the configuration of an antifouling device for an underwater structure according to the present invention. In the example of FIG. 1, a corrosion-resistant metal layer 2 is formed on the surface of an underwater structure 1, and a potential is applied between the underwater structure 1 and a counter electrode 3 in the water from a DC power supply 4. The applied potential is controlled by a potential control device (function generator) 5 in a predetermined pattern.

In the example shown in FIG. 2, a three-electrode system having a reference electrode 6 in addition to the configuration shown in FIG. The reference pole 6
The potential of the corrosion-resistant metal layer 2 can be more accurately controlled by controlling the potential between the electrode and the corrosion-resistant metal layer 2 to a predetermined pattern by using a reference potential, for example, a saturated calomel electrode. .

The present inventors have already confirmed that sterilization can be performed by applying a positive potential of 0.4 V vs. SCE or more to electrodes made of various conductive materials, and that negative electrodes of 0 to -0.8 V vs. SCE can be obtained. It has been found that cells are detached from the electrode by applying an electric potential. However, it was confirmed that the same sterilization and cell detachment effect can be obtained with an electrode made of a corrosion-resistant metal such as stainless steel.

However, as will be described in the following embodiment,
A positive potential of about 1.0 V vs. SCE is applied for a long time (for example,
It was found that Cr, Fe, etc., elute when applied. In addition, it was found that when the positive and negative alternating potentials were applied, the amount of elution of Cr, Fe, and the like was significantly reduced as compared with the case where only the positive potential was applied. Therefore, in the present invention, positive and negative alternating potentials are applied to the corrosion-resistant metal layer 2 as shown in FIG.

In the present invention, the negative potential application time t ₂
Is preferably longer than the positive potential application time t ₁ . The reason is that, even when t ₂ > t ₁ , the same bactericidal effect as in the case of t ₂ ≦ t ₁ can be maintained, and as shown in Examples described later, it is better to set t ₂ > t _1. , Cr, Fe and the like are further reduced.

The ratio of t ₂ / t ₁ is preferably 2 to 20. If this ratio is less than 2, the effect of suppressing the elution of metal ions as described above is not sufficient, and this ratio is 2
If it exceeds 0, the application time of the positive potential is too short and the bactericidal effect becomes insufficient. In addition, more preferably, the above ratio is 3 to 10.

In the present invention, the positive potential is set to +1.5
V vs. SCE or less, and the negative potential is -0.1 to -1.
It is preferable to be 0 V vs. SCE. If the positive potential exceeds this value, the amount of metal eluted from the electrode increases, and chlorine may be generated.

When the negative potential is higher than -0.1 V vs. SCE (the negative value is small), the effect of cell detachment becomes insufficient, and the negative potential is lower than -1.0 V vs. SCE (negative value). Is large), there is a possibility that the generation of hydrogen and the pH around the electrode may change due to this. More preferable potential ranges are a positive potential of 0.6 to 1.2 V vs. SCE and a negative potential of -0.4 to -0.8 V vs. SCE.

It should be noted that the potential pattern in the present invention does not necessarily have to be a complete step shape as shown in FIG. 3, but may be a trapezoidal, saw-tooth or sinusoidal pattern. In this case, it is sufficient that the maximum value of the positive potential and the minimum value of the negative potential fall within the above range.

Further, in the present invention, it is preferable that the application period (one positive and negative period) of the positive potential and the negative potential is set within 60 minutes. According to the findings of the present inventors, even when the potential level is the same, a tendency is observed that the shorter the period, the shorter the period, the smaller the amount of metal eluted, and when the period is 60 minutes or less, compared to the case where the period exceeds 60 minutes. , Cr, Fe, etc., because the amount of elution decreases.

In the present invention, the term "corrosion-resistant metal material" refers to a metal or an alloy which exhibits necessary and sufficient corrosion resistance in water for a period during which the attachment of aquatic organisms becomes a problem, for example, for several months to several years. The range of the target metal or alloy cannot be specified unconditionally because it greatly differs depending on the corrosive environment in water. However, from the viewpoint of corrosion resistance in seawater, stainless steel, particularly seawater-resistant stainless steel, titanium, and the like are the main targets.

The underwater structure itself may be made of a corrosion-resistant metal, or only the surface thereof may be made of a corrosion-resistant metal, such as a plated steel material or a clad steel material. Furthermore, the surface of a material such as steel, concrete, or plastic may be covered with a corrosion-resistant metal sheet.

The material constituting the counter electrode may be any material having conductivity and corrosion resistance in water, and may be a corrosion-resistant metal, a material coated with the metal, a conductive plastic, or the like. The shape may be appropriately selected according to the shape of the underwater structure such as a plate, a tube, a mesh, and a line.

The antifouling method of the present invention relates to a corrosion-resistant metallic material or corrosion-resistant material such as a cooling water intake pipe for a power plant, a chemical plant or a ship, a ship propulsion system, a marine station, a pier, a marine pipeline, a buoy or a fishing net. It can be easily applied to a site using a metal coating material, and can prevent marine organisms from adhering while suppressing elution of heavy metals and the like.

[0032]

EXAMPLES Using stainless steel as a working electrode, positive and negative potentials were applied in water, and the relationship between the potential application conditions, the bactericidal effect, and the amount of metal elution was investigated. FIG. 4 schematically shows the experimental apparatus used.
Shown in This experimental apparatus includes a working electrode 11, a counter electrode 12 and a reference electrode 13 in a test tank 10 storing 50 ml of sterilized seawater.
These three poles are connected to a potentiostat 14 so that a function generator 15 can apply a potential to the working electrode 11 in a predetermined pattern.

The working electrode has a size of 20 × 50 mm and a thickness of 0.6.
mm seawater-resistant stainless steel sheet (YUS270: 20% C
r-18% Ni-6% Mo-0.7% Cu-0.2%
N), a platinum plate was used as a counter electrode, and a saturated calomel electrode was used as a reference electrode.

The bactericidal effect was investigated as follows.
The marine bacterium Vibrio alginoly
ticus), the working electrode is immersed in a cell suspension of 1.0 × 10 ⁶ cells / ml, and the cells are allowed to adhere. After applying the potential, the cells on the surface of the working electrode were collected and the colony method (25
At 24 ° C. for 24 hours).

The metal elution amount is measured by applying an electric potential under predetermined conditions to the working electrode for 30 days in a test tank and determining Fe, Cr, and Ni in seawater in the tank by an atomic absorption method (flame method). )
And the elution amount of each was calculated.

As examples of the present invention, experiments were conducted under the following two potential application conditions. (1) 1.0 V vs. SCE: 10 min / -0.6 V vs. S
CE: 10 min (2) 1.0 V vs. SCE: 10 min / -0.6 V vs. S
CE: 30 min Further, as comparative examples, experiments were performed when a constant positive potential of 1.0 V vs. SCE was applied and when no potential was applied. Table 1 summarizes the results of these experiments.

[0037]

[Table 1]

As can be seen from Table 1, the viable cell count after 30 minutes is almost 0 in both Examples 1 and 2 and Comparative Example 1, and is constant even when positive and negative alternating potentials are applied. It was confirmed that a bactericidal effect equivalent to the case of the positive potential was obtained.

Further, it was confirmed that the elution amounts of Fe, Cr and Ni were remarkably large in the case of a constant positive potential (Comparative Example 1), but were significantly reduced by the application of the positive and negative alternating potentials. It was also found that Example 2 having a longer negative potential application time had a smaller Cr elution amount than Example 1 having the same positive and negative application times.

Next, using the same working electrode as described above in the above experimental apparatus, the positive and negative alternating application cycles were set to 60 msec, 60 sec,
The effect of the potential application cycle on the amount of Cr eluted was investigated in three steps of 60 minutes. In each of these three conditions, the application time of the negative potential was set to five times the application time of the positive potential. Also,
As a comparative example, the amount of Cr eluted when no potential was applied was also measured.

As in the case of Table 1, after applying a potential in a predetermined pattern for 30 consecutive days (no application in the comparative example),
Table 2 shows the results of measuring the amount of Cr eluted in seawater in the test tank by the atomic absorption method.

[0042]

[Table 2]

As can be seen from Table 2, when the potential application cycle is in the range of 60 msec to 60 minutes, the amount of Cr eluted is extremely small, and when it exceeds 60 minutes, the amount of elution tends to increase. It has been found that the application cycle of is desirable.

[0044]

According to the antifouling method of the present invention, when the surface of an underwater structure is made of a corrosion-resistant metal or has a coating of a corrosion-resistant metal, a potential is directly applied to the surface to prevent elution of heavy metals and the like. Thus, a sufficient bactericidal effect can be obtained while preventing corrosion of the antifouling surface, thereby preventing aquatic organisms from adhering. Therefore, it is not necessary to use an expensive conductive material for the antifouling surface, and it is possible to reduce the cost of preventing aquatic organisms from attaching.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of the configuration of an antifouling device for an underwater structure according to the present invention.

FIG. 2 is a schematic view showing another example of the configuration of the antifouling device for an underwater structure according to the present invention.

FIG. 3 is an explanatory diagram showing an example of a potential application pattern to an antifouling surface in the present invention.

FIG. 4 is a schematic diagram of an experimental apparatus used in an example.

[Explanation of symbols]

1 underwater structure 2 corrosion resistant metal layer 3 counter electrode 4 direct-current power supply 5 potential control device 6 reference electrode 10 the test chamber 11 the working electrode 12 counter electrode 13 reference electrode 14 potentiostat 15 function generator 16 stirrer 17 stir bar t ₁ positive potential applied time t ₂ negative potential application time

Continued on the front page. (72) Inventor Toyo Ando 2-9-19-1 Iwamotocho, Chiyoda-ku, Tokyo Nikko Corrosion Protection Co., Ltd. (72) Inventor Yoshiyuki Kawase 2-11-9 Iwamotocho, Chiyoda-ku, Tokyo Nippon Steel F-term in Corrosion Protection Co., Ltd. (reference) 4D061 DA09 DB03 EA02 EB02 EB05 EB30 EB39 GC14 GC15 GC16

Claims (8)

[Claims] An antifouling surface of an underwater structure is made of a corrosion-resistant metal material, and a positive potential of 0 V vs. SCE or more and a negative potential of 0 V vs. less than SCE are alternately and periodically applied to the antifouling surface. An antifouling method for underwater structures, characterized in that: 2. The antifouling method according to claim 1, wherein the application time of the negative potential applied to the antifouling surface is made longer than the application time of the positive potential. 3. The antifouling method according to claim 2, wherein the application time of the negative potential is set to 2 to 20 times the application time of the positive potential. 4. A positive potential applied to the antifouling surface is +1.5.
V vs. SCE or less, negative potential is -0.1 to -1.0 V vs.
The antifouling method according to any one of claims 1 to 3, wherein the antifouling method is SCE. 5. The antifouling method according to claim 1, wherein the period of the positive potential and the negative potential applied to the antifouling surface is 60 minutes or less. 6. The antifouling method according to claim 1, wherein the corrosion-resistant metal material is stainless steel. 7. An apparatus used in the antifouling method according to claim 1, wherein a direct current is applied between an antifouling surface made of a corrosion-resistant metal material and a counter electrode immersed in water. An antifouling device for an underwater structure, comprising: a power supply device; and a potential control device that controls a potential applied to the antifouling surface in a predetermined periodic pattern of alternating positive and negative. 8. The antifouling device according to claim 7, further comprising a reference electrode, wherein the potential between the reference electrode and the antifouling surface is controlled in a predetermined periodic pattern of alternating positive and negative. Antifouling device for underwater structures.