JP2009275257A - Optically and cathodically corrosion-protecting agent, and metal material coated with optically and cathodically corrosion-protecting agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optically and cathodically corrosion-protecting agent which less oxidizes a metal material even when coated on the surface of the metal material, and can maintain a corrosion protective effect for a long period of time. <P>SOLUTION: The optically and cathodically corrosion-protecting agent includes a photocatalyst made from titanium peroxide or a composite compound of titanium peroxide as a main component, and consequently shows a higher reduction power than an oxidation power with respect to the metal material. Thereby, even when having been coated on the surface of the metal material, the optically and cathodically corrosion-protecting agent does not oxidize the metal material and can inhibit the formation of rust. Such a photocatalyst is not consumed even when having generated a corrosion-protecting current, is superior in weathering resistance, and accordingly can maintain the corrosion protective effect for a long period of time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photocathode anticorrosive agent that is coated on the surface of a metal material and that converts, for example, light energy of sunlight or ultraviolet light into electric energy by photocatalytic action to prevent photocathode corrosion. The present invention relates to a photocathode anticorrosive containing a photocatalyst composed of a titanium oxide composite compound as a main component and a metal material coated with the photocathode anticorrosive.

  Metal materials used in many technical fields have a long-standing problem of corrosion. The anticorrosion technologies that have been studied in the past can be broadly classified as follows: (1) Environmental treatment that adjusts the amount of oxygen and moisture, which are corrosion factors, (2) Environmental barrier that covers the surface with a coating material to block the corrosion factors, (3) Corrosion-resistant material selection, (4) Electrocorrosion protection, etc.

  As the above-mentioned cathodic protection, cathodic protection that is corrosion-resistant by energizing a metal material as a cathode (cathode) has been put into practical use. Cathodic protection methods include the galvanic anode method and the external power supply method. Among them, the galvanic anode method coats the surface of a metal material with a low potential metal such as magnesium, zinc, or aluminum as an anode (anode), and uses the metal material as a cathode (cathode), and uses the potential difference between the two to prevent corrosion. Since it does not require an external power supply, it is widely adopted as a simple method.

  However, in the case of the above-described cathodic protection, the anode serving as a so-called sacrificial electrode is consumed, so that the anticorrosion effect becomes weaker as time passes. Therefore, the low potential metal that becomes the anode must be recoated every few to ten years. Furthermore, there is a problem that the weather resistance against acid rain or salt damage is low.

  By the way, in recent years, studies on cathodic protection using titanium oxide as a photocatalyst have been made. Titanium oxide, which is a photocatalyst, is a functional material that develops photocatalytic action when irradiated with sunlight or ultraviolet light. At that time, electrons that jump out of the surface (photogenerated electrons) are supplied to the metal material to prevent corrosion. (For example, refer to Patent Documents 1 to 3). Cathodic protection using such a photocatalyst is referred to as photocathodic protection.

Japanese Patent No. 3278425 Japanese Patent No. 3278426 JP 2001-247985 A

  However, in the case of titanium oxides (also referred to as titanium oxides) described in Patent Documents 1 to 3, corrosion of metal materials may be promoted on the contrary due to a strong oxidizing action expressed by the photocatalytic action. . That is, the hole from which the photogenerated electrons have escaped becomes a positive hole and has a positive charge. Since this positive hole exerts a strong oxidizing power, the metal material is oxidized and corrosion is promoted. Originally, a photocatalyst is a functional material that has attracted attention for its strong oxidizing power. As in Patent Documents 1 and 2, if a photocatalyst is not in contact with a metal material by interposing a conductive wire or a conductive film, the oxidizing power of the photocatalyst is reduced. Little affected. However, on the other hand, the configuration becomes complicated and the cost may increase.

  On the other hand, if the photocatalyst is coated on the metal surface, the configuration is simplified. In this case, the oxidation action by holes is more than the reduction action by photogenerated electrons, and the metal material is oxidized and rusted. May occur. In Patent Document 3, amorphous titanium oxide is used and no conductive wire or conductive film is interposed. However, amorphous titanium oxide, which is amorphous, has a small photocatalytic action as compared with anatase type or rutile type titanium oxide, and there is a concern that sufficient anticorrosive effect cannot be obtained.

  The present invention has been made based on such circumstances, and the purpose thereof is to oxidize the metal material even if it is coated on the surface of the metal material, and to maintain the anticorrosion effect for many years. An object of the present invention is to provide a photocathode anticorrosive that can be applied, and a metal material coated with the photocathode anticorrosive.

  The photocathode anticorrosive agent of the present invention is a photocathode anticorrosive agent coated on the surface of a metal material for photocathode anticorrosion of the metal material, and a photocatalyst composed of titanium peroxide or a titanium peroxide composite compound as a main component. By including as, it is characterized by raising the reducing power rather than the oxidizing power with respect to the said metal material, and preventing corrosion.

  The photocathode anticorrosive is preferably coated on the surface of the metal material so that the coverage per unit area is 30 to 80%. The photocathode anticorrosive is preferably coated by applying a photocatalyst solution containing a photocatalyst made of titanium peroxide or a titanium peroxide composite compound to the surface of the metal material and drying it. As such a photocatalyst solution, an aqueous solution containing titanium peroxide obtained by dissolving titanium oxide in hydrogen peroxide water and peroxodized can be applied.

  In addition, the metal material of the present invention is characterized by being coated with the photocathode anticorrosive described above.

  According to the present invention, by including a photocatalyst composed of titanium peroxide or a titanium peroxide composite compound as a main component, the reducing power is increased more than the oxidizing power of the metal material, and thus the surface of the metal material can be coated. It becomes possible to suppress the occurrence of rust. Such a photocatalyst is not consumed due to the generation of the anticorrosion current and has excellent weather resistance, so that the anticorrosion effect can be maintained for many years. In addition, since the oxidizing power is not lost, it is possible to expect decomposition (antifouling function) of the contaminants adhering to the metal material.

  A photocathode anticorrosive according to a preferred embodiment of the present invention and a metal material coated with the photocathode anticorrosive will be described in detail with reference to the accompanying drawings. However, the present invention is not limited by the embodiments described below.

  The photocathode anticorrosive according to the present embodiment contains a photocatalyst composed of titanium peroxide or a titanium peroxide composite compound as a main component, and the action and effect of photocathode anticorrosion can be achieved by coating the surface of a metal material in a thin film shape. Demonstrate. Examples of the other components include a binder for enhancing adhesion, and these are optional components. Furthermore, the kind of metal material is not particularly limited, and can be any metal material that can corrode in a natural environment. As such an anticorrosive, for example, it is preferable to prepare a photocatalyst solution in which fine particles of titanium peroxide or a titanium peroxide composite compound are dispersed and coat the surface of the metal material by a coating method.

  The titanium peroxide composite compound is a composite of titanium peroxide and another metal compound, and an example thereof is a composite of titanium peroxide and silica. In this composite, titanium peroxide and silica are bonded by a peroxide bond, and a superhydrophilic function can be added.

  The photocatalyst solution is, for example, a sol, suspension, or emulsion in which titanium peroxide fine particles having a particle diameter of several nanometers to several tens of micrometers are dispersed in water, an organic solvent, or a mixture thereof. For example, a high-concentration solution may be used at the time of manufacture and sale, but when actually applied, the concentration of titanium peroxide or titanium peroxide composite compound is adjusted to be 0.05 to 3% by mass, for example. It is preferable to apply from the above.

As a preferable preparation example of the photocatalyst solution, for example, it can be prepared as follows.
First, a mixture of titanium tetraisopropoxide (TIP) and isopropanol (IPA), which is a raw material of titanium oxide, and a mixture of IPA and water are mixed, and TIP is hydrolyzed to generate fine particles of titanium oxide. . The blending molar ratio can be, for example, TIP: IPA: H ₂ O = 1: 10: 4. Then, the titanium oxide fine particles are separated by filtration and dried at, for example, 100 ° C. to obtain a titanium oxide powder. When the titanium oxide obtained by filtration is a powder lump, a pulverization process is appropriately performed. The raw material of titanium oxide is not limited to TIP, and other titanium alkoxides (compounds in which H of the OH group of the alcohol molecule is substituted with Ti) such as titanium tetraethoxide can be used.

  Subsequently, for example, by adding 35% by mass of hydrogen peroxide to the titanium oxide and dissolving it, a peroxotitanium peroxide gel is formed. Further, for example, 35% by mass of hydrogen peroxide is added as a dispersant to form a sol. Further, an alkali solution such as ammonia is added to the sol body to adjust the pH to, for example, 6 to 8, thereby obtaining a photocatalyst solution in which a photocatalyst made of titanium peroxide is dispersed.

  The above preparation method is a method of preparing a photocatalyst solution in which fine particles of titanium peroxide are dispersed. However, when preparing a photocatalyst solution in which fine particles of a titanium peroxide composite compound are dispersed, the titanium oxide is peroxidized. When dissolved in hydrogen, another metal compound forming a complex or a precursor thereof is added. As an example, when forming a composite with silica, a mixture of tetramethyl orthosilicate (TEOS), which is a silica precursor, and ethanol is added.

  The photocatalyst solution prepared as described above is a substantially neutral aqueous solution in which fine particles of titanium peroxide or a titanium peroxide composite compound are dispersed, and a component (for example, a chlorine component or the like) that may have an adverse effect on a metal material. ), It is suitable as an anticorrosive. However, in this embodiment, as long as a photocatalyst solution in which fine particles of titanium peroxide or a titanium peroxide composite compound are dispersed can be obtained, the photocatalyst solution is not limited to the above preparation method, and can be prepared by a known method.

  Subsequently, a photocatalyst solution in which a photocatalyst made of titanium peroxide or a titanium peroxide composite compound is dispersed is applied to the surface of a metal material by a generally known coating method such as spraying, dipping, hand coating, or spin coating. The coating film is obtained by drying. Thereby, a metal material coated with the photocathode anticorrosive of the present embodiment is formed.

  At this time, it is preferable that the photocathode anticorrosive of the present embodiment is not coated over the entire surface of the metal material, but is formed so that the surface of the metal material is partially exposed. More specifically, it is preferable to coat so that the coverage of the anticorrosive per unit area of the metal material is 30 to 80%. By partially coating in this way, it becomes possible to enhance the anticorrosion effect as will be apparent from the examples described later.

Here, as schematically shown in FIG. 1, when sunlight or ultraviolet light hits the photocatalyst, a phenomenon occurs in which electrons jump out of the surface. In this example, since the photocatalyst and the metal material are in contact with each other, the jumped-out electrons (photogenerated electrons) move to the metal material having a high potential, and a corrosion prevention current is generated. As a result, the oxidation reaction of the metal material (for example, in the case of iron, Fe → Fe ²⁺ + 2e ⁻ ) is suppressed, and the generation of rust is suppressed. On the other hand, the hole from which the electron has escaped becomes a positive hole and has a positive charge, and this positive hole has a strong oxidizing power. The antifouling function of the photocatalyst is due to decomposition of pollutants and bacteria by OH radicals generated by the holes taking electrons from hydroxide ions and the like.

Here, even in the case of titanium oxide, which is a typical photocatalyst, although it has a reducing power due to photogenerated electrons, the oxidizing power is too strong to exceed the oxidizing action on the metal material. Direct coating may promote rusting. On the other hand, in this embodiment, since titanium peroxide has extra oxygen (O), the number of electrons increases and the reducing power increases, and the reducing power and the oxidizing power are in an effective balance for suppressing rust. I think. As a result, the corrosion protection of the metal material can be realized. Although the detailed mechanism has not yet been clarified, the present inventors have found that the titanium peroxide produced by the above-described method has a crystal structure, and the structure represented by the following chemical formula contained in the crystal structure is reduced. I guess it contributes to the improvement of power. It is also speculated that the antirust effect is enhanced when the crystal structure is anatase / rutile type including both anatase type and rutile type. More specifically, when visible light or ultraviolet light is irradiated, electrons in the O valence band of Ti—O—Ti are excited and move to the conduction band of Ti, but these electrons reduce oxygen molecules in the vicinity. It is thought that it contributes to the oxidation suppression of the base metal directly. On the other hand, the holes of Ti—O—Ti with strong oxidizing power that are generated simultaneously with the removal of electrons are from many unshared electron pairs of two peroxide bonds —O—O— between Ti and Ti. Apparently, electrons are supplied, and generation of OH radicals with strong oxidizing power is suppressed. For this reason, it is considered that the reducing power is superior to the oxidizing power, and the function of rust prevention is effectively exhibited. Therefore, it is considered that a peroxy type rutile anatase crystal which is not an amorphous type but is a crystalline type rutile anatase crystal having a high photocatalytic activity and having a peroxide bond is effective for rust prevention.

  That is, according to the above-described embodiment, by containing a photocatalyst composed of titanium peroxide or a titanium peroxide composite compound as a main component, the reducing power is increased more than the oxidizing power with respect to the metal material, whereby the surface of the metal material is coated. Even so, it becomes possible to suppress the occurrence of rust. Such a photocatalyst made of titanium peroxide or a titanium peroxide composite compound is not consumed due to the generation of an anticorrosion current, and is excellent in weather resistance, so that the anticorrosion effect can be maintained for many years. In addition, since the oxidizing power is not lost, it is possible to expect decomposition (antifouling function) of the contaminants adhering to the metal material.

  Then, Example 1 which confirmed the anticorrosion effect by the photocatalyst consisting of titanium peroxide will be described.

(Test Example 1)
The photocatalyst solution obtained by the preferred preparation method described above was coated on the test piece by spraying. This photocatalyst solution is a PT solution of Fluorescent (registered trademark) sold by Titania Integrated Science and Technology Limited Liability Partnership. As the test piece, a steel material used for a bridge having a size of 4 mm × 100 mm × 150 mm was used. In the spray method, one reciprocation in the vertical and horizontal directions was 1 coat, and this was repeated to obtain 20 coats. And the stand with the stainless steel plate inclined 45 degree | times to the height of 0.5 m from the ground was installed in the outdoors toward the south, and each test piece was fixed to the upper surface, and the exposure test was done.

Evaluation of anticorrosion was performed by measuring the color difference of the test piece every week using a color difference meter (CM2600d, manufactured by MINOLTA). 15 points were measured for each test piece, and the color difference ΔE for each measurement day was calculated from the average using the following formula. Since it changed to brown so that rust generate | occur | produced, it evaluated that it was anticorrosion, so that color difference (DELTA) E was small. The result of the color difference ΔE is shown in FIG. Furthermore, the photograph which image | photographed the test piece when 62 days passed is shown in FIG.

(Test Example 2)
This example is a test example 2 in which an exposure test was performed in the same manner as the test example 1 except that the photocatalyst solution was applied by a dip method instead of the spray method. In the dip method, an operation of dipping in a photocatalyst solution for 10 seconds and then naturally drying was repeated 5 times. The result of the color difference ΔE is also shown in FIG.

(Test Example 3)
This example is a test example 3 in which an exposure test was performed in the same manner as the test example 1 except that a photocatalyst solution in which anatase-type titanium oxide was dispersed was used instead of titanium peroxide. The result of the color difference ΔE is also shown in FIG. Furthermore, the photograph which image | photographed the test piece when 62 days passed is combined with FIG.

(Test Example 4)
This example is a test example 4 in which an exposure test was performed in the same manner as the test example 3 except that the photocatalyst solution was applied by a dip method instead of the spray method. The result of the color difference ΔE is also shown in FIG.

(Test Example 5)
In this example, a blank was subjected to an exposure test using a test piece not coated with a photocatalyst. The result of the color difference ΔE is also shown in FIG. Furthermore, the photograph which image | photographed the test piece when 62 days passed is combined with FIG.

(Test results and discussion)
As is apparent from the results shown in FIG. 2, Test Examples 3 and 4 using a photocatalyst made of anatase-type titanium oxide have a significantly larger color difference ΔE than Test Example 5 which is a blank. It can be confirmed from the photograph of FIG. 3 that rust is generated from the blank. On the other hand, in Test Examples 1 and 2 using a photocatalyst made of titanium peroxide, the color difference ΔE is smaller than that in Test Example 5 which is a blank, and the rate of change due to the elapsed days is small. Also from the photograph of FIG. 3, it can be confirmed that the occurrence of rust is less than that of the blank. From the above, it was confirmed that corrosion protection was possible by coating a photocatalyst made of titanium peroxide.

  Hereinafter, Example 2 which confirmed the difference in the anticorrosion effect by changing the coverage of a photocatalyst is demonstrated.

(Test Example 6)
In this example, fine particles of titanium peroxide were dispersed in the same manner as in Test Example 1, but the photocatalyst solution was applied to the test piece by a spray method, and as shown schematically in FIG. This is Test Example 6 in which the coverage is 30%. The coverage was adjusted by pasting a tape as a mask on the test piece in advance, spraying the tape, and then removing the tape. The number of coatings was 5 coats. Evaluation of anticorrosion was performed by calculating the mass loss Δm [g] from the difference between the mass W1 of the test piece before the exposure test and the mass W2 of the test piece after removing the rust according to ISO 8407 after the exposure test. This was done by calculating the corrosion degree rcorr. The result is shown in FIG.

(Test Example 7)
This example is a test example 7 similar to the test example 6 except that the coverage is adjusted to 50% as schematically shown in FIG. The results of the corrosion degree rcorr are also shown in FIG.

(Test Example 8)
This example is a test example 8 similar to the test example 6 except that the coverage is adjusted to be 80% as schematically shown in FIG. The results of the corrosion degree rcorr are also shown in FIG.

(Test Example 9)
This example is a test example 9 similar to the test example 6 except that the coverage is 100% as schematically shown in FIG. The results of the corrosion degree rcorr are also shown in FIG.

(Test Example 10)
In this example, a blank was subjected to an exposure test using a test piece not coated with a photocatalyst. The results of the corrosion degree rcorr are also shown in FIG.

(Test results and discussion)
As is apparent from the results shown in FIG. 5, the degree of corrosion is reduced by coating the photocatalyst, and the degree of corrosion is particularly small in the range of 30 to 80%. The smallest corrosion degree is Test Example 7 in which the coverage is adjusted to 50%. From the above results, it was confirmed that the anticorrosion effect can be obtained more reliably by setting the coverage to 30 to 80%.

It is a figure which shows typically the mechanism of the photocathode anticorrosion by embodiment of this invention. It is a characteristic view which shows the result of the exposure test done in order to confirm the effect of this invention. It is a photograph which shows the result of the exposure test done in order to confirm the effect of this invention. It is a figure for demonstrating the test done in order to confirm the effect of this invention. It is a characteristic view which shows the result of the exposure test done in order to confirm the effect of this invention.

Claims (5)

  A photocathode anticorrosive agent coated on the surface of a metal material for photocathode protection of the metal material, comprising a photocatalyst composed of titanium peroxide or a titanium peroxide composite compound as a main component. A photocathode anticorrosive, characterized by increasing the reducing power rather than the oxidizing power to prevent corrosion.   2. The photocathode anticorrosive according to claim 1, wherein the surface of the metal material is coated so that the coverage per unit area is 30 to 80%.   2. The photocathode anticorrosive agent is obtained by coating a surface of the metal material with a photocatalyst solution containing a photocatalyst made of titanium peroxide or a titanium peroxide composite compound, and drying it. Or the photocathode anticorrosive according to 2.   4. The photocathode anticorrosive agent according to claim 3, wherein the photocatalyst solution is an aqueous solution containing titanium peroxide obtained by dissolving titanium oxide in hydrogen peroxide solution and peroxoating.   A metal material, which is coated with the photocathode anticorrosive according to any one of claims 1 to 4.