JP3332907B2 - Corrosion protection method and corrosion protection material for metal materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing a metal material from being corroded during light irradiation and non-irradiation, and to an anticorrosion material.

[0002]

2. Description of the Related Art Metal is a very good structural material,
It has the disadvantage of deterioration due to rust. Recently, photocathode protection using a titanium oxide film has been proposed as a new technology.
In JP-A-6-10153, a coating containing titanium oxide in an amount of 1 mg / m ² or more in terms of titanium metal weight is formed on the surface of a stainless steel material. When light is applied to the steel surface (that is, the coating surface),
The stainless steel material acts as a cathode, the titanium oxide film acts as an anode, and the immersion potential of the stainless steel material shifts toward the base side by 300 mV. It is described that the stainless steel material can be cathodic protected by this.

Japanese Patent Application Laid-Open No. 11-71684 describes that corrosion of a stainless steel material on which a titanium oxide film is formed progresses when the light source is poor. And in order to solve this problem, an intermediate film is provided between the surface coating containing titanium oxide and the stainless steel material, and the intermediate film is made of iron, vanadium,
A titanium oxide film containing copper was used. by this,
The valences of iron, vanadium and copper are low (reduced) during light irradiation and high (oxidized) during light blocking.
Therefore, it is claimed that electrons are generated from iron, copper, and vanadium when the light is blocked, and the electrons are injected into the stainless steel material, so that the anticorrosion effect is maintained.

[0004]

However, it is clear that the anticorrosion action in the dark can hardly be achieved due to the change in the valence of the dissimilar metal element slightly doped in the titanium oxide.

[0005] Of course, the corrosion of metals, particularly the corrosion of metals exposed to the external environment, progresses even at night, and therefore anticorrosive materials having an anticorrosive action even in the dark are required.

An object of the present invention is to provide a method for effectively preventing a metal material from being corroded both when light is irradiated and when light is not irradiated, and to provide an anticorrosion material.

[0007]

SUMMARY OF THE INVENTION The present invention is a method for preventing corrosion of a metallic material during light irradiation and non-irradiation,
A photo-excited semiconductor that is excited when irradiated with light to generate electrons,
Using an electrochromic material having a redox potential that is more negative than the corrosion potential of the metal material, and having a more positive redox potential than the potential of the conductor of the photoexcited semiconductor,
The electrochromic material is contacted with a proton source.
In addition, during light irradiation, electrons from the photoexcited semiconductor are injected into the metal material and electrons are stored in the electrochromic material, and when not irradiated, electrons are injected from the electrochromic material into the metal material.

The principle of the present invention will be described with reference to the schematic diagrams of FIGS. 1 (a) and 1 (b).

Under a reducing condition, the electrochromic material is reduced in the presence of protons and the like, and takes in electrons and protons to form a bronze structure. Then, under oxidizing conditions, electrons are released, and the crystal structure returns to the original structure. This oxidation-reduction reaction is reversible. And, it has a property of developing a specific color with the oxidation-reduction reaction. As such materials, specifically,
Transition metal oxides WO3, MoO3, Nb2O5, V2O5, Ir
Ox, TiO2, NiOx, Cr2O3 and WO3-MoO3 can be mentioned. As the electrochromic material, a completely color developing material is particularly preferable, and WO3, MoO3, Nb2O5, TiO2, WO3-
MoO3 is particularly preferred.

A photoexcited semiconductor is a semiconductor that generates electrons when irradiated with light. Specifically, TiO2, SrTiO2, Fe2O3,
CdS, CdSe, ZrO2, GaP, SiC, Si, Nb2O5, ZnO, WO
3, SnO2 and the like, among which TiO2, SrTiO3 and SiC are particularly preferred.

As shown in FIG. 1A, at the time of light irradiation,
The semiconductor is excited from the ground level to the conduction band. The potential of this conduction band must be more negative than the corrosion potential of the metallic material. The electrons generated in the semiconductor move to the metal material, reduce the metal material, and maintain the potential of the metal material more negative than its corrosion potential. At the same time, electrons from the metal material move to the electrochromic material (EC material). The electrochromic material takes in these electrons, preferably takes in protons from the outside, changes into a bronze structure, and stores the electrons. At this time, the absorption characteristics of visible light may be changed.

When the light irradiation is stopped, the potential of the semiconductor moves in a positive direction as shown in FIG. On this occasion,
It has been discovered that electrons from the electrochromic material are injected into the metal material, maintaining the potential of the metal material more negative than its corrosion potential and exerting an anticorrosive action. This method is a practical method for preventing corrosion of a metal material even in the dark, and is industrially useful.

[0013] The electrochromic material must have a redox potential that is more negative than the corrosion potential of the metal material.
Thereby, as shown in FIG. 1B, electrons can be injected into the metal material during non-irradiation. Further, the electrochromic material needs to have a redox potential that is more positive than the potential of the conduction band of the photoexcited semiconductor. Thus, when the semiconductor is excited during light irradiation, electrons from the semiconductor can be injected into the electrochromic material, as shown in FIG.

In the schematic diagram of FIG. 1A, electrons generated in a semiconductor once enter a metal material,
Electrons are moving from the metal material to the electrochromic material. However, it is also possible to inject electrons from the semiconductor directly into the electrochromic material without the intervening metal material.

The positional relationship between the metal material, the photoexcited semiconductor, and the electrochromic material and the respective structures are not particularly limited.
However, the photoexcited semiconductor must be at least at a position where light irradiation can be performed. Also, the electrochromic material is in contact with the proton source. As the proton source, there are a fluid and a solid containing protons in addition to the atmosphere and the outside air.

Specifically, the following form is preferable. (1) An electron storage layer made of an electrochromic material and a semiconductor layer made of a photoexcited semiconductor are provided on a metal material. In this case, it is preferable that the electron storage layer and the semiconductor layer do not overlap each other on the metal material. FIG.
(A) is an example of this mode. The electron storage layers 12 and the semiconductor layers 13 are alternately formed on the surface of the metal material 11, and the layers 12 and 13 are not stacked.

(2) An electron storage layer and a porous semiconductor layer on the electron storage layer are provided on the metal material. FIG. 2B shows this embodiment. The electron storage layer 14 is formed on the metal material 11, and the semiconductor layer 15 is formed on the layer 14. Since the semiconductor layer 15 is porous, the surface of the electron storage layer 14 microscopically contacts the outside air.

(3) A layer of a sintered body of a mixture of a powder made of an electrochromic material and a powder made of a photoexcited semiconductor is provided on a metal material. FIG. 2C relates to this mode. On the metal material 11, a layer 18 of a sintered body of a mixture of a powder 16 made of an electrochromic material and a powder 17 made of a photoexcited semiconductor is provided. According to this embodiment, since the electron generation source and the electron storage source are microscopically close to each other, it is considered that the electron storage efficiency is higher.

(4) A semiconductor layer made of a photoexcited semiconductor is provided on a metal material. An electrochromic material is provided on a substrate separate from the metal material, and the electrochromic material and the metal material or the semiconductor layer are combined. Make an electrical connection. In this manner, the metal material to be protected from corrosion and the electrochromic material as an electron storage source can be spatially separated.

The method for producing the semiconductor film and the method for producing the film of the electrochromic material are not particularly limited, but can be produced, for example, as follows. (1) A sol of an organometallic compound such as a titanium alkoxide and a bis (2,4-pentanedionato) titanium oxide ethanol solution (acetylacetone titanium oxide ethanol solution) is applied on a metal material and thermally decomposed. (2) A fine particle dispersion sol or slurry of a metal oxide is applied on a metal material, and is baked by heating. (3) A film is formed on a metal material by a thermal spraying method, a sputtering method, or the like.

As the coating method, dip coating,
Spray coating, spin coating, brush coating, etc.

Although the metal material is not limited, stainless steel, carbon steel and metal-plated steel are particularly preferred. Examples of the plating material include zinc, zinc-iron, zinc-aluminum, aluminum, and chromium.

The substrate separate from the metal material may be a metal bulk such as a metal plate. Further, the substrate may be a film made of a plastic such as polyethylene, polypropylene, polyester, and polyacrylonitrile.
In this case, the anticorrosion device of the present invention can be easily constructed by attaching the film on a separate appropriate structure, and the film can be easily replaced. An existing structure such as a gas tank can be used as such a separate base.

On the surface of the metal material, another anticorrosion coating, particularly a sacrificial anticorrosion coating, can be formed separately from the anticorrosion material of the present invention. As the material of the anticorrosion coating, all known materials can be used, but the following are preferable. Oil-based paint (oil-based paint): Nitrocellulose lacquer (clear lacquer, lacquer enamel, high solid lacquer, hot lacquer, special lacquer): Synthetic resin paint (phthalic acid resin paint, amino alkyd resin paint, epoxy resin paint, vinyl resin paint, Polyurethane resin paint,
Unsaturated polyester resin paint, acrylic resin paint, chlorinated rubber resin paint, water-based paint, silicon resin paint, fluororesin paint): Special performance paint (powder paint, electrodeposition paint, vinyl sol paint, non-aqueous dispersion paint, ultraviolet ray) Cured paint,
Electron beam curing paint): Special appearance paint (metallic paint, multi-color paint).

[0025]

EXAMPLES (Experiment 1) W was placed on conductive glass (ITO).
Fine particles of O ₃ (particle size: 45 μm) and a TEOS binder were coated by spin coating (1500 rpm), and baked at 200 ° C. for 30 minutes. The WO ₃ electrode thus obtained was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode, and a platinum wire electrode was used as a counter electrode. The cyclic voltammogram (CV) was measured, and the results are shown in FIGS. FIG. 3 shows the results of measurement at pH 1 in a 0.1 M aqueous HCl solution. FIG.
It is the result measured at pH 5 in an aqueous M NaCl solution. The measuring machine is a digital potential stat “HZ-300
0 "(manufactured by Hokuto Denko KK). Note that FIG.
In FIG. 4, the circles indicate the photopotential of TiO2 (light intensity 10 mW / cm2) in the same solution.

From these results, it was found that WO ₃
Is considered to be reduced and changed to a tungsten bronze structure.

(Experiment 2) In Experiment 1, +100 m
V, 0mV, -100mV, -200mV, -400m
When a constant voltage of V was applied, a change in the distribution of the reflectance with respect to visible light of 400 to 700 nm was examined. The results are shown in FIGS. FIG. 5 shows the result of measurement in a 0.1 M HCl aqueous solution at pH 1. FIG.
It is the result measured at pH 5 in an aqueous M NaCl solution. As the constant potential applying device, a digital potential stat “HZ-3000” (manufactured by Hokuto Denko KK) was used. As a reflectance measurement machine, "handy-color-COLORIMETE
R "(manufactured by BYK-GARDNER, USA) was used. In each case, it can be seen that the color tone of WO ₃ changes significantly by the application of the negative potential.

(Experiment 3) On a substrate made of SUS304 (aluminum buffing process of 0.05 μm), 0.0
Using a 5M bis 2,4-pentanedionato titanium oxide (acetylacetone titanium oxide) ethanol solution (300 ml) as a raw material, a film was formed by spray pyrolysis. The film formation temperature was 300 ° C.

Also, WO on a conductive glass (ITO)
A dispersion obtained by dispersing the fine particles (particle diameter 500 nm) of No. _{3 in} a silica binder (“NDC-100A” manufactured by Nippon Soda Co., Ltd.) at a rate of 0.116 g / ml is applied by spin coating to form a film, 3 at 200 ° C
Bake for 0 minutes. This WO ₃ electrode was connected to a metal material.

The WO ₃ electrode and the titanium oxide electrode were immersed in an aqueous 0.1 M NaCl solution (pH 5). WO ₃
The electrode was the working electrode. A silver / silver chloride electrode was used as a reference electrode, and a platinum wire electrode was used as a counter electrode. The change in the reflectance of WO ₃ was measured under light irradiation (mercury-xenon lamp: wavelength 360 nm: light intensity 10 mW / cm ² : “LA-200UV” manufactured by Hayashi Watch Industry) and under no irradiation. As a reflectance measurement machine, "handy-color-CO
LORIMETER "(manufactured by BYK-GARDNER, USA).
The result is shown in FIG.

FIG. 7 shows that the WO ₃ electrode has a length of -370 m.
The change in reflectance when a constant voltage of V is applied is also shown. As the constant potential applying device, a digital potential stat “HZ-3000” (manufactured by Hokuto Denko KK) was used. As can be seen from this result, the reflectance characteristic of the WO ₃ electrode changes greatly as in the case where a negative constant voltage is applied by connecting the titanium oxide electrode to the WO ₃ electrode and irradiating light.

(Experiment 4) An apparatus similar to that of Experiment 3 was manufactured. Then, the above-described light was irradiated for 60 minutes, and then the light irradiation was stopped. The change in the potential of the titanium oxide electrode during this time was measured and is shown in FIG. As can be seen from this result, immediately after the light irradiation was stopped, the potential of the titanium oxide electrode increased, but the increase stopped near -0.2 V,
The electric potential is suppressed to -0.2 V or less for about 00 minutes. Since the corrosion potential of SUS is around -0.15 V, it can be seen that the corrosion can be prevented for a long time.

(Experiment 5) The main surface of a substrate made of SUS304 (aluminum buffing process of 0.05 μm) was divided into two equal area regions. Then, a film was formed on this one region by a spray pyrolysis method using 300 ml of a 0.05 M bis 2,4-pentanedionato titanium oxide (acetylacetone titanium oxide) ethanol solution as a raw material. The film formation temperature was 300 ° C.

Next, on the other region of the substrate, WO ₃ fine particles (particle diameter: 500 nm) were mixed with a silica binder (“ND
C-100A ”manufactured by Nippon Soda Co., Ltd.
The dispersion dispersed at a rate of g / ml was applied by spin coating, formed into a film, and baked at 200 ° C. for 30 minutes.

The substrate was immersed in a 3% by weight aqueous solution of NaCl (pH 5). A silver / silver chloride electrode was used as a reference electrode, and a platinum electrode was used as a counter electrode. Then, light (mercury-xenon lamp: wavelength 360 nm: light intensity 10 mW / cm)
² ) was irradiated for 60 minutes and then the irradiation was stopped. FIG. 9 shows the potential change of the electrode on the substrate surface at this time.

As a result, it was found that the potential of -0.15 V or less was maintained for a long time even after the light irradiation was stopped after 60 minutes.

FIG. 10 shows the result when the entire main surface of the substrate is covered with a titanium oxide film alone for comparison. When there is only a titanium oxide film on the substrate surface, the potential of the electrode rapidly rises to around -0.05 V at the time of stopping the light irradiation after 60 minutes. Therefore, it can be seen that the SUS steel formed with only the titanium oxide film cannot practically obtain the anticorrosion action in the dark.

(Experiment 6) In this experiment, the possibility of using strontium titanate instead of titanium oxide was examined. 0.02 M bis 2,4-pentanedionato strontium in methanol (150 m
l) and a mixed solution of 300 ml of an ethanol solution (150 ml) of bis2,4-pentanedionato titanium oxide of 0.02 M were used as a raw material, and a film was formed on conductive glass (ITO) by a spray pyrolysis method. . The film forming temperature is 300 ° C. After film formation, 300-60 in an electric furnace
Annealing treatment was performed at 0 ° C.

The electrode was immersed in a 3% by weight aqueous solution of NaCl (pH 5) to obtain a working electrode. A silver / silver chloride electrode was used as a reference electrode, and a platinum electrode was used as a counter electrode. Then, light (mercury-xenon lamp: wavelength 360 nm: light intensity 1)
(0 mW / cm ² ) for 60 minutes, and the photopotential was measured. FIG. 11 shows the relationship between the annealing temperature and the light potential.

According to this result, the annealing temperature was set to 400
It is understood that the photopotential is further reduced by setting the temperature to not more than ° C. This temperature is more preferably 500 ° C. or lower.
By obtaining such a low potential, metal materials having a lower corrosion potential, such as carbon steel, can also be protected by the present invention.

In one embodiment of the present invention, the metal material is
It is an existing structure that is irradiated with sunlight during the day, such as a gas tank, a guardrail, and a streetlight.

[0042]

As described above, according to the present invention, it is possible to provide a method and an anticorrosion material for effectively preventing corrosion of a metal material during both light irradiation and non-light irradiation.

[Brief description of the drawings]

FIGS. 1A and 1B are schematic views for explaining the principle of the present invention.

FIGS. 2 (a), (b), and (c) are diagrams schematically showing an example of an anticorrosion film of the present invention.

FIG. 3 shows a cyclic voltammogram of an electrode composed of WO ₃ (pH 1).

FIG. 4 shows a cyclic voltammogram of an electrode composed of WO ₃ (pH 5).

FIG. 5 shows the electrochromic reaction of an electrode made of WO ₃ and shows the relationship between the wavelength and the reflectance when the voltage applied to the electrode is changed (pH 1).

FIG. 6 shows the electrochromic reaction of an electrode made of WO ₃ and shows the relationship between the wavelength and the reflectance when the voltage applied to the electrode is changed (pH 5).

FIG. 7 is a graph showing the effect of the WO ₃ electrode on the electrochromic reaction when the titanium oxide electrode and the WO ₃ electrode are connected.

FIG. 8 shows a case where a titanium oxide electrode and a WO ₃ electrode are connected, light irradiation is continued for 60 minutes, and then light irradiation is stopped.
6 is a graph showing a change in potential.

FIG. 9 is a graph showing a change in potential when both a titanium oxide electrode and a WO ₃ electrode are provided on a SUS substrate surface, light irradiation is continued for 60 minutes, and then light irradiation is stopped.

FIG. 10 is a graph comparing the graph of FIG. 9 with a change in potential when only a titanium oxide electrode is provided on the SUS substrate surface.

FIG. 11 is a graph showing the relationship between the annealing temperature of the coating and the potential of the electrode at the time of light irradiation, for an electrode made of a mixed coating of titanium oxide and strontium titanate.

[Explanation of symbols]

Reference Signs List 11 metal material 12, 14 electron storage layer made of electrochromic material 13 semiconductor layer made of photoexcited semiconductor 15 porous semiconductor layer made of photoexcited semiconductor 16 particles made of electrochromic material 17 particles made of photoexcited semiconductor 18 made of electrochromic material A layer made of a sintered body of a mixture of a powder and a powder made of a photoexcited semiconductor

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuichi Saito 2-880, Takaragi-cho, Utsunomiya-city, Tochigi Prefecture Inside (72) Katsuhisa Kashiwazaki 2-880, Takaragi-cho, Utsunomiya-shi, Tochigi Kouyo Electric Construction Examiner Akihiro Kitamura (56) References JP-A-11-71684 (JP, A) JP-A-10-158860 (JP, A) JP-A-9-302479 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C23F 13/00 C23F 15/00 C23C 30/00

Claims (9)

(57) [Claims] 1. A method for preventing corrosion of a metal material during light irradiation and at the time of non-irradiation, comprising: a photo-excited semiconductor that is excited when irradiated with light to generate electrons;
An electrochromic material having a redox potential that is more negative than the corrosion potential of the metal material, and having a more positive redox potential than the potential of the conduction band of the photoexcited semiconductor , Proton source
Contact , injecting electrons from the photoexcited semiconductor into the metal material during light irradiation and storing electrons in the electrochromic material, and injecting electrons from the electrochromic material into the metal material during non-irradiation A method for preventing corrosion of a metal material. 2. The method according to claim 1, wherein an electron storage layer made of the electrochromic material and a semiconductor layer made of the photoexcited semiconductor are provided on the metal material. 3. An electron storage layer comprising the electrochromic material is provided on the metal material, and a porous semiconductor layer comprising the photoexcited semiconductor is provided on the electron storage layer. The described method. 4. The method according to claim 1, wherein a sintered body of a mixture of the powder made of the electrochromic material and the powder made of the photoexcited semiconductor is provided on the metal material. 5. A semiconductor layer comprising the photoexcited semiconductor is provided on the metal material, and the electrochromic material is provided on a substrate separate from the metal material. 2. The method according to claim 1, wherein the metal material or the semiconductor layer is electrically connected. 6. An anticorrosion material for preventing corrosion of a metal material during light irradiation and non-irradiation, comprising: a photoexcited semiconductor that is excited when irradiated with light to generate electrons; has a negative redox potential than the potential, and has an electrochromic material having a positive redox potential than the potential of the excitation semiconductor conductor, said electrochromic
The material is in contact with a proton source, and at the time of light irradiation, injects electrons from the photoexcited semiconductor into the metal material and stores the electrons in the electrochromic material. An anticorrosion material characterized by injecting electrons into the material. 7. The protection according to claim 6, further comprising an electron storage layer made of said electrochromic material and a semiconductor layer made of said photoexcited semiconductor, provided on said metal material. Foodstuff. 8. An electron storage layer made of the electrochromic material provided on the metal material, and a porous semiconductor layer made of the photoexcited semiconductor provided on the electron storage layer. 7. The anticorrosion material according to claim 6, wherein 9. The anticorrosion material according to claim 6, comprising a sintered body of a mixture of the powder made of the electrochromic material and the powder made of the photoexcited semiconductor.