JP2004333468A - Metal structure superior in corrosion resistance, material for manufacturing the metal structure and manufacturing method for the metal structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide firstly, a metal structure superior in corrosion resistance used under irradiation of electromagnetic wave, secondly, a material for manufacturing metal structure and thirdly, a manufacturing method for the metal structure. <P>SOLUTION: The metal structure used under irradiation of electromagnetic wave is provided with a function layer generating electrons by radiating electromagnetic wave to a part of or whole base material by way of conductive intermediate layer for raising adhesion. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a metal structure used under irradiation of electromagnetic waves, a material for producing the metal structure, and a method for producing the metal structure.

  In a nuclear power plant, carbon steel, stainless steel, nickel alloy or the like is used as a constituent material, and water is used as a reactor coolant. This cooling water undergoes radiolysis when irradiated with radiation, and generates oxidizing substances such as oxygen and hydrogen peroxide. These generated oxidizing substances are known to dissolve in cooling water and cause corrosion or stress corrosion cracking in structures such as the reactor itself and water cooling system piping. However, even if corrosion or stress corrosion cracking occurs in the structure, it is necessary to stop the reactor for repair and replacement, and it is difficult to frequently repair and replace in actual operation.

  Spent nuclear fuel is discharged from nuclear power plants, and carbon steel, stainless steel, etc. are also used as materials for structures such as sealed containers (canisters) for storing or transporting spent nuclear fuel. Even when condensation or the like occurs in the sealed container, water adhering to the container is decomposed by irradiation with radiation to generate an oxidizing substance. Furthermore, generally used concrete cask removes heat by convection of the outside air between the concrete cask main body (shielding body) and the canister. At this time, highly corrosive substances such as chloride ions are added to the outside air. If it is included (eg, sea breeze), this material may adhere to the surface of the sealed container and cause corrosion or stress corrosion cracking. However, in the case where spent nuclear fuel is stored in the container, even if corrosion or stress corrosion cracking occurs in the sealed container, it cannot be repaired or replaced.

  By the way, it is known that the occurrence of corrosion or stress corrosion cracking and the development thereof affect the corrosion potential, and the lower the corrosion potential of the environment, the less likely the corrosion or stress corrosion cracking occurs. As a measure to reduce corrosion or stress corrosion cracking, the generated electrons are structured by attaching a photocatalytic substance that is generated by irradiation with light or radiation received in the reactor to the surface of the reactor structural material. A technology for suppressing the occurrence of corrosion or stress corrosion cracking by supplying to a material and lowering the corrosion potential of the environment is disclosed (for example, Patent Document 1 and Patent Document 2). In these technologies, as a method of directly attaching the photocatalytic substance to the surface of the nuclear reactor structural material, (1) a method of circulating cooling water injected with the photocatalytic substance into the nuclear reactor structural material and (2) a robot Examples are a method of spraying a photocatalytic substance on a predetermined site using a method such as (3) a method of directly forming a photocatalytic substance film on the surface of a nuclear reactor structure material by a PVD method, a CVD method, or the like.

  However, the present inventors have examined that in the method (1), it is difficult to determine an appropriate injection amount of the photocatalytic substance, and whether the photocatalytic substance is reliably attached to the surface of the reactor structural material. It was also difficult to confirm. In the method (2), the photocatalytic substance can be attached to a predetermined site, but the photocatalytic substance is easily peeled off due to poor adhesion between the photocatalytic substance and the reactor structural material. In the method (3), when the photocatalytic material film is directly formed by the PVD method or the CVD method, it is necessary to reduce the pressure in the chamber, and the photocatalytic material film is adhered to a specific part of the reactor structural material. It is not easy to adhere well. Therefore, in the techniques proposed in Patent Documents 1 and 2, the corrosion potential of the reactor structural material may not be lowered, and the occurrence of corrosion or stress corrosion cracking may not be sufficiently suppressed.

In addition, it is difficult to form a photocatalytic material film, and when a film defect occurs, there is a problem that the corrosion resistance of the structural material is deteriorated in combination with peeling from the substrate.
JP 2001-4789 A (see [Claims], [0018], [0049] to [0050], [0081] to [0083]) JP 2001-276628 A (see [Claims], [0029], [0034] to [0035], [0087])

  This invention is made | formed in view of such a condition, and the 1st objective is to provide the metal structure which shows favorable corrosion resistance, even when used under irradiation of electromagnetic waves. The second object is to provide a material that can be suitably used for producing the metal structure. A third object is to provide a method for producing the metal structure.

  The metal structure excellent in corrosion resistance according to the present invention that has solved the above problems is a metal structure that is used under irradiation of electromagnetic waves, in order to enhance corrosion resistance in part or all of the substrate. The point is that a functional layer for generating electrons by irradiation of electromagnetic waves is provided through the conductive intermediate layer.

  The material that can be suitably used for producing the metal structure having excellent corrosion resistance is an electron by irradiation of electromagnetic waves through a conductive intermediate layer for enhancing corrosion resistance on a part or all of the base material. The gist of the present invention is that a functional layer that generates the above is provided.

  The conductive intermediate layer preferably contains one or more selected from the group consisting of Fe, Cu, Ni, Co, Cr, Ti and Zr. Further, the conductive intermediate layer preferably has an action of reducing the corrosion potential. The conductive intermediate layer preferably has a thickness of 0.05 μm or more, and the functional layer preferably has a thickness of 1 μm to 13 mm. The functional layer preferably contains at least one selected from the group consisting of metal oxides, metal carbides, and metal nitrides.

  The method for producing a metal structure having excellent corrosion resistance is a method in which a conductive intermediate layer for enhancing corrosion resistance is provided on a part or all of the surface of the base material, and an electromagnetic wave is further formed on the surface of the conductive intermediate layer. The main point is that a functional layer for generating electrons by irradiation is provided.

  ADVANTAGE OF THE INVENTION According to this invention, even when used under irradiation of electromagnetic waves, the metal structure which shows favorable corrosion resistance can be provided. Moreover, the material for manufacturing the said metal structure can be provided. Furthermore, the manufacturing method of the said metal structure can be provided.

  As described above, the adhesion between the nuclear reactor structural material and the photocatalytic substance cannot be said to be good, and when the photocatalytic substance is peeled off, the anticorrosion effect is not exhibited. In addition, it is difficult to form a photocatalytic material film, and when a film defect occurs, the surface of the structural material is exposed to a corrosive environment in combination with peeling from the structural material, which causes a significant deterioration in the corrosion resistance of the structural material. On the other hand, it is very difficult to repair and replace structures used under radiation.

  Therefore, the present inventors have studied from various angles with the aim of improving the corrosion resistance of the structural material. As a result, it has been found that a conductive intermediate layer for enhancing corrosion resistance may be provided between the material constituting the structural material and the photocatalytic substance, and the present invention has been completed. Hereinafter, the function and effect of the present invention will be described.

  The metal structure of the present invention is one in which a functional layer that generates electrons by irradiation of electromagnetic waves is provided on a part or all of a base material via a conductive intermediate layer for enhancing corrosion resistance.

  A functional layer that generates electrons when irradiated with electromagnetic waves is a layer that emits electrons by being excited from a valence band to a conduction band when irradiated with electromagnetic waves having relatively high energy. As will be described later, electrons generated in the functional layer are supplied from the functional layer to the base material through the conductive intermediate layer, whereby the cathode reaction in the base material is promoted and the corrosion potential is lowered. In addition, stress corrosion cracking (hereinafter sometimes referred to as “corrosion”) is greatly suppressed.

  Here, an electromagnetic wave having a relatively high energy is an electromagnetic wave having a wavelength of 400 nm or less (that is, an electromagnetic wave having a shorter wavelength than visible light), and specifically, ultraviolet rays or radiation (for example, α rays, β rays, γ rays, X rays, neutron rays, etc.).

  The position and area of the functional layer are not particularly limited, and may be provided on a part of the base material or on the entire base material. However, if the functional layer is provided on the entire base material (entire surface), the cost increases. Therefore, the functional layer is preferably provided on a part of the base material. In particular, since corrosion and stress corrosion cracking are likely to occur at a site such as a welded portion where the substrates are connected to each other, it is recommended to provide a functional layer around the connection between the substrates. In addition, the functional layer may be provided only on one side (front side or back side) of the base material, or may be provided on both sides (front side and back side). It is necessary to provide it.

  In the metal structure of the present invention, it is important to provide a conductive intermediate layer for enhancing the corrosion resistance of the base material between the functional layer and the base material. By providing a conductive layer as an intermediate layer, electrons generated in the functional layer are supplied to the base material through the conductive intermediate layer, the cathode reaction in the base material is promoted, the corrosion potential is lowered, and an anticorrosive effect is obtained. Because it is. By providing a conductive intermediate layer between the functional layer and the base material, the surface of the base material is not exposed to the corrosive environment even if some defects occur in the functional layer, and the corrosion resistance of the metal structure. Can be increased.

  Therefore, the conductive intermediate layer is not particularly limited as long as it does not block electrons generated in the functional layer from moving to the base material, and may be a semiconductor as well as a good conductor. That is, the conductive intermediate layer only needs to supply even a small amount of electrons generated in the functional layer to the base material. However, even if a material having the same composition as that of the base material is provided as an intermediate layer, the effect of improving the adhesion with the functional layer cannot be expected, and thus the material having the same composition as that of the base material is excluded.

  In addition, the kind of base material is not specifically limited, Metals, such as carbon steel, stainless steel, nickel alloy, a zircaloy (zirconium metal), are generally used.

  As will be described later, the metal structure of the present invention can be produced by providing a functional layer on a part or all of the metal structure via the conductive intermediate layer. You may manufacture using the material for metal structures provided with the functional layer which generate | occur | produces an electron by irradiation of electromagnetic waves through the electroconductive intermediate | middle layer for improving corrosion resistance. That is, this metal structure material can be provided with a conductive intermediate layer and a functional layer on the surface of the substrate in an environment in which the temperature and atmosphere are strictly controlled. Can be obtained. As a result, the metal structure manufactured using this metal structure material has excellent corrosion resistance.

  By the way, as a constituent material of the conductive intermediate layer, a material containing at least one selected from the group consisting of Fe, Cu, Ni, Co, Cr, Ti and Zr is preferable. Layers containing these elements have fewer defects than oxides and the like, and metals are particularly ductile, so thermal stress during film formation can be relieved. This is because it is difficult to be exposed in a corrosive environment, and the corrosion resistance of the base material is improved.

  More preferably, it contains at least one selected from the group consisting of Ni, Co, Cr, Ti and Zr. This is because these elements have the effect of reducing the corrosion potential of the environment.

  The content of an element selected from the group consisting of Fe, Cu, Ni, Co, Cr, Ti, and Zr is not particularly limited. However, if these elements are contained in an amount of about 10% by mass or more with respect to the conductive intermediate layer, conductivity is improved. Since it becomes favorable, it is preferable. More preferably, it is about 20 mass% or more, More preferably, it is about 50 mass% or more. The remainder is not particularly limited, and examples thereof include oxides.

  More specifically, (1) an iron alloy, a copper alloy, a nickel alloy, a cobalt alloy, a chromium alloy, a titanium alloy containing 50 mass% or more of any one of Fe, Cu, Ni, Co, Cr, Ti, or Zr Or a zirconium alloy, (2) a metal containing 90% by mass or more of one selected from the group consisting of Fe, Cu, Ni, Co, Cr, Ti and Zr, and (3) Fe, Cu, Ni, Co, Cr, Ti And pure iron, pure copper, pure nickel, pure cobalt, pure chromium, pure titanium, pure zirconium, etc. containing 99% by mass or more of one selected from the group consisting of Zr.

The conductive intermediate layer may be an alloy containing two or more elements arbitrarily selected from the above element group, and examples thereof include nickel and cobalt alloys, cobalt and chromium alloys, and chromium and nickel alloys. The alloy composition at this time is not particularly limited. For example, the composition of Co and Cr may be 50% by mass: 50% by mass. In particular, a metal mainly containing Co, Ni, or Cr can be suitably used as a conductive intermediate layer because it enhances the corrosion resistance in addition to the effect of increasing the adhesion with the functional layer. Co is activated by neutron irradiation as shown below, and ⁶⁰ Co becomes a γ-ray source. Therefore, by including Co as a conductive intermediate layer, it can be expected that the Co will be activated in advance or that it will be used as a γ-ray source by irradiating neutrons during use. It is also possible to excite electrons in the functional layer.
⁵⁹ Co + n → ⁶⁰ Co

  The thickness of the conductive intermediate layer is not particularly limited as long as it increases the adhesion between the base material and the functional layer and does not block the flow of electrons generated in the functional layer, but as is apparent from the examples described below, In order to exhibit these effects effectively, the thickness is preferably 0.05 μm or more. More preferably, it is more than 0.05 μm, more preferably 0.1 μm or more, still more preferably 0.5 μm or more, and particularly preferably 1 μm or more. However, if the conductive intermediate layer becomes too thick, the adhesion with the functional layer does not deteriorate, but the intermediate layer itself becomes a resistance, making it difficult for electrons excited and generated in the functional layer to reach the substrate, and the cost. Since it becomes high, the thickness of the conductive intermediate layer is preferably 1.3 mm or less. More preferably, it is less than 1.0 mm, more preferably 0.5 mm or less, and still more preferably 0.3 mm or less. Most preferably, it is the range of 20-100 micrometers.

  On the other hand, the thickness of the functional layer is not particularly limited as long as electrons can be generated by the irradiation of electromagnetic waves. However, as apparent from the examples described later, the thickness is set to 1 μm or more in order to effectively exhibit this effect. Is preferred. More preferably, it is 10 μm or more, and further preferably 50 μm or more. However, if the functional layer becomes too thick, the functional layer itself is peeled off. Therefore, the thickness is preferably 13 mm or less. More preferably, it is 10 mm or less, more preferably 5 mm or less, and particularly preferably 1 mm or less.

Examples of preferable constituent materials of the functional layer include those containing at least one selected from the group consisting of metal oxides, metal carbides and metal nitrides used as photocatalysts, and two or more kinds arbitrarily combining these You may provide the layer which mixed. As the metal oxide, e.g., TiO ₂ or _{ZrO 2, Al 2 O 3,} PbO, BaTiO 3, Bi 2 O 3, ZnO, WO 3, SrTiO 3, Fe 2 O 3, FeTiO 3, KTaO 3, MnTiO 3 , SnO _{2 and the} like. Examples of the metal carbide include Al ₄ C ₃ , UC, U ₂ C ₃ , CaC ₂ , SiC, ZrC, W ₂ C, WC, TaC, TiC, Fe ₃ C, HfC, B ₄ C, and Mn ₃ C. Is mentioned. Examples of the metal nitride include AlN, CrN, SiN ₄ , BN, Mg ₃ N ₂ , and Li ₃ N.

Among the functional layers, a layer containing a metal oxide is more preferable because vacancies are likely to occur in the oxygen sites of the crystal lattice. Among the metal oxides, titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), and oxidation are more preferable. A layer containing one or more selected from aluminum (Al ₂ O ₃ ) is more preferable. Particularly preferred is ZrO ₂ . This is because ZrO ₂ has a large band gap, so that once excited electrons can be used without waste. That is, by supplying excited electrons to the substrate, the corrosion potential of the environment can be lowered, and corrosion can be suppressed. Moreover, since ZrO ₂ has a band gap in a region extending between the hydrogen generation potential and the oxygen generation potential due to the decomposition of water, the progress of corrosion can be suppressed more efficiently. Zirconium-based metals have already been put into practical use as materials for channel boxes and fuel cladding tubes used in nuclear reactors, and have been used in nuclear reactors. From this point of view, it is most preferable to use ZrO ₂ as the functional layer.

  As described above, the metal structure of the present invention can be produced using a metal structure material in which a functional layer is provided on the surface of a base material via a conductive intermediate layer. Alternatively, it can also be produced by providing a conductive intermediate layer for enhancing corrosion resistance and providing a functional layer for generating electrons upon irradiation of electromagnetic waves on the surface of the conductive intermediate layer.

  As a method for forming the conductive intermediate layer or the functional layer, for example, a known method such as thermal spraying, vapor deposition [physical vapor deposition (PVD), chemical vapor deposition (CVD), etc.], sputtering, or the like can be employed. In addition, a conductive intermediate layer (or functional layer) formed in a sheet shape may be provided on the surface of the substrate (or conductive intermediate layer). In particular, the material for a metal structure of the present invention is a material having good properties because the temperature and atmosphere can be managed when the conductive intermediate layer and the functional layer are provided on the substrate surface.

  The metal structure in the present invention is a structure mainly used in an environment in contact with cooling water or an aqueous solution in a nuclear power plant. For example, a channel box, a shroud, a reactor vessel, a reactor vessel lid, water Refers to metal structures such as cooling pipes. Further, a metal structure used in the atmosphere, such as a sealed container (canister) for transporting or storing spent nuclear fuel, is also included in the metal structure of the present invention. This is because condensation can occur in the canister and the container may come into contact with water.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

Example 1
A test piece having a conductive intermediate layer and a functional layer with various thicknesses provided on the substrate surface was prepared, and the natural immersion potential when this test piece was irradiated with electromagnetic waves was measured. Based on this potential, the corrosion potential was measured. Degradability (stress corrosion cracking resistance) was evaluated. The reference electrode is shielded with a lead block so that the influence of electromagnetic wave irradiation can be sufficiently ignored.

  Further, the produced test piece was bent at 90 °, and the adhesion with the functional layer was evaluated from the peeled state of the functional layer.

  As the base material, JIS standard SUS316L was used. The size of the substrate is 20 mm × 20 mm × 1 mm (L × W × T).

The surface (front surface) of this substrate was coated with a CoCr alloy as a conductive intermediate layer, and then coated with ZrO ₂ as a functional layer to obtain a test piece. The thicknesses of the conductive intermediate layer and the functional layer are shown in Table 1 below. The composition of the CoCr alloy is 50% by mass: 50% by mass of Co and Cr. Further, masking is performed on the end surface of the front surface on which the functional layer is not provided and the back surface of the base material.

The obtained test piece was immersed in a 0.05 mol / L Na ₂ SO ₄ solution deaerated with argon gas, and the test piece was irradiated with electromagnetic waves. As an electromagnetic wave, γ rays using ⁶⁰ Co as a radiation source were irradiated. After irradiating γ rays at an irradiation intensity of 600 Gy / h, the potential (natural immersion potential) that spontaneously occurs from the test piece after 23 hours was measured. The reason for measuring the natural immersion potential after 23 hours is that it has been experimentally confirmed that the time required for the electrolyte solution to penetrate into the functional layer is required for the effect to be exhibited.

  The corrosion potential lowering property was evaluated based on the measured natural immersion potential. The reason why the corrosion potential lowering ability can be evaluated based on the natural immersion potential is that the more electrons that are spontaneously generated in the functional layer by the irradiation of electromagnetic waves, the more the electrons are transferred from the functional layer to the conductive intermediate layer to the base material (metal structure). This is because it reaches a large amount, and this reduces the corrosion potential. The evaluation criteria for the corrosion potential lowering property are as follows. The evaluation results are also shown in Table 1 below. The natural immersion potential is a hydrogen electrode reference potential.

<Evaluation criteria for corrosion potential reduction>
◎: Excellent (natural immersion potential is -350 mV or less)
A: Excellent (natural immersion potential is over -350 mV to -300 mV)
○: Good (natural immersion potential is over -300 mV to -250 mV)
Δ: Normal (natural immersion potential is over -250 mV to -200 mV)
□: Although effective, small (natural immersion potential exceeds -200 mV)

  On the other hand, the test piece obtained above was bent at 90 ° to evaluate the adhesion with the functional layer. The evaluation criteria are as follows, and the evaluation results are also shown in Table 1 below.

<Adhesion evaluation criteria>
A: Peeling area is 10% or less (good)
○: Peeling area exceeds 10% to 20%
Δ: Peeling area exceeds 20% to 50%
□: peeling area is over 50% to 60%
×: Peeling area exceeds 60% (defect)

  As is apparent from Table 1, by providing a conductive intermediate layer between the functional layer and the substrate, the corrosion potential of the environment can be lowered and the adhesion with the functional layer can be increased.

Example 2
Next, test pieces in which the types of the conductive intermediate layer and the functional layer provided on the surface of the base material were changed were produced, and the corrosion potential lowering property and adhesiveness of the test pieces were evaluated.

  As the base material, stainless steel (SUS316L) having a size of 20 mm × 20 mm × 1 mm (L × W × T) was used.

  A conductive intermediate layer shown in Table 2 below was coated on the surface of the substrate. As the conductive intermediate layer, pure Fe, pure Cu, pure Ni, pure Co, pure Cr, pure Ti, pure Zr, CoCr alloy or NiCr alloy was used. Pure means that the content of each element is 99% by mass or more. The composition of the CoCr alloy is 50 mass%: 50 mass% for Co and Cr, and the composition of the NiCr alloy is 50 mass%: 50 mass% for Ni and Cr. The thickness of the conductive intermediate layer is all 10 μm.

A functional layer shown in Table 2 below was formed on the surface of the conductive intermediate layer. As the functional layer, either WO ₃ , TiO ₂ , ZrO ₂ or Al ₂ O ₃ was formed by coating. The thickness of each functional layer is 100 μm.

  About the obtained test piece, the corrosion potential lowering property and adhesion were tested and evaluated under the same conditions as in Example 1. The evaluation results are also shown in Table 2 below.

  As is apparent from Table 2, by providing a conductive intermediate layer between the functional layer and the substrate, the corrosion potential can be lowered and the adhesion with the functional layer can be increased. In particular, when a layer containing Ni, Co, Cr, Ti, or Zr is provided as the conductive intermediate layer, the adhesion with the functional layer can be further enhanced.

Claims (7)

A metal structure used under the irradiation of electromagnetic waves,
A metal structure having excellent corrosion resistance, wherein a functional layer for generating electrons upon irradiation with electromagnetic waves is provided on a part or all of a substrate via a conductive intermediate layer for enhancing corrosion resistance. A material for producing the metal structure according to claim 1,
For metal structures with excellent corrosion resistance, characterized in that a functional layer that generates electrons upon irradiation with electromagnetic waves is provided on a part or all of the base material through a conductive intermediate layer for enhancing corrosion resistance. material.   The metal structure or metal structure material according to claim 1 or 2, wherein the conductive intermediate layer contains at least one selected from the group consisting of Fe, Cu, Ni, Co, Cr, Ti, and Zr.   The metal structure or metal structure material according to any one of claims 1 to 3, wherein the conductive intermediate layer has an action of reducing a corrosion potential.   5. The metal structure or metal structure material according to claim 1, wherein the conductive intermediate layer has a thickness of 0.05 μm or more, and the functional layer has a thickness of 1 μm to 13 mm.   The metal structure or metal structure material according to claim 1, wherein the functional layer contains at least one selected from the group consisting of metal oxides, metal carbides, and metal nitrides. A method for manufacturing a metal structure according to claim 1, comprising:
Corrosion resistance, characterized in that a conductive intermediate layer for enhancing corrosion resistance is provided on part or all of the substrate surface, and further a functional layer for generating electrons upon irradiation of electromagnetic waves is provided on the surface of the conductive intermediate layer. The manufacturing method of the metal structure excellent in.