JP2005103505A - Method for manufacturing magnesium metallic material having photocatalytically active surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop such a material that the photocatalytic effect per unit area of the material is heightened by depositing/fixing a large quantity of a photocatalyst on the surface of a magnesium alloy. <P>SOLUTION: This magnesium metallic material having a photocatalytically active surface is manufactured by pretreating magnesium alloy materials having various shapes mechanically or chemically so that the surface of each of the magnesium alloy materials is changed from a two-dimensional surface to a three-dimensional surface and the surface area is increased, anodizing the surface area-increased magnesium alloy material by non-spark discharge to form a transparent or translucent porous film having many minute pores and metallic luster and filling the minute pores of the film with the photocatalyst. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnesium-based metal material having a photocatalytically active surface and a method for producing the same, which are used in a wide range of applications such as water purification, deodorization, sterilization, oil stain prevention, and decomposition of harmful gases.

When a semiconductor is irradiated with light having a wavelength greater than its band gap, the organic matter that contacts these is decomposed by redox reaction due to the generation of holes in the valence band and the transfer of electrons to the conductor by photoexcitation. Photocatalysts are well known.

However, since it is difficult to fix the photocatalyst to the substrate surface, development of various materials having a photocatalytic active surface is delayed. This is because the redox ability generated when the photocatalyst is excited is very strong and decomposes most organic substances, so that the organic substances cannot be used as a binder for fixing the photocatalyst to the substrate surface. In order to produce the above-mentioned photocatalytic effect, the binder must be transparent and porous because it is necessary to irradiate the catalyst body with ultraviolet light or the like and to make direct contact between the material to be treated and the catalyst body. is required. For this reason, inorganic binders such as silicates have been mainly used for immobilizing photocatalysts on substrates.

For example, Patent Document 1 proposes a method for immobilizing a photocatalyst on a substrate surface, and the binder used at this time is a silicate. However, since the silicate binder is cracked when it is thickened, there is a drawback that it is peeled off from the base material upon impact, and it is difficult to increase the amount of photocatalyst provided by thickening. Since the photocatalyst decomposes only the organic matter in contact with this by oxidation-reduction decomposition, if it is applied in a small amount, the ability to decompose oil stains and harmful gases is inevitably small. Development of a method for adhering a large amount of photocatalyst to the surface of a substrate roughened in structure has been desired.
JP-A-9-1724

In the case of conventional photocatalysts, for complex shapes, for example, when zeolite is used as a raw material, the powder is solidified in a mold, adhered to the surface in the form of a powder, or the powder is confined in a closed region In the former, the catalytic effect was small even when a large amount of raw material was used, and only an insufficient amount could be fixed by surface adhesion.

The present invention has been proposed in order to solve the disadvantage that the photocatalyst is immobilized on the substrate surface in a small amount in the prior art, and an object of the present invention is to provide a photocatalyst having a high ability to decompose harmful substances.

The present invention forms a porous non-spark discharge type anodic oxide film having a large number of fine pores having an average pore diameter of 50 to 1000 nm on the surface of magnesium or a magnesium alloy, and a photocatalyst inside the fine pores of the porous film and on the metal surface Is a magnesium metal material having a photocatalytically active surface, and a method for producing the same.

On the surface of the magnesium metal material of the present invention, there is a porous anodic oxide film having many fine pores having an average pore diameter of 50 to 1000 nm by non-spark discharge type anodic oxidation. This film has a regular hexagonal column or columnar shape from the surface toward the magnesium substrate and reaches the barrier layer.

Many such pores can be formed on the surface by applying an anodized film under conditions that do not involve spark discharge. The thickness of the porous non-spark discharge type anodic oxide film can be set freely in the range of 3 to 50 μm. Therefore, the amount of the photocatalyst filled in the pores has a considerable degree of freedom as required. Can be changed.

The pores formed by anodic oxidation on the surface of the metal material of the present invention mainly have a three-layer structure of pores, walls, and non-porous layers. The main components of the film are magnesium hydroxide 60% or more and magnesium oxide 0 to 40%. It consists of the following composition. These pores have openings on the surface, have an average pore diameter of 50 to 1000 nm, and occupy 80% or more of the entire film, and therefore have a particle size of about 10 to 500 nm as a photocatalyst. For example, when titanium oxide is used, it is easy to fill or adhere to the inside and surface of the micropore. Examples of titanium oxide having such a particle size include ST series powders and STS series dispersions commercially available from Ishihara Sangyo Co., Ltd. Since the number of pores formed on the surface of the metal material is at least 100 per square millimeter, usually 10,000 or more, the photocatalyst can be uniformly supported and immobilized on the entire surface of the substrate.

In the present invention, in order to form a film having specific fine pores on the surface of the magnesium metal material, the metal material is alkali, alkaline earth metal hydroxide, carbonate, bicarbonate, silicate or fluorosilicate. Current density in an aqueous solution containing 0.2 to 7 mol / liter of one or more of the above and 0.01 to 5 mol / liter of a film-forming stabilizer (surface hardening additive) at a rate of 0.5 to 5 A / deci It is achieved by anodizing at a square meter, voltage 2-25V without spark discharge.

Specific examples of the alkali, alkaline earth metal hydroxide, carbonate, bicarbonate, silicate or silicofluoride used in the present invention include caustic soda, caustic potash, barium hydroxide and the like. Examples thereof include carbonates such as oxide, sodium carbonate, calcium carbonate, and magnesium carbonate, and bicarbonates such as sodium bicarbonate, potassium bicarbonate, and calcium bicarbonate.

It is preferable to add a film formation stabilizer to the electrolytic solution for the purpose of improving the life of the solution. As the stabilizer, inorganic compounds and organic compounds are used. Specifically, mineral salts such as NaNO ₃ , CaNO ₃ , MgNO ₃ , Na ₂ SO ₄ and MgSO ₄ , fluorides such as KF and NH ₄ F, Na ₂ SiO ₃ , Na ₄ SiO ₄ , silicic acid compounds such as K ₂ SiO ₂ , silicofluorides such as Na ₂ SiF ₆ , MgSiF ₆ , (NH ₄ ) ₂ SiF ₆ , (CH ₂ OH) ₂ as organic compounds, Alcohol groups such as (CH ₂ CH ₂ OH) O, (CH ₂ OH) ₂ CHOH, (COOH) ₂ , (CH ₂ CH ₂ COOH) ₂ , [CH (OH) COOH] ₂ , C ₆ H ₄ (OH _{· COOH), C 6 H 5} COOH, C 6 H 4 (COOH) 2 which carboxyl _{group, C 6 H 4 (SO 3} H · COOH), C 6 H 3 (COOH · O · SO 3 _H) an organic compound having a sulfone group such as is used.

These film formation stabilizers may be used alone or in combination. In particular, when an inorganic compound and an organic compound are used in combination, liquid management becomes easy, which is preferable. The amount of the stabilizer added is preferably in the range of 0.01 to 4 mol / liter in the electrolytic solution.

The anodizing treatment of the magnesium alloy in the electrolytic solution thus adjusted is particularly preferably carried out in a weak to strong alkaline range of pH 9 or higher at a bath temperature of 10 to 90 ° C.

There is drying as a treatment after the anodizing treatment. Drying is performed at 50 to 80 ° C. for 20 to 60 minutes.

Forming a porous non-spark discharge type anodic oxide film on the surface of a magnesium-based metal material and supporting and fixing the photocatalyst fine particles in the pores are the normal pressure impregnation method, the vacuum impregnation method, the pressure impregnation method, the sol-gel method. Method, electrophoresis method, immersion ultrasonic impregnation method and the like, and impregnation method using immersion under reduced pressure and immersion ultrasonic impregnation method are particularly preferable.

As a specific impregnation method, a magnesium alloy material in which an anodized film is formed is placed in a suitable vacuum vessel, the inside of the STS series or the like is introduced by introducing a titanium oxide suspension such as the STS series after reducing the pressure inside the surface pores. Titanium oxide can be densely filled inside. It is also possible to fill the catalyst by pressurizing the container after introducing the suspension. Such immobilization is characterized in that it can be carried out in a series of conventional manufacturing processes as in the post-process such as plating, alumite treatment, and painting after forming the magnesium metal material.

The magnesium metal material used in the present invention can be widely applied, pure magnesium system, magnesium-aluminum system, magnesium-aluminum-zinc system, magnesium-aluminum-silicon system, magnesium-zirconium-rare earth-silver system, magnesium-zinc -Zirconium, Magnesium-Zinc, Magnesium-Rare Earth-Zirconium, Magnesium-Aluminum-Rare Earth, Magnesium-Yttrium-Rare Earth, Magnesium-Calcium-Zinc, etc. Is possible.

These materials include wrought materials, cast materials, die-cast materials, forged materials, etc., and the processing and molding methods are also presses from wrought materials, sheet metal, impact, bulge method, sand molds from casting. , Mold, lost wax, plus star mold, squeeze casting method, die casting to hot chamber, cold chamber, semi-melting method, forging, hot and warm methods, shapes desired by these various molding methods, for example It can be used as a plate, a tube, a rod, a sphere, or a two-dimensional or three-dimensional fibrous or honeycomb structure. In particular, when the material of the present invention is used for deodorization or the like, it is preferable to use a material processed into a fibrous or honeycomb shape having a large surface area.

These molding materials are preferably anodized after mechanical or chemical pretreatment as necessary. As the mechanical pretreatment method, a dry or wet honing method, a belt, a buffing method, a scratch method, a hairline method, or the like is used. Further, as a chemical pretreatment method, etching, chemical finish, etching method or the like is used, and one or two or more of these pretreatments may be combined. Such pretreatment has the effect of increasing the surface area because the surface of the metal material is three-dimensionally changed, and the effect of increasing the amount of photocatalyst supported.

The metal or high-surface-area metal material having a shape such as a plate, one or a plurality of tubes or rods, a spherical structure, a two-dimensional or three-dimensional fibrous structure, a honeycomb structure, etc. When the coating and the film formation process by porous non-spark discharge type anodization are added, the surface area further increases, and the amount of photocatalyst immobilized tends to increase accordingly, and the catalyst efficiency per unit area of the substrate is increased. Has a tendency to increase.

The magnesium material thus obtained has a large amount of photocatalyst supported and fixed on the surface, and various planes, housings, frames, complex shaped parts, one or many pipes or rod-like structures, spherical structures, It is used for dimensional or three-dimensional fibrous structures, honeycomb structures, and the like. Depending on the type of UV or photocatalyst, the surface of this material will produce photocatalysis when irradiated with visible light, so that it exhibits antibacterial properties, prevention of wrinkles, antifouling, etc., and contact with harmful or odorous gases such as aldehyde and mercaptan Has the effect of decomposing.

The magnesium-based metallic material of the present invention is not peeled off even if there is an impact because the photocatalyst is filled in the micropores of the film formed by the porous non-spark discharge type anodizing treatment including pretreatment, stable.

In addition, the amount of photocatalyst that is supported and fixed per unit area is much higher than that of the conventional method because it has a three-dimensional structure by pretreatment, and therefore, it is effective in preventing contamination by oil, antibacterial, antifungal, and harmful gases. It is excellent in decomposing effect and can make a small device using photocatalytic action.

Hereinafter, embodiments of the present invention will be specifically described.

Using magnesium alloy AZ31B rolled material having a plate thickness of 1 mm and 70 × 150 mm, after degreasing and acid treatment, potassium hydroxide 2 ± 0.05 mol / liter, sodium metasilicate 0.05 ± 0.005 as a film forming stabilizer In a DC waveform with a liquid temperature of 69 ± 2 ° C., a current density of 2 ± 0.5 A / square decimeter, and a voltage of 4 to 8 V with an electrolyte added with 0.1 / 0.05 mol / liter of diethylene glycol. Anodizing was performed for 30 minutes. When the surface of this film was observed with a laser microscope, micropores having an average pore diameter of 200 to 600 nm could be confirmed, and when the cross section was observed with an optical microscope, a film thickness of about 10 μm could be confirmed. After the treatment, it was immersed in an STS-21 titanium oxide dispersion (Ishihara Sangyo Co., Ltd., average particle size 20 nm) for 15 minutes and then dried to obtain a magnesium metal material having titanium oxide immobilized on the surface.

The same rolled material as in Example 1 was used, and mechanical treatment dry honing (iron powder # 100, pressure 0.25 MPa, working time 1 minute) was performed as a pretreatment, followed by degreasing and acid treatment in the same manner. Anodization was performed under electrolytic conditions, and a photocatalyst was supported and immobilized on the obtained material in the same manner as in Example 1.

As pretreatment, wet honing (glass beads, # 100, pressure 0.25 MPa, working time 1 minute) of mechanical treatment was performed, and then the photocatalyst was immobilized in the same manner as in Example 2.

The material used and the anodic oxide film treatment were the same as in Example 1, and the photocatalyst was supported and immobilized by placing the product in a SUS vacuum container, reducing the pressure to 4 mmHg, holding for 20 minutes, and holding the STS-21 titanium oxide dispersed The liquid (Ishihara Sangyo Co., Ltd., average particle size 20 nm) was poured in until the product in the container was completely immersed, held for 15 minutes, taken out and dried.

In Example 4, at the time of supporting and fixing the photocatalyst, the product in the container was immersed in the titanium oxide dispersion, further treated with ultrasonic waves of 25 Hz for 15 minutes, and then taken out and dried.

In Example 5, after the anodizing treatment, the photocatalyst carrying and fixing treatment of Example 5,
It was taken out after 15 minutes under pressure at 0.4 MPa.

As a comparative example, the same existing test piece was degreased, acid-treated, immersed in an STS-21 bath for 15 minutes, and then dried.

These Examples 1 to 6 and Comparative Example were evaluated by the following method. The product obtained in each example was placed in a closed box having a volume of 2.8 L, and acetaldehyde was allowed to flow for 3 minutes at an initial flow rate of 150 ml / min. Next, light irradiation of 0.5 mw / square centimeter was performed with a black light. The flow rate of acetaldehyde at this stage was 100 ml / min. It carried out similarly about the other Example. The content of acetaldehyde was analyzed by gas chromatography at each elapsed time. The results are shown in FIG. It is clear that the method is superior to the conventional photocatalyst-supported immobilization method.

The magnesium material of the present invention can be used as an antibacterial, antifungal or antifouling material, or as a decomposition or deodorizing material such as harmful or offensive odor gas.

It is a figure which shows the relationship between the reduction | decrease of acetaldehyde content, and elapsed time about the photocatalytic effect by the product obtained by this invention.

Explanation of symbols

1: Comparative Example 2: Example 1 3: Example 4 4: Example 5
5: Example 6 6: Example 3 7: Example 2

Claims (13)

A porous non-spark discharge type anodic oxide film having a large number of fine pores having an average pore diameter of 50 to 1000 nm was formed on the surface of magnesium or a magnesium alloy, and a photocatalyst was supported and fixed inside the fine pores and on the film surface. A method for producing magnesium metal having a photocatalytically active surface. 2. The process according to claim 1, wherein the photocatalyst is an ultraviolet ray excitation type or visible light excitation type titanium oxide. 3. The process according to claim 1, wherein the photocatalyst is titanium dioxide or a precious metal or heavy metal doped therein. The porous non-spark discharge type anodic oxide film is a three-layer structure mainly composed of pores, walls and non-porous layers formed by an anodic oxidation method without spark discharge. The main component of the film is 60% or more of magnesium hydroxide. 4. The production method according to claim 1, wherein the composite film comprises magnesium oxide in an amount of 0 to 40% or less. 5. The porous non-spark discharge type anodic oxide film is transparent, brown to dark brown, has a gloss of metal to semi-gloss, and has a film thickness of 1 to 50 μm. Manufacturing method. 6. The method according to claim 1, wherein the porous non-spark discharge type anodic oxide film can be dyed or colored with an organic dye, an inorganic pigment or electrolytic coloring. The formation of a porous non-spark discharge type anodic oxide film consists of one or more of alkali, alkaline earth metal hydroxide, carbonate, bicarbonate, silicate or silicofluoride, and fluoride as a film-forming stabilizer. Spark discharge in an electrolytic bath containing one or more of inorganic compounds such as salts, bifluoride salts, silicofluoride salts, mineral salts, or cyclic or chain organic compounds containing alcohol groups, carboxyl groups, sulfone groups, etc. 7. The method according to claim 1, wherein the anodizing treatment is performed without any accompanying process. 8. The method according to claim 7, wherein the anodizing electrolysis conditions are a current density of 0.5 to 5 A / square decimeter, a voltage of 2 to 25 V, and a bath temperature of 10 to 90 ° C. As a power supply waveform at the time of anodizing, one or two or more of a DC wave, a pulsating wave, a pulse wave, a PR wave, an inverted wave, and an AC waveform having a frequency of 20 Hz to 2 KHz are used in combination. The manufacturing method of Claim 7 or 8. Magnesium or magnesium alloy is subjected to mechanical pretreatment such as dry or wet honing, belt, buffing, scratching, barreling, cleaning, hairline, etc., or etching, chemical finishing, etching before anodized film formation. 10. The method according to claim 1, wherein chemical pretreatment such as a method or a pretreatment combining one or more of these is performed. 11. The method according to claim 1, wherein the magnesium and the magnesium alloy are selected from all wrought materials, cast materials, die casts, forged materials and the like capable of forming an anodic oxide film. 12. The manufacturing method according to claim 1, wherein the shape of magnesium or magnesium alloy to be anodized has a plate, tube, rod shape, spherical shape, two-dimensional or three-dimensional fiber shape, or honeycomb structure. The method for supporting and fixing the photocatalyst inside and on the surface of the micropores is the immersion impregnation method, immersion ultrasonic impregnation method, vacuum (decompression-pressurization) impregnation method, and post-immersion vacuum (decompression-pressurization) impregnation method. The method according to claim 1, comprising filling and adhering by one or a combination of two or more of sol-gel method, electrophoresis method, or immersion method.

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