JP4784722B2 - Magnesium metal material having photocatalytic active surface and method for producing the same - Google Patents

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 the surface of a base material. The binder used at this time is silicates. 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 attaching a large amount of photocatalyst to a roughened substrate having a three-dimensional structure on the surface 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 anodic oxide film having a large number of fine pores having an average pore diameter of 50 nm to 50 μm on the surface of magnesium or a magnesium alloy, and the porous anodic oxide film is a spark discharge type anodic oxidation method accompanied by a spark discharge. Is a film composed of pores, walls, and a barrier layer, and has a two-layer structure with a large pore layer on the surface side and a smaller pore layer below the pore, and the pores and magnesium. Magnesium having a photocatalytically active surface, comprising a four-layer structure in which a barrier layer is present between the substrates, wherein the photocatalyst is supported and fixed inside the micropores and on the surface of the porous film It is a manufacturing method of a metal material.

On the surface of the magnesium metal material of the present invention, there is a porous anodic oxide film having a large number of fine pores having an average pore diameter of 50 nm to 50 μm due to anodic oxidation accompanied by spark discharge. Thus, the magnesium metal material having irregular, discontinuous, and sometimes very large pores on the surface has been conventionally regarded as a defect from the viewpoint of appearance, gloss, etc. Is actively used to develop photocatalytic activity.

Many such pores can be formed on the surface by anodizing under conditions involving spark discharge. The thickness of the porous film can be set fairly freely in the range of 1 to 100 μm. Therefore, the amount of the photocatalyst filled in the pores can be changed with a considerable degree of freedom as required. When the micropore distribution in the film is captured in the thickness direction, pores with a large average pore diameter occupy 60% or more in the film thickness direction from the surface toward the material, and the remaining 40 or less is composed of a small microporous layer and a barrier layer. As a whole, the structure is composed of pores larger than the surface, small pores, barrier layers, and materials. The term “pores with a large average pore diameter” as used herein means that 70% or more of the pore diameters have an average pore diameter of 5 μm or more. On the other hand, “small pore” means that the pore diameter of 50 nm to less than 5 μm occupies 70% or more.

The film formed on the surface of the metal material of the present invention mainly has a four-layer structure of two levels of pores, walls, and barrier layers, and the composition of the film is composed of magnesium oxide and spinel or a structure close thereto. Since these pores have openings on the surface and an average pore diameter of 50 nm to 50 μm, this fineness is obtained when, for example, titanium oxide having a particle diameter of about 10 to 500 nm is used as a photocatalyst. It is easy to fill or adhere to the inside and surface of the hole. 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 10 per square millimeter, usually 100 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 a magnesium metal material, the metal material is made of an alkali or alkaline earth metal phosphate, borate, hydroxide, silicate or fluorosilicate. In an aqueous solution containing one or more salts at a rate of 0.2 to 7 mol / liter and a film additive at a rate of 0.01 to 5 mol / liter, a current density of 0.5 to 5 A / decimeter square and a voltage of 25 V or more. This is achieved by anodizing while producing a spark discharge.

Examples of alkali or alkaline earth metal phosphates, borates, silicates, or hydroxides used in the present invention include H ₃ PO ₄ , Na ₃ PO ₄ , Na ₂ HPO ₄ , _{NaH 2 PO 4, Na 4 P} 2 O 6, Na 2 H 2 P 2 O 6 Na 4 P 2 O 7, Na 2 H 2 P 2 O 7, Na 5 P 3 O 10, K 3 PO 4, K 2 HPO ₄ , KH ₂ PO ₄ , K ₄ P ₂ O ₇ , phosphate of K ₆ (PO ₃ ) ₆ , NaBO ₂ , Na ₂ B ₄ O ₇ , NaBo ₃ , KBO ₂ K ₂ B ₄ O ₇ Examples thereof include silicates such as acid salts, Na ₂ SiO ₃ , Na ₄ SiO ₄ , K ₂ SiO ₃ , K ₂ SiO _{7, and} K ₂ Si ₄ O ₉ , and hydroxides such as NaOH, KOH, and BaOH.

A coating additive is added to the electrolytic solution for the purpose of improving the life of the solution, uniformity of the coating, stability, and performance. As the additive, inorganic compounds such as fluoride salts, bifluoride salts, silicofluoride salts, and mineral acid salts, or cyclic or chain organic compounds containing alcohol groups, carboxyl groups, and sulfone groups are used. Includes fluorides such as KF and NH ₄ F, dehydrofluorides such as NH ₄ FHF, NaFHF and KFHF, silicate compounds such as Na ₂ SiO ₃ , Na ₄ SiO ₄ and K ₂ SiO ₂ , Na ₂ SiF ₆ , Silicides such as MgSiF ₆ and (NH ₄ ) ₂ SiF ₆ , organic compounds such as (CH ₂ OH) ₂ , (CH ₂ CH ₂ OH) O, alcohols such as (CH ₂ OH) ₂ CHOH, (COOH) ₂ , (CH ₂ CH ₂ COOH) ₂ , [CH (OH) COOH] ₂ , C ₆ H ₄ (OHCOOH), C ₆ H ₅ COOH, C ₆ H ₄ (COOH ) ₂ which carboxylic _{acids, C 6 H 4 (SO 3} H · COOH), an organic compound having a C 6 H 3 (COOH · OH · SO 3 H) 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 5 mol / liter in the electrolytic solution.

It is particularly preferable that the anodic oxidation treatment of the magnesium alloy in the electrolytic solution thus adjusted is performed in a weak to strong alkaline range of pH 9 or higher at a bath temperature of 10 to 60 ° C.

The method of forming a porous spark discharge type anodic oxide film on the surface of magnesium-based metal material and supporting and fixing the photocatalyst fine particles in the pores is the normal pressure impregnation method, the vacuum impregnation method, the pressure impregnation method, the sol-gel method. Electrophoretic 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 having an anodized film formed thereon is placed in a suitable vacuum vessel, and the inside of the surface pores is introduced by introducing a titanium oxide suspension such as the STS series after reducing the pressure inside. Titanium oxide can be densely filled. 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 is widely applicable, 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 available.

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, warm method, desired shape 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.

The above-mentioned mechanical or chemical pretreatment and porosity are applied to a metal material having a large surface area, such as a plate, one or many tubes or rod-like structures, spherical structures, two-dimensional or three-dimensional fibrous structures, honeycomb structures, etc. When a film formation process by quality spark discharge type anodic oxidation is added, the surface area increases synergistically, and the amount of photocatalyst immobilized increases accordingly, and the catalyst efficiency per unit area of the substrate increases.

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 three-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 aldehydes and mercaptans. Has the effect of decomposing.

The magnesium-based metallic material of the present invention is stable because it does not fall off even if there is an impact because the photocatalyst is filled in the fine pores of the porous film formed by spark discharge type anodizing treatment including pretreatment. is doing. Furthermore, when the activity of the catalyst surface deteriorates due to adhesion of inorganic substances due to long-term use, it is fixed in three dimensions, so it is possible to put out a new surface layer by cleaning or scraping the surface layer, and improving the initial performance. Has the advantage of easy recovery.

In addition, it has a three-dimensional structure by pre-treatment, and the amount of photocatalyst supported and immobilized per unit area is much larger than that of the conventional method. Therefore, the effect of preventing contamination by oil, antibacterial, antifungal, harmful The gas decomposition effect is excellent, and a small device using photocatalysis can be made.

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

Using magnesium alloy AZ31B rolled material with a plate thickness of 1 mm and 70 × 150 mm, after degreasing and acid treatment, NaOH: 3 ± 0.05 mol / liter, Na ₂ HPO ₄ ; 0.3 ± 0.01 mol / liter coating As molding stabilizers, Na ₂ SiO ₃ ; 0.05 ± 0.005 mol / liter and sodium tartrate; 0.1 ± 0.05 mol / liter, KF; 0.2 ± 0.01 mol / liter were added. Spark discharge type anodic oxidation treatment was performed with the electrolyte at a liquid temperature of 28 ± 2 ° C., a current density of 2 ± 0.5 A / square decimeter, and a spark discharge starting voltage of about 50 V. When the cross section of this film is observed with an electron microscope, pores of 10 to 20 μm have a fine film thickness of about 3 μm or less to a film thickness of about 4 μm on the substrate side up to about 16 μm from the surface side in the film thickness of about 20 μm. A hole was 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 the pretreatment, wet honing (glass beads, # 100, pressure 0.25 MPa, working time 1 minute) of mechanical treatment was performed, and thereafter 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.

(Example 5) In Example 4, when the photocatalyst was supported and fixed, the product in the container was immersed in the titanium oxide dispersion, and further subjected to treatment with ultrasonic waves of 25 KHz for 15 minutes. Removed and dried.

In Example 5, after anodic oxidation treatment and photocatalyst carrying and fixing treatment in Example 5, the sample was taken out after pressurizing at 0.4 MPa for 15 minutes.
The catalyst was immobilized and fixed.

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

Claims (5)

A porous anodic oxide film having a large number of fine pores having an average pore diameter of 50 nm to 50 μm was formed on the surface of magnesium or a magnesium alloy, and the porous anodic oxide film was formed by a spark discharge type anodic oxidation method accompanied by a spark discharge. A film composed of a pore, a wall and a barrier layer. The pore has a two-layer structure having a large pore layer on the surface side and a smaller pore layer below the pore layer, and between the pore and the magnesium substrate. A method for producing a magnesium metal material having a photocatalytically active surface, characterized in that it is a film comprising a four-layer structure in which a barrier layer is present, and a photocatalyst is supported and fixed inside the fine pores and on the film surface. 2. The method for producing a magnesium metal material according to claim 1, wherein the porous spark discharge type anodic oxide film is a spinel with magnesium oxide or a structure close thereto, and the film thickness is 1 to 100 [mu] m. Magnesium or magnesium alloy, phosphates of the alkali or alkaline earth metals, and one or more silicates or hydroxides as a film additive is a fluoride salt, heavy fluoride salt, sulfuric acid salt or nitrate In a liquid containing one or more of an inorganic compound or a cyclic or chain organic compound containing an alcohol group, a carboxyl group or a sulfone group, a bath temperature of 10 to 60 ° C., a current density of 0.5 to 20 A / dec square meter, a voltage of 25 V A spark discharge type anodic oxidation treatment is performed while generating a spark discharge as described above, and a film composed of pores, walls, and a barrier layer. The pore has a large pore layer on the surface side and a smaller pore layer below it. It has a layer structure, and is composed of a four-layer structure in which a barrier layer exists between the pores and the magnesium base, and the average pore diameter is 50 nm to 50 μm A magnesium metal material having a photocatalytically active surface, characterized by forming a porous anodic oxide film having a large number of pores and having a film thickness of 1 to 100 μm, and supporting and fixing the photocatalyst inside and on the surface of the micropores Manufacturing method. The power supply waveform at the time of anodization is a DC wave, a pulsating wave, a pulse wave, a PR wave, an inverted wave, or a combination of one or two or more AC waves having a frequency of 20 Hz to 2 KHz. The manufacturing method of the magnesium metal material in any one of 1-3. The method for supporting and fixing the photocatalyst inside the micropores and on the surface of the coating is the immersion impregnation method, immersion ultrasonic impregnation method, vacuum impregnation method, pressure impregnation method, pressure impregnation method, after immersion in water containing titanium oxide fine particles Magnesium according to any one of claims 1 to 4 , comprising filling and adhering by one or a combination of two or more of a reduced pressure impregnation method, a post-immersion pressure impregnation method , a sol-gel method, an electrophoresis method, or an immersion method. Manufacturing method of metal materials.

Images