JP2008297184A - Photocatalytic titanium oxide film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a titanium dioxide photocatalyst film without forming a thick film on a large-area substrate without using a binder such as an organic binder, so that there is no deterioration of the organic binder due to the photocatalytic action of titanium dioxide. Forms a long-term stable photocatalytic film.
An aggregated form of anatase-type titanium dioxide is used as a raw material powder, and the raw material powder is heated and accelerated at a relatively low gas pressure and at a temperature lower than the crystal transformation temperature of anatase-type titanium dioxide to form on the substrate. By making it collide, an anatase type titanium dioxide photocatalyst film is formed on a substrate.
[Selection] Figure 1

Description

The present invention is a photocatalytic titanium oxide suitable for coating of a noise barrier, an outer wall of a building, a bridge, etc., which requires decomposition, antifouling, and anticorrosion properties of nitrogen oxides which are harmful substances contained in automobile exhaust gas and the like. The present invention relates to a film, a member coated with the film, and a method for producing the same.

Photocatalytic titanium oxide has been used for surface coating on the outer walls of buildings and the like because it has excellent physical properties for removing harmful substances, antifouling, sterilization, and anticorrosion. Since photocatalytic titanium oxide is a material having such excellent physical properties, it is required to establish a technique for forming a thick film over a large area at a low cost in order to use it more widely.

As a photocatalytic titanium oxide film production technique that has been reported so far, as a chemical method, a titanium alkoxide is dissolved in a solvent and calcined in an oxidizing atmosphere (for example, see Patent Document 1) or a titanium dioxide powder sol. There is a method of forming a film (see, for example, Patent Document 2), which is used for application to the outer wall of a building.

Examples of physical methods include film formation by sputtering (for example, see Patent Document 3), film formation by thermal spraying (for example, see Patent Document 4 and Non-Patent Document 1), and film formation by an aerosol deposition method (for example, see Patent Document 5). Is practically not used. Although there is a report of film formation by the cold spray method (see, for example, Non-Patent Document 2), a practical film has not been obtained.

Patent 2849177 Patent 2930347 Patent 2995250 Patent Publication JP-A-11-47609 Patent publication gazette JP, 2006-130703, A Fukumoto, Kaoru, Suzuki, Atsuta, Yasui, Welding Society Proceedings, Vol. 22, No. 1, 47-52, (2004) C. -J. Li, G. -J. Yang, X. et al. -C. Huang, W.H. -Y. Li and A.L. Ohmori: Formation of TiO2 photocatalyst through cold spraying, Processes of International Thermal Spray Conference 2004, CD

In the method using a solvent or the method using a sol, there is a problem that a waste liquid is generated, so that an environmental load is large, and depending on the type of the binder, it deteriorates with time. Since sputtering is performed in a controlled atmosphere, there are problems that the size of an object is limited and that only a thin film can be formed. Although a thick film can be produced in a large area by the thermal spraying method, there is a problem that phase transformation from anatase-type titanium dioxide to rutile-type titanium dioxide having lower photocatalytic properties occurs due to thermal effects. The aerosol deposition method is non-heated but has a problem that the size of the object is limited because the film is formed in a vacuum chamber. Since the cold spray method is a technique in which soft metal particles are plastically deformed and adhered, it has heretofore been difficult to produce a thick film by using titanium oxide, which is a hard and brittle material.

The object of the present invention is to provide a thick film composed only of anatase-type titanium dioxide and a member coated with the thick film by proposing a novel method in the production of a photocatalytic titanium oxide film, and at the same time, a simple manufacturing method thereof. It is to provide.

As a result of intensive investigations in view of the above-described present situation, the present inventors have generated a gas having a relatively low pressure range of 0.3 to 1.0 MPa from the high-pressure gas generation unit as compared with the conventional method. In the cold spray method in which the gas is heated to about 200 ° C. to 800 ° C. with a gas heater, the raw material powder is introduced into the gas flow accelerated in the gas accelerating unit, and the raw material powder collides and forms a film, It has been found that a film composed only of anatase titanium dioxide can be obtained by using secondary particles having a particle diameter of 1 μm to 100 μm obtained by agglomerating anatase titanium dioxide having a primary particle diameter of 0.1 nm to 1 μm. Furthermore, the member obtained by coating the base material with the anatase-type titanium dioxide obtained in the present invention is found to be an extremely high-performance photocatalytic titanium oxide film having excellent ability to decompose nitrogen oxides in the air, and the present invention has been completed. It has come to be.

The photocatalytic titanium oxide film of the present invention is a thick film formed by a cold spray method, and is different from a thin film obtained by a conventional sputtering method or CVD method. The film thickness is preferably 1 μm or more and 3 mm or less, and more preferably 100 μm or more and 1 mm or less. When the film is thinner than 1 μm, there is a problem in durability due to wear or the like. On the other hand, a thickness exceeding 3 mm is not generally required in the technical field using the film of the present invention and is not economical.

The photocatalytic titanium oxide film of the present invention is a film composed only of anatase-type titanium dioxide and does not contain other components. However, those having impurities in these raw materials and having the same performance as the photocatalytic titanium oxide film of the present invention due to the impurities are not excluded from the present invention.

Since the photocatalytic titanium oxide film of the present invention is a film composed only of anatase-type titanium dioxide, it has high photocatalytic properties and can exhibit high nitrogen oxide decomposition properties when coated on a member.
The production method of the photocatalytic titanium oxide film of the present invention is simple because the film made of only anatase-type titanium dioxide can be produced only by the cold spray method.

The structure of the photocatalytic titanium oxide film of the present invention is not particularly limited, and can take any morphology from a dense film to a porous film.

Furthermore, this invention provides the member which formed the above-mentioned photocatalytic titanium oxide film on the base material. A member is not specifically limited, A metal, ceramics, a plastics, etc. can be utilized.

A method for producing a photocatalytic titanium oxide film comprising only anatase-type titanium dioxide according to the present invention will be described using an example of the apparatus shown in FIG.

In the method of the present invention, a film is formed by mounting a base material on an apparatus having a part for generating a high-temperature and high-pressure gas, a gas acceleration part, and a part for holding the base material.

The gas temperature in the high temperature / high pressure gas generating part under the film forming conditions of the present invention is 200 ° C. or higher and 800 ° C. or lower. When the temperature is lower than this, the particles do not adhere to the base material, and when the temperature is higher, the anatase-type titanium dioxide undergoes phase transformation to rutile-type titanium dioxide having lower photocatalytic properties, and is not economical.

The gas pressure in the high temperature / high pressure gas generating part under the film forming conditions of the present invention is 0.3 MPa to 1.0 MPa. When the pressure is lower than this, the particles are not sufficiently accelerated and do not adhere to the substrate, and when the pressure is high, the particles do not collide with the substrate due to a shock wave generated near the substrate surface.

Although the acceleration nozzle is used for the gas acceleration site used in the present invention, its shape and structure are not particularly limited.

The substrate for forming the photocatalytic titanium oxide film used in the present invention is not particularly limited. For example, a metal substrate such as stainless steel or carbon steel, graphite, quartz, ceramics, plastic, or the like can be used as the substrate 108 in FIG. . In order to improve the adhesion with the photocatalytic titanium oxide film, the substrate used is preferably mounted on the substrate holder 109 after the surface is roughened by a blast method or the like.

The cold spray method of the present invention uses a hot gas. Although the generation method of the high temperature gas is not particularly specified, it can be generated by a high frequency, electric furnace or the like.

The cold spray method of the present invention utilizes high pressure gas. The generation method of the high-pressure gas is not particularly specified, but it can be generated by a compressor, a high-pressure gas cylinder or the like.

The position of the substrate in the thermal spraying of the present invention may be a position where it is exposed to a high temperature / high pressure gas flow, that is, a position where a portion where the photocatalytic titanium oxide film is formed contacts the high temperature / high pressure gas flow. Although the base material may be fixed, it is preferable to move the base material 108 up and down, left and right to expose the entire base material to a high-temperature and high-pressure gas flow to form a uniform film. The movement of the base material may be performed under the condition that the high-temperature and high-pressure gas flow is in contact with the film formation site, and can be exemplified as a range in which 5 to 100 mm can be maintained at the film formation distance 106 in FIG.

The gas species used in the present invention is not particularly limited, and for example, compressed air, nitrogen, helium, or the like can be used. In particular, helium is preferable because the gas flow becomes faster.

The method of the present invention forms a photocatalytic titanium oxide film by introducing anatase-type titanium dioxide powder into a high-temperature, high-pressure gas stream. As the anatase-type titanium dioxide powder to be introduced, secondary particles having a particle size of 1 μm to 100 μm obtained by agglomerating anatase-type titanium dioxide particles having a primary particle size of 0.1 nm to 1 μm are used. The measuring method of the average particle diameter of the photocatalytic titanium oxide powder can be measured by a general particle size measuring device, for example, a light transmission type particle size distribution measuring device.

In the present invention, the powder charging part is not particularly limited. FIG. 1 illustrates a method of supplying anatase-type titanium dioxide powder to the acceleration nozzle portion. The carrier gas 110 is introduced into the powder feeder 109, the anatase-type titanium dioxide powder is fed into the high-temperature, high-pressure gas stream, and the supply rate of the anatase-type titanium dioxide at this time is preferably uniform.

A photocatalytic titanium oxide film was formed on a steel (SS400) substrate using the apparatus shown in FIG. A 100 × 50 × 2 mm SS400 base material 108 having a roughened surface by blasting was mounted on the base material holder 109. The film formation distance 106 was previously adjusted to 10 mm. A gas cylinder was used as the high-pressure gas generator 101, and He was used as the gas species. The gas pressure was adjusted to 0.6 MPa, and heating was performed at room temperature without heating by the heater 102. A tapered nozzle having a tapered wide cylindrical shape was used for the gas acceleration portion 105. The SS400 base material 108 was moved up and down and left and right at a speed of 20 mm / second to deposit the sprayed film uniformly on the base material 101.

Next, a fine powder feeder manufactured by Technoserve is used as the powder feeder 110, compressed air is introduced as a carrier gas 111 at a flow rate of 1 L / min, and anatase-type titanium dioxide aggregated powder having an average particle size of 20 μm is about 10 g / Was fed into the hot and high pressure gas stream in minutes. The film formation was repeated while moving the substrate under the above conditions, and two film formation layers were deposited.

The obtained film had a thickness of about 30 μm and the deposition rate of the supplied powder was about 10%. When the crystal structure was analyzed by X-ray diffraction, only the peak of anatase-type titanium dioxide was observed.

FIG. 2 shows an image obtained by cutting the obtained film, polishing the cross section and observing it with an electron microscope. It can be seen that a dense film structure is formed.

A film was prepared in the same manner as in Example 1 except that the gas temperature was 400 ° C.

The obtained film had a thickness of about 200 μm and the deposition rate of the supplied powder was about 25%. When the crystal structure was analyzed by X-ray diffraction, only the peak of anatase-type titanium dioxide was observed. Further, as a result of cross-sectional observation of the film, it was a dense film as in Example 1.

(Comparative example)
A film was prepared in the same manner as in Example 1 except that an anatase-type titanium dioxide powder having a particle size of 180 nm that was not aggregated was used as the raw material powder.

Some particle adhesion was observed, but no film formation was achieved.

The photocatalytic properties of the films prepared in Examples 1 and 2 were measured by the nitrogen oxide gas removal rate. 1ppm simulated polluted air mixed with air of 100ppm NO gas supplied from a cylinder is continuously flowed into the measuring device at a flow rate of 3-4L / min. The photocatalytic reaction was developed by irradiating with UV light with light, and the nitrogen oxide concentration after the reaction was measured. The removal rate was about 90% for the film of Example 1 and about 80% for the film of Example 2. In the embodiment of the present invention consisting of only anatase type titanium dioxide, high nitrogen oxide gas removal characteristics were obtained.

The present invention can be used as a method for forming a photocatalytic titanium oxide film on indoor and outdoor structures.

It is a figure which shows an example of the cold spray apparatus for manufacturing the photocatalyst film | membrane in this invention. The electron micrograph of the film | membrane cross section produced with the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101: High pressure gas generation part 102: Gas heating heater 103: Gas temperature sensor 104: Gas pressure sensor 105: Gas acceleration part 106: Film formation distance 107: Film | membrane 108: Base material 109: Base material holding part 110: Powder feeder 111: Carrier gas

Claims (6)

A method for producing a photocatalytic titanium oxide film, which is formed by spraying anatase-type titanium dioxide particles that do not contain a binder such as an organic binder and are composed of aggregates at a high temperature and a high pressure. A member obtained by coating the substrate with the photocatalytic titanium oxide film of claim 1. A method of forming a photocatalytic titanium oxide film by introducing a titanium oxide raw material powder into the high temperature / high speed gas flow in an apparatus having a high temperature / high pressure gas generating part, a gas accelerating part and a base material holding part. A method for producing a photocatalytic titanium oxide film, characterized in that the raw material powder is deposited in a solid state without melting and phase transformation of the raw material powder. The production method according to claim 3, wherein secondary particles having a particle size of 1 to 100 µm obtained by aggregating anatase-type titanium dioxide having a primary particle size of 0.1 to 1 µm are used as the titanium oxide raw material powder of claim 3. The manufacturing method according to claim 3, wherein the supply gas pressure from the high-temperature / high-pressure gas generating section according to claim 3 is 0.3 MPa to 1.0 MPa. The manufacturing method of Claim 3 which consists of 200 to 800 degreeC of the temperature of the supply gas from the high temperature / high pressure gas generation | occurrence | production part of Claim 3.

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