JPH04152296A - Photo electron emission material - Google Patents

Abstract

PURPOSE:To enable fine particles to be efficiently electrified by constituting a multiplet structure of a base material or the like comprising an element or the like emitting photo electron upon exposure to ultraviolet and radial rays, and a thin film of specific thickness having a large work function for service at or below specific relative humidity. CONSTITUTION:For photo electron emission from a thin film, a thin film of a stable material having a large work function is formed on a pertinent shape of base material having no photoeffect. For photo electron emission from both of a thin film and a base material, a thin film of such a material as having a large work function is formed on a pertinent shape of base material having a small work function. The material having a large work function may be a stable material having a work function value equal to or above approximately 3.4eV, and strength capable of carrying a thin film. For this purpose, Cu, Ag, stainless steel or the like is used. As a thin film material, Au, Ag or a high molecular compound is used. The thickness of the thin film is taken at 0.01mm or less determined in a preliminary test. For photo electron emission from both of the base material and thin film, the base material is such a material as having a small work function. For example, Ba, Sr or the like, or a compound or an alloy thereof is used.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a photoelectron emitting material having a photoelectric effect.

Fields in which fine particles are charged and utilized using photoelectron emitting materials include (a) fields in which surface modification of fine particles, control of charge amount, and separation and classification of fine particles are performed; (b) charged fine particles are used to charge and utilize fine particles in the air or exhaust gas. Fields that measure the concentration and particle size of fine particles in gases such as (C)
There are fields such as collecting and removing charged particles to obtain clean gas.

[Prior Art] The present inventor has made many proposals regarding the charging of fine particles by photoelectrons generated by irradiating a photoelectron emitting material with ultraviolet rays and/or radiation, and the use thereof. Among the things proposed by the present inventor in relation to gas purification, the following are particularly relevant to the present invention.

(1) Japanese Patent Publication No. 61-178050 (US Patent No. 4.750.917), 18
2-244459, 63-54959, 〃 63-77557, 〃 63-78471, 〃 63-97747, 〃 63-100955, 1163-100956, 1163-100956, 1163-147556, 〃 63-147565 , (11) JP-A-1-262953, (12) JP-A-1-282954, (13) 〃1-286864, (14)
No. 112-8638, (15) No. 2-8639, (1B) No. 2-10034, (17) Japanese Patent Application No. 2-52688, (18) No. 2-89185, and also proposed in relation to measurement. (1) Japanese Patent Application Laid-Open No. 62-2428
No. 38, (2) Japanese Patent Application Publication No. 2-47536, and (3) Japanese Patent Application No. 1-134781.

A further proposal related to separation and classification is Japanese Patent Application No. 1-177198.

Other proposals related to charging conditions include: (1) Patent Application No. 1-120563, (2) There is Japanese Patent Application No. 1-120564.

Furthermore, the published documents are as follows.

(1) Itamoto, Toyo, Fujii, Shinozuka, 6th Aerosol Science φ Technique Ball Research Symposium, August, 13-15.
1988 (2) Sakamoto, Togava
, Fujii, 5hinozuka.

Man and his Ecosystem, Pr
oceedings of the8th World
C1ean Air Congress, 3735
〜740゜(3) Shinozuka, Fujii, Yoshiyama, Kogure, Shiranase, Tamori, Koukou 24 (5) 63-71.1989 [Problem to be solved by the invention] Conventional photoelectron emitting materials are made of one type of bulk material. (lumped) material was used. This emissive material has limitations in the amount of photoelectron emission and stability, and there is a need for improvement. That is, photoelectron emitting materials are preferably materials with a small work function, but materials with a small work function are generally susceptible to deterioration and lack long-term stability, and improvements have been sought. As a countermeasure for this improvement, the present inventors previously filed a patent application on patent application No. 2-15
No. 3335 was proposed.

Furthermore, the present invention aims to further improve the above-mentioned problems, and aims to provide a photoelectron emitting material that emits a large amount of photoelectrons and can be used stably for a long time, and to effectively charge fine particles. It is something to do.

Here, the work function is the minimum energy required to emit electrons from the inside of a substance, exceeding the binding energy that binds electrons inside the substance, expressed as e.

[Means and effects for solving the problem] As a result of research to achieve the above object, the present inventors have found that materials that can be used as photoelectron emitting materials (the smaller the work function is, the better) are generally altered to varying degrees. Among these substances, substances with a relatively large work function, such as certain metals such as Au, are susceptible to oxidation and lack long-term stability.
Preferably, in an environment of 60% or less, these substances are relatively stable even when exposed to air in the form of a thin film, and photoelectrons can be emitted by forming these substances into a thin film alone or from both the thin film and the base material. This discovery led to the present invention.

Therefore, in the present invention, a base material made of an element, an inorganic compound, an alloy, a mixture thereof, or a composite thereof that emits photoelectrons when irradiated with ultraviolet rays and/or radiation, or a base material that emits photoelectrons when irradiated with ultraviolet rays and/or radiation is used. A base material made of a non-emitting material and a thickness of 0.0 on the base material.
A stable substance with a relatively large work function thinner than 1El is added, and photoelectrons are emitted from the thin film alone or from the thin film and the base material.

Further, the present invention will be specifically explained. The photoelectron emitting material of the present invention consists of a base material and a thin film on the base material.

The present invention is based on the novel finding of the present inventors that photoelectron emission becomes effective when a stable substance with a relatively large work function is made into an ultra-thin film.

That is, by adding a stable substance with a relatively large work function in the form of a thin film onto a suitable base material, an effective photoelectron emitting material can be obtained.

The photoelectron emitting material of the present invention can have the following configuration and role.

(2) A stable substance with a relatively large work function is added in the form of a thin film onto a suitably shaped base material of a substance that does not have a photoelectric effect, and photoelectrons are emitted from the thin film alone.

2. The material having a relatively large work function described in 1 above is added in the form of a thin film onto a base material of an appropriately shaped material having a low work function, and photoelectrons are emitted from both the base material and the thin film.

That is, photoelectron emission in 1 and 2 occurs in the thin film in 1, and in both the thin film and the base material in 2.

Here, a substance with a relatively large work function (stable substance) is a substance with a relatively large work function (,
Specifically, it refers to a substance whose value is about 3.4 eV or more.

Next, a case where photoelectron emission is performed from a thin film will be explained.

Since the base material plays the role of supporting the thin film, it may be any stable material to which the thin film can be attached and which can be formed into an appropriate (arbitrary) shape. Examples include Cu alloys (e.g. Cu
-Zn, Cu-3n, Cu-Afl), Ag alloys (e.g. Ag-Mg, AgIn, Ag-N1.Ag-T
i, Ag-Fe.

Ag-Cu, Ag-Zn, Ag-AM, AgZn), A
There are g-alloys (for example AfI-Cu-Mg) and stainless steel.

The shapes used for these base materials are plate-like, pleated-like,
There are lattice shapes, net shapes, etc., and the surface shape can be appropriately roughened. Further, the tip of the convex portion can be made into a sharp point or a spherical shape.

Examples of the thin film material are Au, Ag, Ap.

Zr, ZH, In, Nb, Pb, Ti, Nl.

Any of Cu, Ta, Si, W, C, or a polymer compound, or a compound thereof, an alloy or mixture of these substances,
There are composite materials, and these can be used alone or in combination of two or more.

Examples of polymer compounds include epoxy resins, and examples of compounds include ZrC, TaC, and Tic.

There are WC, TiN, and ZrO2.

The thickness of the above-mentioned thin film is the thickness at which the photoelectron emission effect becomes noticeable when the thin film is irradiated with ultraviolet rays and/or radiation, and is determined by conducting preliminary tests as appropriate depending on the application method, strength, effect, etc. of the electric field. be able to.

Usually the thickness is less than 0.01uyl, preferably less than 0.01uyl.
It becomes effective at 0051M or less.

Next, a case where photoelectron emission is performed from both the base material and the thin film will be explained. The material of the base material is UV and/or UV rays from the thin film mentioned above.
Alternatively, any material may be used as long as it emits photoelectrons when irradiated with radiation, and the smaller the photoelectric work function, the more preferable it is. From the viewpoint of effectiveness and economy, Ba, Sr, Ca, Y, G
d.La.

Ce, Nd, Th, Pr, Be, Zr, Fe.

Nl, Zn, Cu, Ag, Pt, Cd, Pb.

Al, C, Mg, Au, In, Bi, Nb, Si.

Any one of Ta, T1, U, B, Eu, Sn, P, or a compound or alloy thereof is preferred, and these may be used alone or in combination of two or more. As the composite material, a physical composite material such as amalgam can also be used.

Compounds include oxides, ferrides, and carbides, and oxides include Bad, SrO, Cab, Y2O6゜GdO
, NdO, ThO, Zro2°F e20s,
Z n O, Cu O, Ag2O, L a 20s.

PtO, PbO, Aρ2032Mg02In203゜B
There are ib, NbO, BaO, etc., and borides include
Yb6. GdB6. LaB6. NdB5゜Ce B 6
, E u B 6 , P r B 6 , Z
There are r B 2, etc., and carbides include UC,
ZrC.

There are TaC, TiC, NbC, etc., and TiN as a nitride.
There is.

In addition, alloys include brass, bronze, phosphor bronze, and Ag (!
: Alloy with Mg (2 to 20 wt% Mg), Cu and Be
(Be is 1 to 10 wt%) and an alloy of Ba and Ag can be used.
An alloy of u and Be and an alloy of Ba and All are preferred.

The shape of the base material is as described above, and the optimal shape can be determined by conducting preliminary tests as appropriate, taking into account the scale of the device, shape, type of electron-emitting material, method of applying electric field, effect, economical efficiency, etc.

The thin film on the base material is as described above, and the type and thickness of the thin film can be determined as appropriate depending on the type of base material, shape, field of application, effect, etc.

The role of the thin film here is to emit photoelectrons by itself and to protect the base material (protect the base material by not exposing it directly to the operating atmosphere).

The above-mentioned thin film can be made by coating or adhering it to the surface of the base material by an appropriate method. For example, there are an ion blasting method, a sputtering method, a vapor deposition method, a CVD method, a method of heat-treating the material to form an oxide layer on the surface, or a method of treating the material with chemicals to form a film-like substance, which can be used as appropriate.

The selection of the configuration of the photoelectron emitting material (whether the photoelectron emitting part is only a thin film or both a thin film and a base material) depends on the field of application of this technology, device shape, scale, method of applying electric field, strength, effect, economical efficiency, etc. You can make a decision by conducting a preliminary test as appropriate. For example, depending on the field of application, it is necessary to perform charging with considerably high efficiency.
In this case, photoelectrons are emitted from both the thin film and the base material, and the particles are charged with high efficiency.

An example of this is the use as a purifier in the clean zone of a super clean room (in the field of obtaining high performance or lean gas).

As another field of application, for example, in particle measurement, even if the charging efficiency of particles is not necessarily high, it can be put to practical use as long as a constant charge remains stable for a long time. That is, even if the charging efficiency is about 80 to 90%, there is no problem as long as it is stable for a long time. In this case, photoelectron emission from only the thin film can be used.

Next, regarding the irradiation of ultraviolet rays and/or radiation, the light source for ultraviolet rays may be any material that emits photoelectrons when irradiated with ultraviolet rays, such as a mercury lamp, a hydrogen discharge tube, a xenon discharge tube, a Lyman discharge tube, etc. can be used as appropriate.

Similarly, when using radiation, any radiation source may be used as long as it emits photoelectrons upon irradiation, and α-rays, β-rays, γ-rays, etc. are used, and cobalt-60, cesium-13, etc. are used as the irradiation means.
7. Radioactive isotopes such as strontium-90, radioactive waste generated in nuclear reactors, and radioactive substances processed appropriately can be used as appropriate.

The use of these materials, ultraviolet light or types of radiation,
It can be determined as appropriate depending on the shape of the device, field of application, accuracy, economic efficiency, etc.

Furthermore, when the photoelectron emitting material is irradiated with ultraviolet rays and/or radiation in an electric field, photoelectron generation from the photoelectron emitting material occurs effectively.

The method for forming the electric field can be appropriately selected depending on the shape, structure, field of application, expected effect (accuracy), etc. of the device.

The strength of the electric field can be appropriately determined depending on the coexisting moisture concentration, the type of photoelectron emitting material, etc., and this is another invention of the present inventor. The strength of the electric field is generally 0. IV
/ cm to 2 kV/cm.

The electrode material and its structure may be those used in ordinary charging devices; for example, a tungsten wire or rod is used as the electrode material.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

[Example 1] Measurement of suspended particles in the air at a relative humidity of 60% according to the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a schematic diagram in which a classification plate is used as a part for classifying charged fine particles and an electrometer is used as a detection part.

Air 1 containing floating particles from which large particles of 10μ or more have been removed by an impactor (not shown) or the like is introduced from the air inlet, and the particles contained in the air are transferred to the charging section A1 by an ultraviolet irradiation source. It is charged by photoelectrons emitted from the photoelectron emitting surface 3 that has been irradiated with ultraviolet light from the (lamp) 2.

The charging section A1 mainly includes an ultraviolet lamp 2 and a photoelectron emitting material 3.
and an electrode 4. In the charging section A1, an electric field is formed between the photoelectron emitting material 3 and the electrode 4, and photoelectrons are effectively generated from the photoelectron emitting material 3 irradiated with the ultraviolet lamp 2. Fine particles in the air 1 introduced from the air inlet are charged by the action of the photoelectrons.

The fine particles charged in the charging section A1 are transferred to a charged fine particle classification section B,
It is classified in

The charged fine particle classification section B1 has a compact and simple structure, and has a function of classifying charged fine particles by changing the voltage applied to the classification material.

Below, the effect when using a classification plate equipped with pores 5 and 6 will be described.

An electric field is formed between the classification plates 7 and 8 by a power source. Let b be the total charged particles in the classification section B1. When a weak electric field al is first formed between the classification plates 7 and 8, fine charged particles b2 affected by the electric field are collected on the classification plates. As a result, the remaining large-sized charged particles (
bl-b2), the charge amount d1 is measured by a detection section C consisting of an electrometer 9 located downstream, and the particle concentration is measured.

Next, when an electric field a stronger than al is formed between the classification plates 7 and 8, charged fine particles b3 (larger in particle size than b 2) affected by the electric field are collected on the classification plates. As a result, the remaining charged fine particles (b - b3
) is similarly measured by the downstream niretrometer 9.

Thereafter, the same procedure is carried out by sequentially changing the electric field of the classification plate as appropriate.

In this way, by performing classification and measuring the concentration of fine particles, the particle size (distribution) and concentration of fine particles in the air 1 at the air inlet can be determined.

C1 is a detection section for charged particles, and the electrometer 9 detects the charged particles classified by the classification section B1 as described above.

The electrometer 9 measures the amount of charge of the charged fine particles,
Any method that allows the concentration of classified fine particles to be determined from this is sufficient. 10 is an air outlet.

The photoelectron emitting material of this example is made of Cu-Znn matrix, All
0.0051M coating.

Next, the structure of the photoelectron emitting material 3, which is a feature of the present invention, will be explained in a second manner.
This will be explained with reference to FIG.

FIG. 2 is a partial cross-sectional view of the photoelectron emitting material 3. The photoelectron emitting material 3 mainly consists of a base material 11 of a stable substance (material) and a thin film 12 on the base material.

As described above, the thin film 12 is a thin film made of a material (stable material) having a relatively large work function, and may be any material that can effectively emit photoelectrons when irradiated with ultraviolet rays and/or radiation.

FIG. 3 shows another example of a photoelectron emitting material 30. The photoelectron emitting material 30 consists of a base material 110 of a substance with a small work function and a thin film 120 of the base material 110.

In this example, photoelectron emission is performed from both the base material 110 and the thin film 120.

As described above, the base material 110 of the photoelectron emitting material may be any material that emits photoelectrons upon irradiation with ultraviolet rays and/or radiation, and the smaller the photoelectric work function, the better. In addition, the thin film 120 on the base material allows photoelectrons emitted from the base material to pass through and effectively emits photoelectrons from itself, thereby protecting the base material (isolating it from the operating atmosphere and preventing deterioration of the base material. ) are also doing.

The photoelectron emitting material 3.30 of this example has a double structure of a base material 11.110 and a thin film 12.120 on the base material. It goes without saying that a plurality of layers (compound) can be used as appropriate to form a triple structure or more than one structure.

[Example 2] In an environment with a relative humidity of 60%, cigarette smoke was appropriately diluted with air and blown into the air purifier shown in FIG. 4 at a rate of 5N/win, and the performance was examined using a particle measuring device. We also conducted long-term continuous operation to examine performance.

That is, a thin film of 0.003 knots was provided on a Cu-Zn base material as the photoelectron emitting material 13, a low-pressure mercury lamp 14 was used as the ultraviolet lamp, and the electric field strength was 50V/
The microparticles were charged at cn+. 17 and 18 are an inlet and an outlet, 15 is an electrode, and 16 is a dust collecting plate.

The measurement results are that the inlet concentration is 5.4 million pieces/ρ and the outlet concentration is 31.
Even after one month of continuous operation at 0 pieces/g, no change in performance was observed.

[Comparative Example] In Example 2, a similar test was conducted using a material made of Cu-Zn (bulk).

The measurement results were an inlet concentration of 5.4 million pieces/g and an outlet concentration of 75.
When continuous operation was performed at 800 particles/ρ, the outlet concentration after 3 days was 260.500 particles/D, and the outlet concentration after 10 days was 591.100 particles/D.

[Example 3] Gold or silver was deposited on a base material, and the amount of photoelectron emission was examined in the atmosphere at a relative humidity of 60%.

That is, a material made of ZrC, Cu-Zn, or a ceramic with a small amount of photoelectron emission was used as the base material, and an atmospheric ultraviolet photoelectron analyzer was used as the measuring instrument.

The test results are shown in Table 1. The amount of photoelectron emission is expressed as Y, which is the value of the 1/2 power of the amount of photoelectron emission per second.

In addition, for bulk gold and silver Y, Au11.0,
It was silver 13.5.

[Effects of the Invention] As explained above, the present invention provides the following effects.

1. By making a material with a relatively large work function into a thin film, (1) photoelectron emission became more effective.

(2) Since a substance with a larger work function is more stable, the stability of the photoelectron emitting material has been improved.

2゜ Photoelectron emission has become more effective by thinning a material with a relatively large work function. Since the film can be made into such a thin film, a photoelectron emitting material of any shape can be obtained by selecting a material with good workability as the base material.

(2) Since the base material is made of a substance with a small work function and the thin film is made of a substance with a relatively large work function, photoelectrons can be emitted from both the base material and the thin film, improving the effect (performance). Since the surface of the base material is protected by the thin film, the effect is stable for a long time.

3. From 1 and 2 above, charging of fine particles becomes effective,
This has made it possible to downsize the device and increase throughput.

4. 1 to 3 above produced the following effects in their respective fields of application.

(1) In the field of measuring the concentration and particle size of fine particles in gases such as air or exhaust gas, measurement accuracy has been improved and stability has been achieved over a long period of time.

(2) In the field of obtaining clean gas, improved performance and long-term stability have made it possible to downsize equipment and increase processing capacity.

(3) In the field of fine particle separation, classification, surface modification, and charge control, performance is improved, stability is maintained over a long period of time, equipment can be made smaller, and throughput can be increased, especially smaller than 0.1 section. It has become effective in improving the processing performance of ultrafine particles.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for measuring suspended particles in the air according to an embodiment of the present invention. Figures 2 and 3 are partial cross-sectional views of photoelectron-emitting materials. This is an example in which photoelectrons are emitted from both the base material and the thin film. FIG. 4 is a schematic diagram of an air purifier according to an embodiment of the present invention. Explanation of symbols 1... Air 2, 14... Ultraviolet lamp 3, 13. 30... Photoelectron emitting material 4.15... Electrode 5, 6... Pore 7.
8... Classifying plate 9... Electrometer 10... Air outlet 11.110... Mother
Materials 12, 120...Thin membrane 16...Dust collecting plate 17...Inlet for smoke diluted with tobacco 18...Outlet for smoke after cleaning treatment...Charged part...Charged particulate classification Section: Detection section

Claims (11)

[Claims] (1) From a base material consisting of an element, an inorganic compound, an alloy, or a mixture thereof or a composite thereof that emits photoelectrons when irradiated with ultraviolet rays and/or radiation, or from a material that does not emit photoelectrons when irradiated with ultraviolet rays and/or radiation. Among the substances that emit photoelectrons upon irradiation with a thickness of less than 0.01 μm on the base material, which is used in an environment with a relative humidity of 80% or less, preferably 60% or less, A photoelectron emitting material with a multilayer structure consisting of a thin film of a stable substance with a relatively large work function. (2) The photoelectron emitting material according to claim 1, wherein at least a portion of the base material that emits photoelectrons is made of a substance with a small photoelectric work function. (3) The thin film of the photoelectron emitting material has a thickness of 0.001μ
The photoelectron emitting material according to claim 1, which is a thin film with a thickness of less than m. (4) The base material of the photoelectron emitting material is Ba, Sr, Ca,
Y, Gd, La, Ce, Nd, Th, Pr, Be, Zr
, Fe, Ni, Zn, Cu, Ag, Pt, Cd, Pb,
Al, C, Mg, Au, In, Bi, Nb, Si, Ta
, Ti, U, B, Eu, Sn, P, and compounds thereof, or an alloy, mixture, or composite of two or more of them. (5) The thin film of the photoelectron emitting material is made of a material having a relatively large photoelectric work function, such as Au, Ag, Al, Zr, or I.
n, Nb, Pb, Ti, Ni, Cu, Ta, Si, W,
2. The photoelectron emitting material according to claim 1, comprising one material, an alloy, a mixture, or a composite material of two or more selected from C, its compounds, and polymer compounds. (6) A method for charging fine particles in which the photoelectron emitting material according to claim 1 is used to charge fine particles in an electric field. (7) The method for charging fine particles according to claim 6, wherein the electric field has a strength of 1 V/cm to 2 kV/cm. (8) A method of charging fine particles by the method according to claim 6 or 7, modifying the surface of the fine particles, and controlling the amount of charge. (9) A method of charging fine particles and separating and classifying the fine particles by the method according to claim 6 or 7. (10) A method of charging fine particles by the method according to claim 6 or 7 and measuring the concentration and particle size of the fine particles in a gas. (11) A method according to claim 6 or 7, in which the particles are charged, the particles in the gas are collected and removed, and a purified gas is obtained.