JPH02303558A - Method for charging fine particle in gas - Google Patents

Abstract

PURPOSE:To allow measurement with high accuracy even if the sizes of particles are fine and to allow the execution of sepn., classification or surface reforming and control with high efficiency by charging the fine particles after previously growing the fine particles to large grain sizes. CONSTITUTION:The fine particles in gas 1 are charged by the photoelectrons generated when a photoelectron releasing material 3 (e.g. Fe, Cu, Al) is irradiated with the UV rays from a UV lamp 2 and/or radiations in the electric field formed between the photoelectron releasing material 3 and electrodes 4. A condensable material (e.g. alcohol) is condensed on the fine particles to largely grow the grains sizes of the fine particles in a grain size growing section 6 and thereafter, the fine particles are charged at this time. As a result, the measurement with the high accuracy is executed even when the sizes of particles are fine. The sepn., classification or surface reforming and control are thus executed with the high efficiency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for charging fine particles in a gas, and particularly relates to a method for charging fine particles in a gas by growing the fine particles in the gas to a large size in advance and then charging the fine particles. .

Fields in which charged particles are used include: a) Fields in which charged particles are used to measure particles in the air or gases such as exhaust gas.

b) A field in which purified gas is obtained by collecting and removing charged particles.

C) Field of separation, classification, surface modification, and control of fine particles;
etc.

[Conventional technology]

The conventional technology will be explained in the field of measurement.

Conventionally, methods for measuring the concentration of fine particles suspended in the air include (1) a light scattering method, such as a method using a light scattering counter, a photometer, a light transmission method, or a dark field microscope;

(2) There is a gravimetric method, etc.

The drawbacks of these conventional methods are: (1) In the light scattering method, the concentration of ultrafine particles such as (1) 061- or less cannot be measured. ■The accuracy is insufficient when measuring the concentration of particles with multiple particle sizes instantly. ■
If the particles are large, there are drawbacks such as loss of particles during the journey to the detection unit, resulting in insufficient accuracy; (2) In the gravimetric method, ■The concentration of ultrafine particles cannot be measured. (2) There were drawbacks such as insufficient accuracy in measuring the instantaneous concentration of particles with multiple particle sizes.

To address these drawbacks, the present inventors differed from the conventional method in principle by irradiating the photoelectron emitting material with ultraviolet rays and/or radiation, and using the generated photoelectrons to charge the fine particles suspended in the gas. We then proposed a method for measuring fine particles in the air by measuring the amount of charge or by classifying charged fine particles by changing the applied voltage and detecting the classified charged fine particles. 61-85
No. 997, Japanese Patent Application No. 197189/1989).

Although the fine particles are efficiently charged by this method, the charging efficiency decreases as the fine particle size (particle diameter) becomes finer.
There was an issue with the accuracy of the measuring device decreasing. That is, since measurement is performed by charging the particles and utilizing the charge, if the charging efficiency of the particles decreases, the measurement accuracy decreases accordingly.

The reason for this decrease in charging efficiency is explained in the case of charging by photoelectrons, for example.As the particle size becomes finer, the probability of collision between photoelectrons and fine particles and the probability of attachment due to diffusion of photoelectrons onto fine particles increase. It is possible that this will decrease.

[Problem to be solved by the invention]

As described above, in the prior art, there was a problem that as the particle size became finer, the charging effect decreased, and the accuracy of the measuring instrument decreased.

Therefore, the purpose of the present invention is to solve the above-mentioned problems and provide a method that can measure even minute particles with high precision, as well as separation, classification, surface modification, and control with high efficiency. do.

[Failure to solve the problem]

In order to achieve the above object, in the present invention, in a method of charging fine particles in a gas with photoelectrons generated by irradiating a photoelectron emitting material with ultraviolet rays and/or radiation, the fine particles are grown in size in advance and then It is characterized by being electrically charged.

Next, the present invention will be explained in detail.

In the present invention, as the method for growing the particle size, any method that can increase the particle size of fine particles may be used, and any known method can be used as appropriate.

As this method, a method of condensing a condensable substance on fine particles is usually used because it is effective and simple.

Any condensable substance may be used as long as it condenses on fine particles and increases the particle size, and alcohol is generally used because it is effective and simple.

Next, the photoelectron emitting material will be explained.

The material of the photoelectron emitting surface may be any material as long as it emits photoelectrons upon irradiation with ultraviolet rays, and the smaller the photoelectric work function, the more preferable it is. From the viewpoint of effectiveness and economy, Ba,
5rSCa, Y, Gd, La.

(:eS Nd1 Ths Pr, Be, ZrS R
e, NIS Zn, Cu, Ag.

PtS CdS PbS Al, C1Mg, Au, In
S Bi, Nb, Si.

Any one of Ti5TaSSn and 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, Y2O5, and Gd2.
L.

NdxOs, Th0z, ZrL, Fe2es,
ZnO, Cub, AgzO.

PtO, PbO, Al2O3, MgO, InzOs,
There are Bin, NbO, BeO, etc., and borides include YL, GdBg, LaBg.

Examples include Prys, 2rL, and carbides such as lrC, Tag:, TiC, and NbC.

In addition, alloys include brass, bronze, phosphor bronze, Ag and Mg.
(2-20wt% Mg), Cu and Be
(Be is 1 to 10 wt%) and an alloy of Ba and A1 can be used, and an alloy of the above formula g and Mg,
An alloy of Cu and Be and an alloy of Ba and AI are preferred.

Oxides can also be obtained by heating only the metal surface in air or by oxidizing it with chemicals.

Still another method is to heat the material before use to form an oxidized layer on the surface to obtain a stable oxidized layer over a long period of time. As an example of this, an oxide thin film can be formed on the surface of an alloy of Mg and Ag in water vapor at a temperature of 300 to 400°C. This thin oxide film is stable over a long period of time.

These materials can be used in various shapes, such as plate, pleat, lattice, and net shapes, and can be used with their surfaces appropriately roughened. Further, it is possible to use a material having an appropriate shape by plating or attaching other materials. As an example of this, Cu-
It is possible to use Au plating or fixing particulate ^U on Zn material.

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, the radiation source may be one that emits photoelectrons upon irradiation, and α-rays, β-rays, T-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,
Appropriate decisions can be made based on the shape of the measuring instrument, 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 and is effective.
(As for the method of forming the electric field,
The shape and structure of the measuring device can be appropriately selected depending on the expected effect (accuracy), etc.

The voltage of the electric field is 0.02 to 15 kV, preferably 0.0
The voltage ranges from 2 to 5 kV, and the voltage varies depending on the components in the gas, the concentration, the shape of the device, the material and structure of the electrodes or metals used, and the desired effect.

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.

In the above, a method using photoelectrons has been described as a method for charging fine particles, but the method is not limited to this method, and any known method can be used as appropriate.

Examples of the charging method include methods using photoelectrons, methods using corona discharge, and methods using radioactive substances.

Among these methods, the method using photoelectrons is preferably used because it has high charging efficiency, does not generate ozone, and has a sharp charge distribution.

[Example] The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Measurement of particulates in combustion exhaust gas according to the present invention will be specifically explained with reference to FIG.

FIG. 1 is a schematic diagram in which an electrometer is used as a particulate detection section. Air 1 containing fine particles from which large particles of 0.1 OS or more have been removed in advance by a classifier (not shown) is introduced from the air inlet, and the fine particles contained in the air are first separated by particle size. The grain size is increased in the growth section ^1, and then in the charging section B, the particles are charged by photoelectrons emitted from the photoelectron emitting surface 3 that has been irradiated with ultraviolet rays from the ultraviolet irradiation source 2.

The grain size growth part A1 will be explained.

The particle size growth part A+ is a part where the particle size of fine particles is increased.

The method for forming the core part A may be any method as long as it can increase the particle size of the fine particles, and any known method can be used as appropriate.

In this example, air containing 0.1- or less fine particles is introduced into a container containing alcohol, so that the alcohol condenses on the fine particles. (Fine particles are particles with a large apparent particle size.) The charging section B1 will be explained.

The charging section B mainly includes an ultraviolet lamp 2 and a photoelectron emitting material 3.
and an electrode 4. In the charging section B1, an electric field is formed between the photoelectron emitting material 3 and the electrode 4, and photoelectrons are effectively generated from the electron emitting material 3 irradiated with the ultraviolet lamp 2. Fine particles in the air 1 introduced from the air inlet are grown in size in the particle size growth section A, and are efficiently charged by the action of the photoelectrons.

The amount of charge of the particles charged in the charging section B is measured by a detection section C8 comprising an electrometer 5 located downstream, and the concentration of the particles is measured.

In this example, fine particles with a particle size of 0°IFm or more in the combustion exhaust gas are removed in advance by a classifier, so the measurement results are 0.
．． A concentration of fine particles below IP can be continuously obtained.

By appropriately changing the range of particle sizes classified by the classifier, the concentration of particles in an appropriate particle size range can be measured.

Any cough classifier may be used as long as it can classify fine particles in the sample gas into a suitable particle size range.

As an example of the classifier, a diffusion classifier is used because it has relatively high performance and is simple. The diffusion classifier can classify fine particles having a particle size of about 0.005 to 0.3- to an appropriate particle size range.

In addition to the above-mentioned classifiers, there are cyclone type, impactor type, and membrane filter type classifiers, which can be used as appropriate.

Example 2 Air purification (clean room) in the semiconductor industry will be explained based on drawings.

FIG. 2 shows a schematic diagram of a clean bench combined method used in a clean room, that is, a method in which only a part of the working area is kept at a high level of cleanliness.

FIG. 3 is a schematic diagram showing an embodiment of a photoelectron emission section using ultraviolet irradiation.

In FIG. 2, inside the clean room 11, coarse particles of the outside air introduced from the piping 12 are filtered by a pre-filter 13, and then the circulating air taken out from the air outlet 14 of the clean room 11 is air-conditioned via the fan 15. After adjusting the temperature and humidity in the device 16, the air from which particulates have been removed by the IBP^ filter 17 is circulated and supplied, maintaining the cleanliness level (class No. 000).

On the other hand, in the clean room 11, there is a fan and voltage supply member 8, a part of the H8PA filter, a part 9 for irradiating ultraviolet rays onto the particle size growth part and the photoelectron emission material, and a charged particulate collection filter 1.
The workbench 20 in the clean bench 18 provided with a vacuum cleaner is maintained in a sterile atmosphere of high cleanliness (class 10).

That is, in the clean bench 18, air with a cleanliness (class) of about 10,000 in the clean room 11 is absorbed by the fan 8, and most of the fine particles are removed by the 88P filter 21, as shown in detail in FIG. roughly collected and removed.

The HBP^ filter 21 has a particle size of 0.0 among fine particles.
It is difficult to collect fine particles of about 3 to 0.3
The fine particles flow out. The outflowed fine particles undergo particle size growth in the rear particle size growth section 6, and then are charged with photoelectrons, and the charged fine particles are collected and removed by the charged fine particle collection filter 10, resulting in highly clean particles. degree of air 2
3 is obtained.

The ultraviolet irradiation section 22 consists of an electrode 4, a photoelectron emission material 3, and an ultraviolet lamp 2, and a voltage is applied between the electrode 4 and the photoelectron emission material 3 from a fan and a voltage supply section 8, and the ultraviolet rays are applied to the photoelectron emission material 3. By irradiating the photoelectron and passing the fine particles whose particle size has grown between the electrode 4 and the photoelectron emitting material 3, the fine particles are efficiently charged. The charged fine particles are efficiently collected by the charged fine particle collection filter 10.

The configuration and operation of each of the above components are as described in the first embodiment.

In this example, a HOP^ filter is used, but the use of the filter is not limited in any way, and it goes without saying that it can be implemented in the same way even without a filter.

Example 3 Particles generated from a particle generator were introduced into the particle size growth section and charging section shown in Figure 1 at 0.51/min, and the charging efficiency was investigated. compared.

The charging conditions are as follows.

Particle generator; Particle: Polystyrene latex Particle size: 3
．． IPIll, 0.1. cm, 0.05ty
Charged part: Photoelectron emitting material: Brass plated with gold Ultraviolet lamp: Mercury lamp Electric field voltage: 500 V Grain size growth part: Condensation method using alcohol The results are shown in Table 1.

〔Effect of the invention〕

According to the present invention, the following effects are achieved.

1. In the field of measurement, ■ Measurement accuracy has improved.

(2) It is particularly effective in measuring ultrafine particles of <0.1-, which have been difficult to measure in the past.

(2) By separating the fine particles into particle sizes using a classifier or the like before the particle size growth of the particles, the concentration of fine particles on the particle size side can be measured with high accuracy.

■ By classifying the grown fine particles after charging them, the concentration of fine particles on the particle size side can be measured with high accuracy.

2. In the field of obtaining clean gas (by collecting charged fine particles): (1) The efficiency of collecting fine particles, especially ultrafine particles such as <0.1-> has been increased, and highly clean gas has been obtained.

■ Conventional methods for obtaining clean gas using HBPA or ULPA filters have a concentration of 0.03 to 0.
Although the collection efficiency of the three types of particles was low, by using the method of the present invention in combination with the method using the filter, it was possible to collect particles over a wide range of particle sizes, and an ultra-clean gas was obtained.

3. In the field of separation, classification, surface modification, and control of fine particles, charging efficiency is increased, so separation, classification, surface modification, and control are performed.
Control has become easier.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a particulate measuring device according to an embodiment of the present invention, Fig. 2 is a schematic diagram of a system in which a part of the working area is made highly clean, and Fig. 3 is a schematic diagram of a system in which a part of the working area is made highly clean. FIG. 2 is a schematic diagram showing a photoelectron emission section using irradiation. At... Grain size growth part, B1... Charged part, C1...
Detection unit, 1...Air, 2...Ultraviolet lamp, 3...
- Photoelectron emission material, 4... Electrode, 5... Electrometer, 6... Particle size growth section, 8... Fan and voltage supply member, 9... Particle size growth section and ultraviolet irradiation section, 10
...Charged particle collection filter patent applicant: Ebara Corporation Representative: Yoshimine Katsurado Matsu 1) Daidai 1
Figure 2

Claims (1)

[Scope of Claims] 1. In a method of charging fine particles in a gas by photoelectrons generated by irradiating a photoelectron emitting material with ultraviolet rays and/or radiation, the particle size of the fine particles is grown in advance and then charged. Characteristic method of charging fine particles in gas. 2. The method for charging fine particles in a gas according to claim 1, wherein the fine particles are charged in an electric field. 3. The method for charging fine particles in a gas according to claim 1 or 2, wherein the growth of the particle size of the fine particles is carried out by condensing a condensable substance onto the fine particles. 4. The method for charging fine particles in a gas according to claim 3, wherein the condensable substance is alcohol. 5. The method for charging fine particles in a gas according to claim 1, 2 or 3, wherein the photoelectron emitting material is made of a substance with a small photoelectric work function. 6. 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,
6. The method for charging fine particles in a gas according to claim 1, 2, 3, or 5, which is made of one kind of material selected from Sn, P, and compounds thereof. 7. 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,
7. The method for charging fine particles in a gas according to claim 1, 2, 3, 5, or 6, comprising an alloy, a mixture, or a composite material of two or more selected from Sn, P, and compounds thereof.