JP2020051784A - Fine particle classification measurement device - Google Patents

Abstract

An object of the present invention is to provide a fine particle classification measuring device capable of suppressing a reduction in particle size resolution due to a leakage electric field from a flow dividing region.
A charging device is disposed on an inlet side of a parallel flow path in which a sample gas flowing inside can become a laminar flow, and charges fine particles in the sample gas. The collection electrode is disposed on one of the pair of opposing surfaces of the flow channel 10 downstream of the charger. The classification electrode 30 is disposed on the other of the pair of surfaces so as to face the collection electrode 24, and collects the charged fine particles in the sample gas flowing through the flow path 10 between the collection electrode 24 and the collection electrode 24. A trapping electric field is generated that is attracted to the side. A classification region is formed between the classification electrode 30 and the collection electrode 24 for classifying charged fine particles in the sample gas according to the particle diameter. At least one intermediate electrode 50 having an intermediate potential between the potential of the classification electrode 30 and the potential of the collection electrode 24 is disposed between the classification electrode 30 and the collection electrode 24 at the upstream boundary of the classification region. .
[Selection diagram] FIG.

Description

  The present invention relates to a particle classification measuring device.

  WO 2013/183652 (Patent Document 1) discloses a fine particle classification measuring device that classifies and measures fine particles having a particle size on the order of nanometers according to the particle size. This fine particle classification measuring device is configured such that a classifying electrode and a collecting electrode are respectively arranged on a pair of opposing surfaces of a parallel flow path in which a sample gas can be a laminar flow, and a voltage is applied to the classifying electrode, so that the flow direction of the fine particles is A trapping electric field is generated perpendicular to.

  In the above configuration, after the sample gas introduced from the inlet of the flow path is charged, it moves along the flow direction of the sample gas to the classification region where the trapping electric field exists, and when it reaches the classification region, the flow of the sample gas flows. While moving along the direction, it starts to move in the direction of the collecting electrode by the collecting electric field. In the process in which the charged fine particles move in the direction of the collecting electrode, the fine particles can be classified according to the particle size by receiving a resistance depending on the particle size from the fluid.

International Publication No. WO 2013/183652

  However, in the above-described fine particle classification measuring apparatus, an electric field may leak to the outside of the classification region due to a potential difference between the classification electrode and the pair of surfaces of the flow path near the boundary located at the upstream end of the classification region. . In this case, the charged fine particles in the sample gas are attracted to a pair of surfaces by the electric field leaking from the classification region (hereinafter, also referred to as leakage electric field) upstream of the classification region, and thus reach the classification region. Will be hindered. As a result, there is a concern that the particle size resolution for classifying the fine particles according to the particle size is reduced.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a fine particle classification measuring apparatus capable of suppressing a decrease in particle size resolution due to a leaked electric field from a branch region. It is.

  According to an aspect of the present invention, a fine particle classification measuring device has an inlet and an outlet, and a parallel flow path in which a sample gas flowing inside can be a laminar flow, and sucks the sample gas from the inlet of the flow path, A blower mechanism driven under conditions in which the sucked sample gas flows in a laminar flow in the flow path; a charging device arranged on the inlet side of the flow path to charge fine particles in the sample gas; On one of the pair of surfaces, a collecting electrode disposed downstream of the charger, and on the other of the pair of surfaces, the collecting electrode is disposed to face the collecting electrode. A classifying electrode for generating a collecting electric field that attracts the charged fine particles in the sample gas flowing through the flow path to the collecting electrode side. A classification region for classifying charged fine particles in the sample gas according to the particle size is formed between the classification electrode and the collection electrode. The fine particle classification measuring device is disposed between the classification electrode and the collection electrode at an upstream boundary of the classification region, and has at least one intermediate electrode having an intermediate potential between the potential of the classification electrode and the potential of the collection electrode. Further prepare.

  According to the fine particle classification measuring apparatus, the generation of the leakage electric field to the outside of the classification region can be suppressed by the intermediate electrode disposed between the classification electrode and the collection electrode at the boundary on the upstream side of the classification region. According to this, the charged fine particles in the sample gas flowing through the flow path can reach the classification region without being hindered by the leakage electric field, so that the fine particles can be evenly distributed in the classification region. As a result, it is possible to suppress a decrease in the particle size resolution for classifying the fine particles according to the particle size.

  Preferably, the at least one intermediate electrode generates an electric field having an electric field strength equal to the electric field strength of the trapping electric field between the classifying electrode and the collecting electrode.

  According to this, since the charged fine particles can be prevented from being captured by the intermediate electrode near the boundary of the classification region, the charged fine particles that have reached the classification region can be moved in the direction of the collection electrode.

  Preferably, the fine particle classification measuring device further includes a classification power supply for applying a voltage to the classification electrode, and a resistance voltage dividing circuit configured to divide the voltage of the classification power supply to generate an intermediate potential.

  According to this, since the potential can be applied to the intermediate electrode using the classification power supply, it is possible to prevent the device from being enlarged due to the provision of the intermediate electrode.

  Preferably, the collection electrode includes a plurality of measurement electrodes arranged at different distances from the inlet of the flow path along the flow direction. The fine particle classification measuring device further includes a plurality of galvanic circuits connected to the plurality of measuring electrodes and detecting the amount of charge of the charged fine particles reaching the corresponding measuring electrodes. According to this, the fine particles can be classified with high resolution based on the charge amount detected by the galvanic circuit.

  According to another aspect of the present invention, a fine particle classification measuring device has an inlet and an outlet, and a parallel flow path in which a sample gas flowing inside can be a laminar flow, and sucks a sample gas from an inlet of the flow path. A blower mechanism driven under the condition that the sucked sample gas flows in a laminar flow in the flow path, a charging device disposed on the inlet side of the flow path and charging fine particles in the sample gas, A collecting electrode disposed on one side of the pair of opposing surfaces on the downstream side of the charger; and a collecting electrode disposed on the other of the pair of surfaces opposite to the collecting electrode. And a classifying electrode for generating a collection electric field that attracts the charged fine particles in the sample gas flowing through the flow path to the collection electrode side. A classification region for classifying charged fine particles in the sample gas according to the particle size is formed between the classification electrode and the collection electrode. The fine particle classification measuring device is disposed between the classification electrode and the collection electrode at an upstream boundary of the classification area, and has at least one first potential having an intermediate potential between the classification electrode potential and the collection electrode potential. It further comprises an intermediate electrode and at least one second intermediate electrode disposed between the classification electrode and the collection electrode at a downstream boundary of the classification region and having an intermediate potential.

  According to the fine particle classification measuring device, at the upstream and downstream boundaries of the classification region, the generation of a leakage electric field to the outside of the classification region is suppressed by the intermediate electrode disposed between the classification electrode and the collection electrode. Can be. Therefore, the above-described fine particle classification measuring apparatus is applied to a film forming apparatus configured to form a nanoparticle film by attracting charged particles in a sample gas to a collecting electrode side and depositing the particles on a nanoparticle film forming substrate. In this case, a nanoparticle film having a uniform particle concentration distribution can be formed.

  According to the present invention, it is possible to provide a fine particle classification measuring device capable of suppressing a decrease in particle size resolution due to a leakage electric field from a branch region.

It is a figure showing roughly composition of a fine particle classification measuring device concerning an embodiment of this invention. It is sectional drawing along the flow path of the fine particle classification measuring device. FIG. 4 is a diagram showing a relationship between the particle size of fine particles and electric mobility. FIG. 4 is a diagram conceptually showing a moving trajectory of charged fine particles in a classification area. It is a schematic sectional drawing which shows a leak electric field typically. It is a figure which shows typically the density distribution of the fine particle of a specific particle size. It is a figure for explaining the example of composition of the intermediate electrode in the fine particle classification measuring device concerning an embodiment of the invention. FIG. 8 is a diagram illustrating a first configuration example of the intermediate electrode illustrated in FIG. 7. FIG. 8 is a diagram illustrating a second configuration example of the intermediate electrode illustrated in FIG. 7. It is a figure for explaining other examples of composition of an intermediate electrode in a particulate classification measuring device concerning an embodiment of the invention. It is a figure for explaining other examples of composition of an intermediate electrode in a particulate classification measuring device concerning an embodiment of the invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, the same or corresponding parts have the same reference characters allotted, and description thereof will not be repeated in principle.

  FIG. 1 is a diagram schematically showing a configuration of a fine particle classification measuring apparatus according to an embodiment of the present invention.

  With reference to FIG. 1, the fine particle classification device according to the present embodiment has a flow path 10. The flow channel 10 has openings formed at the inlet 12 and the outlet 14, and has a flat shape with a rectangular cross section in both the flow direction and the flow channel width direction. The size and shape of the flow path 10 are not particularly limited. For example, the flow path 10 is a flat rectangular parallelepiped having a length (height) of 4 mm, a width (flow path width) of 250 mm, and a depth (flow path length) of 450 mm. is there.

  An air blowing mechanism (not shown) for sucking the sample is arranged on the outlet side of the flow path 10. The blowing mechanism is driven by a drive circuit. A flow control valve is provided on the sample gas suction side of the blower mechanism, and the flow rate of the sample gas can be changed by adjusting the flow control valve.

  The blowing mechanism uniformly sucks the entire width of the flow channel 10 and sucks the sample gas from the inlet 12 of the flow channel 10. The blowing mechanism is driven under the condition that the sucked sample gas flows in the flow path 10 as a laminar flow. The condition for the laminar flow is a condition where the Reynolds is approximately 2000 or less.

  A charger for charging fine particles in the sample gas is disposed near the inlet 12 of the flow channel 10. In the example of FIG. 1, the charger is configured to take the form of unipolar charging. The charger includes a wire-shaped discharge electrode 20 attached to one side of the flow path 10, and a counter electrode 22 disposed on the other side of the flow path 10 to face the discharge electrodes 20. You. A charging power supply 21 is connected to the discharge electrode 20 so as to cause a discharge between the discharge electrode 20 and the counter electrode 22. The shape of the discharge electrode 20 is not limited to a wire shape, and may be one or a plurality of needles vertically attached to the counter electrode 22. As shown in an embodiment of FIG. 2 to be described later, a counter electrode 22 which is provided perpendicular to the gas flow in the flow channel 10 and has an opening at the center, and a tip of the needle at the center of the opening of the counter electrode The discharge electrode 20 may be configured to include the discharge electrode 20 disposed to face the discharge electrode 20. The structure of the charger is not limited as long as it can discharge between the discharge electrode 20 and the counter electrode 22.

  A pair of wide opposed bottom surfaces (the ceiling surface 40 and the lower bottom surface 42 in the example of FIG. 1) of the flow path 10 are parallel to each other and have the same size. A plurality of collecting electrodes are arranged on the lower bottom surface 42 which is one of the pair of bottom surfaces, at different distances from the inlet 12 along the flow direction. The plurality of collection electrodes include a plurality of measurement electrodes 24_1 to 24_n (n is an integer of 2 or more). The measurement electrodes 24_1 to 24_n may be collectively referred to as the measurement electrodes 24. In the example of FIG. 1, n = 4, but n may be 2 or 3, or 5 or more.

  Current detection circuits 28_1 to 28_n are connected to the measurement electrodes 24_1 to 24_n, respectively, for detecting the amount of charge of the fine particles that have reached the measurement electrode 24. The measurement electrodes 24_1 to 24_n can be arranged close to each other. As shown in FIG. 1, it is also possible to dispose a gap between adjacent measurement electrodes 24. The current detection circuits 28_1 to 28_n may be collectively referred to as a current detection circuit 28. Between the adjacent suction electrodes 24, the electrodes are electrically separated from each other via an insulating member or an air layer. Note that the insulating member need only be electrically separated between the suction electrodes 24, and therefore does not need to be thick, and may be, for example, about 0.5 mm. The thickness of the insulating member depends on the volume resistivity of the insulating member.

  A classifying electrode 30 is disposed on a ceiling surface 40 which is the other bottom surface of the pair of wide opposed bottom surfaces of the flow channel 10 so as to face the collection electrode. The classifying electrode 30 generates an electric field that attracts charged fine particles in the sample gas flowing through the flow path 10 to the collecting electrode between the classifying electrode 30 and the collecting electrode. In the present specification, the electric field that attracts the charged fine particles to the collection electrode side is also referred to as “collection electric field”.

  The classifying electrode 30 and the collecting electrode are such that the area of the classifying electrode 30 and the total area of the collecting electrode are substantially equal, and the classifying electrode 30 and the collecting electrode are spatially facing each other from the front. Is preferred. With this configuration, the trapping electric field can be generated so as to be perpendicular or substantially perpendicular to the flow direction of the sample gas flowing through the flow channel 10. Therefore, the plurality of collecting electrodes are electrically separated from each other, but it is preferable that the gap between the adjacent collecting electrodes is small.

  Note that the collecting electrode may be constituted only by the measuring electrode 24 for measuring the amount of charge of the charged fine particles that have arrived as in the example of FIG. 1, but the charged fine particles reach but are not used as the measuring electrode. A trap electrode (not shown) may be included. When a trapping electrode is included, the same potential as the measuring electrode 24 is applied to the trapping electrode in order to apply a trapping electric field in a direction perpendicular or substantially perpendicular to the flow direction of the sample gas flowing through the flow path 10. Is given. The potentials of the trap electrode and the measurement electrode 24 include the ground potential. The trap electrode is arranged on the upstream side of the first measurement electrode 24_1 closest to the inlet 12 of the flow channel 10 among the measurement electrodes 24.

  The space between the classifying electrode 30 and the collecting electrode forms a "classifying region" for classifying fine particles in the sample gas according to the particle diameter. The upstream end position of the first measurement electrode 24_1 and the upstream end position of the classification electrode 30 are positioned so as to be at the same position in the flow direction, and that position is the base point of the classification region. . In the following description, the position and width of the measurement electrode 24 are specified as a distance from the base point of the classification area. The distance from the inlet 12 of the flow path 10 to the base point of the classification area is called the "running distance". Since the charged fine particles have not reached the classification region at the approach distance, they are moved by the flow of the sample gas without being affected by the classification electric field.

  In the example of FIG. 1, the measurement electrodes 24_1 to 24_4 are set to the same potential, and a trapping electric field is formed between the measurement electrodes 24_1 to 24_4 in the direction perpendicular to or substantially perpendicular to the flow of the sample gas flowing through the flow path 10 with the classification electrode 30. . A classification power supply 32 for applying a classification voltage is connected to the classification electrode 30. By applying a voltage from the classification power supply 32, an electric field (collection electric field) is formed between the classification electrode 30 and the collection electrode in a direction in which the charged fine particles in the sample gas are attracted to the collection electrode side.

  For example, in the case where the operation is confirmed using gas ions after removing a particle component by providing a filter, when the operation is to be confirmed using a gas ion having a positive charge, the voltage of the classification electrode 30 is set to a positive voltage, and the collection electrode is used. Is the ground potential. Conversely, when it is desired to confirm the operation using a gas having a negative charge as a gas ion, a voltage is applied from the classification power supply 32 to the classification electrode 30 so that the voltage of the classification electrode 30 becomes a negative voltage. Depending on the dimensions of the flow path 10, the voltage applied to the classifying power supply 32 at the time of measurement can be several kV, for example, 1 to 4 kV, and a voltage in a range that generally does not cause dielectric breakdown can be applied.

  At the time of measurement, a constant voltage is continuously supplied from the classification power supply 32 to the classification electrode 30. For example, when the unipolar discharge is performed with the counter electrode 22 at the ground potential and the discharge electrode 20 at the positive side, the fine particles in the sample gas have a positive unipolar charge. Therefore, the classification electrodes are set with the measurement electrodes 24_1 to 24_4 at the ground potential. Set 30 to the positive side.

  In the configuration of FIG. 1, when the charger (discharge electrode 20 and counter electrode 22) is operated and the air blowing mechanism is operated in a state where the trapping electric field is applied, the sample gas is introduced from the inlet 12 of the flow channel 10. The sample gas is charged by the discharge of the charger. Since a collection electric field is generated in the classification region between the classification electrode 30 and the collection electrode, the charged sample gas is sent along the flow into the collection electric field. The sample gas charged by the charger moves along the flow direction of the sample gas to the classification area where the collected electric field exists, and when it reaches the classification area, moves along the sample gas flow direction while moving along the sample gas flow direction. And starts to move in the direction of the collecting electrode.

  The charged fine particles move toward the collection electrode while flowing toward the exhaust side along the flow of the sample gas in the collection electric field. Fine particles having a small particle diameter are collected by the collecting electrode near the inlet 12. However, fine particles having a large particle diameter sucked at a position near the collecting electrode, that is, at a position on the lower bottom surface 42 side of the flow path 10 are also collected by the collecting electrode near the inlet 12. The electric charge of the fine particles that has reached the measurement electrodes 24_1 to 24_4 is detected by the galvanometer circuits 28_1 to 28_4 connected to the measurement electrodes 24_1 to 24_4, respectively.

  Next, a specific configuration example of the particle classification measuring device shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a cross-sectional view along the flow path 10 of the particle classification measuring device.

  Referring to FIG. 2, channel 10 has a flat rectangular parallelepiped shape, and rectifier resistors 11a and 11b are arranged at its inlet and outlet, respectively, to make the flow of the sample gas parallel. . The rectifier resistors 11a and 11b are set so as to have a flow path resistance such that the sample is uniformly dispersed in the flow path width direction. Although the cross-sectional area of the flow of the sample introduction port 13a and the discharge port 13b connected to the flow path 10 is smaller than that of the flow path 10, the flow of the sample gas in the flow path 10 is reduced by the rectifying resistors 11a and 11b. And a uniform parallel flow is obtained.

  A blower 44 is connected as a blower to the discharge port 13 b connected to the outlet of the flow path 10, and an airflow sensor 46 is arranged upstream of the blower 44. The flow control valve 18 is arranged between the air flow sensor 46 and the blower 44. The flow control valve 18 is adjusted so that the air flow detected by the air flow sensor 46 becomes a predetermined constant amount so as to make the sample gas a laminar flow. The flow control valve 18 can be manually adjusted, and can be configured to perform feedback control based on a signal from the air flow sensor 46.

  There is a sample inlet 12a for introducing a sample gas into the sample inlet 13a. An impactor 13 and a charger are arranged between the sample inlet 12a and the sample inlet 13a. The impactor 13 has a structure in which a nozzle is opened at the center of a plate that blocks the flow path 10, and a collecting plate is disposed downstream of the nozzle so as to face the nozzle. This is a device that uses an inertial collision of aerosol ejected from a nozzle to collect and remove large particles in the aerosol by a collecting plate and pass small particles in the aerosol.

  The charger includes a discharge electrode 20 and a counter electrode 22, and is disposed between the impactor 13 and the sample introduction port 13a. The discharge electrode 20 has a needle shape. The counter electrode 22 is formed of an electrode plate that blocks the flow path 10, and has an opening formed in the center thereof. The tip of the discharge electrode 20 is arranged toward the center of the opening of the counter electrode 22. The counter electrode 22 is grounded. A charging voltage from a charging power supply 21 is applied to the discharge electrode 20. When a positive voltage is applied to the discharge electrode 20, the charging unit positively charges the fine particles in the sample gas. On the other hand, when a negative voltage is applied to the discharge electrode 20, the charging unit negatively charges the fine particles in the sample gas. The structures of the discharge electrode 20 and the counter electrode 22 are not limited to this.

  A charging voltage regulator (not shown) is connected to the charging power supply 21 in order to adjust a voltage applied to the discharge electrode 20 according to a desired ion concentration, a charging polarity, and the like.

  On the lower bottom surface 42 of the flow channel 10, four measurement electrodes 24_1 to 24_4 are arranged in order from the upstream side at different distances from the inlet in the flow direction. The measurement electrodes 24_1 to 24_4 are arranged close to each other, and are arranged with a gap between the adjacent measurement electrodes 24. The measurement electrodes 24_1 to 24_4 are connected to current detection circuits 28_1 to 28_4, respectively. In the example of FIG. 2, the galvanometer circuit 28 is provided in all the measurement electrodes 24_1 to 24_4, but may be connected only to the measurement electrode 24 whose current value is to be detected. The lower bottom surface 42 is grounded. One classification electrode 30 is arranged on the ceiling surface 40 of the flow channel 10 so as to face the measurement electrodes 24_1 to 24_4. The upstream end position of the first measurement electrode 24_1 matches the upstream end position of the classification electrode 30, and the downstream end position of the fourth measurement electrode 24_4 and the downstream end position of the classification electrode 30 are different from each other. Matches.

  The current detection circuits 28_1 to 28_4 are connected to a computer (not shown) for performing calculations for classification. At the time of measurement, the detection signals of the galvanometer circuits 28_1 to 28_4 reflect the result of the classification of the charged particles in the sample gas flowing through the flow path 10 and the attraction to the measurement electrodes 24_1 to 24_4. Classification measurements can be made based on the signal.

Here, the relationship between the particle size of the charged fine particles and the moving speed in the trapping electric field will be described.
FIG. 3 shows the relationship between the particle size of the fine particles and the ease of movement (electric mobility) in an electric field. The data in FIG. 3 are actual measurement values supplemented by a simulation based on literature values. When charging conditions mainly based on diffusion charging are set, the charge amount of the fine particles is approximately proportional to the particle size. When charged microparticles are placed in an electric field, the microparticles having a small particle diameter are quickly attracted to the electrostatic force and move in the electric field because of their small charge amount and small resistance received from air. On the other hand, as the particle size increases, the resistance from air becomes more dominant, and the moving speed in the electric field decreases. However, as the particle size further increases, the resistance received from air increases, but the effect of the electrostatic force due to the increase in the amount of charge increases, so that the moving speed of the fine particles having a certain particle size or more in the electric field changes. Disappears.

  The charged fine particles move toward the collection electrode while flowing toward the exhaust side along the flow of the sample gas in the collection electric field in the classification region. Fine particles having a small particle diameter are captured by the collecting electrode near the entrance. However, fine particles having a large particle diameter sucked in at a position near the collecting electrode, that is, at a position on the lower bottom surface 42 side of the flow channel 10 are also captured by the collecting electrode near the entrance. Of the collection electrodes, the charges of the fine particles that have reached the measurement electrodes 24_1 to 24_4 are detected by galvanic circuits 28_1 to 28_4 connected to the measurement electrodes 24_1 to 24_4, respectively. However, the detection of the charged fine particles that have reached the measurement electrode 24 is not limited to the detection by the galvanometer circuits 28_1 to 28_4, but may be another detection method such as weight measurement using a quartz oscillator.

  Here, a calculation method of the ratio (capture rate) of reaching the measurement electrode 24 for each particle diameter of the charged fine particles will be described. The calculation model is as follows.

The sample gas in the flow path 10 flows under a condition that causes a laminar flow in a classification region between the classification electrode 30 and the collection electrode. The velocity distribution at this time is represented by equation (1).

Here, v is the sample gas flow velocity, and x is the distance between the electrodes with respect to the lower bottom surface 42 of the flow channel 10.

Assuming that the direction toward the outlet 14 of the flow path 10 from the point at which the classification region starts along the flow path 10 (that is, the point at which the trapping electric field starts to act) is the y direction, as shown in FIG. microparticles consisting in a laminar flow moves at a speed v relative to the y direction, and moves at a speed v _x in the collecting electrode side by collecting field. The velocity v _x can be expressed by the formula (2) as a product of the electric mobility Zp and the electric field intensity E of the trapping electric field.

The electric field intensity E is given by the following equation (3), based on the classification voltage V applied between the classification electrode 30 and the collection electrode and the distance d between the electrodes.

Here, a time t _x0 until the charged fine particles having the electric mobility Zp at an arbitrary position x 0 in the x direction at the base point (y = 0) of the classification area reaches the collection electrode is represented by Expression (4). .

The moving distance L0 in the y direction when the charged fine particles reach the collection electrode can be expressed as in equation (5).

Here, the electric mobility Zp is

N is the number of charges, e is the elementary charge, Cc is the Cunningham correction coefficient, π is the circular flow rate, μ is the viscosity coefficient, and Dp is the particle diameter.

  As shown in the equation (6), since the electric mobility Zp is a function of the particle diameter Dp of the charged fine particles, various particle diameters at an arbitrary position x0 in the x direction at the base point (y = 0) of the classification area. The moving distance L0 in the y direction when the charged fine particles reach the collection electrode can be obtained.

Assuming that the concentration distribution of particles having a certain particle diameter Dp at the entrance of the classification region can be ignored, the moving distance L of the sucked fine particles from x = 0, which is the position closest to the collection electrode, is given by Expression (7).

On the other hand, the moving distance L of the sucked fine particles from x = d (d is the distance between the electrodes), which is the farthest position from the collecting electrode, is given by equation (8).

Here, assuming that the sample gas flow rate is Q and the opening width of the inlet 12 of the flow channel 10 is W, Lmax is given by Expression (10) since the relationship of Expression (9) holds.

Assuming that the particle concentration per unit time and per unit area captured by the collecting electrode from Lmin to L0 is q (particles / m ² / sec), q is represented by the following equation (11).

By rearranging this based on Equations (5) and (12), Equation (12) is obtained.

As can be seen from Equation (12), the particles are uniformly distributed between 0 <x0 <d, that is, between the moving distance Lmin and Lmax of the particles, regardless of the position x0 in the inter-electrode direction x. Here, C is the particle concentration (particles / m ³ ) of the electric mobility Zp sucked into the device. By equation (12) is satisfied, the length of the flow direction of the collecting electrode when L _1, the current value measured is the formula (13).

  When the measurement electrodes 24 having the same flow rate are placed between Lmin and Lmax, the same amount of measurement signal can be obtained with respect to the particle diameter Dp. Further, since the signal amount is proportional to the length of the electrodes, the ratio is determined by the ratio. The effect of non-uniform electrode length can also be eliminated.

  According to this, in the configuration of FIG. 2, by taking a difference signal between a ratio (capture rate) captured by the first measurement electrode 24_1 and a capture rate captured by the second measurement electrode 24_2, a specific particle size range is obtained. Can be extracted. The meaning of the particle size distribution obtained from the difference is as follows. Before the difference, each electrode contains particles having a large particle size infinitely, but by taking the difference, only particles within a certain particle size range can be counted. Further, by taking the difference, noise such as vibration, temperature, and radiation can be canceled, and as a result, a measurement signal with a high S / N ratio can be obtained.

  In the configuration example of FIG. 2, the galvanometer circuits 28_1 to 28_4 are connected to a calculation unit via a difference circuit (not shown), and a predetermined calculation process is performed based on the charge amount of the charged fine particles. The calculation unit can be realized by a dedicated computer for controlling the operation of the particle classification measuring device, or an external general-purpose computer (for example, a personal computer). The calculation unit calculates the number of fine particles, the total surface area, the total weight, or their concentration as the amount of the classified fine particles of the charged fine particles that have reached the measurement electrode 24. The details of the arithmetic processing in the arithmetic unit are disclosed in Patent Document 1.

(Issues in fine particle classification measuring equipment)
As described above, in the fine particle classification measuring device, the charged fine particles are generated by generating the trapping electric field in the classification region so as to be perpendicular or substantially perpendicular to the flow direction of the sample gas flowing through the flow path 10. It is distributed evenly between the movement distance Lim and Lmax for each diameter. Thus, a signal in a specific particle size range can be extracted by taking the difference between the capture rates of the adjacent measurement electrodes 24.

  However, in an actual apparatus, the trapping electric field may leak out of the classification area at the boundary of the classification area, which is the upstream end position and the downstream end position of the classification area. In the following description, the electric field leaking from the classification region is also referred to as “leakage electric field”.

  FIG. 5 is a schematic sectional view schematically showing a leakage electric field. In FIG. 5, the upstream end position of the first measurement electrode 24_1 is the base point (y = 0) of the classification area, and the distance from the entrance of the flow path 10 to the base point of the classification area is the approach distance.

  At this approach distance, the same potential (ground potential) as that of the collection electrode is applied to each of the ceiling surface 40 and the lower bottom surface 42 of the flow path 10. Therefore, a potential difference equal to that between the classification electrode 30 and the collecting electrode is generated between the classification electrode 30 and the ceiling surface 40 and between the classification electrode 30 and the lower bottom surface 42. As a result, as shown by arrows in the figure, a leakage electric field is generated between the classification electrode 30 and the ceiling surface 40 and the lower bottom surface 42.

  When the leakage electric field is generated, the charged fine particles in the sample gas flowing through the flow channel 10 are attracted to the ceiling surface 40 or the lower bottom surface 42 at the approach distance, and are prevented from reaching the classification region. The effect of the leakage electric field will be described with reference to FIG. FIG. 6 is a diagram schematically showing a concentration distribution of fine particles having a specific particle size. The horizontal axis in FIG. 6 shows the position in the direction (y direction) toward the outlet of the flow channel 10, and the vertical axis in FIG. 6 shows the particle concentration. Y = 0 in the figure corresponds to the base point of the classification area.

  In FIG. 6, a waveform k1 shows the concentration distribution of the fine particles when no leakage electric field is generated, and a waveform k2 shows the concentration distribution of the fine particles when the leakage electric field is generated. When no leakage electric field is generated, the particle concentration is evenly distributed between the moving distances Lmin and Lmax of the fine particles. In the example of FIG. 6, the particle concentration is evenly distributed over the measurement electrodes 24_1 and 24_2, and the waveform k1 has a substantially rectangular shape.

  On the other hand, when a leakage electric field as indicated by an arrow in the drawing is generated, the ceiling surface 40 and the lower bottom surface are caused by the leakage electric field generated upstream from the base point (y = 0) of the classification area. The fine particles are trapped by 42. Therefore, in the concentration distribution, as shown by the waveform k2, the particle concentration near the boundary on the upstream side of the classification area decreases and the particle concentration on the downstream side decreases. In particular, fine particles having a small particle diameter are more frequently captured by the collecting electrode on the entrance side, and thus tend to be more susceptible to the leakage electric field than fine particles having a large particle diameter.

  The decrease in the particle concentration on the upstream side in the waveform k2 is due to the influence of the fine particles captured on the lower bottom surface 42, and the decrease in the particle concentration on the downstream side is due to the influence of the fine particles captured on the ceiling surface 40. . As a result, the waveform k2 changes from the rectangular shape of the waveform k1 to a trapezoidal shape.

  When the leakage electric field is generated as described above, the distribution of the particle concentration for each particle size becomes uneven. Therefore, it is difficult to accurately extract a signal in a specific particle size range even if the difference between the capture rates of the adjacent measurement electrodes 24 is calculated. As a result, there is a concern that the particle size resolution for classifying the fine particles according to the particle size is reduced.

  Therefore, in the fine particle classification measuring device according to the present embodiment, at least one electrode is arranged between the classification electrode 30 and the collection electrode at the boundary on the upstream side of the classification region. Thus, an intermediate potential between the potential of the classification electrode 30 and the potential of the collection electrode is provided. In the present specification, an electrode arranged between the classification electrode 30 and the collection electrode is also referred to as an “intermediate electrode”.

  FIG. 7 is a diagram for explaining a configuration example of the intermediate electrode in the particle classification measuring device according to the present embodiment.

  Referring to FIG. 7, three intermediate electrodes 50_1 to 50_3 are arranged on the upstream boundary of the classification area. The intermediate electrodes 50_1 to 50_3 are arranged at regular intervals along the inter-electrode direction (x direction) between the upstream end position of the classification electrode 30 and the upstream end position of the collection electrode. The intermediate electrodes 50_1 to 50_3 may be collectively referred to as an intermediate electrode 50.

  As shown in FIGS. 1 and 2, when the collecting electrode does not include the trapping electrode and includes only the measuring electrode 24, the tip position on the upstream side of the classification electrode 30 and the upstream side of the first measuring electrode 24 </ b> _ <b> 1. At least one intermediate electrode 50 is disposed between the first and second side electrodes. On the other hand, although not shown, when the collection electrode includes a trap electrode, at least one intermediate electrode 50 is disposed between the upstream end position of the classification electrode 30 and the upstream end position of the trap electrode. Is done.

  In FIG. 7, the distance between the classification electrode 30 and the first measurement electrode 24_1 is d, the distance between the classification electrode 30 and the first intermediate electrode 50_1 is d1, and the distance between the first intermediate electrode 50_1 and the second intermediate electrode 50_2 is d. d2, the distance between the second intermediate electrode 50_2 and the third intermediate electrode 50_3 is d3, and the distance between the third intermediate electrode 50_3 and the first measurement electrode 24_1 is d4. The relationship d1 = d2 = d3 = d4 = d / 4 holds between d and d1 to d4.

  In the configuration example of FIG. 7, a voltage is applied from the classification power supply 32 to the classification electrode 30 so that the potential of the classification electrode 30 becomes a positive potential V (V> 0), and a ground potential (zero potential) is applied to the measurement electrode 24. Shall be given. When the charger is activated to give the fine particles in the sample gas a positive charge, the charged fine particles are attracted in the direction of the measuring electrode 24 by the trapping electric field.

Assuming that the potential V1 is applied to the first intermediate electrode 50_1, the potential V2 is applied to the second intermediate electrode 50_2, and the potential V3 is applied to the third intermediate electrode 50_3, the potentials V1 to V3 are expressed by the equations (14) to (16). Respectively represented.

  By doing so, the electric field intensity between the classification electrode 30 and the first intermediate electrode 50_1, the electric field intensity between the first intermediate electrode 50_1 and the second intermediate electrode 50_2, and the electric field intensity between the second intermediate electrode 50_2 and the third intermediate electrode 50_3 , The electric field intensity between the third intermediate electrode 50_3 and the first measurement electrode 24_1 is E = V / d, and is equal to the electric field intensity of the trapping electric field generated in the classification region (see the equation (3)). Can be.

  By arranging the intermediate electrode 50 between the classification electrode 30 and the first measurement electrode 24, as shown by arrows in FIG. 7, near the boundary of the classification region, between the classification electrode 30 and the intermediate electrode 50, and An electric field is generated between adjacent intermediate electrodes 50. Since the generated electric field is focused on the first measurement electrode 24_1, the generation of the leakage electric field as shown in FIG. 5 is suppressed. According to this, it is possible to prevent the charged fine particles in the sample gas from being captured by the ceiling surface 40 and the lower bottom surface 42 at the approach distance upstream of the classification region.

  As described above, by arranging the intermediate electrode 50 so as to generate an electric field having the same electric field strength as the trapping electric field also near the boundary of the classification region, the charged fine particles are captured by the intermediate electrode 50 near the boundary. Can be suppressed. As a result, the charged fine particles that have reached the classification region can be moved in the direction of the collecting electrode, and as a result, the concentration distribution of the fine particles can be made closer to the waveform k1 in FIG.

FIG. 8 is a diagram showing a first configuration example of the intermediate electrode 50 shown in FIG.
Referring to FIG. 8, intermediate electrode 50 has a wire-like shape. The intermediate electrode 50 is electrically connected between the classification power supply 32 and the collecting electrode (ground potential). Specifically, one end of the first intermediate electrode 50_1 is electrically connected to the classification power supply 32 via the resistance element r1, and the other end of the first intermediate electrode 50_1 is grounded via the resistance elements r4, r5, r6. It is electrically connected to a potential. One end of the second intermediate electrode 50_2 is electrically connected to the classification power supply 32 through the resistance elements r1 and r2, and the other end of the second intermediate electrode 50_2 is electrically connected to the ground potential through the resistance elements r5 and r6. Connected. One end of the third intermediate electrode 50_3 is electrically connected to the classification power supply 32 through the resistance elements r1, r2, and r3, and the other end of the third intermediate electrode 50_3 is electrically connected to the ground potential through the resistance element r6. Connected. The resistance elements r1 to r6 correspond to an embodiment of a “resistance voltage dividing circuit”.

  In the configuration example of FIG. 8, the resistance elements r1 to r6 have the same electric resistance value r. The potential V1 of the first intermediate electrode 50_1 is obtained by dividing the applied voltage V of the classifying power supply 32 by the resistance elements r1, r4, r5, and r6, and becomes the potential shown in Expression (14). The potential V2 of the second intermediate electrode 50_2 is obtained by dividing the applied voltage V of the classifying power supply 32 by the resistance elements r1, r2, r5, and r6, and becomes the potential shown in Expression (15). The potential V3 of the third intermediate electrode 50_3 is obtained by dividing the applied voltage V of the classifying power supply 32 by the resistance elements r1, r2, r3, and r6, and becomes the potential shown in Expression (16).

FIG. 9 is a diagram showing a second configuration example of the intermediate electrode 50 shown in FIG.
Referring to FIG. 9, the second configuration example is different from the first configuration example of FIG. 8 in that intermediate electrode 50 has a plate shape. Also in the second configuration example, the potentials V1, V2, and V3 can be respectively applied to the intermediate electrodes 50_1, 50_2, and 50_3 by dividing the voltage V applied from the classification power supply 32 by resistance.

  8 and 9, the configuration example in which the voltage to be applied to the intermediate electrode 50 is generated using the voltage of the classification power supply 32 has been described. A configuration for generating a voltage to be applied may be adopted.

  In addition, the number of intermediate electrodes 50 disposed between the classification electrode 30 and the collection electrode may be at least one. Further, the distance between the classifying electrode 30 and the intermediate electrode 50, the distance between the adjacent intermediate electrodes 50, and the distance between the intermediate electrode 50 and the collecting electrode are equal to each other if the electric field strength generated between the adjacent electrodes is equal to each other. It does not have to be an interval.

  Therefore, as shown in FIG. 10, a configuration in which the two intermediate electrodes 50_1 and 50_2 are arranged at irregular intervals between the classification electrode 30 and the collection electrode may be adopted. In the example of FIG. 10, the distance d1 between the classifying electrode 30 and the first intermediate electrode 50_1, the distance d2 between the first intermediate electrode 50_1 and the second intermediate electrode 50_2, and the distance d3 between the second intermediate electrode 50_2 and the collecting electrode are d1: d2: d3 = 1: 2: 2.

  The potential V1 = V × 4/5 is applied to the first intermediate electrode 50_1, and the potential V2 = V × 2/5 is applied to the second intermediate electrode 50_2. In this case, the electric field strength between the classification electrode 30 and the first intermediate electrode 50_1, the electric field strength between the first intermediate electrode 50_1 and the second intermediate electrode 50_2, and the electric field strength between the second intermediate electrode 50_2 and the collecting electrode are: In each case, E = V / d, which can be made equal to the electric field intensity of the trapping electric field generated in the classification region.

  As described above, according to the fine particle classification measuring apparatus according to the present embodiment, by disposing at least one intermediate electrode 50 between the classification electrode 30 and the collecting electrode at the upstream boundary of the classification region, Can be suppressed from being generated outside. According to this, the charged fine particles in the sample gas flowing through the flow path can reach the classification region without being hindered by the leakage electric field, so that the fine particles can be evenly distributed in the classification region. As a result, it is possible to suppress a decrease in resolution for classifying the fine particles according to the particle diameter.

  In the above-described embodiment, the configuration in which the intermediate electrode 50 is arranged at the boundary on the upstream side of the classification area has been described. However, as shown in FIG. ing. Therefore, as shown in FIG. 11, by arranging the intermediate electrode 50 also at the boundary on the downstream side of the classification area, it is possible to suppress the generation of the leakage electric field on the downstream side of the classification area.

  The configuration example of FIG. 11 is suitable for, for example, a film forming apparatus configured to form a nanoparticle film by attracting charged particles in a sample gas to a collecting electrode side and depositing the particles on a nanoparticle film deposition substrate. Can be used for The charged fine particles reaching the downstream side of the branching region are collected on the nanoparticle film deposition substrate without leaking from the classification region, and a nanoparticle film having a uniform particle concentration distribution can be formed. it can.

  In the above-described embodiment, the flow path has a cross-sectional shape in a direction perpendicular to the flow direction that is flat in the horizontal direction. However, the cross-sectional shape of the flow path is rotated by 90 degrees from that in the example. The shape may be flat in the vertical direction. Further, the flow path is not limited to a rectangular cross section as shown in the embodiment, but may be a circular one or a structure in which a classifying electrode and a collecting electrode are arranged so as to face each other in a double cylindrical shape. Good. The present invention can be applied to any classifier using a principle of applying a classification voltage between a pair of electrodes and classifying the charged fine particles according to the particle diameter by a trapping electric field generated by the classification voltage.

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention relates to a fine particle measuring device suitable for use in monitoring the concentration of nanoparticles in automobile exhaust gas, building satellite management and occupational safety and health, and more particularly, a fine particle classifying device for classifying and measuring fine particles according to particle diameter. The present invention can be suitably used for a sample preparation device having a uniform particle concentration distribution, a nanoparticle film formation device, and a catalyst dispersion device.

  Reference Signs List 10 flow path, 12 inlet, 13 impactor, 13a sample inlet, 13b outlet, 14 outlet, 18 flow control valve, 20 discharge electrode, 21 charging power source, 22 counter electrode, 24, 24_1 to 24_4 measuring electrode, 28, 28_1 -28_4 Current detection circuit, 30-class electrode, 32-class power supply, 40 ceiling surface, 42 bottom surface, 44 blower, 46 air flow sensor, 48 flow monitor, 50, 50_1 to 50_3 intermediate electrode.

Claims (5)

A parallel flow path having an inlet and an outlet, wherein the sample gas flowing therethrough can be laminar;
An air blowing mechanism driven under conditions in which the sample gas is sucked from the inlet of the flow channel and the sucked sample gas flows as a laminar flow in the flow channel.
A charger that is disposed on the inlet side of the flow path and charges fine particles in the sample gas,
On one of the pair of opposing surfaces of the flow path, a collecting electrode disposed downstream of the charger.
On the other of the pair of surfaces, the charged fine particles in the sample gas, which are disposed to face the collection electrode and flow through the flow path between the collection electrode and the collection electrode, are attracted to the collection electrode. A classification electrode for generating a trapping electric field,
A classification region for classifying the charged fine particles in the sample gas according to a particle size is formed between the classification electrode and the collection electrode,
At least one intermediate electrode, which is disposed between the classification electrode and the collection electrode at an upstream boundary of the classification region and has an intermediate potential between the potential of the classification electrode and the potential of the collection electrode, Equipped with a particle classification measuring device.   The particle classification measurement according to claim 1, wherein the at least one intermediate electrode generates an electric field having an electric field intensity equal to an electric field intensity of the trapping electric field between the classification electrode and the collection electrode. apparatus. A classification power supply for applying a voltage to the classification electrode,
The particle classification measuring device according to claim 1, further comprising: a resistance voltage dividing circuit configured to divide a voltage of the classification power supply to generate the intermediate potential. The collection electrode includes a plurality of measurement electrodes arranged at positions different from each other from the inlet of the flow path,
The microparticle according to any one of claims 1 to 3, further comprising a plurality of galvanic circuits respectively connected to the plurality of measurement electrodes and detecting a charge amount of the charged microparticle reaching the corresponding measurement electrode. Classification measuring device. A parallel flow path having an inlet and an outlet, wherein the sample gas flowing therethrough can be laminar;
A blower mechanism driven under the condition that the sample gas is sucked from the inlet of the flow channel and the sucked sample gas flows as a laminar flow in the flow channel,
A charger that is disposed on the inlet side of the flow path and charges fine particles in the sample gas,
On one of the pair of opposing surfaces of the flow path, a collecting electrode disposed downstream of the charger.
On the other of the pair of surfaces, the charged fine particles in the sample gas that are disposed to face the collection electrode and flow through the flow path between the collection electrode and the collection electrode are attracted to the collection electrode side. A classification electrode for generating a trapping electric field,
A classification region for classifying the charged fine particles in the sample gas according to a particle size is formed between the classification electrode and the collection electrode,
At least one first intermediate disposed between the classification electrode and the collection electrode at an upstream boundary of the classification region and having an intermediate potential between the potential of the classification electrode and the potential of the collection electrode; Electrodes and
A fine particle classification measuring device, further comprising: at least one second intermediate electrode having the intermediate potential and disposed between the classification electrode and the collection electrode at a downstream boundary of the classification region.

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