JP2008020408A - Number concentration standard gas generator and method for producing number concentration standard gas - Google Patents

Abstract

The present invention provides a gas in which nanoparticles having a specific particle size are present at a known number concentration, a number concentration standard gas generating device for generating a so-called number concentration standard gas, and a method for producing the number concentration standard gas. The task is to do.
A liquid W containing standard nanoparticles P having a specific particle size of 100 nm or less in a known number concentration is sprayed by a spraying means 1 to contain or contain only one of the standard nanoparticles P. After the droplets D floating in the gas are generated in a non-conducting state, only the droplets d having a specific particle size are selected from the generated droplets D by the selecting means 2, and the selected specific particle size is selected. After the number of droplets d is counted by the counting means 3, the droplets d are dried by the drying means 4, thereby producing a gas G in which the standard nanoparticles P in a floating state are present at a predetermined number concentration. It is characterized by that.
[Selection] Figure 1

Description

  The present invention relates to a number concentration standard gas generating apparatus and a method for producing a number concentration standard gas necessary for performing calibration (verification) of a particle measuring device in order to accurately measure the number concentration of nanoparticles. .

  Conventionally, it has been recognized as a major social problem that particulate matter contained in exhaust gas from diesel vehicles and the like is harmful to health. For this reason, various efforts have been made to date, and as a result of the development of clean engines and filters attached to diesel vehicles and various legal regulations, so-called soot etc. are visible. A certain effect has been achieved in removing particulate matter having a relatively large particle size (specifically, about several hundred nm).

  In research on these particulate materials, in addition to optical methods using laser light scattering, etc., SMPS (Scanning Mobility Particle Sizer) and DMS (Differential Mobility Spectrometer) are used as particle measurement methods. ) Or DMA (Differential Mobility Analyzer), and ELPI (Electrical Low Pressure Impactor) using particle inertial collision has been used. These various methods have been established as being capable of accurately measuring particulate matter having a relatively large particle size as described above.

  By the way, in recent research, the above-mentioned particulate matter having a relatively large particle size is also used, but particles having a particle size that is smaller and invisible (for example, 100 nm or less) have a great adverse effect on the human body. It has become clear. Here, FIG. 3 shows the ratio of particles having a specific particle size to the particulate matter contained in the exhaust gas as a distribution for each particle size. The mass concentration (broken line in FIG. 3) occupies a large proportion of relatively large particles having a particle size of about several hundred nanometers, while the number based (so-called number concentration, solid line in FIG. 3). ) Shows that the proportion of particles having a particle size of 100 nm or less is large (see Non-Patent Document 1, page 6, Figure 3).

  For this reason, recently, in the measurement of particulate matter, the number concentration as well as the mass concentration has become an important measurement item. Here, the measurement methods such as SMPS, DMS, DMA, ELPI and the like can measure not only the mass concentration but also the number concentration, so that they are conventionally used as they are in the number concentration measurement. . However, the optical method using laser light scattering or the like can be detected because the scattered light intensity is proportional to the sixth power of the particle diameter, and the scattered light intensity rapidly decreases as the particle diameter decreases. The limit of the particle size is about 100 nm, which is not particularly suitable for measuring particles having a particle size of 100 nm or less.

  However, even with the measurement methods such as SMPS, DMS, DMA, ELPI, etc., ultra-fine particles having a particle size of 100 nm or less are accurate because of their small size. The problem is that measurement is difficult. In addition, this is an obstacle to promoting the development of a clean engine that does not generate particles having a particle size of 100 nm or less or restricting the discharge of such particles.

  More specifically, as described in Non-Patent Document 2, in a comparative experiment of various particle measurement methods or apparatuses using a particle measurement program (PMP) in the European Forum for Automotive Technology Standards, for example, the particle size is When nanoparticles of about 60 nm were measured, as shown in FIG. 4, it was found that the number concentration showed an order of magnitude variation between particle measurement methods or apparatuses. The vertical axis in FIG. 4 is the number concentration, and the results of the measuring devices are arranged along the horizontal axis. Details of this are also disclosed in pages 126 to 127 of FIGS.

  In the present situation, it is impossible to determine which particle measurement method or apparatus can perform accurate measurement.

David B. Kittelson, Ph.D., Winthrop F. Watts, Jr., Ph.D. and others, “REVIEW OF DIESEL PARTICULATE MATTER SAMPLING METHODS Supplemental Report # 2 AEROSOL DYMAMICS, LABORATORY AND ON-ROAD STUDIES”, [online] July 31, 1998, University of Minnesota, Department of Mechanical Engineering, Center for Diesel Research, Minneapolis, MN, Internet <URL: http://www.me.umn.edu/centers/cdr/reports/EPAreport2. pdf> Martin Mohr, Urs Lehmann, “Comparison Study of Particle Measurement Systems for Future Type Approval Application”, [online], May 2003, EMPA, Research-report No. 202779, Internet <URL: http: //www.empa. ch / plugin / template / empa / * / 20988 / --- / l = 2, PMP-EMPA-Report 202779.pdf>

  In order to solve such a situation, it is necessary to evaluate which measurement method or measurement apparatus is suitable for measuring particles having a small particle diameter. A gas (so-called number concentration standard gas) in which nanoparticles having a particle size of only a certain number concentration exist is required. Here, a method for producing a nanoparticle having a specific particle size in a liquid at a known number concentration has already been established, and is generally sold and available as a so-called “standard particle”. is there.

  However, a method for producing such a number concentration standard gas as described above has not yet been developed, and for this reason, it is impossible to perform calibration of the particle measuring apparatus.

  Therefore, the present invention provides a gas having a known number concentration of nanoparticles having a specific particle size, a number concentration standard gas generating apparatus for generating a so-called number concentration standard gas, and a method for producing the number concentration standard gas. For the purpose.

  The number concentration standard gas generating device according to the present invention sprays a liquid containing standard nanoparticles having a specific particle size of 100 nm or less in a known number concentration, and contains only one of the standard nanoparticles. Alternatively, spraying means for generating droplets floating in the gas without containing, sorting means for selecting only droplets having a specific particle size from the generated droplets, and droplets selected by the sorting means A drying means for drying the liquid and a counting means for counting the number of droplets introduced into the drying means, wherein the standard nanoparticles in the suspended state generate a gas having a predetermined number concentration. To do.

  In addition, the method for producing a number concentration standard gas according to the present invention includes spraying a liquid containing standard nanoparticles having a specific particle size of 100 nm or less in a known number concentration, so that only one standard nanoparticle is obtained. After generating droplets floating in the gas with or without being contained, only the droplets with a specific particle size are selected from the generated droplets, and the selected droplets with a specific particle size The gas is counted and the droplets are dried to produce a gas in which the standard nanoparticles in a floating state are present in a predetermined number concentration.

  According to the number concentration standard gas generating apparatus and the number concentration standard gas manufacturing method configured as described above, it is possible to use an already established particle measurement method as a state in which nanoparticles are present in a droplet. By setting the particle size to a certain size, it is possible to accurately grasp the number of nanoparticles that are difficult to measure at a reliable level.

  That is, in the above, a measurement method in which only droplets having a relatively large specific particle size (for example, a particle size larger than 100 nm) are selected from the sprayed droplets and the number of such droplets has already been established. Used to measure accurately. Therefore, if such selected droplets are collected, the amount corresponding to the total volume of the collected droplets can be determined from the particle size and number of the droplets, and the number concentration of standard nanoparticles is known. The number of standard nanoparticles obtained is known. And if the liquid of a droplet is dried, it will be in the state where the standard nanoparticle contained in this droplet floats in gas. At this time, from a droplet containing only one standard nanoparticle, one standard nanoparticle is released into the gas phase, and a droplet not containing the standard nanoparticle evaporates and disappears.

  By the way, the reason why a plurality of standard nanoparticles are not contained in the droplet is that the plurality of standard nanoparticles are initially present in the droplet even when the plurality of standard nanoparticles are present independently in the droplet. This is because the nanoparticles are fixed and become a single particle having a different particle size from the original standard nanoparticles. In order to obtain droplets containing only one standard nanoparticle or not containing one standard nanoparticle, a commercially available liquid containing standard nanoparticles in a predetermined number concentration is sufficient with water or the like (for example, 1 It has been empirically found that it is necessary to dilute (1,000 to 10,000 times).

  As described above, according to the present invention, it is possible to obtain a gas in which nanoparticles having a specific particle size are present at a known number concentration, so-called number concentration standard gas. And by using this number concentration standard gas, it is possible to calibrate the particle measuring device, and as a result, development of a clean engine that does not generate ultrafine particles and regulation of emission of ultrafine particles are effective. Can be performed.

  Embodiments of a number concentration standard gas generating device and a number concentration standard gas manufacturing method according to the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the number concentration standard gas generating apparatus according to this embodiment is a liquid containing standard nanoparticles P having a specific particle size of 100 nm or less only in a known number concentration (hereinafter, standard liquid). The spray means 1 for spraying W to generate droplets D, D... Floating in the gas with or without only one standard nanoparticle P, and the generated droplets D, D. Sorting means 2 for sorting only droplets d having a specific particle diameter, drying means 4 for drying the droplets d, d... Sorted by the sorting means 2, and liquid introduced into the drying means 4 A number concentration standard gas generating device that includes a counting means 3 for counting the number of droplets d, d..., And generates a gas G in which the standard nanoparticles P, P. .

  The number concentration standard gas generating apparatus having such an overall configuration is divided into two temperature regions consisting of a low temperature region L and a high temperature region H, and the spraying means 1, the sorting means 2 and the counting means 3 up to the low temperature region L. In addition, the drying means 4 is set to a high temperature region H. The low temperature region L is set to a low temperature (for example, normal temperature) to create a saturated state in which the evaporation of the liquid that is the solvent of the standard nanoparticles P, P... Is suppressed, and the high temperature region H promotes the evaporation of the liquid. Set as high as possible.

When using this number concentration standard gas generating apparatus, first, a standard liquid W containing standard nanoparticles P, P... Only with a specific particle size (that is, particle size distribution is monodisperse) at a known number concentration. Prepare. The particle size of the standard nanoparticles P, P ... is the same as the particle size of the standard nanoparticles P, P ..., which will be present in a suspended state in the finally obtained number concentration standard gas G. Just choose. Specifically, for example, a colloidal liquid (hereinafter referred to as a stock solution) containing polystyrene latex particles having a particle size of 20 nm at a number concentration of 3,000 / ml in 15 ml of a solvent such as water is obtained. By diluting with double to 10,000 times of water, a standard liquid W having a number concentration of, for example, about 0.3 to 3 / ml is prepared. As standard nanoparticles P, in addition to polystyrene latex particles, C ₆₀ fullerene molecules having a diameter of 1 nm, dendrimer molecules having a fixed size for each generation of 1 to several nm, diamond particles of 5 nm, and the like are conceivable. .

  Next, the spraying means 1 for spraying the standard liquid W will be described. The spraying means 1 is a device called a nebulizer or an electrospray, for example, and sprays polydisperse droplets D, D... Having a particle size distributed in a range of about 20 to 1000 nm to produce an aerosol. Further, the spraying means 1 can appropriately transport the sprayed droplets D, D... To the sorting means 2 disposed at the subsequent stage, and sheath gas (or carrier gas) S1 that wraps the droplets D, D. The one that can supply is used. As the sheath gas S1, for example, a low-reactivity gas such as nitrogen is used, and the sheath gas S1 is set to a low temperature (for example, normal temperature) in order to suppress the evaporation of the droplets D.

  The sorting means 2 is a so-called DMA device, which classifies the polydisperse droplets D, D... Sprayed by the spray means 1 and sorts only the droplets d, d. Specifically, the particle size of the droplets D sorted by the sorting unit 2 is set to 300 nm in accordance with the performance of the counting unit 3 described later.

  The DMA device as the sorting means 2 will be described in detail. The DMA device is an electrostatic classifier that utilizes the particle size dependence of the electric mobility of charged particles. As shown in FIG. An outer cylinder 22) is provided. The inner cylinder 21 is formed with an introduction hole 23 for introducing the droplets D, D... To be classified into the space between the inner cylinder 21 and the outer cylinder 22 together with the carrier gas C. A slit 24 through which the classified droplets d, d... Pass is formed. In addition, the sheath gas S2 flows in a laminar flow state in the space between the inner cylinder 21 and the outer cylinder 22, and a voltage is applied to the inner cylinder 21.

  According to the DMA device having such a configuration, a droplet having a specific particle size is obtained by balancing the resistance force received by the droplets D, D... From the sheath gas S2 and the Coulomb force acting on the charged droplets D, D. Only d, d... reach the downstream slit 24 from the introduction hole 23. Then, the droplets d, d... Reaching the slit 24 (that is, sorted) are discharged to the outside. The voltage applied to the inner cylinder 21 and the flow rate of the sheath gas S2 are configured to be adjustable. The droplets D, D... Are charged by radiation or the like before classification.

  By the way, when the flow rate of the sheath gas S2 is smaller than the flow rate of the carrier gas C containing droplets, the droplet D having a particle size that cannot originally reach the slit 24 can reach due to molecular diffusion. For this reason, it is preferable that the flow rate of the sheath gas S2 is set to 5 times or more the flow rate of the carrier gas C.

  Returning to FIG. 1, the number of droplets d, d... Sorted and discharged by the sorting means 2 is then counted by the subsequent counting means 3. That is, the counting means 3 is disposed between the sorting means 2 and the drying means 4. The counting means 3 is, for example, a counting device called a particle counter using laser light scattering or the like, and irradiates the laser beam Op1 to the droplets d that sequentially pass through the counting device and scatters by the droplets d. By sequentially detecting the scattered light Op2 to be detected by the sensor 31, the number is measured. In addition, this particle counter can accurately count particles of about 100 nm.

  A drying means 4 is arranged at the subsequent stage of the counting means 3. The drying means 4 is a heating furnace that dries the droplet d, and heats the droplet d to evaporate the liquid constituting the droplet d, so that the standard nano-particle contained in the droplet d is contained. Particles P are released.

  Specifically, the heating furnace has a cylindrical main body, and the droplets d, d... Are ejected from the central part of the base end of the main body, and the sheath gas S3 is supplied from the periphery of the base end. . A heater 41 for heating droplets is provided at the middle portion in the longitudinal direction of the main body so as to wrap the main body, and the dried gas G is discharged from the front end of the main body. Here, as the sheath gas S3, a gas having low reactivity such as nitrogen is used, and the sheath gas S3 is set to a high temperature of about 50 ° C. in order to maintain a high temperature state as described above.

  Further, the main body is applied with a voltage to prevent the droplet d and / or standard nanoparticles P emitted from the droplet d from adhering to the inner wall to realize a state of floating in the gas, The inner wall of the main body functions as a repelling electrode. Specifically, the droplet d and / or the standard nanoparticle P released from the droplet d is in a charged state when the droplet d is sorted by the sorting means 2, and the main body Since a voltage having the same polarity as that of the charged droplet d is applied to the droplet d, the droplet d and / or the standard nanoparticle P emitted from the droplet d repels the inner wall.

  By the way, since the number concentration standard gas G is generated while the droplets are transported in a floating state and the number concentration standard gas G is generated, there is a possibility that the number concentration standard gas generation device may aggregate or adhere to the object. For this reason, each said component (especially the selection means 2, the counting means 3, the drying means 4) is arrange | positioned mutually close, and it is considered so that the loss of the droplet conveyed between components may be suppressed little. .

Next, the principle and method of generating the number concentration standard gas G in which the suspended standard nanoparticles P are present at a predetermined number concentration by the number concentration standard gas generating apparatus having the above-described configuration will be described. For convenience, the case where a stock solution in which standard nanoparticles P having a particle diameter of 20 nm are contained at a number concentration of 3 × 10 ³ particles / ml in 15 ml of water will be described as an example.

  First, the stock solution is diluted with water to prepare a standard liquid W in which the number concentration of standard nanoparticles P is 3 / ml. Next, the standard liquid W is sprayed by the spraying means 1 to generate droplets D, D... Having a particle size of about 20 to 1000 nm. Here, since the standard liquid W is sufficiently diluted, a state in which only one standard nanoparticle P or none is contained in the droplets D, D. . In addition, most or all of the volume of the droplet D is occupied by the liquid, and the shape of the droplet floating in the gas is an ideal spherical shape. The droplets D, D... Sprayed in this way are then introduced into the DMA device as the sorting means 2 and classified, and only the droplets d, d.

  Then, the selected droplets d, d... Are introduced into a heating furnace as the drying means 4. At that time, the number of droplets d, d... Is measured by a particle counter as the counting means 3, and the total amount of the measured droplets d, d. Here, since the droplet d has an ideal spherical shape, the volume of one droplet is accurately calculated from the particle diameter. Therefore, if all of the droplets d, d... Having a constant particle size are introduced into the heating furnace, the amount corresponding to the total volume of the introduced droplets d can be determined from the particle size and number of the droplets d. On the other hand, since the number concentration of standard nanoparticles P contained in the standard liquid W is known, the number of introduced standard nanoparticles P can be known. And if the liquid of the droplet d is dried, the standard nanoparticle P contained in the droplet d will be in a state of floating in the gas. At this time, one standard nanoparticle P is released from the droplet d containing only one standard nanoparticle P into the gas, and the droplet d not containing the standard nanoparticle P evaporates and disappears.

Based on this principle, the spraying of the standard liquid W, the selection, measurement, and drying of the droplets d are successively performed, and the number concentration standard gas G is continuously discharged from the number concentration standard gas generator. Will be. Specifically, by adjusting the spray amount of the standard liquid W, a number concentration standard gas G containing standard nanoparticles P having a number concentration of 1 × 10 ⁴ particles / cm ³ is generated. In order to obtain the number concentration standard gas G having the target number concentration, the dilution ratio of the stock solution, the spray amount of the standard liquid W, the supply amount of the sheath gas S3 of the drying means 4 and the like can be adjusted. In order to obtain the number concentration standard gas G including the standard nanoparticles P having a diameter, a stock solution including the standard nanoparticles P having a target particle diameter may be used.

  By the way, as a method for confirming whether or not the number concentration standard gas G actually contains the standard nanoparticles P for the target number concentration, the number concentration standard gas G is filtered with a filter or the like and collected in the filter. A method is conceivable in which the standard nanoparticles P are counted using a microscope or the like.

  As described above, according to the number concentration standard gas generating apparatus and the number concentration standard gas manufacturing method according to the present embodiment, a gas in which standard nanoparticles P having only a specific particle diameter exist at a known number concentration, so-called A number concentration standard gas G can be obtained. And by using this number concentration standard gas G, it is possible to calibrate the particle measuring device, and as a result, development of a clean engine that does not generate ultrafine particles and regulation of emission of ultrafine particles. It becomes possible to carry out effectively.

  Note that the number concentration standard gas generating device according to the present embodiment may be a dedicated device for producing the number concentration standard gas G, and is integrally incorporated in the particle measuring device, It may be one that can be calibrated periodically.

  The number concentration standard gas generating apparatus and the number concentration standard gas manufacturing method according to the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. .

  For example, in the above-described embodiment, the particle size of the droplets selected by the selection unit has been described as 300 nm. However, the particle size is not limited to such a value, and may be any particle size that can be counted by the counting unit. In other words, it is sufficient that the particle size is such that an established method can be used for accurate counting, and the particle size of the selected droplet is set to about 100 nm, for example. There may be. Thus, the numerical values to be arbitrarily set in the present invention are not limited to those of the above-described embodiment, and can be changed as necessary.

  In the above embodiment, the standard nanoparticles have been described as having only a 20 nm particle size whose theoretical particle size distribution is monodisperse. However, in practice, a certain amount of width is allowed, for example, a particle size of 20 nm. If there is an error, the error may be about ± 1 nm, and if the particle size is 50 nm, the error may be about ± 2 nm. In addition, although it has been described that the particle size of the droplets selected by the selection unit is 300 nm, it is a matter of course that a certain width is allowed.

1 is a schematic view showing a number concentration standard gas generating device according to an embodiment of the present invention. FIG. The figure explaining the selection means which comprises the production | generation apparatus of the number concentration standard gas which concerns on the embodiment is shown. The graph which represented the ratio for which the particle of a specific particle size accounts with respect to the particulate matter contained in exhaust gas by distribution for every particle size is shown. The figure showing that there is variation in number concentration by a particle measuring device or a particle measuring method is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Spraying means, 2 ... Sorting means, 3 ... Counting means, 4 ... Drying means, 21 ... Inner cylinder, 22 ... Outer cylinder, 23 ... Introduction hole, 24 ... Slit, 31 ... Sensor, 41 ... Heater, C ... Carrier Gas, D ... droplet, d ... droplet, G ... number concentration standard gas, H ... high temperature region, L ... low temperature region, Op1 ... laser light, Op2 ... scattered light, P ... standard nanoparticle, S1 ... sheath gas, S2 ... Sheath gas, S3 ... Sheath gas, W ... Standard liquid

Claims (2)

By spraying a liquid containing standard nanoparticles having a specific particle size of 100 nm or less in a known number concentration, droplets floating in a gas with or without only one of the standard nanoparticles Spraying means to be generated;
Sorting means for sorting only droplets having a specific particle size from among the generated droplets;
Drying means for drying the droplets sorted by the sorting means;
Counting means for counting the number of droplets introduced into the drying means,
An apparatus for generating a number concentration standard gas, wherein the standard nanoparticles in a floating state generate a gas having a predetermined number concentration. By spraying a liquid containing standard nanoparticles having a specific particle size of 100 nm or less in a known number concentration, droplets floating in a gas with or without only one of the standard nanoparticles After generating
Select only droplets of a specific particle size from the generated droplets,
By counting the number of droplets of the selected specific particle size and drying the droplets,
A method for producing a number concentration standard gas, comprising producing a gas in which the standard nanoparticles in a floating state are present at a predetermined number concentration.

Images