RU2555353C1 - Device to determine spectrum of size of suspended nanoparticles - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device is used to determine spectrum of size of suspended particles in gases, comprising the following components installed along the analysed gas flow: an inlet nozzle with supply channels; diffusion batteries of meshed type for passage of aerosol particles of certain size; an aggregating device of condenser growth; a counting volume; a vacuum pump; temperature sensors, a heater, a cooler and a microcontroller for control of heating and cooling processes in the aggregating device of condenser growth; an optical system comprising a pulse source of radiation, a lighter and lenses for focusing of optical radiation in the field of counting volume of particle flow and generation of images on a CCD array; an analogue-digital converter and a PC for control of the microcontroller of thermostatting, the vacuum pump and processing of six images of aggregated particles for analysis of the spectrum of their size. The device makes it possible to process simultaneously six images of aggregated particles on a PC, which characterise various size ranges of nanoparticles.

EFFECT: invention makes it possible to reduce time of measurements and to increase their accuracy.

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Description

The invention relates to analytical measuring systems associated with the determination of microimpurities, primarily aerosol and nanoparticles, in various gases and their mixtures, including in the air. It can find application in many fields of science and technology, in particular in solving various environmental problems, in creating ultra-clean production facilities, in controlling the dispersed phase for targeted delivery of drugs to the respiratory system.

A device for analyzing particle images is known (US Pat. US 2007 0273878 A1, G01N 21/00 of November 29, 2007), comprising: a lighting unit, an image capturing unit and an image processing unit. The operation of the device is to illuminate the particles, capture the obtained image and process the obtained images using a threshold device for analyzing the extracted particles and obtaining their morphological features.

The disadvantage of this device is that it does not allow measurements of nanoparticles.

A known method for the study of microobjects (Pat. RU 2154815, G01N 15/02 from 05.20.1998). which consists in the fact that the investigated microobjects are irradiated with a radiation beam, the maximum linear size of the coherence volume of which in the irradiation zone of microobjects does not exceed 30% of the average distance between particles in space. Using an optical system, images of the studied microobjects are formed and, after reading, their geometric parameters are measured at the signal level, which depends on the coherence of the illumination and the aperture angle of the optical imaging system.

The disadvantage of this method is that. that this method is not possible to determine the particle size of the nanometer range.

The methods for measuring the concentration of the dispersed composition of aerosol particles of nanosize are based on the enlargement of particles due to their condensation growth in a medium of supersaturated vapor (for example, water) and measurement of the concentration and size of grown droplets using conventional optical-electronic methods.

The process of vapor condensation on particles of substances suspended in a gas mixture (condensation core) and fog formation begins when a certain supersaturation is reached:

S = (p / p ₀ ) -l,

where p ₀ is the saturated vapor pressure above the flat surface of the condensate; p is the vapor pressure above the drop. In a state of thermodynamic equilibrium between a drop and a gaseous medium, p is defined as the vapor pressure in the gas mixture.

For sufficiently large supersaturations, the relation between the drop radius r and the effective supersaturation S is expressed by the Kelvin equation with Thomson correction for the electric charge of the nucleus:

where σ and ρ _W - surface tension and density of the condensate; k is the Boltzmann constant; T is the gas temperature; m is the mass of the vapor molecule; e is an electric charge.

Using formula (1), it is easy to estimate what supersaturation is necessary to create so that the droplets grow to the boundary size that the optical device can fix.

With sufficiently large supersaturations (S> 3) of water vapor in the air, light air ions (r <10 ^-7 cm, e = 1.6 · 10 ^-19 C) can be the centers of condensation. All nuclei, starting from r <0.1 μm up to the size of ions, are called Aitken nuclei in the literature.

Particles that appear at small supersaturations S <0.1 in air are called cloud condensation nuclei, i.e. nuclei on which droplets of clouds and fogs form.

The first design of condensation nucleus counters was described in 1888 by Aitken and then improved by Scholz in 1932. In these devices, droplets grown in air saturated with water vapor are counted visually after they are sedimented on a glass substrate (Belyaev S.P., Nikiforova N.K., Smirnov V.V. et al. "Optoelectronic Methods for Studying Aerosols", Moscow: Energoizdat, 1981, p. 102).

The disadvantage of the first designs of condensation core counters is the lack of automatic control.

A known method for the analysis of impurities in gases, based on the formation of aerosol particles on individual molecules (AS 188132, G01N 15/00 from 06/23/1961). At the first stage, to enlarge the smallest nuclei, supersaturated steam of some very non-volatile substance, for example dioctylsebacinate, is introduced into the gas. At the second stage, adding supersaturated vapors of a more volatile substance, for example, diisobutyl phthalate, at room temperature, transform the growing condensation nuclei into particles of a sufficiently stable monodisperse aerosol suitable for nephelometric or ultramicroscopic measurements.

The disadvantages of this method are its operational inconvenience. In it, the sequential effect of a supersaturated steam, first showing the substance, then enlarging, was considered obligatory. Accordingly, two devices of the same type are required. In the first device, an auxiliary small gas stream is contacted with a heated developer substance and mixed with a main room-temperature gas stream containing condensation nuclei. In the second device, another auxiliary small stream is in contact with the heated substance of the enlarger and mixed with the main stream coming from the first device with the particles of ultrafine aerosol of the enlarger formed in it.

Another operational disadvantage of this method is that saturated vapors in auxiliary flows, in contact with the diaphragm of the mixers, partially condense on it and oxidize in air. The oxidized condensate is a viscous and sometimes solid substance that gradually clogs the aperture, changing the mode of operation of the method.

To eliminate these drawbacks, various methods and devices for the formation of molecular condensation nuclei (MOX) are known.

A device for creating a metered supersaturation of a vapor of substances in a gas stream (A.S. 1741105 G05D 11/00, B01F 3/02, B01F 15/04 of 06/15/1992), which contains the evaporation and mixing parts connected using a metal capillary tube. In the case of the evaporating part there is an electric heater and a sleeve with a carrier of the evaporated substance, designed to saturate a small gas flow with vapor of the substance at elevated temperature. The mixing part consists of a tube with a nozzle for the main dilution stream with condensation nuclei.

The disadvantage of this device is the design complexity and large weight and size characteristics and power consumption of the corresponding equipment.

A known method for the determination of small impurities in a gas (US Pat. 2253857 G01N 15/00 dated 03/01/2004), which includes the formation of molecular condensation nuclei (MCN) in a gas stream from impurities or with their participation, the evaporation of developing and enlarging MCN substances by dosing heating in gas flows, the formation of aerosol particles and the measurement of their concentration, which determines the concentration of impurities. Heated gas streams with vaporized substances are combined into a common stream, create a supersaturation of a mixture of vapor of substances and form aerosol particles by the joint condensation of mixtures of developing and enlarging substances on the SSC.

The disadvantage of this method is the use as a heater of wire made of gold, platinum or their alloys, as well as high energy consumption. In addition, this method does not allow to determine the size spectrum of condensation nuclei.

A known method of enlargement of condensation nuclei and a device for its implementation (Pat. 2061219, G01N 15/00 of 05/27/1996), in which supersaturated steam of enlarging substance is obtained by passing a stream with nuclei into the gap between two equidistant surfaces with a given temperature difference, one of which (having a higher temperature) is coated with an enlarging substance. The method is implemented using a device containing a chamber for creating a supersaturation, equipped with a cooler, inside of which an evaporator with an electric heater is installed. The camera can be made, for example, in the form of a tube, and the evaporator is cylindrical in shape located along its axis.

The disadvantage of this method is the inability to determine the spectra of condensation nuclei (nanoparticles) spectra of their sizes.

A method for determining the microconcentration of metal carbonites in an air stream (Pat. 2356029 G01N 15/06 from 05/20/2009). which includes the conversion of carbonyl molecules into molecular condensation nuclei, the subsequent manifestation and enlargement of nuclei in supersaturated vapors of developing and enlarging detecting substances in condensation devices, and the nephelometric measurement of light scattering of the resulting aerosol. In this case, the conversion of carbonyl molecules into molecular condensation nuclei is carried out by passing the analyzed stream through the heated part of the tube of the developing condensation device with the developing substance deposited on its inner walls. The manifestation of the nuclei is carried out in a supersaturated pair of the developing substance with the further passage of the stream through the cooled part of the same tube.

The disadvantage of this method is the inability to determine the size spectrum of the measured microconcentrations.

The closest in technical essence to the proposed method is a method of measuring the size spectrum of the nuclei of condensation of aerosol particles and a device for its implementation (Pat. 2340885, G01N 15/02 from 10.26.2006), including the transmission of gas (or gas mixture) containing the analyzed particles, through grid-type diffusion batteries, introducing them into supersaturated vapors of a low volatile coarsening substance, vapor condensation on the nuclei of particles with the formation of an aerosol, the concentration of which is determined by an optical counter. The operation of a Model 2702 diffusion aerosol spectrometer manufactured by AeroNanoTech LLC (Moscow) is also based on this method.

The disadvantage of this method and the spectrometer based on it is that the calculation of the particle size spectrum is carried out indirectly using the gamma distribution and solving a complex system of nonlinear algebraic equations, since the analysis of the size spectrum of aggregated aerosol particles is performed by sequentially measuring particle breakthroughs through five diffusion batteries mesh type and battery-free channel (zero channel).

The technical result that can be obtained by carrying out the invention is to reduce the measurement time and increase their accuracy.

This result is achieved by the fact that the device for determining the size spectrum of suspended nanoparticles consists in passing a gas (gas mixture) containing the analyzed particles through diffusion batteries of a mesh type, introducing them into supersaturated vapors of a low volatile enlarging substance, illuminating the particle flux with a light beam and recording light parameters signals generated by enlarged particles during their passage through the selected region of the stream. To improve the accuracy of determining the size spectrum, the main stream is divided into six parallel streams, five of which are passed through five diffusion batteries with different slipthroughs, and one directly, then these flows pass through six condensation growth devices and then enter the field of view of the CCD, and six areas of images of enlarged particle flows are transmitted to a computer for analysis of their size spectrum.

Figure 1 presents a block diagram of a device. Figure 2 shows the design of the device of condensation growth. Figure 3 shows the design of one channel of the condensation growth device.

The proposed device of figure 1 contains a pulsed radiation source 1. The optical system of the illuminator 2, the optical imaging system of micro-objects, consisting of lenses 3 and 8 and focusing the optical radiation in the region of the counted volume of particle flow 7, CCD matrix 9, analog-to-digital converter 10 , computer 11. The device also contains an inlet nozzle with feed channels 4, diffusion mesh batteries 5, condensation growth devices 6, a vacuum pump (blower) 12, temperature sensors 13 and 14, heating spruce (nichrome wire) 15 and a cooler (Peltier elements) 16, 17 thermostatic control microcontroller.

The optical system of illuminator 2 includes a lens system that implements, for example, any of the known methods for illuminating microobjects (Keller illumination, dark and bright field methods, critical illumination, etc.).

The device operates as follows. The analyzed flow of air or other gas containing aerosol particles through an inlet nozzle with supply channels 4 is passed through five diffusion batteries 5.1-5.5, which are a series of grids passing aerosol particles above a certain size. In order to determine the concentration of particles passing through diffusion batteries, they must be enlarged to a size at which they can be detected by a CCD matrix in a countable volume of 7. This is achieved by condensation of the dibutyl phthalate vapor on the particle nuclei with the formation of an aerosol in the enlarging device 6, consisting of enlargement devices for six channels 6.1-6.6 and an additional enlargement device 6.0 in channel 6.1 for the possibility of enlargement of molecular size nanoparticles.

The enlargement takes place in each channel 6.0-6.6 by heating the upper plane with heater 15 (nichrome wiring) and cooling the lower plane with cooler 16 (Peltier elements). The control of the heating and cooling processes is provided by the thermostat control microcontroller 17, information on the temperature of which comes from temperature sensors 13 and 14.

Next, six enlarged particle fluxes enter the CCD control area of matrix 9, which is formed by an optical system containing a pulsed radiation source 1, illuminator 2, lenses 3 and 8, focusing optical radiation in the region of the counted volume of particle flow 7. From the CCD image enters the analog-to-digital Converter 10 and then to the computer 11. The computer digitally processes the six areas obtained, characterizing the five transmission channels sorted by diffusion batteries and direct (through the zero battery) enlarged particles in order to determine the size spectrum of nanoparticles. The computer also controls the temperature control microcontroller 17 and the vacuum pump 12.

Figure 2 shows the design of the six channels of the condensation growth device 6.0-6.6.

Figure 3 shows the design of one channel of the condensation growth device, which contains a heater 15, a cooler 16, as well as an evaporator 18, impregnated with a coarsening substance (dibutyl phthalate).

Thus, the considered device, in contrast to the known ones, allows processing on a computer simultaneously six images of enlarged particles characterizing different size ranges of nanoparticles.

Claims (1)

A device for determining the size spectrum of suspended nanoparticles in gases, comprising an inlet nozzle with supply channels located along the analyzed gas stream; mesh-type diffusion batteries for passing aerosol particles of a certain size; condenser growth enlarging device; counting volume; Vacuum pump; temperature sensors, heater, cooler and microcontroller for controlling heating and cooling processes in a condenser growth enlarging device; an optical system including a pulsed radiation source, a illuminator, and lenses for focusing optical radiation in the region of the counted volume of the particle stream and forming images on a CCD; an analog-to-digital converter and a computer for controlling the thermostat microcontroller, a vacuum pump and processing six images of enlarged particles for analyzing the spectrum of their sizes.

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