Particle size detection method 5, laser particle size analysis method to measure particle size

When a laser is used as the light source and the light is monochromatic light of a certain wavelength, the spatial (angle) distribution of diffracted and scattered light energy is only related to the particle size.

Physical properties (e.g. optical, electromagnetic, etc.) And chemical composition, particles of different sizes are very different, so the characteristics of particles vary with their size.

Generally speaking, most of the pollutants emitted into the atmosphere by cities are concentrated in small particle sizes, and some toxic and harmful substances, such as cadmium, lead, nickel, benzopyrene, etc., are concentrated in particles with a particle size of microns; Nature** (including dust, wind, sand, etc.) ).

1.Laser particle size analyzers have a wide measuring range and are suitable for a wide range of applications. It depends not only on the range reported by the instrument, but also on how to detect the scattering of small particles outside the main detector area.

The best way to do this is to check the whole process directly, so as to ensure the consistency of the background deduction. Mixing tests of different methods, and then the computer synthesizes a map, will certainly introduce errors.

2.Typically, a 2MW laser is used as a laser light source. The power is too small, and the light energy of the scattered jujube is low, resulting in low sensitivity; In addition, gas light sources have shorter wavelengths and more stability than solid light sources.

Because the larger the radius of the laser diffraction ring, the weaker the light intensity of the detector, it is easy to cause the signal-to-noise ratio of small particles to decrease and miss detection, so the distribution detection of small particles can reflect the quality of the instrument. The development of the detector has gone through several stages: circular, semicircular and fan-shaped.

3.Use the full Mie theory.

Due to the complexity of Mie optical dispersion theory and the large amount of data processing, some manufacturers have suddenly omitted the optical properties such as refraction and absorption of particles, and adopted the approximate Mie theory, which leads to the limitation of the application range and the increase of the probability of missed detection.

The introduction of laser particle size analysis is as follows:

Laser diffraction began with small-angle scattering, which is why it is also known as Fraunhofer diffraction, (approximately) forward light scattering, and small-angle laser scattering (Lalls).

The range of this technique has now been expanded to include light scattering in a wider range of angles, and in addition to approximate theories such as Frann and Fee diffraction and irregular diffraction, Mie theory is now used by instrument manufacturers as one of the important advantages of their products.

At present, it is widely used in building materials, chemical industry, metallurgy, energy, food, electronics, geology, military industry, aerospace, machinery, universities, laboratories, research institutions, etc.

Michaelis theory. Michaelis theory describes the radiation of uniform spherical particles and their surroundings in a homogeneous, non-absorbing medium, which can be either fully transparent or completely absorbed. Michaelis theory describes light scattering as a resonant phenomenon.

If a beam of light of a particular wavelength encounters a particle, the particle produces electromagnetic vibrations at the same frequency as the emitting source – independent of the wavelength, the diameter of the particle, and the refractive index of the particle and medium.

1.Methods for particle size analysis of conglomerates.

The particle size analysis of conglomerates is mainly carried out in the field, and two methods are generally used: sieve analysis and direct measurement. For the gravel with weak cementation and loose gravel layer, it is screened with a sieve with a pore size of 10mm and 1mm, and the matrix and cement less than 1mm can be brought back to the room for subdivision; If the content of fine gravel of 0 1mm is large and the difference is large, the sieve analysis method should be used for subdivision. Crushed stone above 10mm is generally measured directly with a ruler on site, and then the crushed stone of each particle size is weighed separately and recorded in the particle size analysis table.

In the sampling process, it is necessary to choose a representative sampling site with a sample mass of not less than 25 30 kg, otherwise the error will be considerable. For conglomerates with strong cementation, grain size can be measured on the weathering zone; Or take the sample back to the room, cement it, separate the gravel, and measure the particle size.

2.Methods for particle size analysis of sandstone and siltstone.

The grain size analysis of sandstone and siltstone often uses sieve analysis, sedimentation rate method and thin section method, and the commonly used sedimentation rate method is Azni method, Sabanin method and Robinson method. The sieve analysis method and the sedimentation velocity method are suitable for unconsolidated loose rocks, such as coarse clastic rocks, and generally only the sieve analysis method is used; However, medium-fine clastic rocks tend to contain more silt and clay, so the sedimentation rate method is often used in combination with the sieve method. The thin slice method is mainly used to reinforce hard rock.

In general, the sieving method is suitable for particles larger or larger, and the sedimentation method is suitable for particles smaller than that.

3.Granularity classification.

The Wood Windward Standard is generally used, which is a grading scheme in millimeters. Later, Querubin (1934) proposed a logarithmic transformation (Table 3-1) called Value:

Principles of sedimentology.

where d is the particle diameter.

Table 3-1 Grading Criteria Comparison Table.

Particle size analyzer measurement steps:

1. Turn on the instrument first.

Plug in the power socket and turn on the power switch on the rear panel of the cell with a beep-beep sound to indicate that the instrument is turned on.

2. Wait 30 minutes for the laser to stabilize.

Note! Significant! (All measuring instruments with lasers should be turned on and warmed up for about 30 minutes before taking measurements.) This is to prevent internal temperature imbalances from affecting the measurement results. )

3. Open the software.

For specific operations, please refer to "Software Operation Bad Calling Steps".

4. Prepare samples.

For each type of sample material, there is an optimal range for measuring the sample concentration: if the sample concentration is too low, there may not be enough scattered light for the measurement. If the concentration of the sample is too concentrated, the scattered light of one particle will also be scattered by other particles.

The appropriate sample concentration should be chosen, i.e. the sample exhibits a slight milky appearance or, in more technical terms, the sample yields slight turbidity.

5. Select the sample cell.

Choose the right cell for your sample and measurement type.

6. Inject the prepared sample into the sample cell.

In the status bar, the software prompts you when it is time to insert a sample cell. When and how the cell is inserted depends on the application and the measurement option chosen.

1) When measuring particle size: Note that the polished optical surface of the quartz glass must face the front of the instrument (towards the button). The injection amount is one-third of the sample cell to one-half of the shed branch.

2) When measuring zeta potential: note that the more prominent side of the cell must be facing the front of the instrument (towards the button). After the injection is completed, make sure that the U-shaped tubing is free of air bubbles, close the upper plug tightly, and place the electrode sheet on the sample cell clean and free of water.

7. Take measurements.

Open or create a new survey file. Select Measure Start from the software. Select the desired SOP and select Open. Follow the steps that appear on the screen.

8. Display the measurement window.

When requested, insert the sample cell into the instrument and wait for the temperature to equilibrate. Click Start. That is, the measurement is taken, the results are displayed and saved to the open measurement file.

9. Display the result.

The results can be displayed in two ways. One is the recordview in a measurement file that displays a list of chain sensitive series of measurement records; Second, on the Reports tab, the measurement details of the selected measurement record are displayed.

Measuring principle of particle size analyzer:

This instrument uses the principle of dynamic light scattering and photon correlation spectroscopy technology to determine the particle size according to the speed of the Brownian motion of the particles in the liquid. Small particles have fast Brownian motion, large particles have slow Brownian motion, and the laser irradiates these particles, and the particles of different sizes will cause the scattered light to fluctuate in different speeds.

Photon correlation spectroscopy analyzes the particle size of photons based on their fluctuations in a specific direction. Therefore, this instrument has the characteristics of advanced principle and high precision, so as to ensure the authenticity and validity of the test results; It is an instrument for the determination of nano-excited particle size.

To put it simply, choose the detection method of circular letter, add the sample to the sample cell of the particle size analyzer, and then operate according to the equipment process to obtain the size and distribution of the sample.

Laser particle size analyzer is a kind of physical property testing equipment that measures the particle size and particle size distribution through various types of light hitting the particles. It is usually divided into wet and dry testing.

Wet laser particle size analyzer is a traditional and classic detection method. And what does the wet process often mean? It refers to the sample to be tested in water or alcohol and other common dispersion media mixed and dispersed, with a circulating pump to transport the mixed solution to the detection window for testing, so the detection scope covers solid powder, suspension, emulsion and other substances that are insoluble and do not react to common dispersion media such as water or alcohol.

The dry test is only for the detection of the particle size of loose solid particles. The detection process does not require any dispersion orange agent and solvent, and a silent oil-free air compressor is used, which is powered by air, fully mixed and dispersed by a dispersion device, and the sample is blown to the detection window for analysis and testing.

Reference: What is the difference between wet and dry laser particle size analyzer and how to choose?

The laser particle size analyzer measures the particle size distribution based on the physical phenomenon that the particles can scatter the laser. Due to the good monochromaticity and strong directionality of the laser, a parallel laser beam will shine at an infinite distance in an infinite space without hindrance, and there is little divergence in the propagation process. When the beam is blocked by particles, a portion of the light will be scattered.

The direction of propagation of the scattered light will form an angle with the direction of propagation of the main glory. Scattering theory and results prove that the size of the scattering angle is related to the size of the particle, and the larger the particle, the smaller the angle of the scattered light produced; The smaller the particle, the greater the angle of the scattered light produced.

The laser particle size analyzer is composed of three parts: the optical route, the emission route, the acceptance and the measurement window. The emission part is composed of a light source and a beam processing device, which mainly provides a monochromatic parallel light as illumination light for the instrument. The receiver is the key to the optical structure of the instrument.

The measurement window is mainly to allow the measured sample to pass through the measurement area in a completely dispersed suspension state, so that the instrument can obtain the particle size information of the sample.

The laser beam emitted by the laser is focused, low-pass filtered, and collimated to become a parallel light. When the collimated beam hits the particles within the measurement window, scattering occurs. After the scattered light passes through the Fourier lens, the light at the same scattering angle is focused on the same radius of the detector.

The photoelectric signal output by a detection unit represents the scattered light energy in an angular range (the magnitude is determined by the difference between the inner and outer radii of the detector and the focal length of the lens), and the signal output by each unit constitutes the distribution of scattered light energy. Although the intensity distribution of scattered light is always large in the center and small at the edges, the peak of the measured light energy distribution is generally at a cell between the center and the edge, since the area of the detection unit is always small inside and large outside. When the particle diameter becomes smaller, the distribution range of scattered light becomes larger, and the peak value of light energy distribution also shifts outward.

Therefore, particles of different sizes correspond to different light energy distributions, and conversely, the particle size distribution of the sample can be inferred from the measured light energy distribution.