Basic concepts and basic knowledge of particle size testing
First, the basic concepts and basic knowledge of the particle size test Q & A
1. What is granules?
A particle is a tiny object having a certain size and shape and is a basic unit constituting a powder. It is small in macroscopic, but the microscopic contains a large number of molecules and atoms.
2. What is the granularity?
The size of the particles is referred to as the particle size of the particles.
3. What is the granularity distribution?
A certain method reflects that a series of particles of different particle sizes account for the percentage of the total powder, respectively, called the particle size distribution.
4. How is the representation of the particle size distribution?
1) Tabular method: A representation of the percentage of certain particle sizes given by a list. There are usually interval distributions and cumulative distributions.
2) Graphic method: A method of expressing a particle size distribution by means of a histogram and a curve.
3) Function method: A method for representing a granularity distribution by a function. Commonly there are RR distribution, normal distribution and so on.
5. What is the particle size?
The particle size is the diameter of the particles, typically in microns.
6. What is the equivalent particle size?
The equivalent particle size means that when a physical property of a particle is the same as or similar to a homogenous spherical particle, we use the diameter of the spherical particle to represent the diameter of the actual particle. According to different measurement methods, the equivalent particle size can be specifically divided into the following types:
1) Equivalent volume diameter: the diameter of a homogenous spherical particle having the same volume as the measured particle. The particle size measured by the laser method is generally considered to be the equivalent volume diameter.
2) Equivalent weighted particle size: the diameter of a homogenous spherical particle having the same sedimentation velocity as the measured particle. The particle size measured by gravity sedimentation method and centrifugal sedimentation method is equivalent sedimentation velocity, also called Stokes diameter.
3) Equivalent resistance diameter: the diameter of a homogenous spherical particle having the same resistance as the measured particle under certain conditions. The particle size measured by the Coulter method is the equivalent resistance particle size.
4) Equivalent projected area diameter: the diameter of the spherical particles having the same projected area as the measured particles. The particle size measured by the image method is the equivalent projected area diameter.
7. Why use the concept of equivalent particle size?
Since the shape of the actual particles is generally non-spherical, it is difficult to directly represent the size of the particle size, and the diameter is the simplest one to describe the size of a geometry, so the concept of equivalent particle size is employed.
8. What is D50?
D50 refers to the particle diameter value corresponding to the cumulative distribution percentage reaching 50%. It is one of the important indicators reflecting the particle size characteristics of the powder. D50 is also known as the median diameter or median particle size. If a sample has a D50 = 5 μm, it means that among the particles of all the particle diameters constituting the sample, particles larger than 5 μm account for 50%, and particles smaller than 5 μm also account for 50%.
9. What is the average diameter?
The average diameter is an amount that reflects the average particle size of the powder obtained by weighted averaging of the particle size distribution. Specifically, there are a weight average diameter, a volume average diameter, an area average diameter, and an average number of diameters.
10. What are the common methods of particle size testing?
Commonly used particle size test methods include sieving method, microscope (image) method, gravity sedimentation method, centrifugal sedimentation method, Coulter (resistance) method, laser diffraction/scattering method, electron microscopy method, ultrasonic method, gas permeable method and the like.
11. What are the advantages and disadvantages of each common particle size test method?
1) Screening method: advantages: simple, intuitive, low equipment cost, commonly used for samples larger than 40μm. Disadvantages: Can not be used for fine samples of 40μm; the results are greatly affected by human factors and mesh deformation.
2) Microscopy: Advantages: Simple, intuitive, and morphological analysis. Disadvantages: slow speed, poor representativeness, unable to measure ultrafine particles.
3) Settlement method (including gravity sedimentation and centrifugal sedimentation): Advantages: easy operation, continuous operation of the instrument, low price, accuracy and repeatability
Ok, the test range is large. Disadvantages: Long test time.
4) Kurt method: Advantages: easy to operate, can measure the total number of particles, the equivalent concept is clear, the speed is fast, and the accuracy is good. Disadvantages: the test range is small,
The pores are easily blocked by particles and the medium should have strict electrical conductivity.
5) Laser method: advantages: easy operation, fast test speed, large test range, good repeatability and accuracy, and can be used for on-line measurement and dry measurement.
Disadvantages: The result is greatly affected by the distribution model, and the instrument cost is higher.
6) Electron microscopy: Advantages: Suitable for testing ultrafine particles or even nanoparticles with high resolution. Disadvantages: few samples, poor representativeness, and expensive instruments.
7) Ultrasonic method: Advantages: Direct measurement of high concentration slurry. Disadvantages: lower resolution.
8) Breathing method: Advantages: The instrument price is low, and the sample material is not dispersed, and the magnetic material powder can be measured. Disadvantages: Only the average particle size value can be obtained, and the particle size distribution cannot be measured.
12. What is the frequency distribution and cumulative distribution?
Since the powder is usually composed of a large number of particles of different sizes, it is necessary to divide into a plurality of particle size intervals when performing the particle size test. A series of percentages of the relative content of particles within each particle size interval is referred to as a frequency distribution; a series of percentages less than the relative content of a particle size is referred to as a cumulative distribution. The cumulative distribution is obtained by accumulating the frequency distribution.
13. What is repetitive?
The relative error of the results of multiple measurements of the same sample is called repeatability. Repeatability is the main indicator for measuring the pros and cons of particle size instruments and particle size test methods.
14. What is the authenticity of the granularity test?
Since the actual particles are mostly not spherical, it is impossible to accurately express the size of an actual particle with a numerical value. In addition, different standards and instruments of different manufacturers have different standards, so often the same sample will get several different measurements. The result of the situation. Although the main reason for these different test results is due to the complexity of the shape of the particles themselves, the test results can not be infinitely bound and should be within a reasonable range. The requirement that the difference in the results of such different instruments should be within a reasonable range is called the authenticity of the particle size test. There is no uniform quantitative standard for the authenticity of particle size testing, and there are only some relative qualitative basis. For example, the sample before pulverization should be coarser than that after pulverization; the pulverization time should be shorter than the pulverization time; the grading should be coarser than the grading; the test results for the spherical particles should be consistent.
15. Principle of Particle Size Testing of Settlement Method - Beer's Law:
According to Stokes' law, as long as the sedimentation velocity of the particles is measured, the particle size of the particles can be obtained. In the actual measurement process, it is very difficult to directly measure the sedimentation velocity of the particles. Therefore, in the particle size test of the sedimentation method, the rate of change of the light intensity through the suspension is often used to indirectly reflect the sedimentation velocity of the particles. So, what is the relationship between the rate of change of light intensity and the particle size? Beer's law gives the quantitative relationship between light intensity and particle size at a certain time: so that we can obtain the change rate of light intensity by testing the light intensity at a certain moment, and then the particle size distribution can be obtained by computer processing.
16. Principle of laser particle size testing:
The laser beam emitted by the laser is filtered, expanded, and quasi-valued into a beam of parallel light. When the parallel beam is not irradiated to the particle, the beam passes through the lens and then converges to the focus. As shown in the figure below:
When the particles are evenly placed in a parallel beam in a specific way, the laser will diffract and scatter, and a portion of the light will diffuse outward at an angle to the optical axis. Both theory and practice have proved that the scattering angle of scattered light caused by large particles is small, and the smaller the particles, the larger the scattering angle of scattered light. These different angles of scattered light will pass through the Fourier lens and will form a series of halos on the focal plane. The alternating light and dark spots consisting of these halos are called Airy patches. Airy contains a wealth of granular information. It is simply understood that a halo having a large radius corresponds to a particle having a smaller particle diameter, and a halo having a smaller radius corresponds to a particle having a larger particle diameter; the light energy of the halo at a different radius includes information on the content of the particle of the particle diameter. In this way, we install a series of light electric receivers on the focal plane, convert these optical signals scattered by particles of different particle sizes into electrical signals, and transmit them to a computer, and then use the Mie scattering theory to carry out these signals through a computer. Mathematical processing, you can get the particle size distribution.
17 Why use a laser as a light source?
The laser is a light source with good collimation and monochromaticity, which gives a clear scattering spectrum distribution.
18. What is the difference between Mie scattering and Fran and Fr. diffraction?
The Mie theory can more accurately reflect the scattering law of particles of different particle sizes, so that the lower limit of the laser particle size analyzer is smaller and the result is more accurate. The Fran and Foll diffraction theory is an approximation of the Mie theory, and the error on fine particles is large. Baxter's laser particle size analyzers have now adopted full-scale Mie scattering theory.
19. Basic methods for sample dispersion:
In order to keep the particles in a monomer state, the sample is subjected to dispersion treatment before the particle size test. Dispersion methods include wetting, stirring, ultrasonic vibration, dispersing agents, etc., and sometimes these methods are often used at the same time.
20. What are the requirements for media for particle size testing?
Particle size testing is usually carried out by placing the sample in a liquid to make a suspension. The liquid used at this time is called a medium. The medium for particle size testing usually has the following requirements: 1) pure; 2) no physical or chemical reaction with the particles; 3) good affinity with the particles, ie good wetting on the surface of the particles; 4) making the particles Has a suitable sedimentation state.
21. What are the commonly used media?
The most commonly used liquid medium for particle size testing is water. In addition, commonly used media are water and glycerin mixtures, ethanol and glycerin mixtures, ethanol, gasoline, kerosene, and the like.
22 What is a dispersant?
Dispersant refers to a substance that is added to a medium to cause a significant reduction in the surface tension of the medium to provide good wetting of the surface of the particles.
23. Usage and amount of dispersant.
The dispersant should be mixed with water in a certain ratio and completely dissolved before testing. The ratio of dispersant to water is between 0.2% and 0.5%.
24. Do you need to add a dispersant when using an organic solvent (ethanol, etc.) as a medium? Why?
Most organic solvents are used as media. 24. What are the reasons for the "coagulation" of particles?
Particle "coagulation" refers to the phenomenon in which a plurality of particles adhere together to become "agglomerates". The main reason for "coagulation" is the result of the interaction of the particles by the charge, water, van der Waals force, etc. carried by the particles. The finer the particles, the greater the surface energy and the more opportunities for "coagulation".
25. How to check the dispersion effect?
1) Microscopy: See if there is a "coagulation" phenomenon.
2) Measurement method: Take two samples after different dispersion processes for measurement. If the values ​​of the two tests are stable, the sample has been well dispersed.
26 Requirements for dry powder sampling:
1) When sampling from the workshop, take more samples from the stream.
2) When scooping the sample, the sample should be stirred evenly and then sampled at multiple points (to four small points).
27. What are the requirements for suspension sampling?
1) Stir well.
2) Extract from the middle of the liquid to the bottom of the vessel.
1. What is granules?
A particle is a tiny object having a certain size and shape and is a basic unit constituting a powder. It is small in macroscopic, but the microscopic contains a large number of molecules and atoms.
2. What is the granularity?
The size of the particles is referred to as the particle size of the particles.
3. What is the granularity distribution?
A certain method reflects that a series of particles of different particle sizes account for the percentage of the total powder, respectively, called the particle size distribution.
4. How is the representation of the particle size distribution?
1) Tabular method: A representation of the percentage of certain particle sizes given by a list. There are usually interval distributions and cumulative distributions.
2) Graphic method: A method of expressing a particle size distribution by means of a histogram and a curve.
3) Function method: A method for representing a granularity distribution by a function. Commonly there are RR distribution, normal distribution and so on.
5. What is the particle size?
The particle size is the diameter of the particles, typically in microns.
6. What is the equivalent particle size?
The equivalent particle size means that when a physical property of a particle is the same as or similar to a homogenous spherical particle, we use the diameter of the spherical particle to represent the diameter of the actual particle. According to different measurement methods, the equivalent particle size can be specifically divided into the following types:
1) Equivalent volume diameter: the diameter of a homogenous spherical particle having the same volume as the measured particle. The particle size measured by the laser method is generally considered to be the equivalent volume diameter.
2) Equivalent weighted particle size: the diameter of a homogenous spherical particle having the same sedimentation velocity as the measured particle. The particle size measured by gravity sedimentation method and centrifugal sedimentation method is equivalent sedimentation velocity, also called Stokes diameter.
3) Equivalent resistance diameter: the diameter of a homogenous spherical particle having the same resistance as the measured particle under certain conditions. The particle size measured by the Coulter method is the equivalent resistance particle size.
4) Equivalent projected area diameter: the diameter of the spherical particles having the same projected area as the measured particles. The particle size measured by the image method is the equivalent projected area diameter.
7. Why use the concept of equivalent particle size?
Since the shape of the actual particles is generally non-spherical, it is difficult to directly represent the size of the particle size, and the diameter is the simplest one to describe the size of a geometry, so the concept of equivalent particle size is employed.
8. What is D50?
D50 refers to the particle diameter value corresponding to the cumulative distribution percentage reaching 50%. It is one of the important indicators reflecting the particle size characteristics of the powder. D50 is also known as the median diameter or median particle size. If a sample has a D50 = 5 μm, it means that among the particles of all the particle diameters constituting the sample, particles larger than 5 μm account for 50%, and particles smaller than 5 μm also account for 50%.
9. What is the average diameter?
The average diameter is an amount that reflects the average particle size of the powder obtained by weighted averaging of the particle size distribution. Specifically, there are a weight average diameter, a volume average diameter, an area average diameter, and an average number of diameters.
10. What are the common methods of particle size testing?
Commonly used particle size test methods include sieving method, microscope (image) method, gravity sedimentation method, centrifugal sedimentation method, Coulter (resistance) method, laser diffraction/scattering method, electron microscopy method, ultrasonic method, gas permeable method and the like.
11. What are the advantages and disadvantages of each common particle size test method?
1) Screening method: advantages: simple, intuitive, low equipment cost, commonly used for samples larger than 40μm. Disadvantages: Can not be used for fine samples of 40μm; the results are greatly affected by human factors and mesh deformation.
2) Microscopy: Advantages: Simple, intuitive, and morphological analysis. Disadvantages: slow speed, poor representativeness, unable to measure ultrafine particles.
3) Settlement method (including gravity sedimentation and centrifugal sedimentation): Advantages: easy operation, continuous operation of the instrument, low price, accuracy and repeatability
Ok, the test range is large. Disadvantages: Long test time.
4) Kurt method: Advantages: easy to operate, can measure the total number of particles, the equivalent concept is clear, the speed is fast, and the accuracy is good. Disadvantages: the test range is small,
The pores are easily blocked by particles and the medium should have strict electrical conductivity.
5) Laser method: advantages: easy operation, fast test speed, large test range, good repeatability and accuracy, and can be used for on-line measurement and dry measurement.
Disadvantages: The result is greatly affected by the distribution model, and the instrument cost is higher.
6) Electron microscopy: Advantages: Suitable for testing ultrafine particles or even nanoparticles with high resolution. Disadvantages: few samples, poor representativeness, and expensive instruments.
7) Ultrasonic method: Advantages: Direct measurement of high concentration slurry. Disadvantages: lower resolution.
8) Breathing method: Advantages: The instrument price is low, and the sample material is not dispersed, and the magnetic material powder can be measured. Disadvantages: Only the average particle size value can be obtained, and the particle size distribution cannot be measured.
12. What is the frequency distribution and cumulative distribution?
Since the powder is usually composed of a large number of particles of different sizes, it is necessary to divide into a plurality of particle size intervals when performing the particle size test. A series of percentages of the relative content of particles within each particle size interval is referred to as a frequency distribution; a series of percentages less than the relative content of a particle size is referred to as a cumulative distribution. The cumulative distribution is obtained by accumulating the frequency distribution.
13. What is repetitive?
The relative error of the results of multiple measurements of the same sample is called repeatability. Repeatability is the main indicator for measuring the pros and cons of particle size instruments and particle size test methods.
14. What is the authenticity of the granularity test?
Since the actual particles are mostly not spherical, it is impossible to accurately express the size of an actual particle with a numerical value. In addition, different standards and instruments of different manufacturers have different standards, so often the same sample will get several different measurements. The result of the situation. Although the main reason for these different test results is due to the complexity of the shape of the particles themselves, the test results can not be infinitely bound and should be within a reasonable range. The requirement that the difference in the results of such different instruments should be within a reasonable range is called the authenticity of the particle size test. There is no uniform quantitative standard for the authenticity of particle size testing, and there are only some relative qualitative basis. For example, the sample before pulverization should be coarser than that after pulverization; the pulverization time should be shorter than the pulverization time; the grading should be coarser than the grading; the test results for the spherical particles should be consistent.
15. Principle of Particle Size Testing of Settlement Method - Beer's Law:
According to Stokes' law, as long as the sedimentation velocity of the particles is measured, the particle size of the particles can be obtained. In the actual measurement process, it is very difficult to directly measure the sedimentation velocity of the particles. Therefore, in the particle size test of the sedimentation method, the rate of change of the light intensity through the suspension is often used to indirectly reflect the sedimentation velocity of the particles. So, what is the relationship between the rate of change of light intensity and the particle size? Beer's law gives the quantitative relationship between light intensity and particle size at a certain time: so that we can obtain the change rate of light intensity by testing the light intensity at a certain moment, and then the particle size distribution can be obtained by computer processing.
16. Principle of laser particle size testing:
The laser beam emitted by the laser is filtered, expanded, and quasi-valued into a beam of parallel light. When the parallel beam is not irradiated to the particle, the beam passes through the lens and then converges to the focus. As shown in the figure below:
When the particles are evenly placed in a parallel beam in a specific way, the laser will diffract and scatter, and a portion of the light will diffuse outward at an angle to the optical axis. Both theory and practice have proved that the scattering angle of scattered light caused by large particles is small, and the smaller the particles, the larger the scattering angle of scattered light. These different angles of scattered light will pass through the Fourier lens and will form a series of halos on the focal plane. The alternating light and dark spots consisting of these halos are called Airy patches. Airy contains a wealth of granular information. It is simply understood that a halo having a large radius corresponds to a particle having a smaller particle diameter, and a halo having a smaller radius corresponds to a particle having a larger particle diameter; the light energy of the halo at a different radius includes information on the content of the particle of the particle diameter. In this way, we install a series of light electric receivers on the focal plane, convert these optical signals scattered by particles of different particle sizes into electrical signals, and transmit them to a computer, and then use the Mie scattering theory to carry out these signals through a computer. Mathematical processing, you can get the particle size distribution.
17 Why use a laser as a light source?
The laser is a light source with good collimation and monochromaticity, which gives a clear scattering spectrum distribution.
18. What is the difference between Mie scattering and Fran and Fr. diffraction?
The Mie theory can more accurately reflect the scattering law of particles of different particle sizes, so that the lower limit of the laser particle size analyzer is smaller and the result is more accurate. The Fran and Foll diffraction theory is an approximation of the Mie theory, and the error on fine particles is large. Baxter's laser particle size analyzers have now adopted full-scale Mie scattering theory.
19. Basic methods for sample dispersion:
In order to keep the particles in a monomer state, the sample is subjected to dispersion treatment before the particle size test. Dispersion methods include wetting, stirring, ultrasonic vibration, dispersing agents, etc., and sometimes these methods are often used at the same time.
20. What are the requirements for media for particle size testing?
Particle size testing is usually carried out by placing the sample in a liquid to make a suspension. The liquid used at this time is called a medium. The medium for particle size testing usually has the following requirements: 1) pure; 2) no physical or chemical reaction with the particles; 3) good affinity with the particles, ie good wetting on the surface of the particles; 4) making the particles Has a suitable sedimentation state.
21. What are the commonly used media?
The most commonly used liquid medium for particle size testing is water. In addition, commonly used media are water and glycerin mixtures, ethanol and glycerin mixtures, ethanol, gasoline, kerosene, and the like.
22 What is a dispersant?
Dispersant refers to a substance that is added to a medium to cause a significant reduction in the surface tension of the medium to provide good wetting of the surface of the particles.
23. Usage and amount of dispersant.
The dispersant should be mixed with water in a certain ratio and completely dissolved before testing. The ratio of dispersant to water is between 0.2% and 0.5%.
24. Do you need to add a dispersant when using an organic solvent (ethanol, etc.) as a medium? Why?
Most organic solvents are used as media. 24. What are the reasons for the "coagulation" of particles?
Particle "coagulation" refers to the phenomenon in which a plurality of particles adhere together to become "agglomerates". The main reason for "coagulation" is the result of the interaction of the particles by the charge, water, van der Waals force, etc. carried by the particles. The finer the particles, the greater the surface energy and the more opportunities for "coagulation".
25. How to check the dispersion effect?
1) Microscopy: See if there is a "coagulation" phenomenon.
2) Measurement method: Take two samples after different dispersion processes for measurement. If the values ​​of the two tests are stable, the sample has been well dispersed.
26 Requirements for dry powder sampling:
1) When sampling from the workshop, take more samples from the stream.
2) When scooping the sample, the sample should be stirred evenly and then sampled at multiple points (to four small points).
27. What are the requirements for suspension sampling?
1) Stir well.
2) Extract from the middle of the liquid to the bottom of the vessel.
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