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Yuan Lei Small Classroom | Powder Particle Size Detection Method and Selection Principle

Release time:

2024-01-29 09:35

 

Yuan Lei Small Classroom | Powder Particle Size Detection Method and Selection Principle

 

Particle size and distribution are the most concerned indicators of powder, and these data need to be obtained by various particle size detection methods, so it is very important to objectively and truly reflect the particle size distribution of powder.

 

1

Commonly used powder particle size detection methods

 

(1) Screening

① Wire mesh screen
Basic principle: through a set of sieve frame size has a certain proportion, sieve hole width and sieve wire diameter are manufactured according to the standard sieve group for powder screening, weighing each particle size, particle size distribution and weight cumulative particle size distribution.
Measurement range: 38-7950μm.
Features: The method is simple and fast, and the average particle size and particle size distribution can be obtained. It is divided into two kinds of sieve analysis methods: dry method and wet method, and wet method for fine particles and viscous materials.
② Electrodeposition screen
Basic principle: The material is graded by the electroformed microporous sieve.
Determination range: 5-56 μm.
Features: In recent years, a new type of sieve analysis instrument used in engineering technology.

 

(2) Gravity settlement
① Pipette method
Basic principle: the sample particles dispersed in the settling medium, the settling velocity is a function of the particle size, and the particle size and particle size distribution are determined by measuring the concentration change of the dispersion due to the settling of the particles.
Determination range: 1~100 μm.
Features: The instrument is cheap, the method is simple, and the Anderson liquid tube method is widely used; the disadvantage is that the measurement time is long, and the workload of analysis and calculation is large.
② Grazometer method
Basic principle: The particle size distribution is not determined by using a hydrometer to show the change of the specific gravity of the suspension with time at a certain position.
Determination range: 1~100 μm.
Features: The instrument is cheap and the method is simple, but the workload of the determination process is large.
③ Turbidity method
Basic principle: the use of photometry or X-ray transmission method for the determination of dispersion concentration caused by turbidity changes, determination of sample size and particle size distribution.
Determination range: 0.1~100 μm.
Features: Automatic determination, data can be obtained without processing the distribution curve, can be used for online particle size analysis.
④ Balance method
Rationale: Particle size and particle size distribution are determined by measuring the cumulative weight of particles that have settled.
Determination range: 0.1~150 μm.
Features: automatic measurement and automatic recording, but the instrument is more expensive, the determination of small particles error is larger.

 

(3) Centrifugal sedimentation
Basic principle: in the centrifugal force field, particle sedimentation also obeys Stokes law, using a circular centrifuge to make particles settle and determine the concentration change of the dispersion; Or make the sample in the air medium centrifugal force field classification, so as to obtain the particle size and particle size distribution.
Determination range: 0.01 ~ 10μm.
Features: The determination speed is fast, is one of the basic particle size determination method of ultrafine powder particles, particle size and particle size distribution can be obtained, is one of the more advanced determination methods, widely used.

 

(4) Coulter Counter
Basic principle: When the particles suspended in the electrolyte pass through a small hole, the liquid resistance changes due to the discharge of a part of the electrolyte. The change is a function of the particle size, and the electronic instrument automatically records the particle size distribution.
Determination range: 0.4~200 μm.
Features: fast speed, high precision, good statistics, fully automated, widely used in recent years, can get particle size and particle size distribution.

 

(5) Laser particle size analyzer
Basic principle: According to the principle of Fraunhofer diffraction, the particle size and particle size distribution are determined.
Determination range: 0.05~3000 μm.
Features: High degree of automation, simple operation, fast determination speed, good repeatability, can be used for online particle size analysis.

 

(6) Microscope
① Optical microscope
The sample is dispersed in a certain dispersion to prepare a sample, the particle image is measured, and the measured particles are classified according to size, and the particle size distribution with the number of particles as its quasi-size can be obtained.
Determination range: 1~100 μm.
Features: intuitive, observable particle shape, but the accuracy of the analysis by the operator's subjective factors.
Scanning and transmission electron microscopy
Basic principle: Similar to the optical microscope method, an electron beam is used instead of a light source, and a magnet is used instead of a glass mirror. The particles are shown in microscopic photographs.
Determination range: 0.001~100 μm.
Features: The basic method for determining the distribution of submicron particles and the beginning of particles is widely used in scientific research. The instrument is more expensive and requires special operation.

 

(7) specific surface area measuring instrument
① Through the law
Basic principle: the sample is compacted, by measuring the resistance of the air wave through the sample, the specific surface area of the sample is calculated by the theory of Koeney-Carman, and the shape coefficient is introduced, which can be converted into the average particle size.
Determination range: 0.01~100 μm.
Features: The instrument is simple, rapid determination, good reproducibility, but can not determine the particle size distribution data. In addition, the sample must be compacted during the measurement.
② BET method
Basic principle: According to the BET adsorption equation, the specific surface area is calculated by the measured gas adsorption amount, and the shape coefficient is introduced, which can be converted into the average particle size.
Determination range: 0.003 ~ 3μm.

Features: This is a commonly used specific surface area measurement method, with good reproducibility and high precision, but the data processing is more complicated.

 

2

Selection principle of powder particle size detection method

 

Due to the different physical basis of various particle size determination methods,The physical meaning of particle size and particle size and particle size distribution of the same batch of samples obtained by different measurement methods or measuring instruments are also different..

 

The statistical diameter is obtained by microscope, Coulter counter, laser particle size analyzer, etc.; the equivalent diameter (I. e. equal to the diameter of a sphere with the same final sedimentation velocity) is obtained by the sedimentation method; and the specific surface area diameter is obtained by the permeation method and the adsorption method.

 

Modern laser particle size analyzers, Coulter counters, image analyzers and various sedimentation particle size analyzers based on the Otox principle can not only determine the particle size distribution of powders, but also automatically process the data and print out the particle size distribution table and d.25、d50、d75、d90、d97Such as characteristic data, but also to draw histograms, frequency distribution maps and cumulative particle size characteristic curves.

 

When selecting the determination method, it is necessary to comprehensively consider the particle size distribution range of the material, the purpose of the determination, the required accuracy and characteristic particle size distribution data, and the nature of the material.

 

In the particle size determination of ultrafine powders, the pre-dispersion of the sample has a significant impact on the measurement results.. No matter what method or instrument is used for the determination, the determination result may be accurate only if the particles are well dispersed.

Methods, determination, particle size, distribution, particles, range, characteristics, basic principles, samples

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