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Particle Size Distribution Of Diamond Powder

May 12,2023

Artificial diamond micropowder is mainly used in the grinding and polishing processes of workpiece precision machining. Users often require the lowest diamond concentration, the fastest cutting speed, to obtain the best surface smoothness, geometric shape of the workpiece, and the smallest possible surface micro damage. To achieve such usage requirements, it is not possible to do so without suitable micropowder. Therefore, the following indicators must be strictly controlled: particle size distribution, particle shape, impurity content, diamond strength, etc. Today, let’s introduce the particle size distribution and detection method of diamond powder.

Diamond powder particle size
The diameter of diamond micro powder refers to the diameter of the micro powder particles, which is a numerical value that measures the size of the particles. For regular spherical particles, particle size is the diameter of the sphere. However, diamond micropowder particles are generally not regular spheres, but irregularly shaped, such as rod-shaped, needle shaped, etc. Therefore, it is difficult to use a numerical value to represent the size of diamond micropowder particles, thus introducing the concept of equivalent particle size to represent the particle size of diamond micropowder particles. When a physical property of a particle is the same or similar to that of a homogeneous spherical particle, we use the diameter of the spherical particle to represent its diameter, which is the equivalent particle size of the particle. There are several types of equivalent particle sizes: the equivalent projected area particle size is the diameter of a spherical particle with the same projected area as the actual particle, and the particle size measured by the image method is the equivalent projected area diameter; The equivalent volume particle size is the diameter of a sphere that is the same as the actual particle volume, and it is generally believed that the diameter measured by the laser method is the equivalent volume particle size.

Particle size distribution of diamond powder
The particle size distribution of diamond micro powder refers to the distribution ratio of various diamond particles, which is a very important parameter to measure the quality of diamond micro powder. In a sense, the concentration of particle size distribution determines the quality of products. In application, products with various particle sizes have corresponding grinding efficiency and surface finish. Users can choose products with different particle sizes according to different processing requirements. Generally speaking, there is strict control over the coarse particles in diamond powder, as they can cause scratches on the processed components and cause serious quality problems in applications. Especially in some precision polishing fields, scratches caused by coarse particles can directly lead to the scrapping of expensive processing devices, resulting in huge losses. The presence of fine particles can also lead to corresponding problems, such as reducing grinding efficiency in grinding processing. Therefore, there will also be clear requirements.

Main characterization parameters of particle size distribution
The main characterization parameters of particle size distribution are D50, Mv, D5, D95, etc. D50: also called median or median diameter. It is commonly used to represent the average particle size of the powder. It is the corresponding particle size when the cumulative particle size distribution percentage of a sample reaches 50%. Its physical meaning is that particles larger than it account for 50%, and particles smaller than it account for 50%. Mv: Average particle size in volume distribution. It is another way to express the average particle size. This value is more affected by large particles, and is more indicative when controlling large particles. D5: It is the particle size corresponding to the cumulative particle size distribution percentage of a sample reaching 5%, and is usually used to measure the particle index of the fine end of the sample. D95: refers to the particle size corresponding to the cumulative particle size distribution percentage of a sample reaching 95%, which is usually used to measure the particle index at the coarse end of the sample.

Measurement method of particle size distribution of diamond powder
The particle size distribution of diamond powder can be measured by image method, sedimentation method, centrifugal method, laser method, coulometric method, etc. 1. Image method is a method of particle size detection for diamond powder using a particle imager. Particle imagers generally consist of optical microscopes, cameras, computers, and analysis software. When conducting particle size testing, the sample is first made into an observation sample using a glass slide and glycerol, which is placed under an optical microscope for observation. Sample images are taken by a camera, and then transmitted to a computer for particle size analysis using analysis software (as shown in the following figure).

▲ Particle image analyzer

▲ Particle size distribution detection results by image method

The advantage of image method is its intuitive detection and the ability to analyze particle morphology. However, the disadvantage is that the sampling amount is small, the representativeness of the detection results is not strong, and the entire operation process is relatively cumbersome and time-consuming.

1. Sedimentation method Sedimentation method particle size measurement technology refers to the instrument and method to measure particle size distribution by particle sedimentation velocity in liquid. A method for measuring the particle size distribution of diamond powder according to the different settling velocity of particles with different particle sizes in the liquid. Its basic process is to place the sample in a certain liquid to make a suspension of a certain concentration, and the particles in the suspension will settle under the action of gravity. The settling speed of particles is related to the size of particles. The settling speed of large particles is fast while that of small particles is slow. The settling speed of particles is indirectly reflected by measuring the change rate of light intensity through suspension at different times, and then the particle size distribution is calculated. However, in the actual measurement process, it is difficult to directly measure the settling velocity of particles. Therefore, it is usually used to measure the change rate of suspension concentration at a certain depth below the liquid surface to indirectly judge the settling speed of particles, and then measure the particle size distribution of samples.

2. The centrifugal method requires a longer settling time for finer particles, and is greatly influenced by factors such as convection, diffusion, and Brownian motion during the settling process, resulting in larger measurement errors. To overcome these problems, centrifugal sedimentation method is usually used. During measurement, the sedimentation tank is placed in a high-speed rotating disk to accelerate the settling speed of particles, greatly reducing measurement time, improving measurement accuracy, and making the detection of ultrafine particles possible. The current centrifugal particle size analyzer has a rotational speed of over 20000 revolutions per minute. The detection limit reaches the nanometer level.

3. Laser method Laser method is based on the physical phenomenon that particles can cause laser scattering to test particle size distribution. In practical applications, this analysis method has a short measurement time and stable measurement data results, especially for particle sizes less than 150 μ The practical application of m powder measurement has been recognized by people.

4. The Kurt method, also known as the resistance method, adopts the principle of small pore resistance. When micro powder particles pass through a small micropore, they occupy a portion of the space in the micropore and expel the conductive liquid in the micropore, causing changes in the resistance at both ends of the micropore. The instrument can process these resistance signals and calculate the particle size distribution. This measurement method is suitable for measuring powder samples with uniform particle size (i.e. narrow particle size distribution range), as well as the size and number of rare solid particles in water. It has the advantages of high resolution, fast measurement speed, and easy operation. However, there are also shortcomings such as small dynamic range and insufficient measurement lower limit.

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