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Although Micro Powder Is Small, It Also Has Many Shapes?

May 12,2023

01 The Particle Shape of Diamond Micropowder
The particle shape is the main factor for evaluating the quality of diamond powder, and the parameters that characterize the particle shape include particle roundness, particle ellipticity, specific surface area, needle rod shaped particles, sheet shaped particles, etc. It is generally recommended to use two parameters, particle roundness and number of flaky particles, to characterize particle shape.

Particle roundness refers to the ratio of the equivalent circumference of the projected area of a particle to the actual projected circumference of the particle, which is a dimensionless number less than 1. Roundness is a comprehensive parameter that characterizes the shape of particles, which can reflect both the roundness, ellipticity, and surface roughness of particles.

Flaky particles refer to particles that are thin and have high light transmittance under a microscope and are considered as flaky particles. To facilitate the implementation of the inspection, further quantify the transmittance and treat those with a transmittance greater than 90% as flaky particles.

According to the current situation of diamond powder, the proportion of flake particles is between 0% and 10%. At present, the percentage of flaky particles should be less than 10%. The previous requirement for the number of flaky particles was less than 5%. In fact, even if the number of flaky particles is greater than 5%, it can still be used, but it only affects the effectiveness of use. Therefore, this indicator has been relaxed as a guiding property indicator.

Due to the fact that particle roundness and percentage of flaky particles are guiding indicators, no high requirements have been put forward, mainly to guide production and application.
In the quality inspection of diamond powder, needle like particles refer to the ratio of the long axis to the short axis exceeding 3:1. Needle like particles exceeding the maximum particle size are not allowed in micro powder, and needle like particles with a length between the maximum nominal size and the maximum particle size are not allowed to exceed 3%.

The shape of particles can affect particle size detection. When there are many non spherical particles, it is difficult to obtain products with concentrated particle size. Products with more needle like particles have large changes in particle size detection and poor consistency. In application, the particle shape can also affect the grinding efficiency of the product, resulting in many uncertain factors. Usually, during polishing, the particle shape of diamond powder is better to be close to spherical and isomorphic. However, with the expansion of applications, there is also a demand for irregularly shaped diamond micropowders. The following figure shows diamond micropowders with more needle like shapes.

▲ Diamond micropowder with more needle like shapes

02 Different shapes of micro powders are suitable for different applications
Micropowders with good roundness in particle shape have good polishing effects. Block shaped, multi angular, multi blade, low magnetic and high-strength micro powders have good application effects in diamond electroplating wire saws, while other shapes of micro powders, such as strip shaped, block shaped, and sheet shaped, are more sharp and are often used in resin bonded grinding wheels.

03 Method for particle shape detection of diamond powder
Optical microscopy is often used to detect the particle shape of diamond powder. The maximum magnification of a general optical microscope is 1600 times, which is suitable for detecting coarse particles up to 2 microns (the following image is a photo of a diamond powder optical microscope). During testing, glass slides and glycerol are used to make samples of the sample to be tested, and they are placed on the stage of the biological microscope for observation. It is required that the particles are evenly distributed and do not overlap when making the sample. Observations are made along the horizontal and vertical directions, and the percentage of equiformed particles is counted.
A particle image analyzer can also be used, which can capture sample images through a video capture system and perform particle shape analysis through software. It can provide shape parameters such as sphericity, which can reduce the subjectivity of direct observation by an optical microscope (the following figure is the detection report of the particle image analyzer).

▲ Optical microscope photos of diamond powder

▲ Particle shape detection report
The shape detection of fine particles requires the use of an electron scanning microscope. For particles finer than 1 micron, the shape of the particles cannot be clearly observed using an optical microscope. Electronic scanning microscopy can achieve magnification of tens of thousands or hundreds of thousands, allowing for clear observation of the shape of nanoscale particles.

▲ Scanning electron microscope

▲ SEM photos of diamond powder

Although the particle size composition is the same, the difference in particle shape of micro powders can lead to significant differences in their effectiveness. Therefore, production enterprises must classify and manage products based on particle shape to ensure stable product quality. Users must also choose qualified products based on the particle shape to ensure stable usage.

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