The Problem of Particle Dispersion in the Measurement of Diamond Micropowder

For many current measurement methods of diamond powder, the samples to be tested and the sub-micron/micron-level diamond particles need to be fully dispersed in order to achieve accurate and stable measurement data. Diamond micropowder involves a variety of optical particle measurement methods. How to ensure that the particles can be uniformly dispersed in the dispersion medium, so that the particles do not agglomerate and do not chemically react with the dispersion medium, is an important prerequisite for accurate particle size measurement. Therefore, for a special particle measurement object, selecting the appropriate dispersion medium, dispersant and dispersion method to ensure that the measurement object is fully dispersed is the key to obtaining reliable results in the end. It is also a difficulty in particle size characterization.

With the development of particle measurement technology, the objects of particle size measurement are also diversified, and their properties vary widely. On the other hand, the particles of the measurement object are getting smaller and smaller. For example, nano-sized diamond particles, due to their large specific surface area and high surface energy, are prone to particle agglomeration during the measurement process, resulting in secondary agglomeration. which directly affects the accuracy, repeatability and reproducibility of the measurement results, increasing the difficulty of particle measurement and the degree of confidence in the data.

particle dispersion method

Particle dispersion is the separation and dispersion of diamond micron powder particles in a special dispersion medium. And form a uniform distribution, maintaining a relatively stable dispersion process for a certain period of time. At present, particle dispersion technology has become a new specialized discipline. It is widely used in many fields.

The dispersion process is generally divided into three stages:

1. The liquid dispersion medium wets the solid micropowder particles

2. Disperse larger agglomerates into smaller particles by external forces

3. Stably disperse the particles to ensure that the powder particles remain uniformly dispersed in the liquid state at least for the time of the measurement process, and prevent the re-agglomeration of the dispersed particles.

dispersion method
Generally, it can be divided into two methods: physical dispersion and chemical dispersion.

Common physical dispersion methods are: mechanical stirring, vibration, ultrasonic dispersion. Chemical dispersion is a method of realizing pattern dispersion by adding dispersing reagents and using surface chemistry.
A dispersant is a substance that can reduce the surface tension of the liquid, so that the surface of the micropowder particles can be well wetted. The dispersing effect of the dispersant on the fine particles is to use the adsorption on the surface of the particles to enhance the repulsion energy between the particles. The enhancement of repulsion is mainly achieved in the following ways.

Increase the absolute value of the potential on the particle surface to improve the electrostatic repulsion between particles.
The adsorption layer is formed on the surface of the particles by the dispersant, which produces and strengthens the steric hindrance effect, resulting in a strong repulsive force between the particles.
Regulate the polarity of the particle surface, enhance the wettability of the dispersion medium to it, and enhance the degree of surface structure while satisfying the wetting. The repulsive force is greatly enhanced.

Classification of Dispersing Reagents

Generally divided into three categories:

Inorganic electrolytes, surfactants, polymer dispersants, etc. The choice of dispersant is critical, because the size of the particles and the properties of the particle surface are different, and the dispersant will also be different.

It should be noted that when using the dispersion medium, the amount and concentration should not be too much, and multiple experiments are needed to find the optimal amount. In addition, in optical measurement, the dispersion medium is also an important index that needs to be referred to when selecting. The amount of dispersion medium is to ensure that the optical properties are not destroyed. Otherwise, the repeatability and reproducibility of the measurement will be affected.

In the process of practical application, a method of combining physical dispersion and chemical dispersion should be considered, one of which can quickly release the agglomeration, and the other to maintain dispersion stability, so as to achieve the ideal dispersion effect.