Laser particle size analyzer measures the particle size distribution of spray powder.

Overview

In the spraying process, the particle size distribution of powders is a critical parameter that affects coating uniformity, adhesion, and final properties. The laser particle size analyzer is based on the scattering principle of light and enables fast, non-contact measurement of the particle size distribution of powder samples. This method has the characteristics of wide measurement range, good repeatability and convenient operation, and is suitable for quality control and research and development of various spraying powders such as metals, ceramics, and polymers.

Measurement principle

The working principle of laser particle size analyzers is based on the theory of Mie scattering. When the laser beam passes through the suspension of dispersed powder particles, the particles scatter the laser, and the intensity distribution of the scattered light is related to the particle size of the particles. The particle size distribution of the sample can be obtained by collecting the scattered light signals from different angles through the detector and performing inversion calculations using the appropriate optical model. The particle size distribution is usually expressed as the volume fraction or quantity fraction with the size of the particle size, and the commonly used characteristic parameters include D10, D50, D90 and other cumulative distribution values.

The core calculation formula can be expressed as:

I(θ) = ∫₀^∞ i(d,θ,m) f(d) dd

Among them, I(θ) is the scattered light intensity measured at the scattering angle θ, i(d,θ,m) is the scattering function of a single particle with a particle size of d and a refractive index of m at the θ angle, and f(d) is the particle size distribution function to be solved.

Measurement process

To ensure that the measurements are representative, sample preparation is essential. First, the spraying powder to be tested should be thoroughly dried to prevent agglomeration and dispersion. Subsequently, an appropriate amount of powder is added to the suitable dispersion medium, and the selection of the medium should consider that there is no chemical reaction with the powder and the refractive index matches. The particles are evenly dispersed and stable by mechanical agitation or sonication, avoiding settling or agglomeration. During measurement, the uniformly dispersed suspension is introduced into the instrument sample cell, appropriate measurement parameters are set, such as shading rate range, pump speed, etc., and the measurement is started and the data is recorded. It is recommended to repeat the measurement at least three times per sample to assess repeatability.

Influencing factors

The accuracy of the measurement results is influenced by several factors. First, the dispersion of the powder is critical, and agglomeration can lead to a large measured particle size. Secondly, the selection and concentration of dispersion media need to be optimized to ensure that the particles are fully dispersed and the signal strength is moderate. Instrument background calibration, optical alignment status, and model parameter settings can also affect the reliability of the inversion results. Relevant standard methods should be followed in operation, and reference materials should be used regularly for instrument verification.

Application:

The measured particle size distribution data can be used to evaluate the batch consistency and process suitability of the powder. For example, a narrower distribution is generally beneficial for creating a uniform coating, while the D50 value reflects the average thickness of the powder. This data can be correlated with the spraying process parameters to optimize the powder feed rate, spraying distance, etc., to improve the coating quality. The following is an example of the particle size distribution range of common spraying powders:

Method comparison

Laser diffraction is one of the common methods for measuring the particle size of sprayed powders. Compared with other methods such as screening and image analysis, the laser method has the advantages of fast measurement speed and good statistical representativeness, but it is necessary to pay attention to its equivalent particle size interpretation for non-spherical particles. In practical applications, you can refer to relevant domestic and foreign standards, such as standard literature on general principles and guidelines for particle size analysis.

Epilogue

Laser particle size analysis provides an efficient and reliable means for measuring the particle size distribution of sprayed powders. Through standardized sample preparation, rigorous measurement operations, and reasonable data analysis, particle size data that accurately reflects powder characteristics can be obtained, providing strong support for spraying material selection, process optimization, and quality control. Continuous attention to the standardization of measurement conditions and instrument maintenance is the basis for ensuring long-term data comparability.

References

1. International Organization for Standardization, General principles of particle size analysis-laser diffraction.

2. China National Standardization Administration, Determination of particle size distribution of powder coatings - laser diffraction method.

3. Technical reports on particle size testing of thermal spray powders in related industries.