Definition
A laser particle size meter is an analytical instrument based on the principle of light scattering to measure the size distribution of particles in a particle system. It analyzes the scattering signal of particles to lasers and acquires particle size information non-contact, making it suitable for particle measurement in the range from nanometers to millimeters. The instrument is used as a conventional particle size characterization tool in many industrial and scientific fields.
Principle
The working principle of laser particle size meter is mainly based on the Mie scattering theory and the Franchoff diffraction theory. When a monochromatic laser beam passes through a scattered particle sample, the particles scatter the laser, and the intensity distribution of the scattered light is directly related to the size of the particles. Large particles mainly produce small angle scatter forward, while small particles produce large angle scattering. The instrument collects scattered light signals from different angles through a multi-detector array, and uses appropriate scattering models and inverse algorithms to convert the light intensity distribution data into particle size distribution. The basic relationship can be expressed as a function of the scattered light intensity I(θ) and the particle size d and the scattering angle θ: I(θ) = f(d, θ, n), where n is the refractive index of the particle.
Measurement method
The measurement methods of laser particle size meters are mainly divided into static light scattering method and dynamic light scattering method. Static light scattering, also known as laser diffraction, is suitable for particle measurements from microns to millimeters. It inverts the particle size distribution by measuring the angular distribution of scattered light intensity that is stable in space. Dynamic light scattering is mainly used for nanometer to sub-micron particle measurement. The method analyzes the signal of the scattered light intensity caused by Brownian motion with time, calculates the diffusion coefficient of the particle by using the autocorrelation function, and then calculates the fluid mechanical diameter through the Stokes-Einstein equation. The two methods complement each other and cover a wide measurement range.
Influencing factors
The accuracy of the measurement results is influenced by several factors. Sample preparation is a critical part of the process, including the selection of dispersion medium, the dispersion of the particles, and whether agglomeration occurs. Optical parameter settings, such as the refractive index of particles and dispersed media, have a direct impact on calculations based on Mitchell's theory. The optical alignment of the instrument, background noise, and the sensitivity of the detector are also factors to consider. In addition, for dynamic light scattering, the concentration, temperature stability, and presence of polydispersity all affect the resolution and final results of the correlation function.
Applications
Laser particle size meters have a wide range of applications. In the field of materials science, it is used to characterize the particle size of materials such as ceramic powders, metal powders, calcium carbonate, and more. In the chemical industry, it can be used to monitor the particle stability of products such as emulsions, coatings, inks, etc. In environmental monitoring, it helps to analyze atmospheric dust, river sediments. In the food industry, it can be used to detect the particle size of flour, milk powder, and seasonings. In the energy field, it has guiding significance for the particle size analysis of battery cathode and anode materials and catalysts. These applications rely on their ability to quickly and statistically characterize particle systems.
Instrument selection
When choosing a laser particle size meter, it is necessary to conduct a comprehensive evaluation based on specific needs. The primary consideration is the measurement range, ensuring that the instrument covers the expected particle size of the sample to be tested. The choice of measurement principle depends on the dominant particle size interval, with static light scattering for coarser particles and dynamic light scattering for nanoparticles. The repeatability, resolution and validation reports of the instrument in compliance with relevant national and international standards such as ISO 13320 are key points to measure performance. The user-friendliness of the operating software, the richness of the data analysis model, and the support for wet and dry dispersion modules also need to be taken into account. In addition, the maintenance cost of the instrument, the requirements for the use environment, and the technical support capabilities of the supplier should also be evaluated.