Definition
A laser particle size meter is a physical analytical instrument based on the principle of light scattering to measure the particle size distribution of particle samples. It calculates the size of the particles and their volume or number in the sample by analyzing the scattered light signals generated by the laser irradiation. The instrument is suitable for measuring the particle size of solid particles, droplets, or bubbles in dispersion media, typically ranging from sub-micron to millimeter, and is widely used in particle characterization across multiple industries.
Principle
The working principle of the laser particle size meter is based on the theory of Mie scattering or the theory of diffraction of Flanghefer. When a monochromatic laser beam passes through a sample cell with scattered particles, 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 cause scattering at small angles, while small particles produce scattering at large angles. The instrument collects scattered light signals from different angles through a multivariate detector, and uses appropriate scattering models and mathematical inversion algorithms to convert the light intensity distribution into the particle size distribution of particles. Commonly used algorithms include non-independent mode algorithms and independent mode algorithms, the core formulas of which can be expressed as:
I(θ) = ∫0∞ i(θ,d) n(d) dd
I(θ) is the scattered light intensity received by the detector at the θ angle, i(θ,d) is the function of the scattered light intensity of a single particle size d at the θ angle, and n(d) is the particle size distribution function. By solving the integral equation, the particle size distribution of the sample can be obtained.
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 is suitable for measurements in the particle size range of microns and above, usually using dry or wet dispersion of samples. The dry method measures the dispersion of the powder sample through a gas stream, while the wet method disperses the sample in a suitable liquid medium, using a circulation system or ultrasound to ensure uniform dispersion of the particles. Dynamic light scattering is mainly used for the measurement of nano or submicron particles, and the particle size is estimated by analyzing the scattered light fluctuations caused by the Brownian motion of the particles. Both methods require the appropriate dispersion conditions and optical parameters to be selected based on the sample characteristics to ensure representativeness of the measurement results.
Factors that affect measurement results
The measurement results of a laser particle size meter are influenced by a variety of factors. Sample preparation is a critical part of the process, including the selection of dispersion medium, the addition of dispersants, and the intensity and timing of ultrasonic or agitation. The accuracy of optical parameters such as refractive index can also affect the reliability of data inversion and should be set according to the actual optical properties of the sample and medium. In addition, instrument background noise, detector sensitivity, multiple scattering effects caused by high sample concentrations, and temperature stability of the measurement environment may all have an impact on the results. Operators need to reduce interference with these factors through standardized sample handling and instrument calibration processes.
Applications
Laser particle size meters have a wide range of applications in many industrial and scientific research fields. In materials science, it is used to characterize the particle size distribution of ceramic powders, metal powders, catalysts, and composites to optimize production processes. In the pharmaceutical industry, particle size data can be used to control the particle size of APIs and excipients, influencing the dissolution rate and bioavailability of drugs. In the chemical sector, it helps monitor the particle properties of pigments, coatings, emulsions and spray products. In terms of environmental monitoring, it can be used to analyze the particle size of air dust and suspended solids in water. In addition, in food, energy, geology and other disciplines, laser particle size meters are also used as routine analysis tools to support product quality control and basic research.
Selection considerations
When choosing a laser particle size meter, it is necessary to comprehensively consider the measurement needs and technical parameters. The particle size measurement range should cover the expected size of the sample to be tested, and pay attention to the resolution and accuracy of the instrument in different particle size ranges. For nanoparticle measurements, dynamic light scattering capabilities may be necessary. The sample type determines the need for a dry or wet measurement module and whether special accessories such as automated injections, high-temperature or corrosive sample cells are required. The optical configuration of the instrument, such as the stability of the laser light source, the number and layout of detectors, can affect the dynamic range and sensitivity of the measurement. The software's data processing capabilities, compliant standard methodologies, and after-sales technical support and service are also aspects that need to be evaluated during selection. Users should conduct comprehensive comparison and verification tests according to the characteristics of their own samples, routine testing volume and budget.