Definition
A laboratory laser particle size meter is an instrument based on the principle of light scattering to measure the particle size distribution of particle samples. It calculates the size information of the particles by analyzing the scattered light signals generated by the particles in the laser beam, usually in the nanometer to millimeter range. The instrument is widely used in materials science, environmental monitoring, chemical production, food processing, geological research and other fields, providing key data support for the characterization of particle systems.
Principle
The core principle of laboratory laser particle size meters is the Mie scattering theory. When the laser hits the particles dispersed in the medium, the particles scatter light, and the intensity distribution of the scattered light is closely related to the particle size. The instrument collects scattered light signals from different angles through the detector and calculates the particle size distribution using appropriate mathematical models such as the Flanghefei diffraction model or the Mie scattering model. For small particles, typically smaller than microns, dynamic light scattering can also be used to measure scattered light fluctuations caused by Brownian motion of the particles.
In terms of mathematical expression, the relationship between scattered light intensity I(θ) and particle size d can be roughly described as: I(θ) ∝ ∫ f(d) * S(d,θ) dd, where f(d) is the particle size distribution function and S(d,θ) is the scattering cross-sectional function. The particle size distribution results can be obtained by solving the equation by the inverse algorithm.
Measurement method
Common measurement methods include static light scattering and dynamic light scattering. Static light scattering is suitable for a wide range of particle sizes (about 0.1 microns to several millimeters), where the sample needs to be uniformly dispersed in a liquid or gaseous medium, and is inverted by measuring the scattered light intensity at multiple angles. The dynamic light scattering method is mainly used for submicron and nanoparticles (about 1 nanometer to 1 micron), and the diffusion coefficient of the particles is obtained by analyzing the autocorrelation function of the scattered light intensity, and then the particle size is calculated. Sample preparation, such as dispersion, dilution, or sonication, is usually required before measurement to ensure that the particles are in a monodispersed state and that agglomeration does not affect the accuracy of the results.
Influencing factors
The accuracy of the measurement results is influenced by several factors. In terms of sample properties, the particle shape, refractive index, concentration and agglomeration state may cause scattering model deviations. If the particles are non-spherical, the equivalent spherical diameter assumption introduces errors. Instrument parameters such as laser wavelength, detector layout, and optical alignment can also affect signal quality. The operating conditions include the selection of dispersion medium, temperature stability and sample circulation speed. A mismatch in the refractive index of the medium can cause distortion of the scattering signal. In addition, the selection of mathematical models needs to match the particle size range, and improper inversion algorithms may cause distortion of the results.
Application:
Laboratory laser particle size meters have a wide range of uses in several industries. In materials science, it is used to characterize the particle size distribution of ceramic powders, metal particles, and composites to optimize the preparation process. It is commonly used in the field of environmental monitoring to analyze the dimensional characteristics of atmospheric dust, river sediments or particulate matter from industrial emissions. In chemical production, the particle size control of catalysts, pigments and polymer emulsions relies on this instrument to provide data. In the food industry, it is used for particle analysis of flour, emulsions, and condiments to ensure texture and stability. In geological studies, the particle size distribution of sediments or mineral powders helps reveal geological process information.
Selection
When selecting a model, it is necessary to comprehensively consider the measurement requirements and technical parameters. The particle size range should cover the expected size of the sample to be tested, and a wide range of instruments may be more applicable. Measurement accuracy and repeatability can be evaluated by standard sample testing. Whether the instrument supports multiple scattering models (such as the Mie model and the Flanghefei model) to accommodate samples with different refractive indices. The cell design needs to be compatible with liquid or dry dispersion and consider the need for temperature control for temperature-sensitive samples. Operating software should provide clear data processing and reporting capabilities, and inverse algorithm configuration flexibility can help accommodate complex samples. In addition, instrument maintenance requirements, calibration intervals, and technical support are also reference factors for long-term use.