Definition
A particle size meter is an instrument used to measure the size of particles in a particle system and its distribution. In many industrial and scientific research fields, particle size is one of the key parameters that affect material properties, process and final product quality. The instrument provides a quantitative basis for process control and quality assessment by rapidly characterizing particles in samples such as suspensions, emulsions, or dry powders through non-contact or indirect measurement.
Principle
The measurement principle of particle size meters is mainly based on the theory of light scattering. When a beam of monochromatic light hits the particles dispersed in the medium, the particles scatter the light, and the intensity distribution of the scattered light is closely related to the size of the particles. According to the principle of diffraction of Flanghefei, the scattering angle produced by small particles is larger, while the scattering angle of large particles is smaller. The particle size distribution of particles can be calculated by collecting scattered light signals from different angles by detector and mathematically inverting by using the Mie scattering theory or the Flanghefei approximation model. The process typically follows the following relation: I(θ) ∝ ∫ f(D) · S(θ,D) dD, where I(θ) is the scattered light intensity, θ is the scattering angle, f(D) is the particle size distribution function, and S(θ,D) is the scattering cross-section.
Particle size measurement method
According to the measurement principle and applicable scenarios, the measurement methods of particle size meters can be divided into static light scattering, dynamic light scattering and laser diffraction. Static light scattering inverts particle size distribution by measuring the intensity of scattered light at multiple angles and is suitable for sub-micron to millimeter-level particles. Dynamic light scattering methods obtain hydrodynamic diameters by analyzing scattered light fluctuations caused by Brownian motion of particles, and are commonly used for particle characterization in the nanometer to sub-micron range. The laser diffraction method is based on the principle of Flanghefei diffraction, using wide-angle scattering signals for rapid measurement, usually covering tens of nanometers to several millimeters. In addition, some instruments also incorporate techniques such as image analysis or ultrasonic attenuation to meet the measurement needs of special samples.
Influencing factors
The accuracy of particle size measurement is influenced by several factors. Sample preparation is a key step, and the dispersion state, concentration and media properties of the particles may cause measurement deviations. If the particles agglomerate or settle, the result will be biased towards the direction of large particle size; Too low a concentration may reduce the signal-to-noise ratio. The optical parameter settings, such as the selection of refractive index, need to match the actual characteristics of the sample, otherwise model errors will be introduced. The calibration status of the instrument and the cleanliness of the optical components also directly affect the measurement stability. In addition, ambient vibration and temperature fluctuations can interfere with optical signals, which need to be measured under suitable experimental conditions.
Applications
Particle size meters have a wide range of applications in many industrial and scientific research fields. In the chemical industry, it is used to monitor the particle size of catalysts, pigments, and polymer emulsions to optimize product performance. In the field of building materials, the particle size distribution of cement and ceramic powders affects their curing strength and process characteristics. In the food industry, the particle size of emulsions and powdered beverages is related to taste and stability. For environmental monitoring, the instrument can analyze the particle size distribution of atmospheric dust or water treatment flocs. In addition, in industries such as energy, electronic materials, and cosmetics, particle size meters also provide reliable data support for R&D and quality control.
Selection considerations
Choosing the right particle size meter requires a comprehensive consideration of the measurement range, sample properties, and testing needs. First, it is necessary to define the expected size of the particles to be measured to ensure that the instrument covers the required range from nanometer to millimeter. For samples that are easily agglomerated or soluble, the dispersion module and measurement speed of the instrument should be evaluated. Dynamic light scattering instruments are suitable for high-resolution nanoparticle analysis, while laser diffractometers are better suited for rapid screening of wide distribution samples. Users also need to pay attention to the repeatability of the instrument, compliance with relevant standards (e.g. ISO 13320) and compatibility with data output formats. The user-friendly design, maintenance cost and technical support of the operation interface are also aspects worth paying attention to in the actual selection.