Definition
Wet laser particle size meter is an instrument based on the principle of laser diffraction to measure the particle size distribution in liquid dispersion media. It calculates the particle size and distribution of particles in the sample by analyzing the scattering signal of the laser from the particle swarm, combined with the corresponding optical model and mathematical algorithm. This instrument is mainly suitable for particle systems that need to be dispersed in liquids and maintained in stable suspension for measurement.
Principle
The working principle of wet laser particle size meter is based on the Flanghe-Fee diffraction theory and the Mie scattering theory. When a monochromatic laser beam passes through a uniformly dispersed suspension of particles, the particles scatter the laser. The intensity distribution of scattered light is closely related to the particle size. Large particles mainly cause scattering at small angles, while small particles produce scattering at large angles. The instrument collects these scattered light signals at different angles through a multi-detector array.
The collected scattered light energy data is inverted and calculated according to the mathematical model of light scattering through the computer built into the instrument. Commonly used calculation models such as Mice theory, the core formulas involve parameters such as particle size d, laser wavelength λ, scattering angle θ, and relative refractive index m of particles and dispersion medium. In the inversion process, the particle size distribution results that match the measurement of scattered light energy are finally solved through iterative algorithms.
Measurement method
The typical measurement process for a wet laser particle size meter involves sample preparation, dispersion, measurement, and data analysis. First, a small number of representative samples need to be taken and added to the circulating dispersion cell of the instrument, which is already filled with a suitable pure dispersion liquid. The instrument then activates the stirring and ultrasonic circulation system to ensure that the particles are fully dispersed in the liquid and form a homogeneous, stable suspension while avoiding air bubble interference.
When the dispersion system reaches a steady state, the laser emits a laser through the sample cell, and the detector begins to collect scattered light data. Measurements are usually completed quickly, and the instrument software displays the light energy distribution in real time. Finally, based on the preset optical parameters and algorithm model, the software automatically converts the light energy distribution data into a volume or quantity-based particle size distribution report, and gives characteristic particle size values such as D10, D50, and D90.
Influencing factors
The accuracy and repeatability of measurement results are affected by a variety of factors. Sample preparation is key, including the representativeness of the sample, the sample concentration, and the dispersion of the particles in the dispersion. Too high a concentration can lead to multiple scattering, and too low a signal signal-to-noise ratio is insufficient. The selection of dispersion medium should consider its chemical inertness to the sample, its wettability to particles, and the relative refractive index between the particles and the medium.
The accuracy of the optical parameter setting is also critical, especially the real and imaginary parts of the refractive index of particles and dispersion media. Entering inaccurate refractive index values can lead to biases in particle size calculations. In addition, the optical alignment of the instrument, background subtraction, and the chosen inversion algorithm and model can all affect the final result. The stability of the operating environment, such as temperature changes and vibrations, also needs to be controlled.
Applications
Wet laser particle size meters are widely used in many industrial and scientific research fields. In the ceramic and powder metallurgy industry, it is used to measure the particle size of ceramic powders and metal powders to control sintering properties. In the coating and ink industry, it is used to detect the particle size distribution of pigments and fillers, which affects the coloring power and leveling of products. In the field of cement and building materials, it is used to analyze the fineness of cement and slag powders, and correlate their hydration activity and strength.
In the chemical industry, it is used for particle size control of catalysts, polymer emulsions, and grinding slurries. In environmental monitoring, it can be used to analyze suspended sediments in water bodies. In the food industry, it can be used to measure the particle size of powders such as milk powder and starch. In addition, it is also a common tool for characterizing the basic physical properties of particulate materials in scientific research fields such as geology, mineral processing, and new material research and development.
Instrument selection considerations
When choosing a wet laser particle size meter, it is necessary to comprehensively consider the technical indicators and specific application requirements. The measurement range is a core parameter to ensure that the entire particle size of the sample to be tested is covered. The stability of the laser light source and the angular range and number of channels of the detector directly affect the resolution and dynamic range of the instrument. The performance of the dispersion system, including the adjustment range and stability of stirring speed and ultrasonic power, has a great impact on the processing capacity of difficult-to-disperse samples.
Software functions are equally important, evaluating whether they comply with relevant industry standards, whether the algorithm models are rich, whether the operation is convenient, and whether the data reporting meets the analysis requirements. The long-term stability of the instrument, the convenience of maintenance, and the technical support and service capabilities of the manufacturer are also important considerations. Users should conduct comprehensive evaluation and selection based on the characteristics of their own samples, conventional test volume, and data accuracy requirements.