Definition
The automatic laser particle size analyzer is an analytical instrument based on the principle of laser diffraction to measure the size distribution of particles in a particle system. It automates sample dispersion, measurement, and data processing for particle size analysis of solid particles or droplets ranging from sub-micron to millimeter-sized. This instrument is regarded as one of the conventional characterization tools in many industrial and scientific fields.
Principle
The core working principle of the instrument is laser diffraction, also known as static light scattering. When a monochromatic laser beam passes through a well-dispersed suspension of particles, the particles scatter the laser. The angular distribution of scattered light is related to the size of the particles, with large particles mainly scattering in small angle areas, while small particles scattering more pronounced in large angle areas. The volume or quantity-weighted particle size distribution of the sample can be obtained by measuring the scattered light intensity distribution at different angles by measuring the scattered light intensity distribution at different angles by measuring the multi-detector array and inverting the calculation using the appropriate scattering model (such as the Mice theory or the Flanghefei approximation).
The basic relationship of light scattering followed by this process can be expressed as follows: the scattered light intensity distribution is a function of particle size and scattering angle. The Mie theory provides a rigorous mathematical solution to the calculation of the complex refractive index of particles versus the medium. For particles with particles with a particle size much larger than the wavelength of light, a more simplified approximation of the Flanghehe approximation can be used.
Measurement method
Typical measurement processes include sample preparation, background measurement, sample measurement, and data analysis. First, a representative sample needs to be added to the instrument's circulation dispersion system, and mechanical stirring, ultrasonics, or liquid circulation are used to ensure that the particles are fully dispersed and do not agglomerate. Subsequently, the system automatically measures the scattering signal of the pure dispersed medium as a background and subtracts. Next, the sample suspension is measured and the scattered light data is collected. Finally, the built-in software converts the light intensity angular distribution data into particle size distribution results through inversion algorithms, which are often presented in the form of cumulative distribution or interval distribution, and gives characteristic particle size parameters such as D10, D50, D90 and so on.
Influencing factors
The reliability and accuracy of measurement results are affected by multiple factors. Sample preparation is a critical part, and insufficient dispersion can lead to agglomeration of particles, resulting in large measurements. The selection of dispersion medium takes into account the wettability, chemical stability of the sample, and the appropriate refractive index contrast. The setting of optical parameters, especially the real and imaginary parts (absorbance) of the refractive index of particles and dispersed media, has a significant impact on the calculations based on the Mie theory. In addition, the optical alignment of the instrument, the accuracy of background measurements, and the models and parameters selected in the inversion algorithm all affect the final result. Operators need to reasonably set and verify relevant parameters according to the characteristics of the sample.
Application:
The application range of automatic laser particle size analyzer is relatively wide. In the ceramics and powder metallurgy industry, it is used to monitor the particle size of raw material powders to control sintering properties. In the field of coatings and inks, it is used to evaluate the dispersion of pigments and fillers and their effects on product gloss and stability. In the cement and building materials industry, it is used to analyze cement particle size distribution to optimize hydration reactions and strength development. In environmental science, it can be used for the study of particle classification of soils or sediments. In addition, in many fields involving particulate matter, such as chemicals, food, metal processing, and geology, the instrument plays a role in process control and quality inspection.
Selection considerations
When choosing an instrument, it is necessary to comprehensively consider technical indicators and actual needs. The measurement range should cover the main particle size interval of the sample to be tested. For the measurement of sub-micron particles, the optical configuration of the instrument needs to be able to detect scattered light at a sufficiently large angle. Dynamic range refers to the ratio of the upper and lower limits of particle size that can be covered in a single measurement, and a wider dynamic range helps reduce gear shifting when measuring different samples. The degree of automation, such as automatic light matching, automatic cleaning, automatic dispersant addition, and other functions, can improve operational efficiency and result consistency. The software's analytical capabilities, conformity certifications, and data traceability capabilities are also worth paying attention to. At the same time, the instrument's adaptability, long-term stability, maintenance complexity, and supplier technical support capabilities need to be evaluated.