Definition
Particle image particle size meter is a particle size measurement instrument based on static image analysis technology. It directly acquires microscopic images of particles and uses digital image processing algorithms to statistically analyze the size and morphological characteristics of particles. The instrument can provide a variety of morphological parameters such as equivalent diameter, length-to-diameter ratio, roundness, etc. of particles, which is an intuitive particle size and morphology characterization tool.
Principle
The core working principle of particle image particle size meter is optical imaging and image analysis. The instrument typically consists of an optical microscope module, a high-resolution digital camera, a sample dispersion system, and image processing software. The workflow can be summarized as follows: First, a well-dispersed particle sample is placed on a sample stage, and a clear digital image of the particles is captured by the microscope optical system and camera by transmitted or reflected illumination. Subsequently, the software performs binarization, edge detection, and other processing on the image to identify and segment the contours of individual particles. Finally, based on the projection area or profile characteristics of each particle, its equivalent diameter (such as area equivalent diameter, Ferrett diameter, etc.) and other morphological parameters are calculated, and a large number of particles are statistically analyzed to obtain the particle size distribution results.
A commonly used formula for calculating equivalent diameter is area equivalent diameter DA：
DA = 2 × √(A / π)
where A represents the projected area of the particles. This formula equates the projected area of an irregular particle to the diameter of a circle with the same area.
Main measurement methods
According to the different sample dispersion and imaging methods, the common measurement methods are mainly divided into static wet dispersion imaging and static dry dispersion imaging. Static wet dispersion imaging typically disperses particles in a suitable liquid medium and is imaged through a flowing sample cell or slide. This method helps reduce particle agglomeration and is suitable for suspensions or samples that are easily dispersed in liquids. Static dry dispersion imaging is suitable for dry powder samples by blowing and sedimenting powder particles through a dry dispersion device, and instantaneous capture imaging is performed during the sedimentation process. Both methods need to ensure that the particles are well dispersed in the field of view and that overlap is avoided to ensure the accuracy of the analysis.
Factors influencing measurement results
The accuracy and repeatability of measurement results are affected by a variety of factors. Sample preparation is a key link, and the dispersion state of particles directly affects the image analysis. Severe agglomeration or overlap can lead to measurement bias. The resolution and depth of field of the optical system determine the clarity of the image, and insufficient resolution may not be able to distinguish fine particles or details. The accuracy of the image processing algorithm, especially the setting of threshold segmentation and edge detection, has a direct impact on particle recognition. In addition, statistical representativeness requires a sufficient number of particles to be analyzed (often thousands to tens of thousands are recommended), and insufficient sample size may lead to unrepresentative statistical results. Illumination uniformity, sample concentration, and operator experience are also factors to consider.
Applications
Particle image particle size meters are widely used in many industrial and scientific research fields because they can provide particle size and morphology information at the same time. In the field of metal powders and additive manufacturing, it is used to analyze the particle size distribution and sphericity of powders to evaluate their flow and printability. In the cement, ceramics and other building materials industry, it is used to monitor the particle morphology of raw materials and finished products. In the coatings and pigments industry, it helps to study the effect of filler or pigment particle shape on product performance. In the energy field, such as in the research and development of battery materials, it is used to observe the particle morphology and size of positive and negative electrode materials. In environmental science, it can be used to analyze particulate matter in atmospheric dust or water treatment. In addition, it is an effective characterization method in many fields involving particulate matter such as food, chemical industry, and geology.
Key points for instrument selection considerations
When choosing a particle image particle size meter, it needs to be comprehensively considered based on specific application needs and technical indicators. First, the measured particle size range should be clarified to ensure that the optical magnification and camera resolution of the instrument can cover the sample to be tested. Secondly, pay attention to the imaging quality of the instrument, including the quality of optical components, the uniformity and stability of the lighting system. The analytical capabilities of the software are equally important, as the reliability of its image processing algorithms, the flexibility of parameter settings, and the richness of the morphological parameters provided need to be evaluated. The suitability of the sample dispersion system should also be determined to ensure that it supports the desired dry or wet dispersion method and can effectively handle samples that are prone to agglomeration. In addition, the degree of automation of the instrument, the compatibility of data export formats, the ease of maintenance, and the technical support capabilities of the supplier are also aspects that need to be evaluated in practical use. It is recommended to verify the suitability of the instrument by testing actual samples.