Abstract

Objective To address the unclear measurement upper limits of laser particle size analyzers in China， the study develops millimeter-scale particle size standard materials to evaluate performance of these devices， filling a significant gap in this field.

Methods Polystyrene （PS） microbeads with nominal diameters of 0. 6，0. 8，1. 0， and 1. 1 mm were prepared using suspension polymerization-partial sulfonation-sieving method. These microbeads were designed to serve as particle size standard materials. An optical microscope calibrated with an NIST SRM2800 micrometer was employed to measure the particle sizes of these four standard materials. Their homogeneity and stability were evaluated， and the measurement results were traceable to the wavelength of He-Ne lasers. These millimeter-scale particle size standards were subsequently used to assess several commonly used laser particle size analyzers available on the Chinese market.

Results and Discussion The polystyrene microbeads exhibited excellent sphericity， a narrow particle size distribution， and outstanding homogeneity and stability. The volume median diameters of these samples were（0. 553±0. 007），（0. 749±0. 008），（0. 925±0. 008）， and（1. 07±0. 01） mm， respectively. These measured diameters were accurate， reliable， and traceable to the He-Ne laser wavelength. When tested， only certain particle size analyzers were capable of accurately measuring all four types of millimeter-scale standard materials. Some analyzers could only measure 1-2 sample types accurately， while others failed to measure millimeter-scale particle size standards at all. Analyzers with the smallest measurement deviations were produced by three companies and used He-Ne laser sources， whereas those with larger deviations used more affordable semiconductor laser sources.

Conclusion The four types of millimeter-scale particle size standard materials fill a critical gap in millimeter-scale particle size standards in China and enhance the country’s overall particle size standard system. To evaluate the measurement upper limits of laser particle size analyzers， multiple reference samples are required. The measurement upper limit of an analyzer is influenced not only by the radius of the innermost unit of the light-receiving detector （i.e.，the minimum receiving angle） but also by the quality of the laser light source used. Higher laser quality is associated with a higher measurement upper limit for the particle size analyzer. Analyzers equipped with He-Ne lasers exhibit a higher measurement upper limit compared to those using semiconductor lasers.

Keywords：particle size； standard reference materials； polystyrene microspheres； laser particle size analyzer； measurement upper limit