The combination of these parameters is then used to define the shape factor.
#Laser diffraction vs dynamic light scattering iso#
Of note, the ISO standards providing guidance for performing particle size determination by static and dynamic image analysis (respectively ISO 1) recommend to define particle size by a combination of 3 primary measurements, namely the area-equivalent diameter, the maximum Feret diameter, and the minimum Feret diameter. Since the particle’s orientation at the time of image capture has a large influence on all these parameters, the equivalent spherical diameter is obtained by averaging a large number of measurements, corresponding to the different particle orientations. Enabled by the introduction of digital image analysis, this corresponds to a direct measurement of the projection area by pixel counting. The area-equivalent diameter D A, also termed circular-equivalent diameter, is the diameter of a sphere having the same projected area as the particle’s projection.
In other terms, it is the length of the line dividing the projection in two areas of equal surfaces. The Martin diameter D M, defined as the chord length of the outline of the particle, which bisects the area of particle projection.The Feret diameter D F, which corresponds to the distance between two parallel tangents on opposite sides of the particle’s projected image.The most commonly used methods for determining the equivalent spherical diameter from the particle’s projected outline are: The principle used to match the real-life particle and the imaginary sphere vary as a function of the measurement technique used to measure the particle.įor optical-based particle sizing methods such as microscopy or dynamic image analysis, the analysis is made on the projection of the three-dimensional object on a two-dimensional plane. Here, the real-life particle is matched with an imaginary sphere which has the same properties according to a defined principle, enabling the real-life particle to be defined by the diameter of the imaginary sphere. The concept of equivalent spherical diameter has been introduced in the field of particle size analysis to enable the representation of the particle size distribution in a simplified, homogenized way. However, real-life particles are likely to have irregular shapes and surface irregularities, and their size cannot be fully characterized by a single parameter. The particle size of a perfectly smooth, spherical object can be accurately defined by a single parameter, the particle diameter. The equivalent spherical diameter of an irregularly shaped object is the diameter of a sphere of equivalent geometric, optical, electrical, aerodynamic or hydrodynamic behavior to that of the particle under investigation. The diameter of a sphere of the same volume as an irregularly-shaped subject
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