Particle Shape
Particles can come in a wide range of shapes. Characterising and classifying these shapes is important, because particle shape can have an important influence on the way particles behave in applications such as drug delivery, catalysis and various manufacturing processes.
When studying particle shape, the most commonly considered parameters are size, aspect ratio, surface area, surface roughness and roundness. These parameters are not, however, sufficient to fully characterise a particle shape. A more thorough approach to particle shape characterisation and classification involves analysing the particle using scanning electron microscopy (SEM) images, image processing and geometric morphometrics. This approach can provide detailed information about particle shapes that the more traditional parameters are unable to capture.
Size is an important parameter for characterising particle shape. It is defined as the average longest cross-sectional dimension of the particle. Usually, particle size is expressed in terms of equivalent diameter, which is the diameter of a circle of the same projected area as the particle. Smaller particles usually have high surface area-to-volume ratios, and thus often behave differently in applications compared to larger particles.
The aspect ratio is the ratio of the longest cross-sectional dimension of the particle and its shortest cross-sectional dimension. Large aspect ratios indicate particles which are more elongated, while small aspect ratios indicate more spherical or cubic particles.
The surface area of a particle is another important parameter. It is defined as the total surface area of the particle. In general, surface area increases with decreasing particle size, and also increased with increasing particle aspect ratio as elongated particles have more surface area than spherical ones.
Surface roughness is another important parameter for characterising particle shape. It is defined as the mean surface deviation from a smooth surface. Rough surfaces are indicative of particles with a lot of irregularities, while smoother surfaces tend to indicate more spherical or cubic particles.
Roundness is concerned with the degree of curvature of a particle. A perfectly round particle would have a roundness of 100% while a perfectly angular particle would have a roundness of 0%. Roundness is usually determined by looking at SEM images and quantifying the edges and corners of the particle.
In addition to the traditional size, aspect ratio, surface area, surface roughness and roundness parameters, particle shape can also be characterised and classified using SEM images, image processing and geometric morphometrics. In SEM, particles are viewed under an electron microscope, where their shapes and internal structures are visible in detail. Image processing is then used to analyse the SEM images and extract shape parameters, such as cross-sectional area, area of convex hulls and principal axis lengths. Finally, geometric morphometrics is used to compare different particle shapes and classify them into different categories.
By using a combination of traditional parameters for size, aspect ratio, surface area, surface roughness and roundness and more advanced techniques such as SEM imaging, image processing and geometric morphometrics, particle shape can be effectively and comprehensively characterised and classified. This information can then be used by industry for a variety of applications ranging from drug delivery to manufacturing processes.
