Powder Characterization: The Importance of Segregation Mechanisms

Powder segregation is defined as the modification of a bulk material’s particle size distribution (PSD) that results in a homogeneous mixture separating into distinct portions. This can result in undesirable inconsistencies in granulated end-products and is one of the primary contributors to process failure in systems handling powdered products. The importance of powder characterization for determining the segregation mechanisms of distinct mixtures is therefore self-evident. However, there is no single underlying cause of segregation and its mechanisms are extremely varied.

In this blog post, Particulate Systems explores powder characterization of segregation mechanisms in more detail.

What Affects Segregation?

All powders that are mixed from individual components at industrial scales comprise a mixture of particles with different physiochemical properties. Even those that are mixed within extremely tight tolerances with regards to uniformity and breadth of the PSD are subjected to forces that cause segregation. This is due to the intrinsic differences of the powder’s various components. Particle characterization of the underlying raw materials can assist in predicting their behavior in processing conditions, but it cannot reliably characterize the segregation mechanics of the overarching mixture.

Particle cohesivity, density, shape, and size all play a role in segregation downstream of the mixing unit. Any physical disturbance affecting the powder presents the opportunity for discriminatory motion, which causes particles of a similar size or density to group together and separate from dissimilar particles within the bulk material. High cohesivity can regulate segregation, making it more difficult for motion to separate mixtures. However, the interplay between these various properties is extremely dynamic with different disturbing forces causing different mechanisms of segregation.

For example, lightweight powders that are transported through shoots and hoppers may adopt a semi-fluidized state in response to flow. This can have an impact on the textural qualities and dispensability of the end-product. Electrostatic powder coatings rely on outstanding powder uniformity while in a semi-liquidized state to ensure that coatings applied via spray deposition are uniform. If the material mixture separates in a fluidized state, it will not be suitable for application.

Fluidization segregation is merely one example of a range of segregation mechanisms that must be explored for robust powder characterization of bulk mixtures. Sifting, trajectory, angle-of-repose, dusting, and agglomeration are all common segregation mechanisms that can result in product failure. In fact, it is estimated that roughly 30% of all unscheduled downtime in powder handling systems comes as a result of segregation-related quality issues.

Powder Characterisation with Particulate Systems

Particulate Systems offers the SPECTester system to help you identify both primary and secondary segregation mechanisms in powder mixtures containing up to six distinct components. It offers fully-automated analyses of how much of a powder mixture is segregating by simulating sifting, fluidization, and angle-of-repose conditions. It then provides a simple report using 50 individual sample points from across the sample bed.

This innovative system is ideal for quality assurance and control of powdered products and for powder characterization for segregation mechanics in simulated manufacturing conditions. If you would like to learn more, please do not hesitate to contact us directly.

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