Particle size distribution

The particle size distribution describes the size and number of particles. A dispersed solid system, a suspension or an emulsion can be considered. Sometimes it is also referred to as a grain size distribution. What is meant is the same thing, namely the particle size distribution. A narrow particle size distribution means that most of the particles have a similar size. This mostly low-dust state of the material usually allows good flow and conveying properties. Good flow behavior is required when bulk materials are filled at high speed (tea bag filling, sachet filling, capsule filling, adaptive manufacturing, ...) Instant products are also usually agglomerated and have a narrow particle size distribution. This is necessary to achieve rapid sinking, dispersing and dissolving behavior in the liquid during preparation.

A broad particle size distribution means that the particle sizes differ greatly from each other. This material state is of interest when a bulk material is to be compacted or agglomerated. It is also of interest in powder metallurgy and advanced ceramics, where powder volumes are required to have high mass densities.

Frequently used forms of representation are the bar chart or the sum function. For example, the cumulative distribution function is well suited for determining percentiles. In addition to the absolute frequency, the relative frequency can also be displayed. There is then a reference to cumulative properties of the particle system such as number, volume, mass or extinction.

Many properties of bulk materials can be better explained using particle size distribution. For example, the flow and conveying behavior of a bulk material, specific surface area and reactivity, abrasiveness, dissolution behavior, sedimentation, drying behavior in a vacuum mixer dryer, flavor intensity, compressibility, and agglomeration suitability.

A frequently used measurement method is the classical sieve residue analysis. Other offline techniques include image analysis, laser diffraction, dynamic light scattering, or sedimentation analysis. Modern sensor technology increasingly enables so-called in-situ particle size analysis. In this process, measuring probes are installed in the process chamber, which measure the particle sizes in the moving bed of bulk material and immediately calculate the required statistical evaluation. This even includes particle size distributions. This is interesting for continuous or batch milling processes, but also for agglomeration processes. The type of grinding process and the type of agglomeration have a great influence on particle shape, particle strength and particle size distribution. In contrast to batch processing, continuous processes can usually be better adjusted to the desired target variables.

In addition to the particle size distribution, the porosity and strength of the particles are also important in the production of baby food. The nutrient agglomerate of a baby food contains hydrophilic substances as well as hydrophobic substances such as fats. However, the solvent/dispersant is hot water.

The spray drying process favors the attachment of suitable emulsifiers to the particles. When handling, note that dust is undesirable. Dust not only interferes with the preparation process at the end user. Dust is also a problem for the closure of packaging. High-performance closure seals are only permanently tight if they are applied dust-free. For high-quality bulk solids, particle size distributions are usually specified and insofar important quality parameters.