Do you know the secret of superfine powders flowability?

Powder is not a single particle but a mixture of particles with different shapes and sizes. Powder plays a vital role in pharmaceuticals, food processing, and chemical industries. It typically refers to a dispersed system composed of solid particles and voids. Particle size is generally less than 1000 μm. In engineering, materials that exist in fine powder form under normal conditions are called powders. Superfine powders have unique physical properties, such as flowability, hygroscopicity, fillability, cohesiveness, charge, high specific surface area, and low bulk density. Flowability is fundamental to powder engineering and connects particle properties with unit operations in powder technology, such as storage, feeding, transport, and mixing.

Factors affecting powder fluidity

The properties of the substance itself (such as particle size, shape, surface state, density, etc.) and the temperature and humidity of the environment determine the flowability of superfine powders.

Granularity

Particle size refers to the linear dimension occupied by particles in space. Particle size distribution refers to the percentage of particles within a certain size range relative to the total amount. Smaller particle size increases the specific surface area, enhancing molecular and electrostatic forces, which affect powder flow. Smaller particle size increases the tendency for adsorption, agglomeration, and cohesion, leading to a larger repose angle and poorer flowability. Additionally Smaller particles are more likely to form dense packing, reducing permeability, increasing compressibility, and worsening flowability.

Form

Even if the particle size is the same, superfine powders with different shapes have different flowability. Spherical particles have the best flowability because their contact area is minimal. Flaky or branched particles, with numerous flat contact points and irregular shear forces between particles, have poor flowability.

Powder-particle interaction

The friction and cohesiveness between particles affect powder flowability. For different particle sizes and shapes, friction and cohesiveness impact flowability differently. For larger particles, cohesive forces are much smaller than volume forces, so flowability mainly depends on particle shape. Powders with rough surfaces or irregular shapes usually have poor flowability. For smaller particles, cohesive forces dominate over volume forces, making flowability mainly dependent on cohesion.

Temperature

As temperature increases, powder flowability initially increases and then decreases. At low temperatures, particle density increases with temperature. However, at very high temperatures, powder adhesion increases due to the effects of heat.

Moisture

Generally, when the moisture content of powder is low, the surface adsorbs water, and this adsorbed water has little effect on flowability.
As moisture increases, a thin layer of water forms around the adsorbed water, making it difficult for particles to move relative to each other, restricting overall flow. When moisture exceeds the maximum molecular bound water, powder flowability worsens and may even be lost.

Methods to improve powder fluidity

Powder surface modification

Modification technology is a process that alters the physicochemical properties of powder surfaces or interfaces, such as surface atomic structure, functional groups, polarity, and charge properties, to improve powder performance.

Physical modification technology mainly alters the morphology and size of powder particles, using methods like co-milling and surface coating. Surface coating, also known as surface layering or coating technology, connects modifiers to powder particles through physical methods or van der Waals forces, without triggering chemical reactions. Common modifiers include dispersants, surfactants, and typical methods involve mechanical grinding, mixing, and powder deposition.
Chemical modification involves using chemical reactions between modifiers and powder particles to effectively change powder properties. This method is well-researched in fields like food ingredients and traditional Chinese medicine.

Application of carrier

By selecting suitable carriers or flow aids based on powder properties, you can improve hygroscopicity and flowability. Adding the right amount of flow aid to the powder allows it to attach to the surface, smoothing rough areas.
This reduces friction between particles, which improves flowability to some extent. The carrier’s properties can be targeted to address the defects of a single carrier or flow aid.

Conclusion

Powder is a collection of many individual solid particles, a special form of solid. Flowability is a key parameter of powder that is of common concern across industries, directly affecting production efficiency and product quality. Measuring and improving powder flowability is crucial for production processes, transportation, storage, filling, and the shaping and weighing of powder products.

Epic powder

Epic Powder, 20+ years of work experience in the ultrafine powder industry. Actively promote the future development of ultra-fine powder, focusing on crushing,grinding,classifying and modification process of ultra-fine powder.  Contact us for a free consultation and customized solutions! Our expert team is dedicated to providing high-quality products and services to maximize the value of your powder processing. Epic Powder—Your Trusted Powder Processing Expert !