Powder And Mixing -2. What Is Powder Particle Size? Why Does Particle Size Affect Mixing Uniformity?

In modern powder processing industries, particle size plays a critical role in determining powder behavior, mixing performance, drying efficiency, and final product quality.

Whether in food processing, pharmaceuticals, chemicals, lithium battery materials, fertilizers, pigments, or industrial minerals, engineers constantly face challenges such as:

• Poor powder mixing uniformity

• Ingredient segregation after mixing

• Difficulty dispersing micro additives

• Ultrafine powder agglomeration

• Dust floating during processing

• Inconsistent mixer performance across materials

Behind many of these issues relies one core factor: Powder Particle Size

Understanding particle size is one of the fundamental principles of powder engineering and powder mixing technology.

1. What Is Powder Particle Size?

Powder particle size generally refers to the size of individual powder particles.
Since actual powder particles are often irregular in shape, powder engineering commonly uses the concept of equivalent diameter to describe particle size.

Internationally, the most commonly used units include:

• mm (millimeter)

• μm (micron)

• nm (nanometer)

Examples:

2. Why Is Particle Size So Important?

In powder engineering, particle size is not simply about "how large" a particle is. It directly affects:

• Powder flowability

• Mixing uniformity

• Dispersion efficiency

• Segregation tendency

• Drying performance

• Conveying behavior

• Packing density

• Surface adsorption

• Agglomeration tendency

• Chemical reaction activity

Especially in powder mixing processes:

The greater the particle size difference, the more difficult uniform mixing becomes.

This is one of the most important principles in powder mixing technology.

3. Common Methods for Describing Particle Size

In modern powder engineering, particle size is usually not represented by a single value, but by: 

Particle Size Distribution(PSD)

This is because actual powder contain:

• Large particles

• Medium particles

• Fine particles

Therefore, the industry commonly uses:

• D10

• D50

• D90

to describe particle size distribution.

3.1 D10

D10 means 10% of the particles are smaller than this size.

3.2 D50

D50 is also known as media particle size. It means 50% of the particles are smaller than this size.

3.3 D90

D90 means 90% of the particles are smaller than this size. It is commonly used to evaluate the presence of coarse particles.

4. Why Does Particle Size Affect Mixing Uniformity?

This is one of the core issues in powder mixing. Unlike liquids, powders do not naturally become uniform during movement.

Particles with different sizes may exhibit behaviors such as:

• Floating

• Settling

• Layering

• Segregation

• Agglomeration

during processing.

4.1 Particle Size Influences Particle Movement

Generally speaking:

• Larger particles tend to sink

• Smaller particles tend to float

For example, when mixing salt and chili powder:

• Salt particles are larger and heavier

• Chili powder particles are finer and lighter

During mixing, fine particles tend to remain near the top, while coarse particles settle toward the bottom. This can easily result in poor mixing uniformity.

4.2 Particle Size Differences Cause Segregation

During:

• Mixing

• Conveying

• Feeding

• Vibration

• Packaging

Particles of different sizes tend to separate automatically. This phenomenon is known as: Powder Segregation.

For example:

• Larger particles may roll outward

• Smaller particles may fall into gaps

As a result, even after mixing is completed, segregation may occur again.

4.3 Ultrafine Powders Tend to Float and Agglomerate

When particle size becomes extremely small, powder behavior changes significantly.

Especially for ultrafine powders, typically referring to powders: above 1000 mesh or below 10 μm.

At this stage:

• Gravitational effects weaken

• Electrostatic effects increase

• Surface energy rises

• Particle adhesion becomes stronger

As a result, powders may exhibit:

• Floating

• Agglomeration

• Pseudo-particle formation

• Poor dispersion

This is why: Mixing ultrafine powders is far more difficult than mixing ordinary powders.

5. Relationship Between Particle Size and Powder Flowability

Particle size also strongly affects powder flowability.

Smaller particles:

• Have better flowability

• Move more easily

Larger particles:

• Have higher internal friction

• Tend to adhere to each other

• Exhibit poorer flowability

However, in some metallic powders, very fine particles may also show excessive flowability due to smooth surfaces. Therefore, powder flowability is actually a complex issue. It depends not only on particle size, but also on Density, Particle shape, Moisture content, Electrostatic effects, Surface roughness and other factors.

6. Why Do Traditional Mixers Struggle with Particle Size Differences?

Some machines like V-type mixers, 3D mixers, double cone mixers mainly rely on Gravity Diffusion Mixing.

For powders with similar particle size, similar density, good flowability, these mixers can often achieve acceptable results.

However, when dealing with:

• Light and heavy powders

• Ultrafine powders

• Micro ingredients

• Fibrous materials

• Agglomerated particles

Simple vessel rotation is often insufficient to achieve true micro-scale uniformity.This is because particle size differences continuously promote re-segregation.

7. Why Do Complex Powders Require Stronger Mixing Mechanisms?

For difficult powder systems, mixing requires more than bulk movement, low segregation and micro-scale dispersion.

This is because natural powder flow alone cannot overcome problems such as:

• Floating

• Settling

• Agglomeration

• Pseudo-particles

• Fiber entanglement

Therefore, modern advanced powder mixing technologies increasingly emphasize:

• Shear mixing

• Dispersion capability

• Micro-scale distribution

• Anti-segregation performance

• and related mechanisms

8.Why Is Particle Size Analysis Becoming More Important?

With the rapid development of industries such as new energy materials, advanced materials, pharmaceuticals, powder metallurgy, modern industry requires increasingly higher levels of mixing uniformity. For example: Battery materials, Conductive additives, Carbon nanomaterials Metal powders and Trace additives. 

As a result, particle size analysis has become a critical foundation in powder process design. In practical engineering applications, many companies now analyze particle size distribution, evaluate particle differences, predict segregation tendencies before mixing begins. This helps determine mixing difficulty in advance.

9. Future Trends in Powder Mixing Technology

With industrial upgrading, future powder mixing technology is no longer focused only on "Mixing", but rather on high uniformity, low segregation, and micro-scale dispersion.

As a result, modern powder engineering increasingly emphasizes particle size control, particle size distribution optimization, powder behavior analysis, micro-uniformity theory and anti-segregation technology.

10. Conclusion

Particle size in powders is not merely a concept of “how large the particles are.” In fact, it determines a series of critical process behaviors, including:

• Powder movement behavior

• Flow characteristics

• Segregation tendency

• Dispersion capability

• Mixing uniformity

and many other key processing outcomes.

Understanding particle size is a fundamental step toward understanding powder mixing technology.

In subsequent articles, we will continue to explore in greater depth:

• What is powder flowability?

• What is the angle of repose of powders?

• Why do powders segregate?

• What is microscopic homogeneity?

• Why are ultrafine powders difficult to mix?

as well as:

How modern powder mixing technologies address these challenges?