Introduction
One of the most common misunderstandings I see in powder processing projects is that customers focus only on average particle size.
A customer may ask:
“Can you produce 10 microns?”
At first glance, this seems like a straightforward question. However, from an engineering perspective, it is often incomplete.
In reality, two powders can have the same average particle size while performing very differently in production.
The reason is simple:
Particle size distribution often has a greater impact on product performance than average particle size alone.
Whether you are processing minerals, battery materials, chemicals, coatings, or food ingredients, understanding particle size distribution (PSD) can help you make better equipment and process decisions.
In this article, I’ll explain why PSD matters, how it affects product quality, and why many successful powder processing projects focus on distribution rather than just a single particle size number.
Why Average Particle Size Can Be Misleading
Average particle size is usually expressed as D50.
D50 means:
- 50% of particles are smaller than this size
- 50% of particles are larger than this size
For example:
A powder with D50 = 10 μm sounds simple enough.
However, this number tells us very little about the overall particle population.
Consider these two products:
Powder A
- D10 = 3 μm
- D50 = 10 μm
- D97 = 25 μm
Powder B
- D10 = 1 μm
- D50 = 10 μm
- D97 = 80 μm
Both products have the same D50.
But their behavior in production may be completely different.
Powder B contains a much larger proportion of coarse particles, which can affect:
- Flowability
- Product consistency
- Surface finish
- Downstream processing
This is why relying only on average particle size can be misleading.
What Is Particle Size Distribution?
Particle size distribution describes how particle sizes are spread throughout a powder sample.
Common PSD indicators include:
D10
10% of particles are smaller than this size.
D50
The median particle size.
D90
90% of particles are smaller than this size.
D97
97% of particles are smaller than this size.
This value is commonly used in powder processing and equipment specifications.
The narrower the distribution, the more uniform the powder tends to be.
The wider the distribution, the greater the variation between fine and coarse particles.
Why PSD Matters in Real Production
From my experience, PSD often affects production performance more than many buyers initially expect.
Battery Materials
In lithium battery applications, PSD can influence:
- Packing density
- Electrode consistency
- Product stability
Even small changes in particle distribution may impact final battery performance.
Coatings and Paints
In coatings, PSD affects:
- Surface smoothness
- Hiding power
- Dispersion behavior
A controlled distribution often produces a more consistent finish.
Calcium Carbonate and Mineral Fillers
For mineral applications, PSD can affect:
- Flowability
- Bulk density
- Mixing behavior
- Product uniformity
Two powders with the same D50 may perform very differently during processing.
Food Ingredients
In food processing, PSD can influence:
- Mouthfeel
- Solubility
- Mixing consistency
A narrow distribution often results in more predictable product quality.
How Air Classifiers Help Control Particle Size Distribution
This is where air classifiers play a critical role.
Many people think an air classifier simply separates coarse particles from fine particles.
In reality, a properly designed classifier helps shape the entire particle size distribution.
The classifier wheel creates a specific cut point.
Particles finer than the cut point pass through.
Coarser particles are rejected and returned for further grinding.
By adjusting:
- Classifier wheel speed
- Airflow volume
- Feed rate
operators can optimize both particle size and PSD.
In many projects, the goal is not simply to make particles smaller—it is to achieve a stable and repeatable particle size distribution.
How Jet Milling Influences PSD
Jet mills are widely used when ultra-fine particle sizes are required.
Because grinding occurs through particle-to-particle collisions, jet mills can produce:
- Fine particle sizes
- High purity products
- Relatively narrow particle size distributions
This is one reason why jet milling remains popular in:
- Pharmaceuticals
- Battery materials
- High-value specialty chemicals
However, even with a jet mill, classifier settings remain critical for achieving the desired PSD.
Common Mistakes Buyers Make
One of the most common mistakes I see is focusing only on a target particle size.
For example:
“We need 10 microns.”
This statement often raises additional questions:
- Is that D50 or D97?
- What PSD range is acceptable?
- How much coarse material is allowed?
- What is the final application?
Without this information, equipment recommendations may not be accurate.
What Information Should You Provide Your Supplier?
If PSD is important for your application, consider providing:
- D10
- D50
- D90 or D97
- PSD curve if available
- Product application information
- Existing laboratory test data
The more complete the information, the more accurately a supplier can recommend equipment and process parameters.
Conclusion
Average particle size is important.
But in many powder processing applications, particle size distribution is even more important.
A well-controlled PSD can improve:
- Product quality
- Production consistency
- Downstream processing performance
- Overall process efficiency
Whether you are evaluating an air classifier, a jet mill, or a complete powder processing system, understanding PSD will help you make better decisions.
The right particle size matters. The right particle size distribution often matters even more.
If you are evaluating a grinding or classification project and would like to discuss your PSD requirements, feel free to contact us.
Mills Powder Engineering — Helping Customers Achieve Consistent Powder Performance Through Better Process Design.