Particle‑size distribution (PSD) is a core technical index for talc, calcium carbonate, graphite and other mineral powders. D50, D90 and D97 are common cumulative particle‑size percentile values widely used in powder production, quality inspection and equipment selection for talc‑mill processing lines. These parameters describe how particle sizes are distributed across the whole powder sample.
Basic Definition of Cumulative Particle‑Size Percentiles
The “D” value represents cumulative volume percentage (laser diffraction standard for mineral powder):
- Dₓ = X% of the total particle volume is smaller than this numerical size value.
D50 (Median Particle Size)
D50 is also called the median particle size.
D50: 50 % of the total particle volume consists of particles smaller than this value; 50 % are larger.
It is the most frequently quoted single‑number indicator to reflect the overall fineness of talc powder.
- Example: Talc powder D50 = 5 μm → Half of the powder volume is below 5 μm, half above 5 μm.
- Note: D50 only shows the median. Two talc batches with the same D50 can have very different coarse‑particle tails and different product performances. D50 cannot reflect the maximum coarse‑particle content.
D90
D90: 90 % of total particle volume is smaller than this size; only 10 % of volume is larger than this value.
D90 reflects the main coarse‑particle trend of the powder.
- Example: Talc D90 = 12 μm → 90 % volume is under 12 μm, 10 % volume is above 12 μm.
- Use case: Evaluate how quickly particle size rises toward the coarse end; widely used for general‑grade filler quality control.
D97
D97: 97 % of total particle volume is smaller than this size; merely 3 % of volume is larger.
D97 is the critical coarse‑tail index for high‑end talc powder. That small 3 % coarse fraction heavily influences downstream applications:
- In plastics: Oversized talc grains cause surface defects, fish‑eyes and scratch marks on finished parts.
- In coatings and cosmetics: Coarse residues lead to rough texture and poor smoothness.
- In powder processing: D97 is a key target for air‑classifier tuning. Grinding and classification equipment from JACAN is commonly set to strictly control D97 to keep the coarse tail low.
Example: Talc D97 = 20 μm → Only 3 % of particle volume exceeds 20 μm. Even if D50 looks fine, a high D97 means harmful coarse particles still exist.
Practical Comparison for Talc Powder
Suppose one talc sample shows: D50 = 4 μm, D90 = 11 μm, D97 = 18 μm
- Half of the powder volume is finer than 4 μm.
- 90 % volume is finer than 11 μm.
- Only 3 % volume is larger than 18 μm.
⚠️ Important reminder for lamellar talc:
Laser diffraction gives equivalent spherical diameter. Talc platelets lie flat during measurement, so D‑values do not represent real sheet thickness. Two talc powders with identical D50/D97 may have totally different lamellar aspect ratio, BET surface area and reinforcing performance. Always combine PSD data with BET specific surface area and SEM morphology analysis.
Industrial Application Guidance
- D50: Judge overall powder fineness; used for quick‑comparison of different talc batches.
- D90: Routine quality check for general‑purpose talc fillers.
- D97: The most critical parameter for high‑grade talc for plastics, coatings and cosmetics. Controlling D97 is the main goal of ultra‑fine grinding and precision classification.
A narrow particle‑size distribution means D50, D90 and D97 values are close to each other. Broad distribution indicates a big gap between D50 and D97, with more coarse‑particle fractions.
D50, D90 and D97 are cumulative volume‑based particle‑size percentiles. D50 shows median fineness, D90 reflects major coarse trend, and D97 monitors the critical coarse tail fraction. For talc production, focusing only on D50 is insufficient. Manufacturers must pay close attention to D97 to limit oversized particles, while combining BET and morphology observation to fully evaluate lamellar talc powder quality.
