Particle size distribution (PSD) describes the full range of particle sizes present in a metal powder, not just a single average figure. Understanding PSD, and the D-values used to summarise it, is essential for specifying and comparing powders with confidence.

What particle size distribution actually means

Real metal powders are never a single uniform size. Instead they contain a spread of particles, from fine to coarse, and PSD is the statistical picture of that spread. A powder might be described as having a distribution running from roughly 15 to 75 microns, but two powders sharing the same range can still behave very differently depending on how the volume is distributed within it. That is why a single number can mislead, and why buyers should specify the shape of the distribution rather than an average alone.

How D10, D50 and D90 are defined

D-values are cut points on the cumulative distribution, read by volume. Each states the size below which a given percentage of the material falls. D50, the median, is the most quoted value, but reading D10 and D90 together tells you how wide or narrow the distribution is.

  • D10: Meaning: 10% of the powder by volume is finer than this size; Why it matters: Indicates the fine fraction, which affects flow, dust and reactivity
  • D50: Meaning: Median size; half the powder is finer, half is coarser; Why it matters: The headline size used for quick comparison between grades
  • D90: Meaning: 90% by volume is finer than this size; Why it matters: Flags the coarse tail, important for surface finish and sieve limits

The span, calculated as (D90 minus D10) divided by D50, gives a simple measure of how tight the distribution is. A lower span means a more uniform powder.

How PSD is measured

Two methods dominate. Sieve analysis passes the powder through a stack of graded meshes and weighs what is retained on each; it is robust and inexpensive but has limited resolution below about 38 microns. Laser diffraction measures how particles scatter a laser beam and reports a continuous volume-based distribution, giving detailed D-values across a wide range. Because the two techniques measure different physical properties, results will not match exactly, so always compare like with like and note the method used.

Why PSD matters in practice

Distribution shape drives real performance. A well-graded PSD improves packing density, because finer particles fill the voids between coarser ones, which in turn aids compaction and green strength. During sintering, finer fractions increase surface area and can accelerate densification, while a controlled coarse tail helps manage shrinkage. PSD also governs powder flow and feeding behaviour, the achievable surface finish, and, above all, batch-to-batch reproducibility. Specifying PSD tightly is the most reliable way to keep a process consistent.

How PSD relates to mesh and micron

Mesh size and micron are two ways of expressing a single cut point, and our companion guide on mesh and micron conversion covers that relationship in detail. PSD is the fuller picture: rather than one pass or fail threshold, it describes the whole population of particles and how that population is spread. For demanding applications, both the cut points and the distribution shape should appear on the specification.

Key takeaways

  • PSD describes the full spread of sizes in a powder, not a single average.
  • D50 is the median; D90 means 90% by volume is finer than that size.
  • Reading D10, D50 and D90 together reveals how tight the distribution is.
  • Sieve analysis and laser diffraction give different results; state the method.
  • PSD influences packing, compaction, sintering, flow, finish and reproducibility.
  • Mesh and micron give cut points; PSD gives the complete profile.

Ronald Britton has supplied metal powders since 1945, with ISO 9001 and 14001 certification and 48-hour UK dispatch. If you need help specifying or comparing powders by PSD, request a quote or contact our technical team and we will match the right grade to your process.