Satellite Formation

Collision Mechanism

Recirculation of gas within the cooling tower is the primary driver of the interactions between particles of different sizes. During the production of metallic powders, the smallest droplets solidify almost instantly due to their high surface area to volume ratio. These fines are then easily swept up by the eddies and vortices created by the high velocity atomizing gas.

When these solid fines strike a larger, slower cooling droplet, they become permanently embedded in its surface. The number and size of these satellites depend on the gas pressure, the nozzle design, and the density of the spray. Minimizing the amount of recirculating dust is a key goal for engineers looking to produce premium grade spherical powders.

Flowability Impact

Presence of irregular surface features on the powder grains increases the interparticle friction and leads to poor performance in automated feeding systems. Satellite formation causes the powder to be more cohesive, which can lead to bridging in hoppers or uneven spreading in additive manufacturing machines. A powder with many satellites will have a lower apparent density because the irregular shapes prevent the particles from packing tightly together.

This can result in a lower green density in pressed parts and more shrinkage during the sintering process. For applications like laser powder bed fusion, where a smooth and consistent layer of powder is required, a high satellite count can lead to visible defects in the final part.

Particle Geometry

Characterization of the powder batch often includes a visual assessment of the surface quality using scanning electron microscopy. While most gas atomized powders are described as spherical, the degree of satellite formation can vary significantly between different production runs. Technicians look for the ratio of smooth spheres to those with attached fines to determine the quality of the batch.

Some modern atomization techniques use secondary gas flows or modified chamber shapes to reduce the collision probability and produce cleaner powders. Reducing satellites is particularly important for reactive alloys where the high surface area of the fines can also lead to increased oxygen pickup. Ensuring a clean particle geometry is a hallmark of a well controlled and optimized atomization process.