Meaning
Shear flow instabilities occur at the contact boundary between a high velocity gas jet and a slower moving stream of molten metal during atomization. These kelvin-helmholtz waves cause the liquid surface to ripple and break up into ligament structures. This physical mechanism governs the initial droplet size distribution before surface tension pulls the metal into spherical particles.
Understanding this instability allows powder producers to design nozzle configurations that yield narrow size distributions.
Boundary Instability
Velocity differences generate pressure variations across the liquid metal sheet, which amplify surface disturbances. These disturbances grow into waves that eventually shear off into droplets.
Powder Morphology
Rapid wave growth generates smaller ligaments that solidify into fine powders suitable for battery applications. Slow wave growth leads to larger droplets and coarse powder.
Process Yield
Optimizing the gas velocity profile maximizes wave amplitude at the nozzle exit, which increases fine powder yield. This optimization reduces the energy required for secondary grinding.