Fundamentals of Close Coupled Atomization for Battery Metal Powders
Close coupled atomization controls melt superheat, aspiration pressure, and supersonic gas shear to yield ultrafine spherical powders for battery manufacturing.
Powder Oxidation Passivation
Meaning
Finely divided metallic powders can react violently with atmospheric oxygen and moisture when exposed to air. To prevent such reactions, powder oxidation passivation is applied to create a thin, stable oxide barrier on each particle surface. This layer prevents further oxygen penetration while keeping the powder safe for transport and handling.
This chemical stabilization is carried out in a controlled environment before the powder leaves the atomizer.
Passivation Layer
Introducing a low concentration of oxygen into the inert gas stream during the final cooling stage initiates this process. The oxide skin must be thick enough to resist atmospheric reactions but thin enough to avoid degrading the consolidated metal properties. This oxide typically measures only a few nanometers in thickness.
Process Safety
Unpassivated powders of titanium, aluminum, or magnesium are highly pyrophoric and pose a severe fire hazard in the factory. Controlled exposure to oxygen reduces the chemical reactivity of the fresh surfaces in a predictable manner. This safety step is required by international transport regulations for metal powders.
Material Impact
Thick oxide layers can act as barriers to sintering during subsequent compaction or additive manufacturing steps. This resistance to melting can cause porosity and weak bonds in the finished components. Sourcing contracts therefore specify the maximum allowable bulk oxygen content of the powder.
Refined control of the oxidation stage is needed to ensure that safety does not come at the expense of material strength.