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.
Melt Erosion Ceramic
Meaning
Refractory delivery nozzles are subjected to extreme thermal and chemical environments during molten metal processing. This degradation is known as melt erosion ceramic wear, which limits the operational lifetime of critical nozzle components. Dissolution and mechanical scouring by the liquid metal alter the nozzle geometry during a run.
This degradation makes it difficult to maintain a constant metal flow rate over long runs.
Wear Mechanism
Chemical reactions between the alloy elements and the ceramic oxides lead to the formation of low-melting-point compounds. These compounds are easily swept away by the high-velocity metal stream, exposing fresh ceramic beneath. Turbulence at the nozzle entry accelerates this wear, particularly when processing highly reactive alloys.
This progressive damage increases the nozzle diameter, leading to an uncontrolled rise in the metal feed rate.
Material Selection
High-purity alumina, zirconia, and boron nitride are commonly selected to withstand these harsh melt conditions. Zirconia offers excellent resistance to thermal shock but can undergo phase transitions that cause cracking. Boron nitride is highly resistant to wetting by molten metals, reducing the rate of chemical dissolution.
The choice depends on the specific alloy chemistry and melt temperature.
Process Consequence
Changes in nozzle diameter directly alter the gas-to-melt ratio during atomization. This instability shifts the powder particle size distribution, reducing the yield of the desired powder fraction.