Machinery's Handbook, 31st Edition
Production of Metallic Powder 1533 Electrolytic Deposition.— Electrolytic deposition is often categorized as a fourth mode of powder fabrication. In this process, an electrolytic cell is set up in which the source of the desired metal is the anode. The process involves the precipitation of a metallic element at the cathode of an electrolytic cell (Fig. 9).
Bath
Anode
+
DC
–
Cathode
Electrolyte
Fig. 9. Electrolytic Cell Operation for Deposition of Powder By the choice of suitable conditions, composition and strength of the electrolyte, temperature, current density, and so on, many metals can be deposited in a spongy or powdery state. Extensive further processing—washing, drying, reducing, annealing, and crushing—may be required. Copper is the main metal produced in this way, but chro- mium and manganese powders are also produced by electrolysis. In these cases, how- ever, a dense and normally brittle deposit is formed and needs to be crushed to powder. Electrolytic iron was at one time produced on a substantial scale but it has been largely superseded by powders made by less costly processes. Electrolytic powders are of high purity with a dendritic morphology. Hybrid Atomization.— There is increasing demand for fine spherical powder with uni form particle size applicable to advanced powder metallurgy such as metal injection molding, solder for electronics parts, and joining and conductive inks. However, conven- tional technologies cannot easily produce powders that satisfy such requirements, so a new powder production technology is needed. The National Institute for Materials Science (NIMS) developed the world’s first pow - der production method, hybrid atomization (Fig. 10), which can easily produce powder having 0.0004 in. (0.01 mm) or smaller spherical particles, with uniform size and low oxygen content. Such powders cannot be produced by conventional powder production technology. Molten Metal
Melting Crucible Melting Furnace
Gas Atomizing Nozzle
Metal droplets turn into powder several tens to several hundred micrometers ( µ m) in size by gas atomized jet.
Gas Jet
Fine Powder Stable Liquid Film (thin liquid formation with thickness of 0.0004 in. [0.01 mm])
Rotating Disk High-speed Motor
Fig. 10. Schematic Illustration of Hybrid Atomization
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