Methods of Production

There are various methods available for the production of powders. Some of the important processes are as follows: atomization, machining, crushing and milling, reduction, electrolytic deposition, shotting, and condensation.

Atomization: In this method, molten metal is forced through a small orifice and is broken into small particles by a powerful jet of compressed air, inert gas, or water jet. These small particles are then allowed to solidify. These are generally spherical in shape. Atomization is mostly used for low melting point metals such as brass, bronze, zinc, tin, lead, aluminium, etc.

Machining: In this method, first chips are produced by filing, turning, etc. and then pulverized by crushing and milling. The powders produced by this method are coarse in size and irregular in shape. Hence, this method is used for only special cases such as production of magnesium powder.

Crushing and Milling: These methods are used for brittle materials. Jaw crushers, stamping mills, and ball mills are used to breakdown the metals by crushing and impact.

Reduction: Pure metal is obtained by reducing its oxide with a suitable reducing gas environment at an elevated temperature (below the melting point) in a controlled furnace. The reduced product is then crushed and milled to a powder. Sponge iron powder is produced this way.

Electrolytic Deposition: This method is specially used to produce iron and copper powders. This is similar to electroplating process. To produce copper powder, copper plates are placed as anodes in the tank of electrolyte, whereas the aluminium plates are placed into electrolyte to act as anode. When DC current is passed through the electrolyte, the copper gets deposited on cathode. The cathode plates are taken out from electrolyte tank and the deposited powder is scrapped off. The powder is washed, dried, and pulverized to produce powder of the desired grain size.

Shotting: In this method, the molten metal is poured through a siever or orifice and is cooled by dropping into water. This produces spherical particles of large size. This method is commonly used for metals of low melting points.

Condensation: In this method, metals are melted and boiled to produce metal vapours and then condensed to obtain metal powders. This process is applied to volatile metals such as zinc, magnesium, and cadmium.