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When dealing with powders, metal or otherwise, it is often stated weather the powder grains are spherical or flakes. Is it the grinding process that determines the shape of the powder, or is the shape obtained through some other means?

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It depends partly on the properties of the material and partly on the manufacturing process.

High quality metal powders used for sintering and powder metallurgy for example are often produced by gas atomisation. Here molten metal is sprayed through a fine jet in an inert atmosphere and the droplets formed are allowed to solidify. This process naturally produces spherical beads of reasonably uniform and controllable size. Variations on this process may use a centrifuge or various gas and liquid jets or an electric arc to disperse the metal. You also get a similar effect as a side effect of some arc welding processes.

Fumed silica, which is widely used as a desiccant, thickening agent and filler for, paints, resins, adhesives etc. is produced by pyrolysis of quartz sand in a flame.

Brittle materials such as hard metal alloys and many minerals can be pulverised in a ball mill, here the particle size and shape will depend on the mill setup and the fracture characteristics of the material in question.

Powders can also be produced by various chemical and electrolytic precipitation processes.

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The manufacturing process determines the shape.

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