Process description: Brightening

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Brightening

In the brightening of steel, concentrated nitric acid is used to form a very clean surface. Note that this process forms nitrous gases in the exhaust gas.

Copper and brass are brightened by oxidising a surface layer.

Aluminium and some of its alloys can be brightened by chemical or electrochemical processes for special applications such as lighting and decorative finishes.

Phosphoric acid pickles have specific uses such as chassis parts and bicycle frames. It is usually used at a concentration of 10-15% at temperatures of 40-50°C and sometimes as high as 80°C.

Metal surfaces must be degreased thoroughly. Poor results, such as uneven attack or stained surfaces after brightening, are frequently due to insufficient pre-degreasing.

Source: BAT Surface Treatment of Metals and Plastic, Aug. 2006.

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