Iron Heat Treat Scale
This very over exposed image is required to show
the small amount of light that is actually transmitted.
Transmitted Brightfield Illumination
Definition/Function:
When iron is hot rolled or heat-treated a layer of iron oxide forms on the surface. The
mechanical and termal properties of iron oxide are very
different than the underlying metal. As a result the oxide film that forms on the flat
sheet flakes off as flakes. These flakes are often black but
may also be yellow, orange, or red with reflected light due to a coating of different
oxides of iron.
Significance in the Environment:
Characteristic Features:
Mill scale tends to be flat to slightly wavy flakes with well defined edges. They tend
to be opaque but may transmit some light if the light is
intense enough, the flake is thin enough, and/or oxidation has gone beyond magnetite or
maghemite. If light is transmitted it tends to be orange to
red in color. Mill Scale tends to be black but may also be yellow, orange, or red with
reflected light, depending on the oxidation state of the
surface of the flake.
Associated Particles:
References:
