What is the composition of mill scale?

The composition of mill scale is primarily an iron oxide film that is formed during the hot rolling process of steel manufacturing. When steel is subjected to high temperatures during production, a layer of iron oxides forms on its surface as the steel reacts with oxygen in the air. This layer is known as mill scale and consists mainly of wüstite (FeO), magnetite (Fe3O4), and hematite (Fe2O3), which are all different forms of iron oxide.

Understanding the formation of mill scale is essential for those involved in surface preparation and painting processes since mill scale can affect the adhesion and performance of coatings applied to steel substrates. Proper removal of mill scale prior to coating is crucial to ensure that paint and other protective systems properly bond to the metal surface.

The other options refer to different types of oxide films or compounds that are not related to the production of mill scale. While they may involve metal oxidation or corrosion processes, they do not accurately describe the specific composition created during hot rolling of steel.