Cast iron continued oxidation

Although more and more zinc sheet and strip are produced in continuous mills, some is stiU produced by rolling slabs cast in open or closed book-type molds made of cast iron (124—127). The casting temperatures are between 440 and 510°C, mold temperatures between 80 and 120°C. The contact surfaces of the mold must be smooth and clean to allow unrestricted shrinkage of the cast slab. Mold lubricant is not necessary, but if used should be held to a minimum. Slabs cast in open molds must be skimmed immediately to remove surface oxide. Rolling slabs are cast 1.87—10 cm thick. 

Zinc and its alloys are widely used because they have low melting points and can be easily cast. Therefore, various objects are made from zinc and its alloys. Zinc is widely applied to iron and steel as a protective coating by the process known as galvanization that consists of coating an iron object with a thin layer of zinc. Relative to iron, zinc is an anode, so it is preferentially oxidized. If the coating is broken, the zinc continues to corrode rather than the iron object. When iron is coated with a less reactive metal such as tin, a break in the coating causes the more easily oxidized iron to be corroded at an accelerated rate. 

The mill scale utilized in this study is formed in a continuous casting plant and is of non-oily nature. Other than iron oxides of different valence states, it contains metallic iron and impurities. Table I displays the chemical analysis of the mill scale. In the SHS experiments, a mixture of Mill-scale, NiO, Cr203, M0O3 and A1 powders were used in order to produce metallic Fe, Fe-Ni, Fe-Ni-Cr, and Fe-Mo alloys. The metal oxide powders have over 96 % purity and 200 pm average grain sizes. The advanced thermochemical simulations of the reactions were... 

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