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|Title:||A study of the mechanisms of degradation of iron ore pellets during reduction|
|Abstract:||<p>Minor impurities in iron ore pellets such as lime and alkali oxides or in the reducing gas (alkali metal vapors) may cause the pellets to degradate when reduced under conditions relevant to the operation of the iron blast furnace. New techniques have been designed to clarify the mechanisms of iron whisker formation during metallization, since the relationship between their growth and abnormal swelling has been established. In the absence of a significant amount of impurities, it has been observed that the reduction of heterogeneous wustite incurs iron whisker growth. Calcium oxide, as the main impurity with wustite, promotes iron whisker growth when it is unevenly distributed in the calcio-wustite. It is reasonably confirmed that nucleation and growth of iron occurs at sites higher in calcium oxides on the wustite surface. Magnesium oxide has no pronounced effect on the growth of the iron whiskers. In the present work, the effect of magnesium oxide has been surmounted when lime is also added. The influence of CaO and MgO in solid solutions on enhancing the kinetics of wustite metallization have been related to the extent of disturbing the wustite lattice structure. Alkalis cycling inside the blast furnace affect the stability of the silica-rich gangue in iron ore. The mechanism and certain measures to control the degradation of commercial pellets subject to alkali, attack have been investigated. The silica-rich gangue plays an important role in bearing with the destructive forces suffered by the iron oxide grains during reduction. When they are available during reduction of pellets, alkalis would flux the silica and react with ferrous oxide to form low melting point primary liquid slags which cause the pellets to degradate long before metallization.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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