Stability of Cementite under CO–CO₂–H₂ Gas Mixture at 1200 K

Abstract

Suppression of CO2 discharged from iron and steelmaking companies is an example of the biggest issues for the protection of global environment and sustainable growth of steelmaking industry. One of the efforts made to decrease the emission of CO2 in ironmaking process is blowing of hydrogen gas into blast furnace. Hydrogen gas can reduce iron oxide and form harmless H2O. Cementite (Fe3C) may be formed by introduction of hydrogen into blast furnace and play an important role on carburization and smelting behavior of reduced iron. In the present work, Fe3C sample was held at 1 200 K under various CO-CO2-H2 gas mixtures to clarify the stability of Fe3C phase. It was confirmed that metastable Fe3C phase will decompose into Fe and C, and FeO will form under high CO2 partial pressure. Also, it was found that existence of H2 will suppress decomposition of Fe3C. It was confirmed that CO2 gas will be continuously converted into CO by C formed by decomposition of Fe3C.

Influence of Corrosion Inhibitor in Chemical Conversion Coatings on Corrosion Performance in Scratches in Zinc-Coated Steels

“…Currently, chromate-free chemical conversion coatings mainly comprise an organic base coating with a corrosion inhibitor mixed into it. 2) Various types of compounds are used as corrosion inhibitors, including colloidal silica 5,6) and phosphate compounds. [7][8][9] Regarding the corrosion resistance of chemical conversion coatings with added colloidal silica, Horiba et al demonstrated that employing silica as filler is effective in inhibiting water permeation.…”

“…5) Miki et al mentioned that a mixed corrosion product of colloidal silica and zinc hydrates eluted in a corrosive environment is effective as a barrier against corrosion-accelerating factors. 6) On the other hand, phosphate is one of the most widely employed compound as a corrosion inhibitor and a pigment. 9,10) Regarding the corrosion resistance of chemical conversion coatings with added phosphoric acid for zinc-coatings, Okai et al analyzed the relationship between corrosion resistance on a flat area and the initial crosssectional structure by using a galvanized steel sheet etched with phosphoric acid in the chemical conversion coating.…”