Development of Porous Iron based Material by Slag Foaming and its Reduction

Metal foams have potential for variety of applications such as ultra-light weight structural components, heat insulations and energy absorber. Commercially available metal foams are made mostly by aluminum alloys, which are manufactured using titanium hydride as a foaming agent. Iron based metal foam has several advantages over aluminum alloy foam such as high strength, high energy absorbability and low cost. However, it is hard to manufacture iron foam using conventional foaming agents because of a significant difference between their decomposition temperatures and melting point of iron. Further, even if good foaming agent can be utilized, it is also difficult to obtain iron foam with high porosity. In this study, therefore, new manufacturing method of porous iron by foaming of molten oxide and reduction of foamed oxide was studied. This foaming phenomenon is very famous in the field of steel making, while it should be suppressed.The tablet of Fe, Fe2O3, Al2O3, and CaCO3 was heated rapidly in the crucible to foam the molten oxide by carbon dioxide generated from carbonate in the inert atmosphere. The target oxide system is FeO–Fe2O3–CaO–Al2O3. The time, at which maximum porosity was obtained, became longer with decreasing the foaming temperature. This is because the decomposition rate of CO2 from CaCO3, which is foaming agent of this method, decreases with decreasing temperature. Maximum porosity of the oxide was approximately 57% at 1350 °C, and the pore shape obtained in this study was spherical. After reduction of the iron oxide in the obtained foam to the reduction degree of 95%, the composite material of metallic iron, oxide, and pore was obtained with higher porosity than this oxide.