Microwave absorption and antioxidation properties of flaky carbonyl iron passivated with carbon dioxide

Carbonyl iron particle is a typical magnetic microwave absorbing material. Because of the effect of particle shape, the flaky carbonyl iron has large values of microwave permeability and can be an excellent super-thin absorber. However, the flaky carbonyl iron prepared by high-energy ball milling has high activity and is apt to be oxidized. Based on a reverse reaction of the blast furnace iron-making process, this work developed a facile passivation method with carbon dioxide to improve the antioxidation property of the flaky carbonyl iron. The antioxidation property of the passivated carbonyl iron was improved greatly while the excellent microwave absorption property maintained. - Highlights: • We demonstrated a facile passivation method with carbon dioxide to improve the antioxidation property of the flaky carbonyl iron. • This method may be applied to passivate other ultrafine metal powders such as copper and zinc. • The passivation greatly improves the antioxidation property and only has slight influence upon the microwave absorption properties