Influence of Crystal Structure and Chemical Composition on the Reducibility of Silico-Ferrite of Calcium and Aluminum in CO–CO₂–H₂–H₂O Atmosphere

Abstract

In this study, influence of crystal structure and chemical composition for Silico-Ferrite of Calcium and Aluminum (SFCA) on its reducibility are examined. Eight types of the powder samples containing SFCA and SFCA-I phases were prepared using chemical reagents by the heat treatments in air. The samples were heated up to 800℃ in the different atmospheres of CO–CO₂–H₂–H₂O systems. The reducibility of the samples was evaluated using the peak intensity ratio identified by XRD before and during the reduction experiment. The intensity of SFCA peak is not decreased up to 700℃ in CO–CO₂ atmosphere, whereas the intensity become weak in CO–CO₂–H₂–H₂O atmosphere. The intensity of SFCA-I peak is decreased above 500^oC in all atmospheric condition and the reduction reactions are enhanced by the addition of H₂–H₂O gas. Decrease in intensity of SFCA peak is independent of Fe composition, whereas that of SFCA-I is decreased with decreasing Fe concentration. The difference in reducibility is attributed to the difference in the crystal structure of multi-component CF. SFCA and SFCA-I are composed of pyroxene and spinel units. Since the pyroxene unit contains more gangue minerals than spinel unit, it implies that the pyroxene unit shows low reducibility than the spinel units. Since SFCA-I contains more the spinel units than SFCA, SFCA-I is easily reduced than SFCA.