Shrinking core model is widely applied to describe the reduction of iron ore pellets, but limited to the illustration on powder sample. The reduction of powder materials is commonly observed in blast furnace production but has been rarely investigated. In this study, thermal kinetics analysis was conducted to describe the powder reduction of dicalcium ferrite (2CaO center dot Fe2O3, C2F), calcium ferrite (CaO center dot Fe2O3, CF), and hematite (Fe2O3, H), with particle sizes below 70 mu m. Isothermal reduction experiments were performed through thermogravimetry analysis under CO atmosphere. The reduction degrees and reaction rate constants increased in the order of C2F, CF, and H at 1123,1173, and 1223 K The reduction rate analysis illustrated that the reduction of C2F, CF, and H appeared as one-, two-, and three-stage reactions, respectively. Moreover, the reduction of C2F and CF proceeded as the 2D reaction mechanism described by Avrami-Erofeev (A-E) equation. The reduction of H was initially controlled by 2D, followed by the 3D A-E kinetics equation. Phase with superior reducibility could be reduced by CO in more dimensions of sample layers. The reduction degrees and rate change expressed by A-E equations were verified to be in accordance with the experimental data. A new kinetics model was proposed to elucidate the reduction of C2F, CF, and H in ultrafine powder compared with that in pellets. The reduction process in the powdered samples comprised independent reduction stages caused by uniform CO diffusion in powdered particles. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.