Silico-ferrite of calcium (SFC) is a key transitional phase in the formation process of complex silico-ferrites of calcium and aluminum (SFCA-I and SFCA), and SiO2 plays an important role in the formation of SFC. To study the formation mechanism of SFC by solid-state reactions is conducive to understanding the process of SiO2 involved in the formation of SFCA-I and SFCA. Experiments were carried out under air at different temperatures from 600 degrees C to 1200 degrees C by a certain amount of SiO2 mixing with Fe2O3 and Ca(OH)(2). X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used to characterize the phase change of the sintered samples. The results show that the initial product of SiO2 that participated in the formation process of SFC is 2CaO center dot SiO2 (C2S) that mainly forms by the reaction of SiO2 and CaO center dot Fe2O3 (CF) at approximately 1000 degrees C. Subsequently, C2S that disappears with it reacts with Fe2O3 and CF respectively to form SFC at approximately 1100 degrees C. The reaction of C2S and Fe2O3 is more easily to occur compared with C2S and CF through the thorough solid-state reaction experiments between C2S, Fe2O3, and CF, and the formation of SFC will be promoted by the co-existence of Fe2O3 and CF that the optimal mole ratio of Fe2O3 to CF is approximately 1.00:0.55. Finally, melt appears at approximately 1200 degrees C due to the effect of the eutectic structure composed of SFC and CF. (C) 2016 Elsevier B.V. All rights reserved.