Figure 1
Phase transformation of the crystal structure in the sintering process.
(Top) Crystal structures of Fe10O14(OH)2, γ-Fe2O3, ε-Fe2O3 and α-Fe2O3. Red and blue polyhedra in the crystal structure indicate the octahedral and tetrahedral Fe sites, respectively. Yellow balls represent oxygen atoms. (Middle) Sintering temperature dependence of the particle size (vertical panel) and phase diagram showing the phase ratio versus sintering temperature (horizontal panel). (Bottom) XRPD patterns of (i) the precursor Fe10O14(OH)2, (ii) S-250, (iii) S-1020 and (iv) S-1295. The silica matrix in the precursor and the remaining silica in S-1295 are extracted. Grey dots and the orange, blue, green and red areas indicate the observed pattern and the calculated patterns of Fe10O14(OH)2, γ-Fe2O3, ε-Fe2O3 and α-Fe2O3, respectively.
