Factors influencing the microstructures of iron ore sinters

Abstract

The phases and the phase assemblages present in selected industrial iron ore sinters have been analysed. A new experimental laboratory-based procedure has been developed that enables sintering experiments to be undertaken under controlled temperature and gas conditions. The results indicate that the formation of the complex silico ferrite of calcia and alumina phase (SFCA) phase is strongly influenced by the sinter bulk composition. Within the range of compositions of interest to industrial iron ore sintering, an increase of CaO/SiO 2 ratio facilitates the growth of the SFCA phase and the addition of Al 2 O 3 increases the stability of the SFCA at elevated temperatures. Decreasing the oxygen partial pressure not only decreases the liquidus temperature but also lowers the relative stability of the SFCA phase. These observations are consistent with results obtained from phase equilibria studies of these systems, and indicate clear links between phase equilibria, melt solidification processes and sinter product microstructures.

Mechanisms of Phase and Microstructure Formation during the Cooling of “Fe₂O₃”–CaO–SiO₂–Al₂O₃ Melts in Air and Implications for Iron Ore Sintering

“…10) By analogy with the phase equilibria in the SFC system, 5) this is equivalent to the temperature for the peritectic reaction, H + L → SFCA + L. The critical temperature for decomposition of hematite and SFCA formation in samples containing 2wt%Al 2 O 3 in air have not been determined explicitly but SFCA has been observed in samples containing 1wt%Al 2 O 3 at 1 513 K (1 240°C) 10) and 2wt%Al 2 O 3 at 1 523 K (1 250°C). 4) It is therefore anticipated that, in the sample 88 wt% Fe 2 O 3 , 2 wt% Al 2 O 3v and CaO/SiO 2 = 3.5, SFCA will be present at 1 523 K (1 250°C).…”

“…This common plane represents a potential nucleation site for SFCA minerals during the solidification process. It should be pointed out, however that magnetite has four (4) sets of close packed planes of oxygen within its crystal structure, represented by the < 111 > family of planes, (111), (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11), and (-111). 30) This being the case it would be expected that the probability of nucleation of SFCA on magnetite crystal surfaces would be greater than on hematite.…”

“…Fundamental experimentallydetermined information on phase equilibria in the "Fe 10) systems have provided the essential first steps for understanding and interpreting these changes. The authors have argued in recent research [3][4][5][6][7][8][9] that the phases and microstructures observed in sinter products are primarily formed as a result of solidification of the melts, and that the complexity of the system can be best understood by systematic experimental studies of these solidification processes and reactions taking place on cooling.…”

“…1) During the iron ore sintering process the material in the sinter bed experiences a range of process conditions, in particular changes in temperature and oxygen partial pressure over time. 2,3) Recent research 4) has indicated that the phases and microstructures present in the final structures are formed principally during the cooling of the sample from the peak…”

Iron Ore Sinter Macro- and Micro-Structures, and Their Relationships to Breakage Characteristics

“…The industrial iron ore sinter product and return fine samples examined in the present study are the same as those reported in a previous study [27]. The bulk compositions of the sinter samples are adapted with permission from Ref.…”