Phase relations in the Fe-rich part of the system Fe_2O_3(-Fe_3O_4)-CaO-SiO_2 at 1240-1300 deg C and oxygen partial pressure of 5X10~(-3) atm: implications for iron ore sinter

摘要

Equilibrium phase relations in the Fe-rich portion of the system Fe_2O_3(-Fe_3O_4)-CaO-SiO_2 (FCS) have been determined at 1240-1300 deg C and under an oxygen partial pressure of 5Xl0~(-3) atm, typical for iron ore sintering. Experiments were performed with the use of a rapid-quench technique and the chemical compositions of the melts and coexisting condensed phases were determined by combined optical microscopy and electron-probe microanalysis. At temperatures greater than ca 1250 deg C the major phase fields comprise Mt+Liq, C_2S+Liq, G_2S+G_2F+Liq and C_2F+Liq (where Mt represents magnetite, C valence CaO, F valence Fe_2O_3, S valence SiO_2 and Liq denotes a quench liquid phase) plus an extensive, continuous, Liq-only phase field that extends from Fe-rich to SiO_2-rich compositions. At less than about 1250 deg C the Liq-only melt region segregates into two distinct melt fields-one at high Fe contents and basicities greater than 1.8-2.0 and a second melt at low basicities (<1.8) and high SiO_2 contents. At all temperatures examined the reduced oxygen conditions significantly enlarged the field of silicate melt present relative to that of Ca-ferrite melt. Magnetite (predominantly) or hematite may be the stable Fe-oxide phase; however, the occurrence of any particular Fe-oxide phase is strongly linked to the overall basicity (CaO/SiO_2) of the charge.Experiments show that SFC_(ss) (silico-ferrite of calcia solid solution), which is the major ferrite bonding phase in low-Al sinter, cannot be produced as a single, unique, crystalline phase within the FCS system at 5X10~(-3) atm O_2. At this oxygen partial pressure the bulk composition lies within the partially reduced Fe_2O_3(-Fe_3O_4)-CaO-SiO_2 pseudo-ternary with the three-phase assemblage Mt+SFC_(ss)+Liq_(#alpha#) stabilized at low temperatures (1240 deg C). Combined with data for the FCS ternary in air the results indicate that to maximize the formation of SFC_(ss) bonding phase a low-temperature (<1260 deg C), semi-reduced heating environment followed by a relatively slow, oxidizing,