Oral Presentation Crystal36-AXAA Conference 2026

In-situ XRD reveals effects of iron ore sintering variables on SFCA-III formation (142664)

Nathan Webster 1 , Mark Pownceby 1 , Shu Huang 1 , Dylan Guja 1 , Nick Owen 1
  1. CSIRO, Clayton South, VIC, Australia

SFCA (silico ferrite of calcium and aluminium), SFCA-I and now SFCA-III are well-known iron ore sinter bonding matrix phases. SFCA (n = 0), SFCA-I (n =1) and SFCA-III (n = 2) form a polysomatic series with general formula M14+6nO20+8n. Each structure consists of distinct ordering of spinel (S) and pyroxene (P) modules; SPSPSP for SFCA, SSPSSP for SFCA-I, and SSSPSSSP for SFCA-III. The SFCA-III phase, which has only been identified and described relatively recently, has general formula M26O36 – for example, Ca2.99Al4.56Fe15.35Si0.43Mg2.67O36 – and triclinic crystal structure (Kahlenberg, Krüger and Goettgens, 2019). SFCA-III can be a significant component of industrial and pot-grate iron ore sinter, up to 20 wt% (Webster and Pownceby, 2024; Clout et al, 2026), and more detailed and extensive fundamental knowledge about its formation is important for the field of iron ore sintering research and characterisation.

In-situ X-ray diffraction (XRD) based experimentation has revealed mechanistic information about SFCA-III formation and the effect of several variables on its formation. Previous experimentation conducted in the range 298-1623 K and at oxygen partial pressure (pO2) of 5 x 10-3 atm has shown that SFCA-III forms during cooling as the first phase to crystallise from a Fe2O3(FeO)-CaO-SiO2-Al2O3 melt, coexisting with Fe3O4 until SFCA-I and/or SFCA form at lower temperatures as cooling continues. Observation of SFCA-III in sinter has been suggested to be a possible indicator of localised high basicity and/or high MgO concentration within a sinter blend (Webster et al, 2019a), whereas increasing Ti results in the formation of SFCA being favoured over SFCA-III (Webster et al, 2019b). This presentation will highlight outcomes of recent in-situ XRD experimentation which has revealed effects of alumina concentration and cooling rate on SFCA-III formation. It will be shown that for iron ore sinter mixtures with basicity = 4, the lower limit of alumina concentration such that SFCA-III forms as the first phase to crystallise from the high-temperature melt phase is close to 0.09 wt%. And that to preserve SFCA-III in the cooled sinter microstructure, a regime of slow cooling (e.g. 2 K min-1) down to some intermediate temperature (~1430 K), followed by cooling at greater than 20 K min-1 thereafter, is required.

  1. Kahlenberg, V, Krüger, H, and Goettgens, V.S, 2019, Structural elucidation of triclinic and monoclinic SFCA-III – killing two birds with one stone, Acta Crystallographica B, 75:1126-1136.
  2. Webster, N.A.S, and Pownceby, M.I, 2024, Exploring the Relationship Between Fe-rich SFCA and SFCA-III and Their Presence in Sinter Strand and Pot-grate Sinter, ISIJ International, 64:803-807.
  3. Clout, J.M.F, Ware, N.A, Manuel, J.R, Webster, N.A.S, and Pownceby, M.I, 2026, Fundamental Analysis of Sinter Solid Structure: Implications of Mineral Associations for Understanding Industrial Iron Ore Sinter Formation, Minerals, 16:129.
  4. Webster, N.A.S, Pownceby, M.I, Pattel, R, Manuel, J.R, and Kimpton, J.A, 2019a, Fundamentals of Silico-Ferrite of Calcium and Aluminium (SFCA) Iron Ore Sinter Bonding Phase Formation: Effects of Basicity and Magnesium on Crystallisation during Cooling, ISIJ International, 59:263-267.
  5. Webster, N.A.S, Pownceby, M.I, Pattel, R, Manuel, J.R, and Kimpton, J.A, 2019b, Fundamentals of Silico-Ferrite of Calcium and Aluminium (SFCA) Iron Ore Sinter Bonding Phase Formation: Effects of Titanium on Crystallisation during Cooling, ISIJ International, 59:1007-1010.