Iron partitioning during firing of clay-based ceramic materials: An integrated mineralogical, spectroscopic, and magnetic study

Fired clay bodies contain complex Fe-bearing assemblages formed during thermal alteration. However, the identification of structurally bound Fe and iron oxide-related magnetic components remains difficult using individual analytical techniques alone. This study employs an integrated mineralogical, spectroscopic, and magnetic approach to investigate Fe-bearing components in black fired roof tile bodies. X-ray diffraction and Raman spectroscopy indicate quartz, feldspar-group minerals, and residual illite/mica-related phyllosilicate components, whereas distinct iron oxide phases are not independently resolved by diffraction- or Raman-based analyses. Mössbauer spectroscopy indicates the coexistence of FeIII- and FeII-bearing paramagnetic components together with magnetically ordered Fe-bearing components identified at low temperature. Field- and temperature-dependent magnetic measurements provide complementary constraints on magnetic behavior and coercivity distributions and indicate systematic differences between surface and core regions. Low-temperature Mössbauer and magnetic measurements further indicate magnetically ordered Fe-bearing components broadly consistent with hematite- and/or ferrimagnetic Fe-bearing phases that are difficult to resolve by diffraction-based analyses. The combined results suggest that integrated spectroscopic and magnetic approaches provide complementary constraints on Fe-bearing assemblages in fired clay materials.