Effects of time and temperature of firing on Fe-rich ceramics studied by Mössbauer spectroscopy and two-dimensional ¹H-nuclear magnetic resonance relaxometry

The combined effects of firing temperature and soaking time on the microstructure of iron-rich porous ceramics have been studied by ⁵⁷Fe-Mössbauer spectroscopy and 2D ¹H nuclear magnetic resonance (NMR) relaxometry using a single-sided probe. Examining water-saturated ceramics using the relaxation correlation method, where longitudinal (T ₁) and transverse (T ₂) relaxation times are measured concurrently, provides information about firing-induced changes in both porosity (related to T ₁) and magnetic properties (related to T ₂). Comparing the information obtained from ¹H-NMR analyses with that obtained from Mössbauer spectroscopy (which characterizes changes in iron-bearing species) shows that the T ₁-T ₂ NMR correlation technique is very sensitive to even subtle modifications in the magnetic behavior of Fe-bearing species. Moreover, the single-sided NMR approach allows us to perform millimeter-scale depth-resolved measurements, which can be used to non-invasively study the microstructural heterogeneities associated with non-uniform firing effects inside ceramics. This is in contrast to Mössbauer spectroscopy, which requires that the ceramic samples be ground.