Two-dimensional nuclear magnetic resonance correlation maps as a signature of firing in iron-rich ceramics made from carbonatic raw clays

We investigate the correlated nuclear magnetic resonance (NMR) response of spin–lattice (T1) and spin–spin (T2) relaxation times in iron-rich ceramics made from a carbonatic raw clay. The one-dimensional T1- and T2-distributions tend to correspond to the size distribution of pores, but in the presence of large iron concentrations T2 relaxation becomes more reactive to the magnetic configuration of the pore walls. Aiming at contributing to the characterization of firing-induced ceramic properties, in this work we exploit the different structural responsiveness of the two NMR relaxation parameters in the form of cross-correlation T1–T2 experiments. The test material has been properly chosen so as to observe large modifications of the porous and magnetic features of the solid matrix. The sensitivity of this promising technique has been tested on samples fired at different, but closely spaced, firing temperatures above first vitrification. The T1–T2 correlation maps furnish a detailed picture of the structural rearrangements induced by even small changes of firing temperatures, providing a sort of NMR fingerprint of the firing process which ceramics has undergone.