This movement of sodium ions shifts reaction (1) to the right, generating more sodium cations and boron oxide anions in the coating network. Electrochemical reactions between sodium cations and oxides, (3) and ( ), result in the gradual formation of NaFeO2 and NaCrO2 within the oxide layers, as detected in the TOF-SIMS mass spectra (Fig. ). Complementary in situ XRD heating (Fig. ) verified the formation of NaFeO2 phase at the same temperature range. As sodium ions depart from the glass, the remaining BO 2 -anions result in a negatively charged boron oxide network. To balance the charge of this boron oxide network, metallic cations formed in reaction ( ) and ( ) migrate to the borate coating. Previous studies suggest that metallic ions, including M 2+ and M 3+ cations (M = Fe, Mn, Cr), can integrate into the glass network to form the inorganic glass matrix .