Figure shows NMF maps of the components representing the spatial distribution of 11 B + , Na + , 52 Cr + , and 56 Fe + ions within the same area at 250 °C, 350 °C and 420 °C. Figures show the corresponding maps (when observed) for Na + , 10 B + , Cr + , Cr + , 55 Fe + , and 138 H3B5O5 + . At 250 °C (Fig. ), B + and Na + co-existed primarily in the uppermost coating layer, with some infiltration of 23 Na + into interfacial areas between the coating and oxide layers. This infiltration of sodium could result from reactions between the coating and the oxide layers during sample preparation, where rapid soaking of the samples at 600 °C was conducted, forming the reaction products of sodium and iron oxides . At this temperature, NMF maps indicate a distinct separation of the iron oxide and chromium oxide layers. Additionally, the NMF map for component 4 reveals a spatial distribution of 56 Fe + within the sodium borate coating, suggesting partial dissolution of iron oxide particles as a consequence of sodium infiltration in some dendrite oxide areas.