Characterisation of plasma-sprayed SrFe12O19 coatings for electromagnetic wave absorption

SrFe12O19 coatings, intended as electromagnetic wave absorbers, were produced by atmospheric plasma spraying (APS) using two different kinds of feedstock powders: spray-dried agglomerates of micrometric SrFe12O19 particles (type-A) or spray-dried agglomerates of raw materials (SrCO3, Fe2O3), reactively sintered at 1100 °C (type-B).During spraying, type-A agglomerates either remain unmelted, producing porous coating regions where crystalline hexaferrite is retained, or are disrupted into smaller granules which melt completely, resulting in dense coating regions with no crystalline hexaferrite.The sintered type-B agglomerates possess higher cohesive strength and do not fall apart: the finer ones melt completely, whereas, in the larger ones, the outer region melts and infiltrates the porous unmelted core which retains crystalline hexaferrite. Dense coatings can therefore be obtained while preserving high amounts of crystalline hexaferrite even inside the dense areas. Such coatings show magnetic properties that are promising for electromagnetic wave absorption applications.