Preparation of barium hexaferrite coatings using atmospheric plasma spraying

Effect of Ho3+ substitutions on the structural and magnetic properties of BaFe12O19 hexaferrites

“…Magnetic properties can be varied by substituting the Fe ions with another substitution [6], to tailor the magnetic properties of the barium hexaferrites, Fe 3+ ions are partially substituted by various di-, tri-, and tetravalent ions, aiming to occupy the spin down sites and, consequently, to increase the net magnetization [7].…”

Preparation and magnetic properties of barium ferrites substituted with manganese, cobalt, and tin

“…In a combustion method, Castro et al [26] detected the intermediate Fe 3 O 4 though this is surprising as only Fe 3 + was used in their starting material and the likelihood of reducing Fe 3 + to Fe 2 + in a combustion environment seems remote even though organic reducing reagents were included. Lisjak et al [27] also detected Fe 3 O 4 in their preparation of BaCoTiFe 10 O 19 coatings on glass using atmospheric plasma spraying and with no Fe 2 + provided from outside. Seifert et al [28] found Fe 3 O 4 in their preparation of La-substituted M-type Sr hexaferrites, but in this case it seems possible that trivalent La 3 + may force Fe 3 + to be reduced to Fe 2 + when it substitutes for divalent Sr 2 + .…”

Characterisation of plasma-sprayed SrFe12O19 coatings for electromagnetic wave absorption

“…Very large quenching stresses arising in those stackings of well-bonded lamellae 27,28 also cause extensive transverse microcracking across the coating. Previous studies on plasma-and HVOF-sprayed Bahexaferrites clearly showed that, when such extensive melting of the sprayed agglomerates occurred, no hexaferrite phase could ever be retained in the coatings, [20][21][22] because the time required to complete the crystallisation process of Ba-hexaferrite, which involves various peritectic reactions, 29 is definitely too long, compared to the very short solidification times (of the order of few microseconds, with cooling rates of ∼10 6 K/s) of impactquenched molten lamellae. 30,31 A similar phenomenon can be expected for Sr-hexaferrite as well; indeed, according to the most recent phase diagram published on the SrO-Fe 2 O 3 system, 32 the Sr-hexaferrite compound exhibits incongruent melting: as temperature increases, the stoichiometric hexagonal ferrite compound is progressively altered by three peritectic reactions, each involving loss of oxygen and partial reduction of some Fe 3+ to Fe 2+ .…”

“…They have shown that, when processing BaFe 12 O 19 and BaCoTiFe 10 O 19 compounds by atmospheric plasma spraying (APS) or HVOF-spraying, excessively "hot" process parameters result in the formation of undesirable secondary phases 20,21 ; therefore, the retention of large amounts of crystalline hexaferrite requires special adjustments.…”