The Controlling Of Insulated Layer Inside Fe-based Soft Magnetic Composites And Its Influence On Magnetic Properties

SMCs?soft magnetic composite materials?are one kind of important soft magnetic materials and have been widely used for fil-tering inductors in switching power supply,line noise filters and switching power supply etc.As operating frequency increases,the eddy current loss increases rapidly.Eddy current loss not only worsens the overall magnetic properties but also can produce lots of heat due to Joule effect.Thus it is critical to keep the banlance of decreasing the eddy current loss and improve the magnetic properties of SMCs.In order to decrease the core loss and improve the magnetic properties of SMCs,Fe-based/SiO₂ core-shell particles were synthesized by chemical coating and the following high temperature sintering was used to obtain intergranular insulated composite cores.The phase composition,microstructure,electrical and magnetic properties of composite particles and composite cores have been investigated systemically.It has been also investigated systemically for the influence of intergranular insulated layer on the the electrical and magnetic properties of sintered compacts.The main conclusions are as follows:1.The FeSiAl/SiO₂ core-shell particles with homogeneous coating layer were prepared successfully by chemical coating and the thickness of coating layer can be adjusted effectively by varying the added TEOS contents.The thickness of coating layer increased with increasing the TEOS contents,while the density and static magnetic property changed in the opposite direction.The Fe SiAl/SiO₂ core-shell particles were pressed,sintered and annealed into intergranular insulated composite compacts.The replacement reaction between Al of Fe SiAl and SiO₂ has taken place during sintering process and a new insulating layer of Al₂O₃ was formed.Thus Fe₃Si/Al₂O₃ composite cores was formed.2.The influence of the thickness of coating layer on the electrical and magnetic properties of Fe₃Si/Al₂O₃ composite cores has been investigated.With increasing the TEOS contents,the thickness of insulated layer inside Fe₃Si/Al₂O₃ composite cores increased.The insulated layer owned maximum thickness and it showed best insulating effect when the TEOS content was 20 ml.The electrical resistivity of composite cores increased with increasing the TEOS contents,while the static magnetic property,effective permeability and core loss changed in the opposite direction.Fe₃Si/Al₂O₃ composite cores showed best properties while the TEOS content was 20 ml,which displayed more excellent soft magnetic properties,better frequency stability at high frequencies,much higher electrical resistivity?21.86 ??×m?than Fe SiAl core?0.8 ??×m?and lower core loss of P500Gs/50KHz?480 W/Kg?than the raw FeSiAl core?589 W/Kg?.3.The Fe/SiO₂ core-shell particles with homogeneous coating layer were prepared successfully by chemical coating and the thickness of coating layer can be adjusted effectively by varying the added TEOS contents.The thickness of coating layer first increased then deceeased with increasing the TEOS contents,while the density changed in the opposite direction.The Fe/SiO₂ core-shell particles could be prepared into intergranular insulated composite compacts by RPS process.4.The influence of the thickness of coating layer on the electrical and magnetic properties of Fe/SiO₂ composite cores has been investigated.With increasing the TEOS contents,the thickness of insulated layer inside Fe/SiO₂ composite cores first increased then decreased.The insulated layer owned maximum thickness and it showed best insulating effect when the TEOS content was 15 ml.The electrical resistivity of Fe/SiO₂ composite cores first increased then decreased with increasing the TEOS contents,while the static magnetic property,effective permeability and core loss changed in the opposite direction.Fe/SiO₂ composite cores showed best properties while the TEOS content was 15 ml,which exhibited better frequency stability at high frequencies,much higher electrical resistivity,high Q and lower core loss.The Fe/SiO₂ composite core displayed much higher electrical resistivity?8.53 ??×m?than raw Fe core?0.13 ??×m?.And its core losses?P10mT/130 KHz = 284 W/Kg?decreased by 36.7%.than that of raw Fe core.