Effect Of Low Frequency Performance Of Carbonyl Iron Powder With Compound Auxiliary Agent By High-energy Ball Milling

Carbonyl iron powder had good absorbing properties.It was one of the widely used magnetic loss absorbing materials,but it was easily agglomerated,its complex permittivity was large,spectral characteristic and low frequency wave-absorbing performance was poor.Usually the complex permittivity of carbonyl iron powder came down by coupling agent or surfactant.Via high-energy ball milling,its texture was changed to be flake which broke the limit of Snoek,and enhanced complex permeability.Impedance matching and wave-absorbing performance were improved by the above treatment.Flaky modified carbonyl iron powder was prepared by compound auxiliary agent.The morphology,phase and electromagnetic parameters were investigated by scanning electron microscope,X-ray diffraction and vector network analyzer.Reflection loss(RL)was calculated through the electromagnetic transmission line theory.The main researches as follows:(1)Via silane coupling agent KH-560 and surfactant calcium stearate as a binary compound auxiliary agent,then by high-energy ball milling,the modified carbonyl iron powder composite materials were prepared.Results showed that particles of modified powder dispersed uniformly,possessed flat flaky texture and produced less aggregation by binary compound auxiliary agent.X-ray diffraction(XRD)showed that the phase of the modified powder was not changed obviously,which presented ?-Fe body-centered cubic structure.In contrast with other single auxiliary agents,the modified powder by binary compound auxiliary agent had the best low frequency absorbing properties.The minimum reflection loss(RLmin)value was-13.5d B at 1.8GHz with a matching thickness of 2mm.And the absorption band(RL<-10 d B)was 0.8 GHz.(2)The effect on the modified carbonyl iron powder was discussed by different types and quantity of coupling agents.Results showed that attraction and stacking phenomenon were not obvious,and aggregation was significantly less than other quantity as the binary compound auxiliary agent was KH-560+calcium stearate and the quantity of KH-560 was 2m L.Similarly,titanate coupling agent(DN-101)+calcium stearate as a binary compound auxiliary agent also showed good morphology,when the quantity of DN-101 was 2m L.The modified powder all presented ?-Fe body-centered cubic structure by different types and quantity of coupling agents.With a matching thickness of 2mm and the increasing of the quantity of coupling agent,the minimum reflection loss value first decreased and then rose,the position of the loss peak first moved to high frequency and then backed to low frequency,the frequency width less than-10 d B first widened and then narrowed.As the quantity of KH-560 was 2m L,the minimum reflection loss value of-13.5d B was obtained at 1.8GHz,and the absorption band(RL<-10 d B)was 0.8GHz;as the quantity of DN-101 was 2m L,the minimum reflection loss value of-13 d B was obtained at 2.2GHz,and the absorption band(RL<-10 d B)was 0.9GHz.Both of the above modified powder had the best low frequency absorbing properties than other quantity.The effect on low frequency wave-absorbing performance of carbonyl iron powder with different types of coupling agents were similar,but the degree of the effect was unlike.At the same quantity of coupling agent,t he position of the loss peak with K H-560 was shifted to lower frequency than DN-101,but the minimum reflection loss value and absorption band(RL<-10 d B)were variable.(3)Via KH-560+DN-101+calcium stearate as a ternary compound auxiliary agent,then by high-energy ball milling,the modified carbonyl iron powder was prepared.The effect on the modified carbonyl iron powder was studied by combine and quantity of coupling agents.Results showed that the effect on low frequency absorbing properties of modified powder by ternary compound auxiliary agent was similar to binary compound auxiliary agent,which both got optimum low frequency wave-absorbing performance as the quantity of coupling agent was 2m L.With a matching thickness of 2mm,the minimum reflection loss value of-15.3d B was obtained at 2GHz,and the absorption band(RL<-10 d B)was 1GHz.Ester exchange reaction was produced by the combine of coupling agents.The modified powder prepared by ternary compound auxiliary agent showed flat and smooth texture between flake and oval.The real and imaginary parts of permittivity of electromagnetic parameters were lower from 1GHz to 4GHz;the real part of permeability was not markedly varied,but the imaginary part of permeability rose from 1GHz to 5GHz which were helpful to improve the characteristics impedance match.The position of the loss peak was between the two binary compound auxiliary agents.The minimum reflection loss value is less and the absorption band(RL<-10 d B)was wider than binary compound auxiliary agents.