Effect Of Anisotropic Ball Milling Media On Electromagnetic Properties Of Microwave Absorbing Materials

High energy ball mill has the advantages of simple control,environmental protection,low cost and high efficiency.It is not only the main method for preparing microwave absorbing materials,but also an important means to control the electromagnetic parameters of absorbing materials in the process of preparation.In this paper,a series of researches on the role of non-spherical ball media in the preparation of absorbing materials are carried out.By using two types of absorbing media made of ball milling media(cylindrical and hybrid),the effects of the comparison between spherical and non-spherical milling media The influence of the fast quenching speed on the microwave absorbing properties of nano-composite permanent magnetic materials was also studied.The phase,microstructure,electromagnetic and microwave absorption properties of the samples were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM)and vector network analyzer.Mainly include the following:(1)The use of cylindrical and mixed milling media,prepared at different ball milling time carbonyl iron wave absorbing material.XRD results showed that all the samples showed only a single ?-Fe phase.The SEM results showed that the microscopic size of the sample increased first and then decreased with the increase of milling time,and the microscopic size of the sample increased significantly with the milling time.The changes of complex dielectric constant and dielectric loss tangent of the column mill samples are in direct proportion to the microscopic size,and then increase first and then decrease.However,the complex permittivity and dielectric loss tangent of samples prepared by mixed milling media gradually increase with the increase of ball milling time.At a coating thickness of 1.5 mm,the sample of absorbing material after 12 hours of column grinding obtains the minimum reflection loss of-13.8 dB at 3 GHz,and the peak of the reflection loss of the sample gradually moves to the lower frequency as the milling time increases.The samples prepared with the mixed ball mill medium had a minimum reflection loss of-11.7 dB at 2.9 GHz after ball milling for 12 hours.The change of the reflection loss was inversely proportional to the milling time and the peak of the reflection loss shifted to the low frequency.(2)The absorption characteristics of low Nd composite NdFeB materials obtained under different quenching rates were studied.The X-ray diffraction(XRD)shows that the crystal structures of the samples obtained under different quenching rates are in the form of ?-Fe body-centered cubic structure.SEM shows the samples have flat microstructure,but the homogeneity and passivation degree are different.With the increase of quenching rate,the coercive force and remanence of the alloy tend to increase first and then decrease.The electromagnetic properties of the sample measured by the vector network analyzer basically accord with the dispersion characteristics.The quenching speed is 40 m / s,the magnetic loss ? ")first and then drop,indicating that the sample ?" and intergranular magnetic resonance.Based on transmission line theory,the numerical simulation of sample reflection loss(RL)shows that the minimum reflection loss RLmin obtained at 8.2 GHz with the coating thickness of 1.5 mm and the quenching speed of 30 m / s is-7.69 dB and the quenching speed is 40 m / s The RLmin of the sample is-5.87 dB at 3.1 GHz.When the quenching speed is increased to 50 m / s,the RLmin of the sample at-8.8 GHz is-8.8 dB.The changes of the crystallinity at different quenching speeds significantly affect the wave absorption characteristic.