Peihao Lin

Preparation and microwave absorption properties of NdFeB alloys

In order to improve the microwave absorbing properties of NdFeB alloys, as-jet milled powders were further processed in a planetary mill. The phase structure, morphology and particle size of the alloy powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser diffraction-based particle size analyzer, respectively. The saturation magnetization and electromagnetic parameters of the powders were determined by a vibrating sample magnetometer (VSM) and a vector network analyzer (VNA), respectively. The results showed that the saturation magnetization decreased as the milling time increased. The minimum absorption peak frequency shifted towards the lower region and the reflection loss values increased with increasing the ball milling time. The minimum absorption peak value of the powders milled for 15 h on the basis of jet milling reached −44.4 dB at 11.04 GHz, and the bandwidth of R<-10 dB was 1.2 GHz with the best matching thickness of 1.8 mm.

Microwave Properties of RE(Nd, Tb)FeCoB Alloy System

Abstract The RE(Nd, Tb)FeCoB magnetic powders were prepared by arc melting, high energy ball milling and a partial oxidation treatment method. A X-ray diffraction device and a vector network analyzer were used to analyze the phase structure and microwave absorbing properties of the powders. The results of B addition to the microwave absorbing performances in the NdFeCo alloy, indicate that Nd2Fe14B phase will precipitate and the relative content of the α-Fe phase increases with the increasing of B in Nd10.53Fe77.84Co11.63 alloy powder. When Nd is replaced by the heavy rare earth Tb in NdFeCoB alloy, the powders consist of α-Fe, Tb2Fe14B, Tb2Fe17 and a small amount of Tb2O3 phases. (Nd10.53Fe77.84Co11.63)97B3 powder has a minimum of absorption peak frequency, which is –9.5 dB at 4.5 GHz. After substituting Tb for Nb in (Nd10.53Fe77.84Co11.63)97B3 alloy the absorption peak frequency increases to 6.3 GHz, but the reflectivity value is reduced to –11 dB.

Research on microwave electromagnetic properties of Tb-Fe-Cr alloy

Abstract The Tb-Fe-Cr alloy powders were prepared by the arc melting method and high energy ball milling. The phase structure and the microstructure of the alloys powders were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and then their microwave absorbing properties were analyzed by Vector network analyzer. The results showed that the absorption peak values of Tb 9 Fe 88 Cr 3 alloy with a material thickness of 2.0 mm were lower than −16.5 dB when ball milling time was from 50 to 60 h, and the wide frequency of reflectivity under −10 dB were all more than 4 GHz. When the ball milling time was 50 h, the alloy powders had better electromagnetic properties. The absorption peak value of alloy reached −25.8 dB, and the wide frequency of reflectivity under −10 dB reached 4.8 GHz. When the ball milling time was more than 70 h, the alloy powders would become thinner, leading to worse electromagnetic properties of the alloy, the absorption peak shifted towards low frequency under the same material thickness. The Tb x Fe 97– x Cr 3 ( x =7, 9, 11, 13, 15 mol.%) alloy dealt with 60 h ball milling time had better wide-frequency characteristic under 1.8 mm of material thickness. The absorption peak shifted towards higher frequency region from lower frequency region with increased atom percent of Tb in the alloy, and the inflexion point appeared when x =13. At low frequency, the microwave absorbing properties of Tb 11 Fe 86 Cr 3 alloy was better than those of the others. The absorption peak value of Tb 15 Fe 82 Cr 3 alloy was −24 dB, and the wide frequency of reflectivity under −10 dB was 4.5 GHz.

Microwave absorbing properties of NdFeCo magnetic powder

NdFeCo magnetic powder was prepared by the process of smelting, high-energy ball milling and oxidation heat treating. The effects of oxidation heat treatment and Co content on phase composition and microwave absorbing properties of NdFeCo magnetic powder were investigated by an X-ray diffractometer (XRD) and vector network analyzer. The minimum reflectivity of Nd23.25Fe36.75Co40 powder before oxidation heat treatment was −6.2 dB, and that of oxidized powder decreased to −14.0 dB. The microwave absorbing properties of NdFeCo magnetic powder could be improved effectively by oxidation heat treatment. With the increase of Co content, the Fe2O3 reduced and the Nd2O3 increased; Fe3Co7 phase appeared when the content of Co increased to 40% (mass ratio); the absorption peak was found to move towards lower frequency region first, and then it moved towards a higher frequency region. Nd23.25Fe66.75Co10 powder had better comprehensive properties in absorbing microwave in the frequency band of 3-13 GHz. The value of minimum reflectivity and absorption peak frequency, when the coating thickness (d) was 1.8 mm, were −19.7 dB and 4.8 GHz, respectively.

Microwave absorbing performance of RE-Fe based alloys

RE13Fe84Cr3(RE=Ce, Pr, Tb, Er) and Pr13−xFe84Cr3Tix(x=0, 2, 4, 6) alloy powders were prepared by arc smelting method and high energy ball milling technique. The phase structure and the morphology of the alloy powders were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their microwave absorbing properties were determined by a vector network analyzer. The results show that the alloys with light rare earths (Ce, Pr) have good low frequency absorbing property and those with heavy rare earths (Tb, Er) exhibit an improved high frequency absorbing property. The minimum reflectivity at the absorbing peak frequency of RE13Fe84Cr3(RE=Ce, Pr, Tb, Er) are −9.49 dB at 5.76 GHz, −22.38 dB at 7.92 GHz, −18.52 dB at 11.68 GHz and −17.59 dB at 10.24 GHz, respectively. The absorbing bandwidth under −10 dB of the Pr13Fe84Cr3 powder was widened from 1.91 GHz to 3.89 GHz by adding 2% Ti, but the reflectivity of the alloy was increased from −22.38 dB to −14.91 dB.