Lichun Cheng

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.

Effect of rare earths on microwave absorbing properties of RE-Co alloys

Abstract The powders of RE2Co17 (RE=Y, Ce, Nd, Ho, Er) and HoxCo100–x (x=6, 8, 10, 12) alloys were prepared by the arc melting method and high-energy ball mill process. The compositions and morphologies of the alloys were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the microwave absorbing properties were studied by a vector network analyzer. The results showed that the alloy of Y2Co17 had better absorbing properties at low frequencies and its lowest reflectivity value was −9.5 dB at 3.8 GHz. The lowest reflectivity value of Ho2Co17 alloy was −13.7 dB at 7.02 GHz and it obtained large absorbing bandwidth. Reflectivity value less than −5 dB was from 5.1 to 10.2 GHz. When x=6 and x=8, the alloys of HoxCo100–x consisted of Ho2Co17 phase and Co phase. They had good radar absorbing properties. With increase in Ho content, the minimum reflectivity value worsened and the absorbing peak frequency shifted toward higher frequencies. But when x=12, the absorbing peak frequency shifted toward lower frequencies but the minimum reflectivity value worsened.

Effects of cobalt substitution on structure and microwave absorption properties of PrNi5 alloy

The polycrystalline samples PrNi5–xCox (x=0.0, 0.1, 0.2, 0.3, 0.4) were synthesized by arc smelting and high energy ball milling method. The phase structure, morphology, saturation magnetization and electromagnetic parameters of the alloy powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and vector network analyzer (VNA), respectively. The results revealed that the lattice parameter a and c and unit-cell volume V increased with the increasing amount of Co substitution. The saturation magnetization increased as Co content increased. The minimum absorption peak frequency shifted towards lower frequency region with the increasing amount of Co substitution. And the minimum reflection loss of the PrNi5–xCox powders increased first and then decreased with the increasing amount of Co substitution. The PrNi5–xCox alloys possessed the excellent microwave absorbing properties. The minimum reflection loss of the PrNi4.9Co0.1 alloy all could reach −20.0 dB with the coating thickness ranging from 1.8 to 3 mm. The minimum reflection loss of PrNi4.9Co0.1 powders was −36.20 dB at 7.76 GHz, and the frequency bandwidth of R<–10 dB reached about 1.50 GHz with the best matching condition d=2.0 mm.

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.