The Size Effects Of Fe-based Nanocrystallines On The Microwave Properties And The Flake Processing

Fe-based nanocrystalline alloy powder is one of the best absorber applied because of its good absorbing properties. However, particle size control is one of the key point parameters of microwave electromagnetic control. Its regulation mechanism is not yet clear. It is necessary to study the relationship between particle size and microwave electromagnetic to improve absorbing properties.In this paper, different particle sizes of Fe-based nanocrystallines powder was prepared by dry-milling method using Fe69Si14C13Cu1Nb3 ribbons as raw materials. And the size of samples controled by standard sieve to get Fe-based nanocrystallines powder. X-ray diffraction and field emission scanning electron microscopy were used to test the powder samples of the phase and morphology analysis, using a vector network analyzer to test various samples of 2-18GHz microwive electromagnetic parameters. Results are as follows:The relationship of dry milling time, grain, particle size distribution and annealing process on the electromagnetic parameters were studied. Fe-based nanocrystalline powder grains gradually was refined and the particle size was reduced with the dry-milling time, but large scale particles still remain. The maximum size of 75h dry-milled sample is about 75μm, and the average particle size is 12μm. Real part of permittivityε'of Fe-based nanocrystallines powders increased and then decreased with the milling time. But the change is not great. The real part of permeabilityμ' the increase with milling time, mainly the magnetic loss is eddy current loss. The samples milled 75h is annealed at 500℃,550℃and 650℃. As the annealing temperature increased, the grain size of samples increases, the real part of Permittivityε' is gradually reduced, the magnetic permeability real partμ' increased and then decreased. The resonance absorption peak appear at about 4GHz, reflection loss of the samples annealed at 500℃,550℃and 650℃are-14.3dB,-19dB,-26.6dB.The results show that the sample with narrow particle size distribution is more easily flattened than the sample with wide particle size distribution. The samples were obtained by standard sieve for different particle size (75μm-,75μm-38μm, 38μm-25μm,25μm-15μm,15μm-8μm and the following particle size 8μm). The result is that the sample with narrow particle size permittivity is lower. The real part of permeabilityμ′and imaginaryμ″increase with the particle size decreased. Wet-milling processing has a little effect on the phase structure of particles. With the wet-milling time, samples from spherical to irregular flakes changes, the thickness of flakes reduced and the surface area increases. Real part of Permittivityε'and the magnetic permeability real partμ'increased. Further wet-milling, large pieces will be gradually broken, the real part of permittivityε'growth increased lager. The resonance absorption peak appear at about 4GHz, reflection loss of the samples wet-milled for 5h,8h and 12h are-30dB,-26.7dB,-20dB.