Preparation And Electromagnetic Properties Of FeCo And FeNi Alloy Nanoparticles

CoFe₂O₄ and NiFe₂O₄ nanoparticles were succesfully synthesized by hydrothermal method. The effects of reaction solvent, time and the surfacetant on the phase composition and morphology of the ferreite particles were systematically studied by using XRD, SEM and TEM. Subsequently, the CoFe₂O₄, NiFe₂O₄ nanoparticles were reduced by the hydrogen thermal reduction method. The influnces of the reduction temperature and reduction time on the production were investigated. The magnetic and electromagnetic properties of production were measured by using VSM and VNA and the effect of the phase composition and the particle morphology on the properties was investigated. Furthermore, the electromagnetic wave absorbing efficiency of the resulting particles was evaluated by using Transmission Line Theory.It was shown that when the reaction solvent varied from EG to the mixture of EG, water and alchol, the stacking of the initial nanocrystal was hindered. Consequently, the particle size of the ferrite particles changed from submicro-meter scale to tens nanometers scale. The particle's morphology was also found to be affected by the process parameters such as the reaction time and the surfacetant.Co₃Fe₇ and FeNi solid solution particles were successfully prepared through hydrogen-thermal reducting CoFe₂O₄ and NiFe₂O₄ particles. The phase compo-sition and the microstructure of the resulting particles were found to be affected by the process parameters. The content of the alloy particles as well as the particles size rise with the increase of the reduction temperature and the reduction time. Also coralal like particles were found to shape up when reducted at high temerature or for a long time. Some fine reduced alloy particles possess high reactivity and they may self-ignit at room temperature.The magnetic perperties of the particles were found to be affected by the phase composition and the particles size. The saturation magnetization (Ms) of the ferrite increases with the improvement of the lattice perfection. The Ms of the alloy particles and the alloy/ferrite composite particles increases with the increasing amount of the alloy particles with high Ms. The coercivity of the particles increases with the dedrease of the particles size.The alloy particles obtained through hydrogen-thermal reduction were found to possess high permittvity and permeability far higher than that of the ferrite. A certain kind of FeNi particles can provideμ' high to 40 at the frequency of 2 GHz. The permeability of the FeNi and FeCo particles decrease with the increasing of the particle size and the particle aspect ratio. The decease of the permeability is attributed to the eddy current in the alloy particles. It is also found that resonance can occur in the permittivity and permeability of the big coralal like particles.The alloy obtained through hydrogen-thermal reduction were found to be high performance electromagnetic wave absorbers in the microwave band. The absorption frequency band of the hydrogen thermal reductions is wider and the matching thickness is thin. A coating of 3 mm was found to be able to provide reflecloss higher than -10dB in a frequency band of 6 GHz. Under the matching conditions, the absorption cofficience can even exceed -70dB in a 2.1 mm coating containing 15 vol. % FeCo particles.