| Because of its high saturation magnetization,high permeability,high Curie temperature and low coercivity,soft magnetic properties of FeCo alloy was widely concerned by researchers.When FeCo alloy particle size shrinked to nanoscale size,may be produced on the physics properties changed such as the surface effect,small size effect,quantum size effect and other electromagnetic properties.It will lead to the phenomenon that including the electromagnetic performance of a variety of physical properties changed,for nanoparticles appear special performance.These special properties enable FeCo alloy nanoparticles to be used in fields such as biomedicine,magnetic recording materials and electromagnetic wave absorbing materials.Due to the wide application prospect,the preparation and performance of FeCo alloy nanoparticles had become a hot topic.At present,the preparation methods of FeCo alloy had been developed completely.The method of preparation of FeCo alloy particles by multiple alcohol-reduction method has many advantages such as simple operation,environmental friendly,preparation of nano-particle size and shape with good controllability.However,the synthesis process had high requirements on the anaerobic conditions of the preparation environment,and the samples produced are easy to oxidized,which leads to the low intensity of magnetic energy,especially the saturation magnetization.In this paper,we first attempted to make the FeCo alloy nanoparticles with high purity and high saturation magnetization by means of polyol reduction and annealing in hydrogen environment.First of all,the first step in the experiment was trying to lower annealing temperature of preparating more pure crystalline phase of FeCo nanoparticles which needed,by different annealing temperature under the condition of the preparation of FeCo alloy nanoparticles of XRD and VSM image to contrast,we found 400 ? annealing temperature conditions to produced pure crystalline phase FeCo.The 400 ? is the lowest annealing temperature of the FeCo alloy nanoparticles.Then,in order to get better morphology and magnetic properties of FeCo alloy,we changed the environment that OH-concentration of reaction liquid in the preparation,by changing the NaOH and the proportion of reactant metal salts,test of several groups of samples by XRD,SEM,VSM.Those results were analyzed,and we can concluded that OH-concentration play a role:the help reducing agent,under the proper proportion can reach both the rate of reaction of metal balance.Finally,we explored the FeCo alloy nanoparticles in the field of electromagnetic microwave absorbing application:firstly,the preparation of different coating thickness FeCo@SiO2 composite nanoparticles,by SEM image analysis can be concluded that the SiO2 coating on the particles prompted for the shape from vertical to globular particles,then the samples that is FeCo@SiO2 by microwave absorption performance tests,this experiment adopted coaxial air line jig tested the different samples of S parameters,calculated and processing through experimental treatment software we could get the dielectric constant and magnetic permeability for its real part and imaginary part.Then,through the calculation of the corresponding formula,we got the magnetic guide loss and dielectric loss,as well as the reflection loss of the microwave medium of different samples with different coating thickness.By contrast,the loss of the coated sample is bigger than that not coated FeCo alloy nanoparticles,and after coating,the dielectric loss of composite particle FeCo@SiO2 samples of microwave frequency changes significantly more stable,obviously,after coating the FeCo@SiO2 composite particles has broad prospects in the research on the microwave absorbing especially electromagnetic wave's applications.Then,in order to overcome high requirements on the anaerobic environment and dependence on annealing conditions,the second step experiment decided to improve polyol reduction method,joined autoclave using solvent hot method to prepared FeCo alloy nanoparticles.First of all,as far as possible reduced the reaction temperature of the autoclave solvent thermal method,we found under the experiment temperature 150 ?,could get the pure FeCo alloy nanoparticles.Then,in order to get the dispersivity is good cubic model of particle morphology,the reaction time,the appropriate extension of the autoclave prepared,were found rising as the reaction time,the distribution of the particles dispersion improved.In the end,different polyols were used as the solvent environment of the autoclave reaction,and it was found that with the increase of the carboxyl chain,the defect of the granule was more and more serious.In order to better dispersibility of FeCo particle morphology,the autoclave solvent was trying added the surfactant-oleic acid,by changing the adding amount of oleic acid,controled the proportion of oleic acid and metal salt of reactants,found that with the increase of the amount of oleic acid,particle configuration was more and more regular,from reunion petal shape into a separate branch rod.Then,under the premise of maintaining the proportion of surfactant,the reaction time of the solvent heating of autoclave was reduced,and the distribution of particle morphology was gradually dispersed. |
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