Preparation, Characterization And Magnetic Properties Of CoNi Alloy Micro/Nano Materials

This thesis mainly focuses on the solution-based controllable synthesis of morphologyand structure for CoNi magnetic alloy micro/nano-materials, through researching the effectsof different experimental parameters on the morphology, structure and magnetic propertiesof the samples, and investigating the magnetic dipole directed self-assembly of CoNi alloymicro/nanostructure. The obtained samples were characterized by Scanning ElectronMicroscope (SEM), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD),Energy Dispersive Spectrometer (EDS), and Vibrating Sample Magnetometer (VSM), Themain results are as follows.Chain-like CoNi alloy microstructures with the average diameter of5μm and length upto60μm have been successfully prepared via a solvothermal route with the assistance ofpolyvinylpyrrolidone (PVP) as a growth directing agent. The experimental results showed thatthe surfactant PVP and solvent ethylene glycol (EG) played an critical role in the formation ofsuch chain-like CoNi structures. In this reaction system, the linear polymer PVP primarilyplayed dispersant and structure-directing roles and EG was used as solvent. While EG withhigh viscosity can effectively restrain the diffusion of CoNi nuclei. The typical Chain-likeCoNi alloy possess face-centered cubic (FCC) phase, and present ferromagnetic behavior withthe saturation magnetization of90.3emu/g and the coercivity of162.4Oe at roomtemperature.Novel cauliflower-like, nanoplatelets and nanoparticles CoNi alloy were synthesized viahydrazine hydrate reduction method in ethanol/water mixed solvent system, and the averageparticle size of cauliflower-like structure and nanoparticles ca.2.5μm and21±1.2nmrespectively. The study found that citric acid is essential for the synthesis of cauliflower-like structures. The products are mainly nanoparticles and their aggregates without additionof citric acid. In this experiment, the citric acid was used as complexant and the citrateions can associate with Co2+and Ni2+to form complex compounds [Co(C6H5O7)2]4-and[Ni(C6H5O7)2]4-that were very stable in low concentration alkali solution, which caneffectively suppress the formation of precipitation nickel hydroxide and cobalt hydroxide andreduce the the contents of Ni2+and Co2+in the solution with the result of a lower rate ofreaction. While slow reaction was beneficial for the anisotropic growth of CoNi alloy crystaland formation of cauliflower-like structure. The typical CoNi alloy nanoparticles,nanoplatelets and cauliflower-like structure possess face-centered cubic (FCC) phase, andshow a ferromagnetic behavior at room temperature with the saturation magnetization of111.3,104.3and110.6emu/g and the coercivity of187.4,243.8,178.3Oe respectively.