Deposition Mechanism Electric Magnetic NdFeB Films

As an ancient functional material, magnetic material has been applied in manyfields, such as industrial electric motors, medical instruments, electro-acoustic,magnetic data storage devices, automobiles, etc. NdFeB magnet, which possessesexcellent magnetic properties, is a new type of permanent magnet material, which isdiscovered by Japan and USA in1983. Its research and application has been hot spotsof the study of magnet materials since its discovery. However, the low corrosionresistance of sintered NdFeB magnetic materials has strictly limited their applicationin many environments.Electrodeposition is an attractive method for film preparation and possessesmany advantages, such as low processing temperature, normal handling pressure, highpurity of deposits, etc. On the other hand, electrodeposition is also well known to bean important technique for nano-structured materials with high corrosion resistance.In this thesis, we have tried to prepare NdFeB nanocrystalline magnetic filmswith excellent magnetic properties and higher corrosion resistance by using directcurrent electroplating method and probe into the corresponding depositionmechanisms, especially its nucleation/growth process. The main contents are asfollows:1At first, the influences of principal technological (such as the pH value, temperature,current density, the concentration of the electrolyte and so on) was studied. Then thepreparation of NdFeB film was studied by the orthogonal experient. At last, theoptimal experimental scheme of the preparation of NdFeB film was acquired throughanalyzing experimental data in range analysis method. The microstructure,composition and magnetic properties of NdFeB film was determined using scanningelectron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and avibrating sample magnetometer (VSM). It can be seen that the NdFeB film iscomposed of the nanoparicles with the average grain sizes in the nanometer range, and it also possesses soft magnetic properties.2The kinetics and mechanism of nanocrystalline NdFeB film was studied using CV,chronoamperometry (CHR) and electrochemical impedance spectroscopy (EIS)techniques. The results showed that the electroplating of NdFeB film followed3Dnucleation/growth mechanism. With the increase of the negative potential bias, thecharge transfer resistance reduced, which leads to increasing of nucleation rate andmuch finer of the grains.3The corrosion behavior of nanostructured NdFeB film has been investigated in3％NaCl solution by electrochemical impedance spectroscopy (EIS) and Tafel plotsmeasurements．The results shown that, the NdFeB film possesses higher corrosionresistance. There were two time constants in EIS plots. As the extension of time, thecharge transfer resistance corrosion decreased, but the adhesion of the corrosionproducts has protected the further corrosion of the material in a certain extent.