Preparation And The Electromagnetic Properties Of Ultrafine Nickel Materials With Special Morphologies

As a kind of important multi-functional magnetic metallic materials,ultrafine nickel nanocrystallites with special morphologies have huge potentials in many fields.In particular,they are of extraordinary significance in the theoretical and experimental investigations of electromagnetic shielding and electromagnetic wave absorption. Needless to say,the study of the controllable synthesis of ultrafine nickel nanocrystallites with special morphologies and the establishment of simple,facile, cost-effective,and environment-friendly synthetic routes are of significant theoretical and practical values.Therefore,the following researches have been conducted and the main conclusions are drawn as below:(1)Ultrafine Ni particles were synthesized via a facile and mild chemical route in distilled water.The resulting ultrafine Ni particles were used as a kind of conductive fillers to fabricate conductive composites.The shielding of electromagnetic interference (EMI)and electromagnetic wave absorption behaviors of the composites were evaluated. The results indicated that the ultrafine Ni particles might be potential fillers for shielding of electromagnetic interference and electromagnetic wave absorption as well. The resin-based conductive composite containing 33.3wt%of the ultrafine Ni particles recorded a shielding effectiveness(SE)value as much as above 22 dB within a frequency range of 130 MHz to 1.5 GHz,while the ultrafine Ni particles/wax composite with a thickness of 2 mm had a reflection loss R(dB)of 27 dB at about 7 GHz. Moreover,the distribution state of the ultrafine Ni particles in the composites was found to play a key role in determining the properties in terms of the practical application of the ultrafine nickel particles as fillers for shielding of electromagnetic waves.(2)Based on the above-mentioned work,the effect of an external magnetic field on the morphologies and magnetic properties of the targeted ultrafine Ni particles was investigated under stirring condition.At the same time,the electromagnetic shielding effectiveness and the electromagnetic characteristics of the composites filled with ultrafine nickel particles obtained from distilled water were measured.The results showed that the composites filled with nickel particles obtained in the presence of an external magnetic field showed better EMI shielding effectiveness than the composites filled with nickel particles obtained in the absence of an external magnetic field,while the former had poorer electromagnetic wave absorption effectiveness than the letter.(3)Flake-like Ni powders were fabricated by wet sand-milling of micro-sized nickel powders and the effect of related milling factors on the morphology and microstructure of the Ni powders was studied.The resulting flake Ni powders were used as a kind of conductive fillers to fabricate conductive composites.It was found that the composites filled with flake-like Ni powders had a lower EMI shielding effectiveness than the composites filled with micro-sized nickel powders.Moreover,the composites filled with flake-like Ni powders had better electromagnetic wave absorption effectiveness than the composites filled with micro-sized nickel powders, and the flake-like Ni powders/wax composites with a thickness of 5 mm registered a reflection loss R(dB)of-27 dB at about 2 GHz.(4)Ultrafine chain-like Ni assemblies with a length of about 5μm and an average diameter of about 250 nm were successfully prepared by the reduction of Ni salts with hydrazine hydrate under normal pressure.Moreover,the growth process of the Ni chains was investigated for the first time.Based on the experimental results,the self-assembly mechanisms of the Ni nanocrystallites induced by self-generated magnetic field were investigated for the first time,which could be used as a new general method for the preparation of other magnetic metal nanostructures with a controllable morphologies,so as to fully exploit their peculiar properties and unique applications.(5)Under normal pressure,untrafine nanocrystallite Ni fibers with lengths from several microns up to several hundreds of microns and an average diameter of about 250 nm were fabricated in the presence of external magnetic fields with different intensities. The effects of the reaction conditions on the microstructures and magnetic properties of the Ni fibers target products were systematically investigated.Moreover,the electromagnetic shielding effectiveness and electromagnetic characteristics of the Ni fiber reinforced composites were measured.The results showed that the Ni fibers might be potential conductive fillers for shielding of electromagnetic interference(EMI).