Abstract
In this study, chemical reduction method was adopted to produce ultrafine metallic materials including iron nanoparticles and nickel fibers in aqueous solution from their respective metal salt precursors. Related applications of these metallic materials were also investigated.Nickel fibers were reduced from nickel chloride by hydrazine in the presence of magnetic field. It was found that nickel fibers were composed of nickel particles connected linearly under the effect of the magnetic field. This work showed the morphology of nickel fibers was mainly affected by two factors: nucleation rate and growth rate. In the fast nucleation case, thinner nickel fibers would be obtained, and on the contrary, thicker fibers would be obtained in the slow nucleation case. When the growth rate was fast, the nickel fibers would be loose and weak, and when the growth rate was slow, the nickel fibers would be tight and strong. In the application as electromagnetic interference (EMI) shielding materials, nickel fibers showed a better effectiveness than nickel particles with the same diameter, this is benefited from the high aspect ratio of nickel fibers in the composite materials.Iron nanoparticles can be synthesized by using sodium borohydride as the reducing agent and iron chloride as the precursor in the aqueous solution. In was found that the water-soluble polymer PAA (polyacrylic acid) is beneficial to the dispersion of iron nanoparticles, hence stopping the agglomeration of iron nanoparticles. In order to decrease the diameter of iron nanoparticles, palladium iron considered as the nucleation promoter can be added to increase the nucleation sites. In addition, it was also found that the pH of the solution affected the iron nanoparticle size noticeably, which directly caused from the dispersing capability of dispersing agent under different pH values. When the pH was high, the dispersing capability of PAA increased and the nucleation sites were well-dispersed. The numerous nucleation sites therefore subsequently led to the small iron nanoparticles. On the contrary, when the pH was low, the dispersing capability of PAA decreased and the nucleation sites were agglomerated. Consequently, the loss of nucleation sites led to the large iron nanoparticles. The iron nanoparticle electrode showed the capacity as high as 510 mAh/g-Fe with the discharge current of over 200 mAh/g-Fe. This result indicated the utilization ratio of iron was indeed improved by the decrease of iron nanoparticle size as well as the discharge current was enhanced by the large surface area of iron nanoparticles.The silver nanoparticles could be dispersed on a substrate by the spin-coating method. By controlling the silver colloid concentration, the distribution of silver nanoparticles on the substrate could be varied from dispersed separation to mono-layered close packing, eventually to multi-layered close packing. After heat treatment at different temperatures, the multi-layered silver nanoparticles structure started to exhibit conductivity after 100℃ treatment. The resistivity initially decreased with temperature and then increased to become finally insulated again. On the SEM observation, the silver nanoparticle structure exhibited sintering effect at the increase of temperature and became conductive. But when the temperature continuously increased, the silver nanoparticles structure shrank into large particles and became insulated again.