Chemical synthesis of Nickel fibers and the study of the mechanism

• Main Authors: Kai-Ying Huang, 黃楷熒
• Other Authors: Kan-Sen Chou
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/66341160956613088836

碩士 === 國立清華大學 === 化學工程學系 === 92 === Abstract In this work, we tried to improve as well as to understand the chemical method for synthesizing nickel fibers that was first found in our laboratory. The chemical method utilized nickel chloride solution as precursor, hydrazine in an alkaline solution as a reducing agent, and other necessary additives (such as PAA and NaBH4) to obtain the claimed nickel fibers under the influence of magnetic field. According to our observation, the nickel ion was first reduced to form magnetic nickel particles, and then aggregated along the magnetic line of force to form fibrous products. The diameter of the nickel fibers depended mostly on the reaction rate: with a slower reaction rate the diameter became smaller. The reaction rate was slower with increasing pH values. The use of PAA can prevent aggregation of the nickel particles, however, too much PAA would also affect the aggregation along the magnetic line and thus formed rod-like products. By changing the concentration of reactants, we could synthesize nickel fibers of diameters of 0.5, 1, and 2μm. The addition of NaBH4 lowered the activation energy of nucleation and therefore enabled us to obtain nickel fiber at a lower temperature. Electrical conductivity studies showed that these fibers could have at best about 30% of that for bulk nickel material. It was suspected to be caused by the inclusion of boron into the nickel fibers and also the oxidation of the nickel fibers. In addition, we also discussed the reaction mechanism leading to the formation of nickel fibers. Our results showed that there are two types of nickel compound or complex preceding the chemical reduction, i.e. Ni(OH)2 and Ni(N2H4)32+ and they were reduced independently into nickel. Knowing their individual activation energy, we could have a better control over the reaction rate and thus the characteristics of nickel fibers.