The preparation of Ni nano particles by the chemically controlled polyol process
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The preparation of Ni nano particles by the chemically controlled polyol process Seon-Mi Yoon, Jae-Young Choi, Yong Kyun Lee, Eun Sung Lee and Seul Ki Kim Materials Lab, Materials & Devices Research Center, Samsung Advanced Institute of Technology, P. O. Box 111, Suwon 440-600, Korea Abstract The chemically controlled polyol process, with TMAH and water as OH- donors in the nickel hydroxyglycolate intermediate phase, prepares the nickel nano particles. The water additive acts as the OH- donor and enhances the solubility of salt in polyol for efficient production and monodispersive particles. Water and TMAH, selected to decrease the contamination of alkali metal from inorganic base, as OH- donors control the intermediary solid phase as a reservoir for Ni2+ species. The particle is about 80 nm with a faceted shape when the reaction is controlled by a combination of TMAH and water,. The nucleating agent is powerful to decrease the particle size, but in this basic reaction condition, it is not effective enough to get a small size. Introduction Fine metal particles are needed for high technology application such as conduction inks, magnetic inks, and ferrofluids. They have been used to produce particles of metal and alloy in different forms such as sonochemical[1], microemulsion[2], vapor phase method [3], spray pyrolysis [4], and solution chemical routes such as polyol process [5,6] and the reduction in an aqueous [7] or non-aqueous solution [8]. Polyol process was discovered to produce various metals such as Ni, Co, Pd, Pt, Ag, Au particles [5,9,10] and alloys such as Ag-Pd, Co-Ni, FeCo and Fe-Ni.[6,11] In previous research, monodispersive 1-2 ㎛ nickel particles were made by reducing Ni(OH)2 in ethylene glycol. Further decreases in Ni size were achieved using silver as the nucleating agent.[5] Heterogeneous nucleation was found to produce smaller particles. To prevent sintering, a protective agent such as polyvinylpyrrolidone (PVP) was used in the case of Ag and 0.81㎛ particles were obtained.[10] The polyol process, in which a polyol acts as both a solvent and a reducing agent, is known to be able to prepare uniform and well-dispersed metal powders. In comparison with the reduction in aqueous solution, it takes place slowly and requires high temperature and refluxes for several hours during the reaction. It is well known that the precipitation from solution proceeds in two steps: nucleation and growth. To obtain monodispersive particles, the nucleation step needs to be shortened and there must be a separation between the nucleation and the growth step. If the solute is generated slowly and the nucleation rate is
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high enough, the nucleation stage is very short and is followed by the growth of the particles. In order to generate the solute slowly and avoid a too high supersaturation ratio, it is essential to retain the solute in a kind of reservoir such as chelates or a solid phase with a low solubility. The decomposition or the dissolution of the solute reservoir at equilibrium regulates the releas
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