| Nano silver materials have excellent physical and chemical properties and can be widely used in catalysts,antibacterial materials,biosensors,optical materials and conductive pastes.In general,the performance of nano-silver materials depends mainly on its morphology and size.Among them,flaky silver powder can be widely used in the preparation of conductive silver paste due to its dual functions of micron-scale and nano-scale flake silver powder.In this paper,a series of work have been carried out on the control of the morphology of flaky silver powder and its conductivity.The liquid phase chemical reduction method with ferrous sulfate as reducing agent and the solvothermal method with N,N-dimethylformamide?DMF?as reducing agent were studied,and the effects of different process conditions on the morphology and particle size of the product were investigated.The main work includes the following aspects:?1?Using liquid phase chemical reduction method,using ferrous sulfate as reducing agent,silver nitrate as silver source and PVP as surfactant,the effect of process parameters?eg.the amount of reducing agent ferrous sulfate and PVP,dispersion of PVP,mixing method and reaction solution?on the morphology and particle size of the product was investigated.The experimental results show that a fine flake silver powder having a particle diameter of 200 to 500 nm and a thickness of 70 nm can be prepared with the molar ratio of ferrous sulfate to silver nitrate of 1.6:1,the amount of surfactant PVP of 20 wt%,and reaction time for 10 min.?2?Using liquid phase chemical reduction method,using ferrous sulfate as reducing agent,silver nitrate as silver source,and gum arabic powder as surfactant,the effect of process parameters?eg.the amount of surfactant gum arabic powder and the pH velue?on the morphology and particle size of the product was investigated.The experimental results show that a fine flake silver powder having a particle diameter of of 300-700 nm can be prepared with the amount of surfactant arabic gum powder of 60wt%,the pH value of weakly alkaline.In addition,it was found that a spherical silver powder having a particle diameter of about 2?m was obtained when the pH of the adjustment system was close to 1-2;A doughnut-like silver powder was obtained when the amount of the arabic gum powder was adjusted to 40 wt%.In the system,the silver powder's change of morphology was significantly controlled by the amount of gum arabic powder and the pH of the system.?3?Using solvothermal method,the effect of process parameters?eg.the amount of surfactant PVP,reaction temperature and reaction time?on the morphology and particle size of the product was investigated with the presence of Fe3+,DMF as solvent and reducing agent and PVP as the surfactant.It was resulted that the micro-sheets aliver powder with triangular shape,quadrilateral shape and hexagonal shape with particle size about 500 nm can be obtained with the amount of PVP of 30 wt%,the reaction temperature of 150 oC and the reaction time of 12 h.?4?The fine flake silver powders obtained by the above three methods are named as AgNPs-1,AgNPs-2 and AgNPs-3,and are mixed with an organic carrier obtained by mixing polyurethane,dibasic acid ester?DBE?and isocyanate.A conductive silver paste was prepared from fine flake silver powder,and the electric resistance and film thickness were tested.The resistivity of AgNPs-1,AgNPs-2 and AgNPs-3 was respectively 3.1×10-4?·m,undetectable and 1.8×10-4?·m.?5?In the experiment process of this dissertation,micro-nano silver powder with various morphologies was prepared by adjusting different reaction parameters and process conditions,and its structure and related properties were studied.Among them,PVP and citric acid were used as surfactants to prepare flower-dendritic silver powder with a particle size of 23?m,and the rate constant for catalytic hydrogenation of4-nitrophenol is 230.08 s-1·g-1;Gum arabic was used as surfactants to prepare flower-spherical silver powder with size of 2.5?m,and the rate constant for catalytic hydrogenation of 4-nitrophenol is 191.81 s-1·g-1;Using PVA as a surfactant,a spherical silver powder having a particle diameter of 300 to 500 nm was prepared,which was used to prepare a slurry and measured to have a specific resistance of 4.2×10-4?·m. |
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