湿化学法制备微米级枝状银粉及其生长机理研究

采用抗坏血酸在40℃下还原硫酸铜制备微米铜粉,利用所制备的铜粉与硝酸银溶液反应制备出枝状的微米级银粉,并对枝状银粉的形成机理进行研究.通过SEM和XRD对制备的铜粉和银粉进行表征.结果表明:制备的新鲜铜粉为颗粒状,直径为3～10 μm,具有明显的棱角；制备的银粉为树枝状,长度为5～25.μm；而且当硝酸银浓度、硝酸银/铜粉摩尔比或反应温度较高时,更易生成枝状晶体,但当它们过高时,枝状晶体的二级结构变窄,三级结构逐渐消褪.枝状银粉的形成机理很可能是由于在铜粉表面具有高表面自由能的地方形成银核心,银粒子在此核心周围聚集,在非平衡态下,粒子扩散受动力学控制,自发聚集成高度有序的枝状结构.

Preparation and formation mechanism study of micro-sized silver dendritic crystals synthesized by wet-chemical method

The dendritic crystal silver micro-sized powders were prepared by mixing silver nitrate solution with the uniform and fresh copper microcrystal synthesized by reducing the Copper(II) sulfate pentahydrate with ascorbic acid at 40 ℃.The formation mechanism of silver dendritic crystal was also studied.Scanning electron microscope(SEM) and X-ray diffraction(XRD) were used to characterize the copper and silver powders.The results show that the copper powders consist of large numbers of polyhedral pure copper particles,and their diameters range from 3 to 10 -m.The silver particles have the dendritic microstructure.The lengths of individual dendritic crystals are 5～25 μm.It is favorable for the formation of silver dendritic crystals at a high concentration of silver nitrate or high mole ratio of silver nitrate to copper powders at higher reaction temperature;but when it is too high,the width of the secondary microstructures become narrower and the tertiary microstrtures fade.The growth mechanism of silver dendritic crystal maybe that the silver nuclei are generated at the spots which have high surface free energy on the surface of copper microcrystals.New silver particles are produced around the silver nuclei.In non-equilibrium conditions,the growth process of silver crystals is controlled by the kinetic factors.Silver particles spontaneous aggregate to dendritic microstructure from a disordered environment.