Study On The Preparation Of Cu@Ag Core-shell Submicron Particles And The Conductivity Of Their Sintered Thin Films

Copper(Cu)powders have been widely used in the field of conductive paste because of their low cost and excellent conductivity;however their oxidation-resistance is poor.The preparation of copper@silver(Cu@Ag)core-shell structure not only can improve the oxidation resistance of Cu powders,but also can maintain the good conductivity.In this thesis,submicron Cu particles with uniform size were prepared by chemical liquid-phase reduction method and then Ag shells were grown on the surface of Cu core by the same method to form a core-shell structure.The effects of different reaction parameters on the morphology,size and structure of the particles were studied,and the oxidation resistance and light absorption characteristics of the particles were also characterized.Finally,the effect of sintering conditions on the morphology and resistivity of the films was studied.The main conclusions are as follows:The typical Cu@Ag core-shell submicron particles have a polyhedral shape with an average size of 150±20 nm.Compared with the commonly used galvanic replacement method to prepare Cu@Ag core-shell particles,the method used in this work does not easily to produce defects such as holes or hollow structures in the particles.The use of polyvinylpyrrolidone(PVP)as dispersant helps to form the core-shell structure.When the concentration of PVP is larger than 0.2 mmol/L,the shapes of the core-shell particles are basically the same,and no short rod-like particles appear.The core-shell structure is more complete when the reaction temperature is lower than 40℃ and the injection rate of silver salt is slower.The thickness of silver layer can be controlled by adding different amount of silver salt.Thermogravimetric analysis showed that the initial oxidation temperature of Cu@Ag core-shell particles compared with Cu particles increased from 140 ℃ to 200 ℃.After exposing under air for half a month,the Cu@Ag core-shell particles are not be oxidized.With the increase of the thickness of Ag layer,the absorption peak of Cu cannot be observed in the UV-Vis absorption spectra,which supports the formation of Cu@Ag core-shell structure.With the increase of sintering temperature and the prolongation of holding time,the sintering necks of the Cu-Ag core-shell structure sintered films increase obviously,the degree of cross-linking of the conductive network increases,and the resistivity decreases gradually.When the molar ratio of Cu/Ag is 3:1,the resistivity of the sintered films can be as low as 10.8 μΩ·cm.At the same temperature,the microstructure of the film changed little with the extension of holding time.The microstructure and resistivity of the films are also different under different sintering atmospheres.