A Study On The Preparation Of Spherical Micro-Sized Silver Powder Used In Conductive Silver Paste

The spherical micro-sized silver powder is an important part of conducive paste,the performance of conducive paste is related to morphology,particle size and tap density of silver powder.At present,the spherical silver powder is usually prepared by liquid chemical reduction method,the kind and dosage of dispersant,pH of reaction system,reaction temperature,concentration and mixing conditions of reactant have a certain influence on the morphology,particle size,tap density and other properties of silver powder in the process of liquid chemical reduction method.In this paper,liquid chemical reduction method was intended to be used to synthesize the micro-sized silver powder,the silver nitrate was used as feed solution,ascorbic acid(C₆H₈O₆)as reducing agent during the process of experiment.The SEM was used to observe the morphology and dispersion of silver powder,XRD was used to analyze the purity and crystallization of silver powder,particle size and distribution of silver powder was measured by particle size analyzer,finally,the tap density of silver powder was tested accordance to the related national standard.In the experiment of synthesis of spherical micro-sized silver powder used for the front electrode paste for solar cells,firstly,single element experiment method with the dispersion,size of particle,surface morphology of silver powder as the object of investigation was used to choose the optimal type of dispersant,pH of reaction system,mixing conditions of reactant and the dosage of reducing agent for the subsequent experiment.Then effects which were made by temperature of reaction,pH value of reaction system,dosage of dispersant and the concentration of silver nitrate on tap density of silver powder were investigated with the use of orthogonal design.Finally,the best condition for preparation of micro-sized silver powder was summarized from the analysis of result for characterization and orthogonal design.Orthogonal experiment result showed that:when PVP was used as dispersant,the influencing degree of the four factors in the orthogonal experiment made on the tap density of silver powder was pH>c(AgNO₃)>m(PVP)>t(?)in that order.Nearly spherical silver powder with tap density of 4.2 g/cm³,average particle size of 2.5 ?m and good crystallization can be synthesized under the condition:reaction temperature,40 ?;pH value,1;mass ratio of PVP/AgNO₃,4%;concentration of AgNO₃,1 mol/L.The spherical micro-sized silver powder synthesized under the optimum condition had met the application requirements of conductive silver paste for solar cells.In this paper,starch also was used as dispersant to prepare micro-sized silver powder,experimental result showed that:when starch was used as dispersant,influencing degree of the four factors in the orthogonal experiment made on the tap density of silver powder was pH>t(?)>c(AgNO₃)>m(starch)in that order.Nearly spherical silver powder with d10,0.5 ?m;d50,1.0 ?m;d90,1.6 ?m;tap density of 3.5 g/cm³ can be synthesized under the condition:reaction temperature,50?;pH value,1;mass ratio of starch/AgNO₃,4%;concentration of AgNO₃,1 mol/L.The silver powder synthesized under the optimum condition had basically met the application requirement of the superfine silver powder named PAg-G2.0 in national standard grade.