Research On Preparation And Properties Of Silver Coated Silica Powder

Silver powder is widely used in electronic paste,conductive adhesive,electromagnetic shielding,medical materials and solder,et al.But the price of silver is expensive which limits its application in industry to a certain extent.Therefore,looking for new materials is an important development direction to reduce the amount of silver.The powder with core-shell structure can significantly reduce the amount of silver while maintaining good electrical properties.So the cost is greatly saved.Silica has the advantages of wide source,low cost,stable chemical property,simple preparation method.In recent years,silica is often used on the study of preparation of composite powders.This thesis using electroless plating to prepare silver coated silica（SiO₂@Ag）powder.The SEM,XRD,XPS and other characterization are used to characterized the morphology,size and conductivity.In this thesis,silica microspheres were prepared by STOBER method.The work was focused on the precise control of particle size.Single factor experiments were carried out to study the factors that affect the size of silica,such as the amount of ammonia water,water,ethyl silicate（TEOS）,ethanol and the kind and concentration of electrolyte.The results show that the particle size of silica will decrease when the amount of ammonia is too much or too little.When the water is not enough,silica will agglomerate.The increase of water content will decrease the size of silica particles.The increase of ethyl silicate silica can increase the size of silica microsphere.But too much ethyl silicate silica will lead to the aggregation of silica.Too much ethanol will decrease the size of sillia microspheres,while too little will lead to the aggregation of silica.Electrolyte can increase the size of silica microspheres.At last,by adding the TEOS three times,the large size SiO₂ were prepared and the size of the microspheres was controlled from 300 nm-2 μm range.In order to get the silver coated silica powder with integrity coating,the mercaptopropyltrimethoxysilane was used for the surface modification of silica microspheres.Then the electroless silver plating was used to coated silica with silver.The influence of the parameter of electroless plating,such as reducing agent,complexing agent,concentration of sodium hydroxide and silver nitrate,silver content and silica particle size,on the SiO₂@Ag powder were investigated.It is found that the particle size of the silica spheres has important influence on the coating quality.When the SiO₂ particle size increases,the coating quality can be improved and the amount of silver can be reduced.When it is not effecting the practical application,the large size silica should be used.So the silver content is reduced and cost is saved.The 2 μm SiO₂@Ag with 30% silver content was used to make the electronic paste with 50% powder amount,the square resistance is 90.6 mΩ/sq.