Electromagnetic Shielding The Wallet Copper Powder Technology And Its Mechanism Discussed

It is more and more difficult to neglect the influences of Electromagnetic Interference(EMI)and Radio Frequency Interference(RFI)on social life, economic development and national defense and security in the information society.Al present,all the world countries are developing kinds of electromagnetic shielding materials to solve this problem.Among of conductive fillers using for electromagnetic shielding,silver covered copper powder is in people's good graces for its low price,moderate shielding property,good environment serviceability,the application market of silver covered copper powder is expanded,especially after engineering plastics is largely used in the electronic electricity domain.Besides,silver covered copper powder can substitute for silver powder partially,and have a wide application prospects in catalyst,conductive ink,rubber,antibacterial material and so on.This article introduces the electromagnetic shielding material and conductive fillers briefly,summarizes the current status of silver covered copper powder preparation technology,and makes silver covered copper powder which have good performance such as outward appearance,electrical conductivity and so on,with flake copper powder as raw material in the electroless acid-Based plating.The pretreatment technics,silver-plating technics,post-processing technics and the properties of silver covered copper powders are researched.The surface topography of silver covered copper powder is compared,they are prepared respectively in electroless acid-based plating silver in this test,by inland company and overseas company.The mechanism of electroless acid-Based plating silver is initially assessed.we can obtain following conclusion:1.Pretreatment is the success or failure key of silver-plating,the silver-plating will achieve the best result after adopting the acid picklingalkali wash--acid pickling three steps processes.2.The chelating agent C is the determinant factor which can help achieve the aim that electroless plating silver in acid-based system.The concentration of C should not be too dense,or it may increase the speed of aggradation.The surface bonding strength of silver coating and copper powder may be strengthened and the electric conductivity be improved by reducing agent A and B.The plating solution temperature,AgNO₃ concentration and feeding time of AgNO₃ solution have a great influence on the speed of aggradation.The radio of liquid to solid and intensity of mechanical agitation have a little influence on performance of silver covered copper powders.The better electroless silver-plating conditions is:The concentration of reducing agent A is lg/L;the concentration of reducing agent B is 2g/L;the concentration of chelating agent C is 6.9g/L; the chelating agent of dispersing agent PVP is 0.03 g/L;the concentration of major salt AgNO₃ is 4.2～6.3g/L;the plating solution temperature is 25～40℃;the feeding time of AgNO₃ solution is about 30min;the radio of liquid-to-solid is 15;the intensity of mechanical agitation is 300～500r/min.3.Desorption processing may improve the luster and electrical conductivity of silver covered copper powder,especially the electric conductivity is improved obviously;the suitable concentration of antioxidant is about 5g/L.4.The study on the performance of silver covered copper powder indicates:The copper powder has the great influence on the apparent density grain-size distribution condition and surface topography of silver covered copper powders.Prolonging the ball grinding time properly can improve the electrical conductivity of silver covered copper powders.The silver concentration of silver covered copper powders has a great influence on its color and electrical conductivity,and a little influence on its apparent density.The measurement to the oxidative resistance ability indicates that silver covered copper powder containing 8wt%silver has better oxidized ability at normal temperature;At high temperature,the oxidative resistance ability of silver covered copper powder containing 3wt%silver is close to copper powder,but when the silver concentration is more than 8wt%, increasing silver content is not equal to increasing its oxidation resistance ability.The SEM observation indicates that the surface of silver coating is roughness.5.The compare of surface topography indicates:The surface topography of silver covered copper powder which is prepared in electroless acid-Based plating silver is similar with the inland company's,but they are worse than the overseas company's silver covered copper powder in the smooth degree of coating surface,the neat degree of single powder edge,the distributed uniformity of powder granularity and so on.It has relations to the performance of copper powders which is raw materials.6.The study of aggradation mechanism indicates:Both reduced plates and replacement plates exist in the electroless acid-based plating silver,the beginning of silver reduced must be evoked by the clean copper powders surface,the growth of silver coating is not by monolayer,but is that,the island shape coating is formed at firs on the copper powder surface,then the extension growth is carried.At the end the coating of stack-structure is formed.The chelating agent C simultaneously plays as the silver-plating chelating agent and the copper chelating agent role.