Study Of Preparation Of Electroless Coated Composite Particle And Its Conductive Property

The Ag-coated cenospheres can be of great application interest in war industry, national defence, electronics,optics, medicine, industrial catalysis, bio-engineering and so on. But the silver layer's being brushed off easily causes the rising of the resistance of the Ag-coated cenospheres and weakening of their performance, hunting for a simple and feasible method to make silver coating tight and firm is all the researchers'aim. In this paper, new Pd-free activating agent is introduced, and Ag-coated cenospheres and Ag-coated polymer microspheres are produced, mechanism of activating and the coated layer and its application as conductive filler are studied。The main content of the research and conclusion are as follows:(1) The results show that the formaldehyde can react with silver nitrate-ammonia to form silver layer on the surfaces of cenosphere which is pretreated within four steps: degreaseing, coarsening, sensitizing,activation, activation enlarging specific surface area and reactivity, whose specific surface area is 28.8 times of bebore,which promote silver deposition. A great deal of little holes formed during pretreatment make room for silver ion, whose surface area and energe will drops if reacted, such is of spontaneity.(2) Ultrasonic can effectively disperse the cenosphere particles, enhance surface activity, promote radical deposition, simplify process.The way to make the electroless plating solution remarkably affect the deposit of silver, also the appearance of the micro cenospheres. Lowering feeding rate of silver nitrate-ammonia and reaction temperature can slow plating,so as to prevent big Ag particles from depositing on the cenosphere surface,in this way good samples is manufactured.(3) Emulsion polymerization is fit to prepare polystyrene microspheres of good monodispersion, dialyzer is helpful to separate small molecules from polymer system. The ratio of monomer, emulsifier, nitiator affect the size and distribution of microspheres. electrical resistivity of silver coated microspheres is 6x10^-3Ω·cm,which can be used as conductive fillers.(4) An excellent fomula of conductive adhesive is:epoxy:filler (5μm～8μm)= 100:260, filler(dendritic particles:microspheres=1:3 wt), DDM as curing agent, whose Ag-migratory is 3 times as silver conductive adhesive, fit for use.(5) A successful curing process is:DDM as curing agent,30wt%,according DSC to fix:80℃/2h+125℃/2h+180℃/3h(6) Influence mechanism of cenospheres and the coated layer consist of chemical bond and occluding, which promote to form compact layer and Ag-migratory and increase adhesive's reliabilityThe main innovation are:1) bring Fe(OH)3 gel as activator for the first time in the world, electroless silver deposition on surface of cenospheres and PS microspheres is carried out.2) Deposition mechanism of ferric oxide on surface of cenospheres is studied;3) The effect on configuration of layer and control of morphology of coating is discussed;4) conductive adhesive is prepared and its performances is studied.