Research On Preparation Of Ultrafine Nickel Coated Copper Particles By Electroless Plating

Electromagnetic radiation shielding has become an essential project in societytoday. Conductive paint is a widely used material to shield electromagnetic radiationand nickel coated copper powder is a main additive to it. The preparation of nickelcoated copper powder now has a problem of complex technology and high cost. Ifnickel coated copper particles with good physical and chemical performance wereprepared by electroless plating, they could be used as conductive paints whichcombined the advantages of copper and nickel, and it would be important for thedevelopment of electronic industry and information technology of our country.This paper adopted two methods to prepare nickel coated copper particlesincluding two-step method and one-step method. Two-step method is that copperparticles are prepared by chemical reduction method using copper sulfate as a rawmaterial, sodium hypophosphite as a reductive agent and are filtrated, dried and grindedfirstly. These copper particles are coated by nickel by electroless plating. One-stepmethod is that copper particles are prepared by chemical reduction method using coppersulfate as a raw material, sodium hypophosphite as a reductive agent and then thesolution is mixed with the plating bath directly without filtration, drying and grinding toprepare nickel coated copper particles.The results show that both of two-step and one-step method have the same optimaltechnological parameters as follows:0.05mol/L NiSO₄·6H₂O,0.2mol/L NaH₂PO₂,0.15mol/L CH₃COONa·3H₂O,5g/L Cu, temperature is85oC, pH=5, reaction time is5min. With these technical parameters, nickel coated copper particles with30⁴0%nickel content were prepared and they were fully coated. Adjusting the major technicalparameters such as concentration of Ni²⁺ and reductive agent, pH value, platingtemperature, reaction time and addition amount of copper powder could influence thenickel quantity and deposition rate. The results showed that the most important factorsof the sample preparation were reaction time, concentration of nickel sulfate andreductive agent. If the raw materials were enough, nickel content of the samplesincreased with the increase of reaction time. Nickel content increased with the increaseof the concentration of nickel sulfate and reductive agent within a certain reaction time.But high concentration can result in an unstable plating environment. It must becontrolled within an appropriate range.Both of the two methods prepared a series of nickel coated copper particlessuccessfully. SEM images of the particles show that the shapes of the prepared samplesare spherical and they have the similar particle sizes and are well dispersed. TEM measurements show that the copper particles are fully coated by nickel plating and thecoating thickness are about25nm with a Ni content of30%. EDX patterns show thatboth of the nickel contents are from20%to85%, and P contents are from l%to9%.The nickel and phosphorus content can be controlled in some range by adjusting thecontent of every component in the solution and changing the correlative technicalparameters. Moreover, the impurity content in the composite powder is low. TGAanalysis indicates that nickel coated copper particles have higher oxidation resistancethan copper particles. Furthermore, XPS analysis indicates that surfaces of the copperparticles are fully oxidized to CuO and only a few nickel coated copper particles areoxidized. Test results show that conductivity of the nickel coated copper particles can becontrolled by changing the Ni content of the powder and the powder has a good over-allproperty. Furthermore, the PAN fibers doped with nickel coated copper was prepared byelectrospinning to try to shield electromagnetic radiation.One-step method abbreviates the procedures of filtration, drying and grinding,which avoid the oxidation of copper. It is easier and cheaper than two-step method. Thepowder performance was the same as that of two-step method. But the particle sizedistribution was not very good and further research is needed. To sum up, one-stepmethod is a promising method to prepared nickel coated copper particles.