Study On Electromagnetic Shielding Coating Based On Ni/Fe Powder

With the rapid development of the electronic industry, electromagnetic interference (EMI) is becoming an increasing problem that affects people's health and work.So the electromagnetic interference shielding is increasingly required.Among all the shielding methods, the electromagnetic safety conductive paints have a bright future in this realm because of its low cost, simple process, good applicability, and without special equipments etc. Studies on the development of the EMI shielding coating is particularly important. The normal iron particle is easily oxidized, so the electromagnetic shielding effectivenesss is bad, while the electric conductivity of coating based on the micron nickel particles is better because these particles are not easy to be oxidized, However, the frequency of electromagnetic wave is narrow. Aiming at the above-mentioned problems,The present thesis designed experiments as follows:(1)nickel was coated on iron by the electroless plating in order to improve the oxidization of iron powder;(2) To improve the effect of the electromagnetic shielding and the electric conductivity, nanometer nickel powder combined micron nickel powder was used ,which was able to widen the frequency range of electromagnetic shielding wave;(3)The Ni / acrylic resin electromagnetic shielding coating was prepared, and the effect of every component on properties was also investigated.The electromagnetic shielding effectivenesss of the above composites have been studied systematically at the frequency range from 300KHz to 1.5GHz.Due to its poor function as the metals filler in the coating,the iron powder was modified using the electroless plating which prepared nickel coating around iron powder by means of oxidization resistance of nickel and the ability of absorbing electromagnetic wave.Five major parameters were selected for experimental investigation of powder preparation: initial concentration of nickelion, initial concentration of hydrazine, its pH value, plating temperature, and added amount of Iron powder, and an orthogonal array test L₂₅(5⁵)was designed accordingly. A great number of experiments were performed to get optimal technological parameters as follows: Initial concentration of nickel sulfate was 2.5 g/100mL, initial concentration of hydrazine 8ml/100mL, pH value 12, plating temperature 75℃,added amount of Iron powder 1.5 g/100mL. SEM and XRD were used to analyze the power for nickel plating aroundiron. The results showed that the surface of coating around such powder was rougher than that of original powder and the particles of the powder grew greatly. There was also no inclusion inside the coating layer .It suggested that the plating effect was preferable. The experiment prove that the electric conductivity of the coating with the Ni/Fe was better than that with the pure iron powder.In order to increse the electromagnetic shielding effectivenesss,the thesis analyzed the function of each component.The number of contacting particles and the distance among particles were the key factors, which decided the completeness and denseness of the framework.We studied systematically the influence of manifold factors,such as acrylic resin,the conductive filling and organobentonite, the aminosilane coupling agent and coupling agent of organic titanate.Acrylic resin is cohensive and helpful to combine because the conductive filling blended with resin through coupling agent ,the oxidation resistivity improved. Organobentonite can improve the dispersion of the coating.The electromagnetic shielding coating based on the nanometer nickel powder combined the micron nickel powder, has raised the electromagnetic shielding effectivenesss and the electric conductivity, also has widened the frequency range of electromagnetic shielding wave.The resultant coating based on nickel powder and combined powder showed that 95%～99%of the electromagnetic wave was shielding at the frequency range from 300KHz to 1.5GHz,while the coating based on Ni/Fe the shielding was 95% at the low frequency.