Research On Spherical-graphite@Cu Powders Plating Technology

Metallic coating composite powders is a new type of powder metallurgy materials with multiphase and composite property. Due to its great varieties and special performance, it has been extensively applied in the industries including national defense industry, mechanical manufacture, and chemical industry etc. In the microscopic view, the coating powder features in multiphase, coated integrality and the characteristics of its various components can be shown according to different needs. In the macroscopic view, coating powders has character of its homogeneous property, which realizes uniform metallic phase fabric of products, and meanwhile greatly reduces or eliminates the defects of unstable performance and non-homogeneous components of products caused by non-uniform blending.In this paper, spherical graphite as substrate, the copper were deposited on the surface of micron squama graphite powders by electroplating method. The graphite composite powders were obtained after passivating, washing and dryness. The preparation conditions and mechanism of sodium hypophosphite were studied.The effects of temperature, cathodic density, the reductant concentration and loading capacity on the coating ratio has been researched through single factor experiments. The microscopic structure, surface topography, and coating elements content of composite powders were also analyzed by adopting advanced testing methods including SEM, EDX and XRD. The results indicate that:1. The coating ratio increased with the rise of the temperature, cathodic density and the reductant concentration, but it decreased with the increase of the loading capacity.2. Processing parameters were optimized through contrast test. The optimal conditions of the electroplating copper system are as follows:CUSO4 15 g·dm-3, H2SO4 10 cm3·dm-3, temperature 55℃, cathodic density 30 A·dm-2, NaH2PO2 10 g·dm-3, loading capacity 15 g·dm-3 and pH value 2.3. Composite powders with high copper coating ratio (up to about 70%) could be obtained in the optimal condition. SEM results indicated that copper coating was formed as dot deposits at first, then expanded to be patche structure. XRD and EDX examinations found that the coating was crystalline state and no impurity existed.4. Electric field can move the copper nuclei with plus charge towards negative electrode. The positive copper nuclei collided graphite and then were absorbed on the graphite surface. They grew up when contacting to the cathode and formed high conductivity layer of copper on graphite surface.5. Sodium hypophosphite as an additive played a role of increasing nucleation and accelerating the initial deposition during electrodeposition. It can effectively reduce the polarization resistance of electrodeposition and decrease the deposition overpotential.6. After 1h deposition, sodium hypophosphite was consumed by above 95% because of decomposition. Both of sodium hypophosphite and copper salt were properly added to electrolyte if reproduction in order to keep the bath high life and repitation utilization ratio.