Research On Preparation And Properties Of Expanded Graphite/Copper Composite

Graphite-copper composites are widely used in the self-lubricating materials and electrical contact materials, due to its good mechanical properties, excellent electrical conductivity, and high abrasion resistance. Expanded graphite(EG) is a kind of advanced graphite materials, because of its peculiar reticular and porous structure, it has many useful properties such as: high flexibility, high conductivity, high self-lubrication and high adsorption. The traditional preparation methods of graphite-copper composites are powder metallurgy and electroless plating. Both have defects, such as uneven ingredients, process complexity, etc. Electroplating process many advantages, such as high deposition rate and stable bath, low cost of production, and electroplating process can coat Cu on the unique pore structure of the expanded graphite with simple pretreatment process. In this paper, EG-Cu composite powder is prepared by electroplating method, the preparation process of the composite is studied, the obtained composite is characterized in different ways, and the static physical properties and friction and wear properties of the composites is analyzed.In this paper, the technological scheme of the preparation of EG-Cu composite powder material by electroplating method is systematically studied. First of all, the zetetic experiment is carried out, a new electroplating device was redesigned, H2SO4 system is chosen as the electroplating system in this article, the technological process of the preparation of the composite by electroplating method is determined. And then using product quality, the actual current efficiency and the copper content of the product as experimental index, the basic process parameters of the H2SO4 electroplating system are determined by orthogonal experiment; and through single variable experiment, the best bath Composition of the H2SO4 electroplating system are determined.Optimum parameters of H2SO4 electroplating system is as follows: current density: 3A·dm-2 the amount of expanded graphite: 0.25g·L-1, pre ultrasonic time: 10 min, stirring interval: 30min; bath composition: Cu SO4: 20g·L-1, Na H2PO2: 10g·L-1, CH3COOH: 10 m L·L-1, H2SO4: 25 m L·L-1. Under the optimal process parameters, the copper content of the composite powder material after electroplating 60 min can reach 84wt%, actual electroplating efficiency can reach 36.89%.The prepared EG-Cu composite powder with good plating results was characterized and analyzed. XRD analysis shows the phase composition, it proves that the composite powder material exists only in the two phase of graphite and copper, does not contain other impurities. Through the SEM analysis, the surface morphology of the composite powder is studied, it can be seen after electroplating, a layer of dense, uniform, high plating rate copper coating is obtained on the surface of expanded graphite, the coating is closely linked to the surface of graphite. And the thermal stability of the composite in the air is tested by TG-DTA.The composite powders of 16wt% graphite content were prepared as matrix of ball milling and powder mixing, and then the EG-Cu composite with different graphite contents is prepared by the re-pressing and re-sintering process, and GNP-Cu composite of the same graphite content was prepared by the same process as the contrast samples.Density test of EG-Cu composite and GNP-Cu composite are carried out, density variation law is found; and the relative density of composites after re-sintering reach over 90%, can meet the normal use. Through mechanical, electrical performance test, it is found that while the content of graphite decreasing, composite’s mechanical, electrical properties gradually increased, and under the same graphite content, EG-Cu composite performance is superior to the performance of GNP/Cu composite. When the content of graphite reach 4wt%, the EG-Cu composite has the highest performance: Vickers hardness reaches 56.83, bending strength reaches 86.28 MPa and resistivity reaches 0.151μΩ·m.Through the friction and wear test, on the analysis of the friction coefficient, wear volume and wear morphology, we find that when the content of graphite reach 4wt%, EG-Cu composite show the best anti-abrasion performance, with a load of 10 N, the friction coefficient is 0.028, only 10.3% of copper friction coefficient under the same testing condition, while the amount of wear is only 23% of the copper.