Study On The Preparation And Performance Of Silver-Graphene And Silver-Graphite Composite Coatings

Contact is one of the core components of voltage disconnector which perform a variety of functions like transfer,isolation,connection and breaking.The surface of contacts are usually plated with silver in order to prevent peroxidation and improve conductivity of voltage disconnector.But the silver plating layer is easy to weared and fallen away which subject to environmental impact,close-open operation and arc erosion.The copper exposed of contact lead to more frequent defects of voltage disconnector and it threatens the safe operation of the grid.So the silver plating layer has been difficult to meet the practice requirement,and it need to prepare new silver-based coatings which have excellent overall properties.In this paper,silver-graphite composite coatings were successfully prepared by the composite electrodeposition technique in the cyanide-free system.On this basis,the graphene sheets were incorporated into the silver matrix composite coatings as the second-phase particles.The main work and results of this paper are as follows:1.Preparation and characterization of silver-graphite composite coatings.First of all,the succinimide cyanide-free silver plating system was chosen for the consideration of safety,environmental protection and coating quality.The best bath formulation are as follows:silver nitrate 40g/L,succinimide 90g/L,potassium pyrophosphate 90g/L,Potassium hydroxide40g/L.The optimum technological conditions of silver-graphite composite electrodeposition were as follows: graphite addition amount 30g/L,current density 0.5A/dm²,stirring speed1200r/min,temperature 40℃,electrodepositiontime 120 min which were carried out by single factor experiment.The results of SEM,EDS and XRD showed that the main components of composite coating are silver and graphite,which is a porous coral-like structure containing homogeneously dispersed graphite.And graphite did not change the crystal structure of silver,the preferential growth orientation of silver is alway（111）.2.Preparation and characterization of silver-graphene composite coatings.The graphene used in the experiments were multilayer lamellar structures with a thickness of several nanometers.When the mass fraction of PVP is 30%,graphene has the best dispersion in the aqueous solution.With the increase of the current density,the appearance of the compositecoatings become more darkened.But it become rough or even burning black when current density is too high.The surface of the composite coatings distributed with a large number of cell-structure.With the increase of the amount of graphene,the cell-structure are increased and the binding is more dense.However,when the amount is too high,the graphene is difficult to disperse effectively.The graphene sheets were found in composite coatings by SEM and EDS analysis,and Raman analysis also detected the characteristic peaks of graphene,which determine the graphene sheets incorporated into the composite coatings as the second-phase particles.3.Study on the performance of silver matrix composite coatings.The adhesion and anti-discoloration ability of silver coating,silver-graphite composite coating and silver-graphene composite coating were meet the requirements of the standard GB/T5270-1985 and QJ 484-1990.The corrosion resistance of the coatings was studied by polarization curves: the corrosion resistance of the three kinds of silver matrix coatings was better than pure copper in Na₂S,Na Cl,H₂SO₄ and Na OH solution.In the Na₂S and Na Cl solution,the corrosion resistance of silver-graphene composite coating is the best.The best corrosion resistance in H₂SO₄ and Na OH solution is silver coating and silver-graphite composite coating.The average friction coefficient of pure copper,silver coating,silver-graphite composite coating and silver-graphene composite coating is0.815,0.679,0.204,0.149,and the average wear width is 1.240 mm,0.590 mm,0.467 mm,0.453 mm.The results show that the graphite and graphene can improve the wear resistance and oxidation resistance of the composite coating,while the effect of graphene is better.The results of contact resistance test show that the three kinds of silver matrix coatings can improve the conductivity of pure copper.