| Graphene(Gr),since the discovery in 2004,has caused the research upsurge in fields of science and engineering.Gr is composed of a single atomic layer of carbon materials.The ultra-thin thickness,super-high mechanical properties,ultra-high light transmittance and carrier mobility make graphene possess a areat application prospect of in the field of energy,chemical,ship,electronic circuit,aeronautics and astronautics,etc.Copper is the best metal conductivity after gold and silver,and the price is relatively low,which makes the copper indispensable material in many industrial applications.Zinc electroplating has occupied more than sixty percents market share in our country.Up to now,various nano reinforcement materials were incorporated into copper or zinc matrix,the resultant composites show the remarkable performance improvements.Electrochemical method,with advantages of simple operation,controllable process and large-scaleable continuous production technology,have a broad applications in many fields especially in composite materials.At present,the vast majority of graphene-reinforced copper matrix composites are prepared by powder metallurgy method.Many researches have shown that the incorporation of graphene can significantly improve various properties of metal matrix.It is generally believed that the principle of electrochemical preparation of graphene-reinforced copper matrix composites is as follows:1)the graphene precursor is modified or directly added to the base electrolyte to form a stable suspension;2)under the action of electric field force and agitation,copper ions and graphene co-deposited at the cathode to form the composite film.In the preparation of copper-graphene composites by electrochemical method,many studies have confirmed that Graphene content and dispersion uniformity are the two most important factors.In the graphene-copper composites prepared by electrochemical method,two important problems have not been solved:1)the direct and accurate determination of graphene in graphene-copper composites;2)the correlation between the amount of graphene added in the electrolyte and the amount of graphene entering the composite material.The solution of these problems is of Great significance for the application of graphene in composites.Based on the fully understanding of graphene reinforced copper matrix composites and international frontier research hot topic,this paper conducted systematic studies on the electrochemical preparation of copper-graphene(Cu-Gr)composite,the direct determination of reinforcement content,the optimization of electrodeposition process,the dispersion of reinforcement,the structure design of composite and the codeposition mechanism and so on.A direct and accurate method for the determination of the content of the reinforcement in copper-graphene composites was proposed.A set of optimum technological conditions for electrodeposition of copper-graphene composite films were developed.A self-dispersible hybrid enhanced phase of graphene+carbon nanotubes was investigated.A one-step method for preparation of sandwich structure copper/Graphene/copper composites was designed.Zinc-Graphene composite electrodeposition process was studied.The mechanism of metal-Graphene composite electrodeposition was proposed.The first chapter is introduction,which reviews the research status and progress of graphene-reinforced metal matrix composites in detail and introducing the significance of the topic selection and the main content of the work.The second chapter as the experimental section mainly introduces the materials used in the experiment reagent,preparation technology of specific operations and the apparatus used for the characterization of the microstructure and performance testing of the samples.That is,graphene precursor electrochemical preparation of copper-graphene composite film and the process optimization of carbon nanotubes+graphene hybrid enhanced relative to the influence of copper matrix composite foil sandwich structure of copper/graphene/copper composite foil preparation and the electrodeposition mechanism of metal-graphene composite.The third chapter proposed a direct and accurate method for the determination of Cu-Gr composite films.The content of carbon(C)in foil was determined by high frequency infrared carbon and sulfur analyzer,and the content of Gr in foil was determined directly and accurately.The relationship between the graphene content in the composite foil and the graphene oxide(GO)concentration in the electrolyte was obtained for the first time.The relationship was found to be consistent with the relationship between the GO concentration in the electrolyte and the Graphene content in the composite copper foil.Under the current process conditions,the GO concentration in the electrolyte has an optimal value of 0.5 g/L,and the corresponding mechanical properties also reach the maximum.It is believed that excessive GO concentration in the electrolyte will cause agglomeration and make it more difficult to be co-deposited into the metal matrix.In the fourth chapter,the effects of three important electrodeposition parameters(precursor GO concentration,current density,bath temperature)on the structure and properties of Cu-Gr composite films deposited by DC electrodeposition are systematically studied.It was found that the influence of graphene on the composite foil was the most significant.The thickness of the prepared composite foil was about20 microns,and the optimal deposition conditions were obtained:the concentration of go was 0.5 g/L,the current density was 10-20 A/dm2,and the bath temperature was25-40?.In chapter 5,carbon nanotubes was dispersed by GO to develop a self-dispersing hybrid reinforcement i.e.,carbon nanotubes+GO(CNTs+GO),and Cu-(CNTs+Gr)(CNTs+Gr)ultra-thin composite foil with thickness of about 4 microns was prepared.GO can formed the?-?bonding in the solution with the CNTs so as to form a stable dispersion.Graphene can change the structure of copper,and the preferential orientation changes from(111)plane to(220)plane,while carbon nanotubes do not change the preferential orientation of copper.Due to the synergistic effect of Gr and CNTs,Cu-(CNTs+Gr)composite foils have the highest mechanical properties,corrosion resistance and electrical conductivity compared with pure Cu,Cu-CNTs and Cu-Gr foils.In chapter 6,we designed a one-step method to prepare copper/graphene/copper(Cu/Gr/Cu)ultrathin foil with sandwich structure.The design idea was as follows:firstly,a thin graphene oxide film was prepared by DC electrophoresis deposition(EPD),which allowed copper ions to permeate and contact with the stainless steel substrate.Then,according to the difference of deposition potential of copper on different substrates,an electric potential step method was designed to successfully prepare Cu/Gr/Cu composite films with sandwich structure.The thickness of the composite foil can be as low as 4-5?m;compared with pure copper foil,the tensile strength increased by 98%,while the conductivity is basically unchanged.At the same time,this new preparation method provides a new idea for the electrochemical preparation of layered composites and can be applied to other materials.Different from the copper foil mentioned above,the preparation and corrosion resistance of Zinc-Graphene(Zn-Gr)composite coating by reverse pulse electrodeposition are introduced in chapter 7.Using GO as the precursor,the Zn-Gr composite coating with high corrosion resistance was prepared by reverse pulse electrodeposition in zinc chloride system.GO was reduced to Gr during the co-deposition of zinc and GO.The scratch test shows that the Zn-Gr composite coating has strong adhesion to the substrate.Graphene can provide more nucleation sites for zinc.Due to the increase of nucleation sites,the incorporation of graphene changes the growth mechanism of Zn crystal and changes its preferential orientation.Graphene,as an anti-corrosion barrier layer,plays an important role in the corrosion resistance of Zn-Gr composite coating in the simulated seawater environment.In the optimal range of 0.3-0.5 g/L GO added to the electrolyte,the corrosion resistance is the highest,and the corrosion current density is only one percent of that of the pure zinc layer.In chapter 8,the action mechanism of graphene and copper in the electrodeposition process was preliminarily explored by using various analytical methods of electrochemical testing.The action of GO and copper in the electrolyte,the influence of graphene on the copper deposition process and the interaction mechanism of graphene in the composite materials were studied.1)The role of copper and precursor GO in electrolyte and its binding in composites were experimentally verified,and it was found that GO could form chemical bonds with copper ions in electrolyte.2)electrochemical testing found that go could provide more active sites for copper at the initial stage of deposition,and inhibit the growth of copper at the later stage of deposition;3)TEM and SEAD further demonstrate that in the composite foil,copper and graphene are chemically bonded rather than simply mechanically mixed;4)the process of electrochemical deposition of graphene oxide reduction for graphene mechanism and strengthening mechanism,in the process of codeposition,oxidation reduction of oxygen-containing functional groups on the surface of the graphene into reduction in turn:hydroxyl(OH)is easier to reduce,and alkanes and carbonyl oxygen takes two steps,that is,reducing to the hydroxyl,and then further reduction,in the process of oxygen with copper ion and copper-the interface between the graphene combining Cu2O,eventually forming Cu-Gr composites.5)As for strengthening mechanism,this paper suggest that in the low precursor quantity in the electrolyte,the probability of graphene conctat with cathode is low,namely effective concentration is low,so and copper deposit of the amount of graphene is low,the precursor concentration is too high,and most of the graphene oxide together into larger particles,when in contact with the cathode,also not easy to be deposited into the composite foil,in other word,the effective concentration is also low.Chapter 9 is a summary of the paper.At the end of the paper,it mainly introduces the author's published academic papers,scientific research achievements,invention patents,overseas scientific research projects and awards in school.It also gives thanks to my supervisior and others as well as the author's resume. |
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