Shape-controlled Synthesis And Properties Of Nickel-coated Graphite Core-shell Composite Particles

Nickel-coated graphite core-shell composite particles with excellent electricalconductivity and magnetic property both core and shell materials have been widelyused in electromagnetic shielding, catalytic, communication and military industries.However, there are some problems such as the uncompact nickel shell and theuncontrollable morphologies in present methods for the synthesis of nickel-coatedgraphite composite particles. This limits their application in the field ofelectromagnetic shielding and catalyst. In this thesis, we proposed a method ofpreparing nickel coated graphite composite particles based on electrostatic adsorptioncontrolling the number of nucleation sites, then obtained nickel-coated graphitecomposite particles with different morphologies by regulating reaction kinetics. Themain points can be summarized as follows.Firstly, we prepared nickel-coated graphite composite particles with continuousand compact nickel shells based on the electrostatic adsorption between graphiteparticles and nickel ions through controlling the number of nucleation. The influenceof different NiSO4concentrations to the number of nucleation on graphite particleswas studied and we also analyzed the reasons. When NiSO4concentration was addedto0.76mol·L-1, it was beneficial for preparing continuous and compact nickel-coatedgraphite composite particles by providing maximum rate of nickel nucleation on thesurface of the graphite particles. The adsorption of nickel ions based on electrostaticinteraction would provide active sites to subsequent reaction for preparing acontinuous dense shell of nickel coated graphite composite particles.Secondly, nickel coated graphite composite particles with different morphologies,such as spherical, nanoneedle, were synthesized via dynamic regulation in a facilereaction system by simply adjusting the reaction conditions without any surfactants orapplying external magnetic field. The mechanism of morphology transformation wasalso investigated. The lower concentration of NaOH will decrease the reaction rate.After the nucleation finished, the nickel nuclei would grows along <110> direction ofthe high surface free energy to be a one-dimensional needle-like nickel in order to reduce the surface free energy of the system. The reaction rate would be fast whenthe NaOH concentration increased, and nickel particles exhibit isotropic grain growth.We have studied the properties of nickel coated graphite composite particles withdifferent morphologies. The results show that the volume resistivity of epoxy resinconductive adhesive containing25%spherical nickel coated graphite compositeparticles is4.69×10-2·cm and the saturation magnetization is40.6emu/g. Sphericalnickel coated graphite composite particles has excellent electromagnetic propertiesand can be used for electromagnetic shielding materials. Nanoneedle-like nickelcoated graphite composite particles have excellent catalytic activity which could beused as a catalyst of preparing amino phenol.