| The corrosion behavior of copper has the features of micro,local,and high uncertainty,which usually originates from the oxide film formed on copper surface,named passive film.Therefore,it is of great significance to explore the microscopic breakdown mechanism of passive film and modification strategy for improving the corrosion resistance.In this paper,we take metallic copper as the research object,investigating the microscopic breakdown mechanism of copper passive film in aggressive electrolyte(with chloride ions)via a strategy of combining firstprinciples calculations and electrochemical experiments.Based on the theoretical research results,an interface regulation approach is proposed to improve the corrosion resistance of copper passive film.The main research contents and findings of this paper are as below,(1)This paper firstly studies the effect of aggressive ions(chloride ions)in the solution on the evolution of structure,composition of copper passive film and determines the(electro)chemical reactions occurring on passive film surface.The results show that in the solution containing chloride ions,the copper passive film is gradually transformed from copper oxide to chloride through interfacial(electro)chemical reaction.The interfacial reaction is dependent on the chloride ion concentration and pH in the solution,while chloride ion and hydroxide have a complex competition-synergistic interaction:when chloride ion concentration is higher than(?),hydroxide and chloride competes with each other and the passive film is directly converted from cuprous oxide to cupric chloride;in a solution with chloride concentration below the critical value,hydroxide is conducive to the conversion of copper passive film to chloride,in which the passive film is firstly converted from cuprous oxide to cupric oxide,then transformed to cupric chloride by a chemical reaction.Meanwhile,the passive film breakdown potential is dependent on the electrochemical reaction with cuprous oxide as reactant.(2)Subsequently,we constructed an atomic-scale copper passive film model,and systematically investigate the effects of chloride ions on the atomic structure,electronic properties,surface defects,and internal diffusion of the passive film.The results show that Chloride ions are strongly adsorbed on the surface of the copper passivation film,with an adsorption energy of～-1 eV.The adsorbed chloride ions in turn lead to a decrease of～0.1 eV in the formation energy of copper vacancies on passive film surface,and a～50-fold increase in the defect formation rate.In addition,the adsorbed chloride ions further increase the diffusion coefficient of point defects in the passive film by a factor of 1000,which can kinetically promote the self-diffusion behavior of point defects.(3)Based on the above results,the mechanism of chloride ion on copper passive film is proposed as:chloride ion in solution is spontaneously adsorbed on the surface of copper passive film,which induces the formation of copper vacancies in the film,increases the defect concentration,and promotes the diffusion of point defects in passive film,thereby destroying the dynamic balance along the depth direction,placing the passive film in an unstable condition,and further promoting its breakdown.(4)Finally,this paper builds a relationship between corrosion resistance and the microscopic parameters of copper passive film from the electrochemical point of view,and proposes a method to control the interface properties,with purpose of providing research ideas and schemes for the subsequent experimental design to improve the corrosion resistance of the passive film.In solutions containing chloride ions,the corrosion resistance(breakdown potential)of copper passive films is linearly related to its band gap(Eg),interfacial reaction activation energy(ΔG),and inversely proportional to its electrical conductivity(σ).The firstprinciples calculations show that carbon-decoration on passive film surface would be able to widen its forbidden band width by about 0.1 eV,increase its carrier transition energy barrier by about 50 meV,and increase its interface reaction energy barrier by about 0.3 eV.The experimental results show that the surface carbonization treatment of the copper passive film effectively increases its film breakdown potential by about 300 mV,improving the corrosion resistance to chl... |
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