The Effects Of Several Factors On Electrodeposition/Corrosion Mechanisms Of Copper And Copper-based Alloys

Copper and copper-based alloys are widely used in electric power,electronics,building decoration and other fields due to their excellent features such as electrical conductivity,thermal conductivity and corrosion resistance.With the development of science and technology and production,copper electrodeposited films are also widely used in various fields such as electronics and precision instruments,which have important application prospects.As one of the most important properties of the material service process,the investigation on the corrosion mechanism of copper and copper-based alloys is very important for their development and application.In addition to some irreversible reactions,electrodeposition and corrosion as the inverse processes being the electrochemical reactions,have occurred in the electrode/electrolyte interface.Additives,corrosion inhibitors,alloying elements and other effect factors can significantly alter or affect the complex kinetic behavior of the electrode/electrolyte interface,modifying the surface properties of copper and copper-based alloys.Therefore,the aim of this thesis is to investigate the interaction between additives/inhibitors and adsorptive ions at the electrode/electrolyte interface by employing a multianalytical approach using complementary analytical techniques including spectroscopic,microscopic electrochemical tools.The focus is on the surface properties and microstructure of the material in order to discern the influencing factors such as electrolyte flow rate,current density,and temperature on the electrode dynamics of copper electrodeposition and their effects on the properties of the copper deposits including the corrosion behavior.Moreover,the role of alloying elements,structure of copper alloy,corrosive ions in the environment are investigated in-depth on the mechanisms of the corrosion initiation and patina evolution of copper and copper.The relationship between electrode/solution interface behavior during electrodeposition and corrosion and the properties of copper and copper alloys is established,being beneficial to the selection of additive/corrosion inhibitor and providing theoretical guidance for the application of copper alloys.The content and contribution of the thesis are concluded in the following aspects.(1)The synergistic effects between the concentration of gelatin and the convection electrolyte were investigated and the surface adsorption mechanism and copper foil growth model of gelatin at different electrolyte convections were proposed.It was found that the adsorption of gelatin on the electrode surface can inhibit the copper electrodeposition and the release of the hydrogen gas bubbles generated by hydrogen evolution from the electrode surface,affecting the uniformity of the surface morphology and the current distribution.Under strong convection conditions,it forms a copper foil with spiral-pattern surface morphology.Therefore,an electrolyte convection slightly less than 1000 rpm and an appropriate gelatin concentration(2 ppm)can suppress the hydrogen evolution and increase the deposition current efficiency.Meanwhile,a deposit with relatively less surface defects and finer microstructures can be obtained.This study provides theoretical support for the selection of gelatin concentration and electrolyte flow rate for industrial production.(2)The interaction effect of benzotriazole(BTAH)and chloride ions in copper electrodeposition and corrosion dissolution process were studied,which confirms that BTAH can improve the corrosion resistance of copper deposits when used as an additive.This builds up the relationship between electrodeposition and corrosion dissolution.The results show that with only addition of BTAH,it adsorbs on the surface of the electrode in molecular form(Cu-BTA),suppressing the reduction of copper ions and the lateral growth of crystal grains,leading to the grain refinement,the decreased surface roughness,the increased electrical conductivity and hardness of the copper deposit.The addition of chloride ions diminishes the inhibition of copper deposition caused by BTAH and competes with BTAH on the surface of the electrode,eliminates the effect of BTAH on the characteristics of the copper deposits,such as grain refinement.However,during anodic dissolution of copper in the presence and absence of chloride ions,BTAH adsorbs on the electrode surface in the form of complex Cu(I)BTA,inhibiting the corrosion of copper deposits.(3)By comparing with pure copper,the corrosion initiation and patina evolution of a new copper-based alloy of Cu-5Zn-5Al-1Sn were studied.The alloy microstructure exhibits several favorable properties compared to commercially available Cu metal,including a more random grain orientation and a higher fraction of coherent twin boundaries than Cu metal.The alloy also shows small variations in surface chemical composition and in Volta potential that is beneficial from a microgalvanic corrosion perspective.After diamond polishing the oxide is approximately 5-10 nm thick,and exhibits a compositional gradient with four identified sub-oxides.Cu2O is mainly located in the outer part of the total oxide layer.It is followed by ZnO,SnO2 and with Al2O3 mainly located in the inner part next to the alloy substrate.All four sub-oxides contribute to the overall corrosion resistance,whereby ZnO,SnO2 and Al2O3 possess mainly barrier properties.Furthermore,the role of the alloying elements(Al,Zn and Sn)has been further explored by studying the formation,evolution and barrier properties of the patina formed on the Cu5Zn5AllSn alloy in chloride-containing field and laboratory environments.Samples have been exposed up to five years at unsheltered marine field conditions and at well-controlled laboratory conditions with wet/dry cyclic exposures and different loads of pre-deposited NaCl.By identifying the patina constituents,their spatial distribution,evolution with time and barrier properties,it shows that the atmospheric corrosion resistance is based both on Cu2O,ZnO,Al2O3 and SnO2 within the inner part of the patina and on intercalation of SnO2,Zn5(CO3)2(OH)6,Zn6A12(OH)16CO3·4H20 and Zn5(OH)8Cl2·H2O within the outer chloride rich part of the patina,which is mainly composed of Cu2(OH)3C1.(4)At the last,the characterization of tin-bronze alloy substrate and the initial oxide shows the finer grains than Cu metal.Alloying element of tin exhibits the blocking effect on copper redox process.The corrosion mechanism and patina evolution during long-term exposure(1-5 years)in different atmospheres including marine and urban environments were investigated.At chloride-rich(marine)environments,the patina with a thickness between 10-30 μm was composed of a Cu2O dominated inner layer with the enrichment of Sn02 at bulk/patina interface and a acatamite/paracatamite(Cu2(OH)3C1)dominated outer layer with the presence of amorphous malachite(Cu2(OH)2CO3).The flaking of corrosion products occured and increased with longer exposure time(≥ 4 years)at chloride-riched conditions,resulting in a loosely adherent and more layered patina with intercalation of SnO2 layers.At sulfate-containing(urban)environments,the patina with a approximate thickness of 1 μm formed was primarily containing CU2O enriched with SnO2,following by the formation of posnjakite(Cu4SO4(OH)6·H2O)and brochamite(Cu4SO4(OH)6)after longer exposures(5 years).