Thermal oxidation of single-crystal aluminum at 550°C

Oxygen transport during oxide growth on (110), (111), and (100) Al crystals at 550°C is investigated by¹⁸O/SIMS combined with kinetic measurements and SEM and TEM observations. Starting with an electropolished surface, the experimental evidence suggests oxide growth by oxygen anion transport via local pathways through an outer amorphous Al₂O₃ layer and oxygen incorporation at the periphery of the underlying laterally growing -Al₂O₃ islands. The kinetics, island morphology and epitaxy are sensitive to substrate orientation. This oxide growth behavior is compared with oxide formation on a sputter-cleaned and annealed (111) Al surface.     

Microstructure and crystallographic characteristics of nanocrystalline copper prepared from acetate solutions by electrodeposition technique

Methane sulphonic acid is an alternative electrolyte for conventional sulphuric acid for copper deposition. The electrodeposition of copper from eco-friendly acetate-based electrolytes consisting of copper acetate, sodium acetate and methane sulphonic acid was dealt. Thamine hydrochloride (THC), saccharin and 4-amino-3-hydroxynaphthalene 1-suphonic acid were used as additives in depositing electrolytes. The cathode current efficiency was calculated using the Faraday's law. Metal distrbution ratio of the solutions was determined using Haring–Blum cell. These additives impact the surface morphology of deposited copper films by downgrading, the grain size was analyzed by scanning electron microscopy (SEM) and X-ray diffiraction technique. XRD pattern acquired for electrodeposited copper film shows polycrystalline and face centered cubic structure (FCC). The crystal size of the copper film was calculated using the Debye–Scherrer's equation. The crystal size revealed that deposits produced from additive containing electrolytes exhibited the lowest grain size. Texture coefficient analysis studies revealed that all copper film deposits are polycrystalline and the crystals are preferentially oriented and parallel to the surface. A uniform and pin-hole free surface morphology and grain refining were brought about by the additives.     

The kinetics of the oxidation of aluminum—copper alloys in oxygen at high temperature

The oxidation behavior of high purity aluminum—copper alloys has been studied at temperatures from 475 to 575°C in dry oxygen at a pressure of 76 torr. The oxidation product was found to be duplex in nature consisting of both amorphous and crystalline γ-Al₂O₃. Roughly cylindrical crystals of γ-Al₂O₃ of constant thickness, at any given temperature and alloy content, grow into the metal from the amorphous oxide—metal interface by inward diffusion of oxygen through the overlying amorphous film. The amorphous oxide film, growing by outward diffusion of metal ions, forms between the crystals of γ-Al₂O₃ with accurately parabolic kinetics throughout the temperature and alloy composition ranges. Above the crystalline phase the amorphous oxide forms at a lower rate because of the additional resistance conferred to cation egress afforded by the crystalline oxide. In general, it was found that increasing copper content of the alloy in the range 0·1–4 per cent Cu caused a reduction in the crystal nucleation density and in the depth of intrusion of the crystals into the underlying alloy. Conversely, increasing copper content was also found to increase the rate of formation of amorphous γ-Al₂O₃ between the crystals of γ-Al₂O₃ and to increase the rate of radial growth of the crystals. These results are explained in terms of the defect nature of the oxidation products.     

Stress corrosion cracking of copper and silver, specific effect of the metal cations

Based on stress corrosion cracking (SCC) studies on brass, and on Ag-Cd alloys (a model alloy used to reproduce the behaviour of brass), it was found that both pure copper and pure silver are susceptible to SCC in 1 M copper(II) nitrate and in 1 M silver nitrate aqueous solutions, at the equilibrium potentials for the reactions: Cu²⁺+2e⁻↔Cu and Ag⁺+e⁻↔Ag, respectively. The results were analysed under the light of recent developments in surface science. It was concluded that the same SCC mechanism that operates in brass and in Ag-Cd alloys should be operating during SCC of pure copper and pure silver, under equivalent experimental conditions.     

Structure of corrosion film formed on copper exposed to controlled corrosive environment

This paper describes a transmission electron microscopy (TEM) investigation of copper coupons exposed to a corrosive mixed flowing gas environment (MFG). A focused ion beam (FIB) lift-out technique was used to extract electron transparent specimens for TEM investigation. A duplex corrosion film comprising cuprite (Cu₂O) and chalcocite (Cu₂S) developed on the copper substrate. The oxide demonstrated a dense morphology with evidence of chlorine in the oxide layer showing that chlorine plays an important role in the corrosion of copper transforming the protective Cu₂O layer to a non-protective layer. The outer layer of the Cu₂S demonstrated a porous morphology allowing easy penetration of water and gases.     

Oxygen removal from blister copper by copper oxide formation

In this study, an alternative approach is proposed to remove oxygen from blister copper through copper oxide formation. The addition of fluxes promotes both the copper oxide formation and oxygen reduction in molten copper. Fundamental aspects of this proposed process are described in this article. Three different fluxes (Na₂O-SiO₂, CaO-Na₂O, and FeO-Na₂O-SiO₂) were tested at the laboratory scale. This work showed encouraging results with oxygen in copper being reduced to industrial specifications without the conventional hydrocarbon reduction step. This approach could be used industrially to remove oxygen from blister copper prior to anode casting and points to a new concept in deoxygenation of copper. was with KPM as a coop student during the performance of this work. For more information contact Pascal Coursol, 2625 Saint-Jacques, app. 202, Montreal, H3J 1H8 Canada; coursolp@Yahoo.com.     

Outdoor atmospheric corrosion of copper in Saudi Arabia

Abstract

Copper specimens have been exposed to the action of marine, marine industrial, urban and rural atmospheres of Saudi Arabia. Environmental factors such as average temperature, average relative humidity and deposition rates of atmospheric pollutants (i.e. Cl^- and SO₂) was investigated. By applying the standard ISO 9223, the aggressiveness of the atmospheres corresponding to the different test stations has been determined. Calculations of corrosion rates were made via loss of weight after one, two and three years of exposure and characterisation of the corrosion products formed on samples have been analysed using X-ray diffraction. Three main sequences have been identified on outdoor copper, representing different reaction routes in chloride dominated environments. Many kinds of patina were found on copper specimens such as cuprite (Cu₂ O), atacamite (Cu₂ Cl(OH)₃), paratacamite (Cu₂ (OH)₃Cl), copper amine nitrite hydroxide, gerhardite, copper hydroxide nitrate and copper amine nitrate.     

铜晶体的疲劳损伤微观机制

对Cu单晶体、双晶体和多晶体疲劳损伤微观机制的总结结果表明：在中、低应变范围Cu单晶体的疲劳裂纹主要沿驻留滑移带萌生,而在高应变范围则沿粗大形变带萌生;Cu双晶体中疲劳裂纹总是优先沿大角度晶界萌生和扩展,而小角度晶界则不萌生疲劳裂纹;对于Cu多晶体,疲劳裂纹主要沿大角度晶界萌生,有时也沿驻留滑移带萌生,而孪晶界面两侧由于滑移系具有相容的变形特征而未观察到疲劳裂纹萌生．     

Intergranular stress corrosion cracking of copper - A case study

The objective of this work was to identify the conditions and mechanisms for stress corrosion cracking (SCC) of a hard copper tube employed in a cooling system. The fractured tube was made of deoxidized high phosphorous copper (Cu-DHP). The identification was performed on the ground of fractography, metallography, residual stress measurements and corrosive environment analysis. It was found that humidity and environment containing ammonium and trace amounts of nitrite and nitrate ions were responsible for initiation of SCC yielding to breakdown of oxide surface layer by pitting. Cracking was found intergranular and perpendicular to circumferential stresses. Stress corrosion crack propagation appeared the most consistent with the oxide rupture mechanism. The findings were discussed in relation to the literature data in order to get a better understanding of cracking behaviour.     

Synthesis of aligned copper oxide nanorod arrays by a seed mediated hydrothermal method

The synthesis of ordered copper oxide (CuO) nanorod arrays has been obtained using a seed-mediated hydrothermal method. Aligned CuO nanorods were obtained on fluorine doped tin oxide glass substrates over a large scale at low temperature ranging from 75 to 85 °C. It is found the CuO nanoseeds play an important role to facilitate the growth of those aligned CuO nanorods. The band gap energy of the CuO nanorods was estimated by ultraviolet-visible absorption spectroscopy. The growth mechanism of this method was also investigated.     

The a.c.-induced corrosion of copper neutrals

Electrochemical behaviour of tin-coated copper electrodes in a model soil environment was studied by means of electrochemical impedance spectroscopy (EIS), d.c. polarization, and long-term exposure testing. Comparison of EIS spectra, modelled as a simple R(RC) circuit, taken over a period of time at rest potential, with those taken under anodic and cathodic bias potentials, shows an increase in the electron transfer resistance under conditions of anodic bias or a.c. polarization. This indicates that the tin coating is passivated by the a.c. signal through oxide formation during the anodic half cycle. This observation is supported by rest potential measurements. Without an a.c. signal the potential of tin-coated wire stabilizes at a more negative potential than that of bare copper wire and provides cathodic protection to copper exposed through coating flaws. However, when an a.c. signal is added, the potential of the tincoated wire shifts to a more positive potential than that of the bare wire, passivating the tin coating and rendering it cathodic to the underlying copper. The large area of the tin cathode relative to the small area of exposed copper substrate leads to rapid pit initiation in the copper, resulting in premature failure of the cable in the soil environment.     

The kinetics of copper corrosion in nitric acid

The strategy for the permanent disposal of high-level nuclear waste in Canada involves sealing it in a copper-coated steel container and burying it in a deep geologic repository. During the early emplacement period, the container could be exposed to warm humid air, which could result in the condensation of nitric acid, produced by the radiolysis of the humid air, on the copper surface. Previous studies have suggested that both nitrate and oxygen reduction will drive copper corrosion, with the nitrate reduction kinetics being dependent on the concentration of soluble copper(I) produced by the anodic dissolution of copper in the reaction with oxygen. This study focused on determining the kinetics of nitrate and oxygen reduction and elucidating the synergistic relationship between the two processes. This was investigated using corrosion potential and polarization measurements in conjunction with scanning electron microscopy and X-ray photoelectron spectroscopy. Oxygen reduction was shown to be the dominant cathodic reaction with the oxidation of copper(I) to copper(II) by nitrate, promoting the catalytic cycle involving the reaction of copper(II) with copper to reproduce copper(I).     

Chemical and mineralogical characterizations of a copper converter slag

A copper converter slag was examined chemically and mineralogically to determine its existing phases,in particular those containing Co and Cu.The slag consists predominantly of fayalite and magnetite,together with some glass,chalcocite,and metallic copper,Copper is entrapped in the slag mostly as chalcocite and metallic copper,as well as trace copper oxide,There was no indication of any independent Co was detected in all the phases of the slag by SEM-EDX(scanning electron microscopy equipped with model EDAX-9100 energy dispersive spectrometer)and WDS(model WDX-2AX-ray wave-length dispersive spectrometer.).     

The corrosion of gold and silver coated copper by the thermal degradation products of chloroprene and silicone rubber

The corrosion of gold and silver coatings on copper by the thermal degradation products (100°C) of chloroprene and silicone rubber has been studied by mass-spectrometry, secondary ion mass-spectrometry (SIMS) of interaction products and petrographic analysis of corrosion films. The volatile products of degradation of both organic materials greatly influence the protective coating of gold and silver; the composition of chloroprene rubber is more aggressive and along with decomposition of the protective coating, corrosion leads to the partial removing of the coating with simultaneous corrosion of a copper substrate. Formic acid vapours and chlorine are the most corrosion active components of the atmosphere. These substances produce the unstable gold and silver salts, chlorides and formates, extracting during their degradation fine dispersed crystals of a secondary metal, these being one of the main corrosion products.     

HA coating on titanium with nanotubular anodized TiO2 intermediate layer via electrochemical deposition

Hydroxyapatite（HA） coating has been prepared on titanium substrate through an electrochemical deposition approach. In order to improve the bonding strength between HA coating and Ti substrate, a well oriented and uniform titanium oxide nanotube array on the surface of titanium substrate was applied by means of anodic oxidation pre-treatment. Then the calcium hydrogen phosphate（CaHPO4·2H2O, DCPD） coating, as the precursor of hydroxyapatite coating, was electrodeposited on the anodized Ti. At the initial stage of electro-deposition, the DCPD crystals, in nanometer precipitates, are anchored in and between the tubes. With increasing the deposition time, the nanometer DCPD crystals are connected together to form a continuous coating on titanium oxide nanotube array. Finally, the DCPD coating is converted into hydroxyapatite one simply by being immersed in alkaline solution.     

Adsorption of thiourea on polycrystalline platinum: Influence on electrodeposition of copper

Although previous works have shown the marked influence of thiourea as an organic additive in electrolyte bulk on copper electrodeposition, a variety of mechanisms could be responsible. The present paper concerns the effect of a thiourea layer adsorbed prior to copper electrodeposition. First evidence of a monolayer on platinum substrate was revealed by X-ray photoelectron spectroscopy. Two different times (15 h and 1 min) for platinum immersion were tested, and it was observed that, even for short times, thiourea is chemisorbed on the surface. Then, effects of thiourea adsorption on copper underpotential deposition (UPD) and overpotential deposition (OPD) processes on polycrystalline platinum were investigated by polarisation curves, atomic force microscopy and X-ray photoelectrons. Thiourea monolayer increases the copper UPD process: in fact the current density of UPD cathodic peak is higher in the presence of thiourea on the platinum surface. However no modifications were observed on the AFM images and on the XPS spectra. For the copper OPD process, the presence of thiourea monolayer inhibits copper deposition: the current density of OPD cathodic peak is lower whatever the immersion time of the platinum substrate in the thiourea solution. Moreover, XPS spectra show that the presence of thiourea modified the oxidation state of the copper coating, as an oxide film is formed more quickly on the surface of the coating.     

Hybrid copper complex-derived conductive patterns printed on polyimide substrates

We synthesized new copper complexes that can be readily converted into highly conductive Cu film. Mechanochemical milling of copper (I) oxide suspended in formic acid resulted in the submicron-sized Cu formate together Cu nanoparticles. The submicrometer-sized Cu formates are reactive toward inter-particle sintering and metallic Cu seeds present in the Cu complexes assist their decomposition and the nucleation of Cu. The hybrid copper complex film printed on polyimide substrate is decomposed into dense and uniform Cu layer after annealing at 250 °C for 30 min under nitrogen atmosphere. The resulting Cu film exhibited a low resistivity of 8.2 ???·cm and good adhesion characteristics.     

Formation of oxides on copper in alkaline solution and their photoelectrochemical properties

The anodic formation of Cu(I) and Cu(II) oxides on polycrystalline copper in a deaerated alkaline solution is studied using the technique of the synchronous recording of transients of the photocurrent and polarization current. The oxide formation in a currentless mode is analyzed via the synchronous recording of photopotential and corrosion potential. It is found that copper is susceptible to corrosion oxidation due to traces of dissolved oxygen with the formation of a Cu(I) oxide. The preliminary formation of the underlayer of anodic Cu(I) oxide on copper hinders its further corrosion oxidation. It is confirmed that copper oxides Cu₂O and CuO, which appear on copper in both anodic and corrosion modes of formation, are p-type semiconductors. The initial stage of anodic oxidation of copper is characterized by the formation of an intermediate compound of Cu(I), possibly CuOH, which exhibits n-type conductivity. A film of Cu(I) oxide is thin and has a band gap of 2.2 eV for indirect optical transitions. Anodic polarization in the range of potentials of CuO formation leads to the formation of a thicker oxide film, which is a mixture of Cu(I) and Cu(II) oxides.     

An investigation on the mechanisms of ant nest corrosion of copper tube in formic acid environment

Copper tubes used in air-conditioners and refrigerators often fail due to ant nest corrosion (ANC) in formic acid environment. In this paper, corrosion behavior and corrosion mechanisms of copper tubes in formic acid (HCOOH) were analyzed by vapor corrosion tests, optical microscopy (OM), scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS). The effects of the surface condition on ANC of copper tube were also investigated. Results showed that ANC of copper tube was a spontaneous process. The surface integrity of copper tube surface oxide layer is not the decisive factor of ANC. ANC originated from the dissolution of the surface oxide layer in HCOOH, which exposed fresh copper matrix. ANC is a special electrochemical corrosion, where the copper matrix acts as an anode and the undissolved surface oxide layer acts as a cathode due to the potential difference. The accumulation of corrosion products consisting of Cu(HCOO)₂ and Cu₂O can produce a wedge effect and generate many microcracks until to penetrate the copper tube wall. These findings would provide a deep understanding of the corrosion behavior of copper and copper alloys.     

Direct printing of copper conductive micro-tracks by multi-nozzle electrohydrodynamic inkjet printing process

To overcome the limitation of low production speed of electrohydrodynamic (EHD) inkjet printing technology and to fabricate low cost electronic micro-structures, this paper presents the direct deposition of copper colloidal solution through the multi-nozzle EHD inkjet printing process. Multi-nozzle EHD inkjet printing head, consisting of five nozzles, was used for simultaneous printing of electrically conductive micro-tracks onto the glass substrate. Nozzle-to-nozzle distance and experimental conditions were optimized to prevent the interaction i.e., cross-talk between electrically charged neighboring jets. After sintering in inert (N₂ gas) atmosphere, printed tracks exhibited approximately five times larger resistivity (9.20 μΩ cm) than that of the bulk copper which is a remarkable achievement. These electrically conductive micro-tracks show the feasibility of multi-nozzle EHD inkjet printing technique using the copper nano-colloidal ink for low cost fabrication of microelectronic structures and devices.