Seawater corrosion of 70Cu‐30Ni alloy of incomplete recrystallization of intermittent and full immersion

The corrosion of 70Cu‐30Ni alloy of incomplete recrystallization was investigated by electrochemical technique, intermittent and full immersion in natural seawater, SEM and AES. Exposed to seawater for a short time, 70Cu‐30Ni alloy formed uniform and compact corrosion product films, which were rich in nickel, oxygen and seawater species for intermittent immersion; while the alloy fully immersed displayed loose and thick films, which were of denickelification and intergranular corrosion occurred to the underlying substrate. It was found that some regular crystals situated at the intersection of boundaries or the outer layer of the film and the crystals are ascribed to the reduction of cuprous ions to compensate the deficiency of oxygen for the cathodic process. Intergranular corrosion was observed in the underlying substrate for intermittent immersion after a long‐term exposure. Intermittent immersion can, to some degree, slow down the corrosion but not prevent the alloy of incomplete recrystallization from intergranular corrosion. Consequently, the corrosion mechanism of 70Cu‐30Ni alloy is proposed to be determined by its microstructure, independent of exposure conditions.     

Characteristics and formation of corrosion product films of 70Cu-30Ni alloy in seawater

The corrosion product films of 70Cu-30Ni alloy, composed of recrystallized grains or deformed and recrystallized grains, were investigated in 3.5% NaCl and natural seawater by electrochemical techniques, SEM, EDX and AES. The recrystallized alloy displayed a steady increase in the polarization resistance while the alloy of incomplete recrystallization kept its polarization resistance at a low level as increasing the immersion time in 3.5% NaCl. The films formed on the recrystallized alloy in seawater were thin, uniform and rich in nickel. After long-term immersion, the films, still thin and protective, consisted of convex lines and smooth zones between the lines. The convex lines were richer in nickel and contained more seawater species than the zones, so this led the lines to preferentially dissolve and new lines to appear where the film grew slower. Immersed in seawater, the alloy of incomplete recrystallization showed thick, loose and porous films, of which the inner layer was denickelified and the outer layer contained a great amount of seawater species, and of which the underlying substrate was found with severe intergranular corrosion. The tube specimens of incomplete recrystallization for four-year immersion were perforated by intergranular corrosion.     

The influence of the marine aerobic Pseudomonas strain on the corrosion of 70/30 Cu–Ni alloy

A comparative study of the corrosion behavior of the 70/30 Cu–Ni alloy in a nutrient-rich simulated seawater-based nutrient-rich medium in the presence and the absence of a marine aerobic Pseudomonas bacterium was carried out by electrochemical experiments, microscopic methods and X-ray photoelectron spectroscopy (XPS). The results of Tafel plot measurements showed the noticeable increase in the corrosion rate of the alloy in the presence of the Pseudomonas bacteria as compared to the corresponding control samples. The E1S data demonstrated that the charge transfer resistance, R_ct, and the resistance of oxide film, R_f, gradually increased with time in the abiotic medium; whereas, both of them dramatically decreased with time in the biotic medium inoculated with the Pseudomonas, indicative of the acceleration of corrosion rates of the alloy. The bacterial cells preferentially attached themselves to the alloy surface to form patchy or blotchy biofilms, as observed by fluorescent microscopy (FM). Scanning electron microscopy (SEM) images revealed the occurrence of micro-pitting corrosion underneath the biofilms on the alloy surface after the biofilm removal. XPS studies presented the evolution of the passive film on the alloy surface with time in the presence and the absence of the Pseudomonas bacteria under experimental conditions, and further revealed that the presence of the Pseudomonas cells and its extra-cellular polymers (EPS) on the alloy surface retarded the formation process or impaired the protective nature of the oxide film. Furthermore, XPS results verified the difference in the chelating functional groups between the conditioning layers and the bacterial cells and the EPS in the biofilms, which was believed to connect with the loss of the passivity of the protective oxide film.     

The corrosion behavior of 70/30 copper‐zinc alloy under the biofilm of sulfate‐reducing bacteria

A laboratory study was carried out on the effect of the biofilm of sulfate‐reducing bacteria (SRB), which plays an important role in corrosion of 70/30 copper‐zinc alloy in culture media under anaerobic condition. The API medium was used to culture the SRB in Zhongyuan oilfield. Potential/time measurement showed that the presence of SRB makes the corrosion potential more active with SRB growth metabolite. Electrochemical impedance spectroscopy (EIS) was used to analyse the electrode process of 70/30 Cu‐Zn alloy with SRB biofilm. Scanning electron microscopy (SEM) examinations revealed the formation of biofilm and corrosion products during exposure to SRB‐containing culture medium. X‐ray diffraction and EDS were used to analyse the corrosion products. The results show that the variation of activity of the SRB biofilm changes with SRB growth by the linear polarization resistance (R_p) and the EIS in culture medium inoculated SRB.     

Influence of iron addition on corrosion layer built up on 70Cu-30Ni alloy in sea water

Abstract

The effect of additions of iron on the corrosion behaviour of a 70Cu–30Ni alloy in sea water was studied by electrochemical methods and corrosion tests. Iron additions of 0·5 and 2% increased the average corrosion resistance of the alloy. This beneficial effect is due to the formation of a layer containing a large quantity of nickel and iron oxides. A disadvantage of iron additions is the possibility of pit and crevice formation as a result of segregation of nickel-iron rich precipitates at grain boundaries.     

Corrosion inhibition of 70Cu–30Ni alloy in LiBr + ethylene glycol + H2O mixtures by inorganic compounds

The corrosion inhibition of a 70 wt% Cu–30Ni alloy in a 55 wt% lithium bromide (LiBr) + ethylene glycol + H₂O by inorganic inhibitors has been evaluated at different temperatures by using electrochemical techniques. Inhibitors used included lithium chromate (Li₂CrO₄), lithium molybdate (LiMoO₄), and lithium nitrate (LiNO₃), in a concentration of 5 ppm at 25, 50, and 80 °C. Employed techniques included potenthiodynamic polarization curves, linear polarization resistance, and potentiostatic measurements. Results have shown that the alloy had an active–passive behavior at 25 and 50 °C, and the passive film properties were improved with the addition of inhibitors, whereas at 80 °C the inhibitors did not have any effect. Similarly, in general terms, the best corrosion performance at 25, 50, and 80 °C was obtained by adding Li₂CrO₄, LiNO₃, and LiMoO₄, respectively. However, the alloy was not susceptible to pitting corrosion in presence of inhibitors but it was highly susceptible towards pitting type of corrosion in absence of inhibitors.     

A new chemical route to synthesize Cu–Ni alloy nanostructured particles

Cu–Ni alloys are extensively used in several metallurgic industries. The traditional methods for the synthesis of these alloys have some limitations, mainly related with manufacturing costs and product homogeneity, which makes evident the need to study and develop new methodologies to produce them. In this work, a new route for the synthesis of Cu–Ni alloys is presented. The process involves four steps, including the precursor preparation by the citrate-gel method and the subsequent decomposition, calcination and reduction. The products obtained in the different steps were characterized using thermal gravimetry (TG), X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and other techniques. The Cu–Ni alloy, of homogeneous composition, with a Cu/Ni atomic ratio of 0.92 and with a grain structure at nanometric scale was obtained using the proposed methodology. The studies carried out using SEM and XRD showed the alloy formation with a regular morphology and with an average grain size of about 15.5 nm. The thermal programmed reduction (TPR) profiles showed a unique reduction temperature for the synthesized solid, which is significantly lower than the pure oxides reduction temperature.     

Mass transfer effects of non-cavitating seawater on the corrosion of Cu and 70Cu-30Ni

The present work is concerned with the prediction of corrosion rates of copper and cupronickel in flowing seawater (up to 16 m s⁻¹) and for filmed copper and cupronickel (up to 3.5 m s⁻¹). Such predictions are not available at present and would be of use for the design and maintainance of copper based components subjected to high velocity flows. Pipe systems on board ships often use such components—pumps, valves, elbows etc. The effect of flow on corrosion currents of filmed and polished samples that allows modelling of the behaviour of surfaces of old and newly fitted components is discussed. Equations describing the flow velocity dependence of these currents are developed and used to determine the mechanism controlling the copper dissolution and to identify the dissolution reactions.     

Microstructure identification of devitrified Cu–Ti–Zr–Ni bulk amorphous alloy

The microstructures of devitrified Cu–Ti–Zr–Ni bulk amorphous alloy were identified by X-ray diffractometry (XRD) and transmission electron microscope (TEM). XRD and TEM examinations show that the deep eutectic structures of the tested alloy consist of CuTi₂–Cu₁₀Zr₇, Cu₃Ti–CuZr, Cu₃Ti–Cu₁₀Zr₇–CuZr low-order eutectics. Moreover, short-range ordering clusters in the melt with configuration similar to that of Cu₁₀Zr₇ compound may contribute to the glass forming ability of bulk amorphous Cu–Ti–Zr–Ni alloy.     

Neutron diffraction study in amorphous Ni30Ta70 alloy powders by mechanical alloying

A mixture of elemental Ni and Ta powders with an atomic ratio of 3∶7 was subjected to mechanical alloying (MA). An amorphous Ni₃₀Ta₇₀ alloy was formed after 80 hrs of milling, the amorphization by rapid quenching technique of which has not been reported. The atomic structural changes were observed by neutron diffraction in the amorphization process during MA. The radial distribution function RDF(r) shows that peaks of fcc-Ni and bcc-Ta crystal broaden first and gradually approach those characteristic of an amorphous phase with increasing MA time. A local atomic environment around Ni and Ta atoms was studied by analyzing the first peak in the total pair distribution function g(r) after the completion of amorphization. We reach our conclusion from this analysis that the amorphization in the Ni₃₀Ta₇₀ alloy takes place by the penetration of smaller Ni atoms into the bcc-Ta lattice.     

Surface characterization and corrosion behavior of 70/30 Cu-Ni alloy in pristine and sulfide-containing simulated seawater

The corrosion behavior of the 70/30 Cu-Ni alloy in stagnant, aerated pristine and sulfide-containing simulated seawater as a function of exposure time was investigated with polarization curve measurement and electrochemical impedance spectroscopy (EIS). It was demonstrated that the compact protective oxide film formed on the 70/30 Cu-Ni alloy resulted in the decrease of corrosion rate in aerated pristine seawater; while the corrosion rate of 70/30 Cu-Ni alloy in aerated sulfide-containing seawater increased dramatically due to the catalysis of the sulfide ions or sulfide scale for both the cathodic and anodic reactions. The impedance spectra and the corresponding equivalent circuits confirmed that a duplex layer of a surface film was formed on the 70/30 Cu-Ni alloy in aerated pristine seawater after a period of time and that the inner layer was responsible for the good resistance of the alloy; while only a porous and non-protective corrosion product layer formed on the 70/30 Cu-Ni alloy in aerated sulfide-containing seawater, which made small values of charge transfer resistance (R_ct) to last for a abnormally long time by interfering with the growth of the protective oxide film. The composition of the surface film on the alloy in pristine and sulfide-containing seawater for different exposure times were investigated thoroughly by XPS. It was found that the duplex corrosion product layer formed on the alloy in pristine seawater was composed of an inner Cu₂O and an outer CuO layer. The porous and non-protective corrosion product layer formed on the alloy in aerated sulfide-containing seawater was a mixture of CuCl, Cu₂S, NiS, Cu₂O and NiO with trace amounts of CuO and Ni(OH)₂ and that the most significant component was Cu₂S. In addition, SEM was used to analyze the topography of the 70/30 Cu-Ni alloy in both solutions after different exposure times.     

Preparation, corrosion and structural properties of Cu–Ni multilayers from sulphate/citrate bath

Potentiostatic electrodeposition was used to produce Cu–Ni multilayer by two-wave pulse plating technique from sulphate/citrate electrolyte at pH 4. Cyclic voltammetry studies provide information about the deposition potential. The compositions of multilayers were studied using X-ray fluorescence (XRF). Electrochemical corrosion studies of the deposited multilayer on copper were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The surface of the layer having smooth, small grain and compact structure was confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. The face centered cubic lattices are present in the Ni–Cu multilayer and this is confirmed by the X-ray diffraction (XRD) data. The multilayer structures have better corrosion resistance than the base substrate.     

The effect of recrystallization on corrosion and electrochemical behavior of 7150 Al alloy

By weight loss, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) techniques complemented by optical and scanning electron microscopy observations, the effect of recrystallization on the corrosion, and electrochemical behavior of 7150 Al alloy was studied. The results indicated that the high recrystallization fraction 7150‐1# was worse than the low recrystallization fraction 7150‐2# on corrosion resistance. The analysis of EIS indicated that 7150‐1# exhibited obvious pitting corrosion at 5 h immersion time, whereas 7150‐2# showed no obvious pitting corrosion even at 33 h. The corrosion route developed along the grain boundary of recrystallization grains, not along the grain boundary of unrecrystallization grains.     

Performance of Cu and Cu‐Zn alloy in the Arabian Gulf environment

Corrosion performance of copper and brass coupons during 15 month exposure in atmosphere, underground and splash zone conditions was undertaken at Khaleej Mardumah test site located in the industrial/coastal city of Jubail along the Arabian Gulf coast, Saudi Arabia. The environmental indicators such as soil, groundwater, seawater, and air particulate samples were assessed. The exposed corrosion coupons were examined by scanning electron microscopy (SEM) coupled with energy dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD) and X‐ray fluorescence (XRF) to identify the corrosion products and study their surface morphology. Corrosion rate was determined by weight loss method. The experimental results indicated that a high degree of variation in temperature and humidity in this region combined with high chloride and sulfate concentrations was primarily responsible for the corrosion of copper and brass at Khaleej Mardumah test site. Underground environment was the most corrosive to both copper and brass coupons studied, followed by splash zone. Corrosion rates were found to range from 4.29 to 10.84 µm/y for copper and from 2.47 to 29.31 µm/y for brass. Corrosion rates of copper and brass obtained in this study are also compared with those reported for other locations worldwide.     

Cold rolling and recrystallization textures of a Ni–5 at.% W alloy

The formation of recrystallization texture has been studied in a sintered Ni–5 at.% W alloy after heavy cold rolling (～95%) and annealing. Although the cold-rolled texture is a typical pure metal or Cu-type deformation texture on a global scale, variations in microstructure and microtexture are found in the deformed material between locally sheared regions and away those from these regions. The primary recrystallization texture consists of the cube ({1 0 0}〈0 0 1〉), a RD-rotated cube ({0 1 3}〈1 0 0〉) and twin-related orientations of these two components. The presence of both cube and the RD-rotated orientations are identified in thin bands of materials in the deformed matrix. However, predominantly cube-oriented grains nucleate and grow in regions away from the locally sheared regions. In contrast, the nucleation and growth of non-cube grains are observed in the vicinity of locally sheared regions. The formation of cube texture in Ni–5 at.% W alloy appears to occur primarily via the oriented nucleation of cube grains owing to the special properties of the cube bands.     

Fe70Ni30合金粉体触媒及合成金刚石中杂质元素的原子发射光谱分析

为了分析合成金刚石中的杂质元素,以粉体Fe70Ni30合金触媒及石墨为原料,用静态高压技术合成出金刚石,分别对触媒和金刚石进行了原子发射光谱分析.测试结果表明:触媒里具有Co、Ca和Mn等22种含量值在0.0001～1.5 wt %之间的杂质元素;合成金刚石中有含量值在0.00005 ～ 0.02 wt %之间的Fe、Ni和Ca等10种杂质元素.这些杂质元素对金刚石质量和性能的影响进行了定性讨论.采用粉末触媒合成金刚石,其合成晶体中含有一定量的杂质元素是很难避免的,除合理采用合成工艺外,还可以通过严格控制原材料纯度等一些措?来降低合成晶体中杂质元素的含量,进而提高合成金刚石的质量.