Effects of Hydrostatic Pressure on the Corrosion of Copper in Sea Water

Abstract

A study has been made of the effect of hydrostatic pressure, ranging from 1 to 300 atm. (0·102 to 30·6 N.mm^?2) on the corrosion of copper in sea water at pH 7·8 and at a temperature of 10°c. The experimental technique ensured that the content of dissolved oxygen in the sea water was virtually constant over the pressure range, at a value of 7·0 ppm. The same test series was also carried out in a 3·5% NaCl solution.

The weight loss of the copper was found to increase with increase in pressure, both in sea water and in NaCl, and reached a maximum at a pressure of 150 atm. (～15 N.mm^?2) in both solutions. The increased pressure has no influence on the anodic dissolution process for copper, but accelerates the cathodic process. Protective films adhering to the corroded surfaces are identical for the two solutions at ambient pressure. However, at higher pressures adherent corrosion products form only in NaCl solutions. These products were found to be the same as those formed at ambient pressure.     

A study on cobalt electrodeposition onto a carbon steel electrode

Abstract

The electrodeposition of cobalt on to a carbon steel working electrode was studied through the comparison between theoretical and experimental polarisation curves. The former was obtained using the Butler–Volmer equation with electrochemical parameters, such as Tafel slope values, exchange current densities, cathodic limit current densities and equilibrium potential values. The following results were obtained: the anodic region refers to the iron oxidation with a Tafel slope of about 0·055 V decade^?1, which is near the theoretical value (0·059 V decade^?1); the experimental cathodic region represents the cobalt and hydrogen ion reduction; the limiting current density (?1 × 10^?3 to ?1 × 10^?2 A cm^?2) obtained was near the calculated value, ?3·7 × 10^?3 A cm^?2.     

Characterization of Hydrogen Permeation in Armco-Fe during Cathodic Polarization in Aqueous Electrolytic Media

The study of hydrogen permeation behavior in Armco-Fe showed that 0.1 M H₂SO₄ was a more effective medium for cathodic polarization compared to 0.1 M NaOH. When both electrolytes were “poisoned” with 1.00 g/L Na₂HAsO₄ · 7H₂O, as hydrogen recombination inhibitor, the corresponding hydrogen permeation levels were 3.5 × 10⁻⁵ A/cm² in 0.1 M H₂SO₄ while 0.75 × 10⁻⁵ A/cm² in 0.1 M NaOH. The breakthrough times were less than 30 s in 0.1 M H₂SO₄, while about 100 s in the NaOH. With varying amounts of “poisons”, peak permeation of hydrogen (1.75 × 10⁻⁵ A/cm²) was achieved with 10 g/L Na₂HAsO₄ · 7H₂O in 0.1 M H₂SO₄, while the least permeation resulted with 10 g/L (NH₂CSH₂) Thiourea addition for same level of 1.00 mA/cm² cathodic polarization.     

Zur Korrosion des Hafnium – Oxide und Hydride

Corrosion of hafnium – oxides and hydrides Investigations concerning the growth and behaviour of hafnium as well as electrode kinetics have been performed on hafnium (Goodfellow and Material Research Company) in various electrolytes (acidic, alkaline and Cl^?-containing solutions). Conventional electrochemical methods and impedance spectroscopy were applied. Corrosion rates derived from electrochemical measurements were found to be significantly higher than the published data obtained from the loss weight observed usually over long of time. – The DK was evaluated to be 11.5. – SIMS profiles indicate that the oxide layer in not uniform, due to the nonstoichiometry of the Hf oxide at 22°C. The layer shows a very low n-conductivity – quasi insulator behaviour; the Mott-Schottky-plot leads to the flat band potential U = ? 10 mV. The initial oxide layer was determined by capacity measurements to 2.7 nm. Cl₂-evolution begins at U = 0.5 V in 0.5 M NaCl solution. In the cathodic potential region hydrogen is generated at Hf oxide at U = ? 1.69 ? 0.058 V. With respect to the hydrogen induced cracking of Hf the behaviour of hydrogen in Hf was investigated using the nuclear physics ¹⁵N-method. After cathodic polarisation hydrogen is absorbed by hafnium and the hydride HfH_1.6 is formed. The hydrogen diffusion coefficient is determined to D_20° = 3.8 × 10^?11 cm²s^?1. At 385°C hydrogen is released from HfH_1.6. The results are discussed and compared to those found for titanium and zirconium.     

Influence of hydrostatic pressure on pitting of aluminium in sea water

Abstract

The effect of hydrostatic pressure on the corrosion of aluminium in sea water oj pH 8·2 containing 7ppm dissolved oxygen has been investigated at 20°C. On increasing the pressure from 1 to 300 atm, the corrosion rate increased, an effect attributable to an increase in the rate of the anodic reaction while the cathodic rate remained unchanged. The observed increased susceptibility to pitting corrosion with increasing pressure was found to correlate with the presence of increasing quantities of SO^2?₄ and Cl^? ions in the oxidation layer. The introduction of electron acceptors such as SO^2?₄ and Cl^? into n type compounds such as aluminium oxides increases the density of lattice dejects and promotes breakdown oj the barrier provided by the oxidation layer.     

The high temperature oxidation of aluminium-implanted iron

Aluminium was implanted into iron at different doses between 1 × 10¹⁴ and 1.5 × 10¹⁷ atm cm^?2. Oxidation tests were carried out in oxygen during 100–120 h in the temperature range 720–1020 K. Doses of 5 × 10¹⁶ atm cm^?2 had to be achieved to observe a notable inhibition of the oxidation process. In these conditions, the formation of two ternary oxides was detected but the spinel phase Fe Al₂O₄ seemed to be responsible for the observed blocking effect.     

Hydrogen permeation measurements in natural sea environment

The specially designed, fully equipped, and computerized devices for the underwater long‐term measurements have been used to study the hydrogen permeation rate through the structural steels under natural sea water conditions. By applying constant cathodic potentials, the polarization current and the hydrogen permeation rate were recorded. The temperature and the concentration of S^?2 ions in sea water were also measured. After the tests, the concentration of residual hydrogen in samples and the chemistry of the membrane surface were analyzed. The obtained permeation data were compared with the S^?2 content in sea water and with the chemistry and appearance of formed deposits. The effect of SRB on the hydrogen permeation through structural steels is dependent on the site of the sample placing and on the sea water temperature. At a lower water temperature, the low hydrogen absorption was measured due to a lower activity of SRB. The highest hydrogen uptake accompanied by the highest content of S in corrosion and cathodic deposits was observed for membranes situated on the sea bed. The electric field of cathodically protected wall did not affect the hydrogen absorption. The hydrogen uptake recorded under the natural sea conditions can be higher than that measured in the laboratory tests, which should be taken into account while servicing marine constructions, especially embedded ones.     

Diffusion von Wasserstoff durch Titan

Diffusion of hydrogen through titanium The diffusion coefficient of hydrogen in titanium determined by an electrochemical method is D_{24 °} ～ 7 × 10^?12 cm² /s at a cathodic polarisation of 10 mA/cm² . The variation of the diffusion coefficient with temperature enables the activation energy to be calculated (6,9 kcal/Mole). The diffusion takes place with intermediary titanium hydride formation. The diffusion is measured using an electrochemical method with a metallic membrane where the hydrogen generated at the one side is ionized, after diffusion at the other side. It is then possible to establish a relation between the ionization current and the diffused quantity, also as a function of time.     

Preliminary Investigation of the Corrosion Behavior of Proprietary Micro-alloyed Steels in Aerated and Deaerated Brine Solutions

The corrosion performance of fairly new generation of micro-alloyed steels was compared in different concentrations of aerated and deaerated brines. Electrochemical polarization, weight loss and surface analyses techniques were employed. The results showed a threshold of corrosion rate at 3.5 wt.% NaCl in both aerated and deaerated solutions. The average corrosion current density for steel B, for example, increased from 1.3 µA cm^?2 in 1 wt.% NaCl to 1.5 µA cm^?2 in 3.5 wt.% NaCl, but decreased to 1.4 µA cm^?2 in 10 wt.% deaerated NaCl solutions. The aerated solutions exhibited an average of over 80% increase in corrosion current density in the respective concentrations when compared with the deaerated solution. These results can be attributed to the effects of dissolved oxygen (DO) which has a maximum solubility in 3.5 wt.% NaCl. DO as a depolarizer and electron acceptor in cathodic reactions accelerates anodic metal dissolution. The difference in carbon content and microstructures occasioned by thermo-mechanical treatment contributed to the witnessed variation in corrosion performance of the steels. Specifically, the results of the various corrosion techniques corroborated each other and showed that the corrosion rate of the micro-alloyed steels can be ranked as CR_{Steel A} < CR_X65 < CR_{Steel B} < CR_{Steel C}.     

Environmentally-induced cracking of magnesium

Slow strain rate tensile tests have been carried out on commercially pure and high purity magnesium specimens in air and in de-aerated, pH 10, 10^?3 M Na₂SO₄ solution under different environmental conditions. The results of these tests have been supplemented by studies of the failed specimens using optical metallography and scanning electron fractography. It is shown that under certain environmental conditions magnesium is susceptible to hydrogen embrittlement and environmentally-induced cracking in Na₂SO₄ solution. The source of the hydrogen, even under anodic polarization, is the local action cathodic reaction. Atomic hydrogen can only enter, and embrittle, the metal matrix at active, bare, passive-film-free pit walls. Therefore if pitting is promoted by anodic polarization cracking is more severe; conversely if pitting is prevented by cathodic polarization, embrittlement and cracking are not observed. Atomic hydrogen produced by cathodic polarization is prevented by the presence of the Mg(OH)₂ passive film from entering the metal and causing embrittlement; furthermore even at a strain rate of5.7 × 10^?6 s^-1passivation is sufficiently rapid to prevent entry of hydrogen during tensile testing of cathodically polarized specimens. Depending on the grain size and purity the embrittled magnesium specimens exhibit either a completely transgranular quasicleavage fracture surface morphology or a mixed brittle intergranular and quasi-cleavage transgranular fracture surface morphology. Possible mechanisms for the hydrogen-induced cracking are discussed briefly in light of the demonstrated reversibility of hydrogen uptake. It is suggested that hydrogen embrittlement and cracking may account for spalling and disintegration of magnesium anodes and may contribute to the negative different effect.     

阴极保护下X65钢在模拟海水中的氢脆敏感性研究

采用阴极极化条件下的氢渗透实验和慢应变速率拉伸实验研究了X65钢在模拟海水中的氢渗透行为及其对断裂机理的影响。氢渗透实验结果表明,阴极极化过程中试样表面的钙镁沉积层能显著地降低氢扩散系数,采用Fourier方程、Laplace方程以及时间滞后法计算得出的有效氢扩散系数平均值为1.49×10-7cm2·s-1。结合变电位极化氢渗透测试结果、拉伸试样断口分析以及极化曲线测试,对阴极极化条件下X65钢的氢脆敏感性进行评估。结果显示,随着极化电位的降低,X65钢中的吸附氢浓度呈指数规律上升。当极化电位较高时,X65钢的裂纹扩展受阳极溶解和阴极析氢的双重作用控制。当极化电位较低,如-1200 mV时,钢中的吸附氢浓度急剧增加,脆性断裂区域的比例上升,X65钢发生氢致脆化失效。     

Observation and micro-electrochemical characterisation for micro-droplets in initial marine atmospheric corrosion

Micro-droplets formed around NaCl droplet on carbon steel surface were observed with a confocal laser scanning microscope. Micro-electrochemical characterisation of the micro-droplets zone was also performed by a scanning Kelvin probe (SKP) and the scanning vibrating electrode technique (SVET). Results show that the electric current density and potential distribution of carbon steel under the NaCl droplet are asymmetrical; the peripheral regions of the droplet are cathodic, whilst its centre is anodic. The potential difference between the anode and cathode is 0.36?V, and the cathodic current density reaches 2.02?μA?cm^?2. This kind of asymmetrical distribution of electrochemical characterisation results in cathodic polarisation at the fringe of the NaCl droplet, thus inducing the formation of OH^–, which could promote water adsorption and subsequent formation of micro-droplets around the NaCl droplet. The electrochemical potential difference of the oxygen concentration cell formed between the central and peripheral regions of the NaCl droplet is the main driving force for micro-droplet formation on metal surfaces.     

Cold-Sprayed Al Coating for Corrosion Protection of Sintered NdFeB

A protective Al coating was achieved on the sintered NdFeB magnet by cold spray. The sprayed Al particles generate plastic deformation and hang together. The thickness of the coating is about 170 μm. The corrosion currents of Al coating and NdFeB without immersion tested by potentiodynamic polarization in 3.5 wt.% NaCl solutions are 1.350 × 10^?6 and 4.361 × 10^?6 A/cm², respectively. X-ray photoelectron spectrometry results confirm that the oxide film is Al₂O₃ and the corrosion process can be derived into two different stages. The Al coating can provide long-term protection for NdFeB effectively.     

Effects of 3.5 MeV proton irradiation on pure zirconium

The effects of high energy proton irradiation on pure zirconium were investigated in this study. The annealed Zr specimens (50 mm × 3 mm × 0.8 mm) were irradiated by 3.5 MeV hydrogen ions with dose ranges from 1×10¹³ to 1 × 10¹⁵ ions/cm² at 335 K. The range of the proton beam penetration was measured to be 68-70 μm, depending on the surface, which is in good agreement with the SRIM simulation results. X-ray diffractometer analysis revealed that the peak intensity of the basal plane increased and the position of the peak shifted due to the proton irradiation. Field emission scanning electron microscopy results showed that with increasing irradiation dose hydrogen micro-bubbles formed, concentrated, interconnected, and eventually burst due to the excessive hydrogen pressure inside, causing surface-crack development. Measured yield and ultimate tensile strength seemed to be insignificantly affected by the proton irradiation.     

Hydrogen absorption resulting from the simulated pitting corrosion of carbon-manganese steels

Hydrogen permeation measurements were performed on membranes of BS4360 Grade 50D C-Mn steel in the quenched and tempered condition. The rates of hydrogen absorption resulting from exposure to FeCl₂ solutions in a simulated corrosion pit were measured and found to be lower than those occurring in artificial sea water at applied potentials in the range commonly used for cathodic protection. A progressive decrease in the hydrogen permeation flux was recorded during simulated pitting and was attributed to the formation of a partially protective film of magnetite on the steel surface. At cathodic applied potentials iron plating was observed on the membranes. It is suggested that a similar process occurs in the cathodic protection of steel containing real corrosion pits and leads to a lowering of the Fe²⁺ ion concentration within the pits and a decrease in the aggressiveness of the local environment.     

Korrosionsschwingfestigkeit der Stahlgußsorten G-X5CrNi 13 4 und G-X5CrNi 17 4 für Laufräder von Wasserkraftmaschinen und Pumpen

Fatigue strength of steel types G-X5CrNi 13 4 and G-X5CrNi 17 4 used for blades of water-power turbines and pumps In this project the influence of different corrosive media on the fatigue behaviour of stainless cast steel alloys with 13 and 17% chromium content for hydraulic machines was investigated in the high cycle range (10⁶ < N < 10 ₈). Hereby the possible range of media was covered by using tap water with 28 ppm chlorides, 10 mMol NaCl, as well as 1% NaCl and in the case of the higher alloyed steel additionally artificial sea water without and with cathodic protection. Further the influence of high mean stresses due to rotation of runners was also analysed. The results obtained on the loss of fatigue strength in dependence of corrosive media, mean stress and cycles to failure enable an aimed material's selection as well as an appropriate design and increase the reliability and security of water power machines.     

Study of molybdate–phytic acid passivation on galvanised steel

Abstract

A combined molybdate–phytic acid passivation treatment on galvanised steel is studied in this paper. Both copper decoration drop tests and immersion mass loss tests indicated that the combined molybdate–phytic acid passivated samples showed better corrosion resistance than that of samples treated separately by molybdate or phytic acid. The electrochemical behaviours of the passivated samples were investigated using potentiodynamic polarisation and electrochemical impendence spectra in 0·5 mol L^?1 NaCl solution and showed corrosion current densities of 4·95×10^?5, 5·10×10^?5 and 1·19×10^?5 A cm^?2 respectively. Electrochemical impendence spectra also indicated that molybdate–phytic passivated samples exhibited better corrosion resistance. The mechanism of synergetic effect for molybdate–phytic acid passivation on galvanised steel is discussed in brief.     

The influence of ion implantation on the corrosion behaviour of iron in acid solution

The influence of ion implantation on the aqueous corrosion of pure iron in IN H₂SO₄ was studied. The iron was bombarded with 5 × 10¹⁵–10¹⁷ ions.cm^?2 of Ne, Ar, Cu, Pb and Au. The current density-potential curves of the implanted samples were measured and compared with that of untreated pure iron. Ne⁺ and Cu⁺ bombardments lead to a slightly higher corrosion rate in comparison with untreated iron. Pb⁺ depressed the corrosion rate by orders of magnitude, Au⁺ enhanced it by a factor of more than ten. The effect is attributed to a reduction or an increase of the activity of the electrode surface with respect to the cathodic hydrogen evolution reaction, i.e. the ion implantation influences strongly the exchange current density of the hydrogen evolution reaction. A marked influence of the implantation on the anodic behaviour of the corroding metal could also be observed.     

The corrosion of chromium and nickel-chromium alloys in oxygen-sulfur-carbon gases at 800°C

The simultaneous oxidation and sulfidation of Cr, Ni-10Cr, Ni-20Cr, and Ni-30Cr was studied at 800°C in three gases falling within the Cr₂O₃ stability field of the Cr-S-O system. The sulfur partial pressure remained constant at 1×10^?6 atm, whereas the oxygen partial pressure varied from 5×10²¹ to 5×10^?20 atm, and the carbon activity varied from 0.108 to 0.416. Reaction kinetics were measured, and the reaction products were characterized by X-ray diffraction, metallography, scanning electron microscopy, and X-ray energy dispersive analysis. Reaction rates decreased with increasing oxygen partial pressure and decreased with increasing chromium content of the alloys. Sulfides always formed along with Cr₂O₃, even though the gases fell within the oxide stability field. No carburization was observed even though carbon activities were sufficiently high to form carbides. The reaction mechanisms are discussed, and the absence of carburization is analyzed on the basis of a three-dimensional stability diagram.     

Stress corrosion cracking of 13% Cr martensitic steels in sodium chloride solutions in the presence of thiosulphate

The stress corrosion cracking (SCC) susceptibility of 13% Cr martensitic (UNS S42000) and supermartensitic (UNS S41125) steels in sodium chloride solutions in the presence of thiosulphate was evaluated by slow strain rate tests (SSRT). The tests were performed in 5% sodium chloride solutions buffered at pH 2.7, 3.5, 4.5 and 6.0 in the absence and presence of thiosulphate in a concentration range between 10⁻⁶ and 10⁻³ M, at 25 ± 0.1 °C. The electrochemical behaviour of the two steels in the different solutions was determined by recording the anodic and cathodic polarisation curves. 13% Cr martensitic steel showed SCC in 5% sodium chloride solutions with pH ≤ 4.5 in the presence of 3 × 10⁻⁶ M thiosulphate. Decreasing the chloride ion concentration from 50 to 10 g/l, the critical concentration of thiosulphate to provoke SCC susceptibility increased from 3 × 10⁻⁶ to 1 × 10⁻⁵ M. The resistance to SCC of the supermartensitic steel was higher than that of the martensitic steel. The critical concentration of thiosulphate to induce SCC on the supermartensitic steel were 1 × 10⁻⁵ M at pH 2.7 and 1 × 10⁻⁴ M at pH 3.5. At pH ≥ 4.5 the supermartensitic steel did not crack. The anodic and cathodic polarisation curves evidenced the influence of the thiosulphate on the corrosion and the activation effect on the steels. The SCC of the two steels was attributed to hydrogen embrittlement produced by sulphur and hydrogen sulphide formed by dismutation and reduction of thiosulphate.