Electrochemical noise applied to the study of the inhibition effect of CeCl3 on the corrosion behaviour of Al-Mg alloy AA5083 in seawater

Electrochemical noise measurements have been used to study the corrosion behaviour of aluminium alloy AA5083 in 3.5% NaCl solution with and without doping with CeCl₃ at 500 ppm. Information on the evolution of corrosion activity over a period of 4 days and on the corrosion mechanism itself has been obtained for the two systems. Experimental data obtained have been analysed using robust statistical parameters and wavelet transform; transient shapes were also studied. The various mathematical techniques applied to analyse the electrochemical noise data have been proposed recently. This paper thus not only characterises the corrosion systems studied but also illustrates the usefulness of these new methods.     

Inhibition effect of inorganic and organic inhibitors on the corrosion of Mg–10Gd–3Y–0.5Zr alloy in an ethylene glycol solution at ambient and elevated temperatures

In this study, the corrosion performance of magnesium-based rare-earth containing alloy Mg–10Gd–3Y–0.5Zr (GW103) was evaluated in an ethylene glycol solution with a group of selected aliphatic, aromatic carboxylates and inorganic salts as inhibitors. The dependence of inhibition efficiency on the concentration ratio of sodium phosphate to sodium dodecylbenzenesulfonate (SDBS) and the total inhibitor concentration was measured by means of electrochemical techniques. It was found that the corrosion rate of GW103 decreased by addition of inorganic–organic inhibitors at both ambient and elevated temperatures. The inhibitors were more effective at the ambient temperature than at the elevated temperature. The corrosion of GW103 in the ethylene glycol solution can be effectively inhibited by 1000 ppm of the inorganic–organic inhibitor mixture. It is believed that the added phosphate can interact with SDBS, resulting in a more compact surface film on the GW103 surface. Based on these results, as well as Environmental Scanning Electron Microscope (ESEM) observations, a synergistic mechanism was proposed to explain the inhibition behavior of the sodium phosphate + SDBS combination.     

Biodegradable magnesium alloy coated with TiO2/MgO two-layer composite via magnetic sputtering for orthopedic applications: A study on the surface characterization,corrosion, and biocompatibility

In this study, a coating of thin TiO₂ layer and a TiO₂/MgO double layer were created on the surface of AZ91D alloy by magnetic sputtering method in order to improve the corrosion and biocompatibility properties of this alloy. The microstructural studies by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) showed that coatings were formed continuously and homogeneously on the alloy surface. In the double-layer coating, MgTiO₃ and Mg₂TiO₄ compounds were formed at the coating/substrate interface in addition to TiO₂ and MgO phases as the main phases in the coating structure. The results of corrosion test showed that in general, coating improves the corrosion of AZ91D alloy in simulated-body fluid (SBF). The double-layer coating showed the best corrosion resistance at a corrosion current of 5.743 × 10^?7 μA/cm² and a corrosion potential of ?1.513 V due to its cathodic protection of the substrate and blockage of the path of the corrosive solution towards the substrate. In vitro tests showed that considering the good match between the used materials as the coating and body, no toxic material exits which results in improvement in biocompatibility, adhesion, and bone-cell multiplication.     

Corrosion Behavior of a Superconductor with Different SnO2 Nanoparticles in Simulated Seawater Solution

The corrosion behavior of (SnO₂)_x(Bi_1.6 Pb_0.4)Sr₂Ca₂Cu₃O₁₀-_δ, (SnO₂)_x(Bi,Pb)-2223, in 0.5?M NaCl solutions at 30°C was studied using potentiodynamic polarization curves measurements, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques as well as scanning electron microscopy (SEM) and energy dispersive X-ray emission spectroscopy (EDX). The polarization data indicated that SnO₂ nanoparticles behave as a cathodic type inhibitor for the corrosion of (Bi–Pb)-2223 phase superconductors in simulating seawater solutions. The corrosion current density of (SnO₂)_x(Bi,Pb)-2223 in a NaCl solution decreases with the time elapsed from sample preparation. The CV of (SnO₂)_x(Bi–Pb)-2223 phase superconductors showed features similar to those of ideal capacitive behavior. The results indicated that a pure (Bi,Pb)-2223 phase superconductor is the most suitable choice for electrochemical capacitor applications in simulating seawater solutions. However, EIS measurements at different potentials revealed that the corrosion process is controlled not only by charge transfer but also by the diffusion process. These measurements also confirm that the corrosion rate of a cathodically polarized phase superconductor is less than that of an anodically polarized phase superconductor. SEM images and EDX analysis showed that the reduction of SnO₂ nanoparticles to Sn decreases the corrosion rates of the superconducting materials.     

Electrochemical properties of Al and Al alloys relevant to corrosion protection in seawater environments

A series of electrochemical experiments on Al alloys were undertaken to determine their optimum protection potentials in seawater. With 1050 and 5456 alloys, passive films form during anodic polarization but are destroyed by the Cl in seawater, only to regrow as a result of the self-healing capacity of aluminum. The current density of 5456 Al alloy proved to be lower than that of 1050 as a whole. Any shift to more anodic or cathodic conditions in the potential range of-1.5∼-0.68 V resulted in a sudden increase in current density. Current densities in the high-strength 7075 Al alloy showed the greatest values. In contrast, the current densities of 5456 alloy, known to have excellent corrosion resistance in seawater, were the lowest in the range of -0.70∼-1.3 V, and we concluded that this potential range offered optimal protection.     

Effects of hafnium content on microstructures and properties of newly developed (Ti,Hf)(C,N) ceramics

In this study, novel (Ti,Hf)(C,N) ceramics with varying hafnium contents were fabricated via carbothermal reduction–nitridation and subsequent spark plasma sintering. The influence of Hf addition on the mechanical properties, wear properties, and corrosion resistance of the (Ti,Hf)(C,N) ceramics was systematically studied. The introduction of Hf promoted the sintering densification of the ceramics in the sintering process. The prepared (Ti,Hf)(C,N) ceramics exhibited excellent mechanical and wear properties owing to refinement and solution-strengthening mechanisms. The (Ti_0.9,Hf_0.1)(C_0.5,N_0.5) ceramic demonstrated higher Vickers hardness and fracture toughness, measuring 1997 HV5 and 4.28 MPa m^1/2, respectively, compared to the pure Ti(C_0.5,N_0.5) ceramic which exhibited values of 1635 HV5 and 3.94 MPa MPa m^1/2. The wear scar depth of the (Ti_0.9,Hf_0.1)(C_0.5,N_0.5) ceramic sample was 57.36% to that of the Ti(C_0.5,N_0.5) ceramic. Additionally, the addition of Hf improved the corrosion resistance of (Ti,Hf)(C,N) ceramics in a 0.5 M NaOH solution. The potential applications of (Ti,Hf)(C,N) ceramics include machining tools and wear-resistant parts.     

Corrosion resistance of plasma-anodized AZ91D magnesium alloy by electrochemical methods

Anodic coatings formed on magnesium alloys by plasma anodization process are mainly used as protective coatings against corrosion. The effects of KOH concentration, anodization time and current density on properties of anodic layers formed on AZ91D magnesium alloy were investigated to obtain coatings with improved corrosion behaviour. The coatings were characterized by scanning electron microscopy (SEM), electron dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD) and micro-Raman spectroscopy. The film is porous and cracked, mainly composed of magnesium oxide (MgO), but contains all the elements present in the electrolyte and alloy. The corrosion behaviour of anodized Mg alloy was examined by using stationary and dynamic electrochemical techniques in corrosive water. The best corrosion resistance measured by electrochemical methods is obtained in the more concentrated electrolyte 3 M KOH + 0.5 M KF + 0.25 M Na₃PO₄·12 H₂O, with a long anodization time and a low current density. A double electrochemical effects of the anodized layer on the magnesium corrosion is observed: a large inhibition of the cathodic process and a stabilization of a large passivation plateau.     

A reactive-sputter-deposited TiSiN nanocomposite coating for the protection of metallic bipolar plates in proton exchange membrane fuel cells

To meet the needs of corrosion resistance and electrically conductivity for metallic bipolar plates that are employed in proton exchange membrane fuel cells (PEMFCs), a TiSiN nanocomposite coating was fabricated on to a Ti–6Al–4V substrate using reactive sputter-deposition through the double cathode glow discharge plasma technique. The microstructure of the TiSiN coating comprised nanocrystallite TiN grains embedded in an amorphous Si₃N₄ matrix. Electrochemical measurements were employed to investigate the corrosion behavior of the TiSiN coating in the simulated operating environments of a PEMFC, specifically 0.5 M H₂SO₄ solution containing different HF concentrations (namely 2, 4 and 6 ppm) at 70 °C pumped with H₂ at the anode and air at the cathode. With increasing HF concentration, a higher corrosion current density and lower corrosion potential were observed from both the coating and the uncoated substrate, indicating that the addition of HF accelerated their corrosion rates under these conditions. Compared to the uncoated substrate, the TiSiN coating showed a markedly higher corrosion resistance at all HF concentrations. The passive film that formed on the TiSiN coating, with a resistance of the order of magnitude of ~10⁷ Ω cm², displayed good electrochemical stability and was less affected by changes in HF concentration. For the TiSiN coating, the values of interfacial contact resistance (ICR) were 14.7 mΩ cm⁻² and 18.3 mΩ cm⁻², respectively, before and after 2.5 h potentiostatic polarization with 6 ppm HF under cathodic conditions under a compaction pressure of 140 N cm⁻². Both values are much lower than those for the bare substrate. Moreover, the TiSiN coating was shown to improve the hydrophobicity of Ti–6Al–4V that would help facilitate water management in the PEMFC operating environment. This coating, which exhibited excellent corrosion resistance, electro-conductivity and hydrophobicity, is therefore a promising material for protecting metallic bipolar plates from corrosive attack.     

Zn-5%Al-RE镀层耐蚀性能的研究

试验了在高碳钢丝表面上热浸镀Zn-5%Al-RE合金层。通过湿热试验、晶间腐蚀试验、盐雾腐蚀试验，研究了该合金镀层的耐蚀性能，并与镀锌钢丝的耐蚀性能进行了对比。在水蒸汽的晶间腐蚀试验表明，合金镀层还略逊于锌镀层，但是在采用模拟海水的湿热试验以及盐雾腐蚀试验中，合金热浸镀层的耐蚀性能明显优于普通锌镀层，阳极极化曲线表明，合金层的致钝电流密度小，致钝电位较低，且稳定钝化区较宽，这可能是合金热浸镀层在海水中具有较好耐蚀性能的主要原因。     

Enhanced corrosion resistance of hydroxyapatite/magnesium-phosphate-composite-coated AZ31 alloy co-deposited by electrodeposition method

Magnesium-phosphate-doped hydroxyapatite (HAMP, Mg₃(PO₄)₂-Ca₁₀(PO₄)₆(OH)₂) and magnesium-hydrogen-phosphate-doped dicalcium-phosphate-dehydrate (DCPD-MHP, MgHPO₄-CaHPO₄) composite coatings were successfully electrodeposited onto an AZ31 alloy, and their corrosion behaviour was evaluated via electrochemical and in vitro degradation tests. In addition, the stability of the coatings was evaluated via these electrochemical tests. The results showed that the corrosion resistance and stability of the composite coatings were both significantly higher than those of single coatings; this greater resistance and stability resulted from the denser and more uniform structures of the composite coatings.     

H2SO4 as a passivating medium on the localised corrosion resistance of surgical 316L SS metallic implant and its effect on hydroxyapatite coatings

The localised corrosion resistance of 316L SS metallic implant due to H₂SO₄ treatment is being studied through electrochemical studies involving cyclic polarisation experiments and impedance studies. The efficiency of hydroxyapatite (HAP) coatings on H₂SO₄ treated 316L SS is also been investigated through electrochemical studies and the dissolution characteristics of the coatings. The study reveal that 15% H₂SO₄ treatment was found to be efficient in the corrosion resistance of 316L SS and dissolution of alloy is considerably reduced in the hydroxyapatite coatings on 15% H₂SO₄ treated 316L SS.     

Corrosion behavior of different alloys exposed to continuous flowing seawater by electrochemical impedance spectroscopy (EIS)

The corrosion of four types of alloys, under a dynamic condition, has been studied in continuous fresh seawater system using electrochemical impedance spectroscopy (EIS) technique. The materials used in this study were stainless steel 304, Cu-Ni 70-30, Hastelloy G-30, and titanium. The total exposure time of the test was 180 days, in continuous fresh seawater of the Gulf in Kuwait. The EIS tests were carried out by using EG&G software and hardware instrument. Electrochemical parameters such as the polarization resistance (R_P), solution resistance (R_Sol), and the double layer capacitance (C_dL) of these alloys were determined. Then the obtained EIS parameters were used to study the effect of the seasonal change of the Gulf seawater on the corrosion behavior of the tested materials. All the obtained EIS parameters showed that the seasonal changes of the Gulf seawater have a significant effect on controlling the rate of the formation of the marine bio-film on the surface of tested materials. Consequently, the corrosion behavior of the materials tends to vary as a function of the rate formation of the marine bio-film on the surface of tested materials.     

Influence of rare earth Y on the corrosion behavior of as-cast AZ91 alloy

The influence of different contents of rare earth Y on the corrosion resistance of AZ91 alloy was investigated by the salt spray test and electrochemical measurements. It was found that the proper amount of Y was effective on improving the corrosion resistance of AZ91 alloy. The optimal modification effect was obtained when the Y content in the alloys was 0.3 wt.%. However, with the increase of rare earth Y, the corrosion rate became bigger slightly, and further addition of Y content over 0.3 wt.% resulted in the increment of the corrosion rate. It is suggested that the excessive rare earth Y can reduce the corrosion resistance of AZ91 alloy.     

Effect of pressure on corrosion of Inconel 625 in supercritical water up to 100 MPa with acids or oxygen

The corrosion behavior of Inconel 625 in supercritical water was investigated under high pressure (30–100 MPa at 400 °C) with the addition of acids (5 mmol/kg CH₃COOH or 0.5 mmol/kg HNO₃) or O₂ (2.5–250 mmol/kg). Ni and Cr ions were the main dissolved metal ions in the effluent. The Ni ion concentration showed no clear dependence on the O₂ concentration or pressure in the experiment with O₂; the concentration was lower than 0.05 ppm. The concentration increased with pressure up to 0.09 ppm and 3 ppm (at 100 MPa) in the experiment with CH₃COOH and HNO₃, respectively. The Cr ion concentration increased with the O₂ concentration and pressure; the maximum value of the concentration was about 0.5 ppm. The Cr ion concentration was lower than 0.01 ppm in the experiment with CH₃COOH, while the concentration was considerably higher in the experiment with HNO₃: the concentration increased with pressure up to 0.87 ppm at 100 MPa. The effect of pressure on the corrosion behavior of Inconel 625 was discussed using potential-pH diagrams, metal oxide solubilities, pH, and equilibrium of ionic reactions. Pressure dependence of the metal ion concentrations was analyzed using a model with water density as a parameter; the log–log plots revealed a linear relationship.     

Influence of halide ions on the adsorption of diphenylamine on iron in 0.5 M H2SO4 solutions

Halide ions are found to enhance the inhibition performance of amines due to enhanced adsorption of amines by the adsorbed halide ions on the metal surface. In this work, the synergistic action of halide ions on the corrosion inhibition of iron in 0.5 M H₂SO₄ by diphenylamine has been found out by electrochemical impedance and polarization methods. Analysis of impedance data has been made with equivalent circuit with constant phase angle element for calculation of double layer capacitance values. Experiments have been carried out in the concentration range of 100-1000 ppm of diphenylamine in the presence of 0.5-1.0 × 10⁻³ M of halide ions. Diphenylamine is found to be a cathodic inhibitor and the inhibition efficiency of about 65% is obtained at 1000 ppm. The anodic and cathodic Tafel slopes in the presence of diphenylamine alone and with halide ions are 65 ± 5 and 105 ± 5 mV, respectively. Diphenylamine inhibits corrosion by adsorption and the surface coverage values are increased considerably in the presence of halide ions. In the presence of iodide ions, the inhibition efficiency of diphenylamine at 100 ppm is increased to more than 90%. In the case of other halide ions, the inhibition efficiency of diphenylamine in increased to 80% at 1000 ppm. The order of synergism of halide ions is I⁻ ? Br⁻ > Cl⁻. The highest synergistic effect of iodide ions is due to chemisorption with metal surface due to its larger size and ease of polarizability.     

Discharge behavior of Mg–4 wt%Ga–2 wt%Hg alloy as anode for seawater activated battery

Magnesium–gallium–mercury alloy is one of the new developed anode materials for seawater activated batteries. The potentiodynamic polarization, galvanostatic discharge and electrochemical impedance spectroscopy of Mg–4%Ga–2%Hg alloy in seawater are studied and compared with commercial AZ31 and AP65 alloys in this study. The results show that Mg–4%Ga–2%Hg alloy exhibits different discharge behaviors in as-cast, homogenizing, rolling and annealing conditions. The annealing Mg–4%Ga–2%Hg sheet obtains the most negative corrosion potentials in different current densities. And the Mg–4%Ga–2%Hg alloy provides more negative corrosion potentials than AZ31 and AP65 alloys. EIS studies reveal that the Mg–Ga–Hg alloy/seawater interfacial process is determined by an activation-controlled reaction. The Mg₃Hg and Mg₂₁Ga₅Hg₃ phases improve the electrochemical properties of Mg–4%Ga–2%Hg alloy. The assembled prototype battery with Mg–4%Ga–2%Hg alloy as anode and CuCl as cathodes exhibits a satisfactory discharge performance because of the advantages in discharge characterizations and microstructure of the Mg–4%Ga–2%Hg alloy.     

Effect of NaOH on the decomposition of halogenated hydrocarbon by supercritical water oxidation

To protect alloys from corrosion phenomena in the supercritical water oxidation (SCWO) process, the effects of neutralizer on the conversion and corrosion were investigated. The surface morphologies of all the alloy coupons exposed to 2,4-Dichlorophenol (2,4-DCP) in the SCWO were significantly changed in microscopic images. The theoretical amount of NaOH as a neutralizer was calculated under the assumption of complete oxidation of 2,4-DCP. The pre-dosed NaOH in the range of 100% to 300% stoichiometric amount could not affect significantly the pH value in the SCWO. Moreover, the pH = 7 was not achieved until 700% stoichiometric amount of NaOH was pre-dosed to the reactor. It is noted that the conversion rate recorded over 99% without oxidant when 800% of NaOH was pre-dosed into the reactor. In addition, under the addition of H₂O₂ as an oxidant, the increased amount of NaOH led to the improvement of conversion rate. The pre-dosed NaOH may contribute to the conversion rate of 2,4-DCP in the SCWO. However, due to low solubility of salt in the SCWO, the fouling problem should be solved in the SCWO process.     

Corrosive and mechanical resistance of MgO ceramics under metallizing and mild chlorination of spent nuclear fuel in molten salts

The present work is aimed at the study of the unirradiated and irradiated MgO ceramics corrosion and mechanical properties in the molten LiCl at 650–750 °C with addition of UCl₃ and Li₂O(LiCl + nLi₂O and LiCl + mUCl₃ molten salts with n = 1.0 and 2.0 mol. % and m = 0.25, 0.5 and 1.0 mol. %). MgO ceramics is suggested to be used as one of materials for pyrochemical technology for recycling of spent nuclear fuel.The gravimetric method with the exposure time during 100 h was the primary method of investigation. The investigation of surface and bulk corrosion of MgO samples by scanning electron microscopy (SEM) and X-ray spectroscopy (MRSA) was performed using scanning electron microscope equipped with a x-Act 6 energy-dispersive analytic system for X-rays characteristic (XRС). Determination of corrosion losses and average corrosion rates of MgO samples was based on the assumption that the ejection of the radionuclides ⁹⁵Zr, ¹⁷⁵Hf and ¹⁸¹Hf from the MgO samples.Incorporation of Li₂O and UCl₃ in molten LiCl result in increase in the rate of MgO ceramic corrosion both at 650 °C and 750 °C and acts on MgO compressive strength (σ_cs) and on the elemental composition of MgO surface layers. Besides the increasing of UCl₃ concentration led to the bulk corrosion of MgO sample grains.Short-term mechanical tests demonstrated the transition of MgO sample destruction pattern depending on the concentration of Li₂O and UCl₃ additions in LiCl melt.Doping of molten LiCl by 0.5 mol. % of UCl₃ at 650 °C and by 0.25 mol. % of UCl₃ at 750 °C had no influence on the ultimate compression strength of irradiated and unirradiated MgO samples. Increased UCl₃ concentration totaling 0.5 mol. % in the LiCl melts at 750 °C reduced the ultimate compression strength of irradiated MgO ceramic samples by ~15%.     

Joining of SiC ceramics using the Ni-Mo filler alloy for heat exchanger applications

In order to meet the sealing demands of SiC heat exchanger, the Ni-Mo filler alloy was designed, prepared and employed to braze SiC ceramics. Wetting behavior of the Ni-Mo filler alloy on SiC ceramics and interfacial microstructure of the brazed joints were systematically characterized using optical observation furnace and XRD, SEM, EDS, TEM, respectively. Flexural strengths of the brazed joints at room temperature and high temperature were measured with four-point flexural strength method. HCl immersion test was performed to evaluate the corrosion resistance of the joints. The Ni-Mo filler alloy exhibited excellent wettability on SiC ceramics. During the process of brazing, SiC reacted with element Ni of the Ni-Mo filler alloy, resulting in the formation of Ni₂Si + graphite reaction layer adjacent to the SiC substrate. Ni₃Mo₃C and Ni₂Si compounds were precipitated at the center of brazing seam. When the brazing temperature increased from 1250 ℃ to 1400 ℃, the thickness of Ni₂Si + graphite layer increased gradually. The maximum room-temperature flexural strength of 174 ± 33 MPa was obtained when brazed at 1300 ℃ for 40 min. The joints also exhibited stable high-temperature strength and acid corrosion resistance. When the test temperature was 700 ℃, 800 ℃, 900 ℃, the joints gave the strength retention rate of 92.5 %, 79.8 %, 67.2 %, respectively. It was believed that the formation of high melting point phases played an important role. Residual strength of the joints after HCl corrosion exceeded 130 MPa, revealing a good potential for applications in corrosion environment.     

Influence of rare earths addition on the corrosion behaviour of Zn-5%Al (Galfan) alloy in neutral aerated sodium sulphate solution

The effect of rare earth metal (Ce, Er, Y) additions on the corrosion behaviour of Zn-5Al Galfan alloy has been investigated. The corrosion resistance of Zn-5Al-1Ce, Zn-5Al-1Er and Zn-5Al-1Y alloys has been assessed by various electrochemical tests, such as corrosion potential measurements, polarization curves and electrochemical impedance spectroscopy. They have been performed in a 0.1 M Na₂SO₄ solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on the Zn-5Al alloy. Moreover, the surface morphology and nature of the corrosion products have been investigated. The results indicated that rare earths’ addition improves the corrosion behaviour of Galfan, the effect being more pronounced for the Er- and Y-containing alloys. The mechanism by which the corrosion resistance of Zn-5Al alloy is enhanced in presence of the rare earths is discussed.