Corrosion behavior of Mg,AZ31, and AZ91 alloys in dilute NaCl solutions

Corrosion behavior of extruded Mg, extruded AZ31 alloy, and cast AZ91 alloy was investigated by electrochemical measurements in dilute NaCl solutions. Corrosion products and passivation films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. All specimens exhibit the corrosion and passivation zones in dilute NaCl solutions. The aluminum content and alloy microstructure influence the corrosion and passivation processes. AZ91 alloy shows the broadest passivation zone followed by AZ31 alloy and Mg. AZ91 alloy reveals a highest corrosion resistance, and preferential attack is located at the primary Mg phase. Its relatively fine β-phase (Mg₁₇Al₁₂) network and Al₂O₃/Al(OH)₃ compounds produced on the passivation film are the main factors which limit the corrosion progress as compared with AZ31 alloy and Mg. The thick passivation product on AZ31 alloy is the key factor which restricts the corrosion attack in dilute solutions.     

Evaluation of in vitro bioactivity and MG63 Oesteoblast cell response for TiO2 coated magnesium alloys

The present investigation reports TiO₂ coating on magnesium alloy AZ31 by sol–gel method via dip coating technique. TiO₂ coated surface was characterized by thin film X-ray diffraction (TF-XRD), Fourier transform infrared red (FT-IR) spectroscopy, scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques. From TF-XRD results, the peaks at 2θ values of 25.14, 32.12, 68.73 and 70.11 confirm the presence of TiO₂. The TiO₂ is crystalline in nature and the crystallite size is about 32.4 nm. SEM-EDX, TEM and AFM show that the coated surface is uniform and nanoporous. FT-IR analysis shows that the peak in the range of 692 cm^?1 is assigned to Ti–O–Ti stretching vibration. Contact angle measurements show that the coating is hydrophilic in nature. Bioactivity of the coating in simulated body fluid (SBF) was also examined, the hydroxyl functionalized surface greatly enhances the hydroxyapatite growth. The potentiodynamic polarization studies prove that the corrosion resistance of the TiO₂ coated surface after immersion in SBF for 7 days is improved dramatically. Cell adhesion studies confirm the increased cell attachment on TiO₂ coated surface when compared to uncoated alloy, due to less amount of Mg ion release from the substrate in the culture medium.     

A high performance nano-structure conductive coating on a Crofer22APU alloy fabricated by a novel spinel powder reduction coating technique

A nano-structure conductive coating was fabricated on a Crofer22APU alloy interconnect by an original coating strategy using Mn_0.9Y_0.1Co₂O₄ (MYC) novel spinel nanocrystalline powder. A unique treatment method by which the spinel powder was reduced was used to prepare the green coating. The resulting coating was about 12 μm in thickness, and was composed of MYC nanocrystalline with an average particle size of about 100 nm. The coating was well adhered with the substrate alloy. Less than 4 mΩ cm² of the area specific resistance (ASR) was obtained, and no obvious degradation was observed for a coated alloy (whose coating thickness was about 30 μm) after operated at 800 °C for 538 h under seven thermal cyclings. The coated alloy exhibited excellently electrical performance and long-term stability compared with the uncoated one. The exploration of the novel spinel powder reduction coating technique for alloy interconnect to obtain cheap coatings with excellent microstructure and performance showed a promising prospect for the practical application of solid oxide fuel cells (SOFCs).     

Electrochemical investigation of corrosion and corrosion inhibition of iron in hydrochloric acid solutions

The inhibition effect of 1-methyl pyrazole (MPA) on the acidic corrosion of iron in 1.0 M HCl was studied at different concentrations (10^?3–10^?2 M) by potentiodynamic polarization and electrochemical impedance spectroscopy, and EIS measurements. It is found from the polarization studies that methyl pyrazole (MPA) behaves mainly as anodic inhibitor in HCl. Values of polarization resistance (R_p) and double layer capacitance (C_dl) in the absence and presence of MPA in 1.0 M HCl are determined. The adsorption of MPA on iron surface from HCl is found to obey Temkin adsorption isotherm.     

pH值对AZ31镁合金表面植酸转化膜在模拟体液耐腐蚀性能的影响

采用沉积的方法在镁合金AZ31表面制备植酸转化膜并研究了pH值的影响. 利用极化曲线和电化学阻抗谱方法测定其耐腐蚀性能,用扫描电子显微镜观察转化膜的表面微观结构,用能谱测定转化膜的组成元素. 在理论上通过热力学的方法分析最佳pH值. 植酸转化膜可以提高镁合金AZ31的耐腐蚀性能. 当植酸溶液的pH=5时腐蚀效率达到了89.19%,此时腐蚀电位正移了156 mV,腐蚀电流密度与没有处理的试样相比减小了约一个数量级. 热力学分析表明植酸转化膜的耐腐蚀性能不仅受植酸根离子和镁离子浓度的影响,也与氢气释放的速率有关.     

Corrosion behavior of CoCrMoW cast alloy in lactic acid environment for surgical applications

The corrosion behavior of CoCrMoW alloy in lactic acid environment during 168 h of immersion at 37 °C has been studied and assessed by means of electrochemical techniques (open circuit potential (OCP), potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS)). Further, the oxide film thickness formed after immersion and the quantity of ions released have been evaluated by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical spectroscopy (ICP-OES). A good correlation between the results, related to the oxide film thickness, obtained from these experimental techniques was achieved. The research has also shown that the tendency of growing of oxide film becomes slower as the time of immersion is longer. The higher corrosion resistance of CoCrMoW alloy in lactic acid environment is due to the formation of the oxide film highly enriched in Cr(III) on the alloy surface. With a small corrosion rate, e.g. 45 nm year⁻¹, this alloy is characterized as “Perfect Stable” according to ISO 8044/2000. Overall, the present study provides additional evidences with respect to the benefic influence of tungsten on passivity, explained by a higher resistance to pitting corrosion of the CoCrMoW alloy in lactic acid with sodium chloride.     

Li/LiFePO4 batteries with room temperature ionic liquid as electrolyte

Room temperature ionic liquid (RTIL) was prepared on basis of N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide (PP₁₄TFSI), which showed a wide electrochemical window (?0.1–5.2 V vs. Li⁺/Li) and is theoretically feasible as an electrolyte for batteries with metallic Li as anodes. The addition of vinylene carbonate (VC) improved the compatibility of PP₁₄TFSI-based electrolyte towards lithium anodes and enhanced the formation of solid electrolyte interphase film to protect lithium anodes from corrosion. Accordingly, Li/LiFePO₄ cells initially delivered a discharge capacity of about 127 mAh g^?1 at a current density of 17 mA g^?1 in the ionic liquid with the addition of VC and showed better cyclability than in the neat ionic liquid. Electrochemical impedance spectroscopy disclosed that the addition of VC enhanced Li-ion diffusion and depressed interfacial resistance significantly.     

Electrodeposited PbO2 thin film on Ti electrode for application in hybrid supercapacitor

PbO₂ thin films were prepared by pulse current technique on Ti substrate from Pb(NO₃)₂ plating solution. The hybrid supercapacitor was designed with PbO₂ thin film as positive electrode and activated carbon (AC) as negative electrode in the 5.3 M H₂SO₄ solution. Its electrochemical properties were determined by cyclic voltammetry (CV), charge–discharge test and electrochemical impedance spectroscopy (EIS). The results revealed that the PbO₂/AC hybrid supercapacitor exhibited large specific capacitance, high-power and stable cycle performance. In the potential range of 0.8–1.8 V, the hybrid supercapacitor can deliver a specific capacitance of 71.5 F g^?1 at a discharge current density of 200 mA g^?1(4 mA cm^?2) when the mass ratio of AC to PbO₂ was three, and after 4500 deep cycles, the specific capacitance remains at 64.4 F g^?1, or 32.2 Wh Kg^?1 in specific energy, and the capacity only fades 10% from its initial value.     

AZ31镁合金表面聚吡咯的化学氧化合成及其耐蚀性能

以对甲苯磺酸钠为掺杂剂, 三氯化铁为氧化剂, 用化学氧化聚合法在AZ31 镁合金表面制备聚吡咯(PPy)膜. 采用傅里叶变换红外(FTIR)光谱分析了镁合金表面聚吡咯膜结构, 通过电化学极化曲线、电化学阻抗谱(EIS)研究了其耐蚀性能, 通过扫描电子显微镜(SEM)、X射线能量散射谱(EDS)分析了表面形貌和成分. 和镁合金裸样相比, 聚吡咯膜对镁合金腐蚀有一定的抑制作用. 硅烷预处理改善了镁合金/聚吡咯体系的耐腐蚀性能, 使腐蚀电位较镁合金裸样正移了110 mV, 电流密度减小了约2个数量级.     

Energy release characteristics of impact-initiated energetic aluminum–magnesium mechanical alloy particles with nanometer-scale structure

Aluminum–magnesium alloys, fabricated by bi-directional rotation ball milling, were used as a kind of promising solid fuel in “reactive material” that can be ignited by impact to release a large quantity of heats. Different percentages of Mg were added to Al to yield Al_90%–Mg_10% and Al_70%–Mg_30% alloys in order to probe the effect of Mg content on the microstructure and thermal reactivity of Al–Mg alloys. Structural characterization revealed that a nanometer-scale structure was formed and oxidation of as-fabricated alloy powders was faint. Moreover, as the Mg percentage increased, the particle size of alloy decreased with increasing brittleness of Al–Mg. TGA/DSC curves of the [Al_70%–Mg_30%]–O₂ system exhibited an intense exothermic peak before melting with reaction heat of 2478 J g^?1 and its weight increase reached 90.16% of its theoretical value, which contrasted clearly with 181.2 J g^?1 and 75.35% of [Al_90%–Mg_10%]–O₂ system, respectively. In addition, other than [Al_90%–Mg_10%]–Fe₂O₃ system, the [Al_70%–Mg_30%]–Fe₂O₃ system exhibited a considerable solid–solid reaction and a low activation energy. Finally, target penetration experiments were conducted and the results confirmed that a projectile composed of [Al_70%–Mg_30%]–Fe₂O₃ displayed a more complete ignition of target than that of Al–Fe₂O₃ formulation.     

On the corrosion inhibition of iron in hydrochloric acid solutions,Part I: Electrochemical DC and AC studies

The inhibitive action of 4-methyl pyrazole (4MP) against the corrosion of iron (99.9999%) in solutions of hydrochloric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). At inhibitor concentration range (10^?3–10^?2 M) in 1.0 M acid, the results showed that 4MP suppressed mainly the anodic processes of iron corrosion in 1.0 M HCl by adsorption on the iron surface according to Temkin adsorption isotherm. Both potentiodynamic and EIS measurements reveal that 4MP inhibits the iron corrosion in 1.0 M HCl and that the efficiency increases with increasing inhibitor concentration. Data obtained from EIS were analyzed to model the corrosion inhibition process through an equivalent circuit.     

High capacity and excellent cyclability of vanadium (IV) oxide in lithium battery applications

A VO₂ · 0.43H₂O powder with a flaky particle morphology was synthesized via a hydrothermal reduction method. It was characterized by scanning electron microscopy, electron energy loss spectroscopy, and thermogravimetric analysis. As an electrode material for rechargeable lithium batteries, it was used both as a cathode versus lithium anode and as an anode versus LiCoO₂, LiFePO₄ or LiNi_0.5Mn_1.5O₄ cathode. The VO₂ · 0.43H₂O electrode exhibits an extraordinary superiority with high capacity (160 mAh g^?1), high energy efficiency (95%), excellent cyclability (142.5 mAh g^?1 after 500 cycles) and rate capability (100 mAh g^?1 at 10 C-rate).     

Thermodynamic properties of metal amides determined by ammonia pressure-composition isotherms

Thermodynamic properties of Mg(NH₂)₂ and LiNH₂ were investigated by measurements of NH₃ pressure-composition isotherms (PCI). Van’t Hoff plot of plateau pressures of PCI for decomposition of Mg(NH₂)₂ indicated the standard enthalpy and entropy change of the reactions were ΔH° = (120 ± 11) kJ · mol^?1 (per unit amount of NH₃) and ΔS° = (182 ± 19) J · mol^?1 · K^?1 for the reaction: Mg(NH₂)₂ → MgNH + NH₃, and ΔH° = 112 kJ · mol^?1 and ΔS^o = 157 J · mol^?1 · K^?1 for the reaction: MgNH → (1/3)Mg₃N₂ + (1/3)NH₃. PCI measurements for formation of LiNH₂ were carried out, and temperature dependence of plateau pressures indicated ΔH° = (?108 ± 15) kJ · mol^?1 and ΔS° = (?143 ± 25) J · mol^?1 · K^?1 for the reaction: Li₂NH + NH₃ → 2LiNH₂.     

High-surface-area microporous carbon as the efficient photocathode of dye-sensitized solar cells

This paper reports on the application of cornstalks-derived high-surface-area microporous carbon (MC) as the efficient photocathode of dye-sensitized solar cells (DSCs). The photocathode, which contains MC active material, Vulcan XC–72 carbon black conductive agent, and TiO₂ binder, was obtained by a doctor blade method. Electronic impedance spectroscopy (EIS) of the MC film uniformly coated on fluorine doped SnO₂ (FTO) glass displayed a low charge-transfer resistance of 1.32 Ω cm². Cyclic voltammetry (CV) analysis of the as-prepared MC film exhibited excellent catalytic activity for I₃^?/I^? redox reactions. The DSCs assembled with the MC film photocathode presented a short-circuit photocurrent density (J_sc) of 14.8 mA cm^?2, an open-circuit photovoltage (V_oc) of 798 mV, and a fill factor (FF) of 62.3%, corresponding to an overall conversion efficiency of 7.36% under AM 1.5 irradiation (100 mW cm^?2), which is comparable to that of DSCs with Pt photocathode obtained by conventional thermal decomposition.     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.     

Fabrication and electrochemical properties of the Sn–Ni–P alloy rods array electrode for lithium-ion batteries

A new ternary Sn–Ni–P alloy rods array electrode for lithium-ion batteries is synthesized by electrodeposition with a Cu nanorods array structured foil as current collector. The Cu nanorods array foil is fabricated by heat treatment and electrochemical reduction of Cu(OH)₂ nanorods film, which is grown directly on Cu substrate through an oxidation method. The Sn–Ni–P alloy rods array electrode is mainly composed of pure Sn, Ni₃Sn₄ and Ni–P phases. The electrochemical experimental results illustrate that the Sn–Ni–P alloy rods array electrode has high reversible capacity and excellent coulombic efficiency, with an initial discharge capacity and charge capacity of 785.0 mAh g^?1 and 567.8 mAh g^?1, respectively. After the 100th discharge–charge cycling, capacity retention is 94.2% with a value of 534.8 mAh g^?1. The electrode also performs with an excellent rate capacity.     

Inhibitors for magnesium corrosion: Metal organic frameworks

Electrochemical measurements demonstrate that magnesium surfaces can be protected by alkyl carboxylate. In a nearly neutral pH solution of sodium decanoate, the reduced corrosion rate and a passivation behaviour are attributed to the formation of Mg(C₁₀H₁₉O₂)₂(H₂O)₃ (Mg(C10)₂) at the magnesium surface whereas heptanoate Mg(C₇H₁₃O₂)₂(H₂O)₃ (Mg(C7)₂) is not efficient in such media. The crystal structures of the two metal carboxylates Mg(C7)₂ and Mg(C10)₂ are determined by X-ray diffraction. Single crystal data: Mg(C7)₂, P2₁/a, a = 9.130(5) Å, b = 8.152(5) Å, c = 24.195(5) Å, β = 91.476(5)°, V = 1800.3(15) Å³, D_x = 1.242 g cm⁻³, Z = 4. Synchrotron powder data: Mg(C10)₂, P2₁/a, a = 9.070(3) Å, b = 8.165(1) Å, c = 32.124(1) Å, β = 98.39(1)°, V = 2353.85(8) Å³, D_x = 1.188 g cm⁻³, Z = 4. Their layered structures are quite similar and differ mainly by the length of the hydrophobic chains. They consist of two planes of O-octahedra centred by Mg atoms, parallel to (001). The distorted octahedra are constituted by three oxygen atoms from carboxylate groups and by three oxygen atoms coming from water molecules. The layers are connected by hydrogen bonds. The carboxylate chains are located perpendicularly and on both sides of these planes. One carboxylate chain is bridging the Mg atom along [010] while the other is monodendate. The presence of structural water is confirmed by thermal analyses.     

Electrochemical behavior of polypyrrole-coated AZ31 alloy modified by fluoride anions

The electrochemical polymerization of polypyrrole (Ppy) films on AZ31Mg alloys was carried out using cyclic voltammetery in 0.5 M sodium salicylate solution containing 0.25 M pyrrole and different concentration of sodium fluoride (NaF). Corrosion performance of the Ppy film was assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 % NaCl solution. It was observed that Ppy coatings doped in the presence of 100 ppm NaF provide the best corrosion protection for magnesium and the corrosion potential shifted about 290 mV toward nobler potentials and decrease the corrosion current density about one order of magnitude. The surface analysis of the coatings showed that the addition of F^? dopant anions led to an improvement in the smoothness, thickness, and adhesion quality of the synthesized Ppy coating on the Mg surface. The scanning electron microscopy (SEM) studies of the fluoride-doped Ppy films revealed that the synthesized coating has a closely packed globular structure which was composed of nanoparticles of Ppy.     

Spin transition in heptanuclear star-shaped iron(III)–antimony(V) NCS- and CN-bridged compounds

The precursor [Fe^III(L)Cl] (LH₂ = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mössbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [Sb^V(X)₆]^? (X = CN^?, NCS^?) to yield star-shaped heptanuclear clusters [(LFe^III–X)₆Sb^V]Cl₅. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mössbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant population at both temperatures.     

Surface characterization of growth process for cerium conversion coating on magnesium alloy and its anticorrosion mechanism

Cerium conversion coating is successfully deposited on magnesium alloy AZ31 for corrosion protection. Deposition time on the influence of cerium conversion coating morphology, composition, and electrochemical properties has been investigated in detail. Morphological observation reveals that the cerium conversion coating is a porous agglomerate nanostructure. XPS indicates that the coating exhibits a time‐dependent ingredient. Moreover, the coating is considered as a combination of magnesium oxide/hydroxide and cerium (III) and (IV) oxides/hydroxides. The results of electrochemical impedance spectroscopy indicate that the anticorrosion coating exhibits the best properties during deposition of 5 min. In view of the analysis, the anticorrosion mechanism is pioneered proposed because of the formation of H‐bonding layer, which forms a reasonable barrier to Cl^? ions. Copyright © 2014 John Wiley & Sons, Ltd.