Corrosion of Zinc Ferrite Based Inert Anodes in AlF_3-NaF-Al_2O_3 Melts Under Conditions of Anodic Polarization

ZnFe2O4-based inert anodes were made to conduct the aluminum electrolysis tests. The corrosion behaviors of the inert anodes were examined and discussed. Experiment results prove that: (1) ZnFe2O4-based inert anodes are good corrosion resistant to AlF3-NaF-Al2O3 melts under the conditions of anodic polarization; (2) High anodic current density ( > 1.5 A·cm-2), high alumina concentration and low ratio of NaF/AlF3 in the molten salts will be the most important conditions for using inert anode.

Effects of polyaniline on electrochemical properties of composite inert anodes used in zinc electrowinning

In order to search for a suitable anode material used in zinc electrowinning in place of Pb-Ag alloy,Al/Pb-PANI（polyaniline）-WC（tungsten carbide） composite inert anodes were prepared on aluminum alloy substrate by double pulse electrodeposition（DPE） of PANI and WC particles with Pb2＋ from an original plating bath.Thereafter,anodic polarization curves,cyclic voltammetry curves and Tafel polarization curves for the composite inert anodes obtained under different PANI concentrations in the original plating bath were measured,and the microstructural features were also investigated by scanning electron microscopy（SEM）.The results show that Al/Pb-PANI-WC composite inert anode obtained under PANI concentration of 20 g/L in the original plating bath possesses uniform microstructures and composition distributions,higher electrocatalytic activity,better reversibility of electrode reaction and corrosion resistance in a synthetic zinc electrowinning electrolyte of 50 g/L Zn2＋,150 g/L H2SO4 at 35 °C.Compared with Pb-1%Ag alloy,the overpotential of oxygen evolutions for the composite inert anode are decreased by 185 mV and 166 mV,respectively,under 500 A/m2 and 1000 A/m2.

Electrosynthesis of Al/Pb/α-PbO_2 composite inert anode materials

The α-PbO2 deposition layers were prepared on the surface of A1/Pb substrates by constant current electrosynthesis from an alkaline bath, and A1/Pb/α-PbO2 composite inert anode materials were obtained. The effects of the bath composition and bath temperature on the electrosynthesis of α-PbO2 were investigated by means of anodic polarization method, the phase structures and surface microstructures of AI/Pb and α-PbO2 deposition layers were tested by means of X-ray diffraction （XRD） and scanning electron microscopy （SEM）, respectively. The experimental data have shown that the process of α-PbO2 formation have several stages. The appropriate conditions can effectively improve the formation rate of α-PbO2 and avoid the occurrence of oxygen evolution reaction. The α-PbO2 deposition layer obtained in alkaline bath possesses rhombic structure, and it is composed of well developed spherical unit cells.

Ti Anode with Ti-Mn Coating

A new type anode, Ti anode with Ti-Mn coating, has been used to prepare EMD (Electrolytic Manganese Dioxide) by some Chinese manufacturers for 4 years. The industry test shows that this anode has such characteristics as sturdy, light, fine mechanical performance, very high passivation resistance and corrosion resistance. The passivation of this anode is discussed and the results show that this anode is better than the pure titanium anode in the EMD industry.

Enhancing the formability of FeSi6.5 steel by the anodic polarization

The effect of anodic polarization on the plastic deformation behavior and formability of FeSi6.5 steel at room temperature was experimentally investigated through uniaxial tensile and drawing of wire specimen in sulfuric acid solution with current densities of 0-40 mA/cm2.The formability of the FeSi6.5 steel was significantly improved after the anodic polarization.The plastic elongation of the specimen as an anode in the electrochemical environment was 4.4%-7%,but 2.7%in the air.The drawing force under the anodic polarization decreased by 12.5%-26%compared to that in deionized water.The softening is mainly attributed to the relief in work hardening caused by surface atomic dissolution.The work hardening mechanism of the FeSi6.5 steel wires under anodic polarization condition was analyzed using Hollomon equation and Voce relation combined with the Kocks-Mecking approach.These data support the view that the surface atom dissolution facilitates dislocation slip.FeSi6.5 steel wires were obtained using electrochemical cold drawing and presented a smooth surface and good ductility without crack after five-pass drawing with a total cross-section area reduction of 88%.The drawing with the assistance of anodic polarization is a promising technology for processing hard and brittle metal materials.

Effects of Al and Sn on electrochemical properties of Mg-6%Al-1%Sn (mass fraction) magnesium alloy as anode in 3.5%NaCl solution

Mg-6%Al-1%Sn(mass fraction) alloy is a newly developed anode material for seawater activated batteries. The electrochemical properties of Mg-1%Sn, Mg-6%Al and Mg-6%Al-1%Sn alloys are measured by galvanostatic and potentiodynamic tests. Scanning electron microscopy(SEM) with energy dispersive spectrometry(EDS) is used to characterize the microstructures of the experimental alloys. The results show that the Mg-6%Al-1%Sn alloy obtains more negative discharge potential(-1.38 V(vs SCE)) in hot-rolled condition. This is attributed to the fine dynamically recrystallized grains during the hot rolling process. After the experimental alloys are annealed at 473 K for 1 h, the discharge potentials of Mg-6%Al-1%Sn alloy are more negative than those of Mg-6%Al alloy under different current densities. After annealing at 673 K, the discharge potentials of Mg-6%Al-1%Sn alloy become more positive than those of Mg-6%Al alloy. Such phenomenon is due to the coarse grains and the second phase Mg2 Sn. The discharge potentials of Mg-1%Sn shift positively obviously in the discharge process compared with Mg-6%Al-1%Sn alloy. This is due to the corrosion products pasting on the discharge surface, which leads to anode polarization.

Effects of electrolytic concentration on properties of micro-arc film on Ti6Al4V alloy

To study the effect of electrolytic concentration,bioactive ceramic films containing Ca and P on the surface of the Ti6Al4V alloy were prepared by micro-arc oxidation(MAO) in aqueous solutions of different concentrations.Composition,micro-morphology,wettability of the films and their corrosion behavior in a Hank's SBF were studied.Our experimental results show that the film is mainly composed of anatase,rutile and amorphous phases.With an increase in electrolytic concentration,the ratio of rutile in films enlarge and small amounts of calcium phosphate(Ca3(PO4)2) and hydroxyapatite(HA) appear.The number of micropores in films increases but their dimensions decrease and their porosities increase slightly.As the surface roughness of MAO film increases with concentration,the wettablility of the oxide film improves continually,while micro-hardness increases at first and then decreases.MAO treatment clearly improves the corrosion resistance of substrates in a Hank's SBF.

Non-monotonic influence of a magnetic field on the electrochemical behavior of Fe_(78)Si_9B_(13) glassy alloy in NaOH and NaCl solutions

The corrosion behavior and microstructure of Fe78Si9B13 glassy alloy in NaOH and NaCl solutions under a 0.02-T magnetic field were investigated through electrochemical testing and scanning electron microscopy （SEM）. The current-density prepeak （PP） in the anodic polarization curves in low-concentration NaOH solutions （classified as type I） tends to disappear when the NaOH concentration is increased to 0.4 mol/L and the magnetic field is applied. Under the magnetic field, the height of the second current-density peak is increased in low-concentration NaOH solutions （type I） but decreased in high-concentration NaOH solutions （type Ⅱ）. The non-monotonic effect of the magnetic field was similarly observed in the case of polarization curves of samples measured in NaCl solutions, Ring-like corroded patterns and round pits are easily formed under the magnetic field in NaOH and NaC1 solutions. These experimental results were discussed in terms of the magnetohydrodynamic （MHD） effect.

Electroless Plating of Ni-Fe-P Alloy and Corrosion Resistance of the Deposit

Electroless Ni-Fe-P alloys in an alkaline bath were plated. The effects of deposition parameters on the plating rate and the coating composition were examined. The weight loss test and the anodic polarization measurement of the deposits in 3.5 wt pct NaCI solution (pH7.0) showed that the deposits with the mole ratio of NiS04/FeSO4 being 0.07:0.03, pH8.0 and 7.5 possess better corrosion resistance than that of the other deposits and the Ni-Fe-P deposits did not form passive films in this environment. In 5.0 wt pct NaOH solution, the Ni-Fe-P deposits have better corrosion resistance and formed passive films.

Polarization properties of porous anodic alumina with Y-branched Cu nanowires

Porous anodic alumina （PAA） templates with branch structure are fabricated by the two-step anodic oxidation processes, and then the Y-branched Cu nanowires are synthesized in the templates using an alternating current （AC） deposition method. We observe the morphology image of the samples by scanning electron microscopy （SEM）, and measure the transmission spectrum and the polarization spectrum of the samples by the spectrophotometer. The results show that PAA films with Y-branched Cu nanowires have better transmittance in the near infrared region. An extinction ratio of 15 - 18 dB and an insertion loss of 0.1 - 0.4 dB are obtained in this region. Therefore PAA with Y-branched Cu nanowires can be used as a near-infrared micropolarizer, and this kind of micropolarizer would have a promising future in the field of photoelectricity integration.

Enhancing oxide scale growth and adhesion via electrochemically regulating ion diffusion

Pre-oxidation is a common surface treatment approach to enhance the corrosion resistance of met-als,which suffers from slow ion diffusion kinetics,bad oxide scale adhesion,and weak compactness.Herein,we propose an electrochemical oxidation approach in molten carbonate to improve the oxide scale growth and adhesion via electrochemically regulating ion diffusion in the formed oxide scale.An anodic polarization applied at the metal substrate enlarges the chemical potential gradient of oxygen and offers a favorable electric field across the metal/oxide interface to the oxide scale/molten salt interface,thereby speeding up the oxide scale growth rate in terms of increasing the diffusion rate of metal cations and oxygen ions through the oxide scale.At the same time,the oxide scale adhesion is remarkedly im-proved because the metal vacancies at the oxide/alloy interface are filled by the newly formed oxide.After being treated by electrochemical oxidation,the corrosion rate of the Ni-16Fe-4Mo alloys in molten Li_(2) CO_(3)-Na_(2) CO_(3)-K_(2) CO_(3) decreased ten-fold.Overall,electrochemical oxidation enables the rapid formation of an adherent and corrosion-resistant oxide scale on the metal substrate,offering a general and effective way to fabricate corrosion-resistant films to survive in various aggressively corrosive media.

Electrochemical Behavior and Microstructure of Recyclable Aluminiummagmesium Alloy Hot-dip Coating Deposited on Low Carbon Steel Substrates

With the abundance and good corrosion resistance of aluminium, hot-dip technique was used to prepare the recycled Al with 8.2 mass% Mg alloy coating on low carbon steel substrates. Electrochemical behavior of this coating was investigated by an- odic polarization and open circuit potential measurement. Its microstructure and composition were observed by scanning electron microscope and energy-dispersive X-ray spectrometry, respectively. The long lasting corrosion performance of coated steels was in- vestigated under the salt fog spray test. From anodic polarization curves and open circuit potential, recycled Al with 8.2 mass% Mg coating performed adequate sacrificial ability. At 0.40 V, current density of recycled Al with 8.2 mass% Mg alloy coating was about 200 000 times higher than that of pure recycled Al coating, and was about 0.5 times lower than that of Zn coating. The microstruc- ture of recycled Al with 8.2 mass% Mg alloy coating on the steel substrate consisted ofAl3Mg2, Al-Fe intermetallic compound and Al matrix. The results from salt fog spray test showed that recycled Al with 8.2 mass% Mg alloy coated steel had similar corrosion resistance ability to Zn coated steel.