Effect of scandium doping on the oxidation resistance of Zn5Al and Zn55Al alloys

The influence of scandium on the oxidation kinetics of Zn5Al and Zn55Al alloys is studied. It is observed that small additions (0.005–0.05 wt %) of Sc substantially improve the oxidation resistance of zincaluminium alloys.     

An Effect of Nickel Additives on Anode Behavior of Zinc-Aluminum Alloys Zn5Al,Zn55Al in NaCl Electrolyte

Russian Journal of Applied Chemistry - The results of studying the anodic behavior of Zn5Al, Zn55Al alloys doped with nickel in a NaCl electrolyte are presented. It was found that nickel additives...     

Anodic behavior and oxidation of the thallium alloyed Al + 2.18% Fe alloy

A study of the corrosion-electrochemical and thermal properties of the thallium-alloyed Al + 2.18% Fe alloy demonstrated that the corrosion potential of the alloy can be raised and the heat conductivity be improved.     

Anodic behavior of aluminum-zirconium alloys microalloyed with strontium and cerium

The potentiodynamic method was used to study in solutions of 3% NaCl and 0.01 N NaOH the corrosion-electrochemical behavior of aluminum alloyed with zirconium, strontium, and cerium.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1295–1298.Original Russian Text Copyright © 2004 by Ganiev, Barotov, Inoyatov.     

Oxidation behavior of mechanically alloyed chromium based alloys

The oxidation of chromium and chromium based alloys with yttria additions of 0.5 to 4 wt.%, processed by mechanical alloying, was investigated. Additionally, the effect of milling time on the oxidation behavior was examined. The samples were oxidized at 950°C in air. Weight changes, optical microscopy and SEM were utilized to characterize the oxidation behavior. Although it appeared that the presence of yttria reduced the oxidation rates significantly, the exact concentration of yttria was far less essential for the oxidation properties than the yttria distribution.Therefore the oxidation resistance of ODS (oxide dispersion strengthened) alloys strongly depends on the exact manufacturing process.     

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.     

Electrodeposition behavior of Mg with Zn from acidic sulfate solutions

Electrodeposition of Mg with Zn in acidic sulfate solutions with polyethylene glycol and octadecyl dimethyl benzyl ammonium chloride as additives was investigated by scanning electron microscopy, X-ray diffraction, and potentiodynamic polarization techniques. The results show that these two compounds act in a synergetic way to suppress Zn deposition markedly and facilitate Mg reduction. Zn–0.46%Mg coatings are produced under high cathodic current densities, which have lower corrosion potentials than Zn coatings and hydrogen evolution in neutral chloride solutions. Magnesium hydroxide may cause current oscillations at high cathodic polarizations in plating solutions without zinc salts due to its formation and peel-off. An “induced co-deposition” mechanism is proposed for Zn–Mg alloy electrodeposition.     

Anodic behavior of tungsten in water—organic solutions of sodium chloride

The anodic behavior of tungsten in water-amino alcohol solutions of sodium chloride is studied potentiostatically and potentiodynamically on a rotating disk electrode. The introduction of monoethanol amine (MEA) into an aqueous NaCl solution leads to anodic activation of tungsten. From the dependence of the current density on the disk electrode rotation rate, it is determined that the anodic dissolution obeys the diffusion kinetics equations. The delivery of MEA molecules to the electrode is the slow stage of the reaction. The dissolution rate and the tungsten surface quality after the treatment are the highest at 6 M MEA. The effect of physicochemical properties of solutions on the anodic reaction is shown     

Oxidation behavior of rare earth oxide-coated Fe20Cr and Fe20Cr5Al alloys

This article presents the influence of surface additions of nanocrystalline rare earth (RE) oxides CeO₂, La₂O₃, and CeO₂ + La₂O₃ on the isothermal oxidation behavior of Fe20Cr and Fe20Cr5Al at 1000 °C. Thermogravimetric studies revealed parabolic kinetics in all cases and the scale thickness on specimen surfaces varied with the nature of RE oxide. The oxidation resistance of specimens coated with two RE oxides was significantly higher than those coated with either one of the two oxides. The marked increase in the oxidation resistance of the alloys coated with two RE oxides is due to optimization of RE ion radius and RE oxide grain size/shape.     

Anodic behavior of nickel-based alloys in the electrolytic production of NF3

The Ni-based alloys, such as Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si, prepared by hot isostatic pressing (HIP) at 1000 °C under 2 × 10⁸ Pa for 2 h were employed as the anodes for electrolytic production of NF₃. The current efficiencies for NF₃ formation were 42-38, 52-40, 52-47, 63-62, 50 and 41% for Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloys, respectively. The current efficiencies only on Ni-Cu alloys with Cu concentrations lower than 10 mol% were almost the same as those on Ni sheet and HIPed Ni anodes, whereas those on the other alloys used in this study were smaller compared with those on both Ni anodes. On the other hand, the current losses caused by anodic dissolution of Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloy electrodes were 7.95-4.42, 6.40-7.02, 5.60-6.30, 3.34-6.33, 5.10 and 0.18%, respectively. The anode consumptions of Ni-5 mol% Cu and Ni-5 mol% Si alloys were almost the same or smaller compared with those of Ni sheet and HIPed Ni electrodes, though those of other alloys used were large compared with those of both Ni anodes. Consequently, addition of Cu to the nickel matrix is available for a cheaper cost of anode with keeping a same current efficiency as that on the Ni anode and addition of Si to the nickel matrix is effective for decreasing anode consumption largely. A Ni sheet electrode containing a trace of impurities, such as Co, Mn, Ag and Al, is also favorable as the anode for electrolytic production of NF₃.     

Electrochemical corrosion behavior of nanocrystalline zinc coatings in 3.5% NaCl solutions

The corrosion behavior of electrodeposited nanocrystalline (NC) zinc coatings with an average grain size of 43 nm was investigated in 3.5% NaCl solutions in comparison with conventional polycrystalline (PC) zinc coatings by using electrochemical measurement and surface analysis techniques. Both polarization curve and electrochemical impedance spectroscopy (EIS) results indicate that NC and PC coatings are in active state at the corrosion potentials, and NC coatings have much higher corrosion resistance than PC ones. The corrosion products on both coating surfaces are mainly composed of ZnO and Zn₅(OH)₈Cl₂·H₂O, but the corrosion products can form a relatively more protective layer on NC coating surfaces than on PC coatings. The EIS characteristics and corrosion processes of PC and NC zinc coatings during 330 h of immersion were discussed in detail.     

Anodic behavior of gold in acid thiourea solutions: A cyclic voltammetry and quartz microgravimetry study

It is shown that at potentials E < 0.5 V (NHE) gold undergoes practically no dissolution in thiourea solutions containing no catalytically active species. The dissolution at a perceptible rate (> 100 μA cm^?2) starts at E ≥ 0.65 V, with the primary process being the oxidation of thiourea, which gives rise a current peak at E ? 1.0 V. The thiourea oxidation at E ≥ 1.1 produces the appearance of catalytically active species, which drastically accelerate the gold dissolution process in the potential region extending from a steady-state value to 0.6 V, where the current efficiency for gold approaches 100% and a peak emerges at E ? 0.55 V. The peak’s height is commensurate with the value of the limiting diffusion current associated with the ligand supply. The species in question make no discernible impact on the thiourea oxidation process. Formamidine disulfide, which forms during the anodic oxidation of thiourea or which is added in solution on purpose, exerts no noticeable catalytic influence on the anodic gold dissolution. The catalytically active species is presumably the S^2? ion, product of decomposition and deep oxidation of thiourea and formamidine disulfide. Indeed, adding sulfide ions in solution has a strong catalytic effect on the gold dissolution, whose character is identical to that of the effect exerted by products of anodic oxidation of thiourea at E ≥ 1.1 V μA cm^?2.     

Synthesis of Al Nanopowders in an Anodic Arc

Nanopowders of metals and metal oxides have been produced using an arc operated between a refractory rod anode and a hollow cathode (J. Haidar in A method and apparatus for production of material vapour, Australian Patent No. 756273, 1999). the arc attachment to the anode is through a small region of molten metal located at the tip of the rod anode. Heat from the arc evaporates the molten metal and the vapour is passed through the arc plasma before condensing into sub-micron particles downstream of the cathode. A precursor metal is continuously fed onto the tip of the anode to maintain the molten metal region and compensate for losses of materials due to evaporation. The particle size of the produced powder depends on the pressure in the arc chamber and for production of nanoparticles in the range below 100 nm we use a pressure of 100 torr. Aluminium has been used as a precursor material, leading to production of aluminium metal nanopowders when the arc is operated in argon and to aluminium oxide nanopowders for operation in air. For operation in air, the products are made of γ-Al₂O₃.     

Preparation and phase composition of Ta2O5:Zn alloys having low Zn2+ concentrations

Methods were developed for preparing Ta₂O₅:Zn alloys containing less than 3 wt % Zn²⁺ for the purpose of using them further in preparing lithium tantalate batches and growing from them single crystals having improved properties. A method where zinc is doped directly into a tantalum-containing back-extract followed by precipitation of tantalum and zinc hydroxides with ammonia is confined to a Zn²⁺ concentration of 1.7 wt % in Ta₂O₅; at higher concentrations, Zn²⁺ forms soluble ammine complexes. A method where Zn²⁺ is extracted by high-purity tantalum hydroxide is applicable within the range of Zn²⁺ concentrations studied. Optimal conditions were found for preparing Ta₂O₅:Zn²⁺ alloys of various compositions. X-ray powder diffraction and IR spectroscopy were used to study the phase composition of the alloys synthesized, and Zn²⁺ concentrations were determined at which a ZnTa₂O₆ phase was formed along with the major Ta₂O₅ phase.     

Anodic corrosion of gold in solutions of diaminoalkanes

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Interactions of DL-serine and L-serine with NaCl and KCl in aqueous solutions

The activity coefficients at 25‡C of DL-serine and L-serine in aqueous solutions of NaCl and KC1 were measured. This study examines the effect of the nature of the cation of the electrolyte on the activity coefficients of the optical-isomers of serine in aqueous solutions for molality of serine up to 0.4 and molality of electrolyte up to 1. An electrochemical cell with two ion-selective electrodes, a cation, and an anion ion selective electrode,vs. a double-junction reference electrode was used to measure the activity coefficients of the electrolyte and the results were converted to the activity coefficients of serine in the aqueous electrolyte solution. The comparison of the results obtained for DL- and L-serine indicates that the two optical isomers have identical interactions with electrolytes in aqueous solutions and that for this amino acid the effect of the cation of the electrolyte is not significant. Comparison of these results with previous measurements for DL-alanine in aqueous solutions of the same electrolytes show the notable effect of the backbone of the amino acid.     

Anodic passivation of tin in sodium hydroxide solutions

The passivating processes at a tin anode in NaOH solutions have been investigated by voltammetry. The effects of varying sweep rate, rotation speed, concentration of NaOH and the potential limits have been studied. The results indicate that primary passivation is the results of a dissolution—precipitation mechanism involving the blocking of the electrode by Sn(II) species. There is evidence that during secondary passivation there is not only oxidation of Sn(II) to Sn(IV) species but alos the direct oxidation of Sn to Sn(IV) solution soluble species. At more positive potentials dehydration of the film may occur and result in a more efficient passivation. A possible explanation is advanced for observed current oscillations.     

不同锌铝比水滑石的合成及吸附脱除水中邻苯二甲酸性能的研究

采用共沉淀法合成一系列具有不同锌铝比的水滑石,并利用X射线衍射（XRD）、扫描电镜（SEM）、热重（TG）、氮气吸脱附及电感耦合等离子体质谱（ICP-MS）等表征手段对其结构与组成进行了测试。将上述水滑石材料用于吸附脱除水中邻苯二甲酸污染物,考察了不同锌铝比水滑石吸附邻苯二甲酸性能的差异。结果表明,在较低锌铝比时,随着水滑石锌铝比的增加,其对邻苯二甲酸的吸附量逐渐增大;当锌铝比较大时（>6）,随着锌铝比的增加,水滑石的吸附量基本保持不变。进一步选取锌铝比为6的水滑石,分别对其吸附邻苯二甲酸的动力学和热力学进行了研究,发现其吸附等温线和吸附动力学数据分别符合Freundlich等温吸附模型和准二级动力学模型,且循环吸附性能较好。