Electrochemical investigation of the anode processes in LiF–NdF_3 melt with low oxygen content

The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper. Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF–NdF_3 melt after a lengthy period of pre-electrolysis purification at 1000°C(during which the oxygen content reduced from 413 to 150 mg/kg). The oxidation process of oxygen ions was found to have two stages: oxidation product adsorption and CO/CO_2 gas evolution. The adsorption stage was controlled by diffusion, whereas the gas evolution was controlled by the electrochemical reaction. In comparison with oxygen content of 413 mg/kg, the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred. Fluorine-ion oxidation peaks that occurred at about 4.2 V vs. Li/Li+ could be clearly observed in the reverse scanning processes, in which fluorine ions were oxidized and perfluorocarbons were produced, which resulted in an anode effect.     

Mechanism of electrochemical evolution of chlorine and oxygen at Ti/SnO2-IrO2 anode

The mechanisms of chlorine and oxygen electrochemical evolution at a novel Ti/SnO₂-IrO₂ anode were investigated using cyclic voltammetry and steady state current?potential measurements. For this study a laboratory constructed model cell was employed. Firstly, controlled potential electrolysis of 0.1 mol/L NaCl was performed and chlorine was observed to evolve at potential +1.2 V. The pH values of the solution decreased during electrolysis over the potential range of +1.0 V?+2.0 V, suggesting that oxygen evolution may involve in the reactions. Electrolysis with a de?oxygenated NaCl solution at a fixed potential of +2.0 V confirmed that O2 is one of the products generated at the anode. Further electrolysis of NaCl solution was conducted under steady state conditions. A potential?current density plot was constructed over the potential range of +1.00 V?+1.28 V. The slope of the plot at Tafel section was found to be 41 mV/decade. These results indicate that chlorine evolution at the anode is achieved via an intermediate layer formed by electrosorption of oxygen and chlorine on the electrode surface.     

Co-oxidation of arsenic(Ⅲ) and iron(Ⅱ) ions by pressurized oxygen in acidic solutions

The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200℃ and an oxygen pressure up to 2.0 MPa. Fe(Ⅱ) ions in the solutions did have a catalysis effect on the oxidation of As(Ⅲ), possibly attributable to the production of such strong oxidants as hydroxyl free radicals(OH·) and Fe(IV) in the oxidation process of Fe(Ⅱ). The effects of such factors as the initial molar ratio of Fe(Ⅱ)/As(Ⅲ), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(Ⅲ) and Fe(Ⅱ) were studied. It was found that the oxidation of As(Ⅲ) was limited in the co-oxidation process due to the accumulation of the As(Ⅲ) oxidation product, As(V), in the solutions.     

在酸性溶液中加压氧化三价砷离子和二价铁离子

The co-oxidation of As(III) and Fe(II) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and 2.0 MPa at a temperature of 150°C. It was confirmed that without Fe(II) ions, As(III) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200°C and an oxygen pressure up to 2.0 MPa. Fe(II) ions in the solutions did have a catalysis effect on the oxidation of As(III), possibly attributable to the production of such strong oxidants as hydroxyl free radicals (OH·) and Fe(IV) in the oxidation process of Fe(II). The effects of such factors as the initial molar ratio of Fe(II)/As(III), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(III) and Fe(II) were studied. It was found that the oxidation of As(III) was limited in the co-oxidation process due to the accumulation of the As(III) oxidation product, As(V), in the solutions.     

pH值对β-MnO2颗粒光催化去除银离子的影响

The presence of silver ions (Ag(I)) in wastewater has a detrimental effect on living organisms. Removal of soluble silver, especially at low concentrations, is challenging. This paper presents the use of β-MnO₂ particles as a photocatalyst to remove Ag(I) ions selectively from aqueous solution at various pH levels. Inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), field emission electron microscope (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron microscopy (XPS) were employed to determine the removal efficiency and to characterize the deposition of silver onto the surface of β-MnO₂ particles. The optimum pH for the removal of Ag(I) ions was at pH 4 with 99% removal efficiency under 1 h of visible light irradiation. This phenomenon can be attributed to the electrostatic attraction between β-MnO₂ particles and Ag(I) ions as well as the suppression of electron–hole recombination in the presence of H+ ions.     

不同温度下CeO2预煅烧对甲醇氧化反应中Pt/CeO2–C电催化剂性能的影响

Pt/CeO₂–C catalysts with CeO₂ pre-calcined at 300–600°C were synthesized by combining hydrothermal calcination and wet impregnation. The effects of the pre-calcined CeO₂ on the performance of Pt/CeO₂–C catalysts in methanol oxidation were investigated. The Pt/CeO₂–C catalysts with pre-calcined CeO₂ at 300–600°C showed an average particle size of 2.6–2.9 nm and exhibited better methanol electro-oxidation catalytic activity than the commercial Pt/C catalyst. In specific, the Pt/CeO₂–C catalysts with pre-calcined CeO₂ at 400°C displayed the highest electrochemical surface area value of 68.14 m2·g?1 and I_f/I_b ratio (the ratio of the forward scanning peak current density (I_f) and the backward scanning peak current density (I_b)) of 1.26, which are considerably larger than those (53.23 m2·g?1 and 0.79, respectively) of the commercial Pt/C catalyst, implying greatly enhanced CO tolerance.     

Cyclic oxidation behavior of b-NiAlDy alloys containing varying aluminum content at 1200 1C

b-NiAlDy cast alloys containing varying aluminum content were prepared by arcmelting. The microstructures and cyclic oxidation behavior of the alloys at 1200 1C were investigated. Grain refinement was achieved by increasing aluminum content in the alloy, which is beneficial to selective oxidation. The Ni–55Al–0.1Dy alloy showed excellent cyclic oxidation resistance due to the formation of a continuous, dense and slow-growing oxide scale. In contrast to this, severe internal oxidation as well as large void formation at the scale/alloy interface occurred in the Ni–45Al–0.1Dy alloy. The aluminum content dependence of the reactive element effects in b- NiAlDy was established that Dy doping strengthened the scale/alloy interface by pegging mechanism in high-aluminum alloys but accelerated internal oxidation in low-aluminum alloys during high-temperature exposure.     

Effect of different atmospheres on dry friction behavior of steel sliding against brass at high speed

The atmosphere components have an influence on tribological behaviors of tribo-pairs. Through changing the atmosphere component, the effect of atmosphere component on the tribological behaviors of CrNiMo steel against brass at high sliding velocity was investigated. The wear test was carried out on a high-speed friction and wear test rig whose test atmosphere could be controlled. The tests were performed at four sliding velocities （30, 40, 50, 60 m/s）, one contact pressure （1.33 MPa） and two atmosphere components （N2 or O2）. The morphologies of the worn surfaces of various pins were observed with a scanning electron microscope. The chemical compositions of the surfaces and subsurfaces for steels were determined with an energy dispersion spectroscopy. The results showed that the wear rate of the steel pins were low all the time with the sliding velocity increasing in oxygen atmosphere, and that the wear rate of the steel pin in nitrogen atmosphere was higher than that of the steel pin in oxygen atmosphere. It was found that the thin and compact oxidation layer formed on the worn surface of the steel in oxygen atmosphere played a key role in wear resistance. However, the wear rate of the steel pin increased rapidly with the sliding velocity increasing in nitrogen atmosphere, which was attributed to the thick and loose surface layer formed on the worn surface of the steel.     

Properties of a new type Al/Pb-0.3%Ag alloy composite anode for zinc electrowinning

An Al/Pb-0.3%Ag alloy composite anode was produced via composite casting. Its electrocatalytic activity for the oxygen evolution reaction and corrosion resistance was evaluated by anodic polarization curves and accelerated corrosion test, respectively. The microscopic morphologies of the anode section and anodic oxidation layer during accelerated corrosion test were obtained by scanning electron microscopy. It is found that the composite anode (hard anodizing) displays a more compact interfacial combination and a better adhesive strength than plating tin. Compared with industrial Pb-0.3%Ag anodes, the oxygen evolution overpotentials of Al/Pb-0.3%Ag alloy (hard anodizing) and Al/Pb-0.3%Ag alloy (plating tin) at 500 A·m?2 were lower by 57 and 14 mV, respectively. Furthermore, the corrosion rates of Pb-0.3%Ag alloy, Al/Pb-0.3%Ag alloy (hard anodizing), and Al/Pb-0.3%Ag alloy (plating tin) were 13.977, 9.487, and 11.824 g·m?2·h?1, respectively, in accelerated corrosion test for 8 h at 2000 A·m?2. The anodic oxidation layer of Al/Pb-0.3%Ag alloy (hard anodizing) is more compact than Pb-0.3%Ag alloy and Al/Pb-0.3%Ag alloy (plating tin) after the test.     

Isothermal oxidation behavior and mechanism of a nickel-based superalloy at 1000℃

The oxidation behavior of a nickel-based superalloy at 1000℃ in air was investigated through X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analysis. A series of oxides, including external oxide scales (Cr₂O₃, (TiO₂ + MnCr₂O₄)) and internal oxides (Al₂O₃,TiN), were formed on the surface or sub-surface of the substrate at 1000℃ in experimental still air. The oxidation resistance of the alloy was dependent on the stability of the surface oxide layer. The continuity and density of the protective Cr₂O₃ scale were affected by minor alloying elements such as Ti and Mn. The outermost oxide scale was composed of TiO₂ rutile and MnCr₂O₄ spinel, and the growth of TiO₂ particles was controlled by the outer diffusion of Ti ions through the pre-existing oxide layer. Severe internal oxidation occurred beneath the external oxide scale, consuming Al and Ti of the strength phase γ' (Ni₃(Al,Ti)) and thereby severely deteriorating the surface mechanical properties. The depth of the internal oxidation region was approximately 35 μm after exposure to experimental air at 1000℃ for 80 h.     

Effects of oxygen content on the oxidation process of Si-containing steel during anisothermal heating

The oxidizing behavior of Si-containing steel was investigated in an O₂ and N₂ binary-component gas with oxygen contents ranging between 0.5vol% and 4.0vol% under anisothermal-oxidation conditions. A simultaneous thermal analyzer was employed to simulate the heating process of Si-containing steel in industrial reheating furnaces. The oxidation gas mixtures were introduced from the commencement of heating. The results show that the oxidizing rate remains constant in the isothermal holding process at high temperatures; therefore, the mass change versus time presents a linear law. A linear relation also exists between the oxidizing rate and the oxygen content. Using the linear regression equation, the oxidation rate at different oxygen contents can be predicted. In addition, the relationship between the total mass gain and the oxygen content is linear; thus, the total mass gain at oxygen contents between 0.5vol%-4.0vol% can be determined. These results enrich the theoretical studies of the oxidation process in Si-containing steels.     

Effect of Y_2O_3 content in the pack mixtures on microstructure and oxidation resistance of B–Y modified silicide coating

B–Y modified silicide coatings were prepared on Nb–Si based alloy by pack cementation at 1300 ℃ for 10 h. The effect of Y_2O_3 content in the pack mixtures on microstructure and oxidation resistance of the coatings was investigated. The results show that the four coatings have similar structures, which possess a(Nb,X)Si_2 outer layer and a(Nb,X)_5Si_3 transitional layer. Y_2O_3 content in the pack mixtures has an obvious effect on the Si content in the coating. The mass gains of the coatings prepared with 0.5, 1, 2 and 3 wt% Y_2O_3 in pack mixtures are 2.33, 1.96, 2.05 and 2.86 mg/cm~2 after oxidation at 1250 ℃ for 100 h, respectively. The coating prepared with 1 wt% Y_2O_3 exhibits the best oxidation resistance due to the formation of a dense glass-like borosilicate scale.     

Comparison of corrosion and oxygen evolution behaviors between cast and rolled Pb–Ag–Nd anodes

The corrosion and oxygen evolution behaviors of cast and rolled Pb–Ag–Nd anodes were investigated by metalloscopy, environmental scanning electron microscopy, X-ray diffraction analysis, and various electrochemical measurements. The rolled anode exhibits fewer interdendritic boundaries and a dispersed distribution of Pb–Ag eutectic mixtures and Nd-rich phases in its cross-section. This feature inhibits rapid interdendritic corrosion into the metallic substrate along the interdendritic boundary network. In addition, the anodic layer formed on the rolled anode is more stable toward the electrolyte than that formed on the cast anode, reducing the corrosion of the metallic substrate during current interruption. Hence, the rolled anode has a higher corrosion resistance than the cast anode. However, the rolled anode exhibits a slightly higher anodic potential than the cast anode after 72 h of galvanostatic polarization, consistent with the larger charge transfer resistance. This larger charge transfer resistance may result from the oxygen-evolution reactive sites being blocked by the adsorption of more intermediates and oxygen species at the anodic layer/electrolyte interfaces of the rolled anode than at the interfaces of cast anode.     

单斜相SrAl2Si2O8陶瓷的烧结及其对Sr的固化

Monoclinic SrAl₂Si₂O₈ ceramics for Sr immobilization were prepared by a liquid-phase sintering method. The sintering temperature, mineral phase composition, microstructure, flexural strength, bulk density, and Sr ion leaching characteristics of the SrAl₂Si₂O₈ ceramics were investigated. A crystalline monoclinic SrAl₂Si₂O₈ phase formed through liquid-phase sintering at 1223 K. The introduction of four flux agents (B₂O₃, CaO·2B₂O₃, SrO·2B₂O₃, and BaO·2B₂O₃) to the SrAl₂Si₂O₈ ceramics not only reduced the densification temperature and decreased the volatilization of Sr during high-temperature sintering but also impacted the mechanical properties of the ceramics. Product consistency tests showed that the leaching concentration of Sr ions in the sample with flux agent B₂O₃ was the lowest, whereas that of Sr ions in the sample with flux agent BaO·2B₂O₃ was the highest. These results show that the leaching concentration of Sr ions depends largely on the amorphous phase in the ceramics. Meanwhile, the formation of mineral analog ceramics containing Sr is an important factor to improve Sr immobilization.     

气体扩散层集流体对Ni(OH)2纳米结构电化学性能的影响

We report the electrochemical performance of Ni(OH)₂ on a gas diffusion layer (GDL). The Ni(OH)₂ working electrode was successfully prepared via a simple method, and its electrochemical performance in 1 M NaOH electrolyte was investigated. The electrochemical results showed that the Ni(OH)₂/GDL provided the maximum specific capacitance value (418.11 F·g?1) at 1 A·g?1. Furthermore, the Ni(OH)₂ electrode delivered a high specific energy of 17.25 Wh·kg?1 at a specific power of 272.5 W·kg?1 and retained about 81% of the capacitance after 1000 cycles of galvanostatic charge–discharge (GCD) measurements. The results of scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed the occurrence of sodium deposition after long-time cycling, which caused the reduction in the specific capacitance. This study results suggest that the light-weight GDL, which can help overcome the problem of the oxide layer on metal–foam substrates, is a promising current collector to be used with Ni-based electroactive materials for energy storage applications.     

Copper Adsorption on Olivine

Copper adsorption on olivine supplied by the A/S Olivine Production Plant at Aheim in western Norway was studied. The factors were evaluated which affect the uptake of copper. It is shown that the equilibrium pH of aqueous solution has the greatest influence on copper adsorption thanks to the competitive adsorption between proton and copper ions, and the adsorption of copper to olivine increases rapidly with pH increasing from 4 to 6. Moreover, initial copper concentration and olivine dose possess significant effect on copper adsorption, for the adsorption rate of copper increases with olivine dose increasing or initial copper concentration decreasing at the same pH. In addition, the ionic strength effect on the adsorption was also investigated, but it owns little effect on the adsorption process of copper due to the formation of inner sphere adsorption of copper on olivine. The experimental data show that olivine has a high acid buffer capacity and is an effective adsorbent for copper.     

Annealing temperature-dependent electrochemical properties of Aeroxide P25 TiO_2 nanoparticles as anode material for lithium storage

TiO_2 has been widely studied as an important electrode material for electrochemical energy storage.Understanding its relationship between textural properties and electrochemical characteristics is essential to boosting its practical performances. Herein, Aeroxide P25 TiO_2 nanoparticles annealing at different temperatures(400–600 °C) were investigated as an anode material of lithium ion battery. Their evolution in crystal phase and microstructural characteristics were characterized by XRD and BET surface analysis, and their lithium storage properties in half-cells were evaluated by various electrochemical analyses, including cyclic voltammetry, cycling testing, and electrochemical impedance spectroscopy. It was found that the lithium storage properties were critically dependent on the size of TiO_2 anode materials. Pristine P25 initially exhibited the highest initial discharge specific capacity due to its smallest particle size; however, rapid capacity loss occurred during extended cycling. The annealing process was found to effectively enhance the cycling stability of TiO_2 although possessing a large particle size and smaller surface area. Typically, P400 showed the best performances in cycling stability, capacity retention ratio, and rate capability, which is mainly attributed to the synergistic effect of high crystallinity, reasonable particle size, and less internal resistance. This study provides an instance of optimizing the textural properties of metal oxides for advanced LIB anode material applications.     

AISI 321不锈钢钢钢包精炼过程中钙含量对夹杂物的影响

The effect of three heat processes with different calcium contents on the evolution of inclusions during the ladle furnace refining process of AISI 321 stainless steel was investigated. The size, morphology, and composition of the inclusions were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. After the addition of aluminum and titanium, the primary oxide in the AISI 321 stainless steel was an Al₂O₃–MgO–TiO_x complex oxide, in which the mass ratio of Al₂O₃/MgO was highly consistent with spinel (MgO·Al₂O₃). After calcium treatment, the calcium content in the oxide increased significantly. Thermodynamic calculations show that when the Ti content was 0.2wt%, the Al and Ca contents were less than 0.10wt% and 0.0005wt%, respectively, which was beneficial for the formation of liquid inclusions in molten steel. Moreover, the modification mechanism of calcium on TiN-wrapped oxides in combination with temperature changes was discussed.     

硫酸溶液中IrO2–ZrO2二元氧化物涂层的电化学行为及耐蚀性

In this study, we prepared Ti/IrO₂–ZrO₂ electrodes with different ZrO₂ contents using zirconium-n-butoxide (C₁₆H₃₆O₄Zr) and chloroiridic acid (H₂IrCl₆) via a sol–gel route. To explore the effect of ZrO₂ content on the surface properties and electrochemical behavior of electrodes, we performed physical characterizations and electrochemical measurements. The obtained results revealed that the binary oxide coating was composed of rutile IrO₂, amorphous ZrO₂, and an IrO₂–ZrO₂ solid solution. The IrO₂–ZrO₂ binary oxide coatings exhibited cracked structures with flat regions. A slight incorporation of ZrO₂ promoted the crystallization of the active component IrO₂. However, the crystallization of IrO₂ was hindered when the added ZrO₂ content was greater than 30at%. The appropriate incorporation of ZrO₂ enhanced the electrocatalytic performance of the pure IrO₂ coating. The Ti/70at%IrO₂–30at%ZrO₂ electrode, with its large active surface area, improved electrocatalytic activity, long service lifetime, and especially, lower cost, is the most effective for promoting oxygen evolution in sulfuric acid solution.     

New insights into the effects of silicon content on the oxidation process in silicon-containing steels

Simultaneous thermal analysis (STA) was used to investigate the effects of silicon content on the oxidation kinetics of silicon- containing steels under an atmosphere and heating procedures similar to those used in industrial reheating furnaces for the production of hot-rolled strips. Our results show that when the heating temperature was greater than the melting point of Fe₂SiO₄, the oxidation rates of steels with different silicon contents were the same; the total mass gain decreased with increasing silicon content, whereas it increased with increasing oxygen content. The oxidation rates for steels with different silicon contents were constant with respect to time under isothermal conditions. In addition, the starting oxidation temperature, the intense oxidation temperature, and the finishing oxidation temperature increased with increasing silicon content; the intense oxidation temperature had no correlation with the melting of Fe₂SiO₄. Moreover, the silicon distributed in two forms: as Fe₂SiO₄ at the interface between the innermost layer of oxide scale and the iron matrix, and as particles containing silicon in grains and grain boundaries in the iron matrix.