Enhanced hydrogen entry into iron from 0.1 M NaOH at definite potentials

This work aimed at explaining the enhancement of hydrogen entry into iron from alkaline solution occurring at definite potentials. Hydrogen permeation rate (HPR) through a 35-μm thick iron membrane was measured with the electrochemical technique in 0.1 M NaOH at 25 °C during cathodic and anodic polarizations. Enhanced HPR was observed at potentials of oxide reduction or iron oxidation, and potentials more cathodic than about −1.65 V_NHE during prolonged galvanostatic polarization. XPS analysis showed that after the polarization, surface layers contained hydrated iron oxides and that amount of these products increased with the polarization time. It is suggested that the enhanced hydrogen entry can be explained by acidification of the near-metal solution due to iron oxidation and/or oxide reduction, and probably by a promoting effect of some Fe-O species. It is proposed that these effects are associated with surface layers. They can affect hydrogen entry as a source of protons in the oxide reduction, as a diffusion barrier making the near-metal acidification possible, and as a resistance causing an IR drop. Strong enhancement of HPR after prolonged galvanostatic polarizations can be associated with the formation of thick surface layers with IR drop enabling anodic oxidation of iron under these layers.     

Accelerated entry of hydrogen into iron from NaOH solutions at low cathodic and low anodic polarisations

Hydrogen entry into iron from NaOH solutions and from 0.05 M H₂SO₄ during voltammetric cycling was studied with the electrochemical permeation technique. Measurements were carried out on 35-μm thick membranes at 25 °C. Accelerated entry of hydrogen was revealed by peaks of hydrogen permeation rate (HPR) which occurred at low cathodic and low anodic polarisations in NaOH solutions, but not in 0.05 M H₂SO₄. In cathodic scans the HPR peak occurred at potentials of an oxide reduction, probably of Fe₃O₄ to Fe(II), whereas in anodic scans this peak appeared at potentials of the oxidation of iron to Fe(II) and to Fe₃O₄, and it was distinct especially at high scan rates. X-ray photoelectron spectroscopy (XPS) surface analysis indicated that the fraction of Fe₃O₄ in the surface film during cathodic scans was at the potential of HPR peak significantly larger than that at a nobler potential. It is suggested that the occurrence of HPR peaks can be due to a partial removal of surface layers and to the formation of species promoting the hydrogen entry, supposedly Fe₃O₄ without or with Fe(II). Possibly, these species might be effective by hindering the recombination of H_ads or by blocking adsorption sites.     

Effect of anodic prepolarization on hydrogen entry into iron at cathodic potentials in 0.1 M NaOH without and with EDTA or sodium molybdate

Efficiency of cathodes for water electrolysis decreases after shut-downs due to corrosion at open-circuit potential. In the present work the effect of prepolarization at various potentials on hydrogen entry into iron during cathodic potential sweeps was studied by the measurement of the hydrogen permeation rate (HPR) through a 35-μm thick iron membrane in 0.1 M NaOH without and with EDTA or Na₂MoO₄ at 25 °C. Two types of the enhanced hydrogen entry at low cathodic polarizations were distinguished: one after prepolarization at low cathodic or low anodic potentials, and another after prepolarization at high anodic potentials. It is suggested that both types can be explained by acidification at the metal surface, the former due to anodic oxidation of iron, and the latter due to cathodic reduction of oxide layer (mainly of Fe₃O₄). XPS analysis revealed the presence of hydrated Fe-O species of unidentified valence. EDTA and Na₂MoO₄ increased the efficiency of hydrogen entry (j_H/j_c ratio), and molybdates also strongly increased cathodic currents of HER. Some of the effects of these additives can be explained in terms of their effect on surface layers.     

Hydrogen entry into iron after potential jumps from cathodic to anodic polarization in 0.1 M NaOH without and with EDTA or sodium molybdate

Hydrogen can enter into iron or steel during anodic polarization when bare metal is exposed, e.g. during stress corrosion cracking, erosion or friction. The hydrogen permeation rate (HPR) through a 35-μm thick iron membrane was studied with the electrochemical technique in 0.1 M NaOH without and with EDTA or Na₂MoO₄ during cathodic and anodic polarization at 25 °C. Anodic polarization of the bare metal was performed by applying fast jumps of anodic potentials to the cathodically treated surface. The jumps resulted in transients of enhanced HPR which continued to rise despite the starting decay of anodic current. The enhanced HPR can be ascribed to acidification associated with anodic oxidation of iron. It is proposed that the continued rise of HPR during anodic current decay can be explained by the formation of low-protective layers which hinder diffusion of hydrated protons out of the metal surface and thereby increase their concentration at the surface. The enhancement of HPR was strongly decreased by EDTA, but increased by Na₂MoO₄ at noble potentials. It is suggested that these effects can be explained in terms of the thickness and type of low-protective layers.     

动力波洗涤器中碱液吸收低浓CO_2的传质特性

为研究动力波洗涤器内的气液传质特性,在动力波洗涤器中,进行NaOH溶液吸收混合气体中微量CO2气体的吸收实验。参考填料塔中钠碱溶液吸收低浓气体的传质模型,测定了动力波洗涤器中NaOH溶液吸收低浓CO2的气相体积总传质系数KGa及吸收效率η。研究了气相速度、NaOH溶液质量分数及液气比对KGa的影响,结果表明:KGa随着气相速度及NaOH溶液质量分数的增加而增大,但NaOH溶液质量分数小于气相速度对KGa的影响;随着液气比的提高,KGa逐渐减小,η开始随着液气比的提高而增加,但到一定数值后,效果不明显;回归了KGa的准数关联式,并依据液气比对KGa及η的综合评价,提出洗涤管直径为100 mm,NaOH溶液质量分数为10%,液气比操作范围在0.005—0.025时,动力波洗涤器具有较高的综合传质性能,为工业应用提供参考。     

Investigation of hydrogen adsorption-absorption on iron by EIS

This work concerns the interaction between hydrogen and iron in the cathodic potential region. It was motivated by the need for a better understanding of the hydrogen insertion mechanism in metals. Electrochemical deposits of iron with various thicknesses were carried out on a gold substrate and they were characterized by impedance measurements under hydrogen evolution conditions.The processes occurring at the surface and within the iron films deposited on a gold electrode were studied using various electrochemical techniques. The impedance and voltammetric behaviours were strongly dependent on the film thickness. The main result of this study is that the charge transfer resistance increases with the film thickness. A model of the adsorption-absorption of hydrogen into iron films was proposed. It considered two types of absorbed hydrogen in a sublayer richer in hydrogen than the bulk metal. There, the hydrogen transported in the film coexists with another one coming from a direct absorption mechanism and “trapped” in some sites. The two absorbed hydrogen are reversibly exchanged. The interaction of hydrogen with palladium and iron was compared. It was concluded that for iron, the insertion of hydrogen results from a competition between a one-step direct hydrogen absorption mechanism and the classical two-step indirect penetration in the metal via the adsorbed hydrogen. At the end, a possible explanation of the deep penetration of the direct hydrogen absorption in the metal, detected by the impedance analysis, is proposed. It is based on the imperfections of numerous first layers of the deposited metals on polycrystalline gold.     

Effect of organic additives on hydrogen permeation into an iron membrane studied by frequency analysis techniques

The effects of thiourea and benzotriazole on the hydrogen permeation into iron were studied using a Devanathan-Stachurski electrochemical double cell equipped with a thin iron membrane. Hydrogen was cathodically generated on the entry side and fully oxidized on the exit side. The spectral analysis of both the electrochemical impedance on the entry side and the permeation transfer function between the ac current signals on the two faces of the membrane were recorded according to a method recently proposed. The modifications of the impedance diagrams and the transfer function diagrams induced by the presence of the organic additives were interpreted at the light of the mechanistic model of the transfer function which was recently derived. It is concluded that both additives inhibit the hydrogen evolution reaction, but thiourea promotes hydrogen penetration by inhibiting the recombination reaction, whereas benzotriazole adsorption inhibits the formation of the H_ads and therefore their penetration into the metal matrix.     

NaOH改性花生壳对亚甲基蓝染料吸附性能的研究

花生壳用5%的NaOH溶液改性作吸附剂处理亚甲基蓝染料废水,考察pH值、吸附剂投加量、染料浓度和温度及吸附时间对染料吸附性能的影响。结果表明,吸附最佳的工艺条件为:温度25℃,吸附剂投加量0.3 g,亚甲基蓝的初始浓度3.5 g/mL,反应时间135 min,pH值7。此时改性花生壳对亚甲基蓝的吸附率达99.57%。     

Photochemical production of hydrogen from alkaline solution containing polysulfide dyes

Efficient hydrogen production was achieved by irradiating solutions containing polysulfide dyes as a photoabsorber. In the presence of polysulfide only, considerable amount of hydrogen was initially evolved and followed by the rapid decrease of the evolution rate. On the contrary, in the co-presence of NiO_xx< l/TiO₂ and polysulfide, steady evolution of hydrogen was observed even after long period of illumination. The photocatalytic evolution of hydrogen was divided into two stages: i) in the first stage within 1 hour irradiation, the hydrogen evolution rate was abruptly increased due to the conversion of polysulfide to partially oxidized sulfur, S₂O _x ^2- ii) in the secondary stage after 1 hour irradiation, steady evolution of hydrogen was observed due to the conversion of partially oxidized sulfur to fully oxidized sulfur. The oxidation/reduction of sulfur occurred more favorably over SiC catalyst where more steady evolution of hydrogen was achieved. Presented at the Int’l Symp. on Photocatalysis for Energy and Environment (Daejeon, Oct. 19, 2001), and dedicated to Prof. Wha Young Lee on the occasion of his retirement from Seoul National University.     

Urea/NaOH aqueous solution as new solvent of aeromonas gum

Aeromonas (A) gum, an acidic heteropolysaccharide, formed aggregates easily in NaCl aqueous solution. A novel solvent of the A gum, which can prevent aggregation, was found to be 0.20M urea/0.25M NaOH aqueous solution. The weight‐average molecular weight (M_w), radius of gyration (〈s²〉^1/2), and intrinsic viscosity ([η]) of the samples were determined in 0.20M urea/0.25M NaOH aqueous solution at 25°C by light scattering (M_w, 〈s²〉^1/2) and viscometry ([η]). The values of M_w, 〈s²〉^1/2, and [η] were close to those in 0.20M lithium chloride/dimethylsulfoxide, in which the A gum exists as a semiflexible single chain, implying the same conformation for the A gum in 0.20M urea/0.25M NaOH aqueous solution. The results revealed that 0.20M urea/0.25M NaOH aqueous solution is a good solvent, which effectively avoids the aggregates of the A gum in aqueous solution. Moreover, it can be used to investigate the solution properties and chain conformation of water‐insoluble polysaccharides or the polysaccharides that are easily aggregated in aqueous systems. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1710–1713, 2005     

基于NaOH溶液CO2膜吸收系统的膜结构及传质性能

碳捕集与利用技术是实现减碳目标的有效方案。膜系统气体吸收技术能够实现CO₂以\mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{-}、\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{2}-}形式存储在无机碱性吸收剂中,并还原成甲醇、乙醇等清洁燃料。本文采用膜单侧浸泡实验法和传质实验,分别考察了疏水性微孔滤膜聚四氟乙烯（PTFE）膜、聚偏氟乙烯（PVDF）膜、聚丙烯（PP）膜在NaOH碱性溶液中的结构和CO₂传质特性的变化。结果表明,PTFE膜和PP膜在NaOH碱性溶液中溶胀率上升,孔径减小,孔隙率下降,疏水性下降,传质系数下降;PVDF膜在NaOH溶液中会发生反应,结构被破坏,传质系数接近无膜吸收,但无法起到相界面的作用,不能直接用于以NaOH为吸收剂的膜吸收系统。     

Decolorization of synthetic dyes by hydrogen peroxide with heterogeneous catalysis by mixed iron oxides

Heterogeneous catalysts based on magnetic mixed iron oxides (MO·Fe₂O₃; M: Fe, Co, Cu, Mn) were used for the decolorization of several synthetic dyes (Bromophenol Blue, Chicago Sky Blue, Cu Phthalocyanine, Eosin Yellowish, Evans Blue, Naphthol Blue Black, Phenol Red, Poly B-411, and Reactive Orange 16). All the catalysts decomposed H₂O₂ yielding highly reactive hydroxyl radicals, and were able to decolorize the synthetic dyes. The most effective catalyst FeO·Fe₂O₃ (25 mg mL⁻¹ with 100 mmol L⁻¹ H₂O₂) produced more than 90% decolorization of 50 mg L⁻¹ Bromophenol Blue, Chicago Sky Blue, Evans Blue and Naphthol Blue Black within 24 h. The fastest decomposition proceeded during the first hour of the reaction. In addition to dye decolorization, all the catalysts also caused a significant decrease of chemical oxygen demand (COD). Individual catalysts were active in the pH range 2–10 depending on their structure and were able to perform sequential catalytic cycles with low metal leaching.     

Electrochemical investigation of the effects of hydrogen on the stability of the passive film on iron

The effects of hydrogen on the stability of passive films on iron were investigated by electrochemical methods: open circuit potential decay, cathodic galvanostatic reduction, electrochemical impedance spectroscopy, and breakdown potential measurements. The results show that hydrogen decreases the final static open circuit potential, the cathodic charge for reduction and the charge transfer resistance of the passive film, indicating that hydrogen decreases the stability of the passive film. The charge transfer resistance of the passive film formed on the charged specimen does not change with increasing the film formation potentials, suggesting that increasing film formation potentials under hydrogen charging conditions cannot improve the stability of the passive film. Hydrogen decreases the breakdown potential of the passive film, especially at lower chloride ion concentrations, confirming that hydrogen promotes the susceptibility of the passive film on iron to pitting corrosion. The reasons why hydrogen decreases the stability of the passive film were discussed.     

Changes on iron electrode surface during hydrogen permeation in borate buffer solution

Hydrogen interaction with oxide films grown on iron electrodes at open circuit potential (E_oc) and in the passive region (+0.30 V_ECS) was studied by chronopotentiometry, chronoamperometry and electrochemical impedance spectroscopy techniques. The results were obtained in deaerated 0.3 mol L⁻¹ H₃BO₃ + 0.075 mol L⁻¹ Na₂B₄O₇ (BB, pH 8.4) solution before, during and after hydrogen permeation. The iron oxide film modification was also investigated by means of in situ X-ray absorption near-edge spectroscopy (XANES) and scanning electrochemical microscopy (SECM) before and during hydrogen permeation. The main conclusion was that the passive film is reduced during the hydrogen diffusion. The hydrogen permeation stabilizes the iron surface at a potential close to the thermodynamic water stability line where hydrogen evolution can occur. The stationary condition required for the determination of the permeation parameters cannot be easily attained on iron surface during hydrogen permeation. Moreover, additional attention must be paid when obtaining the transport parameters using the classical permeation cell.     

利用乙醇水溶液从含铁硫酸铝中除铁

  摘 要：为了从硫酸铝中除铁,提出了利用乙醇水溶液对含铁硫酸铝进行除铁的工艺方法。研究了乙醇水溶液的pH、温度、振荡时间对除铁率的影响以及乙醇回收并循环使用的工艺方法。通过实验确定了最佳的工艺参数：乙醇水溶液的pH≤1,温度为25 ℃,振荡时间为2.5 h。经4级逆流除铁,硫酸铝的含铁质量分数可由0.98%降至0.005%以下。负载在乙醇水溶液中的铁经双氧水氧化、氨水沉淀、过滤并蒸馏至干后,乙醇回收率可达99.5%以上。本工艺具有操作简单、无污染、成本低等优点。     

回收铬饼制备碱式硫酸铬的除铁工艺研究

研究了从铬渣常压硫酸浸出液中沉针铁矿的过程。考察了温度、pH值、反应时间和空气流量对除铁率及铬损失率的影响。试验结果表明,反应时间和空气流量对除铁率的影响不显著;在反应温度90℃、pH值为3、搅拌强度150r·min^-1反应时间2h、空气流量0．2m^3·min^-1的条件下,除铁率超过99．5％,铬的损失率仅为17％。     

螯合络合剂法去除活性炭生产回收磷酸液中的铁离子

活性炭生产中用磷酸液进行活化,磷酸液可重复回收利用。由于木屑、炭屑等原材料的影响,用于反复活化浸渍的磷酸液中铁质量分数将从小于10×10-6上升到数百×10-6,甚至更高,不能满足医药、食品等行业对铁离子含量要求较高的活性炭生产之需。采用二甲基肼、15%磷酸液、二硫化碳3种药品于一定条件下反应,制得了螯合络合沉淀剂,于常温下可将回收来的磷酸母液中的铁离子除去,除铁效果显著,达到50×10-6以下,从而使回收的磷酸液满足医药、食品等行业用活性炭的生产要求。该法工艺简单、成本低,且不引入杂质离子,是一种值得推广的应用技术。     

Effect of composition on rheological behavior of iron oxides produced by hydrothermal method

The aim of the present work was to investigate the rheological properties of different iron oxides (Fe₃O₄, NiFe₂O₄, ZnFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄) aqueous suspensions. The oxides were produced through mixing the respective metallic sulfates within a closed isothermal reactor at 100 °C and at pH ≈12, in an oxidant environment (provided by H₂O₂ 0.63% w/v). The reactor was coupled with an adequate real-time data (RTD) acquisition system enabling measurement of temperature, pH and pressure. Obtained RTD data showed that once the isothermal conditions are reached, the pressure slowly decreases over time, which is a result of O₂ consumption through oxidation of Fe²⁺ to Fe³⁺. To characterize the suspensions as a function of temperature and shear rate, the steady rheology was used. The results revealed that the effect of temperature on viscosity of all suspensions was insignificant while steady rheology showed pseudoplastic behavior for all ferrites. The magnitude of viscosity and pseudoplasticity turned out to be in agreement with the hydrodynamic diameters of particles complying with the order: NiFe₂O₄>Fe₃O₄>Ni_0.5Zn_0.5Fe₂O₄>ZnFe₂O₄. Finally, the rheological behavior of suspensions was attributed to the concentration of OH groups on the surface of particles and this hypothesis was effectively supported by DRX, FTIR and TGA/DTA measurements.     

Kinetics of the reactive absorption of hydrogen sulfide into aqueous ferric sulfate solutions

The reactive absorption of H₂S into aqueous Fe₂(SO₄)₃ solutions, was studied in a stirred cell reactor operated batchwise with and without a flat interface. The temperature was varied from 25°C to 65°C and the concentrations of aqueous Fe₂(SO₄)₃ solutions ranged from 0.025 to . The corresponding initial pH values ranged from 2 to 0.8, respectively. Additional measurements were conducted at other pH values by addition of NaOH. The H₂S partial pressure was varied between 0 and . The rate of H₂S absorption was measured by recording the pressure drop as a function of time during batch absorption experiments. In this system the absorbed H₂S reacts with ferric iron and is oxidized to elemental sulfur. The kinetic results are in agreement with enhanced absorption due to a fast chemical reaction according to the film theory. The reaction of ferric sulfate and H₂S appears to proceed irreversibly and is first order in both the total concentrations of ferric iron and H₂S. The activation energy for the reaction was calculated to be .