烯胺阻锈剂对钢筋在模拟碳化混凝土孔隙液中的点蚀抑制

通过电化学噪声(ECN)、电化学阻抗(EIS)及极化曲线研究了四乙烯五胺(TEPA)在碳化模拟混凝土孔隙液中对Q345B碳钢点蚀的抑制机理. 结果表明: 通过吸附成膜和隔离Cl^-离子对钝化膜的侵蚀, TEPA浓度升高导致碳钢点蚀电位正移. 低浓度的TEPA会造成亚稳态蚀点形核速率略微增加, 但会降低其寿命. 随着TEPA浓度增加, 噪声电阻上升, 而亚稳态蚀点寿命和平均点蚀电量则迅速下降, 表明其明显加速了亚稳态蚀点修复, 当TEPA浓度达0.10 mol·L^-1时, 噪声峰消失, 基底电流趋于零, 蚀点全面钝化. TEPA不仅能抑制Cl^-离子引起的亚稳态和稳态蚀点生长, 还可吸附于钝化膜表面, 抑制膜的均匀溶解. 形貌观察表明, 亚稳态蚀点主要在稳态蚀点周围形核和生长, 并不断为稳态蚀点所吞并, 造成碳钢表面蚀坑一般沿平面而不是垂直方式扩展.     

CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究

采用XRD、UV-vis DRS、ESR和微分吸附量热等技术,考察了铬担载量分别为2.5、5和10wt%的CrO_x/SiO₂催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Cr的氧化态和聚集形式。随着Cr担载量从2.5wt%到10wt%的逐渐增大,催化剂表面占主导地位的Cr物种由CrO₃单体转为多聚CrO₃和Cr₂O₃晶相。在CO₂气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为2.5wt%CrO_x/SiO₂>5wt%CrO_x/SiO₂>10wt%CrO_x/SiO₂,反应过程中的原位ESR和UV-visDRS测定结果表明,催化剂表面的反应活性中心为Cr⁵⁺,Cr⁵⁺可由催化剂预处理过程中Cr³⁺的氧化及丙烷反应过程中CrO₃单体的还原产生,在反应中CO₂可使Cr³⁺重新氧化为Cr⁵⁺.     

酸性AlCl3-BMIC离子液体中的铝阳极溶解

采用线性扫描伏安法研究了Lewis 酸性AlCl₃-BMIC (BMIC: 1-butyl-3-methylimidazolium chloride)离子液体中铝电极的溶解. 铝电极在阳极极化时出现了钝化现象, 钝化是由于在铝电极表面形成了固体AlCl₃钝化膜造成的. 铝的电化学溶解过程可以依次分为三个区: 电化学控制区、过渡区和钝化区. 在电化学控制区, 铝的电化学溶解速率随着电位的正移而逐渐增加; 在过渡区, 由于电极表面AlCl₄^-和Al₂Cl₇^-浓度发生改变而析出固体AlCl₃使得铝电化学溶解速率随着电位的正移而逐渐减小; 当钝化膜形成之后, 铝的电化学溶解速率不再随着电位的正移而发生改变, 铝溶解进入钝化区. 增加搅拌、升高温度、降低离子液体AlCl₃摩尔分数都可以增加铝溶解阳极极限电流密度.     

Cr2O3和CrO3/Cr2O3催化剂的2-氯-1,1,1-三氟乙烷气相氟化反应的活性物种和失活

采用沉淀法和浸渍法制备了2种铬基（Cr₂O₃和CrO₃/Cr₂O₃）催化剂,用于气相氟化2-氯-1,1,1-三氟乙烷合成1,1,1,2-四氟乙烷。研究发现含有低价铬（Cr³⁺）物种的Cr₂O₃催化剂上2-氯-1,1,1-三氟乙烷的稳态转化率为18.5%,而含有高价铬（Cr⁶⁺）物种和低价铬（Cr³⁺）物种的CrO₃/Cr₂O₃催化剂初始转化率达到30.6%,然而存在明显的失活。含有Cr⁶⁺物种的CrO₃/Cr₂O₃催化剂的2-氯-1,1,1-三氟乙烷氟化反应初始TOF值为1.71×10^-4 mol_HCFC-133a·mol_Cr（Ⅵ）^-1·s^-1,高于含有Cr³⁺物种的Cr₂O₃催化剂（4.16×10^-5 mol_HCFC-133a·mol_Cr（Ⅲ）^-1·s^-1）。Cr₂O₃催化剂在氟化反应前后催化剂的物相结构保持不变;而含有高价铬物种的CrO₃/Cr₂O₃催化剂经HF反应后生成了CrO_xF_y活性物种。然而,CrO_xF_y物种在反应中挥发或转化成稳定但无活性的CrF₃,从而导致催化剂失活。     

气相中CrO2+和H2反应的理论研究

用密度泛函UB3LYP/6-311++G(3df, 3pdpd)//6-311G(2dd, p)方法计算研究了在二重态和四重态两个势能面上的气相反应：CrO₂⁺ + H₂→CrO⁺+ H₂O. 对影响反应机理和反应速率的势能面交叉进行了讨论, 并运用Hammond 假设和Yoshizawa 等的内禀反应坐标(IRC)单点垂直激发计算的方法找出了势能面交叉点(crossing point (CP)). 运用碎片分子轨道(fragment molecular orbital(FMO))理论, 对初始复合物2IM1和4IM1的轨道相关进行了分析, 解释了CrO₂⁺活化H—H σ键及H₂迁移的机理.     

Cr2O3和CrO3/Cr2O3催化剂的2-氯-1，1，1-三氟乙烷气相氟化反应的活性物种和失活

采用沉淀法和浸渍法制备了2种铬基（Cr₂O₃和CrO₃/Cr₂O₃）催化剂,用于气相氟化2-氯-1,1,1-三氟乙烷合成1,1,1,2-四氟乙烷。研究发现含有低价铬（Cr³⁺）物种的Cr₂O₃催化剂上2-氯-1,1,1-三氟乙烷的稳态转化率为18.5%,而含有高价铬（Cr⁶⁺）物种和低价铬（Cr³⁺）物种的CrO₃/Cr₂O₃催化剂初始转化率达到30.6%,然而存在明显的失活。含有Cr⁶⁺物种的CrO₃/Cr₂O₃催化剂的2-氯-1,1,1-三氟乙烷氟化反应初始TOF值为1.71×10^-4 mol_HCFC-133a·mol_Cr(Ⅵ)^-1·s^-1,高于含有Cr³⁺物种的Cr₂O₃催化剂（4.16×10^-5 mol_HCFC-133a·mol_Cr(Ⅲ)^-1·s^-1）。Cr₂O₃催化剂在氟化反应前后催化剂的物相结构保持不变;而含有高价铬物种的CrO₃/Cr₂O₃催化剂经HF反应后生成了CrO_xF_y活性物种。然而,CrO_xF_y物种在反应中挥发或转化成稳定但无活性的CrF₃,从而导致催化剂失活。     

在离子液体[BMIm][BF4]中电沉积光亮金镀层

在离子液体1-丁基-3-甲基咪唑四氟硼酸盐（[BMIm][BF₄]）中以HAuCl₄·3H₂O为主盐、通过添加5,5-二甲基乙内酰脲（DMH）和胞嘧啶可得到色泽光亮、厚度达1.5 μm的金镀层,沉积过程中阴极电流效率可达到100%。SEM和XRD测试结果表明,DMH和胞嘧啶具有细化晶粒、平整镀层的作用。电化学测试结果表明,DMH可分别与Au³⁺、Au⁺形成配合物Au（DMH）₄^-、Au（DMH）₂^-,抑制了还原过程的表面转化步骤,从而增加了阴极极化,起到光亮镀层、细化晶粒的作用;胞嘧啶可在金核表面吸附,从而可以进一步光亮镀层、细化晶粒,与DMH有协同作用。循环伏安测试研究了镀液的电化学行为,研究表明在此体系中Au³⁺的还原为两步还原过程,分别为Au³⁺→ Au⁺和Au⁺→ Au。此外DMH和胞嘧啶的添加不会带来副反应。     

钨硅系列三元杂多阴离子柱撑阴离子粘土的合成及表征

采用离子交换法将过渡金属离子三元取代钨硅杂多阴离子引入Zn₂Al型阴离子粘土层内，得到柱撑水滑石Zn₂Al(OH)₆-SiW₉Z₃O₄₀(Z=Ti⁴⁺, Mo⁶⁺)及Zn₂Al(OH)₆-SiW₉Fe₃(H₂O)₃     

阴离子对阳离子表面活性剂在Al(OH)3、CaCO3粉体上吸附的影响

研究了阳离子表面活性剂十六烷基二甲基烯丙基氯化铵(CDAAC)在Al(OH)₃/水、CaCO₃/水界面上的吸附,探讨了无机阴离子对吸附量及表面电荷的影响,测定了样品的接触角和比表面。结果表明PO^3-₄的加入可提高Al(OH)₃、CaCO₃表面负电荷,有利于吸附,经吸附改性后的样品具有憎水性。     

La3+对过氧化氢酶电化学和生物电催化活性的影响

本文研究了La³⁺对过氧化氢酶(CAT)的直接电化学反应活性和对H₂O₂还原的生物电催化活性的影响。发现当La³⁺浓度低时,La³⁺能提高CAT的直接电化学反应活性和对H₂O₂还原的电催化活性。当La³⁺浓度高时,La³⁺会降低CAT的直接电化学反应活性和对H₂O₂还原的电催化活性。这是由于La³⁺能与CAT的肽链上的氨基酸残基发生作用而使肽链构象发生变化,导致血红素结构发生变化。当La³⁺浓度低时,La³⁺能使血红素的非平面性增加,活性中心Fe(Ⅲ)的暴露程度增加,因此,低浓度的La³⁺能增加CAT的电化学和生物电催化活性,而高浓度的La³⁺却会使血红素的非平面性降低,活性中心Fe(Ⅲ)的暴露程度降低,因此,降低了CAT的电化学和生物电催化活性。     

Effect of sodium vanadate on corrosion of AD31 aluminum alloy in acid media

Scanning electron microscopy, potentiodynamic polarization method, and electrochemical impedance spectroscopy were used to study the corrosion behavior of AD31 (AA6063) aluminum alloy in acid (pH 3) 0.05 M NaCl solutions containing 3 mmol dm^–3 of NaVO₃ inhibitor. It was found that the corrosion of AD31 alloy in acid sodium chloride solutions predominantly occurs locally at aluminum/intermetallic particle phase boundaries and is limited by the electrochemical stage of charge transfer. It was shown that introduction of sodium vanadate can reduce the rate of selective dissolution of magnesium from the alloy and provides a protective effect on the level of 7–10%.     

The inhibition mechanism of pitting corrosion of pure aluminum by nitrate and sulfate ions in neutral chloride solution

The inhibition mechanism of pitting corrosion of natural oxide film-covered pure aluminum by NO⁻ ₃ and SO²⁻ ₄ ions has been examined in 0.1 M NaCl solution using potentiodynamic polarization experiments, a.c. impedance spectroscopy, Auger electron spectroscopy and a combination of the potentiostatic current transient method and optical microscopy. It was found that NO⁻ ₃ ions can be incorporated into the natural oxide film on pure aluminum at open-circuit potential, but the incorporation of SO²⁻ ₄ ions into the film hardly occurs. The incorporation of NO⁻ ₃ ions lowered the pitting susceptibility of pure aluminum in 0.1 M NaCl solution. Based upon the experimental results, it is suggested that the pitting corrosion inhibition mechanism by anions can be classified into two different groups: inhibition by competitive adsorption of anions (SO²⁻ ₄) with Cl⁻ ions and inhibition by the incorporation of anions (NO⁻ ₃) into the film rather than competitive adsorption. Both cases may impede the incorporation of Cl⁻ ions into the film, thus inhibiting pitting corrosion of natural oxide film-covered pure aluminum in chloride solutions. Received: 16 October 1998 / Accepted: 6 January 1999     

Pitting Corrosion Mechanisms and Characteristics of Aluminum in Solar Heating Systems

The complex characteristics and mechanisms of aluminum pitting corrosion in a solar heating system were studied by the chemical immersion method and electrochemical techniques as well as fractal theory. The results showed that pitting corrosion of Al occurred in a tap water environment due to the local enrichment of Cl^? ions. The higher the Cl^? ions concentration, the more negative the critical pitting potential (E_b) of Al. A linear relationship between E_b and the logarithm of Cl^? ions concentration was observed. The pitting corrosion mechanism of Al in neutral water was explained in terms of complexation corrosion theory. The corrosion surface images of aluminum immersed in tap water were captured and analyzed by image processing technique and box‐dimension method. The fractal characteristics of pit distribution, described by fractal dimension, have been identified. The fractal dimension of the pit distribution increased with the increase of immersion time and had the same trend as that of the weight loss. Fractal dimension can, thus, be used as an important parameter for quantitative evaluation of pitting corrosion of aluminum.     

The effect of chloride concentration and pH on pitting corrosion of AA7075 aluminum alloy coated with phenyltrimethoxysilane

The effect of chloride ion concentration and pH of solution on the corrosion behavior of aluminum alloy AA7075 coated with phenyltrimethoxysilane (PTMS) immersed in aqueous solutions of NaCl is reported. Potentiodynamic polarization, linear polarization, open circuit potential, and weight loss measurements were performed. The surface of samples was examined using SEM and optical microscopy. Elemental characterization of the coating by secondary ion mass spectrometry indicates an intermediate layer between coating and aluminum alloy surface. The corrosion behavior of the aluminum alloy AA7075 depends on chloride concentration and pH of solution. In acidic or neutral solutions, general and pitting corrosion occur simultaneously. On the contrary, exposure to alkaline solutions results in general corrosion only. Results further reveal that aluminum alloy AA7075 is susceptible to pitting corrosion in all chloride solutions with concentrations between 0.05 M and 2 M NaCl; an increase in the chloride concentration slightly shifted both the pitting and corrosion potentials to more active values. Linear polarization resistance measurements show a substantially improved corrosion resistance value in case of samples coated with PTMS as compared to uncoated samples in both neutral (pH = 7), acidic (pH = 0.85 and 3), and alkaline chloride solutions (pH = 10 and 12.85). The higher corrosion resistance of the aluminum alloy coated with PTMS can be attributed to the hydrophobic coating which acts as a barrier and prevents chloride ion penetration and subsequent reaction with the aluminum alloy.     

海水环境中典型阴离子对5083铝合金腐蚀行为的影响

采用析因分析试验及动电位极化曲线、电化学阻抗谱(EIS)等测试方法,研究了海水环境因素中的典型阴离子（Cl^-、HCO₃^-、SO₄^2-交互作用对5083铝合金耐蚀性的影响. 结果表明,三种阴离子中,Cl^-、HCO₃^-对铝合金点蚀起促进作用. Cl-与HCO₃^-交互作用时,在Cl^-浓度一定的情况下,随着HCO₃^-浓度的增加,5083铝合金耐蚀性呈现出上升→下降→再上升的趋势,在70～90mg•L^-1时耐蚀性能明显降低;在HCO₃^-浓度一定的情况下,Cl^-浓度较低时5083铝合金耐蚀性比Cl^-浓度较高时差. 在Cl^-、HCO₃^-浓度较低情况下,SO₄^2-具有抑制腐蚀的作用;当Cl^-、HCO₃^-浓度较高时,SO₄^2-抑制腐蚀的作用不明显.     

Protective Action of Sodium Metavanadate Against Corrosion of AD31 Aluminum Alloy in Neutral Chloride-Containing Media

Russian Journal of Physical Chemistry A - The mechanism of corrosion of AD31 (AA6063) aluminum alloy in 0.05 M NaCl solutions containing 0.03–5 mmol/dm3 NaVO3 as an inhibitor was studied....     

Detection of SCC of 304 NG stainless steel in an acidic NaCl solution using electrochemical noise based on chaos and wavelet analysis

The stress corrosion crack (SCC) of 304 nuclear grade (NG) stainless steel (SS) in 0.5 mol/L NaCl+1.5 mol/L H₂SO₄ was monitored using electrochemical noise (EN) based on chaos theory, statistics and wavelet analysis. The results indicated that the SCC process was divided into three stages according to the transient features in the EN. In the beginning, compared with the sample without applied stress, the enhanced fluctuation amplitude in the electrochemical current noise (ECN) of the stressed samples was attributed to stress-enhanced pitting corrosion and uniform corrosion; then the fluctuations of ECN for all the samples decreased due to a coverage by the corrosion products; however, the ECN fluctuations of stressed sample were larger than the unstressed sample, suggesting that the stress enhanced the SCC initiation and propagation. Chaos analysis revealed that the correlation dimensions increase from 2.1 to 2.5 during the corrosion process, and the applied stress seems increase the complexity and uncertainty of the ECN signal.     

Electrochemical instabilities due to pitting corrosion of iron

Electrochemical instabilities induced by chlorides and bromides due to pitting corrosion of iron in sulfuric acid solutions are investigated. Analysis of the electrochemical instabilities as a function of the applied potential and the nature and concentration of the aggressive chemical species shows that the system exhibits a transition from aperiodic bursting of large-amplitude to small-amplitude chaotic oscillations at a critical potential (bifurcation potential, E _bif). The E _bif is determined by the halide concentration inside the pits and coincides with the repassivation potential defined in corrosion studies to explain pit repassivation due to changes in pit chemistry. Surface observations show that, at E < E _bif, an active-passive state dissolution (etching) occurs, while at E > E _bif, a polishing state dissolution is reached. Spatial interactions between early initiated pits and the adjacent electrode surface, oxide film alteration, aggressive species accumulation around active pits, and formation of ferrous salt layers in front of the Fe electrode are all considered to be associated with electrochemical instabilities emerging during pitting corrosion of iron under different dissolution states. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 535–550. The text was submitted by the authors in English.     

Anodic Dissolution of Samarium in an Acetonitrile Solution in Acetylacetone

Electrochemical dissolution of metallic samarium is studied in an acetonitrile solution containing 0.1 M tetraethylammonium bromide and 0.9 M acetylacetone. The study is performed in an argon atmosphere, at a constant voltage of 3 V and various ratios between the cathode and anode areas. If the cathode area considerably exceeds the anode area, as a result of anodic oxidation of samarium, ions Sm³⁺ form in solution, undergo reduction to Sm²⁺, and 20–25 min later generate chelate complex Sm₄(AA)₈ · 3HAA, which is insoluble in acetonitrile. Simultaneously, Sm³⁺ interacts with deprotonated acetylacetone. Chelate complex Sm(AA)₃ · HAA is extracted from solution. If the anode area exceeds the cathode area, no reduction of Sm³⁺ to Sm²⁺ occurs on the cathode, and eventually adducted samariumtris–acetylacetonate Sm(AA)₃ · 4HAA is extracted from solution. The composition of the obtained compounds is confirmed by IR and mass spectrometry, thermogravimetry, isothermic heating, and elemental analysis for metal.