液相分散程度对气/液/固多相体系腐蚀行为的影响

本文提出用三相线界面区参数描述液相分散程度,研究了三相线界面区阴极过程特征,建立三相线界面区阴极过程模型.并探讨了液相覆盖区阴极极限电流和三相线区状态的相关性,证实了模型计算与实验数据一致性.进而用三相线界面区阴极过程模型分析液相分散程度对大气以及砂土体系腐蚀行为的影响.     

Liquid flow porous electrode: The effect of local variations in liquid-phase conductivity on its operation efficiency

For one-dimensional model of porous electrode (PE), an equation for the ideal ratio between the local conductivities of liquid phase κ_L(x) and solid phase κ_s(x), which provides uniform distributions of potential and current inside the PE, is obtained. It is shown that the principal possibilities of levering action of both phases are similar; however, the shapes of their ideal conductivity profiles are mirror-opposite. To gain a beneficial effect at the expense of conductivity of liquid phase, κ_L(x) should increase monotonically from the rear current lead to the frontal side of PE provided that the conductivities of phases are equal in the middle of PE. The effect of distortions of ideal κ_L(x) profile is analyzed. It is found that, with regard to the natural upper limit of solution conductivity, the best conditions for the levering action of ideal κ_L(x) profile should be expected in the porous matrices with low conductivity. It is shown that the formation of even few zones with opposite-shaped κ_L(x) profile inside PE (the solution conductivity decreases towards the frontal side of PE) leads to more nonuniform potential distribution and a decrease in the PE operation efficiency (especially at high total current density).     

Effect of acetic acid on CO2 corrosion of carbon steel in NaCl solution

Potentiodynamic sweep and electrochemical impedance spectroscopy measurements were applied to investigate the effects of both temperature and acetic acid (HAc) on the anodic and cathodic reactions in CO₂ corrosion of P110 steel in 3.5% NaCl solution. The temperatures were controlled at 30 and 60 °C. The concentrations of HAc were controlled at 0, 1000, 3000 and 5000 ppm. In this work, the corrosion parameters of polarization curves, such as corrosion potential (E_corr), corrosion current density (i_corr), and anodic and cathodic branch slopes (b_a and b_c), are presented and discussed in detail. In addition, the equivalent circuit models and ZsimpWin software were utilized to discuss the Nyquist plots. The plots showed that the E_corr values shifted in the positive direction as the HAc concentration increased. The i_corr values increased with the increase in HAc concentration, indicating that HAc could accelerate the corrosion. The impedance spectra measured at 30 and 60 °C have different time constants and characterization. The coverage fraction θ and the thickness L of corrosion film are two most important controlled variables that influence and control the CO₂ corrosion mechanisms. Copyright © 2010 John Wiley & Sons, Ltd.     

Model calculations of aggregation numbers and radii of w/o microemulsions

Summary A method of calculating aggregation numbers and radii of reversed micellar aggregates is presented and applicated on the alcohol-rich solution phaseL ₂ in the model system water/decanol/sodium octanoate at 293 K. The result showing good agreement with experimental data illustrate the extension of the micellar core at different decanol contents and molar ratios water to sodium octanoate. The influence of a distribution of water between the interior of the micelle and the decanolic medium is demonstrated.

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Zusammenfassung Es wird eine Methode zur Berechnung von Aggregations zahlen und Radien invertierter mizellarer Aggregate angegeben und auf die Alkohol-reichenL ₂-Lösungen im Modellsystem Wasser/Dekanol/Natrium-Oktanoat bei 293 K angewendet. Die Resultate sind in guter Übereinstimmung mit experimentellen Messungen; sie zeigen die Ausdehnung der Mizellkerne bei verschiedenen Dekanol-Konzentrationen und bei verschiedenen molaren Verhältnissen Wasser/Oktanoat. Der Einfluß der Verteilung von Wasser zwischen dem dekanolischen Medium und den Mizellen wird diskutiert.

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With 4 figures and 3 tables     

Simultaneous Detection of Copper,Lead and Zinc on Tin Film/Gold Nanoparticles/Gold Microelectrode by Square Wave Stripping Voltammetry

In this work, three heavy metals (Cu(II), Pb(II) and Zn(II)) in wide potential window were simultaneously detected on tin film/gold nanoparticles/gold microelectrode (Sn/GNPs/gold microelectrode) by the method of square wave stripping voltammetry. The Sn/GNPs/gold microelectrode was fabricated by in situ plating of a Sn film on a gold nanoparticles (GNPs) modified gold microelectrode. The influence of hydrogen overflow on stripping of Zn(II) on the gold microelectrode was reduced by modification of GNPs, which made the stripping potential of target metals shift positively. The interference of sulfhydryl groups was reduced and the selectivity of the microelectrode was improved due to the addition of Sn in the detection solution. After accumulation at ?1.4 V for 300 s in acetate buffer solution (0.1 mol L^?1, pH 4.5), the Sn/GNPs/gold microelectrode revealed a good linear behavior in the examined concentration ranges from 5 to 500 µg L^?1 for Cu(II) and Pb(II), and from 10 to 500 µg L^?1 for Zn(II), with a limit of detection of 2 µg L^?1 for Cu(II), 3 µg L^?1 for Pb(II) and 5 µg L^?1 for Zn(II) (S/N=3). When compared with a Sb/GNPs/gold microelectrode and a Bi/GNPs/gold microelectrode, the Sn/GNPs/gold microelectrode showed the best stripping performance to Cu(II), Pb(II) and Zn(II). As a new type of environment‐friendly electrode, the Sn/GNPs/gold microelectrode has potential applications for detection of heavy metals.     

Study of Scaling Exponents of the Surface Evolved in 2 + 1 Dimension through Competitive Growth between Random Deposition and that with Surface Relaxation

Rough surface develops through computer simulation by competition between growth mechanism random deposition (RD) with a probability of occurrence p and growth mechanism random deposition with surface relaxation (RDSR) with a probability of occurrence 1 − p, on L × L square plane for system size L to record the statistical average of time variation of surface roughness W(L, t) and average height H(t) for the model for specific values of L and p. Other than the pure RD model, the entire evolution may be divided into three regions separated by two specific cross-over times t_x and t_sat. The value of interface width at saturation W_sat depends on both L and p. The first growth exponent β₁ increases exponentially with an increase in p and does not depend on L. The values of the second growth exponent β₂, roughness exponent α, dynamic exponent z( = α/β₂ ), and α + z are 0.0234 ± 0.0008, 0.0506 ± 0.0065, 2.1577 ± 0.0073, and 2.2083 ± 0.0138 respectively and they show no dependence on L and p values. Value of the first cross-over time t_x increases exponentially with an increase in p and does not depend on L. Value of the second cross-over time t_sat increases with an increase in both p and L values. The average growth velocity is unity for the model and is independent of both L and p. For the model, the growth velocity is unity and the fractional porosity is zero. The scaling exponents show some deviation from the relevant universality classes and depend on competitive growth probability for this model. No finite-size effect is present in the model.     

Electronegativity and chemical hardness of organoelement groups

The experimental approaches to estimation of comparative electronegativity and chemical hardness of organometallic groups have been proposed. Qualitative data on the electronegativity of L _nM groups were obtained from ¹⁹F NMR study of model systems 4‐FC₆H₄QML_n (Q = CC, N(R), O, C(O)O, S), (4‐FC₆H₄)₃ SnML _n and (4‐FC₆H₄)₃SnQML _n (Q = O, S), containing a great variety of different organometallic groups containing transition or heavy main‐group metals. The data on chemical hardness of L _nM groups were obtained from NMR study of distribution of different L _nM groups between hard and soft anions. The following basic results have been obtained. (1) The relative electronegativity and chemical hardness of L _nM groups can change in parallel or not with the electronegativity and hardness of the central metal atom. (2) The substituents in Ar can substantially modify electronegativity and hardness of Ar _nM groups; the influence of Ar groups has an inductive nature; the increase in electron‐donating ability of aryl ligands enhances the hardness of Ar _nM cations. (3) The relative electronegativity and hardness of L _nM groups in L _nMX are invariant and do not depend on X.     

Unprecedented μ3-O face-capping ligand in a [Mo6Br6L2Br6] (L = 0.5 O + 0.5 Br) molybdenum cluster unit: crystal structure of the Cs3Mo6Br13O oxybromide

The new Cs₃Mo₆Br₁₃O oxybromide, synthesized by solid-state chemistry, crystallizes in the trigonal system (Rc space group; a = 15.5784(2) Å, c = 19.5103(5) Å, V = 4100.5(1) Å³ and Z = 6). It is based on a [Mo₆L₁₄] unit that contains an unprecedented μ₃ face-capping oxygen. The crystal structure determined by single crystal X-ray diffraction is built up from discrete face-capped [Mo₆Brⁱ₆Lⁱ₂Br^a₆]^3– (L = 0.5 O + 0.5 Br) anionic units in which two inner positions are randomly occupied by one bromine and one oxygen whereas the other ligand positions are fully occupied by bromine. The cesium cations randomly occupy two close crystallographic positions generated by the A-B-C-A′-B′-C′ close-packed stacking of the units. The cesium site occupancy is related to the random distribution of oxygen and bromine on the Lⁱ inner positions. To cite this article: K. Kirakci et al., C. R. Chimie 8 (2005).     

Adsorption Behavior and Inhibition Corrosion Effect of Sodium Carboxymethyl Cellulose on Mild Steel in Acidic Medium

The effect of sodium carboxymethyl cellulose (Na-CMC) on the corrosion behavior of mild steel in 1.0 mol·L⁻¹ HCl solution has been investigated by using weight loss (WL) measurement, potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods. These results showed that the inhibition efficiency of Na-CMC increased with increasing the inhibitor concentration. Potentiodynamic polarization studies revealed that the Na-CMC was a mixed type inhibitor in 1.0 mol·L⁻¹ HCl. The adsorption of the inhibitor on mild steel surface has been found to obey the Langmuir isotherm. The effect of temperature on the corrosion behavior of mild steel in 1.0 mol·L⁻¹ HCl with addition of 0.04% of Na-CMC has been studied in the temperature range of 298–328 K. The associated apparent activation energy (E^*_a) of corrosion reaction has been determined. Scanning electron microscopy (SEM) has been applied to investigate the surface morphology of mild steel in the absence and presence of the inhibitor molecules.     

Ti3C2Tx/MnO2正极在水系锌电池中的电化学性能

二氧化锰(MnO₂)材料具有比容量大、电极电位高、储量丰富以及价格低廉等优势,成为水系锌电池正极最受关注的一类材料,然而其仍然存在着结构稳定性差和电化学储存机理复杂的问题。因此,我们通过两步合成法制备了一种花苞状结构的MnO₂负载在Ti₃C₂T_x表面形成Ti₃C₂T_x/MnO₂复合材料,通过X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)对复合样品的结构、成分和形貌进行表征。通过将Ti₃C₂T_x/MnO₂复合材料作为正极,与锌负极匹配组装成水系锌电池,研究了其分别在2 mol·L^-1 ZnSO₄、2 mol·L^-1 ZnSO₄+0.1 mol·L^-1 MnSO₄、30 mol·L^-1三氟甲基磺酸四乙基铵(TEAOTf)+1 mol·L^-1三氟甲烷磺酸锌(ZnOTf)和3 mol·L^-1 ZnOTf四种电解液中的电化学性能。结果表明,Ti₃C₂T_x/MnO₂在2 mol·L^-1 ZnSO₄中的比容量较高,但循环稳定性很差。将TEAOTf盐和ZnOTf盐共溶于水中,设计了一种新型的含惰性阳离子的超高浓度盐包水电解液(30 mol·L^-1 TEAOTf+1 mol·L^-1 ZnOTf),不仅提高了Ti₃C₂T_x/MnO₂材料的可逆性,而且有效抑制了电极材料在循环过程中的溶解。     

Zn-Al-[V10O28]6-双层氢氧化物掺杂对LY12铝合金表面溶胶-凝胶涂层性能的影响

采用共沉淀法制备Zn-Al-[V₁₀O₂₈]^6-双层氢氧化物(以下简称LDH-V), 研究不同添加浓度(0.0、0.25×10^-3、0.75×10^-3、1.5×10^-3、3.0×10^-3 mol·L^-1)的LDH-V对LY12 铝合金溶胶-凝胶涂层形貌、耐蚀性的影响. 采用扫描电子显微镜(SEM)和傅里叶变换红外(FTIR)光谱研究LDH-V对涂层形貌和结构的影响. 运用中性盐雾实验对涂层进行耐蚀性评估. 利用电化学方法对涂层在0.05 mol·L^-1的NaCl 溶液中的腐蚀行为进行研究. 探讨加入LDH-V后溶胶-凝胶涂层的耐蚀机理. 结果表明, 一定量LDH-V的加入不仅可以提高溶胶-凝胶涂层的耐蚀性能, 还可对涂层被破坏区域进行自修复, 起到延缓铝合金基体腐蚀的作用. 然而, 当LDH-V的添加溶度超过一定值时, 会破坏涂层的完整性并降低涂层的腐蚀防护性能. 实验结果表明LDH-V最佳的添加浓度为1.5×10^-3mol·L^-1.     

In situ investigations of the interaction of small inorganic acidifying molecules in humidified air with polycrystalline metal surfaces by means of TM‐AFM,IRRAS, and QCM

Initial atmospheric corrosion of copper, silver, and iron induced by humidity and oxidizing agents was studied in situ by three highly surface‐sensitive and complementary techniques: infrared reflection‐absorption spectroscopy (IRRAS), quartz crystal microbalance (QCM), and tapping‐mode atomic force microscopy (TM‐AFM). These techniques deliver information about the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first 1300–2800 min of weathering (TM‐AFM), as well as chemical (IRRAS) and kinetic (QCM) data. A completely different mechanism of the initial stages of atmospheric corrosion of the three investigated metals could be observed. A uniform growth of corrosion products was seen on the copper surface (identified by IRRAS and XPS to be cuprite‐like) during exposure to synthetic air with 80% relative humidity (RH), whereas the iron surface remained unattacked. The investigations of the silver surface exposed to humidity revealed that silver is attacked by humidity and tends to form oxide and hydroxide surface species. While an increased humidity content of the surrounding atmosphere causes higher corrosion rates on copper, on the exposed silver sample only a change in the degradation mechanism could be observed. The addition of SO₂ to the humidified air causes the growth of so‐called ‘second‐order’ features on copper, identified to be CuSO₃ · xH₂O‐like, which reveals the formation of a new chemical species on the investigated surface. These features are placed on top of the homogeneous formed oxide layer and tend to form well‐defined islands. In contrast to copper, on a silver surface exposed to humidity and SO₂ no new chemical species are formed; nevertheless an increased corrosion rate could be observed owing to a change of the chemistry in the physisorbed water layer. Iron exposed to humidity and SO₂ still remains unattacked. An iron surface is attacked only if exposed to humidity and SO₂ and NO₂, which show a synergistic effect by the oxidation of four‐valent sulfur‐oxygen species by NO₂. Such an attack leads to the formation of pitting corrosion, which was observed in situ and time‐resolved. The pits mainly occur on predamaged surface structures, such as scratches caused from the polishing process of the samples, and therefore promote the initiation of the corrosion. The results obtained demonstrate the high potential of the surface‐sensitive methods applied for investigating the early stages of corrosion of different metals and for obtaining a better understanding of the molecular mechanisms during degradation. Copyright © 2007 John Wiley & Sons, Ltd.     

Kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode: effects of pore length distribution and solution resistance

The effects of pore length distribution (PLD) and solution resistance, R_sol, on the kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode (ACFCE) were investigated in a 30 wt% H₂SO₄ solution using nitrogen gas adsorption, a.c. impedance spectroscopy, the current transient technique, and cyclic voltammetry. The impedance spectra of the ACFCE were theoretically calculated based upon the transmission line model in consideration of the pore size distribution (PSD) and the PLD. From comparison of both the experimental and theoretical impedance spectra of the ACFCE, it is suggested that the deviation from the ideal impedance behavior of a cylindrical pore in the experimental impedance spectrum of the ACFCE is mainly ascribed to PLD, rather than to PSD. The cathodic current transients and cyclic voltammograms were theoretically calculated based upon the transmission line model as functions of the standard deviation of the PLD and R_sol. From the results, it is concluded that ion penetration into the pores is closely related to both and R_sol during double-layer charging/discharging of the ACFCE, that is, the larger and R_sol, the lower is the rate capability, thus causing higher retardation of ion penetration into the pores.     

Li (i=1–3) subshell fluorescence and Coster-Kronig yields for elements with 70Z92

The atomic inner-shell vacancy decay processes comprised of radiative and nonradiative transitions are characterized by the fluorescence, Auger and Coster-Kronig yields. We present a review of our recent measurements of the L_i (i=1, 2, 3) sub-shell fluorescence yields (ω_i) and the L₁–L₃ Coster-Kronig transition probabilities (f₁₃) for elements with 70Z92 following photoionization. The comparison of the measured ω_i and f₁₃ values with the theoretical ones, based on the relativistic Dirac–Hartree–Slater (RDHS) model calculations, indicated the need for more refined calculations of transition probabilities for different Coster-Kronig transitions.     

Chain structure and thermal behavior of reactive blends of PET/LCP with bis(2-oxazoline)

The sequence structure and thermal behavior of reactive blends of poly(ethylene terephthalate) (PET) with the liquid crystalline copolyester 60 PHB/PET containing 60 mol % of p-hydroxybenzoic acid (PHB) with addition of bis(2-oxazoline) (BOZ) were studied in detail. ¹H NMR results indicate that both the number average sequence length of PET and PHB segments (L _PET and L _PHB) decrease with increasing mixing time and temperature via transesterification between PET and LCP. The transesterification is promoted in the presence of BOZ. As a consequence, the sequence structure and in turn the crystallization both from the glassy and the melt state and the melting behavior are markedly affected.     

RSM analysis of the effects of the oxygen transfer coefficient and inoculum size on the xylitol production by Candida guilliermondii

Biotechnology production of xylitol is an excellent alternative to the industrial chemical process for the production of this polyalcohol. In this work the behavior of Candida guilliermondii yeast was studied when crucial process variables were modified. The K _La (between 18 and 40/h) and the initial cell mass (between 4 and 10 g) were considered as control variables. A response surface methodology was applied to the experimental design to study the resulting effect when the control variables were modified. A regression model was developed and used to determine an optimal value that was further validated experimentally. The optimal values determined for K _La and X ₀ were 32.85/h and 9.86 g, respectively, leading to maximum values for productivity (1.628 g/h) and xylitol yield (0.708 g/g).     

PANI/La2O3复合纳米材料的合成及其电化学降解的抑制作用

作为离子型表面活性剂, 对-甲基苯磺酸可用于氧化镧的预超声分散处理, 同时还可作为质子酸对聚苯胺(PANI)进行掺杂, 从而赋予聚苯胺导电性. 采用化学法合成了聚苯胺/氧化镧复合纳米材料, 用四探针法测定了材料的电导率, 用扫描电镜、电子能谱、X射线衍射、红外光谱等检测分析手段对材料进行了表征. 结果表明, 聚苯胺及聚苯胺/氧化镧复合纳米材料的电导率分别为1.0•和1.9 S•cm^－1, 粒子直径分别约为200和50 nm. 氧化镧的掺杂未降低聚苯胺的电导率, 并使粒径减小. 循环伏安实验结果说明, 氧化镧的掺杂可提高氧化还原峰的电流密度, 并能有效抑制聚苯胺在0.25～2.0 mol•L^－1的H₂SO₄及H₃PO₄水溶液中的电化学降解.     

Delocalization and Valence Tautomerism in Vanadium Tris(iminosemiquinone) Complexes

To survey the noninnocence of bis(arylimino) acenaphthene (BIAN) ligands (L) in complexes with early metals, the homoleptic vanadium complex, [V(L)₃] ( 1 ), and its monocation, [V(L)₃]PF₆ ( 2 ), were synthesized. These complexes were found to have a very rich electronic behavior, whereby 1 displays strong electronic delocalization and 2 can be observed in unprecedented valence tautomeric forms. The oxidation states of the metal and ligand components in these complexes were assigned by using spectroscopic, crystallographic, and magnetic analyses. Complex 1 was identified as [V^IV(L^red)(L^.)₂] (L^red=N,N′‐bis(3,5‐dimethylphenylamido)acenaphthylene; L^.=N,N′‐bis(3,5‐dimethylphenylimino)acenaphthenesemiquinonate). Complex 2 was determined to be [V^V(L^red)(L^.)₂]⁺ at T<150 K and [V^IV(L^.)₃]⁺ at T>150 K. Cyclic voltammetry experiments reveal six quasi‐reversible processes, thus indicating the potential of this metal–ligand combination in catalysis or materials applications.     

Current Methods for Determination of L-Carnitine and Acylcarnitines

L-Carnitine as endogenous compound plays an important role within several metabolic pathways and a deficiency of L-carnitine can cause adverse effects in physiological and/or mental state of health and disease. The prevention of diseases related to carnitine deficiency requires, first of all, the exact determination of L-carnitine and its esters in biological material at pmol/cm³ level. A series of analytical procedures based on biochemical assays as well as on physical methods are available today. Determination of free and total carnitine is sometimes sufficient for a clinical diagnosis, but in most cases, such as in newborn screening for genetic disorders, detailed qualitative and quantitative L-carnitine/acylcarnitine profiling is needed. Technological progress has also revolutionized the determination of carnitines. Today, comprehensive and diagnostically relevant information can be obtained by mass spectrometry. An overview is given of the technical and methodological developments in carnitine analysis and some applications, such as in neonatal screening, diabetes mellitus, and cardiomyopathy.     

Synthesis of metal-organic frameworks from the system metal/L-glutamic acid/TEA/H2O

Three metal-organic frameworks (MOFs) with similar zeolite-like 3-D structures, Zn(L-Glu)(H₂O) · H₂O, Cu(L-Glu)(H₂O) · H₂O, and Co(L-Glu)(H₂O) · H₂O, have been obtained from metal/L-glutamic acid/TEA/H₂O systems, whereby the weak base triethylamine (TEA), rather than the more typically used NaOH or Na₂CO₃, has been used to adjust the pH of the solution. A systematic and detailed exploration of the synthesis conditions has revealed that not all transition metals may be coordinated to L-glutamic acid and that the range of conditions under which the three MOFs remained stable was different. The metal/L-glutamic acid/TEA/H₂O system offers an effective means of obtaining MOFs.