AES- und XPS-Untersuchungen zum Einflu? von Chrom, Nickel und Molybd?n auf das Korrosionsverhalten von rostfreien St?hlen in S?uren

Summary The alloys Fe17.8Cr, Fe16Cr2.4Mo and Fe18Cr14Ni2.5Mo (at%) were polarized in 0.5 mol/l H₂SO₄ or in 0.1 mol/l HC1 + 0.4 mol/l NaCl. The composition of the oxide layer and of the metallic layer beneath the oxide and the kinetics of the passive layer formation were determined by AES and XPS. In the active region, selective dissolution of Fe leads to an enrichment of Cr, Ni and Mo at the metal/electrolyte interface. In the passive region, the thickness of the rapidly formed passive layer is determined by the potential. The chromium content of the passive layer approaches a stationary, high value. The passive layer essentially consists of the anions O^2- and OH^– and of the cations of Cr, Fe, Mo, whereas Ni — and less pronounced Mo — are enriched below the layer.     

Electrochemical characterisation of dental alloys: its possibilities and limitations

Dental alloys are metallic biomaterials which have a broad variation of composition compared to technical alloys. It is therefore in the interest of patients and technicians to conduct a good assessment of the electrochemical behaviour of dental alloys in order to collect information about their corrosion resistance. The purpose of this work was to demonstrate possibilities and limitations of two electrochemical techniques: the voltammetry of immobilised microparticles (ViMP) onto lead, and cyclic voltammetry measurements with the help of the mini-cell system (MCS). Based on fingerprints obtained from ViMP it was possible to analyse and differentiate the dental alloys. The results obtained by MCS were comparable with ViMP, but give a better understanding of the corrosion behaviour of the materials.     

Selective J‐resolved‐HMQC‐1 and ‐2, new methods for measuring proton–proton coupling constants in strongly coupled spin systems

Efficient pulse sequences for measuring ¹H–¹H coupling constants (J_HH) in strongly coupled spin systems, named selective J‐resolved‐HMQC‐1 and ‐2, have been developed. In the strongly coupled spin systems such as ‐CH₂‐CH_A(OH)‐CH_B(OH)‐CH₂‐, measurements of ³J_HAHB are generally difficult owing to the complicated splitting caused by the adjacent CH₂ protons. For easier and accurate measurements of ³J_HAHB in such a spin system, a selective excitation pulse is incorporated into the J‐resolved HMQC pulse sequence. In the proposed methods, only two strongly coupled protons, H_A and H_B which are excited by a selective pulse, are observed as J‐resolved HMQC signals. The cross peaks of H_A and H_B appear as doublets owing to ³J_HAHB along the F₁ dimension in the selective J‐resolved HMQC‐1 and ‐2 experiments. The efficiency of the proposed pulse sequences has been demonstrated in application to the stereochemical studies of the complicated natural product, monazomycin. Copyright © 2011 John Wiley & Sons, Ltd.     

Oxazolochlorins. 14.

The structure of 8‐oxo‐5,10,15,20‐tetraphenyl‐7‐oxaporphyrin N²⁴‐oxide, C₄₃H₂₈N₄O₃, (4B), shows that N‐oxidation of the pyrrole opposite the oxazolidone group cants the pyrrole out of the mean plane of the chromophore. This also affects the oxazolidone group, which is also slightly canted out. This conformation is qualitatively similar to that of the parent meso‐tetraphenylporphyrin N‐oxide, but dissimilar to that of the porpholactone N‐oxide isomer 8‐oxo‐5,10,15,20‐tetraphenyl‐7‐oxaporphyrin N²²‐oxide, (4A), carrying the N‐oxide at the oxazolidone group. While the degree of canting of the N‐oxidized groups in both cases is comparable (and more pronounced than in the porphyrin N‐oxide case), in (4A) the pyrrolic groups adjacent to the N‐oxidized group are more affected than the opposing group. These differences in the conformational modes may contribute to rationalizing the distinctly different electronic properties of (4A) and (4B).     

Surface glass transition of miscible amorphous polymers blends

The surface glass transition temperature (T _g ^surface) of the bulk samples of miscible blends formed of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been characterised in terms of an adhesion approach we proposed recently. T _g ^surface has been measured as the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” by employing a lap-shear joint mechanical testing method. The effect of the reduction in T _g ^surface with respect to the glass transition temperature of the bulk (T _g ^bulk), which had been observed earlier in pure homopolymers, has been found to exist in the blends of PS with PPO as well. The values of this effect for the blends have been compared with those for pure homopolymers, and the differences found have been discussed.     

Selective COSY‐J‐resolved‐HMBC,a new method for improving sensitivity of cross peaks of methine proton signals attached to a methyl group

Improved pulse sequences for measuring long‐range C‐H coupling constants (ⁿJ_C‐H), named selective COSY‐J‐resolved HMBC‐1 and ?2, have been developed. In the spin systems, such as ‐CH_C‐CH_A(CH₃)‐CH_B‐, a methine proton H_A splits into a multiplet owing to several vicinal couplings with protons, resulting in attenuation of its cross‐peak intensity. Therefore, the measurements of ⁿJ_C‐H with H_A are generally difficult in the J‐resolved HMBC or selective J‐resolved HMBC spectrum. With the aim of accurate measurements of ⁿJ_C‐H in such a spin system, we have developed new pulse sequences, which transfer the magnetization of a methyl group to its adjacent methine proton. The proposed pulse sequences successfully enable to enhance the sensitivity of H_A cross peak in comparison with the selective J‐resolved HMBC pulse sequence. Copyright © 2012 John Wiley & Sons, Ltd.     

Conformational behavior of styrene–p-chlorostyrene triblock copolymers in dilute solutions. I. Composition dependence of conformational behavior

Dilute solution properties of (styrene-p-chlorostyrene) triblock copolymers in various solvents were studied over a wide range of molecular weight and composition. Viscosity and osmotic pressure results indicate that the conformational behavior of the B_mA_nB_m and A_mB_nA_m copolymers (A = styrene; B = p-chlorostyrene; m and n denote the number of units) are similar in nonselective solvents such as toluene and 2-butanone, but different in selective solvents such as carbon tetrachloride and cumene. Short-range and long-range interaction parameters of the block copolymers were determined by applying the Stockmayer–Fixman method to viscosity data and also by application of the equation relating the osmotic virial coefficient and the excluded volume. The results show that the unperturbed dimensions of the block copolymers vary linearly with composition, and long-range interaction parameters in nonselective solvents can be expressed by those of the parent homopolymers, the chemical composition, and values of the interaction parameter β_AB between styrene and p-chlorostyrene monomeric units.     

Rational Design of a Confacial Pentaoctahedron: Anisotropic Exchange in a Linear ZnIIFeIIIFeIIIFeIIIZnII Complex

The first confacial pentaoctahedron comprised of transition metal ions namely Zn^IIFe^III_AFe^III_BFe^III_AZn^II has been synthesized by using a dinucleating nonadentate ligand. The face-sharing bridging mode enforces short Zn^II⋅⋅⋅Fe^III_A and Fe^III_A⋅⋅⋅Fe^III_B distances of 2.83 and 2.72 Å, respectively. Ab-initio CASSCF/NEVPT2 calculations provide significant negative zero-field splittings for Fe^III_A and Fe^III_B with |D_A|>|D_B| with the main component along the C₃ axis. Hence, a spin-Hamiltonian comprised of anisotropic exchange, zero-field, and Zeeman term was employed. This allowed by following the boundary conditions from the theoretical results the simulation in a theory-guided parameter determination with J^xy=+0.37, J^z=−0.32, D_A=−1.21, E_A=−0.24, D_B=−0.35, and E_B=−0.01 cm⁻¹ supported by simulations of high-field magnetic Mössbauer spectra recorded at 2 K. The weak but ferromagnetic Fe^III_AFe^III_B interaction arises from the small bridging angle of 84.8° being at the switch from anti- to ferromagnetic for the face-sharing bridging mode.     

Removal of the PsaF Polypeptide Biases Electron Transfer in Favor of the PsaB Branch of Cofactors in Triton X‐100 Photosystem I Complexes from Synechococcus sp. PCC 7002†

Continuous wave (CW) and transient electron paramagnetic resonance studies have implied that when PsaF is removed genetically, the double reduction of A_1A is facile, the lifetime of A_1A^? is shorter and the ratio of fast to slow kinetic phases increases in PS I complexes isolated with Triton X‐100 (Van der Est, A., A. I. Valieva, Y. E. Kandrashkin, G. Shen, D. A. Bryant and J. H. Golbeck [2004] Biochemistry 43 , 1264–1275). Changes in the lifetimes of A_1A^? and A_1B^? are characteristic of mutants involving the quinone binding sites, but changes in the relative amplitudes of A_1A^? and A_1B^? are characteristic of mutants involving the primary electron acceptors, A_0A and A_0B. Here, we measured the fast and slow phases of electron transfer from A_1B^? and A_1A^? to F_X in psaF and psaE psaF null mutants using time‐resolved CW and pump‐probe optical absorption spectroscopy. The lifetime of the fast kinetic phase was found to be unaltered, but the lifetime of the slow kinetic phase was shorter in the psaF null mutant and even more so in the psaE psaF null mutant. Concomitantly, the amplitude of the fast kinetic phase increased by a factor of 1.8 and 2.0 in the psaF and psaE psaF null mutants, respectively, at the expense of the slow kinetic phase. The change in ratio of the fast to slow kinetic phases is explained as either a redirection of electron transfer through A_1B at the expense of A_1A, or a shortening of the lifetime of A_1A^? to become identical to that of A_1B^?. The constant lifetime and the characteristics of the near‐UV spectrum of the fast kinetic phase favor the former explanation. A unified hypothesis is presented of a displacement of the A‐jk(1) α‐helix and switchback loop, which would weaken the H‐bond from Leu₇₂₂ to A_1A, accounting for the acceleration of the slow kinetic phase, as well as weaken the H‐bond from Tyr₆₉₆ to A_0A, accounting for the bias of electron transfer in favor of the PsaB branch of cofactors.     

The viscosities of some lead-antimony and lead-antimony-tin alloys

Abstract

The viscosities of some Pb-Sb alloys up to 10.8% Sb and Pb-Sb-Sn alloys up to 10% Sb and 10% Sn have been determined to an accuracy of ± 0.5% by an absolute method applied to an oscillational viscosimeter. Andrade's equation ηv ^½ = A exp C/vT has been used to describe the viscosity-temperature relationships, and values for the constants A and C are given. For Pb-Sb alloys, isothermal viscosities at 350 °C and 550 °C vary linearly with composition demonstrating ideal mixing. Using earlier data on Pb-Sn alloys, it is possible to demonstrate that the ternary alloys also show ideal solution behaviour over the composition range studied. Some brief comment is given on the state of reliable knowledge of alloy viscosities. It is concluded that much work remains to be done using tractable, accurate mathematical analyses for absolute viscosity measurements.     

Dealloying Ag–Al Alloy to Prepare Nanoporous Silver as a Substrate for Surface‐Enhanced Raman Scattering: Effects of Structural Evolution and Surface Modification

Sensitive detection of molecules by using the surface‐enhanced Raman scattering (SERS) technique depends on the nanostructured metallic substrate and many efforts have been devoted to the preparation of SERS substrates with high sensitivity, stability, and reproducibility. Herein, we report on the fabrication of stable monolithic nanoporous silver (NPS) by chemical dealloying of Ag–Al precursor alloys with an emphasis on the effect of structural evolution on SERS signals. It was found that the dealloying conditions had great influence on the morphology (the ligament/pore size) and the crystallization status, which determined the SERS signal of rhodamine 6G on the NPS. NPS with small pores, low residual Al, and perfect crystallization gave high SERS signals. A high enhancement factor of 7.5×10⁵ was observed on bare NPS obtained by dealloying Ag₃₀Al₇₀ in 2.5 wt % HCl at room temperature followed by 15 min aging at around 85 °C. After coating Ag nanoparticles on the NPS surface, the enhancement factor increased to 1.6×10⁸ owing to strong near‐field coupling between the ligaments and nanoparticles.     

Star-shaped block copolymers. III. Surface and interfacial properties

Surface and interfacial activities of A(B)₂ star-shaped block copolymers, where B is a polyoxirane block and A a polydiene or polyvinyl block, have been measured at 20°C. The surface tension of organic solvents is only slightly lowered by these copolymers, whereas a significant surface activity is noted in water. Interfacial tensions are dependent on both the nature of the organic solvent (aliphatic or aromatic hydrocarbons) and the molecular parameters of the copolymers; 50% polyoxirane seems to be the composition of maximum surface activity. The role played by the molecular architecture [A-B or A(B)₂] of the copolymers is demonstrated. The same limiting interfacial tension is obtained on increasing the concentration of diblock [A-B] or star-shaped block [A(B)₂] copolymer. The limiting value is, however, attained at significantly lower concentration with the star-shaped copolymers. Their ability to fill the interface is accordingly higher.     

稀土元素对R-Y-Ni系A2B7型无镁储氢合金微观结构和电化学性能的影响

采用真空电弧熔炼及退火处理制备R-Y-Ni系A_2B_7型R0.3Y0.7Ni3.25Mn0.15Al0.1(R=Y,La,Pr,Ce,Nd,Gd,Sm)储氢合金,系统研究稀土元素R对合金微观组织与结构、储氢和电化学性能的影响。XRD和SEM-EDS分析表明,合金退火组织由Ce2Ni7型主相、PuNi3型及少量Ca Cu5型相组成,Ce2Ni7型主相的晶格常数a、c及晶胞体积V均随稀土R原子半径的减小而依次降低。该合金均具有明显的吸放氢平台,常温下最大吸氢容量为1.17%~1.48%(w/w),吸氢平台压Peq为0.037~0.194 MPa。电化学分析表明,退火合金电极的电化学活化性能优良,R=La合金具有最高的放电容量(389.2 mAh·g-1)和较佳的容量保持率(充放电循环100次后的S100=85.7%),其中合金微观组织的不均匀性及稀土元素的电化学腐蚀是影响电极循环稳定性的主要原因。合金电极的高倍率放电性能(电流密度为900 m A·g-1)HRD900=71.05%~86.94%,其电极反应动力学控制步骤主要由氢原子在合金体相中的扩散速率所控制。     

Four supramolecular isomers of dichloridobis(1,10‐phenanthroline)cobalt(II): synthesis,structure characterization and isomerization

Crystal engineering can be described as the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding to design new solids with desired physical and chemical properties. Free‐energy differences between supramolecular isomers are generally small and minor changes in the crystallization conditions may result in the occurrence of new isomers. The study of supramolecular isomerism will help us to understand the mechanism of crystallization, a very central concept of crystal engineering. Two supramolecular isomers of dichloridobis(1,10‐phenanthroline‐κ²N,N′)cobalt(II), [CoCl₂(C₁₂H₈N₂)₂], i.e. (IA) (orthorhombic) and (IB) (monoclinic), and two supramolecular isomers of dichloridobis(1,10‐phenanthroline‐κ²N,N′)cobalt(II) N,N‐dimethylformamide monosolvate, [CoCl₂(C₁₂H₈N₂)₂]·C₃H₇NO, i.e. (IIA) (orthorhombic) and (IIB) (monoclinic), were synthesized in dimethylformamide (DMF) and structurally characterized. Of these, (IA) and (IIA) have been prepared and structurally characterized previously [Li et al. (2007). Acta Cryst. E 63 , m1880–m1880; Cai et al. (2008). Acta Cryst. E 64 , m1328–m1329]. We found that the heating rate is a key factor for the crystallization of (IA) or (IB), while the temperature difference is responsible for the crystallization of (IIA) or (IIB). Based on the crystallization conditions, isomerization behaviour, the KPI (Kitajgorodskij packing index) values and the density data, (IB) and (IIA) are assigned as the thermodynamic and stable kinetic isomers, respectively, while (IA) and (IIB) are assigned as the metastable kinetic products. The 1,10‐phenanthroline (phen) ligands interact with each other through offset face‐to‐face (OFF) π–π stacking in (IB) and (IIB), but by edge‐to‐face (EF) C—H...π interactions in (IA) and (IIA). Meanwhile, the DMF molecules in (IIB) connect to neighbouring [CoCl₂(phen)₂] units through two C—H...Cl hydrogen bonds, whereas there are no obvious interactions between DMF molecules and [CoCl₂(phen)₂] units in (IIA). Since OFF π–π stacking is generally stronger than EF C—H...π interactions for transition‐metal complexes with nitrogen‐containing aromatic ligands, (IIA) is among the uncommon examples that are stable and densely packed but that do not following Etter's intermolecular interaction hierarchy.     

Ab initio study of low-lying electronic states of the FNO2 molecule

Ab initio electronic structure calculations are reported for low-lying electronic states, ¹A₁, ¹A₂, ³A₂, ¹B₁, ³B₁, ¹B₂, and ³B₂ of the FNO₂ molecule. Geometric parameters for the ground state ¹A₁ are predicted by MRSDCI calculations with a double-zeta plus polarization basis set. The vertical excitation energies for these electronic states are determined using MRSDCI/DZ+P calculations at the ground-state equilibrium conformation. The oscillator strengths and radiative lifetimes for some electronic states are calculated based on the MRSDCI wave functions. © 1993 John Wiley & Sons, Inc.     

Vertical proton affinities of CH2O and CH2OH+ in their ground singlet,excited triplet and ionized doublet states

Vertical proton affinities were calculated with closed and open shell direct SCF-MO methods for the ground, excited triplet and ionized doublet states of CH₂O and CH₂OH⁺.The computed gas phase basicity of CH₂O follows the order: CH₂O(¹ A ₁) > CH₂O*(³ A ₁ or ³ A ₂) > CH₂O⁺(² B ₂ or ² B ₁).     

Effect of Sn additions on the microstructure,mechanical properties,corrosion and bioactivity behaviour of biomedical Ti–Ta shape memory alloys

Ti–Ta and Ti–Ta–xSn shape memory alloys (SMAs) were produced successfully by microwave sintering. Tin element was added to Ti–Ta SMA with three different atomic percentages (0.37, 0.745 and 2.26 at.%). The influences of Sn addition on microstructure, transformation temperatures, mechanical properties, shape memory behaviours, corrosion resistance and bioactivity were investigated. It was found that the morphologies of the modified and unmodified Ti–Ta alloys contain a plate-like and needle-like structure, where the former structure is related to the β phase and the latter related to the α phase. The transformation temperatures of M _s to M _f with and without Sn additions were observed to be in the range of 389.65 to 355 K, while the transformation temperatures of A _s to A _f were found to be in the range of 250.42 to 365.8 K. By increasing the proportion of Sn, the compressive fracture strength and shape memory behaviour were enhanced; however, the corrosion resistance tended to be decreased. Based on the bioactivity results, antibacterial activity was improved with the addition of Sn. In conclusion, the existent results indicate that Ti–30 at.% Ta SMAs may be a convenient alternative to Ni–Ti for certain biomedical applications.

     

The negative adsorption of chromium atoms on alloy-oxide film boundaries during oxidation in air and anodic passivation of Fe-Cr and Ni-Cr alloys

Equilibrium of Cr atoms between the surface layer and bulk of a binary alloy was analyzed. The Gibbs adsorption equation was used to obtain the dependence of the adsorption activity of atoms in the surface layer on their activity in the bulk. An approximate thermodynamic method was used to calculate the adsorption of Fe (Ni) and Cr atoms in the surface layers of Fe-Cr and Ni-Cr alloys. According to calculations, there was negative adsorption, X _Cr ≪ 1, in the surface layer of the alloys caused by a large difference between the Gibbs surface energies of Cr and Fe (or Ni). The negative adsorption of Cr shifted chemical reaction equilibria on the alloy-oxide film boundary both in oxidation in air and in anodic passivation, 3FeO (NiO) + 2Cr = Cr₂O₃ + 3Fe(Ni), toward oxide film enrichment in the FeO (or NiO) oxide. A unified method for calculating the composition of oxide films on alloys was used for both processes. The method was based on the use of the initial data on the Gibbs surface energy of metals constituting alloys. The calculated oxide film compositions were close to the experimental X-ray photoelectron spectroscopy data.     

Study of anodizing process on aluminium foam to improve the corrosion behavior

Aluminium foam is obtained by the production of air into metallic melt. This material shows a very low density together with good mechanical properties, high impact energy absorption, and fire resistance. Different production ways to obtain metallic foam are possible. Considering the cost, the Alporas process is particularly interesting. By means of this production method, a block of metallic foam with close cells is obtained. By slicing, foam panels are obtained. The mechanical cut promotes the formation of an open cells texture on the surface. In this last case, the complex morphology of aluminium foam could be a critical point considering the corrosion behavior in aggressive environments, where localized corrosion phenomena, as pitting or crevice corrosion, are likely to occur. The anodizing treatment is one of the most used methods to improve the corrosion resistance of aluminium and aluminium alloys. The aim of this paper is to perform an anodization treatment to enhance the corrosion resistance of aluminium foam. Constant voltage anodization (12 V for 60 min) and pulsed current anodization (0.04 A/cm² for 60 seconds and 0.01 A/cm² for 15 seconds, repeated for 15 cycles) have been carried out in 15 wt% H₂SO₄ at 20°C. The anodized samples are observed in cross section by optical and electronic microscopes to investigate the structure of the anodic oxide layer and the presence of defects and to measure the thickness of the layer. The corrosion protection performance and the compactness of layers are evaluated using acetic salt spray test and electrochemical impedance spectroscopy.     

Kinetic studies on state-state coupling and collisional quenching of excited sulfur dioxide

The time-resolved total emission of SO₂ (B¹B₁→X¹A₁) at 354.9 nm were monitored following the direct excitation by a 266 nm laser pulse. A three-level model was proposed to deal with SO₂ (X¹A₁, A¹A₂, B¹B₁) system. From a kinetic treatment of these measurements, the coupling coefficient, ξ, and the relaxation time, τ, relating to the high vibronic levels of A¹A₂ and B¹B₁ states were first obtained. It is found that ξ and τ values keep basically constant, reflecting the characteristics of the studied system. In addition, the quenching rate constants of SO₂ (A¹A₂, B¹B₁) by some alkane and chloromethane molecules were measured at room temperature. The formation cross sections of complexes of SO₂ (A¹A₂, B¹B₁) and quenchers were calculated by means of a collision complex model. It is shown that the dependence of the formation cross section of complex on the number of C(SINGLEBOND)H or C(SINGLEBOND)Cl bonds is generally in agreement with that of the measured quenching cross section. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 831–837, 1998