Chemical stability of hydroxysulphate green rust synthetised in the presence of foreign anions: carbonate, phosphate and silicate

Hydroxysulphate green rust species were precipitated in the presence of various anions. is stable at ∼pH 7 and is transformed into a mixture of magnetite and ferrous hydroxide when the pH raised at ∼12. In the presence of carbonate species, is partially transformed into a mixture of magnetite and siderite at ∼pH 8.5. This transformation is stopped when silicate anions are present in the solution. As already observed for phosphate anions, the adsorption of silicate anions on the lateral faces of the crystals may explain this stabilization effect. Sulphate anions are easily exchanged by carbonate species at ∼pH 10.5. In contrast, anionic exchange between sulphate and phosphate anions was not observed.     

Synthesis and characterisation of the Fe(II–III) hydroxy-formate green rust

A new methodology was envisioned in order to prepare green rust compounds build on organic anions that could intervene in microbiologically influenced corrosion processes of iron and steel. The formate ion was chosen as an example. The formation of rust was simulated by the oxidation of aqueous suspensions of Fe(OH)₂ precipitated from Fe(II) lactate and sodium hydroxide, in the presence of sodium formate to promote the formation of the corresponding green rust. The evolution of the precipitate with time was followed by transmission Mössbauer spectroscopy at 15 K. It was observed that the initial hydroxide was transformed into a new GR compound. Its spectrum is composed of three quadrupole doublets, D ₁ (δ?=?1.28 mm s^?1, Δ?=?2.75 mm s^?1) and D ₂ (δ?=?1.28 mm s^?1, Δ?=?2.48 mm s^?1) that correspond to Fe(II) and D ₃ (δ?=?0.49 mm s^?1, Δ?=?0.37 mm s^?1) that corresponds to Fe(III). The relative area of D ₃, close to the proportion of Fe(III) in the GR, was found at 28.5?±?1.5% (～2/7). Raman spectroscopy confirmed that the intermediate compound was a Fe(II–III) hydroxy-formate, GR(HCOO^?).     

The simultaneous presence of green rust 2 and sulfate reducing bacteria in the corrosion of steel sheet piles in a harbour area

Mössbauer spectroscopy and X-ray diffraction analysis allow to detect the presence of green rust 2, the ferrous-ferric sulfated compound of composition, 4Fe(OH)₂,2FeOOH,FeSO₄,nH₂O, mixed with magnetite at the surface of steel sheets corroded in a harbour area where the presence of sulfate reducing bacteria are also detected.     

Mössbauer effect evidence of a ferrous sulphate layer in the structure of green rust 2 and its atmospheric oxidation

Mössbauer spectra of green rust 2 run under vacuum from 78 K to 460 K, display a gradual change in the abundances of two out of three ferrous sites, with the ferric sites due to electronic exchange. Further oxidation in atmospheric conditions gives spectra displaying that the two first Fe²⁺ ions become oxidized to the ferric state, but that the last Fe²⁺ site remain unoxidized: thus, a ferrous sulphate layer in the structure of green rust 2 is left unchanged.     

The oxidation of Fe(OH)2 in the presence of carbonate ions: Structure of carbonate green rust one

Sodium carbonate Na₂CO₃ is added to a solution containing an Fe(OH)₂ precipitate in order to study the influence of CO ₃ ^2– ions on the oxidation of ferrous hydroxide. The first stage of the reaction leads to a ferrous-ferric compound, the carbonate green rust one (GR1), identified by its X-ray diffraction pattern. The Mössbauer spectrum at 78 K of this GR1 displays two ferrous doublets and one ferric doublet in the 312 abundance ratio. The quadrupole splittingsQS are 2.91, 2.58 and 0.42 mm/s, respectively, and the isomer shifts 75 are 1.25, 1.25 and 0.47 mm/s respectively. These values are very close to those of the three doublets of the chloride GR1, 3Fe(OH)₂Cl·Fe(OH)₂Cl·nH₂O. This fact confirms that the crystallographic structures of these two GR1s are similar, formed by the stacking of hydroxide layers and interlayers containing the considered anions (Cl^– or CO ₃ ^2– ) and water molecules. The chemical formula of carbonate GR1 is Fe ₄ ^(II) Fe ₂ ^(III) (OH)₁₂CO₃·nH₂O, and its standard chemical potential -853 900 cal/mol ifn=0. The second stage of the reaction is the oxidation of GR1, which leads to -FeOOH goethite.     

Controlled extracellular biosynthesis of ZnS quantum dots by sulphate reduction bacteria in the presence of hydroxypropyl starch as a mediator

Metal sulphide quantum dots (QDs) have broad applications. Sulphate-reducing bacteria (SRB) have been recognized as synthesizers of metal sulphides, with the characteristics of a high-production efficiency and easy product harvest. However, SRB are incapable of synthesizing metal sulphide QDs. In the present study, cheap hydroxypropyl starch (HPS) was used to assist SRB in manufacturing the ZnS QDs. The results exhibited that the HPS accelerated the growth of SRB and reduction of SO₄ ²⁺ into S^2?, while it blocked the precipitation between S^2? and Zn²⁺ to control the nucleation and growth of ZnS, resulting in the formation of ZnS QDs. When the HPS concentration increased from 0.2 to 1.6 g/L, the average crystal size (ACS) of ZnS QDs dropped from 5.95 to 3.34 nm, demonstrating the controlled biosynthesis of ZnS QDs. The ZnS QDs were coated or adhered to by both HPS and proteins, which played an important role in the controlled biosynthesis of ZnS QDs. The remarkable blue shift of the narrow UV absorption peak was due to the quantum confinement effect. The sequential variation in the colour of the photoluminescence spectrum (PL) from red to yellow suggested a tunable PL of the ZnS QDs. The current work demonstrated that SRB can fabricate the formation of ZnS QDs with a controlled size and tunable PL at a high-production rate of approximately 8.7 g/(L × week) through the simple mediation of HPS, with the yield being 7.46 times the highest yield in previously reported studies. The current work is of great importance to the commercialization of the biosynthesis of ZnS QDs.     

Positivity of entropy production in the presence of a random thermostat

We study nonequilibrium statistical mechanics in the presence of a thermostat acting by random forces, and propose a formula for the rate of entropy productione() in a state . When is a natural nonequilibrium steady state we show thate()0, and sometimes we can provee()>0.     

Micro‐structural characterization of red decorations of red and green color porcelain (Honglvcai) in China

Red and green color porcelain (Honglvcai) is an important type of polychrome porcelains invented in North China during Song and Jin Dynasties. One of its great successes is its red decoration painted on the surface of glaze and fired at low temperature. Raman spectroscopy and X‐ray absorption fine structure (XAFS) at Fe K‐edge, were used to characterize the microstructure of red decorations from Song and Jin Dynasties to Ming Dynasty. The analyzing results on eight samples showed that hematite (α‐Fe₂O₃) was the main chromogenic substance in red decorations from different dynasties, which indicated a similar technological skill among the investigated samples. The oxidation state of iron in red decorations was determined to be mainly trivalent, indicating that red decorations were fired under oxidizing atmosphere. Besides, it was found that the hematite (α‐Fe₂O₃) in red decorations had a distorted structure, which was presumed to be an important factor influencing the color of red decorations. Copyright © 2009 John Wiley & Sons, Ltd.     

Automated Mössbauer spectroscopy in the field and monitoring of fougerite

A special experimental setup for in-field applications was developed at Mainz. It incorporates hardware for automated positioning of the Mössbauer sensor head, a Plexiglas tube, and a modified version of the space proven Miniaturized Mössbauer Spectrometer MIMOS II (Klingelhöfer et al., Science, 306:1740–1745, 2004; Klingelhöfer et al., J. Geophys. Res., 108(E12):8067, 2003; Klingelhöfer et al., Hyperfine Interact. 144/145:371–379, 2002; Génin et al., Solid State Sci., 7:545–572, 2005). MIMOS operates in backscattering geometry, thus no sample preparation is required. Also dedicated software for running measurement sequences (e.g., different depth positions at different times etc.) was developed. The setup can work autonomously up to several weeks in the field. Preliminary results confirm that fougerite mineral found in hydromorphic soils is Fe^II–III hydroxycarbonate green rust.     

Conductometric and fluorometric studies of sodium dodecyl sulphate in aqueous solution and in the presence of amino acids

The critical micelle concentration (CMC) of sodium dodecyl sulphate (SDS) in pure water and in the presence of amino acids (0.01, 0.02 and 0.03 mol kg^?1), L-valine (Val) and L-leucine (Leu) was determined from conductometric and fluorometric methods using pyrene as luminescence probe. Depression in the CMC at low concentration of amino acids is attributed to the increased hydrophobic–hydrophobic interaction between the non-polar groups of the surfactant, while, at high concentration, amino acids bind strongly with the anion, DS^?, head groups of SDS, thereby, delaying the micelle formation, resulting in increased CMC. A pronounced decrease in the CMC, while a marked increase in λ⁰₊, with decrease in the solvated radius (rather than crystal radius) of the counterions is observed. Negative values of ΔG⁰_m and ΔH⁰_m indicate that micellisation of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. Highest negative value of ΔH⁰_m in 0.01 m Val, with lowest CMC value, shows that 0.01 m aqueous Val is the most suitable medium favouring the micellisation of SDS. Decrease in I₁/I₃ from Val to Leu confirms the relative hydrophobicity of two amino acids. The observed values of the packing parameter, P, of SDS in water and in aqueous amino acids suggest that micelles formed are spherical in nature.     

折叠腔内的偏振效应对绿光输出稳定性的影响

将Jones矩阵法与耦合波方程结合起来分析折叠腔腔内倍频中的绿光问题。在用Jones矩阵法分析折叠镜的偏振效应基础上,通过数值求解耦合波方程讨论了这一效应对绿光输出稳定性的影响,计算结果与相关实验结果的比较表明,合理设计的折叠腔可以比线性腔更有效地抑止绿光波动。     

Phase transformation and shape evolution of iron oxide nanocrystals synthesized in the ethylene glycol-water system

Iron oxide particles with various shapes,sizes and phase concentrations(including--Fe2O3 and Fe3O4) have been synthesized through a simple hydrothermal method in the ethylene glycol(EG)-water system.In the preparation conditions,ferric chloride(FeCl3.6H2O) was used as the iron source in the presence of sodium hydroxide(NaOH) without any surfactants.By adjusting the experimental parameters(EG/H2O ratio,base content,iron ions concentration,etc.),the shape,the size,the phase and the magnetic property of the pr...     

Effects of multiple interruptions with trimethylindium-treatment in the InGaN/GaN quantum well on green light emitting diodes

In this study, the influence of multiple interruptions with trimethylindium(TMIn)-treatment in InGaN/GaN multiple quantum wells(MQWs) on green light-emitting diode(LED) is investigated. A comparison of conventional LEDs with the one fabricated with our method shows that the latter has better optical properties. Photoluminescence(PL) full-width at half maximum(FWHM) is reduced, light output power is much higher and the blue shift of electroluminescence(EL) dominant wavelength becomes smaller with current increasing. These improvements should be attributed to the reduced interface roughness of MQW and more uniformity of indium distribution in MQWs by the interruptions with TMIn-treatment.     

Determination of albumins by its quenching effect on the fluorescence of Tb-oxolinic acid complex in presence of sodium dodecyl sulphate

It is found that the fluorescence intensity of Tb³⁺-oxolinic acid (OA) complex can be greatly quenched by albumins in sodium dodecyl sulphate (SLS). Under optimum conditions, the quenched fluorescence intensity is in proportion to the concentration of proteins in the range of 5.0×10⁻⁸-1.0×10⁻⁵ g ml⁻¹ for bovine serum albumin (BSA), 1.0×10⁻⁷-1.0×10⁻⁵ g ml⁻¹ for human serum albumin (HSA) and 4.0×10⁻⁷-1.0×10⁻⁵ g ml⁻¹ for egg albumin (EA). Their detection limits (S/N=3) are 2.1×10⁻⁸, 2.5×10⁻⁸ and 5.0×10⁻⁸ g ml⁻¹, respectively. In addition, the interaction mechanism is also investigated.     

Kinetics of phase transformation from hBN to cBN in the presence of Mg3BN3 catalyst

Abstract

Transformation kinetics from hBN to cBN has been studied at 6 GPa with changing reaction temperature and content of catalyst mixed with hBN powder. At lower catalyst content (3–10 wt %), rate of transformation was extraordinary rapid between 1300 and 1350 C. At higher catalyst content (30–50 wt %), rate of transformation was decreased. Normal nucleation kinetics was observed at about 1500 C. The rapid transformation temperature region correlates characteristic behavior of the sintering process.     

A methodology for structural health monitoring with diffuse ultrasonic waves in the presence of temperature variations

Diffuse ultrasonic waves for structural health monitoring offer the advantages of simplicity of signal generation and reception, sensitivity to damage, and large area coverage; however, there are the serious disadvantages of no accepted methodology for analyzing the complex recorded signals and sensitivity to environmental changes such as temperature and surface conditions. Presented here is a methodology for applying diffuse ultrasonic waves to the problem of detecting structural damage in the presence of unmeasured temperature changes. This methodology is based upon the prediction and observation that the first order effect of a temperature change on a diffuse ultrasonic wave is a time dilation or compression. A multi-step procedure is implemented to (1) record a set of baseline waveforms from the undamaged specimen at temperatures spanning the expected operating range, (2) select a waveform from the baseline set whose temperature is the closest to that of a subsequently measured signal, (3) adjust this baseline waveform to best match the signal, and (4) calculate an error parameter between the signal and the adjusted waveform and compare this parameter to a threshold to determine the structural status. This procedure is applied to experimental data from aluminum plate specimens with artificial flaws. Probability of detection and the minimum flaw size detected are presented as a function of the size of the baseline waveform set. It is shown that a probability of detection of over 95% can be achieved with a small number of baseline waveforms.     

Geometry optimization in the presence of external forces: a theoretical model for enforced structural changes in molecules

Recently, we proposed a very simple quantum chemical model to simulate the effect of external forces acting on a single molecule [Mol. Phys. 107, 2403 (2009)]. It is based on optimizing the geometry of a molecule with an external force applied to selected pairs of nuclei. In this study we extend this model by considering interactions of external forces not only with the nuclei but also with their electrons, in particular their core electrons, which can be viewed as ‘rigidly’ connected to a nucleus. In the proposed revised model an external force acts on an object which consists of the nucleus of an atom and its 1s core electrons. It is shown in this study that such a model predicts the same conformational (structural) changes in a molecule as our simpler model where the external forces interact with the nuclei only. However, the magnitude of the forces required to cause these changes is now lower and within the range of forces used in real AFM experiments.     

Ultrasonic imaging of an object at the presence of Fourier and non-Fourier transformation in the transmitted through the object acoustic field

A metal object is computer visualized by registration of the amplitudes of the transmitted through the object short acoustic pulses. The pulses are separated by time, because of the presence of holes and internal compact components in the longitudinal section (structure along the propagation direction of acoustic wave). The acoustic field transmitted through the object is composited from a field presenting Fourier transformation of the hole shape and field, transmitted through the metal components in the longitudinal section of the object. A computer Fourier transformation of the digital data of the amplitude fields transmitted through the object components is performed instead of converging lens. The Fourier series of the object obtained as digital data after the transformation is multiplied with a term, describing the angle distribution of the field on spatial frequencies. The reconstruction of the image of the metal components is performed by reverse transformation, i.e. summing up in all spatial frequencies. 3D visualization of the transmitted through the hole acoustic field determines the hole geometry (circular, square, rectangular).It is shown that at the transmission of a short acoustic pulse through the components with different thicknesses and holes, presenting Fourier and non-Fourier transformation can be registered separately in contrast to the optics.     

Protein backbone dynamics from N-HN dipolar couplings in partially aligned systems: a comparison of motional models in the presence of structural noise

Residual dipolar couplings (RDCs) provide excellent probes for the exploration of dynamics in biomolecules on biologically relevant time-scales. Applying geometric motional models in combination with high-resolution structures to fit experimental RDCs allows the extraction of local dynamic amplitudes of peptide planes in proteins using only a limited number of data points. Here we compare the behaviour of three simple and intuitive dynamic modes: the Gaussian axial fluctuation model (1D-GAF), the two-site jump model, and a model supposing axially symmetric motion about a mean orientation. The requirement of a structural model makes this kind of methodology potentially very sensitive to structural imprecision. Numerical simulations of RDC dynamic averaging under different regimes show that the anisotropic motional models are more geometrically stringent than the axially symmetric model making it more difficult to alias structural noise as artificial dynamic amplitudes. Indeed, it appears that the model extracts accurate motional amplitudes even in the presence of significant structural error. We also show that a two-site jump model, also assuming the (alpha)C(i-1)-(alpha)C(i) as rotation axis, can only be distinguished from the previously developed GAF model beyond amplitude/jumps of around 40 degrees. The importance of appropriate estimation of the molecular alignment tensor for determination of local motional amplitudes is also illustrated here. We demonstrate a systematic scaling of extracted dynamic amplitudes if a static structure is assumed when determining the alignment tensor from dynamically averaged RDCs. As an example an artificial increase of 0.14 (0.85 compared to the expected 0.71) is observed in the extracted S2 if a pervasive 20 degrees GAF motion is present that is ignored in the tensor determination. Finally we apply a combined approach using the most appropriate motional model, to complete the analysis of dynamic motions from protein G.     

Hcp-icosahedron structural transformation induced by the change in Ag concentration during the freezing of （CoAg）561 clusters

The synergy effect of alloy elements in bimetallic clusters can be used to tune the chemical and physical properties. Research on the influences of alloy concentration and distribution on the frozen structure of bimetallic clusters plays a key rolc in exploring new structural materials. In this paper, we study the influence of Ag concentration on the frozen structure of the （AgCo）561 cluster by using molecular dynamics simulation with a general embedded atom method. The results indicate that tt~e structure and chemical ordering of the （AgCo）561 cluster are strongly related to Ag concentration. Hcp-icosahedron structural transformation in the frozen （CoAg）561 cluster can be induced by changing Ag concentration. The chemical ordering also transforms to Janus-like Co Ag from core-shell Co-Ag.