Textural evolution in electrodeposits under the influence of adsorbed foreign species: Part II A simulation study on effects of potassium chlorideon textural evolution in copper electrodeposits

The texture of copper deposits produced in the bath containing potassium chloride changes with the content of the potassium chloride. This change in texture was usually explained to be caused by chloride adsorption on the cathode. This paper reports simulation studies on textural evolution in copper electrodeposits under the influence of potassium chloride, using a Monte Carlo simulation approach. The study was conducted based on the assumption that the textural development results from the minimization of the system free energy in which the surface-energy anisotropy plays the most important role. The simulation demonstrates that adsorbed potassium ions may change the surface-energy anisotropy of copper, and therefore, they also affect texture variation in copper deposits in addition to the chloride effect. It was observed the potassium effect on textural variation in copper deposits is even stronger than that of the Cl- adsorption. This revised version was published online in November 2006 with corrections to the Cover Date.     

Solid-phase deformations of disperse systems under the influence of adsorbed water

On the basis of diffractometric investigations, the expansion in volume of kaolinite in the course of hydration is established.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 3, pp. 528–532, March, 1979.     

Part I: surface-enhanced Raman spectroscopy investigation of amino acids and their homodipeptides adsorbed on colloidal silver

Surface-enhanced Raman scattering spectra (SERS) were measured for various amino acids: L-methionine (Met), L-cysteine (Cys), Lglycine (Gly), L-leucine (Leu), L-phenylalanine (Phe), and L-proline (Pro) and their homodipeptides (Met-Met, Cys-Cys, Gly-Gly, LeuLeu, Phe-Phe, and Pro-Pro) in silver colloidal solutions. The geometry and orientation of the amino acids or dipeptides on the silver surface, and their specific interaction with the surface, were deducted by detailed spectral analysis of the SERS spectra. This analysis has allowed us to propose the particular surface geometry of amino acids or dipeptides and also implied that C-C bonds were almost parallel to the surface, as evidenced by the absence of marker bands in the skeletal C-C stretching region of the spectra. Additionally, using "time-dependent" SERS measurements we solved an existing controversy regarding the binding specificity of Gly-Gly on the silver surface.     

Diffusivity evolution under decalcification: influence of aggregate natures and cement type

Since the decalcification of cement paste has been largely reviewed, we focus our studies on the influence of aggregate nature on this phenomenon in relation to the type of cement used, Ordinary Portland Cement or blended cement with fly ash and slag. Some characteristics of similar mortar mixtures where only aggregate nature differs (lime and siliceous sand) are therefore compared for the two types of cement before and after chemical decalcification induced by ammonium nitrate attack: mechanical strength, microstructure (porosity observed by mercury intrusion and profiles of oxide content trough degraded and sound zones determined by electronic microprobe analysis), transport properties (chloride ions diffusivity, gas and water permeabilities). The characterization of sound mortars underlines that siliceous aggregates promote less porous cementitious matrix. The duplication of ammonium nitrate attacks on same material allows testing the experimental parameters governing the degradation. The flows of calcium leached, the microstructure and the evolution of transport properties with decalcification suggest that limestone aggregates are not inert material. Consequently, for the mortars incorporating siliceous sand, the cementitious matrix is more decalcified and this leads to an amplification of ionic transports, especially through blended cement paste.     

Continuous SiC-based model monofilaments with a low free carbon content: Part I: From the pyrolysis of a polycarbosilane precursor under an atmosphere of hydrogen

Pyrolysis of a Yajima-type polycarbosilane (PCS) has been performed under an atmosphere of hydrogen on both bulk samples and model monofilaments up to 1000°C, in order to reduce the free carbon content of the resulting ceramics. The organic/inorganic transition occurs within the 400–800°C temperature range, with mainly an evolution of CH₄. At 1000°C, it yields an hydrogenated amorphous ceramic with a C/Si atomic ratio and a free carbon content significantly lower than for its counterpart obtained under inert atmosphere (namely, 1.18 and 9 at% versus 1.72 and 27 at%). Hydrogen is thought to favour the release of the pendent methyl groups of the PCS via demethanation radical reactions. Continuous model filaments were produced via the melt spinning of the PCS, electron beam curing, pyrolysis under hydrogen up to 1000°C, and a final heat treatment under argon up to 1600°C. The ceramic fibres exhibit a C/Si atomic ratio of 1.10, a free carbon content of ≈8 at%, a Young's modulus of 260–300 GPa and a tensile failure stress of 2100 MPa. Their thermal stability is limited to 1400°C due to some oxygen contamination during the process. This revised version was published online in November 2006 with corrections to the Cover Date.     

Structural evolution of La-Cr-O thin films: Part I. Microstructure and phase development

The structural evolution of La-Cr-O thin films and the formation mechanisms of the LaCrO₃ perovskite phase have been studied. X-ray amorphous La-Cr-O protective coatings were deposited by magnetron sputtering on metallic interconnect materials. During the annealing of the material in air a two-step phase transition from La-Cr-O to a monoclinic LaCrO₄ monazite and further to an orthorhombic LaCrO₃ perovskite phase was observed. The formation of a fine nanoporous structure is a result of the significant increase in density of the final LaCrO₃ perovskite in comparison with monazite LaCrO₄ phase. While the porous structure was not sought after for this application, these distinctive nanostructures may have numerous applications in catalysis, separation membranes or for other SOFC components.     

Deformations of the solid phase of dispersed systems under the influence of adsorbed water and organic compounds

Diffractometric data are used for determining the variation of the volume of the crystal lattice of kaolinite under the simultaneous adsorption of water and organic compounds.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 2, pp. 304–312, February, 1981.     

Appearance of submicroscopic cracks in armco iron under static tension during hydrogen charging

A study was carried out of armco iron subjected simultaneously to static tension and hydrogen charging. Electron microscope examination of specimens strained in air showed that the first submicroscopic cracks appear at 5–8% residual elongation. In the case of specimens strained during hydrogen charging the cracks appear in the earlier stages (at 1.0–1.5% residual elongation).     

Determination of dissolved and adsorbed EDTA species in water and sediments by HPLC

This paper describes a method for determining EDTA species in various environmental samples at low molar concentrations by high-performance liquid chromatography (HPLC). Distinction between Fe(III)EDTA and all the other species can be made. NiEDTA can be detected semiquantitatively. The fraction of EDTA adsorbed to suspended particles or to sediments can be determined after desorption with phosphate. After complexation with Fe(III), the EDTA is detected by reversed-phase ion-pair liquid chromatography as the Fe(III)EDTA complex at a wavelength of 258 nm. The behavior of a variety of metal-EDTA complexes during analysis was checked. Determination of different EDTA species (Fe(III)EDTA, NiEDTA, and adsorbed EDTA) is possible in river water, groundwater, and effluents from wastewater treatment plants. Fe(III)EDTA was found to be the main species, at 30-70%; NiEDTA was <10% in most of the samples. Adsorbed EDTA was detected in suspended particles from rivers and wastewater treatment plants and in sediment cores from a lake. The method is suitable for a variety of different samples with different concentration ranges.     

Investigations on the influence of oxygen on corrosion of steel in concrete—Part I

The main objective of the research programme presented in the two parts of this article is determining the influence of oxygen diffusion through the concrete cover, on the corrosion process of the reinforcement in concrete structures. Altogether, 66 so-called “concrete corrosion cells”, i. e. reinforced concrete specimens with locally separated anodically and cathodically acting steel bars and different concrete compositions, have been used for the laboratory tests. Two testing methods have been used to investigate the influence of oxygen diffusion on the cathodic reaction under different environmental conditions: potentiostatic tests (presented in part I) and the determination of cathodic current density/potential curves (presented in part II). Using the results of these tests and a simplified equivalent electric circuit model for the corrosion process, it was possible to calculate the influence of oxygen diffusion on the corrosion rate of the reinforcement under defined conditions. The results of the laboratory tests and calculations show that the diffusion of oxygen is a significant limiting factor for the corrosion rate only when the concrete around the reinforcement is water saturated and most of the oxygen within the concrete near the reinforcement surface has been consumed by the cathodic reaction of the corrosion process. As a consequence, the corrosion rate is influenced by oxygen diffusion only through the concrete cover in structures which are submerged or exposed to long-term or cyclic water application that causes water saturation of the concrete for periods of several weeks. In the case of common outdoor structures being exposed to rain and not submerged or constantly water saturated due to other reasons, no reduction of the corrosion rate induced by limited oxygen diffusion is therefore to be expected.     

Photodegradation of orange I in the heterogeneous iron oxide-oxalate complex system under UVA irradiation

To understand the photodegradation of azo dyes in natural aquatic environment, a novel photo-Fenton-like system, the heterogeneous iron oxide-oxalate complex system was set up with the existence of iron oxides and oxalate. Five iron oxides, including gamma-FeOOH, IO-250, IO-320, IO-420 and IO-520, were prepared and their adsorption capacity was investigated in the dark. The results showed that the saturated adsorption amount (gamma(max)) was ranked the order of IO-250 > IO-320 > gamma-FeOOH > IO-420 > IO-520 and the adsorption equilibrium constant (Ka) followed the order of IO-250 > IO-520 > gamma-FeOOH > IO-420 > IO-320. The effect of initial pH value, the initial concentrations of oxalate and orange I on the photodegradation of orange I were also investigated in different iron oxide-oxalate systems. The results showed that the photodegradation of orange I under UVA irradiation could be enhanced greatly in the presence of oxalate. And the optimal oxalate concentrations (C(ox)0) for gamma-FeOOH, IO-250, IO-320, IO-420 and IO-520 were 1.8, 1.6, 3.5, 3.0 and 0.8 mM, respectively. The photodegradation of orange I in the presence of optimal C(ox)0 was ranked as the order of gamma-FeOOH > IO-250 > IO-320 > IO-420 > IO-520. The optimal range of initial pH was at about 3-4. The first-order kinetic constant for the degradation of orange I decreased with the increase in the initial concentration of orange I. Furthermore, the variation of pH, the concentrations of Fe3+ and Fe2+ during the photoreaction were also strongly dependent on the C(ox)0 and iron oxides.     

Simulation of evolution of the two cylinders plasma wake under the electric discharge influence

We consider a close wake behind a pair of cylinders at a Reynolds number of Re ~ 1000 defined by the cylinder diameter in the case of small aspect ratio of cylinders, H/D ≈ 3.5. The large-scale structure of such a wake represents a f low like two interacting Karman streets and it is modeled by two coupled Van der Pol oscillators. The mutual inf luence of closely located Karman streets is accounted for by nonlinear (of a general parabolic type) terms in the equations for oscillators. Moreover, the equations are generalized with allowance for explicit dependence of the oscillation frequency on its amplitude. Within the framework of this three-parametric model, five collective modes of the wake behind cylinders were found. In addition, there are the domains of model parameters where qualitatively different modes of intermittent wake exist.     

Effect of hydrogen on the tensile ductility of Ti6Al4V: Part I Orientation effects in slow straining

Smooth tensile specimens were machined from a round Ti6Al4V bar, the crystallographic orientation of which was determined by X-ray diffraction analysis. The preferred orientation was mainly texture. When the specimens of various hydrogen contents were slowly strained, those having more than 2000 p.p.m. hydrogen exhibited slow-strain embrittlement in both rolling and transverse directions, whereas below 2000 p.p.m. hydrogen, the effect of hydrogen on the tensile properties was different in the two directions. Hydrogen decreased both the proportional limit, σ₀ and the 0.2% flow stress, σ_0.2, in specimens parallel to the rolling direction but there was no change in either σ₀ or σ_0.2 with increasing hydrogen content in the transverse specimens. The strain hardening behaviour of all specimens could be divided into two stages, whatever the orientation of specimen or hydrogen content. The first-stage strain-hardening exponent, n₁, increased with increasing hydrogen content, but n₁ for the transverse specimens was smaller than for specimens parallel to the rolling direction, and the variation of n₁ with hydrogen content was also lower in the transverse specimens. These differences were attributed to the differing deformation modes for specimens of different orientation. There was, however, no effect of orientation on the micro-fractography. This revised version was published online in November 2006 with corrections to the Cover Date.     

The effect of lattice defects induced by cathodic hydrogen charging on the apparent diffusivity of hydrogen in pure iron

The variation of apparent hydrogen diffuoivity with the applied current density and the types and amounts of hydrogen -induced damage caused by hydrogen during the cathodic charging of hydrogen in pure iron are investigated by thermal analysis techniques, and analysed in the light of theoretical models. Internal microcracks and microvoids are generated predominantly below 1 mA cm^–2 and are the major trapping sites of hydrogen in pure iron when charging hydrogen cathodically. Blisters on the surface of iron specimens are found tD be interconnected to the surface of the specimen through microcracks remaining in the vicinity of blisters. The peak temperature of hydrogen released from an internal microcrack or microvoid decreased as the applied current density is increased. The apparent diffusivity of hydrogen at 458 K decreases linearly with the reciprocal value of the square root of applied current density during cathodic charging. This implies that the amounts of internal microcracks or microvoids are linearly proportional to the lattice hydrogen solubility or the square root of the applied current density.