As was shown in Chap. 4, the behaviour of real electrochemical systems on long timescales cannot often be predicted from short-term observations. In terms of the approach considered in 1.6, this happens because of the onset of positive feedbacks destabilising the stationary state of the system. Several possible reasons exist for this event to take place. Among them, most significant, however very rarely considered, is the coupling between the electrochemical processes at separate electrodes. To understand how it works, we shall first consider the process of electrochemical decomposition of an electrolyte with mixed ion–electron conductivity.

A general way of kinetic description of a many-electron process, based on the simplified reaction mechanism (1.9), was pointed out in Chap. 1. Again, we must admit that the situation still remains complicated and a general theory of application of the experimental methods to the studies of many-electron kinetics is still poorly developed.

The butyl group in 1-butyl-2,3-dimethylimidazolium (BMMI) salts, a common group of low-melting solids, was found to exhibit different conformations in the solid state. Crystal structures of pure BMMI azide, thiocyanate, propynoate, hexachlorocerate(IV), chlorocyanocuprate(I), nonachlorodititanate(W), and mixed azide/chloride and cyanide/chloride salts were determined by single crystal X-ray diffraction, and their butyl chain conformations were examined. The twist angle of the C(alpha)-C(beta) bond out of the plane of the imidazole ring ranges from 57 degrees to 90 degrees, whereas the torsion angle along the C(alpha)-C(beta) bond determines the overall conformation: 63 degrees to 97 (gauche) and 170 degrees to 179 degrees (trans). The preferred conformations of the butyl group are trans trans and gauche trans, but trans gauche and gauche gauche were also observed. More than one conformer was present in disordered structures. Numerous polar hydrogen bonds between cations and anions were identified. Five structures exhibit stacking of the aromatic imidazole systems, indicated by parallel alignment of pairs of cations with short centroid-centroid distances due to pi-pi interactions, which is surprisingly frequent. Not only imidazole ring protons are involved in the formation of short CH center dot center dot center dot X hydrogen bonds, but also interactions between methylene and methyl groups of the alkyl chain and the anion are visible. Hirshfeld surface analysis revealed that nonpolar H center dot center dot center dot H contacts represent the majority of interactions. The volume-based lattice potential energy, enthalpy, entropy, and free energy were calculated by density functional theory. Calculated and experimental molecular volumes in the range from 0.27 to 0.70 nm(3) agreed favorably, thus facilitating reliable predictions of volume-derived properties.

Titanium oxide layers were prepared on pure aluminium substrates by the anodic spark deposition method. The formed crystalline titania (TiO2) phases rutile and anatase and the sodium titanium oxide (Na0.23TiO2) were identified. The corresponding crystallite size values were obtained from X-ray diffraction data by means of the Rietveld method. The crystallite size of each of these phases continuously increases with rising current density. Furthermore, the two-dimensional distribution of the titania phases on the sample surface was determined by Raman spectroscopy. It was found that the rutile/anatase ratio is inhomogeneous distributed on an observed area of 400×400μm2.

Aerospace applications and energy saving strategies in general boosted the interest and the research in the field of light weight materials, typically on alloys based on aluminium. Aluminium itself does not provide sufficient mechanical strength for structural parts, but there exists a lot of recently developed alloys containing silicon, copper, magnesium, zinc or manganese in various combinations and compositions exhibiting excellent mechanical properties. These alloys require surface treatments or coatings to withstand corrosive ambient conditions. Among those treatments known as chromate replacements, plasma oxidation processes were used for different applications, especially if the surfaces have to face mechanical load or severe environmental conditions. In this work, specimens of different aluminium alloys have been plasma oxidized by micro-arc treatment in silicate and phosphate solutions. The ceramic coatings were characterized with respect to phase composition, micro-hardness and corrosion stability. In addition, the tribological performance of the coatings was investigated using a ball-on-disc tribometer with reciprocating motion against sintered alumina ball. The typical worn surfaces of the Al substrate and the ceramic coatings were observed by a scanning electron microscope. Applying same wear conditions, the wear rates in different depth of the coatings are nearly similar. However, in a defined depth of the coatings, wear rate gradually decreases with wear duration. During friction process, a-stable transfer layer consisting of oxides was formed on the tribo-contact area of the coatings. The friction coefficient in a steady friction state is in the range of 0.8.

Nanostructured nickel and cobalt alloy powder deposits from three different electrolyte compositions were obtained by electrodeposition from an ammonium sulfate-chloride solution in a galvanostatic regime. The influence of current density and the Ni2+/Co2+ ratio in the bath on the microstructure and phase composition of the Ni-Co deposits were studied by SEM and X-ray diffraction methods. Both, bath composition and current density influence strongly the deposit growth mechanism as well as the deposit composition, microstructure, grain size and surface morphology. When electrodeposition was performed at high overpotentials, far from equilibrium conditions, face-centered cubic (FCC) mixtures of Ni and Co were generated while at low ovetpotentials, as well as at higher content of cobalt in the electrolyte, hexagonal close packed (HCP) of Co was formed with a lower rate of hydrogen evolution. The increase in the concentration of HCP phase in the nanocrystalline deposits was caused by increasing the overall Co content in the materials prepared as well as by decreasing deposition current density.Differential scanning calorimetry (DSC) and X-ray diffraction analysis were used to examine the effects of structural changes on magnetic properties of the nanocrystalline powders electrochemically obtained in the temperature interval from room temperature to 650 degrees C. Each stage of the structural changes caused corresponding changes in the magnetic permeability for the alloys prepared.

Ni-Co alloy deposits and their parent metals were formed on Cu substrates by electrolysis under different current densities applied in the galvanostatic regime. A quantitative scanning electron microscopy technique was employed to study the morphology and surface roughness of the obtained deposits. The structure of the deposits is governed by the nature of depositing ions and quantity of evolved hydrogen. The cauliflower morphology and the highest mean surface roughness values are the results of electrodeposition from the Ni containing bath. The structure of the Co deposits formed under the same conditions and determined by the formation of the hexagonal close-packed phase results in a more uniform grain size distribution and formation of smoother platelet deposits. The mean surface values of the parent metals are independent of the current density. The dendritic growth is a special case of a structure formed only in the Ni-Co alloy deposition at selected, high current densities of 220 and 400 mA cm(-2). The dendrites obtained at a higher current density of 400 mA cm(-2) have shown more developed structures with smaller dendrites that have more pronounced secondary branch and high order branches.

TiB2 coatings on Mo substrates were electrodeposited out of a FLiNaK electrolyte in the presence of TaCl5 additive. The results show that a low concentration of TaCl5 in the melt changes significantly the chemical composition and consequently, the properties of the coatings. The energy-dispersive X-ray analysis indicates up to 10 atom % Ta in the TiB2 coatings. X-ray phase analysis demonstrates the changes in the texture of TiB2 in the < 001 > direction. Codeposition of TaB2 in a TiB2 layer decreases the grain size and improves the smoothness of the layer. Addition of TaCl5 in the electrolyte permits to obtain TiB2-TaB2 layers of high quality and makes the process reproducible. In addition, the individual electrochemical behavior of the starting compounds, K2TiF6, KBF4, and TaCl5, as well as their mixtures was investigated in the FLiNaK electrolyte by means of cyclic voltammetry. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3489403] All rights reserved.

C16H20AgBN8, monoclinic, P12(1)/c1 (no. 14), a = 11.2198(4) angstrom, b = 12.3987(4) angstrom, c = 15.4397(5) angstrom, beta = 109.701(2)degrees, V = 2022.1 angstrom(3), Z = 4, R-gt(F) = 0.032, wR(ref)(F-2) = 0.089, T = 233 K.

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Phase relations were established in the Sr-poor part of the ternary systems Sr-Ni-Si (900 degrees C) and Sr-Cu-Si (800 degrees C) by light optical microscopy, electron probe microanalysis and X-ray diffraction on as cast and annealed alloys Two new ternary compounds SrNiSi3 (BaNiSn3-type) and SrNi9-xSi4+x., (own-type) were found in the Sr-Ni-Si system along with previously reported Sr(NixSi1-x)(2) (AlB2-type) The crystal structure of SrNi9-xSi4+x (own-type, x=27, a=0 78998(3), c=1 1337(2)nm; space group P4/nbm) was determined from X-ray single crystal counter to be a low symmetry derivative of the cubic, parent NaZn13-type At higher Si-content X-ray Rietveld refinements reveal the formation of a vacant site (square) corresponding to a formula SrNi5 5Si65 square(10) Phase equilibria in the Sr-Cu-Si system are characterized by the compounds SrCu2-xSi2.x (ThCr2Si2-type), Sr(CuxSi1-x) (AIB(2)-type), SrCu9-xSi4+x (0 <= x <= 1 0, CeNi(8.5)Si(4.5)type) and SrCu13-xSix (4 <= x <= 18; NaZn13-type) The latter two structure types appear within a continuous solid solution. Neither a type-I nor a type-IX clathrate compound was encountered in the Sr-{Cu,N-1}-Si systemsStructural details are furthermore given for about 14 new ternary compounds from related alloy systems with Ba (C) 2009 Elsevier Inc. All rights reserved

The growth of intermetallics phases between molten aluminium and solid steel was investigated via the imaging analysis of the scanning electron microstructures with high accuracy. Results from Focused Ion Beam revealed the isotropic growth of intermetallics phases on the plane parallel to interface between steel and Al. Diffusive controlling mechanism was confirmed during the growth of intermetallics phases, a 3D model was derived to find that the growth of the intermetallics phases was dependent on t0.15 of dipping time.

The trialkyl-substituted imidazolium-based ionic liquids (ILs) are considered to be promising as supporting electrolytes for electroplating and other electrochemical applications because of their increased stability compared to that of dialkyl-substituted compounds. Basic properties like density, viscosity, and conductivity of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMImBF4), 1-butyl-2,3-dimethylimidazolium azide (BMMImN3), and their mixtures were measured. The thermal stability of the azide IL permits its use up to 423.15 K, whereas the upper temperature limit for telrafluoroborate IL extends to 623.15 K. The electrochemical stability with regard to cathodic reduction was the same for both ILs; the decomposition potential was about −1.9 V versus the Ag/AgCl reference electrode. However, the resistance to electrochemical oxidation at the anode was much lower for the azide IL. The decomposition potential was 0.5 V against 2.05 V for the tetrafluoroborate IL.