Raman spectroscopy of the mixtures (x)1-butyl-1-methylpyrrolidinium chloride-(1 - x)TaCl5 in solid and molten states.

A series of novel ionic liquids consisting of 1-butyl-1-methylpyrrolidinium chloride (Pyr14Cl) and TaCl5 were obtained in a wide range of molar compositions for electrochemical application. Raman spectroscopy was used to investigate the complex formation of tantalum(V) in the mixtures of (x)Pyr14Cl-(1 - x)TaCl5 (x = 0.80-0.30) over the temperature range 20-160 degrees C. Depending on the molar composition, different species of tantalum (V) were identified. In the basic and neutral mixtures of (x)Pyr14Cl-(1 - x)TaCl5 (x = 0.80-0.50), tantalum(V) exists in the form of octahedral [TaCl6](-) in both solid and molten states. In acidic ionic liquids (x = 0.45-0.30), [Ta2Cl10] units are the main species of tantalum(V) identified in the solid state. As the temperature rose, the gradual degradation of [Ta2Cl10] units was observed in the solid state, accompanied by the formation of [TaCl6](-) and [Ta2Cl11](-) anions. In the molten state, in the range between 130 and 160 degrees C, the latter two species exist in equilibrium and are the dominant species of tantalum(V). The formation of oxochloride species of tantalum(V) was investigated in mixtures of Pyr14Cl-TaCl5-Na2O (x = 0.65) at various O/Ta mole ratios, and the formation of the oligomeric species with Ta-O-Ta bridging bonds was determined.

Surface analysis of different boundary layers on steel discs formed in a lubricated tribocontact during laboratory test compared with field application.

The aim of this study was to gain knowledge of tribological layers on a steel disc. This steel disc has been used in a transmission system in the field. ATF-oil (automatic transmission fluid), which contains different surface-adhering additives, serves as a lubricant and as a cooling fluid in the tribological system. Over time, the tribological characteristics of the system changed. Special interest in this study lies in the modifications of the steel surface. The field-used disc was therefore compared with model tested discs. In a disc-on-disc tribometer, all samples are tested for a short period of time to evaluate the actual condition of the system regarding friction behaviour. Analysis and characterisation of surfaces and layer formation were carried out with, among other techniques, 3D topography, SEM / EDX, AFM, XPS, and ToF-SIMS. Results indicate that in some regions a complex composed tribological layer is formed. Differences were detected between the steel discs used in the field and the model discs. This indicates the problem of evaluation of long-term behaviour exclusively by use of short or accelerated model experiments. A combination of carefully selected and sophisticated analytical methods is necessary to trace small changes of the system.

A computational investigation of the different intermediates during organoalkoxysilane hydrolysis.

Using a combination of atomistic molecular dynamics (MD) simulations and density functional theory (DFT) calculations, the four steps of hydrolysis of aminopropyl-, thiolpropyl-, and butyltrimethoxysilane have been studied. Large box MD simulations at constant pressure and temperature yield appropriate pair distribution functions--which allows us to quantify the number of surrounding water molecules--as well as the density of the systems. These densities serve as input for small box DFT calculations, which allow further geometry optimization and calculation of the electronic structure of the systems. The periodic DFT calculations are compared with gas-phase simulations. In all cases, the first step of hydrolysis is exothermic with the extent depending on the type of silane as well as on the number of hydrogen bonds in the initial stage.

Adsorption of organosilanes at a Zn-terminated ZnO (0001) surface: molecular dynamics study.

Four different organosilanes (octyltrihydroxysilane, butyltrihydroxysilane, aminopropyltrihydroxysilane, and thiolpropyltrihydroxysilane) adsorbed at a reconstructed Zn-terminated polar ZnO (0001) surface are studied via constant temperature (298 K) molecular dynamics simulations. Both single adsorbed silane molecules as well as adsorbed silane layers are modeled, and the energy, distance, orientation, and alignment of these adsorbates are analyzed. The adsorbed silane molecules exhibit behavior depending on the chemical nature of their tail (nonpolar or polar) as well as on the silane concentration at the solid surface (single adsorption or silane layer). In contrast to the O-terminated ZnO surface studied previously, now adsorption can only occur at the vacancies of this reconstructed crystal surface, thus leading to an arched structure of the liquid phase near the crystal surface. Nevertheless, both nonpolar and polar single adsorbed silanes show a similar orientation and alignment at the surface (orthogonal in the former, parallel in the latter case) as for the O-terminated ZnO surface, although the interaction energy with the surface is considerably increased for nonpolar silanes while it is nearly unaffected for the polar ones. For adsorbed silanes within silane layers, the difference to single adsorbed silanes depends on the polarity of the tail: nonpolar silanes again show an orthogonal alignment, while polar silanes exhibit two different orientations at the solid surface-a head and a tail down configuration. This leads to two completely different but nevertheless stable orientations of these silanes at the Zn-terminated ZnO surface.