Criterion of phase stability of asphaltenes in crude oils

Associate formation processes in crude oils are investigated by viscometry and dielectric spectroscopy. It is shown that fluidity decline in the 36-40 C range is typical for crude oils with a high resin and asphaltene content ratio. The critical polar resin concentration in stable asphaltene nanoaggregates is determined. © 2013 Springer Science+Business Media New York

Surface softening in metal-ceramic sliding contacts: An experimental and numerical investigation

This study investigates the tribolayer properties at the interface of ceramic/metal (i.e., WC/W) sliding contacts using various experimental approaches and classical atomistic simulations. Experimentally, nanoindentation and micropillar compression tests, as well as adhesion mapping by means of atomic force microscopy, are used to evaluate the strength of tungsten?carbon tribolayers. To capture the influence of environmental conditions, a detailed chemical and structural analysis is performed on the worn surfaces by means of XPS mapping and depth profiling along with transmission electron microscopy of the debris particles. Experimentally, the results indicate a decrease in hardness and modulus of the worn surface compared to the unworn one. Atomistic simulations of nanoindentation on deformed and undeformed specimens are used to probe the strength of the WC tribolayer and despite the fact that the simulations do not include oxygen, the simulations correlate well with the experiments on deformed and undeformed surfaces, where the difference in behavior is attributed to the bonding and structural differences of amorphous and crystalline W-C. Adhesion mapping indicates a decrease in surface adhesion, which based on chemical analysis is attributed to surface passivation

Criterion of phase stability of asphaltenes in crude oils

Associate formation processes in crude oils are investigated by viscometry and dielectric spectroscopy. It is shown that fluidity decline in the 36-40 C range is typical for crude oils with a high resin and asphaltene content ratio. The critical polar resin concentration in stable asphaltene nanoaggregates is determined. © 2013 Springer Science+Business Media New York

Criterion of phase stability of asphaltenes in crude oils

Associate formation processes in crude oils are investigated by viscometry and dielectric spectroscopy. It is shown that fluidity decline in the 36-40 C range is typical for crude oils with a high resin and asphaltene content ratio. The critical polar resin concentration in stable asphaltene nanoaggregates is determined. © 2013 Springer Science+Business Media New York

Atomic-scale simulations of nanoindentation-induced plasticity in copper crystals with nanometer-sized nickel coatings

The mechanical behaviour of very small volumes differs from what is typically observed on the macrolevel. In particular, thin metal films with nanometer-sized coatings possess interesting mechanical properties. Here, we use molecular dynamics simulations to elucidate details of plastic deformation and the underlying deformation mechanisms during nanoindentation of thin copper films with epitaxial nickel coatings. Several deformation mechanisms, such as dislocation pile-up on the interface, dislocation cross-slip and movement of misfit dislocations, are observed. Most interestingly, copper films are significantly strengthened by thin nickel coatings. This effect is especially pronounced at a very low temperature. For nickel coatings as thin as 1.6 nm (at low temperature) or 2.5 nm (at room temperature), the coated copper adopts the hardness of bulk nickel, even though the operating deformation mechanism is unique in each case considered and the hardness of bulk copper is significantly lower. The critical thickness at which a coated copper film achieves hardness of bulk nickel depends not only on the temperature, but also on the radius of the indenter tip. Sharper indenters yield higher hardness. The obtained results suggest that thin surface coatings or oxide layers at nanoscale contacts may have a pronounced effect on the perceived hardness of the surface

Criterion of phase stability of asphaltenes in crude oils

Associate formation processes in crude oils are investigated by viscometry and dielectric spectroscopy. It is shown that fluidity decline in the 36-40 C range is typical for crude oils with a high resin and asphaltene content ratio. The critical polar resin concentration in stable asphaltene nanoaggregates is determined. © 2013 Springer Science+Business Media New York

Atomistic simulation of nanoindentation into copper multilayers

Atomic-scale simulations are used to examine the plastic behaviour of copper multi-layered thin films during nanoindentation tests. It is found that glide of nucleated dislocation loops and slip in the grain boundaries are the main operating deformation mechanisms in such multi-layered polycrystals. Furthermore, for a very small layer thickness, slip in the grain boundary dominates over the dislocation mediated plasticity. In order to survey the resistance of a multi-layered metal thin film to plastic deformation during nanoindentation, hardness versus penetration depth curves are plotted. Hardness curves reveal softening of multi-layer films, i.e. a reverse Hall-Petch effect is found for layer thicknesses in the nanometre range

Assessment of welding working properties of power supplies

The welding working properties of power supplies are the basic indicators of efficiency of their application when forming permnanent joints of critical duty constructions. Growth of the share of welded structures made of difficult-to-weld steels and alloys requires more advanced welding equipment characterized by better static and dynamic characteristics and ensuring optimal thermal welding cycles. In the paper the authors present their own view of the necessity of power supplies welding working properties assessment from the perspective of quantitative assessment of welding conditions indicators. It allows most complete characterizing of the process flow parameters