Classical Density Functional Study on Interfacial Structure and Differential Capacitance of Ionic Liquids near Charged Surfaces

We have implemented a generic coarse-grained model for the aromatic ionic liquid [CnMIM+][Tf2N-]. Various lengths for the alkyl chain on the cation define a homologous series, whose electric properties are expected to vary in a systematic way. Within the framework of a classical density functional theory, the interfacial structures of members of this series are compared over a range of surface charge densities, alkyl chain lengths, and surface geometries. The differential capacitance of the electric double layer, formed by ionic liquids against a charged electrode, is calculated as a function of the surface electric potential. A comparison of planar, cylindrical, and spherical surfaces confirms that the differential capacitance increases and varies less with surface potential as the surface curvature increases. Our results are in qualitative agreement with recent atomistic simulations

Ionic liquids at electrified interfaces

Until recently, “room-temperature” (<100–150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)–(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of “first-generation” room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the “later generation” RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in “cocktails” of one’s choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost “universal” solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) “sister-systems”.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules

Właściwości wielomodułowych i gradientowych powłok na bazie CrN/CrCN osadzonych na azotowanej stali 4140

In the present study, samples made of AISI 4140 steel pre-treated with gas nitriding and coated with different PVD coatings (multimodule CrN/CrCN coatings and gradient CrN/CrCN coatings) were investigated in terms of adhesion and wear resistance. Wear tests, in which duplex-treated pins were mated to hardened ball bearing steel discs, were performed with a pin-on-disc machine. To examine the influence of the nitrided layer on the performance of the coating–substrate composite, coatings were deposited on hardened as well as on nitrided samples, which were prepared under different nitriding conditions. The results of the investigation showed improved wear properties of the nitrided hardcoated specimens compared to the non-nitrided ones, especially when the nitrided layer consists of a solely diffusion zone. In the scratch test among investigated samples, the greatest value of LC1 and LC2 were obtained for coatings deposited on the nitrided substrate without a subsurface zone of nitrides (without compound layer). For the gradient coatings, the best adhesion of the coating to the substrate, characterized by LC1 and LC2 factors, was observed for the coating with the parabolic change of carbon concentration in the CrCN layer.Celem przedstawionych badań była ocena adhezji oraz odporności na zużycie kompozytów powłoka PVD/azotowane podłoże ze stali 4140 w zależności od rodzaju powłoki i budowy warstwy azotowanej. Brano pod uwagę powłoki wielomodułowe o dwuwarstwowym module CrN/CrCN oraz powłoki gradientowe ze zmiennym stężeniem węgla ukształtowanym w formie parabolicznej oraz pierwiastkowej. Rezultaty badań wskazują na wzrost odporności na zużycie badanego kompozytu w przypadku azotowanego podłoża w porównaniu z nienaazotowanym. Jest on szczególnie wysoki w przypadku kiedy powłoki są nanoszone na warstwę azotowana zbudowaną wyłącznie ze strefy dyfuzyjnej, bez przypowierzchniowej strefy azotków. W badaniach adhezji metodą zarysowania najwyższe wartości wskaźników Lc1 oraz Lc2 obserwuje się również dla tego przypadku. W przypadku powłok gradientowych najwyższe wartości tych wskaźników otrzymano dla parabolicznej zmiany stężenia węgla w warstwie CrCN

Analysis of Thermal Stability of CrCN Coatings Deposited on Nitrided Substrates Using Modulated Temperature Thermodilatometry

The aim of the research was to investigate the influence of nitriding of the substrate made of 42CrMo4 steel on thermal stability of the antiwear CrCN coating deposited on its surface using Cathodic Arc Evaporation method. Samples of non-nitrided and nitrided substrate/CrCN coating systems were tested with Modulated Temperature Thermodilatometry, which program included system annealing in 26 h, temperature of 290°C and argon atmosphere. Recorded during tests, changes in substrate elongation in response for changes of sample temperature, enabled qualitative determination of changes in stress states in the coatings as a result of samples annealing. Annealing of the system with nitrided substrate resulted in smaller change in residual stress in coating than for the system with non-nitrided substrate, which can indicate its better thermal stability. Values of residual stresses in coatings calculated by sin2ψ method before and after annealing on the basis of tests performed using X-Ray diffraction, agree with results of dilatometric tests