Search

The controlled deposition of thin films on a variety of substrates is a fundamental step in many technological applications, being of great importance to know their thickness. The thickness of a film with known composition, can be determined by using the intensity attenuation of a monochromatic X-Ray beam which traverses the film. In this work, we propose to use a SEM-EDX system to detect the characteristic X-Rays generated by a specially designed target, and that traverse a metal film deposited on a thin polymeric substrate. The target is a Cu film with 800 nm of thickness, deposited on a Ti plate which upon the incidence of a 30 keV electron beam generates three lines of comparable intensity, well separated in energy. EDX spectrums are acquired from this target and, depending on the film thickness, it was selected one of these signals to measure its attenuation, choosing the one which gives the best measure for the particular film under study. The films under study were three Ag films deposited with different deposition times, by magnetron sputtering on transparent polyethylene sheets. The target and the sheets were mounted on a specially designed sample holder, which allows to determine the X-Ray attenuation by simple 90° rotations, in order to face the detector and acquire the non-attenuated emitted signals, the signals attenuated by the uncoated sheet and the signals attenuated by the Ag coated sheet. The film thickness determined were 0.20, 0.59 and 0.99 µm, which agrees linearly with the corresponding 5, 15 and 25 min sputtering deposition times. [ABSTRACT FROM AUTHOR]

We have simulated the operation and functionality of a working Sn-based perovskite solar cell device using GPVDM and compared it against a Pb-based device. The results are extremely promising in that they showcase comparable cell efficiencies, with the Sn-based device showing a highest 21.3% efficiency (Jsc of 332.8 A/m2, Voc of 0.839 V, FF of 0.764) compared to 23.4% of its Pb counterpart (Jsc of 349.3 A/m2, Voc of 0.811 V, FF of 0.828), at similar active layer thicknesses. A deeper study of each of the Jsc, Voc and FF trends provide keen insight into charge transfer kinetics within the device, paving the way to optimal experimental setups for fabricating the most efficient non-toxic perovskite devices. Image 1 • A Sn-based perovskite solar cell is simulated using the GPVDM software and compared against a Pb-based device. • Results showcase a similar optimal efficiency value of the Sn-based device (21.3%) compared to the Pb-based one (23.4%). • The results delineate and clarify the kinetics that drive the efficiency value differences between simulation and experiment. [ABSTRACT FROM AUTHOR]

The development of EHL theory from its tentative beginnings is outlined, with an account of how Ertel explained its relation to Hertz contact theory. The problems caused by the failure of the early numerical analysts to understand that the film thickness depends on only two variables are emphasised, and answers of the form H = F ( P , S ) given. Early methods of measuring the film thickness are described, but these became archaic with the development of optical EHL. The behaviour of surface roughness as it passes through the high pressure region and suffers elastic deformation is described, and the implication for the traditional Λ -ratio noted. In contrast, the understanding of traction is far from satisfactory. The oil in the high pressure region must become non-Newtonian: the early explanation that the viscosity reduction is the effect of temperature proved inadequate. There must be some form of shear thinning (perhaps according to the Eyring theory), but also a limiting shear stress under which the lubricant shears as an elastic solid. It seems that detailed, and difficult, measurements of the high pressure, high shear-rate behaviour of individual oils are needed before traction curves can be predicted.

The automotive industry faces new challenges and fast technological changes [...]

We present an analytical theory for laminar forced convection condensation of saturated vapor on horizontal surfaces. The condensation produces shear-thinning film moving downstream due to the viscous-drag occurring at the vapor-liquid interface. The mathematical model is built based on a few input parameters, viz. power-law index (n), nondimensional film-thickness (η δ , l), Prandtl number (P r), and inertia number (M c). A set of output parameters is used to analyze the distinct characteristics of the fluid-flow and condensation, viz. the condensate's nondimensional mass flow rate (m ^), Nusselt number, specific enthalpy ratio (R h), thermal retention coefficient (Θ), and nondimensional wall-shear stress (τ ^ w). We have identified the subtlety of shear-thinning film flow when liquid's thermophysical properties vary according to the changes in wall-shear and the interfacial drag. Contextually, we illustrate that a rise in shear-thinning effect (obtained by decreasing n), keeping M c and η δ , l fixed, results in a decrease of m ^ , R h , τ ^ w , and (1 / Θ). We have demonstrated that for a fixed R h , a shear-thinning film, compared to the Newtonian film, would exhibit a greater η δ , l but a smaller interfacial velocity (f i ′). Furthermore, a greater film thickness is required for low P r liquids to attain the same degree of subcooling compared to high P r liquids. We perform systematic investigation over a wide range of η δ , l. We observe that for small η δ , l values, the vapor boundary-layer moving onto the liquid-film exhibits similar flow-features as found in the well-known Blasius boundary-layer. Conversely, at large η δ , l , the present solution would remarkably differ from the Blasius solution. Finally, we establish an approximate theory for small η δ , l motivated by the linearity in the cross-stream variations of velocity and temperature within the thin-film. This approximate theory gives rise to analytical correlations for R h , Θ , τ ^ w , and m ^ , which would be useful for engineers. [ABSTRACT FROM AUTHOR]

The Investigation on cam–follower contact is one of the most complex lubricated non-conformal contact due to its continuous variation of load, speed, and geometry. The complexity of the phenomena occurring in the camshaft systems makes experimental verifications very important. In this study, an already existing versatile experimental apparatus for the investigation of non-conformal lubricated contacts, able to measure film thickness using the optical interference method and friction force trough a load cell, has been modified in order to test cam–follower contacts. Some tests have been carried out for investigating the behaviour of some fundamental components of the rig. A theoretical/numerical simulation has been performed to investigate the dynamic behaviour of the system and in order to provide some indications for the interpretation of the experimental results. Purposely developed versions of the programme have been also an important support for the design of a new apparatus specifically addressed to the cam–follower contact with increased potentialities capable of more detailed measurements of film thickness and contact forces. The apparatus is able to reproduce a cam–follower mechanism that uses a rocker as a link device between the cam follower set and the valve. [ABSTRACT FROM AUTHOR]

This work investigates on the plausible interfacial mechanisms of PTFE (submicron particle) SMPs with the metal counterface during the growth of PTFE tribo-film. A series of submicron-oils was prepared to examine the effect on oil performance with variation in concentration of SMPs (0–9 wt%) in a Group III base-oil. Commercially available submicron suspension containing an adequate amount of dispersant for suspending the PTFE particles (avg size 230 nm) was used in various doses. In order to roughly estimate the shelf life of the formulated oils; UV–Vis spectroscopy technique was employed on the diluted oil samples since original samples were too thick. Dynamic light scattering (DLS) studies were carried in order to estimate the changes in the particle size with storage time. Nano-oils were characterized for their physical properties viz. (density, viscosity and viscosity index) and tribo- performance. Results revealed that 6 wt% of PTFE SMPs proved to be an optimum concentration for the highest EP performance with 392% enhancement compared to the base oil, which is not reported in the literature. To understand the mechanisms behind this performance, worn surfaces of pre-weld balls were inspected by FESEM (Field emission scanning electron microscope), 3D profilometry, goniometry and XPS (X-ray photo-electron spectroscopy), which revealed exact reasons for the varied performance of nano-oils as a function of increasing concentration of SMPs. XPS spectroscopy on worn surfaces revealed the formation of chemically modified tribo-film over the asperities. Furthermore, the thickness of tribo-film formed was also evaluated. Since EP trends were so promising, preliminary oils were characterized for AW and AF performance also. AW and AF performance got enhanced by 30% and 40% respectively. • Coalescence of PTFE particles around interfacial contact area in EP test. • Significant (400%) increment in EP-property for 6% PTFE particles as an optimum amount. • Chemical interaction of PTFE particles and metal counterface during EP action led to protective coating. • Shear-scission of PTFE molecules to form a tribo-chemical (FeF 2) film (>150 nm). • Higher the contact pressure, better was the anti-wear action (up to 164%) of particles. [ABSTRACT FROM AUTHOR]

The development of EHL theory from its tentative beginnings is outlined, with an account of how Ertel explained its relation to Hertz contact theory. The problems caused by the failure of the early numerical analysts to understand that the film thickness depends on only two variables are emphasised, and answers of the form H = F (P , S) given. Early methods of measuring the film thickness are described, but these became archaic with the development of optical EHL. The behaviour of surface roughness as it passes through the high pressure region and suffers elastic deformation is described, and the implication for the traditional Λ -ratio noted. In contrast, the understanding of traction is far from satisfactory. The oil in the high pressure region must become non-Newtonian: the early explanation that the viscosity reduction is the effect of temperature proved inadequate. There must be some form of shear thinning (perhaps according to the Eyring theory), but also a limiting shear stress under which the lubricant shears as an elastic solid. It seems that detailed, and difficult, measurements of the high pressure, high shear-rate behaviour of individual oils are needed before traction curves can be predicted. [ABSTRACT FROM AUTHOR]

Keywords: ultra-low viscosity oil; film-thickness; lubrication mechanism; EHL regime; vegetable oil-diesel fuel mixtures; friction losses EN ultra-low viscosity oil film-thickness lubrication mechanism EHL regime vegetable oil-diesel fuel mixtures friction losses 48 1 05/23/20 20200401 NES 200401 The automotive industry faces new challenges and fast technological changes. According to the substantial changes in operating conditions of near future automotive technology, this issue would provide useful support to engineers responsible for developing the most efficient and dependable systems with focus on reduced viscosity lubricant, valvetrain friction and lubrication, vegetable oil-diesel fuel mixtures, friction losses in gasoline and diesel engines of passenger car. Therefore, the article aims at extending the basis provided by the previous works by analyzing the lubrication regime of these three investigated engines. Ultra-low viscosity oil, film-thickness, lubrication mechanism, EHL regime, vegetable oil-diesel fuel mixtures, friction losses. [Extracted from the article]