DJL

Dogs lap because they have incomplete cheeks and cannot suck. When lapping, a dog’s tongue pulls a liquid column from the bath, suggesting that the hydrodynamics of column formation are critical to understanding how dogs drink. We measured lapping in 19 dogs and used the results to generate a physical...

Abstract

Tribochemistry plays a very important role in the behaviour of systems in tribologically loaded contacts under boundary lubrication conditions. Previous works have mainly reported contact mechanics simulations for capturing the boundary lubrication regime, but the real mechanism in which tribofilms reduce wear is still unclear. In this paper, the wear prediction capabilities of a recently published mechanochemical simulation approach (Ghanbarzadeh et al. in Tribol Int, 2014) are tested. The wear model, which involves a time- and spatially dependent coefficient of wear, was tested for two additive concentrations and three temperatures at different times, and the predictions are validated against experimental results. The experiments were conducted using a mini-traction machine in a sliding/rolling condition, and the spacer layer interferometry method was used to measure the tribofilm thickness. Wear measurements have been taken using a white-light interferometry. Good agreement is seen between simulation and experiment in terms of tribofilm thickness and wear depth predictions.

Publication date: April 2016
Source:Tribology International, Volume 96
Author(s): Mitjan Kalin, Eva Oblak, Somayeh Akbari
The evolution of the nano-mechanical properties of tribofilms formed in steel/steel, steel/a-C:H and steel/Si-DLC contacts lubricated with two commercial oils containing different amounts of SAPS additives (E6 and E7 grade) and a mineral base oil containing ZDDP additive were examined in this investigation for two very different time periods. An atomic force microscope (AFM) was used in different modes to measure the topography, film thickness and stiffness, while the nano-hardness was measured with a nano-indenter. In addition, FTIR microscope was used on selected samples to explain some of the tribofilm׳s mechanical modifications with chemical changes. The results have shown that the tribofilm׳s evolution and growth are very much surface and additive dependent, and are different for steel and DLC coatings.

Publication date: 15 February 2016
Source:Wear, Volumes 348–349
Author(s): M. De Feo, M.I. De Barros Bouchet, C. Minfray, Th. Le Mogne, F. Meunier, L. Yang, B. Thiebaut, J.M. Martin
Recently Diamond-Like Carbon (DLC) coatings have attracted considerable attention due to their low friction, high hardness, good wear and corrosion resistance, and high thermal and chemical stability. Although considerable research has been conducted on the effect of molybdenum-based additives, e.g., molybdenum dithiocarbamate (MoDTC), on the boundary lubrication of DLC coatings, the wear mechanisms leading to the coating removal are not fully understood to date. Moreover, the impact of the degradation of the MoDTC-containing base oil on the tribological properties of DLC coatings has not been investigated. This study could help to elucidate the mechanisms by which the coating is worn out in presence of MoDTC-containing base oil. In this work, the friction and wear performances of DLC coatings with different hydrogen contents and doping elements have been investigated in the presence of MoDTC-containing base oil. To enable the correlation between these changes and the modification of the contact surface chemistry, tribofilms generated during friction were investigated by SEM combined with Energy Dispersive X-ray Spectrometry (EDX) and X-ray Photoelectron Spectroscopy (XPS). A new mechanism explaining the severe wear experienced by DLC coatings when lubricated with a MoDTC-containing base oil is proposed.

Entertainment: Bond villain fails neuroanatomy

Nature 528, 7583 (2015). doi:10.1038/528479e

Author: Michael D. Cusimano

The thrills and action in Spectre, the latest James Bond film, were somewhat marred for this viewer by a fundamental neuroanatomical blunder.The scene is a Moroccan desert. Bond's nemesis is torturing our hero using a head clamp fused with a robotic drill. Intending

Prostate cancer: 4 big questions

Nature. doi:10.1038/528S137a

Author: Richard Hodson

Despite advances in detection and therapy, much about this common malignancy remains unknown. Here are some of the most important unresolved issues.

At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal. Authors: Andrew J. Mannix, Xiang-Feng Zhou, Brian Kiraly, Joshua D. Wood, Diego Alducin, Benjamin D. Myers, Xiaolong Liu, Brandon L. Fisher, Ulises Santiago, Jeffrey R. Guest, Miguel Jose Yacaman, Arturo Ponce, Artem R. Oganov, Mark C. Hersam, Nathan P. Guisinger

Publication date: 25 January 2016
Source:Surface and Coatings Technology, Volume 286
Author(s): Denis Music, Richard W. Geyer, Jochen M. Schneider
Hardness, one key property of hard coatings, is proportional to shear modulus, which can be predicted using density functional theory (DFT). Besides considering hardness, a design methodology for hard coatings must include additional physical and chemical properties, such as thermal conductivity. Recently, also the hard coating–environment (or workpiece) and hard coating–substrate interfaces have been described, constituting new research directions. We have reviewed two commercially successful benchmark hard coatings from the DFT perspective: (i) amorphous diamond-like carbon (DLC) and (ii) metastable TiAlN. Major DFT contributions to the DLC research are the correlation between density and electronic structure as well as identification of reaction products formed during atmospheric exposure to be the main cause for low friction at elevated temperatures. In the case of TiAlN based hard coatings, DFT enabled atomic scale understanding of the phase stability, formation of defect structures and interfaces for the elastic properties, enhancement of toughness, initial stages of oxidation, and interaction with molten polymers and metals. Future DFT design challenges include broader high-throughput screening, additional properties, nucleation and growth phenomena, and multiple interfaces.

Graphical abstract

Abstract

Understanding soot nanoparticle interaction with oil additives and the causes of soot-induced thickening would assist in lubricant formulation, prolonging engine life and improving engine efficiency. Three-dimensional measurement of soot structures is currently not undertaken as established techniques are limited to two dimensions. While they give valuable information on the structure and reactivity of soot nanoparticles, it is not easy to correlate this to geometry of primary particles and agglomerates. In this work, we investigate the development and application of 3D-TEM for characterisation of soot agglomerates as a new capability to yield information on the volumetric character of fractal nanoparticles. This investigation looks at the feasibility for volume reconstruction of nanometric soot particles in used engine oil from multiple imaging at different tilt angles. Bright-field TEM was used to capture two-dimensional images of soot. Heptane and diethyl ether washes were used to remove volatile contaminants and allowed for images from −60° to +60° tilt with no sign of carbon build-up to be acquired. Tomographic reconstruction from the aligned tilt-series images based on weighted back-projection algorithm has yielded useful information about complex soot nanoparticle size. Estimation of soot mass in oil by nanoparticle tracking analysis (NTA) can be considerably improved by taking into account the three-dimensional shape of the soot agglomerate including the shape factor in the calculations. 3D-TEM measurements were compared with values calculated by using a single-sphere approach when tracking nanoparticles moving under Brownian motion. A shape factor was calculated, dividing the surface area and volume calculated using spherical geometrical estimates, by the respective values calculated using the 3D models. The spherical model of the particle is found on average to overestimate the surface area by sevenfold, and the volume to the actual soot agglomerate by 23 times. Applying the calculated shape factor as a correction reduces the NTA overestimation by one order of magnitude.

Publication date: 15 February 2016
Source:Wear, Volumes 348–349
Author(s): Ane Maite Martinez, Jon Echeberria
During braking, high temperatures can be generated on the contact surfaces and inside the brake pads. Solid lubricants, i.e., metal sulphides, play an important role in brake performance, but they can react, oxidise or decompose with exposure to temperature, modifying their tribological properties. This paper investigates the chemical reactions between different metal powders (Cu, Fe, Sn and Zn) and Sb2S3 that take place in a low-metallic brake pad during braking in conditions were high temperature is generated. The reaction products were characterised by SEM–EDS and the glancing XRD technique. Moreover, thermal treatments (in air and argon) of binary mixtures, containing the same weight ratio of these metal powders and Sb2S3 contained in the brake pad, were carried out and analysed via DSC–TGA and XRD techniques. The paper finds that the reaction features and reaction products depend on the temperature generated during braking, the specific combination of metal/lubricant and the atmosphere conditions (oxidant or inert). In general, the reaction products are a combination of an intermetallic (metallic antimonide) and a metal sulphide (from the metal powder), which can be found both on the surface and inside the brake pad.