Determination of the Li distribution in synthetic recycling slag with SIMS

The recovery of technically important elements like lithium from slag of pyrometallurgical recycling of lithium traction batteries will be very important in future due to the expected increasing demand of this element with the upcoming world-wide implementation of electro mobility. Therefore, the investigation of possibilities to recover lithium from pyrometallurgical slag from the recycling of lithium traction batteries is mandatory. In this context, the EnAM (engineered artificial mineral) approach is very promising. Solidified melt of synthetic recycling slag with the compounds Li2O-MgO-Al2O3-SiO2-CaO-MnO contains various Li-bearing phases including spinel solid solution, Li-aluminate and eucryptite-like Li-alumosilicate. Most probably, the Ca-alumosilicate matrix (melilite-like solid solution) incorporates lithium as well. These compounds can be determined and calculated to an acceptable approximation with electron probe microanalysis (EPMA). Nevertheless, an adequate precise measurement of lithium is virtually impossible due to the extremely low fluorescence yield and long wavelength of Li Kα. Secondary mass spectrometry (SIMS) can be used to fill this gap in the analytical assessment of the slag. Therefore, the combination of these two analytical methods can distinctively improve the mineralogical and chemical characterization of lithium-containing solidified (slag) melt

Achieving Ultra-Low Friction with Diamond/Metal Systems in Extreme Environments

In the search for achieving ultra-low friction for applications in extreme environments, we evaluate the interfacial processes of diamond/tungsten sliding contacts using an on-line macro-tribometer and a micro-tribometer in an ultra-high vacuum. The coefficient of friction for the tests with the on-line tribometer remained considerably low for unlubricated sliding of tungsten, which correlated well with the relatively low wear rates and low roughness on the wear track throughout the sliding. Ex situ analysis was performed by means of XPS and SEM-FIB in order to better understand the underlying mechanisms of low friction and low-wear sliding. The analysis did not reveal any evidence of tribofilm or transferfilm formation on the counterface, indicating the absence of significant bonding between the diamond and tungsten surfaces, which correlated well with the low-friction values. The minimal adhesive interaction and material transfer can possibly be explained by the low initial roughness values as well as high cohesive bonding energies of the two materials. The appearance of the wear track as well as the relatively higher roughness perpendicular to the sliding indicated that abrasion was the main wear mechanism. In order to elucidate the low friction of this tribocouple, we performed micro-tribological experiments in ultra-high vacuum conditions. The results show that the friction coefficient was reduced significantly in UHV. In addition, subsequently to baking the chamber, the coefficient of friction approached ultra-low values. Based on the results obtained in this study, the diamond/tungsten tribocouple seems promising for tribological interfaces in spacecraft systems, which can improve the durability of the components

An in-depth evaluation of sample and measurement induced influences on static contact angle measurements

Static contact angle measurements are one of the most popular methods to analyze the wetting behavior of materials of any kind. Although this method is readily applicable without the need of sophisticated machinery, the results obtained for the very same material may vary strongly. The sensitivity of the measurement against environmental conditions, sample preparation and measurement conduction is a main factor for inconsistent results. Since often no detailed measurement protocols exist alongside published data, contact angle values as well as elaborated wetting studies do not allow for any comparison. This paper therefore aims to discuss possible infuences on static contact angle measurements and to experimentally demonstrate the extent of these efects. Sample storage conditions, cleaning procedures, droplet volume, water grade and droplet application as well as the infuence of evaporation on the static contact angle are investigated in detail. Especially sample storage led to diferences in the contact angle up to 60%. Depending on the wetting state, evaporation can reduce the contact angle by 30–50% within 10 min in dry atmospheres. Therefore, this paper reviews an existing approach for a climate chamber and introduces a new measuring setup based on these results. It allows for the observation of the wetting behavior for several minutes by successfully suppressing evaporation without negatively afecting the surface prior to measurement by exposure to high humidity environments

Atomistic insights into lubricated tungsten/diamond sliding contacts

The reinforcement of coatings with diamond particles results in superior tribological performance for automotive applications. In addition to improving the coating’s bulk properties, sliding of diamond on metallic counter bodies contributes to improved tribological performance. Therefore, in order to design better diamond reinforced coatings, it is imperative to understand the atomistic mechanisms at sliding metal/diamond interfaces. Here, we investigate the interfacial tribo-chemical mechanisms leading to low friction in lubricated tungsten/diamond sliding contacts by combining reactive atomistic simulations with on-line tribometry experiments linked to chemical analysis. Reactive classical molecular dynamics simulations reveal the dehydrogenation of hexadecane lubricant molecules between tungsten/diamond contacts by proton transfer from the hexadecane to octahedral sites of the tungsten surface. Subsequent chemisorption of the radicalized hexadecane on dangling C-bond sites of the diamond surface leads to the formation of low-density hydrocarbon films, which significantly lower frictional resistance in the tribo-contact. Quasi-static density functional theory calculations confirm the classical molecular dynamics results and reveal that radicalized hydrocarbon molecules can also bond via C-O bonds on a WO3 layer covering the tungsten counter surface. The on-line tribometry experiments confirm the reduction of friction under hexadecane lubrication and ex situ chemical analysis by means of XPS, AES and EELS provide evidence of the formation of a carbon-rich tribofilm on the diamond and tungsten-oxide surfaces as predicted by the atomistic simulations

Fabrication and Characterization of Single-Crystal Diamond Membranes for Quantum Photonics with Tunable Microcavities

The development of quantum technologies is one of the big challenges in modern research. Acrucial component for many applications is an efficient, coherent spin–photon interface, and coupling single-color centers in thin diamond membranes to a microcavity is a promising approach. To structure such micrometer thin single-crystal diamond (SCD) membranes with a good quality, it is important to minimize defects originating from polishing or etching procedures. Here, we report on the fabrication of SCD membranes, with various diameters, exhibiting a low surface roughness down to 0.4 nm on a small area scale, by etching through a diamond bulk mask with angled holes. A significant reduction in pits induced by micromasking and polishing damages was accomplished by the application of alternating Ar/Cl2 + O2 dry etching steps. By a variation of etching parameters regarding the Ar/Cl2 step, an enhanced planarization of the surface was obtained, in particular, for surfaces with a higher initial surface roughness of several nanometers. Furthermore, we present the successful bonding of an SCD membrane via van der Waals forces on a cavity mirror and perform finesse measurements which yielded values between 500 and 5000, depending on the position and hence on the membranethickness. Our results are promising for, e.g., an efficient spin–photon interface

Boron-incorporating silicon nanocrystals embedded in SiO2: absende of free carriers vs. B-induced defects

Boron (B) doping of silicon nanocrystals requires the incorporation of a B-atom on a lattice site of the quantum dot and its ionization at room temperature. In case of successful B-doping the majority carriers (holes) should quench the photoluminescence of Si nanocrystals via non-radiative Auger recombination. In addition, the holes should allow for a non-transient electrical current. However, on the bottom end of the nanoscale, both substitutional incorporation and ionization are subject to significant increase in their respective energies due to confinement and size effects. Nevertheless, successful B-doping of Si nanocrystals was reported for certain structural conditions. Here, we investigate B-doping for small, well-dispersed Si nanocrystals with low and moderate B-concentrations. While small amounts of B-atoms are incorporated into these nanocrystals, they hardly affect their optical or electrical properties. If the B-concentration exceeds ~1 at%, the luminescence quantum yield is significantly quenched, whereas electrical measurements do not reveal free carriers. This observation suggests a photoluminescence quenching mechanism based on B-induced defect states. By means of density functional theory calculations, we prove that B creates multiple states in the bandgap of Si and SiO2. We conclude that non-percolated ultra-small Si nanocrystals cannot be efficiently B-doped

Atomistic Insights Into Lubricated Tungsten/Diamond Sliding Contacts

The reinforcement of coatings with diamond particles results in superior tribological performance in automotive applications. In addition to improving the coating's bulk properties, sliding of diamond on metallic counter bodies contributes to improved tribological performance. Therefore, in order to design better diamond-reinforced coatings, it is imperative to understand the atomistic mechanisms at sliding metal/diamond interfaces. Here, we investigate the interfacial tribochemical mechanisms leading to low friction in lubricated tungsten/diamond sliding contacts by combining reactive atomistic simulations with on-line tribometry experiments linked to chemical analysis. Reactive classical molecular dynamics simulations reveal the dehydrogenation of hexadecane lubricant molecules between tungsten/diamond contacts by proton transfer from the hexadecane to octahedral sites of the tungsten surface. Subsequent chemisorption of the radicalized hexadecane on dangling C-bond sites of the diamond surface leads to the formation of low-density hydrocarbon films, which significantly lower frictional resistance in the tribo-contact. Quasi-static density functional theory calculations confirm the classical molecular dynamics results and reveal that radicalized hydrocarbon molecules can also bond via C–O bonds on a WO3 layer covering the tungsten counter surface. The on-line tribometry experiments confirm the reduction of friction under hexadecane lubrication, and ex situ chemical analysis by means of X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and electron energy loss spectroscopy (EELS) provides evidence of the formation of a carbon-rich tribofilm on the diamond and tungsten-oxide surfaces as predicted by the atomistic simulations

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