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Paper des Monats
- ja (90)
This paper presents a dry sliding tribo-couple (DLC/monolithic oxide ceramics), where the tribological quantities are more or less in a wide ränge independent of the sliding speed. The DLC film is composed of a specific mixture of sp3 /sp2 hybridized carbon. Self-mated ceramic/ceramic couples of MgO-Zr02, alpha-AI203 or SSiC are with their coefficients of friction above 0.45 not so lubricious, whereas the coefficients of friction of the tribocouples MgO-Zr02/DLC and alpha-AbOVDLC ranged between 0.075 and 0.15 under dry sliding. The coefficients of friction for these tribo-couples tend to decrease with increase sliding speed from 0.03 m/s to 6 m/s. The dry wear rates of the thin film is low (<10‘7 mm3/Nm) and perfectly independent from sliding velocity.
The purpose of this paper is to underline the future need for OEMs to receive lowSAP, polymer- and metal-free engine oils with high-viscosity indices and to illuminate for other OEMs the technical feasibility for application of alternative engine oils based on esters or blends of hydrocarbons with esters or polyglycols.
Design/methodology/approach The strategic goal depends technically on the use of intrinsic properties of alternative base fluids, thus substituing some additives, like anti-wear, extreme pressure and viscosity index improvers. The prone wear resistance of novel triboactive/-reactive materials enables higher portions of mixed/boundary lubrication generated by oils with a lower viscosity.
Findings Overall, the different bionotox and low-ash prototype engine oils with reduced additive contents displayed isoperformance regarding the tribological behaviour against cast iron and triboreactive materials. APS-Tin-2Cr2O2n-1 displayed an overall wear resistance comparable with grey cast iron with high-carbon content and liner wear reduction of one order of magnitude when mated with Mo-based rings. Both tests confirmed the potential for substituing molybdenum-based rings by APS-Tin-2Cr2O2n-1. The most significant reduction in system wear down to zero wear was demonstrated by mating the APS-Tin-2Cr2O2n-1 coated piston rings with smooth machined HVOF-(Ti,Mo)(C,N) liner coatings.
Research limitations/implications As lubricants are today not part of the core business of automotive OEMs, the next steps have to be proposed by the petrochemical suppliers. It is recalled here that some OEMs in their history developed and produced lubricants.
Practical implications The customer will appreciate any increase in longevity resulting in reduced maintenance. The OEM now owns, under increased solicitations, now a future-oriented tool box in order to respond to environmental and CAFÉ demands with reasonable cost management.
Originality/value This OEM report displays the complete methodology in order to adopt alternative engine oils in existing engine architectures.
Cryoadsorption on the inner surface of porous materials is a promising solution for safe, fast, and reversible hydrogen storage. Within the class of highly porous metal−organic frameworks, zeolitic imidazolate frameworks (ZIFs) show high thermal, chemical, and mechanical stability. In this study, we selected ZIF-8 synthesized mechanochemically by twin-screw extrusion as powder and pellets. The hydrogen storage capacity at 77 K and up to 100 bar has been analyzed in two laboratories applying three different measurement setups showing a high reproducibility. Pelletizing ZIF-8 increases the packing density close to the corresponding value for a single crystal without loss of porosity, resulting in an improved volumetric hydrogen storage capacity close to the upper limit for a single crystal. The high volumetric uptake combined with a low and constant heat of adsorption provides ca. 31 g of usable hydrogen per liter of pellet assuming a temperature−pressure swing adsorption process between 77 K − 100 bar and 117 K − 5 bar. Cycling experiments do not indicate any degradation in storage capacity. The excellent stability during preparation, handling, and operation of ZIF-8 pellets demonstrates its potential as a robust adsorbent material for technical application in pilot- and full-scale adsorption vessel prototypes.
Agar gel pads have been used for electrochemical measurements for some time. For zinc in particular, a standard method for measuring the stability of the corrosion product layer is being established. The main interpretation factor is the corrosion product layer resistance RL, as it is easy to determine and interpret. A high corrosion product layer resistance indicates a high level of protection. However, it is not yet known how low the corrosion product layer resistance is for freshly produced zinc samples. As zinc is highly active, it reacts immediately with the environment to form a corrosion product layer, which affects the corrosion product layer resistance. The addition of zinc acetate to the agar gel pads prevents the formation of a surface layer and destroys existing ones.
This makes it possible to measure an almost corrosion product-free zinc surface. This is important in defining the range of corrosion product layer resistance for a protective surface.
Zinc anodizing
(1985)
Zn is known to be located in the reactive centers of various enzymes, which play a major role in the mineralization process at sites where new bone formation occurs. In addition, elevated Zn levels are supposed to increase the proliferation rate of osteoblasts [1] and may lead to a stimulation of bone formation in vitro and in vivo [2]. Consequently, Zn seems to play an essential role in bone formation and mineralization through various pathways. We thus expected Zn levels to be altered at sites of extensive bone formation like in the case of fracture healing.
We measured the same areas on human bone samples with both a scanning confocal synchrotron radiation induced micro X-ray fluorescence (SR-μXRF) at the FLUO beamline (ANKA) and a full-field Color X-ray Camera at the BAMline (Bessy II) setup in order to find the ideal SR-μXRF imaging method to investigate trace element distributions in bone samples. As zinc is a trace element of special interest in bone, the setups were optimized for Zn detection. The setups were compared concerning count rate, required measurement time and resolution. We could show that the ideal method is depending on the element of interest. While for Ca (a major constituent of the bone with a low energy of 3.69keV for K) the Color X-ray Camera provided us with a higher resolution in the plane, for Zn (a trace element in bone) only the confocal SR-μXRF was able to sufficiently image the distribution.
Biopsies of healing osteoporotic fractures (Vertebral compression fractures (VCFs)) were investigated in regard to their Zn distribution. The samples were measured with a confocal SR-μXRF setup with a 10 μm x 15 μm resolution at the FLUO beamline at ANKA. As we found increased Zn levels, which seemed to be accumulated in narrow structures between bone packages we also investigated thin cuts (4 μm thick) of two sample areas with a higher resolution of 1 μm x 1 μm (monochromatic beam with E= 17 keV) at B16 at Diamond SR facility.
We will present the advantages and disadvantages of all three SR-μXRF setups (ANKA FLUO beamline, Bessy II BAMline, and Diamond B16) for imaging elemental distributions in bone with a focus on Zn. We will also show the distribution of Zn in healing VCFs.
This paper reports the formation of zinc phosphate nanoparticles from the artificial digestion of zinc chloride. Initially, the formation of amorphous primary particles with a mean radius of 1.1 nm is observed, alongside the formation of larger, protein stabilized aggregates. These aggregates, with a radius of gyration of 37 nm, are observed after 5 minutes of exposure to artificial saliva and are shown to be colloidally stable for a minimum time of two weeks. The initially formed primary particles are thought to consist of amorphous zinc phosphate, which is then transformed into crystalline Zn3(PO4)2·4H2O over the course of two weeks. Our results demonstrate that the interaction of inorganic salts with bodily fluids can induce the formation of de novo nanoparticles, which in turn, provides insights into how zinc‐enriched foods may also facilitate the formation of nanoparticles upon contact with saliva. As such, this may be considered as an undesirable (bio)mineralization.
Zirconium chloro fluoride as catalyst for C-F bond activation and HF transfer of fluoroalkanes
(2023)
In this work, we successfully synthesized amorphous zirconium chloro fluoride (ZCF), which exhibits medium lewis acidity. In addition to investigating the local coordination sphere around the Zr atoms and the material properties, we were able to establish a catalytic behavior of ZCF in C-F bond activation reactions. We present a heterogeneous catalyst that performs dehydrofluorination of a fluoroalkane and consecutive hydrofluorination of an alkyne at room temperature.