Tribological Performances of Diamond-Like Carbon Coatings for Hydraulic Applications

The tribological performance of contacts within hydraulic pumps over a wide range of conditions is essential for the sustainability of mobile hydraulic systems. To reduce the energy consumption of hydraulic systems, mechanical losses and wear rates need to be reduced. Additionally, materials containing lead must also be replaced due to their environmental impact. In this study, the performance of different lead-free combinations of hydrogenated diamond-like carbon (hydr. DLC) coatings were investigated. For this purpose, the tribological behavior of hydr. DLC (Balinit DLC), ceramic-doped hydr. DLC (Balinit C), and ceramic bond-coated hydr. DLC (Balinit DLC Star) coatings on a nitride steel substrate were compared in tribometer tests.     

Feinstaubemissionen trockenlaufender Friktionssysteme in Fahrzeugen

Forschung im Ingenieurwesen - Nicht nur der Verbrennungsmotor eines Fahrzeuges emittiert Feinstaub, auch durch das Bremsen und Abrollen des Reifens entstehen solche gesundheitsschädlichen...     

Biosynthesis of the Fungal Organophosphonate Fosfonochlorin Involves an Iron(II) and 2-(Oxo)glutarate Dependent Oxacyclase

The fungal metabolite Fosfonochlorin features a chloroacetyl moiety that is unusual within known phosphonate natural product biochemistry. Putative biosynthetic genes encoding Fosfonochlorin in Fusarium and Talaromyces spp. were investigated through reactions of encoded enzymes with synthetic substrates and isotope labelling studies. We show that the early biosynthetic steps for Fosfonochlorin involve the reduction of phosphonoacetaldehyde to form 2-hydroxyethylphosphonic acid, followed by oxidative intramolecular cyclization of the resulting alcohol to form (S)-epoxyethylphosphonic acid. The latter reaction is catalyzed by FfnD, a rare example of a non-heme iron/2-(oxo)glutarate dependent oxacyclase. In contrast, FfnD behaves as a more typical oxygenase with ethylphosphonic acid, producing (S)-1-hydroxyethylphosphonic acid. FfnD thus represents a new example of a ferryl generating enzyme that can suppress the typical oxygen rebound reaction that follows abstraction of a substrate hydrogen by a ferryl oxygen, thereby directing the substrate radical towards a fate other than hydroxylation.     

Spatially Resolved Temperature Measurements during Condensation in Presence of a Non-Condensable Gas

Axial temperature profiles of the vapor phase can provide valuable indication of the condensation process along the heat transfer path and highlight the impact of non-condensable gases on a unit's performance. The local measurements at moderate vacuum conditions for condensation of a binary mixture are presented alongside the implementation and assessment of optical sensors in a heat transfer process. The results show a good depiction of the characteristic temperature behavior during the condensation process. The relation between temperature, partial pressure and mole fractions are shown.     

Paste Development for an Optimized Filament Stretching Effect during Parallel Dispensing on Transparent Conductive Oxide Layers for Solar Cell Metallization

The availability of silver as an electrically conductive filler material in printing pastes for solar cell metallization is becoming a more crucial issue for multiterawatt-scale production due to its global constraints. Therefore, the silver consumption for solar cell production needs to be reduced drastically by substituting silver with alternative conductive filler materials or utilizing process-specific phenomena. The phenomenon of filament stretching during microextrusion allows significantly lower paste laydowns. The magnitude of filament stretching is paste-dependent and therefore further knowledge of the pastes’ impact to the filament stretching is required. This study presents nine low-temperature curing pastes differing in the particle system and binder resin. The rheological and thermal behavior of these suspensions are investigated and printing tests onto silicon heterojunction (SHJ) precursors are carried out. Additionally, scanning electron microscopy (SEM)-based microstructure analyses of printed electrodes are performed. Based on these experimental results, the impact of paste compositions regarding the paste behavior during microextrusion and the SHJ solar cell performances are analyzed. The developed paste formulations exhibit a strong filament stretching, leading to a reduced silver laydown of down to Δm_Ag = −60%_rel. and an absolute efficiency gain of up to Δη = +0.75%_abs. due to less shading losses.     

Field-data-based reliability analysis of power converters in wind turbines: Assessing the effect of explanatory variables

Frequent failures of power converters affect the availability of wind turbines and cause considerable maintenance costs. To enhance the reliability of power converters in wind turbines, the prevailing causes and modes of failures have to be identified. This publication contributes to root-cause analysis of the power-converter failures in wind turbines from a statistical point of view. For this purpose, the failure behavior of power-converters is modeled via lifetime models as well as repairable-system models. By means of regression models, covariates are incorporated, including both design-related and site-specific covariates. The analysis is based on a worldwide extensive field-data collection covering more than 9000 turbines, including different turbine designs, sites, and ages. The results obtained by means of the applied regression models indicate that the location of the power converter within the turbine, the cooling system, the converter rated power, the DC-link voltage, the IGBT-module manufacturer, and the commissioning date of the turbine as design-related covariates have a significant effect on the phase-module failure behavior and with that on converter reliability. Among the site-specific covariates, the analysis results confirm humidity as a likely significant driver of failures.     

Extreme High-Speed Laser Material Application-Coated Carbide-Reinforced Control Plates and Conventional Lead-Based Plates in Axial Piston Machines

Hydraulic drive train technology is widely used in both mobile and stationary systems, when high forces or torques are applied. In hydraulic components, high load levels must be supported due to increasing pressure levels of the fluid. Conventionally, leaded brass is used right against steel, where the lead not only aids the manufacturing process but also provides good tribological properties, such as low friction over a wide range of speeds and pressures. Currently promising lead-free coatings using high-speed laser material deposition (EHLA) will be implemented in a state-of-the-art axial piston pump.     

Electrospun Ca3Co4−xO9+δ nanofibers and nanoribbons: Microstructure and thermoelectric properties

Oxide-based ceramics offer promising thermoelectric (TE) materials for recycling high-temperature waste heat, generated extensively from industrial sources. To further improve the functional performance of TE materials, their power factor should be increased. This can be achieved by nanostructuring and texturing the oxide-based ceramics creating multiple interphases and nanopores, which simultaneously increase the electrical conductivity and the Seebeck coefficient. The aim of this work is to achieve this goal by compacting electrospun nanofibers of calcium cobaltite Ca₃Co_4−xO_9+δ, known to be a promising p-type TE material with good functional properties and thermal stability up to 1200 K in air. For this purpose, polycrystalline Ca₃Co_4−xO_9+δ nanofibers and nanoribbons were fabricated by sol–gel electrospinning and calcination at intermediate temperatures to obtain small primary particle sizes. Bulk ceramics were formed by sintering pressed compacts of calcined nanofibers during TE measurements. The bulk nanofiber sample pre-calcined at 973 K exhibited an improved Seebeck coefficient of 176.5 S cm⁻¹ and a power factor of 2.47 μW cm⁻¹ K⁻² similar to an electrospun nanofiber-derived ceramic compacted by spark plasma sintering.