Optische Konstanten von Substraten im NIR/MIR‐Spektralbereich

Determination of the Optical Constants of Common Substrate Materials in the NIR/MIR‐Spectral Regions An approach is reported for determining the optical constants of substrates and single layer coatings in the near and mid‐infrared spectral regions. A combination of the algorithm from Nichelatti and a multi‐oscillator model has been used to determine the optical constants of the substrates. Thus, the approach even works when the sample transmittance is vanishing. We demonstrate the application of the approach to the evaluation of transmission and reflection spectra of common substrates (CaF₂, Q1, Sapphire) measured by a Fourier‐Transform‐Infrared spectrophotometer. The comparison of the calculated optical constants with values reported in literature confirms the validity of the used approach. We also demonstrate the IR characterisation of a tantalum oxide single layer deposited onto a Q1 substrate by means of the multi‐oscillator‐model. The results are again in good agreement with literature data.     

Bowtie‐Shaped NiCo2O4 Catalysts for Low‐Temperature Methane Combustion

Bowtie‐shaped NiCo₂O₄ nanostructures are prepared using a hydrothermal method. Variation of the synthesis parameters, including reaction time, additives, and calcination temperature, allows an understanding of the origin of the bowtie‐shaped structure to be developed. Methane oxidation experiments performed using temperature‐programed oxidation (TPO) show that the new materials, which do not contain precious metals, have excellent activity for low‐temperature methane combustion, with 100% conversion at ≈410 °C (gas hourly space velocity (GHSV): 90 000 mL (STP) g^?1 h^?1). The structure–activity relationships of the bowtie‐shaped nanostructures are explored.     

Magnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria

Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain‐like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro‐ and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain‐like NCs assemblies, their exact shape, arrangement and stray‐fields have to be considered (ideally obtained using ET).     

Quantitative restoration targets for fish and wildlife habitats and populations in the Lower Green Bay and Fox River AOC

The Lower Green Bay and Fox River Area of Concern (LGB&FR AOC) is one of the most ecologically diverse but demonstrably impaired AOCs in the Laurentian Great Lakes. We outline a transparent, quantitative process for setting targets to remove two fish and wildlife-related beneficial use impairments (BUIs). The method identifies important habitats and species/species groups and weights them according to ecological and socioeconomic criteria. These weights are paired with standardized estimates of current condition ranging from 0 (worst possible) to 10 (best possible). A weighted average of the condition scores gives an overall AOC condition for each BUI, creating a baseline for setting future restoration or BUI removal targets. Weighted averages for the LGB&FR AOC yielded a current condition of 3.60 for fish and wildlife habitats and 4.65 for species/species groups. Based on achievable restoration scenarios and discussions with local experts and stakeholders, we propose removal targets of 6.0 for the “loss of fish and wildlife habitat” BUI and 6.5 for the “degradation of fish and wildlife populations” BUI. This quantitative approach illuminates multiple pathways for reaching restoration targets and facilitates informed discussions about cost effective restoration projects. According to our results, species and species groups in this AOC are generally in better current condition than habitats when compared on the same 0–10 scale. This suggests that many (though not all) desirable fish and wildlife populations in the LGB&FR AOC are able to survive in relatively degraded habitats or are able to use these habitats productively during part of their life cycle.     

Exploring a novel cyclic monofunctional peroxide for curing of silicone rubber at elevated temperature

The curing characteristics of silicone rubber (polydimethylsiloxane [PDMS]) in the presence of structurally different peroxides, namely dicumyl peroxide (DCP) and 3,3,5,7,7‐pentamethyl‐1,2,4‐trioxepane (PMTO), have been studied in details. At moderate temperature, DCP is more prominent for curing the silicone rubber but at high temperatures it suffers from low scorch safety. An inhibitor 2,2,6,6‐tetramethylpiperidinyloxyl (TEMPO) was added with DCP to stabilize the radicals in order to increase the scorch safety time. On the other hand, PMTO showed a prolonged scorch safety and better crosslinking efficiency rather than (DCP + TEMPO) mix at higher temperatures. PMTO‐crosslinked PDMS shows better crosslinking efficiency as indicated by a higher gel content and low swelling index value. Also the mechanical properties, thermal stability, and dynamic mechanical behavior of PMTO‐crosslinked PDMS are much superior than (DCP + TEMPO)‐crosslinked PDMS. Apart from thermoplastic vulcanizates (TPVs) made from PMTO‐crosslinked PDMS show better physicomechanical behavior compared to the TPVs made from (DCP + TEMPO)‐crosslinked PDMS. Moreover, DCP undergoes decomposition reactions at a higher temperature and forms acetophenone, which leads to an unpleasant smell in the final products whereas no such phenomenon is observed for PMTO. Therefore, PMTO turns out to be the suitable peroxide for crosslinking of PDMS at higher temperature. POLYM. ENG. SCI., 57:1073–1082, 2017. © 2016 Society of Plastics Engineers     

Werkstoffzuverlässigkeit in der Tribologie

The Reliability of Materials in Tribology. The reliability of materials is, in general, reduced by lack of knowledge or the disregard of reaction mechanisms, by the disturbance of chemical or physical conditions of equilibrium and by changes in systems (e. g. combinations of materials, manufacturing processes, interaction with the environment etc.) entailing serious consequences. In the field of tribology, the following examples may be encountered:

• – Reaction mechanisms: Irreversible single threshold value: Transition from a metastable to a stable system; Crystallisation of synthetic materials; Abrasion phenomena with coating layers. Reversible threshold value: Volume change due to changes in physical state; Reversible structural transition. Irreversible cumulative threshold value: Influence of light on the resinification of lubricants; Crack development in the case of fatigue failures; Structurally unstable surface layers; Structural ageing phenomena.
• – Equilibrium: Wear/repolishing equilibrium; Tribological equilibrium of the surface structure; Compatibility of bearing materials; Consumption of additives in lubricating oil; Tribology and corrosion.
• – Interactions and system changes: General influence of basic materials; Interactions and catalysis; Evaporation of synthetic materials; Cleaning systems; Vibration.

     

Fatty acid composition ofcuphea seed oils

Nineteen species of 10 taxonomic sections ofCuphea were analyzed for fatty acid composition of the seed oils. Two sections of the genus,Trispermum andPseudocircaea, previously unreported, are included. Lauric acid is the major component of the seed oil in seven of the species surveyed; capric andmyristic each predominate in five. Linolenic acid, previously thought to be only a trace component ofCuphea seed oils, is the major constituent of two species. Two others are rich in linoleic acid, another minor component of mostCupbea oils.     

Influence of pressure and crystallization rate on the surface microhardness of high-density polyethylene

The indentation microhardnessMH of high-density polyethylene crystallized at different pressuresp and crystallization rates _c has been investigated. The results confirm thatMH is an increasing function of lamellar thickness and therefore of density. The rate of increase depends on the crystallization conditionsp and _c. Crystallization at high pressure leads toMH values considerably higher than those of samples prepared under atmospheric pressure. The results are discussed in terms of compressed amorphous regions contributing to an elastic release after removal of the indenter. For samples crystallized under different pressures the hardness value turns out to be nearly independent of the elastic modulusE. For samples crystallized at different rates _c there is a steady decrease of microhardness with increasing _c (decrease of lamellar thickness) but no simple relationship withE. With higher rates _c the appearance of strained tie molecules provokes a rapid increase ofE whileMH decreases further because the crystals become smaller.