Chlor-alkali electrolysis with oxygen depolarized cathodes: history,present status and future prospects

The historical development, current status and future prospects of chlor-alkali electrolysis with oxygen depolarized cathodes (ODCs) are summarized. Over the last decades, membrane chlor-alkali technology has been optimized to such an extent that no substantial reduction of the energy demand can be expected from further process modifications. However, replacement of the hydrogen evolving cathodes in the classical membrane cells by ODCs allows for reduction of the cell voltage and correspondingly the energy consumption of up to 30%. This replacement requires the development of appropriate cathode materials and novel electrolysis cell designs. Due to their superior long-term stability, ODCs based on silver catalysts are very promising for oxygen reduction in concentrated NaOH solutions. Finite-gap falling film cells appear to be the technically most mature design among the several ODC electrolysis cells that have been investigated.

Miniaturized low-cost ion mobility spectrometer for fast detection of chemical warfare agents

Ion mobility spectrometry (IMS) is a well-known method for detecting hazardous compounds in air. Typical applications are the detection of chemical warfare agents, highly toxic industrial compounds, explosives, and drugs of abuse. Detection limits in the low part per billion range, fast response times, and simple instrumentation make this technique more and more popular. In particular, there is an increasing demand for miniaturized low-cost IMS for hand-held devices and air monitoring of public areas by sensor networks. In this paper, we present a miniaturized aspiration condenser type ion mobility spectrometer for fast detection of chemical warfare agents. The device is easy to manufacture and allows single substance identification down to low part per billion-level concentrations within seconds. The improved separation power results from ion focusing by means of geometric constraints and fluid dynamics. A simple pattern recognition algorithm is used for the identification of trained substances in air. The device was tested at the German Armed Forces Scientific Institute for Protection Technologies-NBC-Protection. Different chemical warfare agents, such as sarin, tabun, soman, US-VX, sulfur mustard, nitrogen mustard, and lewisite were tested. The results are presented here.     

Size effects in polyurethane bonds: experiments, modelling and parameter identification

In this study we examine polyurethane bonds of varying thickness between anodised aluminium substrates. The performed shear tests showed an intriguing size effect of the kind “thinner equals softer”. This size effect occurs not only in the basic elasticity (relaxed state), but also in the viscoelastic behaviour of the tested material. The cause of such size effects is supposed to be found in the existence of so-called interphases or boundary layers, which may differ considerably from the bulk in terms of mechanical behaviour, thus having an enormous impact on thin bonds. In thick bonds, however, these interphases or boundary layers have a minor effect on the overall mechanical behaviour. To account for these experimental results in bond modelling, an extended phenomenological continuum mechanics-based model, which explicitly includes such size effects in its calculation, is developed and presented. For this purpose, an abstract structure parameter with its corresponding balance equation is established describing the formation of the interphases by means of a phase transition. This makes it possible to define the bond stiffness at a macroscopic level, without entering into the microstructure. The extended model brings up a set of model parameters, which are determined efficiently by an ES (evolution strategy). The study concludes with a summary and an outlook on our further research work.

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Experimental validation of a prototype ejector designed to reduce throttling losses encountered in transcritical R744 system operation

This study presents experimental results obtained from a transcritical R744 system using a refrigerant ejector. The results were compared to that of a conventional system with an expansion valve. For the test conditions considered, the cooling capacity and COP simultaneously improved by up to 8% and 7%, respectively. Experiments were analyzed to quantitatively assess the effects on system performance as a result of changes in basic ejector dimensions such as motive nozzle and diffuser sizing. Small angles of 5° yielded best results for the static pressure recovery of the high-speed two-phase flow entering the diffuser. Experiments confirmed that like in a conventional transcritical R744 system with expansion valve, the high-side pressure control integrated into the ejector could be used to maximize the system performance. Numerical simulation results helped identifying this basic trend. Due to difficulties in the ejector throat pressure measurements, a more practical performance metric was introduced in order to quantify overall ejector efficiencies. According to this definition, the prototype ejector was able to recover up to 14.5% of the throttling losses.     

Novel quinoline-based polyurethane elastomers. The effect of the hard segment structure in properties enhancement

Polyurethane elastomers incorporating a quinoline moiety along their polymeric backbones and aliphatic, aromatic or heterocyclic crosslinkers have been synthesized and characterized. For this, NCO-terminated urethane oligomers were prepared from poly(butylene adipate) diol and methylene diphenyl diisocyanate and were subsequently chain extended with 2,4-quinolinediol and different crosslinkers. This study reports the influence of the different crosslinker chemical structures and the hard segment molar ratio on the thermal and dynamic mechanical thermal properties, as well as on the mechanical properties of these elastomers. The fluorescence spectra of polyurethane elastomers were determined at an excitation wavelength of 290 nm. The different chemical structures of the crosslinkers determine the hard segment cohesion and reduce the mobility of the soft phase, having an important effect on thermal stability and on the mechanical properties of the polyurethane films. Thus the incorporation of aromatic crosslinkers results in polyurethanes with lower elongation and stress at break. The highest mechanical properties were obtained for polyurethanes crosslinked with aliphatic crosslinkers.     

Fabrication of porous silicon by metal-assisted etching using highly ordered gold nanoparticle arrays

ABSTRACT: A simple method for the fabrication of porous silicon (Si) by metal-assisted etching was developed using gold nanoparticles as catalytic sites. Etching masks were prepared by spin-coating of colloidal gold nanoparticles onto Si. Appropriate functionalization of the gold nanoparticle surface prior to the deposition step enabled the formation of quasi-hexagonally ordered arrays by self-assembly which were translated into an array of pores by subsequent etching in a HF solution containing H2O2. The quality of the pattern transfer depended on the chosen preparation conditions for the gold nanoparticle etching mask. The influence of the Si surface properties were investigated by using either hydrophilic or hydrophobic Si substrates resulting from piranha solution or HF treatment, respectively. The polymer coated gold nanoparticles had to be thermally treated in order to provide direct contact at the metal/Si interface which is required for the following metal-assisted etching. Plasma-treatment as well as flame annealing were successfully applied. Best results were obtained for Si substrates which were treated with HF prior to spin-coating and flame annealed in order to remove the polymer matrix. The presented method opens up new resources for the fabrication of porous silicon by metal-assisted etching. Here, the vast variety of metal nanoparticles accessible by well-established wet-chemical synthesis can be employed for the fabrication of the etching masks.     

Large-scale parallel arrays of silicon nanowires via block copolymer directed self-assembly

Extending the resolution and spatial proximity of lithographic patterning below critical dimensions of 20 nm remains a key challenge with very-large-scale integration, especially if the persistent scaling of silicon electronic devices is sustained. One approach, which relies upon the directed self-assembly of block copolymers by chemical-epitaxy, is capable of achieving high density 1?:?1 patterning with critical dimensions approaching 5 nm. Herein, we outline an integration-favourable strategy for fabricating high areal density arrays of aligned silicon nanowires by directed self-assembly of a PS-b-PMMA block copolymer nanopatterns with a L(0) (pitch) of 42 nm, on chemically pre-patterned surfaces. Parallel arrays (5 × 10(6) wires per cm) of uni-directional and isolated silicon nanowires on insulator substrates with critical dimension ranging from 15 to 19 nm were fabricated by using precision plasma etch processes; with each stage monitored by electron microscopy. This step-by-step approach provides detailed information on interfacial oxide formation at the device silicon layer, the polystyrene profile during plasma etching, final critical dimension uniformity and line edge roughness variation nanowire during processing. The resulting silicon-nanowire array devices exhibit Schottky-type behaviour and a clear field-effect. The measured values for resistivity and specific contact resistance were ((2.6 ± 1.2) × 10(5)Ωcm) and ((240 ± 80) Ωcm(2)) respectively. These values are typical for intrinsic (un-doped) silicon when contacted by high work function metal albeit counterintuitive as the resistivity of the starting wafer (～10 Ωcm) is 4 orders of magnitude lower. In essence, the nanowires are so small and consist of so few atoms, that statistically, at the original doping level each nanowire contains less than a single dopant atom and consequently exhibits the electrical behaviour of the un-doped host material. Moreover this indicates that the processing successfully avoided unintentional doping. Therefore our approach permits tuning of the device steps to contact the nanowires functionality through careful selection of the initial bulk starting material and/or by means of post processing steps e.g. thermal annealing of metal contacts to produce high performance devices. We envision that such a controllable process, combined with the precision patterning of the aligned block copolymer nanopatterns, could prolong the scaling of nanoelectronics and potentially enable the fabrication of dense, parallel arrays of multi-gate field effect transistors.     

Rugulactone and its analogues exert antibacterial effects through multiple mechanisms including inhibition of thiamine biosynthesis

Rugulactone is a dihydro-α-pyrone isolated from the plant Cryptocarya rugulosa in 2009. It has been reported to display IkB kinase (IKK) inhibitory activity, as well as antibiotic activity in several strains of pathogenic bacteria. However, its biological targets and mode of action in bacteria have not yet been explored. Here we present enantioselective syntheses of rugulactone and of some corresponding activity-based protein profiling (ABPP) probes. We found that the ABPP probes in this study are more potent than rugulactone against Staphyloccocus aureus NCTC 8325, S. aureus Mu50, Listeria welshimeri SLCC 5334 and Listeria monocytogenes EGD-e, and that molecules of this class probably exert their antibacterial effect through a combination of targets. These targets include covalent inhibition of 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate (HMPP) kinase (ThiD), which is an essential component of the thiamine biosynthesis pathway in bacteria. This represents the first example of a small-molecule inhibitor of ThiD.     

The Iridium‐Catalyzed Synthesis of Symmetrically and Unsymmetrically Alkylated Diamines under Mild Reaction Conditions

An iridium catalyst – stabilized by an anionic P,N ligand – was used for the symmetrical and unsymmetrical monoalkylation of para‐, meta‐, and ortho‐benzenediamines. Benzyl and aliphatic alcohols were used as alkylating reagents. 28 derivatives were synthesized. 14 of them are new compounds. Furthermore, the alkylation of the pharmacological important diamine Dapson^® (dapsone) is described. 14 dapsone derivatives were synthesized among them 9 new compounds.