Clausthal University of Technology

Ionic liquids are defined today as liquids which solely consist of cations and anions and which by definition must have a melting point of 100 °C or below. Originating from electrochemistry in AlCl3 based liquids an enormous progress was made during the recent 10 years to synthesize ionic liquids that can be handled under ambient conditions, and today about 300 ionic liquids are already commercially available. Whereas the main interest is still focussed on organic and technical chemistry, various aspects of physical chemistry in ionic liquids are discussed now in literature. In this review article we give a short overview on physicochemical aspects of ionic liquids, such as physical properties of ionic liquids, nanoparticles, nanotubes, batteries, spectroscopy, thermodynamics and catalysis of/in ionic liquids. The focus is set on air and water stable ionic liquids as they will presumably dominate various fields of chemistry in future.

Demands in the area of electrical energy generation and distribution, as a result of energy policies, are leading to far reaching changes in the structure of the energy supply, which is characterised, on the one hand, by the substitution of conventional power stations by renewable energy generation, a decision which has already been made, and, on the other hand, by the changeover from centralised to decentralised energy generation. From an electrical engineering point of view, a new situation will arise for consumers concerning security of supply and power quality, which calls for further technical measures by the grid operators to ensure that the increasingly stringent supply criteria can be met. This article describes a new power electronics based approach which allows a grid compatible integration of predominantly renewable electricity generators even in weak grids making them appear to be electromechanical synchronous machines. As a consequence, all the proven properties of this type of machine which have so far defined the grid continue to do so, even when integrating photovoltaic or wind energy. These properties include, for instance, interaction between grid and generator as in a remote power dispatch, reaction to transients as well as the full electrical effects of a rotating mass. In addition, this new development can be operated in such a way that it provides primary reserve allowing, from a grid point of view, electricity generators such as wind and PV to be regarded as conventional power stations.

This article identifies and discusses the scientific challenges of hydrogen storage in porous media for safe and efficient large-scale energy storage to enable a global hydrogen economy.

Over the last 2 decades, the quartz crystal microbalance (QCM or QCM-D) has emerged as a versatile tool for investigating soft and solvated interfaces between solid surfaces and bulk liquids because it can provide a wealth of information about key structural and functional parameters of these interfaces. In this Feature, we offer QCM users a set of guidelines for interpretation and quantitative analysis of QCM data based on a synthesis of well-established concepts rooted in rheological research of the last century and of new results obtained in the last several years.

Electrodeposition is an interesting and often used technique to deposit thin films of metals onto conducting substrates. During electrodepositio n, film properties such as morphology or composition can be adjusted by controlling process parameters such as bath composition, temperature and applied potential or current density. The electrodeposition of metals f rom ionic liquids has become a heavily studied topic in the last decade but still lots of challenges remain. This thesis investigates three main topics:1. The use of liquid metal salts to increase the solubility of metals in ionic liquids, hereby improving the mass transport2. Th e application of high vacuum as an environment for electrodeposition 3. Influence of rate constants in chloroaluminatesFurthermore, the f irst electrochemical oscillator in ionic liquids was discovered by seren dipity. The techniques, used in this PhD thesis, consist of Cyclic Volta mmetry (CV), Chronoamperometry, Scanning Electron Microscopy (SEM), Tran smission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Quart z Crystal Microbalance (QCM), Optical Spectroscopy, Raman Spectroscopy a nd Finite Element Modeling. The liquid metal salts tetrakis(acetonitrile) copper(I) bis(trifluoromet hylsulfonyl)imide ([Cu(MeCN)4][Tf2N]) and tetrakis(benzonitrile) copper( I) bis(trifluoromethylsulfonyl)imide ([Cu(PhCN)4][Tf2N]), bis(tetrakis(a cetonitrile) silver(I)) tris((trifluoromethylsulfonyl)imide) silver(I) ( [Ag(MeCN)4]2[Ag(Tf2N)3]) and bis(1-ethylimidazole) silver(I) bis(trifluo romethylsulfonyl)imide ([Ag(EtIm)2][Tf2N]) were electrochemically charac terized: for electrodeposition purposes, low melting salts with a cation ic complex are preferred over anionic complexes. The MeCN complexes are the easiest to be reduced and current densities up to 25 A dm−2 in unstirred solutions could be achieved. The resulting copper or silver d eposits, made at high current densities, have a smooth appearance, did n ot show cracks and were free from entrapped organic compounds. Lower cur rent densities result in nodular deposits. The use of thiourea or 1H-ben zotriazole as additive resulted in smooth morphologies at 1 A dm−2 . It is believed that excellent mass transport in this system is due to the high metal concentration and to the favorable electrostatic interact ions between the cationic electroactive species and the cathode. This ma kes the use of liquid metal salts with electrochemically active cationic complexes interesting for electrochemical applications where mass trans port is important. The fact that comparable results are obtained for two metals, indicates that the complexes with a metal center, surrounded by acetonitrile, lead to ionic liquids that can be used for high current d ensity electroplating. A second interesting property of liquid metal sal ts is that high overpotentials can be applied during electrodeposition. This leads to a small critical size for nucleation, which is advantageou s during the plating of copper on barrier materials such as tantalum. By using [Cu(MeCN)2][Tf2N] as medium for copper electrodeposition on a tantalum substrate, a nucleation density of 8e14 m−2 is reached. The resulting deposits contain very few pinholes and have thicknesses o f 19 nm. Electrochemical vacuum deposition is a technique which exploits the low vapor pressure of ionic liquids. In contrast with aqueous solutions or o rganic solvents, ionic liquids can be placed in a high vacuum environmen t, without noticeable loss of ionic liquid, to strongly decrease the amo unt of oxygen gas and water. Possible applications are the deposition of copper on tantalum, but results indicate that even at the low pressure of a high vacuum environment, the oxidation of tantalum cannot be avoide d. A finite element model of the electrodeposition of aluminium from chloro aluminate ionic liquids was made to study the influence of the rate cons tants kb and kf on the electrodeposition rate of aluminium. These rate c onstants determine the equilibrium between Al2Cl7−, AlCl4−, and Cl−. It was found that thermodynamics and kinetics change in o pposite directions for variations in kb or kf and these opposing effects lead to a minimum in the calculated current density as a function of kb . A comparison of the calculated data and the experimental limiting curr ent densities indicates that the value of kb lies between 1e−7.5 a nd 1e−6.7 m3 mol−1 s−1. Electrochemical oscillations are a phenomenon in which a constant applie d potential leads to an oscillating current or that a constant applied c urrent gives rise to an oscillating potential. A former type of electroc hemical oscillator was found in a mixture of monovalent with divalent co pper ions in 1-ethyl-3-methylimidazolium chloride. The oscillator is an N-NDR-type because the low frequency-end of the impedance spectrum has n egative real impedances and the steep decrease in current in the potenti al-current curve. The presence of chloride is also a necessary, yet not a sufficient condition for the occurrence of current oscillations and th e imidazolium cation also plays a role in the reactions leading to the o scillatory behavior.

Alkaline water electrolysis is a key technology for large-scale hydrogen production powered by renewable energy. As conventional electrolyzers are designed for operation at fixed process conditions, the implementation of fluctuating and highly intermittent renewable energy is challenging. This contribution shows the recent state of system descriptions for alkaline water electrolysis and renewable energies, such as solar and wind power. Each component of a hydrogen energy system needs to be optimized to increase the operation time and system efficiency. Only in this way can hydrogen produced by electrolysis processes be competitive with the conventional path based on fossil energy sources. Conventional alkaline water electrolyzers show a limited part-load range due to an increased gas impurity at low power availability. As explosive mixtures of hydrogen and oxygen must be prevented, a safety shutdown is performed when reaching specific gas contamination. Furthermore, the cell voltage should be optimized to maintain a high efficiency. While photovoltaic panels can be directly coupled to alkaline water electrolyzers, wind turbines require suitable converters with additional losses. By combining alkaline water electrolysis with hydrogen storage tanks and fuel cells, power grid stabilization can be performed. As a consequence, the conventional spinning reserve can be reduced, which additionally lowers the carbon dioxide emissions.

Large hydrophobic monomers stearyl methacrylate (C18) and dococyl acrylate (C22) could be copolymerized with the hydrophilic monomer acrylamide in a micellar solution of sodium dodecyl sulfate (SDS). This was achieved by the addition of salt (NaCl) into the reaction solution. Salt leads to micellar growth and, hence, solubilization of the hydrophobes within the SDS micelles. The hydrogels thus obtained without a chemical cross-linker exhibit unique properties due to the strong hydrophobic interactions. They can only be dissolved in SDS solutions demonstrating the physical nature of cross-links. Results of dynamic light scattering, rheological and mechanical measurements show that the hydrophobic associations between the blocks of C18 or C22 units prevent water solubility and flow, while the dynamic nature of the junction zones provides homogeneity and self-healing properties together with a high degree of toughness. When fractured, the hydrogels formed using C18 associations can be repaired by bringing together fractured surfaces to self-heal at room temperature, after which, they again exhibit the original extensibility of about 3600%. The existence of free, nonassociated blocks in C18 hydrogels is accounted for their high self-healing efficiencies.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Application of Cyclobutane Derivatives in Organic SynthesisJan C. Namyslo and Dieter E. KaufmannView Author Information Institut für Organische Chemie, Technische Universität Clausthal, 38678 Clausthal-Zellerfeld, Germany Cite this: Chem. Rev. 2003, 103, 4, 1485–1538Publication Date (Web):March 15, 2003Publication History Received3 September 2002Published online15 March 2003Published inissue 1 April 2003https://pubs.acs.org/doi/10.1021/cr010010yhttps://doi.org/10.1021/cr010010yresearch-articleACS PublicationsCopyright © 2003 American Chemical SocietyRequest reuse permissionsArticle Views12018Altmetric-Citations591LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Ketones,Precursors,Reaction products,Rearrangement,Substituents Get e-Alerts

Low energy electron microscopy (LEEM) is a new technique for surface imaging, based on the wave nature of the electron. Although it makes use of electron lenses as in conventional electron microscopes it differs from them in that the electrons have energies of the order 1-100 eV when they interact with the surface. As a consequence, the method is very surface-sensitive and the probing depth may be tuned by varying the energy. Contrast is mainly produced by diffraction. Resolution is determined mainly by the chromatic and spherical aberration of the decelerating/accelerating field in front of the specimen. LEEM is easily combined with low energy electron diffraction (LEED), photoemission electron microscopy (PEEM) and other emission microscopies. The specimen is easily accessible which allows a wide variety of in situ studies over a wide temperature range. The review gives an introduction to the basic electron-specimen interaction processes, to the instrumentation and to the factors which govern contrast and resolution. The remaining, larger part of the review deals with applications to clean surfaces, atom-surface interactions and thin films. Topics discussed include topography, phase transitions, adsorption, reaction, segregation, growth, sublimation and magnetic microstructure. Related techniques are also discussed briefly.

The nanotechnology and biomedical sciences opens the possibility for a wide variety of biological research topics and medical uses at the molecular and cellular level. The biosynthesis of nanoparticles has been proposed as a cost-effective and environmentally friendly alternative to chemical and physical methods. Plant-mediated synthesis of nanoparticles is a green chemistry approach that connects nanotechnology with plants. Novel methods of ideally synthesizing NPs are thus thought that are formed at ambient temperatures, neutral pH, low costs and environmentally friendly fashion. Keeping these goals in view nanomaterials have been synthesized using various routes. Among the biological alternatives, plants and plant extracts seem to be the best option. Plants are nature’s “chemical factories”. They are cost efficient and require low maintenance. The advantages and disadvantages of nanotechnology can be easily enumerated. This study attempts to review the diversity of the field, starting with the history of nanotechnology, the properties of the nanoparticle, various strategies of synthesis, the many advantages and disadvantages of different methods and its application.

Power saving has been a central driving force for the development of new materials. In this framework, soft magnetic composites appear as a feasible concept to be applied in strategic topics for modern society including sensing, energy generation, and conversion. With a unique freedom regarding material selection based on powder metallurgy techniques, this engineering magnetic material class allows novel designs able to drive operation conditions to new limits, unlocking the potential of novel applications. This document reviews soft magnetic composites by using a multidisciplinary approach addressing underlying physics responsible for their magnetic performance, limitations, and future trends.

Sensitivity analysis (SA) is en route to becoming an integral part of mathematical modeling. The tremendous potential benefits of SA are, however, yet to be fully realized, both for advancing mechanistic and data-driven modeling of human and natural systems, and in support of decision making. In this perspective paper, a multidisciplinary group of researchers and practitioners revisit the current status of SA, and outline research challenges in regard to both theoretical frameworks and their applications to solve real-world problems. Six areas are discussed that warrant further attention, including (1) structuring and standardizing SA as a discipline, (2) realizing the untapped potential of SA for systems modeling, (3) addressing the computational burden of SA, (4) progressing SA in the context of machine learning, (5) clarifying the relationship and role of SA to uncertainty quantification, and (6) evolving the use of SA in support of decision making. An outlook for the future of SA is provided that underlines how SA must underpin a wide variety of activities to better serve science and society.

Enhanced (or engineered) geothermal systems (EGS) have evolved from the hot dry rock concept, implemented for the first time at Fenton Hill in 1977. This paper systematically reviews all of the EGS projects worldwide, based on the information available in the public domain. The projects are classified by country, reservoir type, depth, reservoir temperature, stimulation methods, associated seismicity, plant capacity and current status. Thirty five years on from the first EGS implementation, the geothermal community can benefit from the lessons learnt and take a more objective approach to the pros and cons of ‘conventional’ EGS systems.

Image edge detection is a process of locating the edge of an image which is important in finding the approximate absolute gradient magnitude at each point I of an input grayscale image. The problem of getting an appropriate absolute gradient magnitude for edges lies in the method used. The Sobel operator performs a 2-D spatial gradient measurement on images. Transferring a 2-D pixel array into statistically uncorrelated data set enhances the removal of redundant data, as a result, reduction of the amount of data is required to represent a digital image. The Sobel edge detector uses a pair of 3 x 3 convolution masks, one estimating gradient in the x-direction and the other estimating gradient in y-direction. The Sobel detector is incredibly sensitive to noise in pictures, it effectively highlight them as edges. Hence, Sobel operator is recommended in massive data communication found in data transfer.

The development of rechargeable zinc ion batteries with high capacity and high cycling stability is a great challenge in aqueous solution due to hydrogen evolution and dendritic growth of zinc. In this study, we present a zinc ion secondary battery, comprising a metallic zinc anode, a bio-ionic liquid-water electrolyte, and a nanostructured prussian blue analogue (PBA) cathode. Both the Zn anode and the PBA cathode exhibit good compatibility with the bio-ionic liquid-water electrolyte, which enables the electrochemical deposition/dissolution of zinc at the zinc anode, and reversible insertion/extraction of Zn(2+) ions at the PBA cathode. The cell exhibits a well-defined discharge voltage plateau of ∼1.1 V with a specific capacity of about 120 mAh g(-1) at a current of 10 mA g(-1) (∼0.1 C). The Zn anode shows great reversibility, and dendrite-free Zn deposits were obtained after 100 deposition/dissolution cycles. The integration of an environmentally friendly PBA cathode, a nontoxic and low-cost Zn anode, and a biodegradable ionic liquid-water electrolyte provides new perspective to develop rechargeable zinc ion batteries for various applications in electric energy storage.

Abstract End-members and species defined with permissible ranges of composition are presented for the true micas, the brittle micas, and the interlayer-deficient micas. The determination of the crystallochemical formula for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusual chemical substitutions or polytypic stacking arrangements. Tables of mica synonyms, varieties, ill-defined materials, and a list of names formerly or erroneously used for micas are presented. The Mica Subcommittee was appointed by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The definitions and recommendations presented were approved by the Commission.

Local positioning will be one of the most exciting features of the next generation of wireless systems. Completely new concepts and features for wireless data transmission and transponder systems will emerge. Self-organizing sensor networks, ubiquitous computing, location sensitive billing, context dependent information services, tracking and guiding are only some of the numerous possible application areas. This article introduces different concepts of several existing and emerging systems and applications.

Abstract Investigations into the kinetics and mechanism of dithiobenzoate‐mediated Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerizations, which exhibit nonideal kinetic behavior, such as induction periods and rate retardation, are comprehensively reviewed. The appreciable uncertainty in the rate coefficients associated with the RAFT equilibrium is discussed and methods for obtaining RAFT‐specific rate coefficients are detailed. In addition, mechanistic studies are presented, which target the elucidation of the fundamental cause of rate retarding effects. The experimental and theoretical data existing in the literature are critically evaluated and apparent discrepancies between the results of different studies into the kinetics of RAFT polymerizations are discussed. Finally, recommendations for further work are given. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5809–5831, 2006

Advanced oxidation procedures (AOPs) refer to a variety of technical procedures that produce OH radicals to sufficiently oxidize wastewater, organic pollutant streams, and toxic effluents from industrial, hospital, pharmaceutical and municipal wastes. Through the implementation of such procedures, the (post) treatment of such waste effluents leads to products that are more susceptible to bioremediation, are less toxic and possess less pollutant load. The basic mechanism produces free OH radicals and other reactive species such as superoxide anions, hydrogen peroxide, etc. A basic classification of AOPs is presented in this short review, analyzing the processes of UV/H2O2, Fenton and photo-Fenton, ozone-based (O3) processes, photocatalysis and sonolysis from chemical and equipment points of view to clarify the nature of the reactive species in each AOP and their advantages. Finally, combined AOP implementations are favored through the literature as an efficient solution in addressing the issue of global environmental waste management.

Metal-organic frameworks (MOFs) have received a lot of attention due to their unique properties and abundant functionalities. Permanent porosity and high surface area are just a few traits that have made them attractive to researchers. They can be prepared as task-specific materials by exploiting the functional group variety and tuning their size and geometry. The main purpose of this review is to present an alternative method of preparing MOF crystals and underline the advantages of ultrasound assisted (sonochemical) synthesis. State of the art ultrasound assisted techniques for the preparation of MOFs in nanoscale are presented. Optimization of morphology and particle size is highlighted throughout this work, as we discuss the effects of various factors, such as energy input, reagent concentration, adequate solvents, reaction time and more.