Influence of the hydrogen reduction time and temperature on the morphology evolution and hematite/magnetite conversion of spindle-type hematite nanoparticles

We report on the transformation via hydrogen reduction of spindle-type hematite nanoparticles into hematite/magnetite hybrid iron oxide particles. The transformation process consists of the reduction of nanoparticles powder in an autoclave using hydrogen gas at a fixed pressure of 11 bars. Both temperature and time of reduction are varied between 300 °C to 360 °C and 0 to 45 h. X-Ray powder diffraction data on the obtained powder and corresponding Rietveld refinement allow the amount of reduced hematite to be determined as a function of these two parameters. Kinetics parameters are measured and an estimation of the activation energy is obtained through linearization of the Arrhenius equation. While reduction is dramatically accelerated at higher temperature, the morphology of the nanoparticles only remain qualitatively unchanged at 300 °C as seen from transmission electron microscopy images. The mechanisms underlying morphology changes are still under study and seem to be closely related to reactor pressure.     

Conceptual design of distillation processes for mixtures with distillation boundaries. II. Optimization of recycle policies

Geometric design methods for the conceptual design of azeotropic distillation processes are fast and efficient tools for the economic screening of different process alternatives. The second article of this two‐part series presents a novel optimization‐based conceptual design framework for azeotropic distillation processes, which allows a rapid screening of the different process alternatives with respect to feasibility and economic incentive. The design framework is based on the economic assessment of distillation columns by the rectification body method. The feasibility limits imposed by the azeotropes are incorporated using the split feasibility test introduced in the first part of this series. The application of the framework is highlighted with several ternary and quaternary process alternatives for the production of high‐purity alcohols. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Modelling Inhomogeneous Mechanical Properties in Adhesive Bonds

Polymers often show an inhomogeneous distribution of their mechanical properties. In adhesive layers these inhomogeneities result from the formation of interphases close to the substrates. In addition, chemical aging processes are driven by diffusive processes entering the specimen from the boundaries and changing the local properties of the polymer. In the present contribution a model is presented that takes into account the local effects of the interphase's formation or of the aging processes, respectively.

The model is based on a phenomenological continuum mechanical approach, i.e., the effects are described by the introduction of an additional field in combination with an additional balance equation and corresponding boundary conditions. In the first part of this paper the formation of interphases is investigated. Comparing the model with experimental results allows for the identification of the model parameters. In the second part the model is enhanced to describe effects due to chemical aging. Some illustrative examples show the general behaviour of the model and motivate a series of experiments allowing for the required parameter identification.     

Molecularly imprinted “bulk” copolymers as selective sorbents for gallic acid

We report the synthesis of molecularly imprinted sorbents, selective for gallic acid. The particles were prepared by using acrylic acid, acrylonitrile, and hydroxyethyl methacrylate as functional monomers, whereas ethyleneglycol dimethacrylate and 1,4‐buthanediol dimethacrylate were used as crosslinkers. Preparation and manipulation protocols were adjusted considering template's nature. To highlight the influence of monomer/crosslinker nature upon imprinted particles, the adsorption capacity, the imprinting factor, and the distribution and selectivity coefficients were calculated. An imprinting factor of 3.53 and a selectivity coefficient of 6.86 were found for hydroxyethyl methacrylate/ethylene glycol methacrylate system. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci. 2013     

A Selection of Alkali and Alkaline Earth Metal Salts of 5,5′‐Bis(1‐hydroxytetrazole) in Pyrotechnic Compositions

The dilithium ( 1 ), disodium ( 2 ), dipotassium ( 3 ) and dicesium ( 4 ) salt as well as the calcium ( 5 ), strontium ( 6 ) and barium ( 7 ) salt of 5,5′‐bis(1‐hydroxytetrazole) were prepared and characterized including NMR‐, IR‐ and Raman spectroscopy, mass spectrometry, elemental analysis and differential scanning calorimetry. The crystal structures of 1 , 2 and 4 – 6 were additionally determined by single‐crystal X‐ray diffraction. The sensitivities of the salts towards impact, friction and electrostatic discharge were determined by means of BAM (Bundesanstalt für Materialforschung‐ und prüfung) methods. The potential use of 1 , 6 and 7 as coloring agents in pyrotechnical mixtures as well as the utilization of 3 and 4 as additives in near infrared (NIR) emitting pyrotechnical formulations was examined.     

Multi‐dimensional modeling of solar cells with electromagnetic and carrier transport calculations

We present a multi‐dimensional model for comprehensive simulations of solar cells (SCs), considering both electromagnetic and electronic properties. Typical homojunction and heterojunction gallium arsenide SCs were simulated in different spatial dimensions. When considering one‐dimensional problems, the model performs carrier transport calculations following a Beer–Lambert optical absorption approximation. We show that the results of such simulations exhibit excellent agreement with the standard PC1D one‐dimensional photovoltaic simulation. Photonic and plasmonic attempts to enhance SC efficiency demand comprehensive electromagnetic calculations to be undertaken in order to acquire accurate carrier generation profiles in two and three‐dimensional systems. Our model provides complete spectral and spatial information of typical optical and electronic behavior. Furthermore, our approach permits the detailed investigation of complex systems, including plasmonic SCs, which cannot be simulated using low‐dimensional modeling tools. We present the results of numerical simulations of an optically thin plasmonic gallium arsenide SC and observe improved device performance arising from the application of plasmonic nanostructures, which agree well with previous experimental findings. Copyright © 2012 John Wiley & Sons, Ltd.     

Trifluoromethylation of 1‐Aryl‐3,3‐diisopropyltriazenes

A new method for the trifluoromethylation of functionalized aromatic diisopropyltriazenes is described. In a facile two‐step, one‐pot synthesis, various functionalized trifluoromethyl‐substituted arenes are accessible in mostly good yields by using methyl iodide as iodination agent and the trifluoromethylation system (trifluoromethyl)trimethylsilane/potassium fluoride/copper iodide. This concept could be expanded to perfluoroethylation as well as ethoxycarbonyldifluoromethylation reactions.