Synthesis of Controlled Spherical Zinc Sulfide Particles by Precipitation from Homogeneous Solutions

Zinc sulfide (ZnS) powders have been obtained by precipitation from homogeneous solutions of various zinc salt compounds, with S^2- as precipitating anion, formed by decomposition of thioacetamide. Spherical particles with a very narrow size distribution can be obtained by controlling the synthesis parameters. The particle sizes are influenced by the nature of the associated anion. For example, nanometer-sized ZnS particles are formed using acetate or acetylacetonate anions under acidic pH conditions, controlled by the addition of acetic acid. Although the nucleation is accelerated by the use of acetic acid, limited particle growth occurs because of the formation of complexes with zinc cations that lowers the concentration of free cations in the solution. Also, the complexing-attachment phenomena of the ZnS particles with acetate and acetylacetonate anions lead to the arrest of particle growth processes. The presence of complexed Zn²⁺ species in the acidic solution is demonstrated both theoretically, using a model based on the calculations of the solubility isotherms of the soluble species, and by Fourier-transform infrared techniques. The nanostructured ZnS particles may provide a suitable semiconductor nanocluster material for optoelectronic applications as well as a phosphor suitable for application in flat-panel display technology.     

Charakterisierung von Rohmaterialien für die Eisenerzherstellung mit Bildverarbeitung

The automatic image processing software VisuMet was developed during the projects KnetMet and K1-Met (2008–2012). VisuMet evaluates the quality of lump iron ore and fine iron ore. During the K1-Met (2012–2015), the programme will be further developed for pellets and sinter. The reduction degree is calculated with image processing and linear regression for semi- and reduced material of standard reduction tests. For the evaluation of pellets, the concentric phase front movement algorithms has to be adapted in order get a context between porosity and glass phase. These parameters are essential.     

Electrochemical Impedance Spectroscopy of Transparent Polycrystalline Magnesium Aluminate (MgAl2O4) Spinel

Transparent polycrystalline magnesium aluminate spinel is one of few materials capable of fulfilling certain demanding optical applications. However, LiF additive typically required to enhance sintering and impart transparency also degrades mechanical properties and causes scatter, precluding wider application. To shed light on the cause of altered properties, electrochemical impedance spectroscopy was performed between 500°C and 900°C, in oxidizing and reducing atmosphere, on fully dense, polycrystalline spinel compacts hot‐pressed with and without LiF. In combination with electron microscopy, chemical analysis, and secondary‐ion mass spectroscopy, bulk and grain‐boundary dielectric behavior were related to microstructure and chemistry. Decades higher conductivity than for comparable single crystals correlated with Al₂O₃‐rich stoichiometry, impurities, and small grain size, and suggested increased conduction and current‐line detouring along Mg‐depleted, impurity‐rich, field‐parallel grain boundaries. LiF addition reduced conductivity by one decade and increased the activation energy for conductivity, attributed to impurity removal, larger grain size, and point defects caused by lithium incorporation.     

First‐principles based group additivity values for thermochemical properties of substituted aromatic compounds

A set of 7 Benson group additive values (GAV) together with 15 correction terms for non‐nearest neighbor interactions (NNI) is developed to calculate the gas phase standard enthalpies of formation, entropies and heat capacities of monocyclic aromatic compounds containing methyl, ethyl, vinyl, formyl, hydroxyl, and methoxy substituents. These GAVs are obtained through least squares regression of a database of thermodynamic properties of 143 molecules, calculated at the post‐Hartree–Fock G4 composite method. Out of the 15 NNIs, which account for several well‐known substituent effects in aromatic molecules, 13 have been determined for the first time. All but two group additively calculated standard enthalpies of formation agree within 4 kJ mol^?1. The entropies and the heat capacities generally deviate less than 4 J mol^?1 K^?1 from the ab initio results. Natural bond orbital analysis is utilized to identify the underlying causes of the observed NNIs. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3858–3870, 2015     

Exploring the role of stearic acid in modified zinc aluminum layered double hydroxides and their acrylonitrile butadiene rubber nanocomposites

The proposed study attempted to explore the role of stearic acid modification on the properties of zinc‐aluminum based layered double hydroxides (LDH) and their composites with acrylonitrile butadiene rubber (NBR). Three distinctive LDH systems were adapted for such comparison; an unmodified LDH and two stearic acid modified LDH. The use of zinc oxide and stearic acid in the rubber formulation was avoided as the modified LDH would be able to deliver the necessary activators for the vulcanization process. Emphasis was predominantly given to reconnoiter the merits of stearic acid modification on the increase in interlayer distance of the LDH. X‐ray diffraction studies and transmission electron microscope morphological investigations of LDH powders indicated that modification with stearic acid increased the interlayer spacing which would favor the intercalation of NBR polymer chains into the layered space. However, stress–strain studies indicated better mechanical properties for composites with unmodified LDH. Composites with LDH showed higher crosslinking densities than conventionally sulfur cured control compounds using zinc oxide/stearic acid as activators. This was evident from equilibrium swelling method as well as statistical theory of rubber elasticity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41539.     

Towards Quantifying Interfacial Adhesion in the Ternary Blends with Matrix/Shell/Core-Type Morphology

We quantified interfacial adhesion in ternary blends with matrix/shell/core microstructure based on mechanical properties assessments. Various HDPE-based ternary blends containing PA-6/EVOH core/shell droplets were prepared by changing composition and processing temperature. The theoretical predictions of tensile properties were compared with experimental data; thereby considerable shift in experimental modulus from lower to upper limit observed over a 10°C increase in melting temperature. This confirmed the impact of blending temperature on matching the predicted values with experimental data. The meaningful trend observed in tensile characteristics of ternary blends simply gives an understanding of interfacial adhesion degree in ternary blend showing matrix/shell/core microstructure.