Mechanochemical synthesis of YNbO4:Eu nanocrystalline powder and its structural,microstructural and photoluminescence properties

In this research we prepared nanocrystalline YNbO₄:Eu³⁺ phosphor, i.e. nanophosphor, powder using an efficient mechanochemical method followed by annealing. X-ray diffraction analysis revealed that YNbO₄:Eu³⁺ crystallizes in monoclinic structure C2/c where, from the point of view of A and B in ABO₄ compounds, cation coordination can be noted as [6+2, 4+2]. Crystallite size of about 40 nm, was estimated using Debye Scherrer's equation. Raman spectroscopy with 785 and 532 nm excitation wavelengths is performed to record a majority of materials phonon modes and to provide more in depth understanding of the YNbO₄ structure. Scanning electron microscopy observations indicate that the mechanical treatment during synthesis is causing non-uniformity of the powder microstructure. High resolution photoluminescent measurements upon UV excitation showed intense emission coming from f–f transitions of the europium ion with the lifetime of 0.68 ms, suggesting that the obtained YNbO₄:Eu³⁺ is a good potential phosphor. A comparison of emissive properties with microcrystalline YNbO₄:Eu³⁺ was made and it showed higher values of emission intensity and lifetime of the nanocrystalline sample.     

Thermoplastic polyurethane elastomers from modified oleic acid

Two novel potentially biodegradable thermoplastic polyurethane elastomers with unique structure and morphology were prepared from modified oleic acid. The hardness and mechanical properties were controlled by adjusting the soft segment concentration (SSC). Epoxidized methyl oleate was converted to methyl‐9‐ or ?10‐hydroxystearate (hydroxystearate) by catalytic hydrogenation. The formed hydroxystearate was transesterified with 1,6‐hexanediol to obtain polyesterpolyol with molar mass 2500. Segmented polyurethanes with 50% and 70% SSC were prepared using the prepolymer method by reacting polyesterpolyol with diphenylmethane diisocyanate and 1,4‐butanediol as chain extender. Thermal and mechanical properties of the polymers indicated good micro‐phase separation. Both soft and hard segments displayed a certain degree of crystallization. Tensile strengths were 18 and 2.4 MPa for samples with 50% and 70% SSC, respectively. Elongations of 130% (50% SSC) and 43% (70% SSC) were somewhat lower than in comparable materials, presumably due to lower molar mass. © 2014 Society of Chemical Industry     

Modelling of V–Hz and vector controlled ASDs in PSCAD/EMTDC for voltage sag studies

This paper deals with modelling and performance of adjustable speed drives (ASDs) subjected to voltage disturbances in electric supply. The aim of this study was to develop appropriate models of typical ASD and investigate their sensitivity to voltage disturbances under various practical modes of operation and control. Accordingly, scalar controlled open and closed loop volts–hertz (V–Hz) and vector controlled closed loop ASDs are modelled in PSCAD/EMTDC environment, and their performance in the presence of voltage disturbances is investigated under typical operating and loading conditions.     

Numerical model of gaseous fuel jet injection into a fluidized furnace

The paper presents a fluid-porous medium model, developed for stationary 2D predictions of fluidized bed. Dense phase is considered a fixed porous medium, while gas–particle interactions and bubbling phase are modeled regarding balance of friction forces between gas and particles. Like referent measurements, predictions of lateral jet injection into the bed suggest the jet penetration length is strongly affected by fluid velocity at the nozzle outlet, while influences of the nozzle vertical position and inclination angle are not significant. Also, the fluid velocity and the nozzle vertical position exert pronounced effects on mixing rate of components (fuel and oxidizer).     

Optimized preparation of alumina based fillers for tuning composite properties

Alumina based particles were prepared from aluminium chloride hydroxide as starting material by sol-gel technique. One series of particles was doped with ferrous oxide. Both series of particles were calcinated at three different temperatures: 700?°C, 800?°C and 900?°C. Poly(methyl methacrylate), PMMA, was used as a matrix and two different types of alumina based particles were added into the matrix to form the composites. All composites consisted of 3?wt% of alumina based particles. The aim of this study was to examine whether and how the temperature of particle calcination affects the microhardness and mechanical properties of the composite. The particles were characterized by the X-ray diffraction (XRD) and physical absorption methods. The morphology of the composites was examined using a field emission scanning electron microscope (FESEM). The microhardness of composites was measured using a traditional Vickers hardness (HV) method. The mechanical characteristics of obtained composites were determined using tensile test and impact testing.     

Modeling of dibenzothiophene oxidative desulfurization using response surface methodology

The effect of reaction temperature, mixing speed and oxidant to catalyst volume ratio, including their interactions on the oxidative desulfurization of dibenzothiophene by using response surface methodology was studied. Hydrogen peroxide was used as oxidant and acetic acid as catalyst. The obtained model accurately predicts conversion of dibenzothiophene and the best conversion of 98.7% was observed at temperature 70°C, mixing speed of 1250 rpm and oxidant to catalyst volume ratio of 1:1. At high temperatures, a major limitation of the desulfurization process is the mass transfer and the high mixing speed is needed to achieve an efficient process.     

Poly[(N‐isopropylacrylamide)‐co‐(itaconic acid)] hydrogels with poly(ethylene glycol)

The aim of the work reported here was to investigate temperature‐ and pH‐sensitive hydrogels of N‐isopropylacrylamide (NIPAM) and itaconic acid (IA) and their semi‐interpenetrating polymer networks (semi‐IPNs) with varying contents of poly(ethylene glycol) (PEG). The stimuli responsiveness, swelling behaviour and mechanical properties of the hydrogels and semi‐IPNs were studied in order to investigate the effect of various amounts of PEG. Pulsed‐gradient spin‐echo NMR experiments were carried out to investigate the diffusion process. The pH sensitivity increased with an increasing amount of PEG in the semi‐IPNs, while the overall rate of water uptake was diffusion‐controlled (n < 0.5). For certain PEG contents (5 and 10 wt%), the semi‐IPNs exhibited better mechanical properties than the poly(NIPAM‐co‐IA) copolymer. The calculated values of the self‐diffusion coefficients of water indicated facilitated diffusion of water through the system with increased amounts of PEG, while the self‐diffusion coefficients of a model compound, metoprolol tartrate, showed no significant dependence on the amount of PEG. According to the results obtained and compared to results reported in the literature, the investigated semi‐IPNs may have potential applications in the controlled release of macromolecular active agents such as proteins and peptides. Copyright © 2009 Society of Chemical Industry     

Mechanochemistry of copper sulphides: phase interchanges during milling

Covellite, CuS and chalcocite, Cu₂S nanoparticles prepared in the explosive manner from elemental precursors were further ball-milled in order to observe additional changes caused by mechanical action. Three phases of chalcocite were interchanging during milling, monoclinic one being major at the equilibrium after 30 min. In the case of covellite synthesis, milling for 15 min brought about a significant diminishment in the content of digenite, Cu_1.8S, impurity. Covellite powder exhibited finer character than chalcocite, as documented by crystallite size, grain size and specific surface area analysis. Finally, the effect of milling speed on the explosive character of the reaction and phase composition of chalcocite was investigated. The most drastic conditions favored the formation of the monoclinic phase with the lowest symmetry and the time and intensity of the explosion was found to depend on the milling speed. The whole process is mechanically driven.     

Suitability of some selected maize hybrids from Serbia for the production of bioethanol and dried distillers' grains with solubles

BACKGROUND: Bioethanol is mostly produced from starchy parts of the corn grain kernel leaving significant amounts of valuable by‐products such as dried distillers' grains with solubles (DDGS) which can be used as a substitute for traditional feedstuff. The suitability of six maize hybrids from Serbia was investigated for bioethanol and DDGS production. The correlation between physical and chemical characteristics of the grain, bioethanol yield and quality of the corresponding DDGS was assessed. RESULTS: All hybrids had very different chemical composition and physical characteristics which could allow various applications. The highest bioethanol yield (94.5% of theoretical) and volumetric productivity (2.01 g l^?1 h^?1) were obtained with hybrid ZP 434 and the lowest with ZP 611k. Regarding chemical composition, all DDGS samples manifested good properties as feed components. Their protein content was higher compared to the kernel. In addition, the samples showed high digestibility and high mineral content, especially of calcium and phosphorus. CONCLUSION: A hybrid ZP 434 was selected as the most promising bioethanol producer. This property is attributed to the highest level of soft endosperm which is more susceptible to starch‐hydrolysing enzymes. A high yield potential per hectare makes it the best candidate for commercial bioethanol production. © 2012 Society of Chemical Industry