Structural and luminescence properties of RE (RE = Eu, Tb):(MgCa)2Bi4Ti5O20 ceramics

Rare-earth ions (Eu³⁺, Tb³⁺) activated magnesium calcium bismuth titanate [(MgCa)₂Bi₄Ti₅O₂₀] ceramics were prepared by conventional solid state reaction method for their structural and luminescence properties. By using XRD patterns, the structural properties of ceramic powders have been analyzed. Emission spectrum of Eu³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ_exci = 393 nm and Tb³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown green emission at 542 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 376 nm. In addition, from the measurements of scanning electron microscopy (SEM), Fourier transform-infrared (FTIR) and energy dispersive X-ray analysis (EDAX) results the morphology, structure and elemental analysis of these powder ceramics have been studied.     

英国国家电网公司在电力系统状态估计器及安全分析方面的经验

本文叙述了由安装在英国国家电网公司新国调中心的新型能量管理系统所提供的实时网络分析的应用，并介绍了第一年的运行经验．对经常出现的某些状态估计问题的解决方法和作者所作的尝试的结论进行了讨论，以对安全估计器的结果与现有的离线研究方法的结果进行比较．文章还对应用实时网络分析时遇到的一些原始缺陷的观察结果和在短时段及较长时段内解决这些问题的方法进行了讨论．     

Poly(dimethylsiloxane-urethane) membranes: effect of linear siloxane chain and caged silsesquioxane on gas transport properties

The effect of poly(dimethylsiloxane) (PDMS) or polypropylene glycol (PPG) linear chain and polyoctahedral oligosilsesquioxanes (POSS) cubic nanoparticles on surface and gas transport properties of poly(dimethylsiloxane-urethane) PDMS-PU or poly(propylene glycol-urethane) (PPG-PU) hybrid membranes were studied. PDMS-PU or PPG-PU hybrid membranes were prepared using PDMS-diol or PPG-diol as a chain extender and diisocyanate with POSS-amine macromonomer as a crosslinker. The macromer synthesized was characterized using FT-IR, ¹H-, ¹³C- and ²⁹Si-NMR spectroscopic methods. The hybrid membranes were characterized by CP-MAS ²⁹Si-NMR, DSC, contact angle, WAXD, AFM and density measurements. The glass transition temperature (Tg) of the hybrid membranes were determined by differential scanning calorimetry (DSC) and were found to be in the range of 176–189°C. The surface free energy was reduced by increasing the POSS-amine crosslinker content of the membranes. The AFM measurement showed phase separation of POSS-amine molecule and PDMS with the urethane matrix on the surfaces. The XRD profiles confirm that the membranes were highly amorphous in nature. The decrease in permeability was observed by increasing the concentration of POSS-amine incorporated hybrid membranes. The selectivities of O₂/N₂ and CO₂/N₂ gas pairs increased with an increase in the POSS concentration. This suggests that the selectivities were dependent mainly on the presence of urethane and ester functional groups in the crosslinker.     

Precursor gas chemistry determines the crystallinity of carbon nanotubes synthesized at low temperature

Despite significant progress in carbon nanotube (CNT) synthesis by thermal chemical vapor deposition (CVD), the factors determining the structure of the resulting carbon filaments and other graphitic nanocarbons are not well understood. Here, we demonstrate that gas chemistry influences the crystal structure of carbon filaments grown at low temperatures (500 °C). Using thermal CVD, we decoupled the thermal treatment of the gaseous precursors (C₂H₄/H₂/Ar) and the substrate-supported catalyst. Varying the preheating temperature of the feedstock gas, we observed a striking transition between amorphous carbon nanofibers (CNFs) and crystalline CNTs. These results were confirmed using both a hot-wall CVD system and a cold-wall CVD reactor. Analysis of the exhaust gases (by ex situ gas chromatography) showed increasing concentrations of specific volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) that correlated with the structural transition observed (characterized using high-resolution transmission electron microscopy). This suggests that the crystallinity of carbon filaments may be controlled by the presence of specific gas phase precursor molecules (e.g., VOCs and PAHs). Thus, direct delivery of these molecules in the CVD process may enable selective CNF or CNT formation at low substrate temperatures. The inherent scalability of this approach could impact many promising applications, especially in the electronics industry.     

Synthesis and electrocatalytic oxygen reduction activity of graphene-supported Pt3Co and Pt3Cr alloy nanoparticles

Graphene-supported Pt and Pt₃M (M = Co and Cr) alloy nanoparticles are prepared by ethylene glycol reduction method and characterized with X-ray diffraction and transmission electron microscopy. X-ray diffraction depicted the face-centered cubic structure of Pt in the prepared materials. Electron microscopic images show the high dispersion of metallic nanoparticles on graphene sheets. Electrocatalytic activity and stability of the materials is investigated by rotating-disk electrode voltammetry. Oxygen reduction activity of the Pt₃M/graphene is found to be 3–4 times higher than that of Pt/graphene. In addition, Pt₃M/graphene electrodes exhibited overpotential 45–70 mV lower than that of Pt/graphene. The high catalytic performance of Pt₃M alloys is ascribed to the inhibition of formation of (hydr) oxy species on Pt surface by the alloying elements. The fuel cell performance of the catalysts is tested at 353 K and 1 atm. Maximum power densities of 790, 875, and 985 mW/cm² are observed with graphene-supported Pt, Pt₃Co, and Pt₃Cr cathodes, respectively. The enhanced electrocatalytic performance of the Pt₃M/graphene (M = Co and Cr) compared to that of Pt/graphene makes them a viable alternative to the extant cathodes for energy conversion device applications.     

Anodic dissolution of U, Zr and U–Zr alloy and convolution voltammetry of Zr|Zr couple in molten LiCl–KCl eutectic

The anodic dissolution of U and Zr metal was studied in LiCl–KCl–UCl₃ and LiCl–KCl–ZrCl₄, respectively, at 773 K by cyclic voltammetry and compared with their respective dissolution behaviour in blank LiCl–KCl eutectic. The anodic dissolution of U–Zr alloy in LiCl–KCl–UCl₃ was also studied at 773 K to compare with the dissolution of U and Zr. The transfer coefficients evaluated by Tafel analysis and the method of Allen–Hickling for U and Zr dissolution were found to be in fair agreement with each other. U dissolution in LiCl–KCl–UCl₃ and Zr dissolution LiCl–KCl–ZrCl₄ were also studied by chronoamperometry and the diffusion coefficient value of U³⁺ was calculated to be in the range of 2.9 × 10⁻⁵ to 3.3 × 10⁻⁵ cm² s⁻¹ which is in agreement with those reported in literature. Convolution voltammetric analysis of Zr⁴⁺/Zr²⁺ redox couple in LiCl–KCl–ZrCl₄ was carried out for the first time to have a comprehensive understanding of the electrode kinetics.     

Design of Efficient Ce<Subscript>x</Subscript>M<Subscript>1−x</Subscript>O<Subscript>2−δ</Subscript> (M = Zr,Hf, Tb and Pr) Nanosized Model Solid Solutions for CO Oxidation

Abstract  

Nanosized Ce_xM_1−xO_2−δ (M = Zr, Hf, Tb and Pr) solid solutions were prepared by a modified coprecipitation method and thermally treated at different temperatures from 773 to 1073 K in order to ascertain the thermal behavior. The structural and textural properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), BET surface area, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) techniques. The catalytic efficiency has been performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. The characterization results indicated that the obtained solid solutions exhibit defective cubic fluorite structure. The solid solutions of ceria–hafnia, ceria–terbia and ceria–praseodymium exhibited good thermal stability up to 1073 K. A new Ce_0.6Zr_0.4O₂ phase along with Ce_0.75Zr_0.25O₂ was observed in the case of ceria–zirconia solid solution due to more Zr⁴⁺ incorporation in the ceria lattice at higher calcination temperatures. The reducibility of ceria has been increased upon doping with Zr⁴⁺, Hf⁴⁺, Tb^3+/4+ and Pr^3+/4+ cations. This enhancement is more in case of Hf⁴⁺ doped ceria. Among various solid solutions investigated, the ceria–hafnia combination exhibited better OSC and CO oxidation activity. The high efficiency of Ce–Hf solid solution was correlated with its superior bulk oxygen mobility and other physicochemical characteristics.     

Miscibility studies of sodium carboxymethylcellulose/poly(vinyl alcohol) blend membranes for pervaporation dehydration of isopropyl alcohol

Miscibility studies of sodium carboxymethylcellulose/poly(vinyl alcohol) (NaCMC/PVA) blends of different compositions (100/0, 80 : 20, 60 : 40, 50 : 50, 40 : 60, 20 : 80, and 0 : 100) were investigated using viscometric method. NaCMC, PVA, and their blend membranes were prepared by solution‐casting technique and were then crosslinked with glutaraldehyde (GA). The effect of blend composition on mechanical, swelling, and pervaporation results (flux and selectivity) was also investigated in this study. Attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR) results showed that the blends are miscible over the entire studied composition range and further confirmed the crosslinking reaction with GA. FTIR studies reveal that the blends containing 50 : 50 (NaCMC/PVA) are an optimum miscible blend. Thermogravimetric analysis confirms that the thermal stability increased with increase in NaCMC content in NaCMC/PVA blend membrane. XRD and DSC showed a corresponding decrease in crystallinity and increase in melting point with increase in NACMC content, respectively. NaCMC/PVA blends of all the composition under study were used for dehydration of isopropyl alcohol at different compositions of IPA/water mixture (90 : 10, 87.5 : 12.5, 85 : 15, and 82.5 : 17.5) at 35°C. Swelling studies and PV results reveal that increase in NaCMC content in the blend leads to an increase in flux of water, whereas selectivity decreases. The optimum flux and selectivity were observed for the blend containing 50 : 50 NaCMC/PVA content at a feed ratio of 87.5 : 12.5 IPA/water. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of pro‐oxidants on biodegradation of polyethylene (LDPE) by indigenous fungal isolate,Aspergillus oryzae

Proxidant additives represent a promising solution to the problem of the environment contamination with polyethylene film litter. Pro‐oxidants accelerate photo‐ and thermo‐oxidation and consequent polymer chain cleavage rendering the product apparently more susceptible to biodegradation. In the present study, fungal strain, Aspergillus oryzae isolated from HDPE film (buried in soil for 3 months) utilized abiotically treated polyethylene (LDPE) as a sole carbon source and degraded it. Treatment with pro‐oxidant, manganese stearate followed by UV irradiation and incubation with A. oryzae resulted in maximum decrease in percentage of elongation and tensile strength by 62 and 51%, respectively, compared with other pro‐oxidant treated LDPE films which showed 45% (titanium stearate), 40% (iron stearate), and 39% (cobalt stearate) decrease in tensile strength. Fourier transform infrared (FTIR) analysis of proxidant treated LDPE films revealed generation of more number of carbonyl and carboxylic groups (1630–1840 cm⁻¹ and 1220–1340 cm⁻¹) compared with UV treated film. When these films were incubated with A. oryzae for 3 months complete degradation of carbonyl and carboxylic groups was achieved. Scanning electron microscopy of untreated and treated LDPE films also revealed that polymer has undergone degradation after abiotic and biotic treatments. This concludes proxidant treatment before UV irradiation accelerated photo‐oxidation of LDPE, caused functional groups to be generated in the polyethylene film and this resulted in biodegradation due to the consumption of carbonyl and carboxylic groups by A. oryzae which was evident by reduction in carbonyl peaks. Among the pro‐oxidants, manganese stearate treatment caused maximum degradation of polyethylene. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Hydrophilic antioxidants of virgin olive oil. Part 2: Biosynthesis and biotransformation of phenolic compounds in virgin olive oil as affected by agronomic and processing factors

The biosynthesis of the phenolic fraction of olive fruits during ripening and the transformations occurring in this moiety during virgin olive oil (VOO) extraction are discussed in this paper. The influence of agronomical factors that can significantly affect the phenolic profile of VOO is also discussed. Particularly, it is worth emphasizing the role of genetic factors, cultivation and climatic conditions such as water availability, atmospheric temperature, altitude, health status of the fruits, alternate bearing in the olive, and some processing factors such as crushing, malaxation time and temperature or volume of water added during milling. Among these parameters, special attention has been paid to genetic factors due to the high variability observed among Olea europaea genotypes for all recorded traits. In this context, interesting experimental results have been obtained with cultivated and wild olive trees, and also with segregating populations resulting from olive breeding programs. To the authors' knowledge, reviews evaluating the influence of the main factors that contribute to the profile of hydrophilic phenols have not been previously published. The discussion concerning olive breeding programs is a major and novel aspect to be emphasized considering recent trends to obtain new olive cultivars that confer better organoleptic properties and better quality to VOO.