An investigation of structure and electrical characteristics of lanthanum strontium manganite nanopowders with different Sr2+ ion concentrations

Generally, the efficiency of solid oxide fuel cells is heavily dependent on the electrocatalytic activity of the cathode toward the oxygen reduction reaction. In order to achieve a better cathode performance, La_xSr_1-xMnO₃ (LSM) nanopowders with different Sr²⁺ ion contents varying from 0.2 to 0.8 have been synthesized using the coprecipitation method. The obtained nanoparticles were characterized by x-ray diffraction, field emission scanning electron microscopy, and electrochemical impedance spectroscopy. It was found that the LSM nanoparticles seemed to exhibit high polarization resistance with the increase of the Sr²⁺ ion molar ratios. The crystallite size was found to increase from 16.4 to 24.3 nm with increasing Sr²⁺ content from 0.2 to 0.8. The lattice parameters were decreased with Sr²⁺ ion content which may be caused by an increase in internal stress with the increasing grain size of LSM. Meanwhile, the real part impedance (Z′) was increased from 10 (Ω) at 0.2 Sr²⁺ to 24 (Ω) at 0.8 Sr²⁺ ion ratio. Alternatively, |Z| of prepared sample was increased from 12 to 26 (Ω) by increasing Sr²⁺ ion molar ratios from 0.2 to 0.8.     

Influence of indium addition on structure, mechanical, thermal and electrical properties of tin–antimony based metallic alloys quenched from melt

The melt-spinning processes of binary Sn–10 wt.% Sb and ternary Sn–10 wt.% Sb–In were analyzed using X-ray diffractometer and differential thermal analysis (DTA). The results showed that supersaturated solid solution and new intermetallic compound In₃Sn were produced during melt-spinning technique not found under equilibrium conditions. It is also found that a small amount of In addition significantly lowers the melting point of the Sn–10 wt.% Sb alloy and reduce the crystal size to ≈60 nm. Also, tin–antimony solder doped with In exhibits good mechanical properties, Vickers hardness and mechanical strength due to refined microstructure. This work was performed to study the influence of rapid solidification and indium addition on structure and properties of tin–antimony based alloys.     

Graft copolymerization of itaconic acid onto chitin and its properties

Modification of chitin by grafting with itaconic acid (IA) was carried out using potassium persulfate as redox initiator. In complimentary experiments, grafting was performed using γ‐radiation. Grafting was confirmed by FTIR spectroscopy. The effect of monomer concentration, initiator concentration and copolymerization temperature on the percentage of grafting were studied. The effect of radiation dose was also investigated. Values for percentages of grafting of up to 300 % were reached. It was observed that the percentage of grafting increased with increasing monomer concentration and showed a tendency to level off at IA concentration of 0.1 mol l^?1. The percentage of grafting increased with temperature up to 60 °C and then decreased. The solubility of the grafted chitin was studied in organic and inorganic solvents. The complexation of the grafted chitin with some cations, namely copper, nickel, cobalt, zinc and lead, was also investigated. The metal uptake was measured by UV spectroscopy. Thermogravimetric analysis of the grafted chitin was also studied. Copyright © 2004 Society of Chemical Industry     

Study of Vinyl Acetate Partitioning in Emulsion Copolymerization of Vinyl Chloride-Vinyl Acetate by FTIR and HNMR Spectroscopy

Emulsion copolymerization of vinyl chloride with vinyl acetate comonomer was performed. Potassium persulfate, a mixture of stearyl alcohol and sodium lauryl sulfate, was used and reactions were performed at 55 °C in a pressurized reactor. By sampling during the reaction in different intervals copolymer composition was investigated using FTIR and NMR spectroscopy. The results showed that the partitioning of vinyl acetate in the copolymerization in general follows the Mayo-Lewis copolymerization equation with some discrepancy. This was attributed to the gaseous nature of vinyl chloride monomer and the differences between polymerization in heterogeneous and homogeneous systems. Both FTIR and NMR spectroscopy showed two peaks in vinyl acetate content of copolymer beyond 65% conversion which was attributed to the elimination of vinyl chloride droplets in the media and replacing them with vinyl acetate monomer. The first increase is related to the consumption of vinyl chloride droplets and the second is related to the consumption of gaseous vinyl chloride; in both instances vinyl acetate governs the polymerization.     

Laboratory Evaluation of the Use of Alkaline Phosphate Wastes for the Control of Acidic Mine Drainage

Pyrrhotite tailings at the abandoned Kettara mine site in Morocco are producing acid mine drainage (AMD). We investigated the use of alkaline phosphate waste (APW) rock from a nearby operating open-pit phosphate mine to control the AMD. The neutralizing potential of the APW, using the Paktunc method, was estimated between 500 and 680 kg CaCO₃/t. In laboratory column tests, the addition of 15 wt% APW to the coarse Kettara tailings produced leachates with significantly lower acidities and metal concentrations than unamended controls. The high calcium concentration in the flushed solutions indicates that calcite was responsible for the neutralization. Dolomite dissolution seems to be negligible and fluorapatite was stable under the testing conditions. It was also observed that when the treated solution comes in contact with unweathered Kettara coarse tailings, the pH becomes acidic, although the metal concentrations remain low.     

Evaluation of dike-type causeway impacts on the flow and salinity regimes in Urmia Lake,Iran

Urmia Lake, located in a closed basin in north-west Iran, is the largest lake (5000–6000 km²) in the Middle East. It is very saline with total dissolved salts reaching 200 g/l compared with a normal seawater salinity of about 35 g/l. The construction of a causeway, which was initiated in 1979 but then abandoned until the early 2000s, is near completion and will provide road access between the western and eastern provinces. The causeway has an opening 1.25 km long and divides Urmia Lake into a northern and southern basin and restricts water exchange. The flow and salinity regimes are affected by the presence of this new causeway, and there are concerns over the well being of the Artemia population. This study investigates the effects of the construction of the causeway on flow and salinity regimes, considers remedial actions, and examines the effects of climatic variability on salinity and flow. Flow and salinity regimes were numerically simulated by using a commercially available two and three-dimensional (2D and 3D) MIKE model. The validity of the numerical model was assessed through sensitivity analysis of the model and comparing the simulated results against field measurements; the 3D model provided the higher correlation between simulated and actual data. Wind input was the main climatic and hydrologic factor influencing flow regime while river discharge, evaporation and rainfall were the key parameters affecting salinity distribution in the lake models. The 3D model was subsequently used to predict lake conditions in typical dry, wet and normal climates, to examine the environmental impacts from the new causeway, and to evaluate possible improvements that some remedial measures may provide.     

A Nano-Hybrid of Molybdenum Oxide Intercalated by Dithiocarbamate as an Oxidation Catalyst

A novel nano-layered material based on molybdenum oxide has been synthesized by hydrothermal method using dithiocarbamate. On the basis of the X-ray diffraction, scanning electron microscopy, thermal analysis and infrared spectroscopy results, a possible arrangement of organic ligands in the interlayer space of molybdenum oxide has been proposed. Moreover, the catalytic activity of the synthesized nanohybrid of molybdenum oxide was investigated in oxygen transfer reactions. This reagent can oxidize alkenes, alcohols, sulfides, and amines in the presence of hydrogen peroxide with high yield and selectivity.     

The Chalan beel in Bangladesh: Habitat and biodiversity degradation,and implications for future management

This study provides an overview of the current resources and fisheries status of the Chalan beel, and identifies the scope of opportunities to evolve existing fisheries management strategies, focusing on fish biodiversity conservation. Chalan beel is the largest, most important watershed in the North Central Bangladesh, and covers an area of about 375 km² during the monsoon season. The watershed serves about 5 million people, predominantly through fisheries and agricultural activities. Although considerably degraded over time, Chalan beel still supports a diverse ichthyofauna of major importance to the local economy and people's livelihoods. The Chalan beel area incorporates 21 rivers and 93 smaller seasonal beels of varying size. Most of the rivers and beels are at risk of partial or total degradation, as a result of agricultural encroachment, siltation and other anthropogenic activities. During the study, ≈ 83% of the rivers, and 68% of the beels in the lean season, shrunk to 0–5% of their maximum (monsoon) water‐spread area during the dry season (i.e. critical levels for survival of many fish species). A fish catch survey was carried out in the main fishing season (July to December) over two successive years in the three most important catchment areas; namely, the Gumani, Baral and Katagang Rivers. A total of 72 sampling episodes yielded 9818 individuals, representing 114 fish species. The most abundant fish species during the 2‐year study period were punti (Puntius sophore and Puntius ticto), followed by chanda (Chanda nama and Parambassis ranga), chapila (Gudusia chapra) and tengra (Mystus vittatus). The study results indicate at least 19 fish species once considered abundant can now be classified as threatened, with a possibility of local extinction. The mean fish catch was 2.08 ± 0.49 kg, and 1.29 ± 0.32 kg per hour per person, by suti jal (set bag net – the most common gear used in the beel) in 2005 and 2006, respectively, with a significant (P < 0.05) variation among catches in months and years at all three sample sites. In 2005–2006, the annual fish production in Chalan beel was 12 217 tonnes, being less than half of the production observed in 1982. The stakeholders identified several major causes they thought were directly responsible for the continued decrease in fish production and biodiversity of the beel area. Several management strategies were suggested by the same stakeholders, and the findings are discussed in the context of overall developments in the Chalan beel fisheries related to habitat and biodiversity management.     

Dynamic study of free volume properties in polyethylene/styrene butadiene rubber blends by positron annihilation lifetime method

Positronium (Ps) formation in low and high‐density polyethylene (LDPE and HDPE) and styrene butadiene rubber (SBR), as well as in their blends (LDPE/SBR: 50/50 and HDPE/SBR: 50/50) has been investigated by positron annihilation lifetime (PAL) measurements as a function of low temperature (100–300 K). The glass transition temperature (T_g) for the initial polymers and their blends are determined by ortho‐positronium (o‐Ps) lifetime, τ₃ versus temperature as well as by differential scanning calorimetry (DSC) measurements. The temperature dependence of nanoscale free volume size shows similar trend for all the investigated samples indicating an abrupt change at T_g, which is found to be higher for SBR sample characterized by its high chain mobility. In addition, The T_g values deduced from PAL measurements are compared with the corresponding data deduced from DSC. The variation of o‐Ps formation probability I₃ versus temperature for polyethylene and their blends were interpreted in the frame work of spur reaction model of Ps formation. On the other hand, the lifetime coefficient below and above T_g is found to be one order of magnitude larger than the linear expansion coefficient. This constitutes evidence that Ps is only probing free volumes. The results obtained from change in free volume–hole distribution with temperature reflect both thermal expansion and increase in free volume–hole size with the rise in temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009