Investigations on chemical interactions between alternate cathodes and lanthanum gallate electrolyte for Intermediate Temperature Solid Oxide Fuel Cell (ITSOFC)

The doped perovskite oxides such as La_0.65Sr_0.30MnO_3-δ (LSM), La_0.70Sr_0.30CoO_3-δ (LSC), La_0.65Sr_0.30FeO_3-δ (LSF), La_0.65Sr_0.30NiO_3-δ (LSN) and La_0.60Sr_0.40Co_0.20Fe_0.80O_3-δ (LSCF) are proposed as alternate cathode materials for solid oxide fuel cells working at reduced temperature (< 1073 K). The critical requirement for their applicability is their chemical compatibility in conjunction with an alternate solid electrolyte, La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ (LSGM) without any new phase formation. To understand the chemical reactivity between these two components, thoroughly mixed different cathode and LSGM electrolyte (1:1 by wt.) powders were pressed as circular components and subjected to annealing at 1573 K for 3 h in air. XRD and SEM were used for the characterization of the annealed samples. XRD measurements revealed that no new secondary phases were formed in LSM, LSC, and LSF with LSGM mixtures whereas LSN and LSCF with LSGM resulted in the formation of new secondary phases after high temperature treatment. The sintering shrinkage for all the components (cathode + electrolyte mixture) was also estimated. For comparison of data, the individual powders (cathode/electrolyte) were also compacted and studied in the same manner. The obtained results are discussed keeping in view the requirements that the candidate cathode material must meet out with respect to its chemical compatibility to qualify for the LSGM based ITSOFC systems at 1073 K.     

Spectral,BVS, and Thermal Studies on Bisdithiocarbamates of Divalent Zn,Cd, and Their Adducts: Single Crystal X-Ray Structure Redetermination of (Diiodo) (Tetraethylthiuramdisulfide)mercury(II), [Hg(tetds)I2]

The current article describes the TG and DT analyses of divalent Zn, Cd, and Hg dithiocarbamato (dtc) complexes and their adducts (dchdtc = N,N-dicyclohexyldithiocarbamate anion, 4-mpzdtc = 4-methylpiperazinecarbodithioato anion, padtc = N,N′-(iminodiethylene)bisphthalimidedithiocarbamate anion, pipdtc = piperidinecarbodithioate anion, 1,10-phen = 1,10-phenanthroline, and 2,2′-bipy = 2,2′-bipyridine) along with the structural reinvestigation of [Hg(tetds)I ₂ ], where tetds = tetraethylthiuramdisulfide. In the case of Zn(II) and Cd(II) dithiocarbamates and their nitrogenous adducts, thermal decomposition of the nitrogenous bases is followed by the decay of dithiocarbamate leading to the formation of ZnS or CdS as residue. The interaction of iodine with [Hg(dedtc) ₂ ] in CHCl ₃ results in the oxidation of diethyldithiocarbamate leading to the formation of [Hg(tetds)I ₂ ], and the structure was redetermined because the earlier determination was by a Polaroid crystallographic technique with a higher R value. The S-Hg-I bond angles [105.09(3); 105.59(3); 109.26(3), and 100.99(3)°] indicate the near tetrahedral environment around the metal ion. ¹ H and ¹³ C NMR spectra of the complex were analyzed. Whether the product formed upon oxidation is a disulfide or an iodo-substituted product, in the present investigation, is clearly decided by the bulkiness of the substituent attached to the nitrogen. Interestingly, the steric influence is a deciding factor only in the case of mercury compounds and the dithiocarbamates involving Zn, Cd forms of the disulfide complexes.     

Molecular characterization and antioxidant assay of pigment producing bacteria,Sphingomonas paucimobilis and Microbacterium arborescens isolated from fresh water sediments

Abstract

This study focuses on isolation of pigment producing bacteria from fresh water sediment. The isolated bacteria were grown in nutrient broth and the maximum absorbance of 2.512 was obtained for the extracted pigment at 500 nm. The effective strains were optimized, pH 11 and temperature 30 °C was found to be more favorable for its maximum growth. The isolates were identified based on their molecular characterestics as Microbacterium arborescens and Sphingomonas paucimobilis, molecular size of the amplified 16S rRNA gene sequence was found to be approximately 1270 and 765 bp respectively. The antioxidant property of the pigment was analyzed using DPPH and ABTS assay. The IC₅₀ value of Microbacterium arborescens was higher in all the three assays in comparison with Sphingomonas paucimobilis. The extracted pigment was characterized for the presence of compounds using GC-MS and FTIR analysis to determine the functional groups. As the pigment obtained from M. arborescens had shown better antioxidant activity it may be used as colorant in food industrial applications.     

Characterization of Astaxanthin Nanoemulsions Produced by Intense Fluid Shear through a Self-Throttling Nanometer Range Annular Orifice Valve-Based High-Pressure Homogenizer

Stable, oil-in-water nanoemulsions containing astaxanthin (AsX) were produced by intense fluid shear forces resulting from pumping a coarse reagent emulsion through a self-throttling annular gap valve at 300 MPa. Compared to crude emulsions prepared by conventional homogenization, a size reduction of over two orders of magnitude was observed for AsX-encapsulated oil droplets following just one pass through the annular valve. In krill oil formulations, the mean hydrodynamic diameter of lipid particles was reduced to 60 nm after only two passes through the valve and reached a minimal size of 24 nm after eight passes. Repeated processing of samples through the valve progressively decreased lipid particle size, with an inflection in the rate of particle size reduction generally observed after 2–4 passes. Krill- and argan oil-based nanoemulsions were produced using an Ultra Shear Technology™ (UST™) approach and characterized in terms of their small particle size, low polydispersity, and stability.     

Studies on optical absorption and structural properties of Fe doped CdS quantum dots

Fe doped CdS quantum dots have been prepared using simple precursors by chemical precipitation technique. Fe doped CdS quantum dots have been synthesized by mixing cadmium nitrate, sodium sulfide and adding Fe under suitable conditions. X-ray diffraction analysis reveals that undoped and Fe doped CdS crystallizes in hexagonal structure. The lattice constants of Fe doped CdS nanoparticles decreased slightly with incorporation of Fe and no secondary phase was observed. The average grain size of the nanoparticles is found to lie in the range of 2.8–4.2 nm. HRTEM results show that undoped and 3.75% Fe doped CdS nanoparticles exhibit a uniform size distribution and average size of the nanoparticles is about 2–3 nm. Raman spectra show that 1LO and 2LO peaks of the Fe doped CdS samples are slightly red shifted compared with those of undoped CdS. Optical absorption spectra of Fe doped CdS nanoparticles exhibited red shift.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Oscillatory and asymptotic behavior of solutions of higher order damped nonlinear difference equations

The asymptotic and oscillatory behavior of solutions of mth order damped nonlinear difference equation of the form where m is even, is studied. Examples are included to illustrate the results.     

What does pressure decide to cook with orientationally disordered plastic phase of cubane: an orientational glass or crystal?

The effect of pressure on the structure and reorientational motion of molecules in orientationally disordered (OD) crystalline phase of cubane has been investigated in detail using variable shape molecular simulations in constant-pressure constant-temperature ensemble. Complete orientational ordering occurs at a pressure of 1.0 GPa and the OD phase transforms to an orientationally ordered phase at this pressure. The transition is associated with a kink in the variation of structural parameters such as cell parameters, unit-cell volume, and interaction energy. This transition is also associated with an anomaly in specific heat. Above this transition pressure, the structural quantities display only smaller changes with further increase in pressure. The structure of high-pressure orientationally ordered (HPOO) phase has been characterized using radial distribution functions and orientational distribution function. From detailed analysis of the structure of HPOO phase we conclude that it is isostructural with low-temperature orientationally ordered phase. The OD phase has four times larger compressibility than the HPOO phase.     

Sonochemical preparation of hollow nanospheres and hollow nanocrystals

Ceramic hollow spheres of MoS2 and MoO3 were obtained by sonochemical synthesis of MoS2 and MoO3 templated on silica nanoparticles (diameters 50-500 nm) followed by acid etching to remove the silica core. The resulting hollow materials have been characterized by elemental analysis, XPS, SEM, TEM, optical absorption, and hydrodesulfurization (HDS) studies. The TEM studies on the hollow ceramic materials indicate the formation of dispersed free spheres with a hollow core. The hollow materials obtained from thermally treated MoS2/SiO2 (450-700 degrees C) show the formation of layered MoS2 (lattice fringes approximately 6.2 A) with a wall thickness of 6-8 layers. The MoS2 hollow spheres are extremely active catalysts for the HDS of thiophene. Hollow spheres of MoO3 are prepared in a similar fashion. Surprisingly, upon heating, hollow crystals of MoO3 with sharp-edged truncated cubes containing inner voids are formed from the initial spheres.