Effect of dehydration on the mechanical properties of sodium saccharin dihydrate probed with nanoindentation

Nanoindentation is used to explore the variation of mechanical properties associated with the dehydration process in sodium saccharin dihydrate. Upon indenting using a Berkovich tip, (011) and (101) faces exhibit explicit mechanical anisotropy that is consistent with the underlying crystal structure and intermolecular interactions. For freshly grown crystals, (011) is stiffer than (101) by 14%, while (101) is harder than (011) by 8%. Being a heavily hydrated system, the measured mechanical responses contain information pertinent to the fluidity associated with lattice water. Indentation on (011) with a sharp cube-corner tip induces a fluid flow; this observation is uncommon in molecular crystals. The crystals effloresce over a period of time with the generation of a more compact crystal structure and consequently increasing H and E.

Influence of the Methane-Zeolite A Interaction Potential on the Concentration Dependence of Self-diffusivity

Studies on the diffusion of methane in a zeolite structure type LTA (as per IZA nomenclature) have indicated that different types of methane zeolite potentials exist in the literature in which methane is treated within the united-atom model. One set of potentials, referred to as model A, has a methane oxygen diameter of 3.14 angstrom, while another set of potential parameters, model B, employs a larger value of 3.46 angstrom. Fritzsche and co-workers (1993) have shown that these two potentials lead to two distinctly different energetic barriers for the passage of methane through the eight-ring window in the cation-free form of zeolite A. Here, we compute the variation of the self-diffusivity (D) with loading (c) for these two types of potentials and show that this slight variation in the diameter changes the concentration dependence qualitatively: thus, D decreases monotonically with c for model A, while D increases and goes through a maximum before finally decreasing for model B. This effect and the surprising congruence of the diffusion coefficients for both models at high loadings is examined in detail at the molecular level. Simulations for different temperatures reveal the Arrhenius behaviour of the self-diffusion coefficient. The apparent activation energy is found to vary with the loading. We conclude that beside the cage-to-cage jumps, which are essential for the migration of the guest molecules, at high concentrations migration within the cage and guest guest interactions with other molecules become increasingly dominant influences on the diffusion coefficient and make the guest zeolite interaction less important for both model A and model B.

First-Principles Study of the Effect of Organic Ligands on the Crystal Structure of CdS Nanoparticles

We show with the aid of first-principles electronic structure calculations that suitable choice of the capping ligands may be an important control parameter for crystal structure engineering of nanoparticles. Our calculations on CdS nanocrystals reveal that the binding energy of model trioctylphosphine molecules on the (001) facets of zincblende nanocrystals is larger compared to that on wurtzite facets. Similarly, the binding energy of model cis-oleic acid is found to be dominant for the (10 (1) over bar0) facets of wurtzite structure. As a consequence, trioctylphosphine as a capping agent stabilizes the zincblende structure while cis-oleic acid stabilizes the wurtzite phase by influencing the surface energy, which has a sizable contribution to the energetics of a nanocrystal. Our detailed analysis suggests that the binding of molecules on the nanocrystalline facets depends on the surface topology of the facets, the coordination of the surface atoms where the capping molecule is likely to attach, and the conformation of the capping molecule.

Effect of calcium stoichiometry on the dielectric response of CaCu3Ti4O12 ceramics

CaxCu3Ti4O12 (x=0.90, 0.97, 1.0, 1.1 and 1.15) polycrystalline powders with variation in calcium content were prepared via the oxalate precursor route. The structural, morphological and dielectric properties of the ceramics fabricated using these powders were studied using X-ray diffraction, scanning electron microscope along with energy dispersive X-ray analysis, transmission electron microscopy, electron spin resonance (ESR) spectroscopy and impedance analyzer. The X-ray diffraction patterns obtained for the x = 0.97, 1.0 and 1.1 powdered ceramics could be indexed to a body-centered cubic perovskite related structure associated with the space group Im3. The ESR studies confirmed the absence of oxygen vacancies in the ceramics that were prepared using the oxalate precursor route. The dielectric properties of these suggest that the calcium deficient sample (x = 0.97) has a reduced dielectric loss while retaining the high dielectric constant which is of significant industrial relevance. (C) 2012 Elsevier Ltd. All rights reserved.

Solvent effect on the fluorescence quenching of biologically active carboxamide by aniline and carbon tetrachloride in different solvents using S-V plots

The fluorescence quenching studies of carboxamide namely (E)-N-(3-Chlorophenyl)-2-(3,4,5-trimethoxybenzylideneamino)-4,5,6,7 tetrahydrobenzob]thiophene-3-carboxamide ENCTTTC] by aniline and carbon tetrachloride in six different solvents namely toluene, cyclohexane, n-hexane, n-heptane, n-decane and n-pentane have been carried out at room temperature with a view to understand the quenching mechanisms. The Stern-Volmer (S-V) plots have been found to be nonlinear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of Finite Sink approximation model, it was possible to check these bimolecular reactions as diffusion-limited and to estimate independently distance parameter R' and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R' and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward's empirical relation and Stokes Einstein relation. (C) 2011 Elsevier B.V. All rights reserved.

Solvatochromic Effect on the Photophysical Properties of Two Coumarins

The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C-1) and 6-methoxy-4-azidomethyl coumarin (C-2) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (mu(g)) of two coumarins were determined experimentally by Guggenheim method. The exited state (mu(e)) dipole moments were estimated from Lippert's, Bakhshievs and Chamma-Viallet's equations by using the variation of Stoke's shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating a substantial redistribution of the pi-electron densities in a more polar excited state for two coumarins.

Photo induced Effects on the Optical Properties of Sb40Se20S40 Thin Film

The thermally evaporated amorphous Sb40Se20S40 thin film of 800 nm thickness was subjected to light exposure for photo induced studies. The as-prepared and illuminated thin films were studied by X-ray diffraction, Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy. The optical band gap was reduced due to photo induced effects along with the increase in disorder. These optical properties changes are due to the change of homopolar bond densities. The core level peak shifting in XPS spectra supports the optical changes happening in the film due to light exposure.

Climate response to changes in atmospheric carbon dioxide and solar irradiance on the time scale of days to weeks

Recent studies show that fast climate response on time scales of less than a month can have important implications for long-term climate change. In this study, we investigate climate response on the time scale of days to weeks to a step-function quadrupling of atmospheric CO2 and contrast this with the response to a 4% increase in solar irradiance. Our simulations show that significant climate effects occur within days of a stepwise increase in both atmospheric CO2 content and solar irradiance. Over ocean, increased atmospheric CO2 warms the lower troposphere more than the surface, increasing atmospheric stability, moistening the boundary layer, and suppressing evaporation and precipitation. In contrast, over ocean, increased solar irradiance warms the lower troposphere to a much lesser extent, causing a much smaller change in evaporation and precipitation. Over land, both increased CO2 and increased solar irradiance cause rapid surface warming that tends to increase both evaporation and precipitation. However, the physiological effect of increased atmospheric CO2 on plant stomata reduces plant transpiration, drying the boundary layer and decreasing precipitation. This effect does not occur with increased solar irradiance. Therefore, differences in climatic effects from CO2 versus solar forcing are manifested within days after the forcing is imposed.

Effect of isothermal aging and electromigration on the microstructural evolution of solder interconnections during thermomechanical loading

The effect of different pre-aging treatments on the microstructural evolution of lead-free solder and growth of interfacial intermetallic compound layers under thermal cycling has been investigated in this work. The results show that there are distinct differences in the microstructural changes between samples with no pretreatment, samples that have experienced thermal annealing at 125A degrees C for 750 h before thermal cycling, and those that have had direct current (DC) stressing for 750 h as pretreatment. The microstructural evolution of the solder matrix is rationalized by utilizing the science of microstructures and analysis of the influence of electron flow on the precipitation phenomena. The finite-element method is utilized to understand the loading conditions imposed on the solder interconnections during cyclic stressing. The growth of intermetallic reaction layers is further analyzed by utilizing quantitative thermodynamic calculations coupled with kinetic analysis. The latter is based on the changes in the intrinsic diffusion fluxes of elements induced by current flow and alloying elements present in the system. With this concurrent approach the differences seen in thermal cycling behavior between the different pre-aging treatments can be explained.

Effect of pressure on the ionic conductivity of Li+ and Cl- ions in water

A molecular dynamics simulation study of aqueous solution of LiCl is reported as a function of pressure. Experimental measurements of conductivity of Li+ ion as a function of pressure shows an increase in conductivity with pressure. Our simulations are able to reproduce the observed trend in conductivity. A number of relevant properties have been computed in order to understand the reasons for the increase in conductivity with pressure. These include radial distribution function, void and neck distributions, hydration or coordination numbers, diffusivity, velocity autocorrelation functions, angles between ion-oxygen and dipole of water as well as OH vector, mean residence time for water in the hydration shell, etc. These show that the increase in pressure acts as a structure breaker. The decay of the self part of the intermediate scattering function at small wave number k shows a bi-exponential decay at 1 bar which changes to single exponential decay at higher pressures. The k dependence of the ratio of the self part of the full width at half maximum of the dynamic structure factor to 2Dk(2) exhibits trends which suggest that the void structure of water is playing a role. These support the view that the changes in void and neck distributions in water can account for changes in conductivity or diffusivity of Li+ with pressure. These results can be understood in terms of the levitation effect. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4756909]

Influence of growth ambience and doping on the structural properties of multiferroic DyMnO3

We report on the single crystal growth of 50% Sr and Y doped multiferroic DyMnO3 using optical floating zone technique. A comparison of the effect of growth ambience and of chemical substitution on the crystal structure of DyMnO3 is attempted. It is observed that DyMnO3 adopts Pm3m cubic structure with 50% Sr doping whereas with 50% Y doping, the crystal structure is hexagonal P6(3)cm. Orthorhombic Pnma structure is adopted by DyMnO3 when grown in air, whereas hexagonal P6(3)cm structure is obtained when grown under the ambience of argon. The structural polymorphism is discussed in terms of difference in ionic sizes of Sr, Y and Dy, comparable Gibbs free energies and coordination schemes of surrounding oxygens for hexagonal and orthorhombic structures of DyMnO3. (C) 2012 Elsevier B.V. All rights reserved.

Studies on the Aging Characteristics of Base Oil with Amine Based Antioxidant in Steel-on-Steel Lubricated Sliding

An industrial base oil, a blend of different paraffin fractions, is heated to 130 degrees C (1) in the ambient and (2) for use as a lubricant in a steel pin on a steel disk sliding experiment. The base oil was tested with and without test antioxidants: dimethyl disulfide (DMDS) and alkylated diphenylamine (ADPA). Primary and secondary oxidation products were monitored continuously by FTIR over a 100 h period. In addition, friction and wear of the steel pin were monitored over the same period and the chemical transformation of the pin surface was monitored by XPS. The objective of this work is to observe the catalytic action of the steel components on the oil aging process and the efficacy of the antioxidant to reduce oxidation of oil used in tribology as a lubricant. Possible mechanistic explanations of the aging process as well as its impact on friction and wear are discussed.

Influence of nature of support on the catalytic activity of supported molybdenum-oxo species in benzyl alcohol conversion

Supported catalysts containing 15 wt.% of molybdenum have been prepared by the incipient wetness impregnation method. CaO, MgO, Al2O3, Zr(OH)4 and Al(OH)3 have been used as supports for the preparation of supported Mo catalysts. Characterisation of all the materials prepared has been carried out through BET surface area measurement, X-ray diffractometry and FT-IR spectroscopy. Catalytic activity measurements have been carried out with reference to structure-sensitive benzyl alcohol conversion in the liquid phase. The percentage conversion of benzyl alcohol to benzaldehyde and toluene varied over a large range depending on the support used for the preparation of catalysts, indicating the importance of the support on catalytic activity of Mo catalysts. Al(OH)3 has been found to be the best support for molybdenum among all the supports used. Support–metal interaction (SMI) has been found to play an important role in determining the catalytic activity of supported catalysts.