Investigations on Pd:SnO2/porous silicon structures for sensing LPG and NO2 gas

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO₂/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO₂ gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO₂ gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO₂ gases, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

The kinetics and thermodynamics of a novel efficient mixed water–1,4-dioxan solvent for the effective complexation of a neutral ruthenium complex with carbon monoxide at atmospheric pressure

Kinetic and thermodynamic investigations were performed for a mixed aqueous-organic, 1:1 (v/v) water–1,4-dioxane medium, which was found to be an efficient solvent for the interaction of a neutral dichlorotris(triphenylphosphine) ruthenium(II), RuCl₂(PPh₃)₃ complex with carbon monoxide at atmospheric pressure. During the interaction, RuCl₂(PPh₃)₃ dissociates to a neutral complex dichlorobis(triphenylphosphine) ruthenium(II), RuCl₂(PPh₃)₂, by losing a coordinated PPh₃ ligand and RuCl₂(PPh₃)₂ coordinates with CO to form an in situ carbonyl complex RuCl₂(CO)(PPh₃)₂. The in situ formed carbonyl complex RuCl₂(CO)(PPh₃)₂ was thoroughly characterized by equilibrium, spectrophotometric, IR, and electrochemical techniques. Under equilibrium conditions, the rate and dissociation constants for the dissociation of PPh₃ from RuCl₂(PPh₃)₃ were found to be favorable for the formation of the carbonyl complex RuCl₂(CO)(PPh₃)₂. The rates of complexation for the formation of RuCl₂(CO)(PPh₃)₂ were found to follow an overall second-order kinetics being first order in terms of the concentrations of both carbon monoxide and RuCl₂(PPh₃)₂. The determined activation parameters corresponding to the rate constant (ΔH^# = 35.9 ± 2.5 kJ mol⁻¹ and ΔS^# = −122 ± 6 J K⁻¹ mol⁻¹) and thermodynamic parameters corresponding to the formation constant (ΔH° = −33.5 ± 4.5 kJ mol⁻¹, ΔS° = −25 ± 8 J K⁻¹ mol⁻¹, and ΔG° = −25.7 ± 2.0 kJ mol⁻¹) were found to be highly favorable for the formation of the complex RuCl2(CO)(PPh3)2. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 359–369, 2008     

Prediction of extrudate swell in polymer melt extrusion using an Arbitrary Lagrangian Eulerian (ALE) based finite element method

Accurate prediction of extrudate (die) swell in polymer melt extrusion is important as this helps in appropriate die design for profile extrusion applications. Extrudate swell prediction has shown significant difficulties due to two key reasons. The first is the appropriate representation of the constitutive behavior of the polymer melt. The second is regarding the simulation of the free surface, which requires special techniques in the traditionally used Eulerian framework. In this paper we propose a method for simulation of extrudate swell using an Arbitrary Lagrangian Eulerian (ALE) technique based finite element formulation. The ALE technique provides advantages of both Lagrangian and Eulerian frameworks by allowing the computational mesh to move in an arbitrary manner, independent of the material motion. In the present method, a fractional-step ALE technique is employed in which the Lagrangian phase of material motion and convection arising out of mesh motion are decoupled. In the first step, the relevant flow and constitutive equations are solved in Lagrangian framework. The simpler representation of polymer constitutive equations in a Lagrangian framework avoids the difficulties associated with convective terms thereby resulting in a robust numerical formulation besides allowing for natural evolution of the free surface with the flow. In the second step, mesh is moved in ALE mode and the associated convection of the variables due to relative motion of the mesh is performed using a Godunov type scheme. While the mesh is fixed in space in the die region, the nodal points of the mesh on the extrudate free surface are allowed to move normal to flow direction with special rules to facilitate the simulation of swell. A differential exponential Phan Thien Tanner (PTT) model is used to represent the constitutive behavior of the melt. Using this method we simulate extrudate swell in planar and axisymmetric extrusion with abrupt contraction ahead of the die exit. This geometry allows the extrudate to have significant memory for shorter die lengths and acts as a good test for swell predictions. We demonstrate that our predictions of extrudate swell match well with reported experimental and numerical simulations.     

Reduction of chromano–piperidine-fused isoxazolidines: Tandem intramolecular rearrangements leading to 2-(methylamino)-4-oxo-N-phenyl-N-propyl-4H-chromene-3-carboxamide

Reductive ring opening of isoxazolidine moiety of chromano–piperidine-fused isoxazolidines (3a–c) with HCOONH₄ and 10% Pd/C in a mixture of solvents (THF/MeOH) at ambient temperature, affords novel 2-(methylamino)-4-oxo-N-phenyl-N-propyl-4H-chromene-3-carboxamide (4), which is apparently derived from reductive NO bond cleavage followed by tandem intramolecular rearrangements. Plausible mechanistic rationale for the formation of compound 4 is proffered.     

Space charge induced surface stresses: implications in ceria and other ionic solids

Volume changes associated with point defects in space charge layers can produce strains that substantially alter thermodynamic equilibrium near surfaces in ionic solids. For example, near-surface compressive stresses exceeding -10 GPa are predicted for ceria. The magnitude of this effect is consistent with anomalous lattice parameter increases that occur in ceria nanoparticles. These stresses should significantly alter defect concentrations and key transport properties in a wide range of materials (e.g., ceria electrolytes in fuel cells).     

Crystal Structure of 3β-Hydroxy-16α-methylpregn-5-en-20-one

Abstract  

The crystal structure of the title compound, 3β-hydroxy-16α-methylpregn-5-en-20-one, C₂₂H₃₄O₂, was determined by direct methods using single crystal X-ray diffraction data. The compound crystallizes in the triclinic space group P1 with unit-cell parameters: a = 6.235(1) ?, b = 6.282(1) ?, c = 12.877(3) ?, α = 96.672(4)°, β = 98.746(4)°, γ = 106.838(4)°, Z = 1. The structure was refined by full-matrix least-squares to R = 0.0573 for 2,196 observed reflections. Rings A and C of the compound are in chair conformation whereas ring B is in half-chair conformation. Ring D is in envelope conformation. The A/B ring junction is quasi-trans, while ring systems B/C and C/D are trans fused about the C8–C9 and C13–C14 bonds, respectively. The steroid nucleus has a small twist, as shown by the C19–C10···C13–C18 pseudo-torsion angle of 8.0°. Molecules are connected via C–H···O hydrogen bonds to form straight chains along the c-axis of the unit cell. The straight chains are packed together to form layers.