Effect of heat treatment on pore structure in nano-crystalline NiO: A small angle neutron scattering study

Nano-crystalline nickel oxide powder was synthesized by a precipitation route. Powder samples were heat treated at 300, 600 and 900 °C, and pore structure evolution was followed by small angle neutron scattering (SANS) technique. SANS measurements were carried out also on pelleted samples in order to study the modifications of pore morphology due to heat treatment. SANS data reveal scattering from pores at two different length scales. The pore structure at various heat treatment temperatures does not follow any scaling behavior.     

Studies on the uptake of Th(IV), U(VI) and Pu(IV) on Dowex 50WX8 resin from TBP-Shell Sol-T mixtures

Batch equilibration studies have been carried out to understand the uptake of Th(IV), U(VI) and Pu(IV) on a conventional gel type cation exchange resin, Dowex 50WX8, from TBP-Shell Sol-T mixtures containing different amounts of nitric acid. Based on the results of the equilibration studies, column experiments have been carried out and conditions optimized to achieve separation of these elements present in binary and ternary mixtures. The influence of water content of the resin phase and the nature of the exchanging cation on the extent of uptake has also been investigated.     

A field-induced poising technique for promoting convergence of standard electrode potential values of thermally oxidized iridium pH sensors

An electrochemical technique based on reversible charge ejection/injection is shown to be an effective procedure for bringing about the convergence of standard electrode potential values in a batch of thermally prepared iridium oxide pH sensors. Such a convergence simplifies electrode calibration procedures. The rationale for the technique and the results obtained are discussed in terms of adjustment of the proportions of iridium(III) and iridium(IV) oxides at the electrode surface.     

γ-Al2O3/triflic acid as cooperative catalysts for the tandem Michael addition/carbocyclization: An easy access to 2-substituted pyrrolo[2,1-a]isoquinolines and 3-substituted pyrrolidine-2,5-diones

A tandem Michael addition/carbocyclization of 3,4-dimethoxyphenethyl maleimide with carbon and sulfur nucleophiles is accomplished via a relay catalysis using γ-Al₂O₃/TfOH binary system. The X-ray Photoelectron Spectroscopy (XPS) analysis of binary system indicates the presence of AlF₃, AlO(OH) species_. This approach provides an easy access to 2-aryl or 2-thio aryl pyrrolo[2,1-a]isoquinolines in good yields in a tandem fashion. With suitable ratio of γ-Al₂O₃/TfOH binary system, the Michael addition of N/C/S nucleophiles to N-benzyl maleimide is also achieved. A key to the success of these reactions would be the generation of AlF₃, AlO(OH) species from γ-Al₂O₃ and TfOH, which might have delineated the disadvantageous background reactions usually displayed by a strong Brønsted acid such as TfOH.     

Direct measurement of porous media local hydrodynamical permeability using gas MRI.

The concept of hydraulic permeability is at the core of modeling single phase or multi-phase flow in heterogeneous porous media, as it is the spatial distribution of the permeability that primarily governs the behavior of fluid flow in the medium. To date, the modeling of fluid flow in porous media has been hampered by poor estimates of local permeability. Magnetic Resonance Imaging is well known for its ability to measure non-invasively the local density and flow rate of different fluids saturating porous media [1,2]. In this paper we demonstrate the first non-invasive method for the direct measurement of a single projection of the local permeability tensor of a porous medium using gas-phase MRI. The potential for three-dimensional imaging of the medium permeability is also discussed. The limitations of the method are listed and results are presented in a model porous medium as well as in a real oil reservoir rock.     

Surface plasmon effects on surface second harmonic generation during Au nanoparticle deposition onto H–Si(1 1 1)

Deposition of Au nanoparticles from aqueous HF onto H–Si(1 1 1) was studied in situ by surface second harmonic generation (SHG) and ex situ by extinction spectroscopy and non-contact atomic force microscopy (AFM). AFM measurements indicate that the maximum SHG intensities occur at lateral particle diameters of approximately 90–100 nm independent of solution phase composition, but with an intensity that depends on solution phase composition.

Employing the evolution of SHG intensity to monitor lateral cluster growth, simultaneous Au deposition and Si oxidation exhibit apparent kinetic reaction orders of 1/2 and zero with respect to HF and Au(CN)₂⁻, respectively. These results are similar to those obtained purely from ex situ AFM analysis. The variations in SHG intensity with Au(CN)₂⁻ concentration can be related to particle nucleation densities. These results demonstrate the utility of SHG as an in situ probe of particle growth.     

Role of pressure dependent viscosity in measurements with falling cylinder viscometer

The falling cylinder viscometer is frequently used in measuring the dependence of the viscosity on the pressure. The viscosity is calculated using an indirect procedure, namely by appealing to the linear relation between the time taken for the fall and the viscosity. Under certain assumptions, the coefficient of proportionality can be derived analytically, and one gets the classical formula for the viscosity as a function of geometric parameters of the device, density of the fluid and the sinker, gravitational acceleration, and the distance and the time of the fall. Although the classical formula is valid only for fluids with constant viscosity, it is indiscriminately used even for fluids with pressure dependent viscosity. We investigate the role of variable viscosity, and we derive a heuristic correction to the classical formula for the case of fluids with pressure dependent viscosities. The systematic error introduced by the unwarranted application of the classical formula for fluids with pressure dependent viscosity is analysed, and it is shown it is measurable and it can in some cases significantly influence the experimental results.     

Synthesis of vanadium dioxide thin films on conducting oxides and metal–insulator transition characteristics

We report on growth and physical properties of vanadium dioxide (VO₂) films on model conducting oxide underlayers (Nb-doped SrTiO₃ and RuO₂ buffered TiO₂ single crystals). The VO₂ films, synthesized by rf sputtering, are highly textured as seen from X-ray diffraction. The VO₂ film grown on Nb doped SrTiO₃ shows over two orders of magnitude metal–insulator transition, while VO₂ film on RuO₂ buffered TiO₂ shows a smaller resistance change but with an interesting two step transition. X-ray photoelectron spectroscopy has been performed as a function of depth on both sets of structures to provide mechanistic understanding of the transition characteristics. We then investigate voltage-driven transition in the VO₂ films grown on Nb-doped SrTiO₃ substrate as a function of temperature. The present study contributes to efforts towards correlated oxide electronics utilizing phase transitions.