Fabrice Audonnet

Simultaneous measurement of density and viscosity of n-pentane from 298 to 383 K and up to 100 MPa using a vibrating-wire instrument

Abstract Experimental results of density and viscosity of n-pentane are reported at temperatures from 303 to 383xa0K and pressures up to 100xa0MPa. The two properties were measured simultaneously using one single vibrating-wire sensor, which is composed of a sinker suspended from a thin metallic wire, both of which are immersed in the sample fluid. The oscillation characteristics of the wire are obtained by means of an electromagnetic coupling. The response of the wire is related to the density of the fluid mainly through the buoyancy force acting upon the sinker, whereas the viscosity of the fluid affects the damping of the oscillations. The technique is based on a rigorous theoretical framework and thus, once all of the sensor parameters are known, either by independent means or from a single reference experiment, no extensive calibration procedures are required for measurements at high pressure or at temperatures away from ambient conditions. The present results of density exhibit a precision of ±0.04% and an estimated accuracy of ±0.2%. The viscosity measurements exhibit a precision of ±0.5% and are judged accurate within ±2.5%. Tests of the instrument with gaseous nitrogen are reported in order to assess the performance of the technique when measuring in a fluid of low viscosity.

Investigation into the Catalytic Activity of Porous Platinum Nanostructures

The catalytic activity of porous platinum nanostructures, viz. platinum nanonets (PtNNs) and platinum nanoballs (PtNBs), synthesized by radiolysis were studied using two model reactions (i) electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate and (ii) the reduction of p-nitrophenol by sodium borohydride to p-aminophenol. The kinetic investigations were carried out for the platinum nanostructure-catalyzed reactions at different temperatures. The pseudofirst-order rate constant for the electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate catalyzed by PtNNs and PtNBs at 293 K are (9.1 ± 0.7) × 10(-3) min(-1) and (16.9 ± 0.6) × 10(-3) min(-1), respectively. For the PtNN- and PtNB-catalyzed reduction of p-nitrophenol to p-aminophenol by sodium borohydride, the pseudofirst-order rate constant was (8.4 ± 0.3) × 10(-2) min(-1) and (12.6 ± 2.5) × 10(-2) min(-1), respectively. The accessible surface area of the PtNNs and PtNBs determined before the reaction are 99 and 110 m(2)/g, respectively. These nanostructures exhibit significantly higher catalytic activity, consistent with the largest accessible surface area reported so far for the solid platinum nanoparticles. The equilibrium of the reactants on the surface of the platinum nanostructures played an important role in the induction time (t0) observed in the reaction. A possible role of structural modifications of PtNBs catalyzed the reaction leading to change in the accessible surface area of PtNBs is being explored to explain the nonlinear behavior in the kinetic curve. The activation energy of the PtNN- and PtNB-catalyzed reduction of p-nitrophenol are 26 and 6.4 kJ/mol, respectively. These observations open up new challenges in the field of material science to design and synthesize platinum nanostructures which could withstand such reaction conditions.

Density and Viscosity of Mixtures of n-Hexane and 1-Hexanol from 303 to 423 K up to 50 MPa

Experimental results for the density and viscosity of n-hexane+1-hexanol mixtures are reported at temperatures from 303 to 423 K and pressures up to 50 MPa. The binary mixture was studied at three compositions, and measurements on pure 1-hexanol are also reported. The two properties were measured simultaneously using a single vibrating-wire sensor. The present results for density have a precision of ±0.07% and an estimated uncertainty of ±0.3%. The viscosity measurements have a precision of ±1% and an estimated uncertainty of ±4%. Representations of the density and viscosity of the mixture as a function of temperature and pressure are proposed using correlation schemes.