CHRONOABSORPTOMETRY FOR THE DETERMINATION OF KINETIC PARAMETERS OF ELECTRON TRANSFER REACTIONS USING LONG-OPTICAL-PATH ELECTROCHEMICAL CELL

A single potential step chronoabsorptometric method for the determination of ki- netic parameters of simple quasi-reversible reactions is described.It is verified by determining the kinetic parameters for the electroreduction of ferricyanide.A long-optical-path electro- chemical cell with a plug-in electrode is used.The thickness of solution layer is 0.55 mm

Analysis of a Stagnation Point Flow with Hybrid Nanoparticles over a Porous Medium

The unsteady stagnation-point flow of a hybrid nanofluid over a stretching/shrinking sheet embedded in a porous medium with mass transpiration and chemical reactions is considered.The momentum and mass transfer problems are combined to form a system of partial differential equations,which is converted into a set of ordinary differential equations via similarity transformation.These ordinary differential equations are solved analytically to obtain the solution for velocity and concentration profiles in exponential and hypergeometric forms,respectively.The concentration profile is obtained for four different cases namely constant wall concentration,uniform mass flux,general power law wall con-centration and general power law mass flux.The effect of different physical parameters such as Darcy number Da^(1-1),mass transpiration parameter V_(C),stretching/shrinking parameter (d),chemical reaction parameter(β)and Schmidt number (Sc)on velocity and concentration profile is examined.Results show that,the axial velocity will decreases as the shrinking sheet parameter increases,regardless of whether the suction or injection case is examined.The concentration decreases with an increase in the shrinking sheet parameter and the chemical reaction rate parameter.

低温CO氧化中担载Co_3O_4催化剂失活的影响因素(英文)

This study focused on the influences of a variety of reaction parameters and guest molecules such as H2O and C3H8 on the deactivation of supported Co3O4 catalysts for CO oxidation.Additionally,the physical features of and carbon deposition on some samples after the reaction under the chosen conditions were determined by BET and X-ray diffraction as well as by carbon analyses to deduce the precursors associated with catalyst deactivation.Activity maintenance profiles of the catalysts for CO oxidation at 100°C significantly depended on the support for Co3O4 nanoparticle dispersion,the loading,the preparation technique and the calcination temperature.The best on-stream performance was achieved using a 5%Co3O4/TiO2 catalyst prepared by the incipient wetness method followed by calcination at 350°C.All the reaction parameters chosen here such as the reaction temperature,the feed gas composition of CO,O2,H2O,and C3H8,and the gas space velocity strongly influenced the extent of catalyst deactivation during CO oxidation and also the rate of catalyst deactivation.However,the deactivation behavior is very complicated.No appreciable changes in the surface area,the porosity,and the phase of the Co3O4 nanoparticles and their size occurred even for the samples that were severely deactivated.Significant deposition of carbon on the catalysts after the reaction was visible and it depended on the reaction parameters chosen here.Consequently,this extensive parametric study on the deactivation of catalysts during oxidation and with the chosen reaction parameters and guest gases can lead to an understanding of the deactivation precursors that are associated with carbonaceous species including carbonates and surface free carbon.

Preparation of β-SiC by combustion synthesis in a large-scale reactor

The feasibility of 5 kg β-SiC synthesized in one batch was demonstrated through igniting the mixture of Si, C-black and polytetrafluoroethylene （PTFE） under different nitrogen pressures. The effect of experimental parameters, including the contents of PTFE, nitrogen pressure, preheating, and raw materials distribution forms were investigated. The results show that the products are β-SiC with equiaxed grains. The average grain size is less than 200 nm. The powders loaded loosely promote reaction heat dispersing, resulting in small grains. High purity β-SiC powders are obtained when the PTFE content is as low as 5wt%, which simplifies the process and decreases the cost effectively. The ceramic sintered from the obtained β-SiC powders presents the hardness of 22.20 GPa, the bending strength as high as 715.15 MPa and the fracture toughness of 8.179 MPa·m^1/2, which are higher than those of ceramics fabricated with α-SiC produced by combustion synthesis.

One-pot and One-step Cu(0)-mediated Reversible-Deactivation Radical Polymerization of N-Isopropylacrylamide(NIPAM) in Water

Copper(0)-mediated reversible-deactivation radical polymerization(Cu(0)-mediated RDRP) of the water-soluble monomer Nisopropylacrylamide(NIPAM) has been challenging with the problems of high dispersity, poor control over the molecular weights(MWs) or complex or multi reaction steps, etc. In this work, we report the well-controlled polymerization of NIPAM in water via a facile one-pot and one-step Cu(0)-mediated RDRP. The results of this approach show that the key for kicking off the Cu(0)-mediated NIPAM RDRPs is to ensure sufficient Cu~I at the very beginning, and the key to achieve a well-controlled chain growth is to provide adequate deactivation strength during the polymerization process. For NIPAM, which has a high propagation rate constant, the deactivation control can be effectively enhanced by extra adding deactivator(i.e., Cu~II) to the system. Moreover, a low reaction temperature(4 ℃) is necessary in the controlled synthesis of higher MW poly(Nisopropylacrylamide)(PNIPAM) to avoid the compromise in control caused by the phase transition from its lower critical solution temperature(LCST). Through this new kinetically controlled strategy, PNIPAMs with well-defined structure, narrow molecular weight distributions(MWDs) and varied MWs were successfully achieved.

Numerical investigation of two-dimensional and axisymmetric unsteady flow between parallel plates

In this study,heat and mass transfer in a viscous fluid which is squeezed between parallel plates Is investigated numerically using the fouith-order Runge-Kutta method.The numerical investigation is carried out for different governing parameters namely;the squeeze number,Prandtl number,Eckert number,Schmidt number and the chemical reaction parameter.Results show that Nusselt number has direct relationship with Prandtl number and Eckert number but it has reverse relationship with the squeeze number.Also it can be found that Sherwood number increases as Schmidt number and chemical reaction parameter increases but it decreases with increases of the squeeze number.