Papers by Keyword: Rate Constant

Abstract: Mg/Al bilayer thin films were successfully deposited by using D.C. magnetron sputtering technique. To study the effect of hydrogenation on structural, optical and electrical properties of Mg/Al thin films, the hydrogenation of the annealed thin films was done under different hydrogen pressure (15, 30 & 30psi). The structural properties of the films were investigated by Raman spectroscopy and decrease in intensity of Raman peaks with increasing hydrogen pressure was observed; this typically confirms the existence of hydrogen in Mg/Al thin films. The thin film is of semiconducting nature and it was found that the electrical conductivity of the film decreases with increasing hydrogen pressure applied. In the hydriding kinetics of the films, it was seen that the resistivity increased along with hydrogen absorption time. Eventually, it attains the equilibrium stage indicating the hydrogen absorption in the thin films. The rate of absorption of hydrogen increases with the pressure of hydrogen over different time ranges and decreases with the absorption of hydrogen over time.

Abstract: The present paper describes an investigation of the adsorption of lead ions (Pb²⁺) on graphene-based nanocomposites obtained via exfoliation of hydrolyzed expanded graphite intercalation compound. Three types of these nanocomposites - suspension of graphene nanoplatelets (SGN), paste of multi-layered oxidized graphene (PMOG), and paste of few-layered oxidized graphene (PFOG) - were used to extract Pb²⁺ from 1,040 mg L^-1 aqueous solutions of Pb (NO₃)₂, and the kinetic of the Pb²⁺ adsorption was studied. It was found that the kinetic data are best fitted by the pseudo-second-order model. The adsorption equilibrium was achieved within 30 min under normal conditions. The maximum Pb²⁺ adsorption capacity of SGN, PMOG and PFOG was found to be 457, 103 and 38 mg g^-1, respectively. Considering the obtained results, it can be assumed that the phenolic and hydroxyl oxygen-containing functional groups located at the surface of the adsorption materials under study play an important role in the Pb²⁺ removal process.

Abstract: TiO₂ powder was synthesized via the solvothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Single phase anatase was obtained without calcination steps. The particle was irregular in shape with average particle size of 1.0 μm. The characteristic X–ray radiation of element was show titanium at 4.510 keV and 4.931 keV and oxygen at 0.523 keV. The photocatalytic degradation of methomyl in aqueous solution over TiO₂ powder under UV irradiation was determined by UV-Vis spectroscopy. The influence of the amount of TiO₂ powder for photocatalytic degradation of methomyl and rate constant were determined. The optimum condition for photocatalytic degradation of methomyl over TiO₂ powder was obtained at 0.05 g.L^-1 for the amount of TiO₂ powder in 60 min. The degradation rate constant at the optimum condition was 0.0243 min^-1.

Abstract: The dynamic experiments about the conversion of CO₂ from simulated flue gas were carried out in a bubbling reactor containing a kind of adsorption with M dissolving in ethanol and water at atmospheric pressure. Based on the results of product analysis and electrode potentials, the reaction mechanism of CO₂ reduced by M was deduced. The results of dynamic experiments showed that the reaction order was 1.0, the rate constant was 5.91×10^-2 s^-1, and the apparent activation energy was 23.47 kJ·mol^-1.

Abstract: Regularities of the dicyclopentadiene cationic oligomerization under influence of the catalytic system AlEt2Cl: TiCl4 in toluene solution were studied. The most probable mechanism of polymerization in this system is the propagation chain on the contact or solvate-separated ion pairs. The effective rate constant of solvation of the catalyst and chain propagation were calculated. The thermal oligomerization effect and heat of the catalyst system components solvation are determined by heat of oligomerization raw material containing dicyclopentadiene. When taking into account the data of both material and thermal balance the experimental data were described adequately.

Abstract: It is known that chemical bonding is only possible when particles with antiparallel valence electrons spins orientation collide [1, 2]. In an external magnetic field unpaired electrons spins precession around the field lines is observed. Precession frequencies of valence electrons of magnetic and nonmagnetic nuclei differ, resulting in a different probability to collide in reactive state for different isotopes. The investigations results of magnetic field influence on the carbon isotopes redistribution between carbon dioxide and disperse carbon in plasmachemical processes are given. Argon-oxygen plasma by a high-frequency generator was produced. Carbon placed into reaction zone by the high-frequency electrode evaporation. The plasmachemical reaction products quenching in the plasma flow at the sampler probe were examined. It is found that the Laval nozzle sampler is more efficient for plasma stream cooling versus the cylindrical sampler. The effects of flow rate, pressure and carbon dioxide concentration on the plasma flow cooling efficiency were estimated.

Abstract: For investigating the competitive ability of denitrifying bacteria and sulfate reducing bacteria on the substrate in the anaerobic environment, denitrification and sulfate reduction experiments were conducted under the conditions of different carbon content and different nitrate/sulfate ratio, and the kinetic difference of denitrification and sulfate reduction was also analyzed. The experimental results showed that denitrification could essentially be completed in 7~9 h at the same condition of carbon source content, but sulfate reduction was completed after 12 h. Denitrification rate constant of the microbes was over one time larger than that of sulfate reduction. When the carbon source was enough (C/N ratio and C/S ratio more than 3), denitrification efficiencies all surpassed 98%, while that of sulfate reduction only reached 84%. Under the same condition, the nitrate reduction ability of microbes was stronger than that of sulfate reduction, and the process of nitrate reduction had much more superiority.

Abstract: Conjugated linoleic acid (CLA) was prepared by alkali isomerization using walnut oil as raw materials, KOH as catalyst and propylene glycol as solvent. The kinetics of alkali isomerization of linoleic acid from walnut oil converted into CLA was experimentally studied under the reaction conditions of 393~453 K,and which the initial mass ratio of propylene glycol, walnut oil and KOH was 3:2:1. The mechanism of alkali isomerization was proposed, and the mechanism model was put forward through theoretical derivation.The rate constants were determined, the mechanism model was verified,and the kinetics parameters were obtained.The results showed that alkali isomerization reaction was first order the concentration of linoleic acid, which the apparent activation energy was 67.22 kJ·mol^-1 and the pre-exponential constant was 8.963×10⁵min^-1.

Abstract: The reaction of Et₃GeCH=CH₂ + Et₃SiOH → Et₃SiO–Ge–Et₃ + CH₂=CH₂ has been studied using quantum chemistry methods. Geometries of reactants, transition states, and products have been optimized respectively at the b3lyp/6-311+g(2d,2p) level. The rate constants were evaluated using canonical variational transition state theory (CVT) and canonical variational transition state theory with small-curvaturetunneling contributions (CVT/SCT) over the temperature range of 200-3500K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior, and a three-parameter rate-temperature formula has been fitted as follows: k(T)=1.43×10^-38T ^5.41exp(-13200/T) (in units of cm³ molecule^-1s^-1).

Abstract: In this work, effect of carboxymethyl chitosan (CMCS) on vulcanization kinetics of natural rubber was studied using the Rheometer MDR2000.The results showed that both the rate constants of induction period and curing period of natural rubber (K-N) was greater than that of natural rubber added CMCS and the dosage is 0.05% of fresh latex (CMCS-1), but less than that of natural rubber added CMCS and the dosage is 0.1% of fresh latex (CMCS-2), and the activation energy 100.8kJ/mol of induction period of K-N is greater than the activation energy 96.7kJ/mol, 93.7kJ/mol of induction period of CMCS-1, CMCS-2, respectively and that the activation energy 104.4 kJ/mol of curing period of K-N is less than the activation energy111.9kJ/mol of curing period of CMCS-1, and bigger than the activation energy 103.4 of CMCS-2 at the same temperature.