Search Results
Summary
The effect of the concentration of benzyl dimethyl amine as a catalyst on the cure reaction of bisphenol-F based epoxy resin(BPF)/nadic methyl ahydride(NMA) system was studied by differential scanning calorimetery using an isothermal approach over the temperature range 115-145C. Kinetic parameters of the curing reaction including the reaction order, activation energy and kinetic rate constants were investigated. The results were dependent on the cure temperature and catalyst concentration and proceeded through an autocatalytic kinetic mechanism. The curing kinetic constants and the cure activation energies were obtained by the Arrhenius kinetic model. The suggested kinetic model with a diffusion term was successfully used to describe and predict the cure kinetic of BPF resin compositions as a function of the catalyst content and temperature.
Summary
The paper contains an analysis of the used of Diefallah's composite integral method of kinetic parameters evaluation. It is shown that the application of this method should be preceded by the application of an isoconversional method through which the dependence of the activation energy, E, on the conversion degree,a, should be established. If Edepends ona, Diefallah's composite integral method leads to erroneous results. If Edoes not depend ona, the true kinetic model should be comprised in the pre-established set of kinetic models. These observations were checked for two sets of non-isothermal data, namely: (a) the TG curves corresponding to the dehydration of CaC2O4H2O; (b) the TG curves corresponding to the thermal decomposition of polyvinyl chloride (PVC).
Abstract
Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO2 composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO2 composite and PANI are all D3, and the corresponding function is ƒ(α)=1.5(1−α)2/3[1−(1-α)1/3]−1. The correlated kinetic parameters are E a=112.7±9.2 kJ mol−1, lnA=13.9 and E a=81.8±5.6 kJ mol−1, lnA=8.8 for PANI/ZrO2 composite and PANI, respectively.
Abstract
Biosorption of uranyl ions from aqueous solution by Saccharomyces cerevisiae was studied in a batch system. The influence of contact time, initial pH, temperature and initial concentration was investigated. The optimal conditions were found to be 3.5 h of contact time and pH = 4.5. Temperature had no significant effect on adsorption. The uptake of uranyl ions was relatively fast and 85 % of the sorption was completed within 10 min. The experimental data were well fitted with Langmuir isotherm model and pseudo-second order kinetic model. According to this kinetic model, the sorption capacity and the rate constant were 0.455 mmol UO2 2+/g dry biomass and 1.89 g mmol−1 min−1, respectively. The Langmuir isotherm indicated high affinity and capacity of the adsorbent for uranyl biosorption with the maximum loading of 0.477 mmol UO2 2+/g dry weight.
Abstract
The uranium(VI) accumulation was studied in detail by using the biomass of mangrove endophytic fungus Fusarium sp.#ZZF51 from the South China Sea. The uranium(VI) biosorption process onto the tested fungus powders was optimized at pH 4.0, adsorption time 60 min, and uranium(VI) initial concentration 50 mg L−1 with 61.89% of removal efficiency. According to Fourier transform infrared spectra for the tested fungus before and after loaded with uranium(VI), the results showed that both of hydroxyl and carboxyl groups acted as the important roles in the adsorption process. In addition, the experimental data were analyzed by using parameter and kinetic models, and it was obtained that the Langmuir isotherm model and the pseudo-second-order kinetic model provided better correlation with the experimental data for adsorption of uranium(VI).
Abstract
The thermal decomposition of new N-methoxy-polynitroanilines was studied using the differential scanning calorimetry (DSC) method. The characteristic melting parameters were measured and the activation parameters of the most probable kinetic models of thermal decomposition were determined using a multivariate non-linear regression method. All investigated compounds followed an autocatalytic decomposition mechanism. Depending on the number and position of substituents on the aromatic ring the thermal decomposition occurs in one, two or three steps.
Abstract
The kinetics of decay of trapped electrons via tunnelling to acceptor molecules in a glassy matrix was computed by the method of stochastic simulation. The kinetic curves of electron decay were obtained for different concentrations of electron acceptor in the matrix. The results of the simulation are compared with the corresponding results calculated on the basis of certain kinetic models of the electron tunnelling in low-temperature glasses.
Abstract
A complex of N,N'-ethylenebis(salicylideneiminato)diaquochromium(III) nitrate, [Cr(salen)(H2O)2]NO3 was characterized and its decomposition mechanism was studied by TG. The IR spectrum and X-ray analysis were examined for the complex. The non-isothermal kinetic data were analyzed by means of the Achar method and the Coats—Redfern method. The most probable kinetic model function was suggested by comparison of the kinetic parameters.
Summary The SCTA methods for the kinetic analysis of solid-state reactions have been reviewed. It has been shown that these methods present two important advantages with regards to the more conventional rising temperature experiments. Firstly, they have a higher resolution power for discriminating among the reaction kinetic models and, secondly, SCTA is a powerful tool for minimizing the influence of the experimental conditions on the forward reaction.
Abstract
The kinetics of thermal dissociation was studied for polydisperse systems (naturally occurring calcite and precipitated calcium carbonate) with normal and Rosin-Rammler-Sperling distributions. Experimental rate constants at selected temperatures and activation energies were calculated. The experimental results (kinetic curves) were compared with the theoretically derived curves and the usability of the selected kinetic models for description of the kinetics in such systems was estimated.
