Search Results
Abstract
This work presents results of research on thermal decomposition of nickel(II) sulfate(VI) hexahydrate in air and in helium atmosphere. On the base of TG and XRD results a mechanism of thermal decomposition of NiSO4 hydrate was established. For calculations of kinetic parameters of the Arrhenius equation, the Coats-Redfern approximation was applied. Choice of g(a) function and thus of a mechanism best describing given stage of decomposition was performed by testing 12 kinetic models.
Abstract
The preparation of rutile type solid solutions in (TiO2)x -(RuO2)1−x system in the 0≤x ≤0.7 concentration range is described. The single phase solid solutions are formed by controlled nanocrystallization of amorphous gels prepared by the sol-gel method. The kinetics of this crystallization process has been analyzed. It was found that the crystallization does not correspond to the Johnson-Mehl-Avrami model and it can be described by the two-parameter Šestk-Berggren kinetic model.
Abstract
Traditionally, the kinetic treatment of adiabatic calorimetry data has been based on the results of one or more experiments, but always with the assumption of the kinetic model that the reaction follows to calculate the kinetic parameters. In this paper a method for the determination of the activation energy that uses a set of adiabatic calorimetry data is developed. To check the method, the thermal decompositions of two peroxides were studied.
Abstract
The acid properties of the Ca/NaY zeolite were investigated by means ofn-butylamine desorption and thermal decomposition, using both thermogravimetry (TG) and differential scanning calorimetry (DSC). The total acidity of the zeolite was calculated from the TG data, while DSC was used with the Borchardt-Daniels kinetic model to determine the relative acid strength of the catalyst, given in J per acid site. The enthalpies of these processes are proportional to the acid site strength in each specific temperature range.
Abstract
This research is focused on the effects of pressure (100–300 Pa) and matrix and on light crude oil combustion in sandstone matrix using pressurized differential scanning calorimetry (PDSC). Light crude oils and sandstone mixtures were prepared to give a composition of 15 mass% crude oil in sandstone matrix. A total of forty-eight PDSC experiments were performed. Roger and Morris kinetic model was used to analyse the data obtained from PDSC experiments and the results are discussed.
Calorimetric characterization of 2′,3′-dideoxyinosine water solution
Stability and interaction with human serum albumin
Abstract
A study of 2′,3′-dideoxyinosine (ddI) stability and its interaction with human serum albumin (HSA) was carried out by differential scanning microcalorimetry DSC. Scan rate dependent and irreversible endothermic thermal degradation of ddI was analyzed with use of kinetic approach. Observed process could be interpreted in terms of simple first-order one step kinetic model. Moreover it was shown that ddI bound weakly to the human serum albumin and stabilized this protein.
Kinetics of radionuclide interaction with suspended solids in modeling the migration of radionuclides in rivers
II. Effect of concentration of the solids and temperature
Abstract
The effects of concentration of the solid phase and of temperature on the kinetics of interaction of radionuclides with the solid phase suspended in river water were analyzed using two kinetic models describing the interaction by two parallel or consecutive reactions. At first the effect of concentration of the solid phase was theoretically described using four parameters and simple relations. Then kinetic curves were determined by laboratory experiments for the uptake of carrier-free58Co from river water on bottom sediment and on suspended solids of a small river. The curves were analyzed using the kinetic models by calculating the parameters through computer fitting to the experimental data. The parameters thus obtained depend on the concentration of solid phase in the predicted way. Some deviations from theory were due either to agglomeration of sediment particles at higher sediment concentratins or to experimental erros. Equal accuracy of description of the curves with both kinetic models was ascertained. Apart from the concentration of solid phase, the following factors are found to significantly affect the parameters: temperature (13 or 23 °C), properties of solid phase (sediment or suspended solids), sediment age and/or water composition. It is recommended that kinetic parameters suitable for modeling the migration of radionuclides in rivers be obtained by experiments on repeatedly taken samples of unfiltered river water.
Abstract
In a recent article, we obtained an approximate solution for the evolution of a transformed fraction under isochronal conditions for a large variety of single-step transformations. We verified that this solution is accurate and can, in many instances, be used instead of the exact numerical solutions of the corresponding differential equations. In this article we want to examine the possibilities offered by an analytical solution in the analysis of thermoanalytical curves. We will show that for single-step transformations, our model predicts that under the proper time scaling the thermograms obtained at different heating rates merge into a single curve. This ‘universal curve’ is exclusively related to the kinetic model. In addition, the universal curve can be obtained from experimental thermograms by means of a simple transformation. In this way, the dependence of the experimental curves on the rate constant and the kinetic model can easily be separated, making it possible to independently determine the kinetic parameters and the kinetic model. In addition, one can easily check the validity of the kinetic analysis as well as calculate a reliable statistical measure of the goodness of the single-step assumption.
Abstract
The following problems concerning the apparent compensation effect (CE) (lnA=a+bE, where A is the pre-exponential factor, E is the activation energy, a and b are CE parameters) due to the change of the conversion function and on which the invariant kinetic parameters method (IKP method) is based, are discussed: (1) the explanation of this kind of CE; (2) the choice of the set of conversion functions that checks CE relationship; (3) the dependencies of CE parameters on the heating rate and the temperature corresponding to the maximum reaction rate. Using the condition of maximum of the reaction rate suggested by Kissinger (Kissinger law), it is pointed out that, for a certain heating rate, the CE relationship is checked only for reaction order (Fn) and Avrami-Erofeev (An) kinetic models, and not for diffusion kinetic models (Dn). Consequently, IKP method, which is based on the supercorrelation relationship between CE parameters, can be applied only for the set Fn+ An of kinetic models. The dependencies of a and b parameters on the heating rate and T m (temperature corresponding to maximum reaction rate) are derived. The theoretical results are discussed and checked for (a) TG simulated data for a single first order reaction; (b) TG data for PVC degradation; (b) the dehydration of CaC2O4·H2O.
Kinetic analysis of the liquid-phase depolymerization of trioxane from programmed-temperature data
I. Integral kinetic analysis
An experimental method for the determination of kinetic data for liquid-phase reactions under linear rise of temperature is explained for the depolymerization of trioxane. Integral kinetic analysis of the data is performed in order to determine the kinetic model and the kinetic parameters. Experiments have been carried out at different heating rates between 0.5 and 2 deg/min, leading to similar kinetic parameters. The obtained results are in agreement with the kinetic model and parameters obtained from isothermal kinetic analysis. The programmedtemperature method seems to be a useful tool for a quick determination of kinetic models, avoiding experimental work.
