Search Results
Accommodation of the actual solid-state process in the kinetic model function
I. Significance of the non-integral kinetic exponents
Abstract
The degree of coordination between the kinetic information from the thermonalytical measurements and the kinetic theory of the solid-state reactions was investigated through the microscopic study of the thermal dehydration of several inorganic salt hydrates. An accommodation function was applied to the conventional kinetic model functionsf(α), in an attempt to reduce the disagreement between the actual process and the idealized one assumed in formulatingf(α). The significance of the non-integral kinetic exponent in the kinetic model function was discussed with its physico-chemical meanings.
Introduction Kinetic models used in heterogeneous catalysis are often based on the assumption that chemical reactions occur in a Langmuir adsorbed overlayer, i.e., on a uniform surface with one type of adsorption sites. With
Abstract
Pb(1,4-BDC)·(DMF)(H2O) (1,4-BDC=1,4-benzenedicarboxylate; DMF=dimethylformamide) has been synthesized and investigated by elemental analysis, FTIR spectroscopy, thermogravimetry (TG), derivative thermogravimetry (DTG). TG-DTG curves show that the thermal decomposition occurs in four stages and the corresponding apparent activation energies were calculated with the Ozawa-Flynn-Wall (OFW) and the Friedman methods. The most probable kinetic model function of the dehydration reaction of the compound has been estimated by the Coats-Redfern integral and the Achar-Bridly-Sharp differential methods in this study.
Simultaneous determination of the activation energy and the reaction kinetic model from the analysis of a single curve obtained by a novel method
CRTA with constant acceleration of the transformation
Abstract
It has been demonstrated that a single plot of the values of Δlnα1/2/Δln(1-α) (taken from a single α−T curve obtained under a controlled linear increase of the reaction rate) as a function of the corresponding values of Δ(1/T)/Δln(1−α) permits the simultaneous determination of both the activation energy and the kinetic model in accordance with a solid state reaction.
Abstract
By kinetic modelling of the possible reactions of diphenylamine (DPA) and its nitrated consecutive products used to stabilize cellulose nitrate (CN), one can get reactivities for the nitrated DPA compounds for the situation inside a real CN formulation and therewith determine their stabilizing contribution. Concentration data of DPA and seven of its consecutive products have been determined by HPLC from isothermal ageing of a CN formulation at temperatures between 65 and 90°C for up to 344 days. A comparison between the modelling presented and modellings published in the literature using the steady-state approximation is made. The steady-state approximation oversimplifies the stabilizer reaction behaviour in a CN formulation. From the applied modelling the question about N—NO—DPA as a key intermediate can be answered.
Abstract
The reaction of ilmenite titanium raw materials with sulphuric acid has been studied in a non-isothermal-non-adiabatic type calorimeter. The influence of different starting conditions, temperature and ilmenite particle-size distribution on the thermo-kinetics of the reaction was investigated. A kinetic model is presented for this heterogeneous system for a specified ilmenite particle-size distribution and starting temperature. On the basis of this model and experimentally determined parameters it it possible to analyse by simulation the autothermic reaction of digestion of different titanium ores with sulphuric acid.
Titanium(IV)–EDTA complex
Kinetics of thermal decomposition by non-isothermal procedures
Abstract
This work aims the evaluation of the kinetic triplets corresponding to the two successive steps of thermal decomposition of Ti(IV)–ethylenediaminetetraacetate complex. Applying the isoconversional Wall–Flynn–Ozawa method on the DSC curves, average activation energy: E=172.49.7 and 205.312.8 kJ mol–1, and pre-exponential factor: logA=16.380.84 and 18.961.21 min–1 at 95% confidence interval could be obtained, regarding the partial formation of anhydride and subsequent thermal decomposition of uncoordinated carboxylate groups, respectively. From E and logA values, Dollimore and Mlek methods could be applied suggesting PT (Prout–Tompkins) and R3 (contracting volume) as the kinetic model to the partial formation of anhydride and thermal decomposition of the carboxylate groups, respectively.
Abstract
A Mangelsdorf's approach to modeling the epoxy-amine cure kinetics has been developed. Analysis of the data by means of Mangelsdorf's approach makes it possible not only to determine the reaction rate constant and the heat of epoxy ring opening, but also to elucidate the reaction mechanism. However, to model the kinetic curves obtained by the calorimetric method for the complicated reaction should be derived an equation expressing the rate of change of the heat with time, as a function of the reaction rate and the extent of conversion. In a detailed examination the thermokinetic data, we found that glassy state transition is kinetically feasible. Using data available in literature, the kinetic model for epoxy-amine cure reaction was developed. Our treatment of glass formation is based on the picture of the reaction system as a miscible mixture of two structurally different liquids. This approach is similar to that presented by Bendler and Shlesinger as a Two-Fluid model. In the application of this model to reaction kinetics, we believe the explanation of glass structure formation lies in the splitting of the homogeneous mixture into two liquid phases.
Abstract
The authors present an original kinetic model and a computer program in order to determine the mass of various types of water from the oxide powders obtained through co-precipitation, using thermogravimetric data. The model is based on kinetic equations in the framework of the ‘reaction order’ desorption of the water loss. The program minimizes the mean square deviation between the experimental TG curve and the approximation curve; it allows visualizing the experimental and the approximated TG curves for the overall process, as well as the approximated TG and DTG curves for the individual processes. The influence of the aging time and temperature on the mass of various types of water to be found in the co-precipitated manganese ferrite powder was investigated based on this original kinetic model and the suitable computer program. Some correlations between the water release and microstructure changes of the powder during aging in mother solution are presented.
Abstract
The oxidation kinetics of Zr-disilicide (ZrSi2) powders up to temperatures of 1550°C were studied in flowing air using non-isothermal and isothermal thermogravimetric (TG) analysis. During the oxidation process two main thermal events were detected. The first stage of the oxidation reaction leads to the formation of elemental silicon as an intermediate reaction product. Upon further temperature increase the newly formed silicon is oxidized. Completely oxidized ZrSi2 samples consist of ZrSiO4, amorphous and crystalline SiO2 as well as some residual ZrO2. The experimental TG data were analysed with a model-fitting kinetic method. The gas-solid reaction is complex and can best be fitted with a multi-step reaction scheme consisting of branching reactions based on 3D diffusion mechanisms and a fractal order reaction.
