Search Results
Abstract
Prediction of thermal explosions using chemical kinetic models dates back nearly a century. However, it has only been within the past 25 years that kinetic models and digital computers made reliable predictions possible. Two basic approaches have been used to derive chemical kinetic models for high explosives: [1] measurement of the reaction rate of small samples by mass loss (thermogravimetric analysis, TG), heat release (differential scanning calorimetry, DSC), or evolved gas analysis (mass spectrometry, infrared spectrometry, etc.) or [2] inference from larger-scale experiments measuring the critical temperature (T m, lowest T for self-initiation), the time to explosion as a function of temperature, and sometimes a few other results, such as temperature profiles. Some of the basic principles of chemical kinetics involved are outlined, and major advances in these two approaches through the years are reviewed.
Abstract
The purpose of this work is to analyse certain kinetic features related to thermoinduced and photoinduced isothermal curing in the 25/75 mass% bis-GMA/TEGDMA system. The kinetic parameters associated with photo and thermal curing were determined and compared using an isoconversional procedure and the kinetic model was obtained by means of a reduced master plot. In photocuring, the kinetic results obtained by means of this phenomenological methodology were compared with those obtained on the basis of mechanistic considerations. In this case, we estimated the propagation and termination constants associated with photocuring at different conversions. When the phenomenological procedure is performed, the rate constant decreases slightly during the curing process and the autoacceleration effect of the process is demonstrated in the kinetic model, which is autocatalytic. However, in the mechanistic model, this same effect is noted through an increase in the rate constants, while it is assumed that the kinetic model is in the order of n with n=1.
], and decomposition of MgFe 2 (C 2 O 4 ) 3 into MgFe 2 O 4 could be simple reaction mechanisms. According to Eq. 3 , mechanism function g (α) and pre-exponential factor log A can be obtained. The results show that the kinetic model, which can
Abstract
The adsorption of n -butane on extruded cylindrical activated carbon grains is studied providing two kinds of information: the influence of the temperature and the hydrocarbon partial pressure on the adsorption dynamics (kinetic study) and on the adsorption capacities (thermodynamic study). The thermodynamic aspect could be interpreted by a Langmuir model. From a kinetic point of view, we have experimentally proved that strong temperature variations occur inside the particles during the adsorption. In this paper, a kinetic model including both mass and heat transfer phenomena is proposed. Good agreement is found between the kinetic model predictions and the experimental mass and temperature variations inside the grain during the hydrocarbon adsorption.
Abstract
The kinetics of ZnFe2 O4 and ZnCr2 O4 formation under non-isothermal conditions using DTA is discussed. It was determined activation energy and kinetic model for studied reactions in the case of used various sources of starting materials (ferric pigments, chromic oxides). The activation energies for ZnFe2 O4 are positioned in a range of 200–475 kJ mol−1 (in dependence of used ferric pigments) and in case of ZnCr2 O4 in a range of 130–160 kJ mol−1 . The autocatalytic kinetic model (Šestk-Berggren) was found to be the most convenient description of the studied processes.
Abstract
For the most common kinetic models used in heterogeneous reactions, the dependencies on x m = E/RT m (E is the activation energy, T m is the temperature corresponding to maximum process rate, R is the gas constant) on the relative errors (e%) in the determination of the activation energy from the slope of the Kissinger straight line ln(β / T m 2) vs. 1/T m (β is the heating rate) are evaluated. It is pointed out that, for x m≥10.7 and all kinetic models, ∣e%∣≤5%. Some possible cases exhibiting high values of ∣e%∣, which can be higher than 10%, are put in evidence and discussed.
Abstract
In this research, thermogravimetry (TG/DTG) was used to determine the kinetic analysis of different coals and effect of cleaning process on kinetic parameters of raw and cleaned coal samples from Soma, Tuncbilek and Afsin Elbistan regions. Kinetic parameters of the samples were determined using Arrhenius and Coats and Redfern kinetic models and the results are discussed.
Abstract
Thermal decomposition of CoSO47H2O was investigated by simultaneous DTA-TG techniques and XRD method. Neural networks were used for DTA-TG curves analysis. Additionally, the network architecture (GRNN - Generalized Regression Neural Networks) and its statistical parameters were calculated. This method permits to generate DTA-TG curves without using kinetic models.
Abstract
Photodegradation of paracetamol in montmorillonite KSF suspension followed the Langmuir–Hinshelwood kinetic model. The influence of KSF dosage, initial paracetamol concentration, initial pH, chelating agents and a radical scavenger on the degradation of paracetamol were studied and described in detail. The degradation mechanism of paracetamol was also proposed in this work.
Abstract
The applicability of the kinetic analysis of data obtained by non-isothermal differential scanning calorimetry (DSC) is discussed. The Johnson-Mehl-Avrami (JMA) model was used for the computer simulation of DSC traces subsequently analysed by common methods of kinetic analysis of non-isothermal data. For the temperature-independent kinetic exponent n of the JMA equation, the kinetic analysis was shown to provide correct results, e.g. a correct kinetic model and apparent activation energy. On the other hand, for the temperature-dependent kinetic exponent, there is a great possibility of erroneous determination of the correct kinetic model and apparent activation energy, especially at higher heating rates. Since the temperature dependence of n cannot be determined on the basis of non-isothermal DSC experiments, conclusions must be drawn with appropriate caution.
