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hydrated form of theophylline-7-acetic acid obtained by recrystallization from water. In particular this study is aimed towards the characterization of the new form as well as providing information on its physical stability and dehydration kinetics
/DTG curve were qualitatively described [ 2 – 4 ]. The dehydration kinetics of cemetitious materials were usually characterized by the modified Arrhenius equation [ 5 ], where the cemetitious materials were considered as pure substance. However, the
In the present study, the kinetic parameters of the thermal decomposition of ulexite were investigated by using TGA data. For the kinetic analysis, the Suzuki and Coats-Redfern methods were applied. It was determined that the process fits a first-order kinetic model, and the value of the activation energies and frequency factors decreased with decreasing particle size, which can be attributed to the increasing particle internal resistance to the escape of water as the grain size increases. The activation energy values were found to be 47.34–60.01 kJ mol−1 for region I and 0.225–1.796 kJ mol−1 for region II for the range of particle size fraction used. The frequency factors were calculated to be 9821.8−524.9 s−1 for region I and 3.05×10−44−2.807×10−5 for region II for the same conditions.
Abstract
Some peculiar properties of lithium sulfate monohydrate dehydration kinetics are investigated. Experiments were carried out under both isothermal and non-isothermal conditions on the bulk single crystals (
1 cm). Under both heating modes some new data were obtained. Uncommon high dehydration process rate under isothermal conditions and linear dependence of this rate under non-isothermal ones were discovered. Experiments over the water saturated porous ceramics drying and over the water vapors transmitting through the layer of preliminary dehydrated lithium sulfate were carried out. It is attempted to explain observed phenomena considering heat- and mass-transfer conditions.
Dehydratation kinetics of aquo-acido complex EDTA chelates CaML · nH2O (M= =Mn, Co, Ni, Cu, Zn, Cd, Ca,n=2 ... 5) were studied under non-isothermal conditions. The existence of two isokinetic temperatures (β 1=42°,β 2=216°) has been detected with a reliability of 95 %. The compensation effect found is explained by the change in the number of bonds formed in the sequence of equal-type dehydratation reactions of analogously built-up, but not isostructural compounds.
Abstract
The kinetic parameters of dehydration were determined under non-isothermal conditions for different polystyrenedivinylbenzene sulfonic acid type cationites (DVB) and their dependence on the degree of cross-linking granulation, porosity, specific surface, content of SO3M groups (M=Li, Na, K, Rb), nature of the alkali metal in partially neutralized -SO3H groups and heating rate was investigated.
The kinetics of thermal degradation of some cementitious calcium aluminates, sulfoaluminates, sulfoferrites and carboaluminates were studied. Activation energies, obtained by Morris and Rogers and Kissinger techniques, were found to be in good agreement with each other.
The thermal treatment of Fe2O3·1.65H2O gives rise to sharp dehydration weight-change waves (310–470 K and 470–670 K) which correspond to the loss of loosely-bound and stronglybound water, respectively. Analysis of the thermal waves was performed by the method of Šatava and Škvara (1969), the modified method of Coats and Redfern (1964) and the method of Blazejowski et al. (1983), and by applying a least squares straight line fit to the data. The A2 andA 3 decomposition mechanisms predominate in the first dehydration step, whereas anF 1 mechanism seems the best to describe dehydration of the structural water. Activation energies of 21 kJ · mol−1 and 95 kJ·mol−1 are estimated for the first and second steps, respectively.
Abstract
The kinetic parameters (reaction order, n, activation energy, E, pre-exponential factor, A, constant rate, k) for the dehydration step due to elimination of osmotic water and hydrogen-bounded water with the carboxylic groups, and for the anhydrifying step owing to the dehydration of two neighboring (-COOH) groups, were determined under non-isothermal conditions for some carboxylic resins with acrylic-divinylbenzene (DVB) matrix. The kinetic parameters were evaluated by means of isoconversional methods from (TG/DTG) thermal analysis data. The results show a dependence of the apparent kinetic parameters on the cross-linking degree, granulation, gel/macroporous matrix nature, exchange capacity and heating rate.
