Search Results
Thermal decomposition of methylxanthines
Interpretation of the results by PCA
Abstract
The thermal decomposition of theophylline, theobromine, caffeine, diprophylline and aminophylline were evaluated by calorimetrical, thermoanalytical and computational methods. Calorimetrical studies have been performed with aid of a heat flux Mettler Toledo DSC system. 10 mg samples were encapsulated in a 40 μL flat-bottomed aluminium pans. Measurements in the temperature range form 20 to 400°C were carried out at a heating rate of 10 and 20°C min−1 under an air stream. It has been established that the values of melting points, heat of transitions and enthalpy for methylxanthines under study varied with the increasing of heating rate. Thermoanalytical studies have been followed by using of a derivatograph. 50, 100 and 200 mg samples of the studied compounds were heated in a static air atmosphere at a heating rate of 3, 5, 10 and 15°C min−1 up to the final temperature of 800°C. By DTA, TG and DTG methods the influence of heating rate and sample size on thermal destruction of the studied methylxanthines has been determined. For chemometric evaluation of thermoanalytical results the principal component analysis (PCA) was applied. This method revealed that first of all the heating rate influences on the results of thermal decomposition. The most advantageous results can be obtained taking into account sample masses and heating rates located in the central part of the two-dimensional PCA graph. As a result, similar data could be obtained for 100 mg samples heated at 10°C·min−1 and for 200 mg samples heated at 5°C min−1.
Thermal decomposition of hydromagnesite
Effect of morphology on the kinetic parameters
for the synthesis of other magnesium-based materials [ 2 – 5 ]. Hydromagnesite is also a well-known bridging component in ancient magnesian lime mortars [ 6 ]. Thermal decomposition of hydromagnesite is usually associated with an endothermic break down
Abstract
Hydrated methanesulfonates Ln(CH3SO3)3 nH2O (Ln=La, Ce, Pr, Nd and Yb) and Zn(CH3SO3)2 nH2O were synthesized. The effect of atmosphere on thermal decomposition products of these methanesulfonates was investigated. Thermal decomposition products in air atmosphere of these compounds were characterized by infrared spectrometry, the content of metallic ion in thermal decomposition products were determined by complexometric titration. The results show that the thermal decomposition atmosphere has evident effect on decomposition products of hydrated La(III), Pr(III) and Nd(III) methanesulfonates, and no effect on that of hydrated Ce(III), Yb(III) and Zn(II) methanesulfonates.
Abstract
The thermal decomposition reactions of calcitic dolomite were investigated. Simultaneous TG/DTG/DTA were applied under non-isothermal conditions. From the recorded curves, the activation energies, pre-exponential factors and thermodynamic parameters of activation were calculated for the two thermal decomposition steps.
Abstract
The thermal decomposition of zirconium molybdate, tungstate and arsenate were investigated. The total mass losses of the investigated materials were 12.5, 11 and 8.5%, respectively. Despite having different crystal dimensions and structure the thermal decomposition of the samples takes place in a similar way. During heating two main endothermic processes with mass loss were observed. At the end of the thermal decomposition, oxides of the original materials were observed. The mentioned mass losses originate partly from the crystal water loss of the materials. The calculated crystal water content in the original molecule was 1.3 and 1 mole/molecule unit, respectively. Furthermore, for zirconium arsenate, a sublimation process was recorded above 960 K.
Barium(II) tetraphenylborate, Ba(Bph4))2·4H2O was prepared, and its decomposition mechanism was studied by means of TG and DTA. The products of thermal decomposition were examined by means of gas chromatography and chemical methods. A kinetic analysis of the first stage of thermal decomposition was made on the basis of TG and DTG curves and kinetic parameters were obtained from an analysis of the TG and DTG curves using integral and differential methods. The most probable kinetic function was suggested by comparison of kinetic parameters. A mathematical expression was derived for the kinetic compensation effect.
Abstract
The thermal decomposition of a series of compounds has been studied by thermogravimetry, mass spectrometry, nuclear magnetic resonance and elemental analysis. The combined use of mass spectrometry and thermogravimetry (MS and TG) in the analysis of these compounds has allowed characterization of the fragmentation pattern which was the objective of this research. The gaseous products, volatile condensed products and solid residues were identified by NMR and MS. Based on the product of thermal decomposition, the mechanism of thermal decomposition has been derived.
Abstract
Barium benzoate was synthesized in a hydrothermal reaction. The complex was characterized by elemental analysis, IR spectroscopy and X-ray powder diffraction. It was monoclinic and had a layered structure. The mechanism of thermal decomposition of the barium benzoate was studied by using TG, DTA, IR and gas chromatography-mass spectrometry. In a nitrogen atmosphere, the barium benzoate decomposed to form BaCO3 and organic compounds: mainly benzophenone, triphenylmethane, etc.
Abstract
Thermal decomposition of silver acetate was studied (TG, DSC, mass-spectrometry, X-ray analysis, electron microscopy). Non-isothermal thermogravimetric data (obtained at two different rates of linear heating) were used for kinetic studies. Kinetic parameters were calculated only for the chosen decomposition step.
Abstract
Mono- and binuclear rubidium-sodium halidothiocyanatobismuthates(III) have been prepared. Thermal, chemical and X-ray analyses were used to establish the thermal decomposition course of these complexes. The pyrolysis occurs in three stages connected with the mass loss and exothermic effects. The decomposition temperatures of the title salts are 190–210°C.
