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A number of 1145 sets of kinetic parameters derived in our earlier papers from TG curves have been worked up. The apparent activation energy and pre-exponential factor values have been found to obey a linear compensation law (isokinetic relation) if the thermal decomposition begins in the same temperature interval, irrespective of the nature of the chemical reaction. The isokinetic temperatureT i has been found to be very close to the mean value of the temperaturesT 0.1 at which the conversion becomes equal to 0.1 and atT i the rate constant has been found to be approximately equal to 10−3s−1 in allT 0.1 intervals investigated. It is concluded that the kinetic compensation effect observed in heterogeneous non isothermal TG kinetics is not a true one.
Abstract
The main component of an emulsion explosive is a water-in-oil emulsion consisting of a supersaturated ammonium nitrate (AN) water phase, finely dispersed in an oil phase. Quantitative determination of nearly all the components in a W/O emulsion is possible using thermogravimetry (TG) and differential scanning calorimetry (DSC). Isothermal TG measurements enable determination of water content, while cycled DSC measurements allow the amount of ammonium nitrate to be determined. In the case that sodium nitrate (SN) is also added to AN as an oxidizing agent, it is necessary to quantitatively separate both salts from organic matter with diethyl ether. On the basis of the TG curve of the precipitated salts, the amount of AN can then be calculated, and that of SN is obtained from TG measurement of the original sample.
Abstract
Pyrolysis of petroleum refinery sludge has received global acclamation as a clean conversion technique for providing solution of sludge disposal as well as efficient resource utilization. This communication reports the kinetics study of pyrolysis of petroleum refinery sludge. Experiments were carried out by means of thermogravimetric analysis at different heating rates of 5, 10 and 20�C min−1. The pyrolytic reaction is significant in the temperature range of 200–350�C and analysis and evaluation of kinetic parameters is done in the 100–500�C region of non-isothermal TG curves obtained in nitrogen atmosphere. The activation energy is calculated by iso-conversional method, then other kinetic parameters are determined by considering single reaction and two reaction global kinetic model. Two-reaction model is found to fit satisfactorily the experimental results.
Abstract
The thermal transformations of muscovite flakes are a key point in many applications because besides dehydroxylation a significant exfoliation process occurs. Dehydroxylation kinetic is experimented by isothermal TG analyses in the 700–850°C temperature range and described with the Avrami theory. Hydroxyl condensation predominates at the onset of the process, but water diffusion is the most important process when the transformed fraction is high. The progressive transition between the two transformation stages contrast with the more accentuated transition for a ground muscovite. The activation energy varies weakly (190–214 kJ mol−1) in the whole transformation process that supports the co-existence of hydroxyl condensation and diffusion phenomena. Dehydroxylation kinetic increases strongly with temperature and decreases with the reaction advancement. Exfoliation is correlated with dehydroxylation kinetic and occurs in a narrow transformation and temperature ranges. An in-situ combination process of hydroxyls occurs and water vapor favors the layer expansion.
Abstract
Stability of drugs and products has a great practical interest, which is facing to strict regulation. Thermal studies, besides the determination of the thermal properties of the investigated product allow the verification of possible interactions between the drug substances and excipients. The objective of this work was to obtain solid pre-formulates of paracetamol (PC) by spray drying (SPDR), as well as to investigate their thermal behavior. Dynamic and isotherm TG, conventional DSC and DSC-photovisual coupled methods were used to characterize the conventional and pre-formulated mixtures obtained by SPDR. The results of both DSC investigations showed slight alterations in melting temperatures, which suggests incompatibilities. The TG decomposition data of the mixtures evidenced that the dry process via SPDR leads to stability enhancement of the pre-formulated mixtures.
Alumina samples were produced by the thermal decomposition of hydrates of aluminium sulphate, nitrate and chloride. The kinetics of the chlorination were studied by means of isothermal TG measurements, using COCl2 as chlorinating agent. Apparent activation energies were determined in the temperature ranges where the reaction was controlled by chemical processes. The reaction rates related to unit surface area were similar for all the samples, and the isothermal TG curves could be described by the models of contracting cylinders and spheres.
Abstract
Isothermal decomposition kinetic of three lanthanide mixed complexes with the general formula of Ln(thd)3phen (where Ln=Nd3+, Sm3+ or Er3+, thd=2,2,6,6-tetramethyl-3,5-heptanodione and phen=1,10-phenanthroline) has been studied in this work. The powders were characterized by their melting point, elemental analysis, FTIR spectroscopy and thermogravimetry. The isothermal TG curves have been recorded under the same conditions at 265–285, 265–285 and 250–270°C for Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen, respectively. The kinetic parameters, i.e. activation energy, reaction order and frequency factor were obtained through the technique of lineal regression using the relation g(α)=kt+g 0. The analysis was done at decomposed fractions between 0.10–0.90. The values of activation energy were: 114.10, 114.24 and 115.04 kJ mol–1 for the Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen complexes, respectively. The kinetic models that best described the isothermal decomposition reaction the complexes were R1 and R2. The values of activation energy suggests the following decreasing order of stability: Nd(thd)3phen<Sm(thd)3phen<Er(thd)3phen.
Abstract
Abstract
The thermal behaviour of three aromatic polymers, poly(3,3-dioxy-4,4-diphenylmethane) (POA), poly(2,2-m-phenylene-5,5-dibenzoxazolemethane) (PBO) and a commercial poly-(phenyleneisophthalamide) (Phenylon) was studied by thermal analysis, i.e. DSC and TG. PBO was formed by the progressive thermocyclization of POA. By transforming POA into PBO the thermal stability was increased proportionally to the degree of cyclization, due to the stiffening of the polymer chain. PBO was found to be more thermally stable than Phenylon. The activation energies of the desorption of moisture, cyclization and thermal degradation of the polymers in both nitrogen and air were determined from non-isothermal TG data.
Through a combination of X-ray diffraction and thermal analysis (simultaneous TG-DTG-DTA and quasi-isothermal TG), it was shown that the molar ratio intercalation agent/kaolinite in all intercalation compounds is approximately 1. In a saturated atmosphere of the corresponding intercalation agent, the intercalation compounds are stable up to more than 150 °C.
