Search Results
Abstract
The kinetics of the thermal decomposition of ammonium perchlorate at temperatures between 215 and 260°C is studied, in this work, by measuring the sample mass loss as a function of time applying the isothermal thermogravimetric method. From the maximum decomposition rate – temperature dependence two different decomposition stages, corresponding to two different structural phases of ammonium perchlorate, are identified. For the first region (215–235°C), corresponding to the orthorhombic phase, the mean value of the activation energy of 146.3 kJ mol–1, and the pre-exponential factor of 3.43⋅1014 min–1 are obtained, whereas for the second region (240–260°C), corresponding to the cubic phase, the mean value of the activation energy of153.3 kJ mol–1, and the pre-exponential factor of 4.11⋅1014 min–1 are obtained.
The kinetic expression commonly used in the thermal analysis of oil shale pyrolysis was derived on the basis of a simple first order kinetic equation of kerogen decomposition. The activation energy, as well as the reaction rate constant of oil shale pyrolysis could be determined by using non-isothermal (NI) or isothermal (I) TG. However, the kinetic parameters determined by using either NI or I did not enable the good prediction of the kerogen conversion at other conditions.
Abstract
The reactions between silicon nitride and carbon take place in two stages, the surface silica of silicon nitride powders reacts with carbon first followed by the decomposition of silicon nitride and the residual silicon reacting with carbon. The kinetics of the two stage reactions has been studied by isothermal thermogravimetric analysis. Physico-geometric models for both of the reaction stages have been proposed, and the kinetic parameters have been calculated. The implications of the kinetic models and parameters are discussed.
Summary Due to the criticism of the non-isothermal kinetic at a single heating rate, in the last period, data obtained at different heating rates are processed by means of elevated methods like Friedman’s (FD) differential-isoconversional method or the one suggested by Budrugeac and Segal (BS). The non-parametric kinetics (NPK) method, suggested by Serra, Nomen and Sempere offers two major advantages: the possibility of separation of two or more steps of a complex decomposition reaction; and the possibility of discrimination between the conversion, with regard to the temperature functions of a rate equation. Comparative data of FD, BS and modified version of NPK method are presented for decomposition of three compounds used as polyisocyanate stabilizer.
Some transition metal nitrate complexes with hexamethylenetetramine
Part LV. Preparation, X-ray crystallography and thermal decomposition
Abstract
Three hexamethylenetetramine (HMTA) metal nitrate complexes such as [M(H2O)4(H2O-HMTA)2](NO3)·4H2O (where M=Co, Ni and Zn) have been prepared and characterized by X-ray crystallography. Their thermal decomposition have been studied by using dynamic, isothermal thermogravimery (TG) and differential thermal analysis (DTA). Kinetics of thermal decomposition was undertaken by applying model-fitting as well as isoconversional methods. The possible pathways of thermolysis have also been proposed. Ignition delay measurements have been carried out to investigate the response of these complexes under condition of rapid heating.
Abstract
The curing of a thermoreactive alkyd-melamine-formaldehyde resin system was investigated by rheologycal, TG and TMA-analysis, in order to construct the time-temperature-transformation diagram. The points of the gelation curve were determined by measuring the increase in viscosity during isothermal curing at different temperatures. A power-function could be fitted to the gelation curve, which is suitable to estimate gelation at any curing conditions, as well as to establish storage conditions. The reaction in the resin matrix was followed by monitoring the loss of mass during isothermal curing at different temperatures. The final section of the resulted iso-curing temperature (iso-T cure) diagrams could be fitted with logarithmic functions, which may be used for estimating the conditions needed to a given, desirable mass loss, i.e. conversion. The steepness of the curves increases with temperature suggesting the forthcoming of degradation during cure with increasing temperature. From these data the iso-mass loss curves of the TTT-diagram were constructed. For determining the iso-Tg curves of the TTT-diagram isothermal curing was carried out in a drying oven at different temperatures, followed by TMA measurements. The iso-Tcure diagrams served to determine T g , and to construct the iso-T g curves of the TTT diagram. Vitrification curve is far beyond conditions of storage, curing and degradation, meaning that the resin matrix is in rubbery physical state before, during and after the cure. Curing conditions resulting degradation can also be estimated from the TTT-diagram.
earlier study, we report here, the preparation, characterization, and thermolysis of transition metal perchlorate complexes with 1,6-diaminohexane ligand. Kinetics of thermolysis has been evaluated using isothermal TG by model-fitting and isoconversional
at a certain temperature, and the heat transfer in the IL is slow thus the temperature lags behind. With these, long-term isothermal TG has become the preferred method to observe and model the decomposition kinetics of ILs [ 14 , 15 ]. Most
