Search Results
Abstract
Conventional thermogravimetric analysis (TG) uses constant heating rates to determine decomposition rates of a material and compositional analysis. Often, the decomposition steps can not be separated clearly enough due to parallel or consecutive reactions. If the reaction rates and the respective activation energies are enough different the TG resolution can be much enhanced by lowering the heating rate during the decomposition steps. The automated discrete adjustment of the heating rate is controlled by a set of parameters, such as threshold values, waiting times and rate factors. This technique, called MaxRes, allows for faster compositional analysis without loss of resolution. The same technique is also applicable to thermomechanical analysis (TMA) if time/temperature dependent events such as softening are to be separated.
Abstract
Thermogravimetric analyses of thermal decomposition (pyrolysis, thermal dissociation and combustion) of 9 different samples were carried out in dynamic conditions at different heating rates. The kinetic parameters (E, A and k m) of thermal decomposition were determined and interrelations between the parameters and heating rate q were analyzed. There were also relations between Arrhenius and Eyring equations analyzed for thermal decomposition of solid phase. It was concluded that Eyring theory is an element, which interconnects used thermokinetic equations containing Arrhenius law and suggests considering kinetic quantities in way relative to 3 kinetic constants (E, A and k m). Analysis of quantities other than km (i.e. E, A, Δ+ H, Δ+ S) in relation to heating rate is an incomplete method and does not lead to unambiguous conclusions. It was ascertained that in ideal case, assuming constant values of kinetic parameters (E and A) towards heating rate and satisfying both Kissinger equations, reaction rate constant k m should take on values intermediate between constants (k m)1 and (k m)2 determined from these equations. Whereas behavior of parameters E and A towards q were not subjected to any rule, then plotting relation k m vs. q in the background of (k m)1 and (k m)2 made possible classification of differences between thermal decomposition processes taking place in oxidizing and oxygen-free atmosphere.
Abstract
Crystallization kinetics of Al91La5Ni4 amorphous ribbons produced by a melt-spinning method were studied by DSC analysis and X-ray diffraction. The effect of heating rate (from 4 to 200C min-1) was investigated in the temperature range from 298 to 700 K. Increases the heating rate from 4 to 200C min-1 resulted in increases of the temperature difference between the two stages of the transformation process: crystallization of Al and crystallization of the Al compounds from 148.9 to 167.4 K. The apparent activation energies for the first step, related to Al crystallization, and to the second step related to crystallization of Al4La and Al3Ni, were found to be 1619 and 19910 kJ mol-1, respectively. The results indicate the possibility of tailoring the heating treatment to produce the required fraction of the amorphous phase.
. Typically thermogravimetric (TG) analysis or hot-stage microscopy (HSM) are employed in tandem with DSC analysis since all can record data with linear heating rates. However, much progress in interpretation of DSC data can be made simply by recording data
revealed here by TG/DTG and DSC methods. In addition, the influence of heating rate and atmosphere on the thermal behavior of cefuroxime lysine was investigated here. Moreover, the kinetic parameters for chemical decomposition were calculated by using the
sizes of sewage sludge and three heating rates were employed to study the pyrolysis process. And a new method is employed to compute the pyrolysis kinetics parameters based on the TG curves. Experimental section
this area. For example, in 1995, Seetarama [ 12 ] tried to study the existing diffusion reactions in MoSi 2 propagation synthesis and the effect of heating rate on the mechanism of the performance of this process by the thermal analysis test. In a
the point of separation between two mass loss stages. The model was verified to be suitable for the mass loss processes of variable wood and leaf samples under relatively lower heating rates (mostly 10 K min −1 ). In the subsequent researches by other
evaluating the solid state kinetic parameters [ 1 , 2 ]. The evaluation of the kinetic parameters has often been done by using a single thermogravimetric curve (TG curve) recorded at a certain heating rate. Some recent results on thermal and thermo
Abstract
This research was aimed to investigate the combustion and kinetics of oil shale samples (Mengen and Himmetoğlu) by differential scanning calorimetry (DSC). Experiments were performed in air atmosphere up to 600�C at five different heating rates. The DSC curves clearly demonstrate distinct reaction regions in the oil shale samples studied. Reaction intervals, peak and burn-out temperatures of the oil shale samples are also determined. Arrhenius kinetic method was used to analyze the DSC data and it was observed that the activation energies of the samples are varied in the range of 22.4–127.3 kJ mol−1 depending on the oil shale type and heating rate.
