Search Results

You are looking at 141 - 150 of 1,545 items for :

  • "activation energy" x
  • Chemistry and Chemical Engineering x
  • All content x
Clear All

Abstract  

Mechanical behaviour play an important role in the election of an epoxidic formulation of well determined properties as it has a marked influence on both structural and external factors. Temperature and time strongly act on polymers properties owing to their viscoelastic nature. Knowledge of the dynamic moduli and properties of polymeric materials is indispensable for the design of this materials. At the same time, the influence of the temperature on polymers behaviour may be studied once the activation energy is known. In this paper the different dynamic moduli and activation energy are measured using a Perkin Elmer DMA 7. The relationships between the dynamic mechanical properties and the molecular weight of the polymers make possible the calculation of the molecular weight. Results reasonably agree with literature values.

Restricted access

Abstract  

Strontium(II) bis (oxalato) strontium(II) trihydrate, Sr[Sr(C2O4)2]·3H2O and mercury(II) bis (oxalato) mercurate(II) hexahydrate, Hg[Hg(C2O4)2]·6H2O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA) in air showed SrCO3 was formed at ca. 500°C through the formation of transient intermediate of a mixture of SrCO3 and SrC2O4 around 455°C. Sharp phase transition from γ-SrCO3 to β-SrCO3 indicated by a distinct endothermic peak at 900°C in DTA. Mercury(II) bis (oxalato) mercurate(II) hexahydrate showed an inclined slope followed by surprisingly steep slope in TG at 178°C and finally 98.66% of weight loss at 300°C. The activation energies (E *) of the dehydration and decomposition steps have been calculated by Freeman and Carroll and Flynn and Wall's method and compared with the values found by DSC in nitrogen. A tentative reaction mechanism for the thermal decomposition of Sr[Sr(C2O4)2]·3H2O has been proposed.

Restricted access

Abstract  

The present paper contains theoretical analysis and a thorough discussion of the applicability of Fick’s approach to modelling CO2 and CH4 diffusion in heterogeneous coal, especially with regard to the estimation of a single diffusion coefficient from the dependence defined by a number series. The computations were performed for high rank coal depending on the grain size of coal samples and within a narrow range of temperature − 293 and 303 K. The results of the model’s application to the experimental data show that the method of estimation of the diffusion coefficient is very important. Our results also show that the diffusion coefficient changes are closely related with the one-parameter analysis of coal grain size distribution. It was shown that for the investigated grain size distribution the diffusion coefficient as expressed by Fick’s law may only be determined as a value which is directly proportional to the diffusion parameter. Hence, the estimation of D/r 2 is recommended.

Restricted access

Abstract  

In this short communication, a recent article published in the Journal of Thermal Analysis and Calorimetry, which presents an erroneous conclusion based on incorrect calculations, is critically discussed. Since the observations made in that report are based on part of the content of a publication of my authorship, trying to reject some expressions I presented, obviously it came to my attention. This brief note emphasizes that some of the arguments used and the main conclusion stressed in the manuscript under discussion are wrong and must be dismissed.

Restricted access

Abstract  

The LPTD-MS method, used to determine kinetic parameters in the thermal degradation of polymers by means of volatilization curves, was applied to TG data and the results were compared with those obtained by the methods of Flynn & Wall, Friedman, Freeman & Carroll, and Coast & Redfern.

Restricted access

Abstract  

In this research, non-isothermal kinetics and feasibility study of medium grade crude oil is studied in the presence of a limestone matrix. Experiments were performed at a heating rate of 10°C min−1, whereas the air flow rate was kept constant at 50 mL min−1 in the temperature range of 20 to 600°C (DSC) and 20 to 900°C (TG). In combustion with air, three distinct reaction regions were identified in all crude oil/limestone mixtures, known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). The activation energy values were in the order of 5–9 kJ mol−1 in LTO region and 189–229 kJ mol−1 in HTO region. It was concluded that the medium grade crude oil field was not feasible for a self-sustained combustion process.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: K. Chrissafis, K. Efthimiadis, E. Polychroniadis, and S. Chadjivasiliou

Abstract  

In this work we study the influence of Mo admixtures on the crystallization process of amorphous Fe78-xMoxSi9B13 (x=1, 2, 3 and 4) alloys by measurements of differential scanning calorimetry and on the soft ferromagnetic properties of the alloys by magnetic measurements. The addition of Mo by replacing Fe, results in magnetic hardening of materials. In DSC curves two peaks appear which are distinct when the concentration of Mo is 1 at.% and partly overlap when the Mo content is 2 at.%. Further increase in the Mo content leads to the appearance of just one peak. The activation energy was calculated both with Kissinger's and isoconversional Flynn, Wall and Ozawa methods.

Restricted access