Authors:Fabiana Felix, L. Cides da Silva, L. Angnes, and J. Matos
The thermal decomposition of salbutamol (β2 — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry
(TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by
the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy
was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage
of the thermal decomposition process. For isothermal experiments the average values were Eact=130 kJ mol−1 (for standard sample) and Eact=252 kJ mol−1 (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min−1). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min−1). The calculated values were Eact=134 kJ mol−1 (for standard sample) and Eact=139 kJ mol−1 (for pharmaceutical sample).
Authors:H.-S. Kim, H.-S. Yang, H.-J. Kim, and H.-J. Park
The thermal degradation and thermal stability of rice husk flour (RHF) filled polypropylene (PP) and high-density polyethylene
(HDPE) composites in a nitrogen atmosphere were studied using thermogravimetric analysis. The thermal stability of pure PP
and HDPE was found to be higher than that of wood flour (WF) and RHF. As the content of RHF increased, the thermal stability
of the composites decreased and the ash content increased. The activation energy of the RHF filled PP composites increased
slowly in the initial stage until α=0.3 (30% of thermal degradation region) and thereafter remained almost constant, whereas
that of the RHF filled HDPE composites decreased at between 30 and 40 mass% of RHF content. The activation energy of the composites
was found to depend on the dispersion and interfacial adhesion of RHF in the PP and HDPE matrix polymers.
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.
Authors:Lunyu Qu, Ronghua Ma, Yaguang Chen, Yu Chen, and Chuntao Liu
The thermal properties of four heteropoly complexes α-K3H3[SiW11Ni(H2O)O39]·11.5H2O (I), α-K3H2[SiW11Fe(H2O)O39]·9H2O (II), α-[(C4H9)4N]3.5H1.5[SiW11Fe(H2O)O39]·4.5H2O (III) and α-[(C4H9)4N]3.5H2.5[SiW11Cu(H2O)O39]·6H2O (IV) were studied by means of TG, DTA and DSC. The activation energy and reaction order of the thermal decomposition reaction
of these complexes have been calculated.
A theoretical approach has been used to show that, except for certain types of reaction mechanism, the ease with which it
is possible to distinguish the form of the reaction mechanism by the reduced-time plot method depends particularly on the
rate of transfer of heat into the sample. The original reduced-time plots  were calculated from model equatioons which
assume that the sample is, from the outset, at a fixed temperature and remains under isothermal conditions throughout the
reaction. The variations produced in the appearance of reduced-time plots when the sample is programmed to rise to a given
fixed temperature through various temperature schedules have been investigated. It is shown that even relatively rapid temperature
rises can produce distortion of the reduced-time plots for various reaction equations. If the reaction mechanism is known,
however, fairly accurate values of the activation energy for the reaction can be determined, even when the furnace used has
relatively poor heat-transfer characteristics.
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.
Thermal analysis increasingly being used to obtain kinetic data relating to sample decomposition. This work involves a comparative study of several methods used to analyse DSC and TG/DTG data obtained on the oxidation of Beypazari lignite. A general computer program was developed and the methods are compared with regard to their accuracy and the ease of interpretation of the kinetics of thermal decomposition. For this study, the ratio method was regarded as the preferred method, because it permits the estimation of reaction order, activation energy and Arrhenius constant simultaneously from a single experiment.
Authors:A. d’Almeida, D. Barreto, V. Calado, and J. d’Almeida
The thermal behavior of four unusual lignocellulose fibers — namely Caroa, Curaua, Piassava and Sponge gourd — is described.
Caroa and Curaua fibers showed a more homogeneous thermal degradation, with a single peak dominating in the DTG curve. Piassava
and Sponge gourd showed two separated peaks, revealing the more pronounced amounts of hemicellulose present at these fibers.
All four fibers are, however, thermally stable up to temperatures of around 200°C. The activation energies for the thermal
degradation of the fibers were similar, except for the Caroa fiber. The lower activation energy associated to this fiber was
attributed to its higher hemicellulose to cellulose ratio.
Authors:I. Kohsari, S. Pourmortazavi, and S. Hajimirsadeghi
Data on the thermal stability of organic materials such as diaminofurazan (DAF) and diaminoglyoxime (DAG) was required in
order to obtain safety information for handling, storage and use. These compounds have been shown to be a useful intermediate
for the preparation of energetic compounds. In the present study, the thermal stability of the DAF and DAG was determined
by differential scanning calorimetery (DSC) and simultaneous thermogravimetery-differential thermal analysis (TG-DTA) techniques.
The results of TG analysis revealed that the main thermal degradation for the DAF and DAG occurs in the temperature ranges
of 230–275°C and 180–230°C, respectively. On the other hand, the TG-DTA analysis of compounds indicates that DAF melts (at
about 182°C) before it decomposes. However, the thermal decomposition of the DAG started simultaneously with its melting.
The influence of the heating rate (5, 10, 15 and 20°C min−1) on the DSC behaviour of the compounds was verified. The results showed that, as the heating rate was increased, decomposition
temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor
for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E698 and Ozawa. Based on the
values of activation energy obtained by ASTM and Ozawa methods, the following order in the thermal stability was noticed:
Vitreous solder glasses, such as Mansol #40 and FEG-2002, are commercialized solder glasses, which are compression sealing
glasses that can be used to solder materials with expansions between 55-68⊙10-7C-1, such as Al2O3.
In order to understand and tailor the thermal behaviour of solder glasses, cylindrical-like glasses were first carefully ground
with a stainless steel mortar and pestle. Initially, no exothermic or endothermic data were obtained from the DTA/DSC curves
except those relating to melting. However, exothermic peaks appeared after the glass samples were re-melted. In this work,
kinetic parameters such as the activation energy, and the morphology of the devitrification mechanisms for two kinds of solder
glasses were also investigated, using non-isothermal DTA techniques. The activation energies ranged from 220 to 235 kJ mol-1 and the devitrification mechanism parameters were close to 1. This indicates that the devitrification mechanisms of the two
kinds of solder glasses involve surface nuclei.