Authors:S. Jingyan, L. Jie, D. Yun, H. Ling, Y. Xi, W. Zhiyong, L. Yuwen, and W. Cunxin
The thermal behavior of nicotinic acid under inert conditions was investigated by TG, FTIR and TG/DSC-FTIR. The results of
TG/DSC-FTIR and FTIR indicated that the thermal behavior of nicotinic acid can be divided into four stages: a solid-solid
phase transition (176–198°C), the process of sublimation (198–232°C), melting (232–263°C) and evaporation (263–325°C) when
experiment was performed at the heating rate of 20 K min−1. The thermal analysis kinetic calculation of the second stage (sublimation) and the fourth stage (evaporation) were carried
out respectively. Heating rates of 1, 1.5, 2 and 3 K min−1 were used to determine the sublimation kinetics.
The apparent activation energy, pre-exponential factor and the most probable model function were obtained by using the master
plots method. The results indicated that sublimation process can be described by one-dimensional phase boundary reaction,
g(α)=α. And the ‘kinetic triplet’ of evaporation process was also given at higher heating rates of 15, 20, 25, 30 and 35 K min−1. Evaporation process can be described by model of nucleation and nucleus growing,
Authors:D Apreutesei, G Lisa, N Hurduc, and D Scutaru
into account the importance of thermal stability in the liquid crystals field,
the study presents thermal behavior of some cholesteric esters, which differ
by the nature of the functional group attached to the cholesteryl unit and
the connecting position of the nitro or amino functions to the aromatic ring.
The cholesteric esters present liquid crystalline properties, with high melting
and clearing points and may be used as intermediates in the synthesis of liquid
crystals. Some other kinetic characteristics, such as reaction order (n), activation energy (Ea)
and pre-exponential factor (lnA) have been
also evaluated. The type of functional units adjacent to the aromatic unit
determines thermal stability of the cholesteryl compounds. Groups with a powerful
withdrawing effect induce a decreasing of the temperatures at which the material
starts to lose mass. An increased thermal stability for the amino esters has
been observed, probably because of some intermolecular hydrogen bonds formation.
The thermal behaviour of the intercalation complex of a dickite from Tarifa, Spain, with dimethylsulfoxide was studied by
high-temperature X-ray diffraction, differential thermal analysis and thermogravimetry, and attenuated total reflectance infrared
spectroscopy. The ATR-FTIR study indicated that the heating between room temperature and 75C produced the elimination of
adsorbed molecules. Above this temperature the elimination of intercalated molecules occurs through several stages. Loss of
6.5% of the intercalated DMSO first causes a slight contraction of the basal spacing at 90şC due to a rearrangement of the
DMSO molecules in the interlayers positions. This contraction is followed by the formation of a single layer complex and the
restoring of the dickite structure, at 300C, when the loss of intercalated species have been completed.
Authors:Yuehua Song, Shupin Xia, Haidong Wang, and Shiyang Gao
The thermal behavior of synthetic schoenite (K2SO4·MgSO4·6H2)) during heating has been studied by thermal methods. The temperatures of dehydration and decomposition of schoenite have
also been determined by DTA, TG and DSC. The thermal reaction equations and the X-ray power diffraction results of the products
have been given and the corresponding kinetic parameters have also been obtained.
The thermal behaviour of H4SiW12O4024.8H2O (SiW12) was investigated by using DTA, TG and FTIR. Endothermic effects were observed at 40, 98 and 217C, corresponding to the
fusion of SiW12 in its own crystallization water, boiling of the solution and decomposition of the remaining tetrahydrate into anhydrous
SiW12, respectively. The mass of the sample remained constant on heating from about 250 to 400C. Subsequently, it slowly decreased
and reached a constant value at about 500C. At 526C a DTA peak appeared. There was an abrupt change in the FTIR spectrum
of the sample heated to 550C. The typical spectrum of the Keggin unit vanished and new bands at 807.5 and 1030 cm−1 indicated the presence of free WO3 and SiO2, respectively.
The topic of the present work is to study the thermal behavior of phenitoine and pharmaceuticals by means of kinetic parameters
determined in non-isothermal conditions.
The TG/DTG data were obtained at four heating rates. These data were processed by the following methods: Friedman (FR), Budrugeac-Segal
(BS) and the modified non-parametric kinetics (Sempere-Nomen).
The main conclusions of the kinetic study are
The FR method is versatile, but the values of the kinetic parameters are not certain, especially by multistep processes.
The BS method offer a non-variant part of the activation energy, but the kinetic description is only formal.
The NPK method is able to discriminate between two or more steps of a complex process. In our case, there are a preponderant
process (more than 70% of the explained variance).
By the NPK method there is a non-speculative separation of the temperature, respective conversion degree dependence of the
Authors:Fillipe V. Rocha, Carolina V. Barra, Silmar J. S. Franchi, Adelino V. G. Netto, Antonio E. Mauro, and Regina C. G. Frem
-thiocarbamoyl-3,5-dimethylpyrazole). However, systematic studies on the thermal decomposition of this class of compounds have not been described yet in the literature.
In pursing our interest on thermalbehavior [ 11 – 16 ], structural aspects [ 17 – 19
Authors:F. Giordano, A. Rossi, R. Bettini, A. Savioli, A. Gazzaniga, and Cs. Novák
The thermal behavior of binary mixtures of paracetamol and a polymeric excipient (microcrystalline cellulose, hydroxypropylmethylcellulose
and cross-linked poly(vinylpyrrolidone)) was investigated. The physical mixtures, ranging from 50 to 90% by mass of drug,
were submitted to a heating-cooling-heating program in the 35–180C temperature range. Solid-state analysis was performed
by means of differential scanning calorimetry (DSC), hot stage microscopy (HSM), micro-Fourier transformed infrared spectroscopy
(MFTIR), and scanning electron microscopy (SEM).
The polymeric excipients were found to address in a reproducible manner the recrystallization of molten paracetamol within
the binary mixture into Form II or Form III. The degree of crystallinity of paracetamol in the binary mixtures, evaluated
from fusion enthalpies during the first and second heating scans, was influenced by the composition of the mixture, the nature
of the excipient and the thermal history. In particular, DSC on mixtures with cross-linked poly(vinylpyrrolidone) and hydroxypropylmethylcellulose
with drug contents below 65 and75%, respectively, evidenced the presence only of amorphous paracetamol after the cooling phase.
Microcrystalline cellulose was very effective in directing the recrystallization of molten paracetamol as Form II.
Authors:K. Gjurova, Chr Bechev, K. Troev, and G. Borisov
By means of a combined thermal analysis technique, the thermal behaviour of rigid polyurethane foams containing additive antipyrenes was studied. The presence of phosphorus- and phosphorus/chlorine-containing antipyrenes based on phosphate and phosphonate and a combination of them led to decreases in the rates of heat and weight loss during heating. More steps of decomposition were formed and the interval of decomposition was widened and shifted to higher temperatures. Some thermal characteristics make it possible to predict the optimum antipyrene compositions and concentrations with minimum time, labour and material consumption under laboratory conditions.
Authors:Hongyan Wang, Chunshan Li, Zhijian Peng, and Suojiang Zhang
. Magaraphan et al. [ 6 ] studied the preparation, structure, properties, and thermalbehavior of rigid-rod polyimide/montmorillonite nanocomposites. Castelein et al. [ 7 ] focused on the influence of heating rate on the thermalbehavior and mullite formation