Authors:M. Bernardi, S. Rojas, M. Andreeta, A. de Rastelli, A. Hernandes, and V. Bagnato
The structural and thermal properties of three different dental composite resins, Filtek™ Supreme XT, Filtek™ Z-250 and TPH®3 were investigated in this study. The internal structures of uncured and cured resins with blue light-emitting diodes (LEDs)
were examined by Micro-Raman spectroscopy. Thermal analysis techniques as DSC, TG and DTG methods were used to investigate
the temperature characteristics, as glass transition (Tg), degradation, and the thermal stability of the resins. The results showed that the TPH®3 and Filtek™ Supreme XT presented very similar Tg values, 48 and 50°C, respectively, while the Filtek™ Z-250 composite resin presented a higher one, 58°C. AFM microscope was
utilized in order to analyze the sample morphologies, which possess different fillers. The composed resin Filtek™ Z-250 has
a well interconnected more homogeneous morphology, suggesting a better degree of conversion correlated to the glass phase
transition temperature. The modes of vibration of interest in the resin were investigated using Raman spectroscopy. It was
possible to observe the bands representative for the C=C (∼1630 cm−1) and C=O(∼1700 cm−1) vibrations were studied with respect to their compositions and polymerization. It was observed that the Filtek™ Z -250 resin
presents the best result related to the thermal properties and polymerization after light curing among the other resins.
Authors:P. Melnikov, A. Guirardi, M. Secco, and E. Nogueira de Aguiar
Mechanisms of formation of polyphosphates MeIII(PO3)3, where MIII=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Fe, Ga, Al and Cr has been simulated by thermal analysis technique.
MeIII oxides and ammonium dibasic phosphate (NH4)2HPO4 were used as starting materials. For MIII=La-Lu, Y and Fe three main stages were observed: 1. elimination of water and ammonia leading to the formation of ammonium
tripolyphosphate (NH4)5P3O10; 2. reaction of the latter with Me2IIIO3 and formation of acidic polyphosphates MeIIIH2P3O10 or their isomers MeIII(PO3)3·H2O; 3. final loss of water and formation of MeIII(PO3)3. For MeIII=Sc and Ga the second stage is prolonged and the polyphosphates form at higher temperatures. Aluminum and chromium polyphosphates
are unstable. It is suggested that thermal behavior of the compounds is determined by MeIII ionic radii.
Temperature oscillation has been used in various applications of thermal analysis, such as relaxation, non-stoichiometry and
chemical reactions. However, there are common essential points in these applications, and these are discussed in this short
communication for further understanding significance of the temperature oscillation in thermal analysis.
Water freezing and supercooling were experimentally studied by methods of thermal analysis in a water droplet of 5 mm in diameter
depending on various temperatures and times of overheating and cooling rates. Degree of water supercooling was influenced
by previous thermal treatment but only to a certain extent. It increased slightly with overheating temperature and time and
decreased with cooling rate. Maximum found values of supercooling ranged between 12 and 13 K. Small degrees of supercooling
and their changes indicate that water freezing was more controlled by heterogeneous nucleation (properties of container contact
surface) than by previous thermal treatment and experimental conditions.
Thermal reactions of model phospho-silicate gels of simple composition has been studied. The investigations demonstrate that
the kind of compounds introducing P2O5 into the gel silicate network, H3PO4, PO(OC2H5)3, POCl3 influence the course and temperature and the xerogel formation. The amount of interstitial water and xerogel porosity is
dependent on the cations, amorphous structure modifiers (Ca, Na) used. Thermal analysis curves appear the convenient carriers
of informations about the processes in gel pores and the formation of xerogel and glass.
Authors:Veronika Vágvölgyi, M. Hales, W. Martens, J. Kristóf, Erzsébet Horváth, and R. Frost
The understanding of the thermal stability of zinc carbonates and the relative stability of hydrous carbonates including hydrozincite
and hydromagnesite is extremely important to the sequestration process for the removal of atmospheric CO2. The hydration-carbonation or hydration-and-carbonation reaction path in the ZnO-CO2-H2O system at ambient temperature and atmospheric CO2 is of environmental significance from the standpoint of carbon balance and the removal of green house gases from the atmosphere.
The dynamic thermal analysis of hydrozincite shows a 22.1% mass loss at 247°C. The controlled rate thermal analysis (CRTA)
pattern of hydrozincite shows dehydration at 38°C, some dehydroxylation at 170°C and dehydroxylation and decarbonation in
a long isothermal step at 190°C. The CRTA pattern of smithsonite shows a long isothermal decomposition with loss of CO2 at 226°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of zinc
carbonate minerals via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of
heat to the sample as a controlling parameter on the process of decomposition. The CRTA technology offers a mechanism for
the study of the thermal decomposition and relative stability of minerals such as hydrozincite and smithsonite.
A thermal analysis study on the reduction of iron oxide rich slags under different conditions is presented in this paper.
The effects of important process variables such as time, temperature, lime-silica ratio, FeO level in slag etc. are discussed.
It is shown that the mechanism of reduction by externally added graphite is different from that by a carbon saturated bath
although the activation energy values are similar.
The application of thermal analysis and other techniques to determine the thermal and mechanical history of an object is extended to investigate the method of manufacturing of ancient papers. The Humboldt Fragment number six of the Codex Huamantla and other Mexican papers are analyzed by means of Differential Scanning Calorimetry (DSC) and Thermogravimetry-Mass Spectroscopy (TG-MS). The results reveal mechanical treatment or beating of the raw material and also indicate, that the two cultures exchanged knowledge about the paper making. The simplicity and speed of thermoanalytical methods make them a good choice to screen samples for composition and origin. With the addition of more elaborate techniques, such as X-ray analysis, IR spectroscopy, evolved gas analysis by mass spectrometry and microscopy, a definitive classification can be reached easily.
Authors:J. Kaloustian, Paulette Lechene De La Porte, T. El-Moselhy, H. Lafont, and H. Portugal
Cholesterol constitutes the major component of most gallstones. It was identified and determined in gallstones by thermal analysis technique (DSC and TG-DTA), mainly by the use of the melting temperature (Tonset=145°C and Tmax=149°C) and by DTG peak decomposition (Tmax=364°C). Cholesterol anhydrous (ChA), which showed endothermic polymorphic peak, Tmax=40°C, without mass loss, was differentiated from cholesterol monohydrate (ChH), which showed a broad endothermic peak, Tmax=59°C, attributed to loss of water of crystallization (theoretical 4.45%). Morphological studies of gallstones were performed by optical microscopy and scanning electron microscopy (SEM). The stones consisted of a pigmented core with a variably-sized irregular central cavity, surrounded by a radially arranged deposits of plate-like ChH. The outer part of the stones showed ChA crystal arborescences. X-ray microanalysis gave a typical spectrum rich in C and O, and in some instances the presence of P, which was attributed to the presence of phospholipids. CaCO3 was easily characterized by TG with the use of DTG decomposition peak at 674°C.
The thermal decomposition of the polypropylene and liquid paraffin mixtures with inorganic additives was studied in dynamic
conditions. Thus, typical thermal analyses were carried out and thermal decomposition of samples in a specially designed apparatus
was also processed. One can observe for samples of sufficiently low mass that thermal analysis allows clear distinction of
samples that contain and do not contain liquid paraffin, respectively. Moreover, it is possible to separate two stages of
the decomposition process. The relationship between the logarithm of conversion degree and temperature (so called three-parameter
model) was used for the description of these processes. Relations between coefficients in three-parameter equation in micro-scale,
and characteristic temperatures of thermal decomposition in laboratory scale were observed in spite of meaningful differences
in the course of the processes.