Endothermic peak presence

The thermal decomposition of hydrated rare earth oxalates, M2(Ox)3 nSLsO, has attracted considerable attention [397—400]. Wendlandt and his coworkers [397, 39S] have used both thermogravimetric (TGA) and differential thermal analysis (DTA) for studying the thermal decomposition of the rare earth, Th4+ and U4+ oxalates. The DTA curve for Eu2(Ox)3 IOH2O consists of three endothermic peaks centered at about 160°, 200° and 285° C respectively. The thermogravimetric analysis [397] shows the presence of unstable intermediate hydrates on going from the decahydrated to the anhydrous oxalate. The thermal decomposition of Eu2(Ox)3 IOH2O can be summarized as... 

It is obvious in Fig. 9 that one characteristic of the DTA curve of a powdery chemical of the quasi-AC type is the presence of the melting point [22]. Another characteristic of the DTA curve of a powdery chemical of this type is that the curve shifts successively from the endothermic peak caused by melting... 

The temperature of the first endothermic peak shifts from 420°C to 450°C for samples prepared in presence of 4 or higher mole numbers of H3BO3. This change was previously interpreted as due to an increase of framework boron content [9]. 

Figures 11-14 to 11-17 show the differential scanning calorimetry (DSC) thermograph of the acetone/ water solvent mixture with and without the presence of imipenem. The DSC curves indicate endothermic peaks which correspond to the phase transitions. The peaks around O C and —95°C represent the melting of the solid water and acetone phases, respectively. The peaks around — 19°C represent the melting of the solid clathrate phase (Rosso et al. 1975). The clathrate is a solid phase complex of 17 water molecules surrounding a single molecule of acetone, niLDOCllOrCO. In addition, the DSC thermograms indicate only slight temperature flucUiations for the endotherms with the addition of imipenem and the sodium bicarbonate. Therefore, the acetone/water binary phase behavior is not affected significantly by the addition of imipenem and sodium bicarbonate.

Differential scanning calorimetry analysis indicated the presence of a major endothermic peak around 0°C during heating (Figure 31.2a) in all the samples analyzed. Such a peak was primarily attributed to ice melting in the sample. The shape of the 0°C peak was quite symmetrical with the samples of low starch content (up to 10% s/w) produced by HP, T, or HP-T. At higher starch concentrations the 0°C endothermic peak maintained a symmetrical shape (although not Lorentian) with the gel-T while with the gel-HP and... 

DSC Thermograms of embryos and seeds equilabrated at various relative humidities (RH). Scanned from -125°C to 100°C at 10°C/min. Ice melting transitions were observed as endothermic peaks close to 0°C indicating the presence of freezable water. Differences in freezable-water content were observed at 88% RH between genot q)es. B Baer II O Ollagiie S. Sajama. 

A differential scanning calorimeter (DSC 1-B, Perkin-Elmer Corporation) was used to determine the extent of cure 10-mg to 20-mg specimens were tested at a scanning rate of 10°C/min. An exothermic peak on the thermograph indicates the heat of reaction whereas an endothermic peak in the amorphous polymer indicates the presence of residual stresses or the occurrence of a transition such as the glass transition. The presence of an exothermic peak in the DSC-scan of a pre-cured sample is an indication of incomplete curing. 

Thermogravimetry measures the weight change of a sample as a function of temperature. A total volatile content of the sample is obtained, but no information on the identity of the evolved gas is provided. The evolved gas must be identified by other methods, such as gas chromatography, Karl Fisher titration (specifically to measure water), TG-mass spectroscopy, or TG-infrared spectroscopy. The temperature of the volatilization and the presence of steps in the TG curve can provide information on how tightly water or solvent is held in the lattice. If the temperature of the TG volatilization is similar to an endothermic peak in the DSC, the DSC peak is likely due or partially due to volatilization. It is usually necessary to utilize multiple techniques to determine if more than one thermal event is responsible for a given DSC peak. 

In order to shed more light on the Interaction of water with these mucopolysaccharides, we employ the DSC method to follow the melting behavior of aqueous solutions of the polysaccharides cooled to -50 C. The polymers chosen here are chondroitin sulfate A (Chn S-A), chondroitin sulfate C (Chn S-C), chondroitin (Chn), heparin (Hpn), and hyaluronic acid (HyA). Their chemical structures are shown in Figure 1. The DSC curves allow us to determine the amount of the non-freezing water In highly concentrated solutions, since any endothermic peak Is not observed for such solutions over a wide temperature range (17. 18). This paper will also describe the presence of more than one endothermic peak In the DSC curves for solutions of relatively low polymer concentrations. 

Morita (144) also studied the DTA of several a- and jS-Iinked polygluco-sans, as well as rice starch. An interesting feature of this investigation was the study of the effect of moisture on the DTA curves obtained. This was illustrated by the study of rice starch stored in various types of atmospheres such as vacuum, 100% relative humidity water vapor, and so on. The presence of moisture altered the endothermic peak with a A7 in of 130°C, but not the 275 or 310°C peaks. The results suggest that the original 130°C peak is not entirely due to the loss of residual moisture and that the dehydration process is not completely reversible. 

Figure 1.2 illustrates, using the same sample, how the rate of cooling through Tg and storage at room temperature bring into evidence the presence of the enthalphy relaxation effect as a superposition on the heat flow curve shift. Figure 1.2 also shows the extent of the Tg(onset)-value differences due to the presence of these endothermic peaks. It will be clear that a standardised Tg-value determination procedure is necessary to obtain reproducible results ... 

The DTA and TG analysis showed similar curve profiles despite the amount of CIO" compounds in the feed, as illustrated in Figure 1. Both curves showed an endothermic peak below 100°C which is mostly due to the presence of adsorbed water and that was also detected in fresh mordenite. One can also see a peak at around 550°C in both DTA profiles which is probably due to the burning of a coke more hydrogenated located outside the pores. This process is accompanied by... 

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