Thermogram, differential thermal

In differential thermal analysis, the starch is intimately mixed with a thermally inert materiaP such as calcined kaolin or alumina the mixture is heated at a uniform rate, and the temperature of the mixture is compared with that of a sample of the pure, inert material heated in the identical manner. Any exothermic or endothermic reaction in the starch causes a positive or negative temperature-difference between the two samples this can be recorded, and appears as a positive or negative peak on the resultant thermogram. Differential thermal analysis can be conducted in different atmospheres, such as air, oxygen, or nitrogen, or under vacuum. 

All heat evolutions which occur simultaneously, in a similar manner, in both twin calorimetric elements connected differentially, are evidently not recorded. This particularity of twin or differential systems is particularly useful to eliminate, at least partially, from the thermograms, secondary thermal phenomena which would otherwise complicate the analysis of the calorimetric data. The introduction of a dose of gas into a single adsorption cell, containing no adsorbent, appears, for instance, on the calorimetric record as a sharp peak because it is not possible to preheat the gas at the exact temperature of the calorimeter. However, when the dose of gas is introduced simultaneously in both adsorption cells, containing no adsorbent, the corresponding calorimetric curve is considerably reduced. Its area (0.5-3 mm2, at 200°C) is then much smaller than the area of most thermograms of adsorption ( 300 mm2), and no correction for the gas-temperature effect is usually needed (65). 

Differential thermal analysis proved to be a powerful tool in the study of compound polymorphism, and in the characterization of solvate species of drug compounds. In addition, it can be used to deduce the ability of polymorphs to thermally interconvert, thus establishing the system to be monotropic or enantiotropic in nature. For instance, form I of chloroquine diphosphate melts at 216°C, while form II melts at 196°C [18]. The DTA thermogram of form I consists of a simple endotherm, while the thermogram of form II is complicated (see Fig. 4). The first endotherm at 196°C is associated with the melting of form II, but this is immediately followed by an exotherm corresponding to the crystallization of form I. This species is then observed to melt at 216°C, establishing it as the thermodynamically more stable form at the elevated temperature. 

Thermograviraetric Analysis and Differential Thermal Analysis Thermograms of Dobutamine Hydrochloride... 

The thermal properties of benzoic acid were evaluated using simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA). This work was performed on a Shimadzu DT-30 Thermal Analyzer system, which was calibrated using indium standard. Using a heating rate of 10°C/min, the thermograms presented in Figure 3 were obtained. 

Figure 3. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) thermograms of benzoic acid.

Figure 6.6 Thermogram of HMX-fS using differential thermal analysis and thermogravimetric analysis...

Figure 10. Records of differential thermal analyses of Martinsburg anthraxolite under limited oxidizing conditions. Solid and dotted traces are heating and cooling records of same samples heated in partial vacuum. Broken trace is thermogram of sample heated in nitrogen-enriched...

Differential thermal analysis (DTA) thermograms of ( )-etodolac sodium salt exhibited endothermic transitions around 80,120, and 297°C and an exothermic transition around 83°C [12]. The exothermic phase change was observed after exposure of the sample to moisture, indicating conversion of the amorphous form of ( )-etodolac sodium salt to a crystalline phase. In contrast, the thermogram of (+)-etodolac sodium salt, after exposure to moisture, showed endotherms at 60, 80, 120, and 297°C, indicating that the salt contained methanol, acetonitrile, and water. There was no sign of degradation product formation. 

Fig. 10 shows the thermograms of cellulose in atmospheres of helium and of oxygen, obtained by Tang and Neill. In the helium atmosphere, there is an endothermic dip in the differential thermal analysis curve and a sharp loss of weight in the thermogravimetric analysis curve beginning at about 300°, which denote the pyrolytic reactions. In the oxygen atmosphere, instead of the endothermic dip, there is an exotherm due to oxidation of the pyrolysis products. 

Fig. 10. —Thermograms of Cellulose. [(A) Thermogravimetric analysis in helium (B) differential thermal analysis in oxygen (C) difiFerential thermal analysis in nitrogen.]...

The DTA (differential thermal analysis) thermograms of diosgenin were obtained on a Shimadzu DT-30 Thermal Analyser. Hie heating rate was 10°C/min. The thermograms are presented in Figure 1. 

The differential thermal analysis (DSC) behavior of indapamide is shown in Figure 10 (20). The thermogram was obtained using a Perkin Elmer Series 7 DSC scanning from 40°C to 220°C at 10°C/minute. A primary endotherm corresponding to melting is observed at a peak onset temperature of 165°C. 

The differential calorimetric curves (DSC) of the various crystalline forms of triamterene grown from organic solutions containing water and from absolute organic solutions, and the DSC curves of triamterene crystals dried under reduced pressure have been described. The differential thermal analysis-thermogravimetry analysis (DTA-TG) thermograms are also given. 

A differential thermal analysis of the Lilly Working Standard was performed using a DuPont 900 Differential Thermal Analyzer at a heating rate of 20°C. per min. with a nitrogen atmosphere8. The thermogram shows an endotherm at approximately 241°C. indicating decomposition. 

The constitnents of binary phenol mixtnres can be identihed by differential thermal analysis of a sample to which any of the aroyl chlorides 184-186 has been added. The thermogram is compared with a bank of differential thermograms of phenols, binary phenol mixtures and binary phenol derivatives. Most snch systems show weU-resolved endotherms corresponding to the melting points of the phenols and their acylated derivatives. The method is proposed for rapid identification of phenols in the solid state . 

The use of the differential thermal analysis in the phase diagram determination is illustrated in Figure 3.52. A hypothetical binary eutectic system A-B with the formation of the incongmently melting compound A4B was chosen. There are three thermograms (a) to (c) shown as examples. In thermogram (a), the first heat effect at temperature ai... 

Figure 3.52. Phase diagram determination using differential thermal analysis. Thermograms (a) to (c) correspond to different compositions of the hypothetical system.

Figure 16. Differential thermal analysis thermograms for BaNg as a function of gamma dose [ 80].

Differential thermal analysis (DTA) measures the temperature difference between a sample and a reference as the temperature is increased. A plot of the temperature difference (thermogram) reveals exothermic and endothermic reactions that may occur in the sample. The temperature for thermal events such as phase transitions, melting points, crystallization temperatures, and others can be determined... 

Differential Thermal Analysis. Acetone-recrystallized tristearin has a very complex differential thermogram. Figure 2 shows a trace which is representative of three separate determinations. This curve resembles those published by Chapman (6) in gross features. Three endotherms and one exotherm are evident. The temperatures of transition are given in Table I. 

Differential Thermal Analysis. Details revealed in the differential thermograms of the 4 MA-Y zeolites (Figure 2) are consistent with the TGA results. They all exhibited an endotherm (122°-190°C) caused by loss of adsorbed water. Over the region where slow decomposition occurred, there were weak endotherms or inflections in the curve, and the rapid decomposition was confirmed by a sharp endotherm (516°-577°C). Dehydroxylation was clearly revealed by the endotherm at 785°C in MMA-Y, but was not as well resolved in the others. The exotherm (977°-1026°C) was owing to mullite transformation (I). However, all the samples were found to be amorphous (by x-ray) after 1 hour at 900°C. 

---