Thermal analysis curves

Fig. 7. Thermal analysis curves for asbestos (a) chrysotile (b) crocidoHte (in inert atmosphere) (10). Reprinted with permission.

Differential thermal analysis curves of iUite show three endothermic peaks in the ranges 100—150, 500—650, and at about 900°C, and an exothermic peak at about 940°C, or immediately following the highest endothermic peak. Minerals formed from iUite at high temperature vary somewhat with the... 

The hydrated alumina minerals usually occur in ooUtic stmctures (small spherical to eUipsoidal bodies the size of BB shot, about 2 mm in diameter) and also in larger and smaller stmctures. They impart harshness and resist fusion or fuse with difficulty in sodium carbonate, and may be suspected if the raw clay analyzes at more than 40% AI2O2. Optical properties are radically different from those of common clay minerals, and x-ray diffraction patterns and differential thermal analysis curves are distinctive. 

The only thermal event in the differential thermal analysis curve of (/))-penicillamine is the melting endotherm at 185 °C. Either polymorph of (z>)-penicillamine gives the same endotherm [2]. 

Figure 7 Differential Thermal Analysis Curve of Hydralazine Hydrochloride.

FIGURE 10 - DIFFERENTIAL THERMAL ANALYSIS CURVE OF SODIUM VALPROATE... 

Fig Differential thermal analysis curve for amorphous poly (ethylene terephthalate). 

Figure shows the Differential thermal analysis curve for poly (ethylene terephthalate). The lower crystalline melting range in the specimen of figure below can be attributed to impurities present in the polymer. 

Fig. 4.4.8 TGA and DTA result of sample 1. (a) Mass loss curve (b) Derivative curve of (a) (c) Differential thermal analysis curve. (From Ref. 10.)...

White (1955) believes that differential thermal analysis curves obtained by him on heating drawn fibers of 6, 6-6 and 6-10 nylons as well as polyethylene terephthalate, indicate that at first crystallites disorient and then melt. He found two peaks in what would correspond to a specific heat-temperature curve. However, it is difficult to understand why the disorientation of oriented crystals would involve the absorption of energy. 

A thermal analysis curve is interpreted by relating the measured property versus temperature data to chemical and physical events occurring in the sample. It is frequently a qualitative or comparative technique. 

Fig. 2. Thermal analysis curves of nickel hydroxide and nickel hydrosilicates.

Quantitative estimation of the sulphate content by the fusion method was found to be difficult because of the low percentage of the impurity. The anatase, thus prepared, was amorphous. The surface area of this anatase sample (B.E.T.) was 54 m2/g and the differential thermal analysis curve of the anatase sample is shown in fig. 2a. Although no exothermic peak due to crystallization was observed, the endothermic peak shows a definite splitting around... 

Fig. 5.3 Thermogravimetric and differential thermal analysis curves for reacted C3S paste experimental conditions as for Fig. 5.2. After Taylor and (T14).

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. 

The heat of pyrolysis (in an inert atmosphere) can be calculated by integrating the area under the differential thermal analysis curve and comparing it with the value obtained for a reference substance according to the following equation... 

For the treated cellulose, the differential thermal analysis curve starts to rise rapidly at about 220°, with no indication of an endotherm, and the thermogravimetric analysis curve shows a continuous weight-loss, which is accelerated at this temperature, and a relatively large residue is left. 

With fresh activated-clay catalyst, endothermic peaks are observed at temperatures of about 300, 1200, and 1600°F. These three peaks are attributed to loss of physically adsorbed water, loss of chemically bound (hydroxyl) water, and collapse of the montmorillonite structure, respectively. The hydroxyl water originally present amounts to 3 or 4%. The magnitude of the peak at 1200°F. decreases if the sample is heated above 800°F. prior to thermal analysis, and disappears completely if the sample is calcined at 1100°F. The thermal-analysis curve for the dehydrated catalyst is flat up to the point at which the montmorillonite structure begins to disappear. If the catalyst has not been heated above 1450°F., it becomes rehydrated upon exposure to moisture and a new endothermic peak appears in the curve between 800 and 1000°F. The size of the new peak increases as that of the original hydroxyl-water peak decreases it corresponds to 1.5 to 2.0% sorbed water with catalyst that has been rehydrated after calcination at 1100°F. The rehydration capacity of the catalyst decreases as the catalyst becomes partially deactivated with use. 

MgCOj decomposes at substantially lower temperatures the dissociation pressure reaches atmospheric pressure at 400—480 C. The reaction enthalpy is 121 kJ (28.9 kcal) per mole at 25 °C. MgC03 bound in dolomite decomposes at a temperature somewhat higher than pure MgC03. The dissociation pressures are plotted in Fig. 27. The decomposition of dolomite proceeds in two stages as illustrated by differential thermal analysis curves, showing two distinctly separate endothermal peaks for MgCOa and CaCOj respectively. The DTA curves for various minerals are shown in Fig. 28 (Ivanova et al., 1974). 

All the displacive inversions of silica exhibit well discernible enthalpic effects on DTA (differential thermal analysis) curves. Pure quartz produces a minor but... 

FIG. 28. Differential thermal analysis curves of various minerals. 

The overall shape of the thermal analysis curve is thus mainly determined by the kinetic model, while the position of this curve on the temperature axis is controlled by the values of A and, to a lesser extent, the heating rate p. 

Most of the information about dehydration because of temperature increase has come from differential thermal analysis curves, which are deceptive with regard to the subsurface environment because of the rapid rate at which temperature is raised (water loss therefore occurs at a higher temperature than it would otherwise), and because the sample is surrounded by air at 0.101 MPa (1 atm.) pressure rather than a saline solution at elevated pressure. Nevertheless, these curves (e.g., Hendricks et at, 1940 Rowland et al., 1956) indicate a relative order of events. 

Barshad, I., 1948. Vermiculite and its relation to biotite as revealed by base exchange reactions, X-ray analyses, differential thermal analysis curves, and water contents. Am. Mineral. 33 655—678. 

FIGURE 6 Thermogravimetric and differential thermal analysis results from a granulation blend of a hydrated API. The thermogravimetric curve is dotted the differential thermal analysis curve is solid the derivative of the thermogravimetric curve is dashed. 

Figure 6. Typical differential thermal analysis curve for lead azide [25].

X-ray diffraction patterns were recorded on a Siemens D5000 diffractometer using CuKa radiation. Thermogravimetric and differential thermal analysis curves were recorded on a Setaram Setsys 12 thermal analysis station by heating in an argon atmosphere from 25 to 1200 -C at a rate of 5 min". Samples were used untreated. The Pt content was determined by the Service Central d Analyse, CNRS (Vernaison, France) and the microanalyses (C, H) were performed at Complutense University (Madrid, Spain). Na isotherms were determined on a Micromeritics ASAP 2000 analyzer. H MAS NMR, Si MAS NMR and C CP MAS NMR spectra were recorded at 400.13, 79.49 and 100.61 MHz, respectively, on a Broker ACP-400 spectrometer at room temperature. An overall 1000 free induction decays were accumulated. The excitation pulse and recycle time for H MAS NMR spectra were 5 ps and 3 s, respectively, those for Si MAS NMR spectra 6 ps and 60 s and those for C CP MAS NMR spectra 6 ps and 2 s. Chemical shifts were measured relative to a tetramethylsilane standard. Prior to measurement, if necessary, samples were dehydrated in a stove at 423 K for 24 h. 

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