Differential thermal analysis crystallinity

Crystallization kinetics have been studied by differential thermal analysis (92,94,95). The heat of fusion of the crystalline phase is approximately 96 kj/kg (23 kcal/mol), and the activation energy for crystallization is 104 kj/mol (25 kcal/mol). The extent of crystallinity may be calculated from the density of amorphous polymer (d = 1.23), and the crystalline density (d = 1.35). Using this method, polymer prepared at —40° C melts at 73°C and is 38% crystalline. Polymer made at +40° C melts at 45°C and is about 12% crystalline. 

Phase equilibria of the isothiazole-water system have been investigated by differential thermal analysis (76BSF1043), and it has been established that a stable crystalline clathrate (isothiazole-34H20) forms below 0 °C. 

Recently we investigated ferromagnetic properties of CoPt bimetallic nanoparticles [232,233]. CoPt3 nanoparticles can be prepared by a two-step reduction using NaBH4 as a reductant. The bimetallic nanoparticles were characterized by thermogravimetry (TG) and differential thermal analysis (DTA), FT-IR, TEM) and XRD. Structural and spectroscopic studies showed that the bimetallic nanoparticles adopt an fee crystalline structure with an average particle size of 2.6 nm. SQUID studies revealed... 

Differential Thermal Analysis (DTA). One of the characteristics of a rubber useful in tire rubber compounds is that it is amorphous at room temperature but readily undergoes strain induced crystallization. For this reason, copolymers were prepared in order to appropriately adjust the crystalline melt temperature. 

XPD [18]. Similarly, mineral impurities in talc were analyzed by polarizing light microscopy, differential thermal analysis, and XPD [19]. It must be recognized, however, that small amounts of crystalline impurities (usually <0.5% w/w) may not be detected by XPD. In case of noncrystalline impurities, mrch higher concentrations may be nondetectable. 

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. 

A variety of techniques have been used to determine the extent of crystallinity in a polymer, including X-ray diffraction, density, IR, NMR, and heat of fusion [Sperling, 2001 Wunderlich, 1973], X-ray diffraction is the most direct method but requires the somewhat difficult separation of the crystalline and amorphous scattering envelops. The other methods are indirect methods but are easier to use since one need not be an expert in the field as with X-ray diffraction. Heat of fusion is probably the most often used method since reliable thermal analysis instruments are commercially available and easy to use [Bershtein and Egorov, 1994 Wendlandt, 1986], The difficulty in using thermal analysis (differential scanning calorimetry and differential thermal analysis) or any of the indirect methods is the uncertainty in the values of the quantity measured (e.g., the heat of fusion per gram of sample or density) for 0 and 100% crystalline samples since such samples seldom exist. The best technique is to calibrate the method with samples whose crystallinites have been determined by X-ray diffraction. 

The measurements of Young s modulus in dependence of the temperature (dynamic-mechanical measurements, see Sect. 2.3.5.2) and the differential thermal analysis (DTA or DSC) are the most frequently used methods for determination of the glass transition temperature. In Table 2.10 are listed and values for several amorphous and crystalline polymers. 

Differential thermal analysis (DTA) has provided a wealth of information regarding the thermal behavior of pure solids as well as solid mixtures [10]. Melting points, boiling points, transitions from one crystalline form to another, and decomposition temperatures can be obtained for pure materials. Reaction temperatures can be determined for mixtures, such as ignition temperatures for pyrotechnic and explosive compositions. 

Other approaches use Laser-Raman spectra to differentiate five conformational states of lactose, including a-lactose monohydrate, /3-lactose, and lactose glass (Susi and Ard 1974). Differential thermal analysis has also been used to measure the concentration of crystalline lactose, especially a-lactose hydrate (Ross 1978B). The specialized equipment required by these procedures may limit their use. 

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. 

The amorphous peroxy titanium oxide, on heating, lost the peroxy oxygen and water around 100°C. The resulting oxide was poorly crystalline. The differential thermal analysis of peroxy titanium oxide (fig. la) showed an endothermic peak... 

The next stage of characterization focuses upon the different phases present within the catalyst particle and their nature. Bulk, component structural information is determined principally by x-ray powder diffraction (XRD). In FCC catalysts, for example, XRD is used to determine the unit cell size of the zeolite component within the catalyst particle. The zeolite unit cell size is a function of the number of aluminum atoms in the framework and has been related to the coke selectivity and octane performance of the catalyst in commercial operations. Scanning electron microscopy (SEM) can provide information about the distribution of crystalline and chemical phases greater than lOOnm within the catalyst particle. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) can be used to obtain information on crystal transformations, decomposition, or chemical reactions within the particles. Cotterman, et al describe how the generation of this information can be used to understand an FCC catalyst system. 

The literature on MKP mineral is scarce. Sivaprasad et al. [33] and Wagh et al. [34] consider this material as an analog of struvite, in which NH4 is replaced by K, and have determined its crystalline structure. Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) indicated that the 6 mol of water in the crystal are loosely bound and escape upon heating at 120°C (Fig. 9.9), after which anhydrous MKP is formed. 

One of the earliest diffraction studies was that of Wilkes et al. (1973) on neonatal-rat stratum comeum carried out using WAXD combined with differential thermal analysis. They also investigated the dependence of the diffraction pattern on the orientation of the sample. With the x-ray beam normal and perpendicular to the surface of the SC, two strong reflections, corresponding to repeat distances of 4.2 and 3.7 A, were observed that were assigned to crystalline lipids. In addition, two halos were observed, at 9.8 and 4.6 A, that were attributed to protein. Because they could not find a 5.15-A reflection that is often seen in a-keratin from hard tissues (Fraser and MacRae, 1973), they... 

Wilkes, G. L., Nguyen, A. L. and Wildnauer, R. (1973). Stmcture-property relations of human and neonatal rat stratum comeum. 1. Thermal stability of the crystalline lipid stmcture as studied by x-ray diffraction and differential thermal analysis. Biochim. Biophys. Acta 304 267. 

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