Differential thermal analyzer

Spectra were obtained using a Digilab FTS-15E Fourier Transform Spectrophotometer. A NaCl crystal mounted in a heated cell (Model 018-5322 Foxboro/Analabs, N. Haven, Ct.) was placed in the infrared beam and the chamber allowed to purge for several minutes while the cell was brought to the desired temperature. The temperature of the cell was controlled using a DuPont 900 Differential Thermal Analyzer interfaced to the spectrometer cell. A chlorobenzene solution (ca. 10 by wt.) of the sample was then applied to the crystal using cotton tipped wood splint. 

A duPont Model 900 Differential Thermal Analyzer shows halcinonide to have one endotherm at 269°. Decomposition on melting precludes differential scanning colorimetry studies for purity. 

Adiabatic calorimeters are complex home-made instruments, and the measurements are time-consuming. Less accurate but easy to use commercial differential scanning calorimeters (DSCs) [18, 19] are a frequently used alternative. The method involves measurement of the temperature of both a sample and a reference sample and the differential emphasizes the difference between the sample and the reference. The two main types of DSC are heat flux and power-compensated instruments. In a heat flux DSC, as in the older differential thermal analyzers (DTA), the... 

A differential thermal analyzer is composed of five basic components, namely ... 

A typical commercial differential thermal analyzer is schematically illustrated in Figure 11.3. 

Figure 11.3 Schematic Diagram of a Differential Thermal Analyzer. (Source E.I. Du Pont De Nemours, Inc, USA)...

Smith et al. [64] prepared a series of PET/PTT copolyesters, and found that addition of the other component suppressed the melting point of the respective homopolymer. Between 37 and 60 % PTT content, the copolymers became amorphous and did not show any melting endotherms in the differential thermal analyzer scans. A similar behavior was observed by Balakrishnan and coworkers [102] in PET/PTT copolyesters prepared by the transesterification of PET with PDO, and by the copolymerization of EG and PDO with DMT [103, 104], The non-crystallizing behavior of copolymers with intermediate contents of the respective component is similar to that of a eutectic mixture, indicating formation of random copolyesters. The 7 g and solubility temperature of the copolyesters were, however, continuous and went through minima with increasing PTT content [64],... 

The XPS data were acquired on a Physical Electronics model 5400 XPS system using a Mg anode. For survey spectra, the pass energy was 44.75 eV with a step size of 0.5 eV. The time per step was 50 msec. High resolution spectra were acquired with a pass energy of 35.75 eV and step size of 0.1 eV, The time per step was 50 msec. Thermogravimetric data were obtained on a Perkin-Elmer, Diamond Thermogravimetric/ Differential Thermal Analyzer (TG/DTA) with Pyris software, version 7.0-0.0110. 

ASTM E 967-92, Standard Practice for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal Analyzers, 1992. 

The general melting characteristics can be established on a Fischer-Johns block or, in a more refined fashion, in a differential thermal analyzer. Should the DTA be available, it can be used on milligram quantities to define not only the melting behavior but also the temperature level and rate of thermal degradation. 

Differential thermal analysis was performed with the DuPont 900 differential thermal analyzer the heating rate was usually 10°C. per minute. To determine heats of reaction, the calorimeter attachment to the Du Pont instrument was employed. Planimeter determinations of peak areas were converted to heat values by using standard calibration curves. For the infrared spectra either a Beckman IR5A instrument or a Perkin Elmer 521 spectrophotometer with a Barnes Engineering temperature-controlled chamber, maintained dry, was used. Specimens for infrared were examined, respectively, as Nujol mulls on a NaCl prism or as finely divided powders, sandwiched between two AgCl plates. For x-ray diffraction studies, the acid-soap samples were enclosed in a fine capillary. Exposures were 1.5 hours in standard Norelco equipment with Cu Ko radiation. For powder patterns the specimen-to-film distance was 57.3 mm. and, for long-spacing determinations, 156 mm. 

Figure 18.11. Schematic of (A) a differential thermal analyzer and (B) differential scanning calorimeter for a TA Instruments, Inc.-type configuration. Modified from Richardson (1989). Reproduced by permission of Elsevier, Ltd.

The products obtained are determined by the energy spectrum for the compositions, mainly for the Ca/P mole ratio, and characterized by infrared spectroscopy with the Fourier transformation intra-red spectrophotometer (FTIR) of Type Nicolet 51 OP made by Nicolet Co., thermal analysis on a thermo- gravimetric/differential thermal analyzer (TG/DTA) of Type ZRY-2P, X-ray diffraction (XRD) analysis with the X-ray diffractometer of Type XD-5 made by Shimadzu Co., scanning electron microscopy (SEM), and transmission electron microscopy (TEM) with the transmission electron mirror microscope of Type JEM-100SX type made by JEOL Co. 

Glass transition temperatures were measured by differential scanning calorimetry (DSC) using a DuPont 900 Differential Thermal Analyzer. The samples were cooled to -100°C in a closed pan and then scanned to 150°C at a rate of 15°/minute. 

Figure 4.43a shows the block diagram of the dielectric differential thermal analyzer, where the dielectric sensor circuit and the capacitors formed by the sample and reference (Cr) and specimen holders (Cx) are schematically represented, and a photo of the home-made equipment is shown in Figure 4.43b [89,109,110],... 

FIGURE 4.43 (a) Block diagram of the dielectric differential thermal analyzer. 

Figure 3.1 is a schematic of the differential thermal analyzer (DTA) design. The device measures the difference in temperature between a sample and reference which are exposed to the same heating schedule via symmetric placement with respect to the furnace. The reference material is any substance, with about the same thermal mass as the sample, which undergoes no transformations in the temperature range of interest. The temperature difference between sample and reference is measured by a differential thermocouple in which one junction is in contact with the underside of the sample crucible, and the other is in contact with the underside of the reference crucible.1 The sample temperature is measured via the voltage across the appropriate screw terminals (Vt,) and similarly for the reference temperature (Vrr) generally only one or the other is recorded (see section 3.5.1). Sample and reference... 

Vapor pressures at ambient temperatures of a number of pesticides can be determined by using a du Pont 900 differential thermal analyzer to measure boiling points for a series of pressures down to 10 mm., or by using an effusion method for compounds having vapor pressures from 10 3 to 10 7 mm. Less than 100 mg. of the sample are required in either case. Accuracy can be determined by comparison with direct measurements available in the literature. Vapor pressures for phenoxy herbicide esters are lower than values reported in the literature. 

Figure 1. du Font 900 differential thermal analyzer for determining boiling point-pressure curves... 

Figure 2. Boiling point vs. pressure for ethylene dibromide as determined by the differential thermal analyzer. Heating rate = 15° C. per minute vertical scale 0.1 °C. per division...

Some measurements with the differential thermal analyzer are summarized in Table I. The data are condensed into the two constants of the Clausius-Clapeyron equation ... 

It would appear from Table I that the available comparison data are just as variable as data obtained with the differential thermal analyzer. The second index of variability, the 95% confidence factor, is a measure of the expected precision for the estimated vapor pressure at 25°C. (or melting point). This includes not only the variation of the experimental points from the regression line but also the uncertainty in the slope of that line. This latter factor has a progressively greater effect as the line is extended—i.e., the further the extrapolation is carried beyond the experimental data. For ethylene dibromide, for example, there is a 95% probability of the vapor pressure lying between 12.0 and 12.8 (12.4 -r-1.032 and 12.4 X 1.032). 

Differential Thermal Analyzer Fitted by Least Clausius-Clapeyron Equation... 

Discs of paper, %-in diameter, were punched from sheets. The discs were placed in 4-in diameter aluminum foil pans and covered with 80-mesh stainless steel screen to prevent coiling. The samples were then linearly temperature programmed at various rates in a DuPont 990 differential thermal analyzer under a 50-cc/min flow of air or oxygen. The paper reaction peaks were recorded, and the peak maximum temperatures were measured and corrected for thermal resistance, thermo-... 

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. 

A differential thermal analysis of vincristine sulfate (Lilly reference standard lot P-89 53) has been run R using the Du Pont 900 Differential Thermal Analyzer at a heating rate of 20° C, per minute. An extremely broad endotherm peaking at 127° C. was observed. 

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