Differential thermal analysis phase measurements

Differential thermal analysis (DTA) measures the amount of heat released or absorbed by a sample as it is heated at a known rate." When the enthalpy change is determined, the method is called differential scanning calorimetry (DSC). The presence of exothermic or endothermic processes at certain temperatnres provides information about the nature of phase changes and chemical reactions occurring in the material as it is heated. DTA can often be used as a sensitive method for establishing the presence or absence of secondary phases in samples if these phases undergo phase transformations at known temperatures. ... 

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... 

Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

Dynamic differential thermal analysis is used to measure the phase transitions of the polymer. IR is used to determine the degree of unsaturation in the polymer. Monitoring of the purity and raw is done commercially using gas phase chromatography for fractionization and R1 with UV absorption at 260 nanometers for polystyrene identification and measurement Polystyrene is one of the most widely used plastics because of fabrication ease and the wide spectrum of properties possible. Industries using styrene-based plastics are packaging, appliance, construction, automotive, radio and television, furniture, toy, houseware and baggage. Styrene is also used by the military as a binder in expls and rocket propints... 

Experimental studies on the thermal decomposition and combushon processes of AP have been carried out and their detailed mechanisms have been reported.P-iil Fig. 5.1 shows the thermal decomposition of AP as measured by differential thermal analysis (DTA) and thermal gravimetry (TG) at a heating rate of 0.33 K s"f An endothermic peak is seen at 520 K, corresponding to an orthorhombic to cubic lattice crystal structure phase transition, the heat of reaction for which amounts to... 

The second section will concentrate on methods of determining phase diagrams. The first part will examine non-isothermal methods, such as differential thermal analysis and cooling curve determinations, while the second will concentrate on isothermal methods, such as metallography, X-ray measurements, etc. The various limitations of both methods will be discussed and some novel techniques introduced. 

Phase transitions Differential thermal analysis (DTA) or differential scanning calorimetry (DSC), light scattering and various spectroscopic techniques, diffraction methods (especially X-ray diffraction), measurement of thermal expansion and any other property changing with the transition... 

There are two types of stages for dynamic microscopy (a) hot and cold stages and (b) tensile stages [1], Hot stages are most commonly used for the dynamic microscopy of polymers [1,43]. Thermal analysis in the OM is complementary to other thermal analysis methods, such as differential thermal analysis (DTA) [1], Direct observation of the structural changes of a polymer as a function of temperature can determine the nature of phase changes and thermal decomposition [1], It also measures the transformation temperatures. 

The phase equilibria and diagrammatic structures in a two-component system are illustrated in Figure 7 (12). The phase diagrams have often been determined by inspection with the naked eye. More exact methods include x-ray and NMR analysis, density measurements, separation by high-speed centrifugation or differential thermal analysis. 

An other method to study structures during cooling and warming is differential thermal analysis (DTA) (Figure 1.25). It measures the different course of temperature between the sample and a probe, which changes its thermal behavior uniformly but does not have a phase transition in the measured temperature range. Such an instrument is illustrated in Figure 1.26. 

Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed in air at a heating rate of lOK/min. on a PTC-lOA thermogravimetric analyzer. The adsorption isotherms for vapor-phase water and ethanol were measured using the BET method. The saturation pressures, Pq, of water and ethanol at 299K are 758 mmHg. Prior to the adsorption experiments, the samples were dehydrated at 673K in air for 4 h. 

Dynamic differential thermal analysis is used to measure the phase transitions of the polymer. IR is used to determine the degree of unsaturation in the polymer. Monitoring of the purity and mw is done commercially using gas phase duomatography for fractionization and R1 with UV absorption at 260 nanometers for polystyrene identification and measurement... 

Secondly, calorimetric measurements from the vapor phase may refer to nonequilibrium distributions of water vv ithin the crystals and through the zeolite bed. The very energetic vv ater-zeolite bond, especially for smaller water uptakes, means that water molecules may stick on sites vv here they first land. Subsequent redistribution can be very slow on the time scale of the experiment, particularly at the low temperatures employed 19, 21), 23° and 44°C. Finally, the information derived from differential thermal analysis is qualitative or at best only semiquantitative. 

Alexander and Carlson ( ) proposed a phase diagram for the V-VO system based on melting point determinations, differential thermal analysis, metallographic observations, and x-ray parametric measurements. These authors ( ) reported that VO(cr) melts congruently at 2063 10 K. We adopt this value for In a phase diagram proposed by Stringer (2) a melting temperature of... 

Thermal Analyses. Thermal techniques such as differential thermal analysis, thermal gravimetric analysis, and derivative thermogravimetric analysis have been successfully applied to characterizing various minerals in coal (58). The methods are based on measurements of weight loss or heat transfer during phase changes at temperatures from ambient to over 1000° C. 

Simultaneous thermogravimetric and differential thermal analysis (TG/DTA) is a useful technique for the solid-state characterization of pharmaceutical materials. Such characterization includes the determinations of loss on drying, phase transition temperatures, thermal stability, and whether or not water is bound or unbound. TG/DTA combines the measurement of a change in mass of a sample as a function of temperature (TG) with the temperature difference of a sample compared with an inert reference material as a function of temperature (DTA). 

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