Calorimetric differential thermal analysis

Interest in the use of calorimetry as a routine diagnostic or analysis tool has gained significant momentum only in the last 50 years. This interest has lead to the development of popular procedures such as differential thermal analysis (DTA) and differential scanning calorimetry (DSC). A wide variety of solution calorimetric techniques exist today. These techniques include thermometric titration, injection and flow emhalpimetry. The major growth of commercial instrumentation for calorimetry has occurred to address applications in routine analysis and the rapid characLerizaiion of materials. 

Differential scanning calorimetric methods are applied for the determination of heat of fusion, purity, specific heat and activation energy of decompn for undiluted, unmixed samples of TNT, TNB, Tetryl, RDX, HMX and PETN (Ref 28). The differential thermal analysis thermo-... 

For the determination of reaction parameters, as well as for the assessment of thermal safety, several thermokinetic methods have been developed such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), accelerating rate calorimetry (ARC) and reaction calorimetry. Here, the discussion will be restricted to reaction calorimeters which resemble the later production-scale reactors of the corresponding industrial processes (batch or semi-batch reactors). We shall not discuss thermal analysis devices such as DSC or other micro-calorimetric devices which differ significantly from the production-scale reactor. 

Differential Thermal Analysis (DTA) earlier DTA data showed an unusually large heat of transformation endothermic in heating and exothermic in cooling. Later, through precision calorimetric methods [13], it was determined that the AH to be as high as 4,150 (J/mole), and also established the nature of the transition to be second order which is in agreement with our earlier single crystal X-ray diffraction study [6],... 

All methods in which the sample to be analyzed is gradually heated and its calorimetric behavior studied. The method includes thermogravimetry (TG) and differential thermal analysis (DTA). 

Figure 11.10. Differential thermal analysis (DTA). (a) Oassical apparatus (S = sample R = reference), (b) Calorimetric...

In the classical differential thermal analysis (DTA) system both sample and reference are heated by a single heat source. The two temperatures are measured by sensors embedded in the sample and reference. In the so-called Boersma system, the temperature sensors are attached to the sample pans. The data are recorded as the temperature difference between sample and reference as a function of time (or temperature). The object of these measurements is generally the determination of enthalpies of changes, and these in principle can be obtained from the area under a peak together with a knowledge of the heat capacity of the material, the total thermal resistance to heat flow of the sample and a number of other experimental factors. Many of these parameters are often difficult to determine hence, DTA methods have some inherent limitations regarding the determination of precise calorimetric values. 

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. 

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. 

The heat of reaction and the rate of heat production in a reaction mixture as a function of temperature are important quantities for the design of reactors in chemical industry. Presently, several methods for the determination of these quantities are available, such as Differential Scanning Calorimetry, Differential Thermal Analysis, Bench Scale Calorimetry / / and adiabatic calorimetric methods. 

In contrast, one finds many DSCs which are used only for qualitative DTA work on transition temperatures. The often-posed question of the difference between DTA and DSC is therefore easily answered DTA is the general term covering all differential thermal analysis techniques, while DSC must be reserved for scanning experiments that yield calorimetric information. 

Micro-thermal analysis (pTA ) micro-modulated differential thermal analysis (pMDTA ) and micro-thermomechanical analysis (pTMA M) are registered trade marks of TA Instruments Inc. For the time being little work has been reported using such instruments [12] and the calorimetric data are non-quantitative, so that results from pTA should be interpreted with caution. 

Historically, DSC is a development of differential thermal analysis (DTA) and both techniques have a common origin in the measurement of temperature. The fundamental concept of both techniques is sim-ple-to measure thermal changes in a sample relative to a thermally inert reference as both are subjected to a controlled temperature program. In classical DTA, the temperature difference between sample and reference is measured as a function of temperature in classical DSC, the energy difference between sample and reference is measured as a function of temperature. Hence, DSC is simply quantitative DTA , or more precisely, DSC is a combination of DTA and adiabatic calorimetry. DSC is the more recent technique and was developed for quantitative calorimetric measurements over a wide temperature range from subambient to 1500 C. DTA is not appropriate for such precision measurements and has been progressively replaced by DSC, even for high-temperature measurements, as the major thermal anal-ysis/calorimetric technique. DSC is a differential calorimeter that achieves a continuous power compensation between sample and reference. 

J. Rouquerol and P. Boivinet, Calorimetric Measurements in Differential Thermal Analysis, Vol. 2, ed. R.C. Mackenzie, London, New York, 1972. 

The calorimetric or differential thermal analysis methods indicate the amount of crystallinity by the size of the area associated with the peak that occurs in the scans (see Fig. 1-34 and 1-35). These areas can be compared to those for a polymer with known crystallinity. The technique is rapid and quite precise. It does, however, require a first-class analytical device, which is not inexpensive. 

Basically, the methods consist of a variety of calorimetric methods and a few non-calorimetric methods. In calorimetry the following methods are nsed adiabatic, isoperibol, isothermal, heat condnction, drop and differential scanning calorimeters, and differential thermal analysis. Cryoscopic, vapor pressure, and enthalpy of solution methods are considered to be non-calorimetric methods. 

Calorimetric methods can also be used to determine the crystallinity of PVA films. They include differential thermal analysis, differential scanning calorimetry (DSC), and thermogravimetric analysis. Typically, the heat of crystallization of a PVA sample, AH, is compared to the heat of crystallization of 100% crystalline PVA, AH< . The degree of crystallinity is expressed as ... 

These examples of time-dependent DTA have shown that much information needed for modern materials analysis can be gained by proper choice of time scale. The thermal analysis with controlled cooling and heating rates has also been called dynamic differential thermal analysis (DDTA). Adding calorimetric information, as is described in Chapter 5, extends the analysis even further. All of this work is, however, very much in its early stage. No systematic studies of metastable crystal properties or information on hystereses in glasses have been made. 

An understanding of the complex physico-chemical phenomena associated with the formation and behavior of cementitious compounds is facilitated through the application of many different types of investigative methods. Techniques such as NMR, XRD, neutron activation analysis, atomic absorption spectroscopy, IR/UV spectroscopy, electron microscopy, surface area techniques, pore characterization, zeta potential, vis-cometry, thermal analysis, etc., have been used with some success. Of the thermal analysis techniques the Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TG), Differential Scanning Calorimetry (DSC), and Conduction Calorimetric methods are more popularly used than others. They are more adaptable, easier to use, and yield important results in a short span of time. In this chapter the application of these techniques will be highlighted and some of the work reported utilizing other related methods will also be mentioned with typical examples. 

Often, the term calorimetric appears in papers dealing with solid state materials used to compose battery electrodes. A frequently applied analytical method is differential scan calorimetry. This method belongs to the arsenal of thermal analysis. It is similar to differential thermal analysis. Such techniques are useful to characterise solid state materials, but they are not electrochemical. 

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