Differential thermal analysis definition

Perhaps the most definitive result to come from the early nickel-aluminia synthesis work was the thermal analysis investigation of Hammetter [88HO 88W01], which showed explicit data on substantial changes in the shockec-but-unreacted mixtures. Differential thermal analysis was carried out on th -starting powder compacts of both the mechanically mixed and composite powders. Shocked and unreacted powders were compared to provide direc evidence for substantial changes introduced by the shock process. 

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... 

The use of a cooling accessory permits XRD patterns to be obtained under subambient conditions. In pharmaceutical systems, the greatest utility of the technique is to monitor the crystallization of solutes in frozen solutions. Conventionally, differential scanning calorimetry has been the most popular technique for the characterization of frozen systems. However, as mentioned earlier, this technique has some drawbacks (i) It does not enable direct identification of crystalline solid phase(s). Moreover, it is difficult to draw any definitive conclusions about the degree of crystallinity, (ii) The interpretation of DSC curves is very difficult if there are overlapping thermal events. Low temperature XRD was found to be an excellent complement to differential thermal analysis in the characterization of water-glycine-sucrose ternary systems. " ... 

Differential thermal analysis DTA is defined as a technique in which the temperature difference between a substance and a reference material is measured as function of temperature, while the substance and reference are subjected to a controlled temperature (ICTAC definition [59]). 

The first question of any solid-state chemist thinking in terms of structure and energetics will definitely be What is the stable polymorph, mercury carbodiimide, HgNCN(I), or mercury cyanamide, HgNCN(ll) Unfortimately, it is impossible to answer this question by means of differential thermal analysis because both polymorphs decompose, prior to interconversion, at about 230 °C to yield a white polymer and mercury metal. Thus, theoretical reasoning and/or electronic-structure theory is needed. Let us attempt to argue using both classical and quantum-chemical means. 

The term thermal analysis (TA) is frequently used to describe analytical experimental techniques which investigate the behaviour of a sample as a function of temperature. This definition is too broad to be of practical use. In this book, TA refers to conventional TA techniques such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermogravimetry (TG), thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA). A selection of representative TA curves is presented in Figure 1.1. 

The definition of a general nature thermooxidative the collapse of the copolymers carried out by the method of differential thermal analysis (DTA) and thermo gravimetric analysis (TGA). 

The specific heat, Cp, is related to H by the definition Cp = dH/dT)p. This is the quantity monitored by differential scanning calorimetry (DSC) or differential thermal analysis (DTA). The sigmoidal variation of Cp with temperature on cooling is shown in the lower part of Fig. 2.4 for the two cooling rates by the lines with... 

Although specimen-type micas give distinguishable differential thermal analysis patterns (Mackenzie [1970]), the application of DTA and other thermal methods to the study of finegrained micas in soils is much less diagnostic than are X-ray diffraction methods. The generally more pronounced thermal reactions of other components of the fraction, modifications of the thermal patterns due to particle size, interstratification, and x-y plane transitions of the mica-expansible mineral make definitive interpretation of the thermal analysis patterns of finegrained micas in soil clays very difficult. 

Examination of the residual solid from solubility samples is one of the most important but often overlooked steps in solubility determinations. Powder X-ray diffraction (PXRD) is the most reliable method to determine whether any solid state form change has occurred during equilibration. The sample should be studied both wet and dry to determine if any hydrate or solvate exists. Thermal analysis techniques such as differential scanning calorimetry (DSC) can also be used to identify any solid-state transformations, although they may not provide as definitive an answer as the PXRD method. Other methods useful in identifying any solid-state changes include microscopy, Raman and infrared spectroscopy, and solid-state NMR (Brittain, 1999). When changes in solid-state properties are identified in solubility studies, it is important to link the new properties to the properties of known crystal forms so the solubility result can be associated with the appropriate crystal form. 

The most basic thermal analysis technique is simple thermometry. The functions of state needed for thermometry are temperature and time. Temperature was discussed already to some degree as the fundamental variable of state for all thermal analysis in Figs. 1.1-1.4. At this point one must add a concise temperature definition that is now, after the review of thermodynamics, easily understood Temperature is the partial differential of total energy U with respect to entropy at constant composition and volume. This definition is written as Eq. (1) of Fig. 2.13 and can easily be derived from Eqs. (1) and (3) of Figs. 2.2 and 2.3. At constant composition and volume no work (i.e. volume work) can be done, so that dw must be zero. In this case... 

The viscosity of a material suddenly changes and loses fluidity at the gel point. Techniques to follow this phenomenon as a function of temperature are called thermal analysis techniques. According to the definition of the International Confederation of Thermal Analysis and Calorimetry, thermal analysis is a series of collective techniques to measure the physical properties of a material (or a reaction product) by changing the temperature according to a certain program [212, 213]. There are various thermal analyses depending on the physical properties to be measured. In this section, differential scanning calorimetry (DSC), which is the technique to measure heat capacity of the sample, and thermomechanical analysis (TMA), which measures the viscosity or modulus, will be discussed. 

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