Characterization calorimetric methods

Giron, D. (1995). Thermal analysis and calorimetric methods in the characterization of polymorphs and solvates, Thermochim. Acta, 248 1-59. 

The study and control of a chemical process may be accomplished by measuring the concentrations of the reactants and the properties of the end-products. Another way is to measure certain quantities that characterize the conversion process, such as the quantity of heat output in a reaction vessel, the mass of a reactant sample, etc. Taking into consideration the special features of the chemical molding process (transition from liquid to solid and sometimes to an insoluble state), the calorimetric method has obvious advantages both for controlling the process variables and for obtaining quantitative data. Calorimetric measurements give a direct correlation between the transformation rates and heat release. This allows to monitor the reaction rate by observation of the heat release rate. For these purposes, both isothermal and non-isothermal calorimetry may be used. In the first case, the heat output is effectively removed, and isothermal conditions are maintained for the reaction. This method is especially successful when applied to a sample in the form of a thin film of the reactant. The temperature increase under these conditions does not exceed IK, and treatment of the experimental results obtained is simple the experimental data are compared with solutions of the differential kinetic equation. 

In this review, the relationships between structure, morphology, and surface reactivity of microcrystals of oxides and halides are assessed. The investigated systems we discuss include alkali halides, alkaline earth oxides, NiO, CoO, NiO-MgO, CoO-MgO solid solutions, ZnO, spinels, cuprous oxide, chromia, ferric oxide, alumina, lanthana, perovskites, anatase, rutile, and chromia/silica. A combination of high-resolution transmission electron microscopy with vibrational spectroscopy of adsorbed probes and of reaction intermediates and calorimetric methods was used to characterize the surface properties. A few examples of reactions catalyzed by oxides are also reported. 2001... 

There a number of interrelated thermal analytical techniques that can be used to characterize the salts and polymorphs of candidate drugs. As noted in Table 3.8, the melting point of a salt can be manipulated to produce compounds with desirable physicochemical properties for specific formulation types. Giron (1995) has reviewed thermal analytical and calorimetric methods used in the characterization of polymorphs and solvates. Of the thermal methods available for investigating polymorphism and related phenomena, DSC, TGA and hot stage microscopy (HSM) are the most widely used. 

Benzophenone triplet states have been characterized by photothermal beam diffraction spectroscopy. This is a calorimetric method which depends upon sensing the temperature dependent refractive index gradient at the edge of the excitation beam and... 

Various calorimetric methods can be used to characterize carbon surfaces from different viewpoints the application of these techniques to carbons has been recently reviewed in detail [35], and only a brief outline will be presented here. Adsorption calorimetry has been used to investigate surface chemical properties more irequently than to characterize porosity in carbons. Terzyk et al. [36] have compared a number of techniques, including benzene adsorption calorimetry, to characterize the microporosily of cellulose-derived carbonaceous films where the majority of micropores possessed the same diameter. The determination of pore size based on the enhancement of potential energy in micropores... 

Thermography Imaging of a hot surface by an infrared sensitive camera Thermoporometry (Thermoporosimetry) A calorimetric method for characterizing the pore texture from the melting or freezing point depression of a liquid confined in a pore, by reason of the added contribution of surface curvature to the phase-transition free energy THE Tetrahydrofuran... 

Although the above approaches may all be amenable to detection of crystallization in finished products, they can also be used to characterize the HME (i.e., prior to downstream processing). Further, many other techniques are often applied exclusively to the HME intermediate. For instance, optical microscopy offers excellent detectability of crystalline material in transparent extrudates. Dielectric analysis (DBA Alie et al. 2004 Bhugra et al. 2007, 2008) and thermally stimulated current IR spectroscopy (Shah et al. 2006 Rumondor and Taylor 2010), atomic force microscopy (ATM Lauer et al. 2013 Marsac et al. 2012 Price and Young 2004), and calorimetric methods have also been used to detect crystallization from an amorphous matrix (Baird and Taylor 2012 Pikal and Dellerman 1989 Avella et al. 1991). 

The specific T] can be measured by different techniques, such as turbidity analysis or calorimetric methods (Fig. 2). The first method is characterized by a turbidity profile showing a sharp step, with T, taken to be the temperature that shows a 50% change in the relative turbidity shape. In contrast, differential scanning calorimetry (DSC) measurements are always characterized by a broad peak covering 20 °C or more. In this case, T, can be considered as either the onset or the peak temperature. The T, values obtained by these methods usually differ because of the influence of several factors [26]. 

This review coneluded by stating that mieroporous activated carbons and CMS, can be characterized in terms of their micropore distributions and the degree of hydrophilicity of their surfaces. The value of this work is the comparison made available between data of traditional adsorption methods and calorimetric methods. Examples of this are given in Table 5.6 and Figure 5.47. 

Semicrystalline PVA is characterized by its degree of crystallinity which is defined as the ratio of the volume of PVA crystallites to the total volume of PVA. Density measurements, calorimetric methods, spectroscopic methods. X-ray analysis, and other methods such as NMR spectroscopy have been used to determine degrees of crystallinity of PVA hydrogels [32]. Using such methods, degrees of crystallinity were determined for PVA samples (Mc=4770) that were prepared under varying annealing conditions (Table 1). 

Murphy, D. K. and Rabel, S. Thermal analysis and calorimetric methods for the characterization of new crystal forms. In Preformulation in Solid Dosage Form Development, (M. C. Adeyeye and H. G. Brittain, eds.). Informa Healthcare Press, New York, pp. 279-321, 2008. chapter 3.6. 

Reviews of calorimetric characterization of polymer blends include [31] (differential scanning calorimetry) and [42] (analog calorimetry). General review of thermal analysis of polymers (including calorimetric methods) include [43, 44]. 

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. 

As evident in the preceding discussions on the metal and metal oxide catalysts, the heat of adsorption plays a key role in characterizing a catalyst. The heat of adsorption can also be used to gain an understanding of the nature of catalytic reactions. Three different experimental methods can be used for the determination of heats of adsorption adsorption experiments (isotherms), the calorimetric method, and temperature-programmed desorption (TPD). In the first method, the adsorption isotherms obtained at different temperatures are used. The values of d In P/dT at constant v (volume of gas adsorbed) are calculated as a function of v through... 

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