Material characterization methods thermal analysis

As indicated in the previous sections, the antioxidant content in plastic material is often determined by chromatographic methods. Another widely used technique for polymer characterization is thermal analysis with differential scanning calorimetry (DSC). When the oxygen induction time (OIT) for a sample containing a phenoHc antioxidant is measured, a significant oxidative exothermic response is obtained in the DSC when all the phenolic antioxidant in a sample is consumed. The OIT is thus directly related to the antioxidant content in the material and to the stabihzing function, i.e. the antioxidant efficiency in the sample, if the consumption of phenolic antioxidants obeys zero-order kinetics at the temperature used [44]. Table 1 shows the amount of the antioxidant Irganox 1081 in polyethylene (PE) determined by HPLC and extraction by microwave assisted extraction (MAE),... 

When solids react, we would like to know at what temperature the solid state reaction takes place. If the solid decomposes to a different composition, or phase, we would like to have this knowledge so that we can predict and use that knowledge In preparation of desired materials. Sometimes, intermediate compounds form before the final phase. In this chapter, we will detail some of the measurements used to characterize the solid state and methods used to foUow solid state reactions. This will consist of various types of thermal analysis (TA), including differentlEd thermal analysis (DTA), thermogravimetric analysis (TGA) and measurements of optical properties. 

Most workers in the pharmaceutical field identify thermal analysis with the melting point, DTA, DSC, and TG methods just described. Growing in interest are other techniques available for the characterization of solid materials, each of which can be particularly useful to deduce certain types of information. Although it is beyond the scope of this chapter to delve into each type of methodology in great detail, it is worth providing short summaries of these. As in all thermal analysis techniques, the observed parameter of interest is obtained as a function of temperature, while the sample is heated at an accurately controlled rate. 

Classical characterization methods (gas sorption, TEM, SEM, FTIR, XPS and elemental analysis) were used to describe the resulting porous carbon structures. Temperature-dependent experiments have shown that all the various materials kept the nitrogen content almost unchanged up to 950 °C, while the thermal and oxidation stability was found to be significantly increased with N-doping as compared to all pure carbons. Last but not least, it should be emphasized that the whole material synthesis occurs in a remarkably energy and atom-efficient fashion from cheap and sustainable resources. 

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

The development of thermal analysis methods in materials research has led to a plethora of new methodologies since the elaboration of the first thermal method by by Le Chatelier and Robert-Austen [16,86], Thermal analysis consists of a group of techniques in which a physical property of a material is measured as a function of temperature at the same time when the substance is subjected to a controlled increase, or in some cases, decrease of temperature. Temperature-programmed techniques, such as DTA [87-89], TGA [87], DSC [53,90], TPR [91,92], and TPD [93-96], contribute to perform a more complete characterization of materials. 

A primary method that is used to characterize the thermal properties of a bulk material is thermogravimetric analysis (TGA). This method provides detailed information regarding the thermal stability and decomposition pathway of a material e.g., stepwise loss of ligands for an organometallic compound), as well as structural information for complex composites (Figure 7.52). The operating principle of TGA is... 

Of all the methods available for the physical characterization of solid materials, it is generally agreed that crystallography, microscopy, thermal analysis, solubility studies, vibrational spectroscopy, and nuclear magnetic resonance are the most useful for characterization of polymorphs and solvates. However, it cannot be overemphasized that the defining criterion for the existence of polymorphic types must always be a non-equivalence of crystal structures. For compounds of pharmaceutical interest, this ordinarily implies that a non-equivalent X-ray powder diffraction pattern is observed for each suspected polymorphic variation. All other methodologies must be considered as sources of supporting and ancillary information, but cannot be taken as definitive proof for the existence of polymorphism by themselves. 

Thermal analysis methods are widely used in all fields of pharmaceutics. They are unique for the characterization of single compounds. The information correlated with the thermodynamic phase diagrams is extremely helpful for rational preformulation and development of new delivery systems. Very rapid and requiring only very small samples of material, these methods are applicable in development and also in production for quality control. The combination with spectroscopic and crystallographic data will allow better insight in complex phase changes behavior. 

According to the structure and composition of materials and analysis requirements of the researcher, the following analysis techniques can be selected for the characterization of mesoporous materials XRD, TEM, adsorption-desorption (N2 or other gas), solid MAS NMR (29Si, 27Al, 13C, etc.), scanning electron microscopy (SEM), catalysis test, Fourier Transform infra-red (FT-IR), thermal analysis, UV-visible, and chemical analysis. IR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure XANES, extended X-ray absorption fine structure EXAFS and other spectral methods are commonly used to analyse metal elements such as Ti in the mesoporous material frameworks. 

ETS-10 is a thermally stable titanosilicate molecular sieve with potential for application in catalysis and adsorption. The as-synthesized Si/Ti ratio is 5. Methods for modification of the Si/Ti of ETS-10 are described. The resulting materials are characterized by elemental analysis, XRD, NMR, IR and raman techniques. These modified sieves show catalytic activity for oxidation of organic substrates with peroxide. 

A method is described for the preparation of zinc-containing zeolite by direct synthesis from hydrogels. The synthesis of Zn-MFI type zeolite materials and the post synthesis introduction of Cu are discussed. The samples are characterized by XRD, AAS, thermal analysis, SEM and Si-NMR spectroscopy. The catalytic results on the cumene conversion are discussed. 

Surface and structural properties of nanoporous solids can be studied directly by employing modem techniques such as atomic force microscopy, electron microscopy, X-ray analysis and various spectroscopic methods suitable for materials characterization and surface imping [4]. In addition, these properties can be investigated by indirect methods such as adsorption [1, 11-13], chromatography [14, 15] and thermal analysis [16]. The quantities evaluated from adsorption, chromatographic and thermodesorption data provide information about the whole adsorbent-adsorbate system. These data can by used mainly to extract... 

It was outlined in chapter 2 in detail that screening tests primarily have the purpose, to provide a first characterization of the safety relevant substance properties as part of the basic assessment. It was further explained that the determination of the thermal stability of a substance is of the greatest importance. The most fi-equently used methods for this puipose are those that investigate thermal stability using very small amounts of sample material only. The most widely used test equipments to perform such investigations are the DTA ( difference thermal analysis ) and DSC ( differential scanning calorimetry). 

Radiation cure adhesives are beconlng Increasingly Important for structural material applications. In order to obtain optimum performance and process efficiency, It Is necessary to analyze these materials using several techniques. Thin film applications have been successfully characterized by traditional methods such as Infrared spectroscopy and thermal analysis. This Investigation Includes comparison of traditional methods and mechanical spectroscopy for characterization of structural adhesive applications. In addition, mechanical spectroscopy provides viscoelastic data dependent on structure property relationships. 

While methods for studying these and other types of changes in the sample have become widely used, the most widely used methods are thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). As a group, thermal methods of analysis now constitute the most widely used experimental techniques in the chemical industry. A major reason for this widespread use is that determination of bulk properties, thermal stabdity, and characterization of materials are as important in industrial appHcations as are the determination of molecular properties. 

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