Thermogravimetric analysis examples

Typical characterization of the thermal conversion process for a given molecular precursor involves the use of thermogravimetric analysis (TGA) to obtain ceramic yields, and solution NMR spectroscopy to identify soluble decomposition products. Analyses of the volatile species given off during solid phase decompositions have also been employed. The thermal conversions of complexes containing M - 0Si(0 Bu)3 and M - 02P(0 Bu)2 moieties invariably proceed via ehmination of isobutylene and the formation of M - O - Si - OH and M - O - P - OH linkages that immediately imdergo condensation processes (via ehmination of H2O), with subsequent formation of insoluble multi-component oxide materials. For example, thermolysis of Zr[OSi(O Bu)3]4 in toluene at 413 K results in ehmination of 12 equiv of isobutylene and formation of a transparent gel [67,68]. 

When heated, many solids evolve a gas. For example, most carbonates lose carbon dioxide when heated. Because there is a mass loss, it is possible to determine the extent of the reaction by following the mass of the sample. The technique of thermogravimetric analysis involves heating the sample in a pan surrounded by a furnace. The sample pan is suspended from a microbalance so its mass can be monitored continuously as the temperature is raised (usually as a linear function of time). A recorder provides a graph showing the mass as a function of temperature. From the mass loss, it is often possible to establish the stoichiometry of the reaction. Because the extent of the reaction can be followed, kinetic analysis of the data can be performed. Because mass is the property measured, TGA is useful for... 

The PSI element of both the OSHA PSM Standard and the EPA RMP regulation can be improved by requiring the inclusion of all existing information on chemical reactivity. Examples of such information are chemical reactivity test data, such as DSC, thermogravimetric analysis (TGA), or accelerating rate calorimetry and relevant incident reports from the plant, the corporation, industry, and government. OSHA and EPA should require the facility to consult such resources as Bretherick s Handbook of Reactive Chemical Hazards,Sax s Dangerous Properties of Industrial Materials, and computerized tools (e g., CHETAH, The Chemical Reactivity Work Sheet). 

The nature of the material to be studied, which means its degree of crystallinity and perfectness of crystal structure, may have a significant effect on the thermoanalytical behavior. In spite of identical chemical composition of a certain material the variations with respect to structure, imperfections, grain boundaries, etc. are almost infinite. Of course many of these will not show in normal thermogravimetric analysis, with very sensitive apparatus characteristically different TG curves18, 19 may be obtained however. As an example Fig. 26 shows the thermal decomposition of hydrozincite, Zn5(OH)6(003)2, whereby equal amounts of samples from natural origin and synthetic preparations are compared. 

Another type of calorimetric technique is called thermogravimetric analysis (TGA). It is the study of the weight of a material as a function of temperature. The method is used to evaluate the thermal stability from the weight loss caused by loss of volatile species. A final example, thermomechanical analysis (TMA), focuses on mechanical properties such as modulus or impact strength as a function of temperature. Both types of analysis are essential for the evaluation of polymers that to be used at high temperatures. 

As an extension of the proximate analysis or coal assay, it is worthy of note that new methods continued to be developed. For example, thermogravimetric analysis has been extended to cover determinations of volatile matter (as well as determination of moisture and ash) in coal and coke. These constituents can be measured by pyrolyzing the samples in oxygen and air, and the weight loss at prescribed temperatures was measured by using a thermobalance. 

In order to predict emissions from AFBC s it is necessary to couple a model of the sulfur capture of individual particles into a system s model which takes into account the SO2 formation, removal, and transport. Because the single particle behavior is so complex, most such models (10, 20, 21, 22) use simplified, usually empirical, fits of single particle behavior determined, for example, from thermogravimetric analysis. 

The [Cr(H20)(0H) 0P(C H8)20 2]a polymer is a green solid which is readily soluble in chloroform, benzene, and tetrahydro-furan but is insoluble in water and diethyl ether. It does not melt before decomposing thermogravimetric analysis indicates decomposition starting at 365°C. A freshly prepared solution in chloroform has an intrinsic viscosity ranging from 0.03 to 0.04 dl./g. The intrinsic viscosity increases slowly when solutions in organic solvents (for example, 1 g./lOO ml. in chloroform) are allowed to stand at temperatures of approximately 55°C., and values of 0.6-0.8 dl./g. are common after a number of days. A sample with an intrinsic viscosity of 0.04 dl./g. 

This monograph provides an introduction to scanning ther-moanalytical techniques such as differential thermal analysis (DTA), differential scanning calorimetry (DSC), dilatometry, and thermogravimetric analysis (TG). Elevated temperature pyrometry, as well as thermal conductivity/diffusivity and glass viscosity measurement techniques, described in later chapters, round out the topics related to thermal analysis. Ceramic materials are used predominantly as examples, yet the principles developed should be general to all materials. 

The next stage of characterization focuses upon the different phases present within the catalyst particle and their nature. Bulk, component structural information is determined principally by x-ray powder diffraction (XRD). In FCC catalysts, for example, XRD is used to determine the unit cell size of the zeolite component within the catalyst particle. The zeolite unit cell size is a function of the number of aluminum atoms in the framework and has been related to the coke selectivity and octane performance of the catalyst in commercial operations. Scanning electron microscopy (SEM) can provide information about the distribution of crystalline and chemical phases greater than lOOnm within the catalyst particle. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) can be used to obtain information on crystal transformations, decomposition, or chemical reactions within the particles. Cotterman, et al describe how the generation of this information can be used to understand an FCC catalyst system. 

TGA, Differential Thermal Analysis (DTA) and Differential Thermogravimetric Analysis (DTG) measurements have been employed to determine the number and nature of water molecules present in the POMs. The results of TGA show the presence of two types of water in POM compounds, namely water of crystalHza-tion and constitutional water molecules. The loss of the former usually occurs at temperatures below 443-473 K [141]. At temperatures exceeding 543 K for H3PM012O40 and 623 K for H3PW12O40, the constitutional water molecules (the acidic protons bound to the oxygens of the polyanion) are lost, according to the literature and for the acid forms [140]. For example the thermolysis of H3PM012O40 proceeds in two steps as schematized below ... 

Thermal analysis techniques (differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and evolved gas analysis (EGA)) provide qualitative, semiquantitative, and in special cases, quantitative measurements of the energetic evolution of nanophase materials on heating. Variation of the heating rate and the atmosphere surrounding the sample provide additional information. Some examples are given below in the context of specific systems. 

Effect of thermostabilizers on the polymer properties was studied by different physicochemical methods. For example, in the work [260] method of DSS (differential spectroscopy) was used to define the effect of polyester-imide on thermo-physical properties of PETP. By this method it was found out that polyester-imide reduces PETP ability to crystallization. Methods of thermogravimetric analysis (TGA) and infrared spectroscopy in the nitrogen atmosphere were used in the work [261] to define thermal stability of the mixture of PETP and polyamide with the additive - modifier - polyethylene. It has been found that introduction of the additive decreases activation energy which positively tells on the ability of PETP to thermal destruction. 

Thermogravimetric analysis indicates high thermal stability for many ILs, generally >350°C. For example, ILs [EMIm][BF ], [BMIm][BF ], and l,2-dimethyl-3-propy-limidazolium bis(trifluorosulfonyl)imide are stable up to temperatures of 445°C,... 

Pharmaceutical examples of studies involving solvates are often linked with investigations into polymorphism hence, there is some overlap with the previous section. In addition, the chapter on thermogravimetric analysis in this book also deals with this subject. The examples given here have been chosen specifically on the basis of their illustrating the use of DSC, rather than outlining the properties of pharmaceutical hydrates in general. 

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