Thermogravimetry quantitative

A second approach to gravimetry is to thermally or chemically decompose a solid sample. The volatile products of the decomposition reaction may be trapped and weighed to provide quantitative information. Alternatively, the residue remaining when decomposition is complete may be weighed. In thermogravimetry, which is one form of volatilization gravimetry, the sample s mass is continuously monitored while the applied temperature is slowly increased. 

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

Thermogravimetry (TG) is a measure of the thermally induced weight loss of a material as a function of the applied temperature [45]. Thermogravimetric analysis is restricted to studies that involve either a mass gain or loss, and it is most commonly used to study desolvation processes and compound decomposition. The major use of TG analysis is in the quantitative determination of the total volatile content of a solid. When a solid can decompose by means of several... 

A third experimental technique, which was first described by Kargc ct al. [36, 39], is based on combined thermogravimetry and gas chromatography (TGA/ GC). The coked catalyst is placed into a thermo-balance. In a first run, desorbable components of the coke and all water adsorbed on the catalyst are removed from the solid catalyst in a purge of dried nitrogen at an appropriate temperature. The desorbed hydrocarbons and water arc quantitatively condensed in a cooling trap, e.g., at liquid nitrogen temperature. When this desorption is completed, the trap is quickly heated,... 

Thermogravimetry (TG) or thermogravimetric analysis (TGA). In this technique, the mass of a sample is followed as a function of temperature or time. The amount and rate of mass change with temperature or time in a controlled atmosphere are obtained. Such information can tell us about thermal stability as well as the compositional profile of a variety of elastomers and polymers. It is an excellent quantitative technique but qualitatively there may be some doubt as to what material is lost during heating. 

Thermogravimetry is an attractive experimental technique for investigations of the thermal reactions of a wide range of initially solid or liquid substances, under controlled conditions of temperature and atmosphere. TG measurements probably provide more accurate kinetic (m, t, T) values than most other alternative laboratory methods available for the wide range of rate processes that involve a mass loss. The popularity of the method is due to the versatility and reliability of the apparatus, which provides results rapidly and is capable of automation. However, there have been relatively few critical studies of the accuracy, reproducibility, reliability, etc. of TG data based on quantitative comparisons with measurements made for the same reaction by alternative techniques, such as DTA, DSC, and EGA. One such comparison is by Brown et al. (69,70). This study of kinetic results obtained by different experimental methods contrasts with the often-reported use of multiple mathematical methods to calculate, from the same data, the kinetic model, rate equation g(a) = kt (29), the Arrhenius parameters, etc. In practice, the use of complementary kinetic observations, based on different measurable parameters of the chemical change occurring, provides a more secure foundation for kinetic data interpretation and formulation of a mechanism than multiple kinetic analyses based on a single set of experimental data. 

Follow-up characterization of the volatiles initially analyzed by TGA could also be conducted. Confirmation of the volatiles may be accomplished using one of several techniques thermogravimetric-infrared (TG-IR) spectroscopy, gas chromatography (GC), or thermogravimetry-mass spectrometry (TG-MS). These techniques may be able to qualitatively and quantitatively determine the content and identification of the solvents present in the material. Additionally, Karl Fisher titrimetric assays may be utilized to quantitate the water content in the material. 

CuiF, J. P., Dauphin, Y., Berthet, P. Jegoudez, J. 2004. Associated water and organic compounds in coral skeletons quantitative thermogravimetry coupled to infrared absorption spectrometry. Geochemistry, Geophysics, Geosystems, 5, 11. doi 10.1029/2004/GC000783. 

Quantitative measurements of the mass-changes are possible by determination of the distance, on the curve mass axis, between the two points of interest or between the two horizontal mass levels. In derivative thermogravimetry, the derivative of the mass-change with respect to time, dm/dt, is recorded as a function of time (r) or temperature (T). or... 

The method of thermogravimetry is basically quantitative in nature in that the mass-change can be accurately determined- However, the temperature ranges in which the mass-changes occur are qualitative in that they depend on the instrumental and sample characteristics. With the wide use of commercial thermobalances, TG data of a sample can be correlated from laboratory to laboratory if similar conditions of pyrolysis are employed. 

It should be mentioned in advance that FT-IR spectrometer is used increasingly in combination with thermogravimetry to identify the released coinxments (solvents or decomposition products) during the heating process. The applicability of some of the IR-sampling methods for the characterization of solid-state forms is discussed in more detail by Threlfall [37] and Bugay [25] and quantitative analysis has been reviewed by Stephenson etal. [38]. 

Applications of thermogravimetry (Q-TG) for the investigation of adsorbed liquid layers and porosity parameters used for the quantitative characterisation of the energetic and geometrical (e.g. total) heterogeneities of typical advanced materials have been presented. The technique is very useful for investigating the physicochemical properties of surface liquid films, adsorbate-adsorbent interactions and total surface heterogeneity. 

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