Thermogravimetric evaluation

In the thermogram (Figure 11.2), which vividly illustrates the thermogravimetric evaluation of CaC204.H20, it is ensured that the weight of this product decreases in several stages, namely ... 

Figure 11.2 Thermogravimetric Evaluation of Calcium Oxalate Monohydrate heated at the rate of 6°C min-1. 

H2) Freeman, S., and B. Carroll The application of Thermoanalytical techniques to reaction kinetics. The Thermogravimetric Evaluation of the Kinetics of the Decomposition of Calcium Oxalate Monohydrate. J. Phys. Chem. 62, 394/ 397 (1958). 

Freeman, E.S. and Carroll, B. (1958) The application of thermoanalytical techniques to reaction kinetics. The thermogravimetric evaluation of the kinetics of the decomposition of calcium oxalate monohydrate. J. Phys. Chem., 62, 394-397. 

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

The definition of polymer thermal stabiUty is not simple owing to the number of measurement techniques, desired properties, and factors that affect each (time, heating rate, atmosphere, etc). The easiest evaluation of thermal stabiUty is by the temperature at which a certain weight loss occurs as observed by thermogravimetric analysis (tga). Early work assigned a 7% loss as the point of stabiUty more recentiy a 10% value or the extrapolated break in the tga curve has been used. A more reaUstic view is to compare weight loss vs time at constant temperature, and better yet is to evaluate property retention time at temperature one set of criteria has been 177°C for 30,000 h, or 240°C for 1000 h, or 538°C for 1 h, or 816°C for 5 min (1). 

Homma, H., Kuroyagi, T., Izumi, K., Mirley, C.L., Ronzello, J. and Boggs, S.A., Evaluation of surface degradation of silicone rubber using thermogravimetric analysis, Proc. Int. Symp. Electr. Insul. Mater., 2nd. 1998, 1, pp. 631-634. 

Nitrogen adsorption was performed at -196 °C in a Micromeritics ASAP 2010 volumetric instrument. The samples were outgassed at 80 °C prior to the adsorption measurement until a 3.10 3 Torr static vacuum was reached. The surface area was calculated by the Brunauer-Emmett-Teller (BET) method. Micropore volume and external surface area were evaluated by the alpha-S method using a standard isotherm measured on Aerosil 200 fumed silica [8]. Powder X-ray diffraction (XRD) patterns of samples dried at 80 °C were collected at room temperature on a Broker AXS D-8 diffractometer with Cu Ka radiation. Thermogravimetric analysis was carried out in air flow with heating rate 10 °C min"1 up to 900 °C in a Netzsch TG 209 C thermal balance. SEM micrographs were recorded on a Hitachi S4500 microscope. 

When a solid is capable of decomposing by means of several discrete, sequential reactions, the magnitude of each step can be separately evaluated. Thermogravimetric analysis of compound decomposition can also be used to compare the stability of similar compounds. The higher the decomposition temperature of a given compound, the more positive would be the DG value and the greater would be its stability. 

The possibility of automatic collection and evaluation of thermoanalytical data should be mentioned here in connection with the thermogravimetric vapor pressure measurements. Principally, any desired quantitative evaluation procedure in thermal... 

The thermal properties of benzoic acid were evaluated using simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA). This work was performed on a Shimadzu DT-30 Thermal Analyzer system, which was calibrated using indium standard. Using a heating rate of 10°C/min, the thermograms presented in Figure 3 were obtained. 

A good-quality CeMCM-41 material with Si/Ce=50 was synthesized by hydrothermal method. For the purpose of comparison a pure siliceous MCM-41 was prepared using the same composition without cerium. Thermogravimetric curves for the synthesized uncalcined samples exhibit shape characteristic for the MCM-41-type materials. The specific surface area of CeMCM-41 evaluated from nitrogen adsorption was equal to 850 m2/g, whereas the pore width and mesopore volume of this material were equal to 3.8 nm and 0.8 cm3/g, respectively. In contrast to the pure silica MCM-41, the CeMCM-41 material exhibits medium and strong acid sites as revealed by thermogravimetric studies of n-butylamine thermodesorption. 

The evaluation of the acid properties of calcined materials was based on the assumption that n-butylamine molecules interact with all acid sites, and the total acidity of the sample studied can be determined from the maximum amount adsorbed. Shown in Fig. 2 are thermogravimetric curves for n-butylamine thermodesorption, which were used to evaluate the amount of medium and strong acid sites for both samples. Thermodesorption of n-butylamine from CeMCM-41 exhibits three distinct ranges (i) desorption of physically adsorbed amine bellow 230 °C (ii) desorption of n-butylamine from medium acid sites at 230 - 410 °C (0.25 mmol/g), and (iii) its desorption from strong acid sites at 410 - 590 °C (0.21 mmol/g). However, only one weight loss was observed for pure silica MCM-41 due to thermodesorption of physically adsorbed amine, indicating negligible acidity of this material. 

Data for calcined samples dioo - XRD (100) interplanar spacing, Sbet - BET specific surface area, V, - total pore volume, Vp - primary mesopore volume, Sex - external surface area, wkjs - primary mesopore diameter. Data for uncalcined samples mreS due - mass percent of residue at 1263 K, mSdir - mass decrease in the temperature range of the surfactant decomposition and desorption of the decomposition products (between about 373 and 623 K). Notes a - no peak on XRD spectrum, d,0o cannot be evaluated, b - no linear region on the Os-plot, which would be suitable for the Vp and Sex evaluation. XRD and adsorption data (except for those for HR-A2 sample) taken from Refs. 24 and 26. Thermogravimetric data for DS-AD taken from Ref. 19. 

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. 

Thermal properties are measured and evaluated by some of the methods also mentioned in Chapter 2. For identification of transition temperatures, measurements of heats of fusion, and so on, differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are much used. Thermal stability is measured by thermogravimetric analysis (TGA), although this technique can give overly optimistic results unless used with great care. 

D. Wang, K. Echols, and C.A. Wilkie, Cone calorimetric and thermogravimetric analysis evaluation of halogen-containing polymer nanocomposites, Fire Mater., 2005, 29 283-294. 

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