Thermal analysis method

Thermal analysis methods are defined as those techniques in which a property of the analyte is determined as a function of an externally applied temperature... 

The sample temperature is increased in a linear fashion, while the property in question is evaluated on a continuous basis. These methods are used to characterize compound purity, polymorphism, solvation, degradation, and excipient compatibility [41], Thermal analysis methods are normally used to monitor endothermic processes (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, and chemical degradation) as well as exothermic processes (crystallization and oxidative decomposition). Thermal methods can be extremely useful in preformulation studies, since the carefully planned studies can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [7]. 

Another thermal analysis method available for catalyst characterization is microcalorimetiy, which is based on the measurement of the heat generated or consumed when a gas adsorbs and reacts on the surface of a solid [66-68], This information can be used, for instance, to determine the relative stability among different phases of a solid [69], Microcalorimetiy is also applicable in the measurement of the strengths and distribution of acidic or basic sites as well as for the characterization of metal-based catalysts [66-68], For instance, Figure 1.10 presents microcalorimetry data for ammonia adsorption on H-ZSM-5 and H-mordenite zeolites [70], clearly illustrating the differences in both acid strength (indicated by the different initial adsorption heats) and total number of acidic sites (measured by the total ammonia uptake) between the two catalysts. 

Autocatalysis happens when a reaction product, formed during reaction, acts as a catalyst which accelerates the progress of the reaction even at constant temperature. An example is the acid-catalysed saponification of various esters and related compounds. Autocatalytic reactions can be easily experimentally identified by means of differential thermal analysis methods. 

Thermal analysis methods investigate the properties of solids as a function of a change in temperature. They are useful for investigating phase changes, decomposition, loss of water or oxygen, and for constructing phase diagrams. 

There are two types of stages for dynamic microscopy (a) hot and cold stages and (b) tensile stages [1], Hot stages are most commonly used for the dynamic microscopy of polymers [1,43]. Thermal analysis in the OM is complementary to other thermal analysis methods, such as differential thermal analysis (DTA) [1], Direct observation of the structural changes of a polymer as a function of temperature can determine the nature of phase changes and thermal decomposition [1], It also measures the transformation temperatures. 

Any study of the polymerization kinetics of a bisbenzocyclobutene monomer is complicated by the lack of understanding of the resulting polymer s structure and the fact that as the polymerization proceeds, the reaction mixture crosslinks and vitrifies. This vitrification limits somewhat the number of quantitative methods which can be used to study the bisbenzocyclobutene polymerization kinetics. Some techniques are however useful under these constraints and good kinetic results have been obtained by both infrared and thermal analysis methods. 

The thermal-analysis methods were also used to determine, not only the heat of combustion, but also the rate of heat release and the seasonal variation of combustibility, matters of practical significance for the protection and conservation of forest resources. 

Dynamic testing DMTA, DMA, torsional braid analysis (Enns and Gillham, 1983) is first used as a thermal analysis method to detect the transitions, using dissipation peaks. Certain commercial DMTA instruments have a relatively low accuracy in measuring forces and/or strains. In contrast, they give relatively accurate values of the damping factor tan 5, so that dissipation spectra tan 8 = f (oo, T), are very useful analytical tools. 

Lyon, R., Walters, R., and Stoliarov, S., A thermal analysis method for measuring polymer flammability. Journal ofASTM International 2006, 3, 1-18. 

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. 

Ideally, the probe molecules used in the chemical characterization experiments should simulate as closely as possible the behaviour of the actual reactants. This is rarely possible and so simple probe molecules (H2, O2, CO, NO) are used instead. Some additional information about the nature of the surface may be obtained using thermal analysis methods, e.g., calorimetry, temperature-programmed desorption, temperature-programmed reaction. 

There has been some interest in thermal analysis methods for permanence evaluation. An attempt was made to correlate various features of differential scanning calorimetry thermograms for a group of papers with their stability under oven aging. In some cases, the correlation coefficient was encouragingly high but the standard error of estimate showed that the relation was no more useful for predicting permanence than was pH. 

The thermal analysis methods reported for the characterization of ezeti-mibe were conducted using thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). As detailed in Table 3.2, the TGA and DSC characterization of polymorphs of ezefimibe was reported in a patent publication. 

The fact that flame retardants and salts alter the kinetics, as well as the products, of the pyrolysis reactions is confirmed by the investigations of Tang and Neil involving thermogravimetric and differential thermal analysis methods (see Section 11,6 p. 446). These investi-... 

Thermal analysis methods, such as pressurized differential scanning calorimetry (PDSC), are popular for the determination of oxidative stabilities of vegetable oils (33, 36, 37). 

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. 

Giron, D. Goldbrorm, C. Piechon, P. Thermal analysis methods for pharmacopea materials. J. Pharm. Biochem. Anal. 1989, 7, 1421-1430. 

In the case of com cob, the results of the sintering tests (Table 3), in combination with those from the SEM-EDX analysis of the thermally treated ash samples, are in full agreement with the results obtained by the DTA-TGA thermal analysis method, clearly showing that mdiing/sintering effects begin at around 750 C or even at lower temperatures. 

Basic Mechanisms. Finally, further work is necessary on fundamental mechanisms of individual fire retardants. These mechanisms are a function of the particular chemicals involved and the environmental conditions of the fire exposure. There is a need to establish common methods and conditions for determining these mechanisms in order to compare different treatments. This would give us a better understanding of how these compounds work in action and would provide a more efficient approach for formulating fire-retardant systems than a trial and error approach. Correlations also need to be established between rapid precise thermal analysis methods and standard combustion tests. Retardant formulations could be evaluated initially on smaller (research and development size) samples. The more promising treatments could be tested for flame-spread index, heat release rate, and toxic smoke production. 

The use of thermal analysis techniques has increased rapidly in the past ten years and their field of application is widening continuously. This new book provides an overview of the principal thermal analysis methods and their application in major areas of importance, and will bring the reader up-to-date with the latest advances in the field. Special Publication No. 117 Hardcover viii+296 pages ISBN 0 85186 375 2... 

Differential scanning calorimetry/differential thermal analysis methods... 

Experimental determination of phase diagrams is convenient by using the thermal analysis method at which the temperature of the investigated sample is registered at its cooling by a constant rate of 2-5°C/min. Due to the thermal effects connected with the phase transformations (crystallization, polymorphic transformation), breaks appear on the cooling... 

Giron-Forest D, Goldbronn Ch, Piechon P. Thermal analysis methods for pharmacopeial materials. J Pharm Biomed Anal 1989 7 1421-1433. 

Bidstrup, W. Senturia, S. (1987) Society of Plastics Engineers ANTEC 87, pp. 1035-1038. Billingham, N.C., Bott, D.C. Manke, A. S. (1981) Application of thermal analysis methods to oxidation and stabilization of polymers, in Grassie, N. (Ed.) Developments in Polymer Degradation - 3, London Applied Science. 

The literature about differential thermal analysis methods for barbiturates was collected by Wollman and Braun.515 Polarographic assays have been reported,516,517 and other electrochemical methods were also used.518... 

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