Thermal Analysis Experimental Parameters

Accurate temperature calibration using the ASTM temperature standards [131, 132] is common practice for DSC and DTA. Calibration of thermobalances is more cumbersome. The key to proper use of TGA is to recognise that the decomposition temperatures measured are procedural and dependent on both sample and instrument related parameters [30]. Considerable experimental control must be exercised at all stages of the technique to ensure adequate reproducibility on a comparative basis. For (intralaboratory) standardisation purposes it is absolutely required to respect and report a number of measurement variables. ICTA recommendations should be followed [133-135] and should accompany the TG record. During the course of experiments the optimum conditions should be standardised and maintained within a given series of samples. Affolter and coworkers [136] have described interlaboratory tests on thermal analysis of polymers. 

In the classical differential thermal analysis (DTA) system both sample and reference are heated by a single heat source. The two temperatures are measured by sensors embedded in the sample and reference. In the so-called Boersma system, the temperature sensors are attached to the sample pans. The data are recorded as the temperature difference between sample and reference as a function of time (or temperature). The object of these measurements is generally the determination of enthalpies of changes, and these in principle can be obtained from the area under a peak together with a knowledge of the heat capacity of the material, the total thermal resistance to heat flow of the sample and a number of other experimental factors. Many of these parameters are often difficult to determine hence, DTA methods have some inherent limitations regarding the determination of precise calorimetric values. 

Besides the multiple techniques given here, a few of the EGD-EGA techniques listed in Table 8.2 are used by themselves and have not been coupled to other thermal analysis techniques. Some of them will no doubt be coupled to TG and DSC techniques in the future. Several of the EGD-EGA techniques will probably never be coupled to other thermal analysis techniques due to the uniqueness of the experimental parameters involved such as thin-layer chromatography. 

One of the important trends in chemical analytical instrumentation during the past decade has been the use of digital computers as data processing aids. Raw experimental data from an instrument is manipulated, displayed, and printed by use of a microcomputer or minicomputer. This trend has become very apparent in thermal analysis instrumentation. A small dedicated microcomputer is used to set the instrument s operating parameters as well as to process and display the experimental data. Unfortunately, the T A instruments such as thermobalances, DTA, DSC, and TMA units are of designs that are at least 20 years or more old. New instrument designs have not been developed but, rather, the emphasis has been on computerization. 

Perhaps the most important advance in commercial thermal analysis instrumentation during the past 10-12 years has been the use of microprocessors and/or dedicated microcomputers to control the operating parameters of the instrument and to process the collected experimental data. This innovation is by no means unique to thermal analysis instrumentation alone since these techniques have been applied to almost every type of analytical instrument. Unfortunately, the automation of thermal analysis has not become a commercial reality. Complete automation is defined here as automatic sample changing, control of the instrument, and data processing. Such instruments were first described by Wendlandt and co-workers in the early 1970s (See Chapters 3 and 5) although they lacked microprocessor control of the operating conditions. 

The application of thermal analysis to the study of kinetics involves so many ramifications that few would dispute that it could fill a book of its own. In principle at least the determination of kinetic parameters requires an investigation of the rate of reaction over all values of extent of reaction and temperature. Only in this way can potential changes in the reaction mechanism be identified. It cannot be accomplished by a single experiment but if the experimental conditions are sufficiently extensive the results are capable of providing useful information. Even so, extrapolation of rate data outside the conditions of the experiment needs to be undertaken with care. Results may be used to obtain predictive curves which relate extent of conversion, time and temperature. The isothermal law has been linked to a variety of mechanistic models but the ultimate determination of mechanisms depends on the input of results from a variety of techniques. 

The solubility parameter values of the polyesterimide (10.76 [182]), the novolae (10.7), and the resole (11.1), imply that these polymers should be thermodynamieally miseible beeause the differenee of these parameters between the polyesterimide and a phenolie resin is a small number. The theoretieally predieted miseibility of polyesterimide with novolae or resole appears to be bom out experimentally sinee differential thermal analysis shows a single glass transition temperature for all the blends, and seanning eleetron... 

Abstract. The Thermal Analsysis (TA) applies a great variety of techniques suitable for determining the thermophysical properties of solids. Here after a wide and detailed review on more conventional methods of differential thermal analysis (DTA) and differential scanning calorimetry (DSC) to study non-equilibrated materials, the experimental results obtained from Short-Range Ordering (SRO) in a Cu-Al alloys is presented and discussed. The kinetic parameters and laws in these materials are deeply discussed focusing attention also to vacancy behavior and effects of quenching conditions. 

In temperature-programmed reduction (TPR), a flow of inert gas (N2 or Ar) containing approximately 5 vol% H2 is passed through the catalyst bed of a flow reactor containing a reducible solid catalyst (66). By monitoring continuously the H2 concentration in the gas flow and its eventual consumption with a thermal conductivity detector when heating the sample with a linear temperature ramp of ca. 10 K/min, the rates of reduction are obtained as a function of time (or temperature). The total amount of H2 consumed determines the reduction equivalents present in the catalyst, and detailed analysis of the experiment permits the kinetic parameters of the reduction process to be determined and provides information on the reduction mechanisms. The characteristic numbers, which depend on the experimental parameters (amount of reducible species present, H2 concentration, flow rate, and temperature ramp), have been defined (66,67). These numbers must be kept in certain ranges for optimal performance of the experiment. 

This handbook is designed to provide general information on the basic principles of TA and a variety of its applications. It is composed of two 1915 parts. Part I deals with information on the transition, reaction and characteristic parameters of substances. It introduces general principles, data 1919 treatment, experimental procedures and data analysis. Part II presents about 1000 typical 1945 thermal analysis curves, with brief explanations, for a wide variety of materials, such as polymers, 1960s foods, woods, minerals, explosives, inorganic compounds, and their coupled simultaneous 1964 curves. TA charts have been contributed by Institutes and Universities in China. Part III cites 1965 various data tables relating to thermal analysis. 

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