Calorimetry and DTA

As it was shown above, both calorimetry and DTA are very informative methods when investigating physical-chemical properties of BAS. They can be successfully applied to solve medical problems, in particular, to diagnose malignant neoplasms [228-233]. Thus, the results of the investigation of physical-chemical properties of human blood erythrocytes and their... 

In addition to these standardised test methods set by regulation (in particular the transport regulations of dangerous substances), there are laboratory methods that can provide more details regarding substance behaviour. In particular, there is differential thermal analysis (DTA), thermal gravimetric analysis, calorimetry and thermomanometry, which will not be described here. 

It was recognized quite some time ago that DTA analysis could be used to deduce the compatibility between a drug substance and its excipients in a formulation. The effect of lubricants on performance was as problematic then as it is now, and DTA proved to be a powerful method in the evaluation of possible incompatibilities. Jacobson and Reier used DTA to study the interaction between various penicillins and stearic acid [17]. For instance, the addition of 5% stearic acid to sodium oxacillin monohydrate completely obliterated the thermal events associated with the antibiotic. Since that time, many workers employed DTA analysis in the study of drug-excipient interactions, although the DTA method has been largely replaced by differential scanning calorimetry technology. 

These parameters need to be considered for reactions that go towards the intended completion as well as for possible upsets (see section C). Measuring methodologies for determining characteristic material property values (Stoffkenngrofcen), e.g., differential thermal analysis ("DTA"), calorimetry, and adiabatic experiments, and their possible use and applications are given in the literature /1, 2, 3, 41. 

The other common category of calorimetry is differential methods, in which the thermal behavior of the substance being measured is compared to that of a reference sample whose behavior is known. In differential scanning calorimetry (DSC), the instrument measures the difference in power needed to maintain the samples at the same temperature. In differential thermal analysis (DTA), the samples are heated in a furnace whose temperature is continuously changed (usually linearly), and the temperature difference between the sample and the reference sample as a function of time can yield thermodynamic information. DSC and DTA are most commonly used for determining the temperature of a phase transition, particularly for transitions involving solids. In addition, DSC experiments can yield values for the enthalpy of a phase transition or the heat capacity. Commercial DSC and DTA instruments are available. 

Accounts of DTA and DSC can be found in the recently published Volume 1 of Handbook of Thermal Analysis and Calorimetry and in Differential Scanning Calorimetry, An Introduction for Practitioners. Both texts provide a valuable source of references to original literature. An older text is the book by Wendlandt which like the Handbook is not restricted to DTA and DSC but nevertheless contains an enormous amount of information. Other texts are available which deal with specific areas of application food, " materials,petroleum analysis,pharmaceuticals and polymers. ... 

For this summary, forms of thermal analyses under extreme conditions are described for the measurement of heat and temperature, as dealt within Sects. 4.1-4. The distinction between DTA and DSC seen in these methods is described in Appendix 9. In Appendix 10, DTA or DSC at very low and high temperatures and DTA at very high pressures are mentioned. This is followed by a discussion of high-speed thermal analysis which, in some cases, may simply be thermometry. Finally, micro-calorimetry is treated. One might expect that these techniques will develop in this century [1]. The numbers in brackets link to references at the end of this appendix. 

The diagram in Fig. A.10.2 displays an instrument based on the classical design of a heat flux DTA (see Appendix 9). With a related design, differential calorimetry and thermogravimetry can be carried out simultaneously. Figure A. 10.3 illustrates a typical high-pressure DTA setup which is usable up to 500 MPa of pressure, 5,000 times atmospheric pressure. The pressure is transmitted by a gas, such as nitrogen. 

Another important application is infrared dichroism measurements for the assessment of chain (or group) orientation. This topic is treated in Chapter 9, and the discussion is not repeated here. It should be mentioned that Raman spectroscopy can also be used for the determination of chain orientation. Both IR and Raman spectroscopy are very useful for characterization of the physical structure of crystalline polymers. Assessment of the degree of crystallinity can be made by several methods. The preferred and internally consistent methods are X-ray diffraction, density measurements and calorimetry (DSC/DTA). This topic is described in detail in Chapter 7. However, both IR and Raman spectroscopy provide information about the crystallinity, although it is common for the actual crystallinity values obtained by these methods to deviate from values obtained by the three preferred methods WAXS, density and DSC/DTA. 

A study of the hydration of cement and cement compounds in the presence of superplasticizers is useful for theoretical and practical considerations. Many t5 es of thermal techniques including DTA, DSC, TG, DTG, Conduction Calorimetry, and EGA have been used for such studies. They have yielded important results that could be correlated with physical and mechanical characteristics of cement systems. Investigations have included the measurementofheat of hydration, the mechanism of reactions, strength development, microstmcture, permeability, durability aspects, compatibility problems between cement and superplasticizers, the prediction of some properties, material characterization and selection, mathematical modeling of hydration, development of test methods, and cement-superplasticizer interactions. 

Differential thermal analysis (DTA), thermogravimetric analysis (TGA), and dynamic differential calorimetry (DDC) are major techniques for the identification and investigation of rapid changes of state under dynamic thermal conditions. The difference between DTA and TGA is well delineated in technique and analysis however, the distinction between DDC and DTA remains poorly established in the experimental literature. It must be noted that DTA and DDC differ in their use of a homogeneous sample block and separated sample cups, respectively. These arrangements produce isolated thermal peaks by the former method and quantitative reaction heat determinations by the latter. In each analytical method, atmospheric effects must be considered in as much detail as are heat transfer conditions, specimen characteristics, and other physical parameters. 

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

Thermal analysis using differential scanning calorimetry (dsc), thermogravimetric analysis (tga), and differential thermal analysis (dta) can provide useful information about organic burnout, dehydration, and decomposition. 

Difl erential thermal analysis (DTA) and differential scanning calorimetry (DSC) are the other mainline thermal techniques. These are methods to identify temperatures at which specific heat changes suddenly or a latent heat is evolved or absorbed by the specimen. DTA is an early technique, invented by Le Chatelier in France in 1887 and improved at the turn of the century by Roberts-Austen (Section 4.2.2). A... 

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