Section G - Thermal methods

A crucible containing the sample is heated in a furnace at a controlled rate and weighed continuously on a balance. Temperature and mass data are collected and processed by a computer dedicated to the system. Control of the atmosphere surroimding the sample is imjxntant. 

There are many factors that affect the results obtained by thermal methods. These must be carefully controlled and recorded. 

Any physical or chemical change involving mass may be studied. Evaporation of volatile material, oxidation, and particularly decompositions of inorganic salts, organic and jxjlymeiic samples are investigated analytically. 

Differential thermal analysis and differential scanning calorimetry (G2) 

While some analytical methods, such as spectrometry, give results that are very specific for the particular sample, thermal methods will respond to the totality of the effects. Anything that changes the mass at a particular temperature evaporation, reaction or oxidation will affect the thermogravimetric measurement. It is sometimes an advantage to combine techniques, or to run two simultaneously (see Section F) to extract the maximum benefit from the analysis. 

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The adaptation of zeolites to a particular purpose can be done by ion exchange and by different chemical and physical treatments. Physicochemical characteristics of zeolites often reflect the modifications introduced in the structure. Different methods are used to study the modifications and their correlations with sorption properties and catalytic activity. In this section G. T. Kerr reviews the chemistry involved in the thermal activation of NH4Y zeolites. 

A detailed account of polymorphism and its relevance in the pharmaceutical industry is given elsewhere in this volume and in the literature [42,46,47]. This section will focus on the use of vibrational spectroscopy as a technique for solid-state analysis. However, it should be noted that these techniques must be used as an integral part of a multidisciplinary approach to solid-state characterisation since various physical analytical techniques offer complimentary information when compared to each other. The most suitable technique will depend on the compound, and the objectives and requirements of the analysis. Techniques commonly used in solid-state analysis include crystallographic methods (single crystal and powder diffraction), thermal methods (e.g. differential scanning calorimetry, thermogravimetry, solution calorimetry) and stmctural methods (IR, Raman and solid-state NMR spectroscopies). Comprehensive reviews on solid-state analysis using a wide variety of techniques are available in the literature [39,42,47-49]. 

This section addresses mitigation methods for SCC since SCC is the prevalent degradation mode for RPVIs. Mitigation methods for other known sources of degradation (e.g. fatigue and thermal) are not addressed. 

Isomerization of coordination compounds is one important class of thermal transformation. In the case of inert complexes such isomerization may be irreversible and so allow the preparation of specific isomers. Some transformations of this type (e.g. isomerization of square-planar complexes) were introduced in Chapter 1 and additional examples will be discussed in Section 12.10. In this Chapter the use of solid state thermal transformations in synthetic coordination chemistry is discussed. Work on the use of thermal methods as analytical tools in coordination chemistry can be found... 

In further sections extensions or adaptations of the PECVD method will be presented, such as VHF PECVD [16], the chemical annealing or layer-by-layer technique [17], and modulation of the RF excitation frequency [18]. The HWCVD method [19] (the plasmaless method) will be described and compared with the PECVD methods. The last deposition method that is treated is expanding thermal plasma CVD (ETP CVD) [20, 21]. Other methods of deposition, such as remote-plasma CVD, and in particular electron cyclotron resonance CVD (ECR CVD), are not treated here, as to date these methods are difficult to scale up for industrial purposes. Details of these methods can be found in, e.g., Luft and Tsuo [6]. 

The phase transition from amorphous to crystalline can sometimes be promoted by thermal treatment (annealing) [ 1.45]. In a laboratory scale, this can be done relatively simple. In a production scale the process must be proven as reproducible and reliable by a validation process, which is time consuming. It is therefore recommended, that a search for CPAs and process conditions, which would lead to crystallization be carried out, using methods such as DTA, DSC, ER and DRS (see Section 1.1.5) also see Yarwood [1.46. If this is not successful, time and temperature for TT should be chosen in such away, that the tolerances for time and temperature are not to narrow, e. g. -24.0 °C 0.5 °C and 18 min 1 min are difficult to operate, while -30 °C 1.5 °C and 40 min 2 min might be easier to control. 

Test Method Section of Chapter 2 Typical Sample Mass (g) Typical Sensitivity (W/kg) Thermal Inertia Phi-factor Principal Applicationa Data Acquired A=Advantage D=Disadvantageb... 

The method of choice for the preparation of Pa metal is a somewhat modified van Arkel-De Boer process, which uses protactinium carbide (Section II,C) as the starting material. The carbide and iodine are heated to form protactinium iodide, which is thermally dissociated on a hot filament 12-15). An elegant variation is to replace the filament with an inductively heated W or Pa sphere 109). A photograph of a 1.4-g sample of Pa metal deposited on a radiofrequency-heated W sphere is shown in Fig. 6. From the analytical data presented in Table V, the impurities present before and after application of this modified iodide transport process (Sections II,D and III,C) can be compared. 

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