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materials, metals, alloys and ceramics, at high/very high temperatures (up to 6000 K or so).

5.2

Experimental methods

for

the

measurement

of

thermodynamic

data at high temperature

Topic description and teaching suggestions: The most used experimental calorimetric and equilibrium techniques for obtaining thermodynamic data of materials are described

Calorimetric methods: various calorimetric techniques such as direct reaction calorimetry, solution calorimetry, combustion calorimetry, DSC adapted for high temperature conditions are employed to get thermodynamic information on various classes of inorganic materials (heats of formation, heats of solution, specific heats, etc.).

Equilibrium methods: vapour pressure methods, electromotive force methods and chemical equilibration methods. Second-law and third-law analysis of equilibrium data. Among the equilibrium VP methods employed, the classical transpiration technique, the Knudsen-effusion and torsion-effusion techniques sometimes coupled with thermogravimetry and their potentialities can be illustrated. Stress that in particular the high- temperature Knudsen cell mass spectrometry (KC-MS) technique yields important and often unique information on the gas phase as well on the solid phase. In fact, most available thermochemical data for high temperature gaseous species of a wide degree of complexity have been and still are determined by this technique. To extend the area of application of HT-MS to higher temperature and high pressure conditions, the mass spectrometer has been coupled with laser heating of the sample (LIV-MS, laser induced vaporization mass spectrometry) and high pressure molecular source (HP-MS, high pressure-mass spectrometry) for sampling and studying vapours in the higher (> 1 atm) pressure regimes. The HT-MS technique under many aspects, significantly contributed and still contributes to the development of high temperature materials chemistry, particularly in the area concerning the characterization of high-temperature vapours and the acquisition of thermodynamic data.

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