Applications of Isothermal Calorimetry

Calorimetry has found many uses within many different disciplines in the scientific community. Over the past 8 years, the primary journals relating to calorimetry have recorded over 24000 references to calorimetry, equivalent to 8 publications a day There are active areas of research in such diverse industries as metals, foods, agriculture, textiles, explosives, ceramics, chemicals, biological systems, pharmaceuticals, polymers and the nuclear industry. 

Isothermal calorimeters typically have exceptional signal stability over extended time, which is useful for the study of slow reactions. Here a study of imidazole-catalysed hydrolysis of triacetin, an example of a second order reaction, was made over 150 days. A plot of power, raised to ( — 0.5), against time was linear, illustrating the stability of the calorimeter over the time of the study 

In the metal industry studies have been made of the phase transitions of metal alloys, modelling capacitors,metal hydration kinetics, precipitation of solutionised aluminium,and mechanisms of solid state transitions.  

Food applications include the shelf life of foods, cooking of rice, oxidation of rapeseed oil, photo-calorimetric study of plants,properties of amorphous sugar, and metabolism of dormant fruit buds.  

The study of minerals systems and ceramics has given valuable information for the construction and materials industry, and the chemical industry has also benefited from studies of reactions and physical processes.  

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Figure 6.11 shows a famous example of the application of isothermal calorimetry. Gordon (1955) deformed high-purity copper and annealed samples in his precision calorimeter and measured heat output as a function of time. In this metal, the heat output is strictly proportional to the fraction of metal recrystallised. 

Another similar application of isothermal calorimetry is the assessment of the thermal power at different curing regimes see Figure 2.11. Sealed conditions, which are the usual case in isothermal calorimetry, are compared to pastes with extra water added on top of the sample. This extra water causes an increase in cumulative heat and thus an increased hydration degree. The effect becomes more pronounced at lower w/c, where the samples tend to undergo self-desiccation. The same effect can be seen also with other types of cement, such as calcium sulfoaluminate cements. As this type of cement needs a higher w/c for complete hydration compared to Portland cement (around 0.5-0.6 instead of 0.4 see Winnefeld and Lothenbach 2010), the effect of the extra water is already very evident at a w/c of 0.7 see Figure 2.12. 

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