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A second generation twin double microcalorimeter

Measurements of sorption isotherms, heats of sorption and sorption kinetics

Journal of Thermal Analysis and Calorimetry
Authors: I. Wadsö and L. Wadsö

Abstract  

A calorimetric method for the study of solid-vapor interactions is described. In one calorimetric chamber a vapor evaporates; in a second calorimetric chamber the vapor is absorbed by a sample. The two chambers are connected by a tube and form part of a double twin microcalorimeter. As vapor is sorbed by the sample the vapor pressure in the sorption chamber will increase from a low value to near saturation. The flow rate of the vapor is governed by diffusion through the tube between the vessels. From the thermal power measured in the vaporization calorimeter it is possible to evaluate the sorption isotherm, and using information from both calorimeters the heat of sorption may be calculated as a function of equilibrium vapor pressure. By conducting experiments with different sized samples it is also possible to study the kinetics of the sorption process. The paper describes some recent improvements of the technique and gives examples of its use.

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Abstract  

A brief survey is given of recent developments and current activities in isothermal microcalorimetry. The discussion focuses on new methods in areas where the techniques have proved to be particularly useful or are promising to be so, in a near perspective. Some problems and limitations with current methods are also discussed.

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Abstract  

Growth of mould fungi is one of the main causes of deterioration of foodstuffs, building materials and textiles. A new microcalorimetric technique has been developed for the study of mould activity as a function of water activity, temperature and atmospheric composition. This paper describes the method, in particular how to measure mould activity as a function of relative humidity.

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Abstract  

Water vapor sorption on morphine sulphate was studied in a twin double sorption microcalorimeter at 25°C. The vapor sorption isotherm and the differential heats of sorption were determined simultaneously from dry condition to a water activity of 0.99. Two well resolved hydration steps were obtained on the sorption isotherm at water activities of 0.01 and 0.22 corresponding to the formation of dihydrate and pentahydrate of morphine sulphate. They were accompanied by constant values of the differential heats of sorption: –24 kJ mol–1(H2O) for the dihydrate formation and –10 kJ mol–1(H2O) for the pentahydrate formation.The calorimetrically obtained sorption isotherms were compared with the results of Karl Fisher titrations of morphine sulphate samples equilibrated at different water activities. The appearance of a liquid phase in the morphine sulphate at high water activities is discussed on the basis of the obtained differential heats of sorption and measured heat capacities of morphine sulphate at different water activities.

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Journal of Thermal Analysis and Calorimetry
Authors: I. Lamprecht, R. Seymour, C. White, P. Matthews, and L. Wadsö

Abstract  

Discontinuous gas exchange cycles (DGCs) are frequently observed with insects, i.e. oxygen take up and carbon dioxide release occur interrupted by periods of a few minutes up to many hours. The paper presents direct and indirect calorimetric experiments on DGCs of the scarabid rhinoceros beetle Oryctes nasicornis. A direct/indirect calorimetric experiment is presented. Total and specific heat production rates amount to 0.56mWand 0.42mWg−1 in the first period without DGCs and to 0.43 mW (0.32 mW g−1) in the second phase, resp. The mean DGC amplitude is 0.184 mW and thus between 33 and 66% of the total turnover.

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