Phase-change adsorption calorimetry

Phase-change adsorption calorimetry. This was the earliest type of diathermal-conduction calorimetry and was originally developed in the form of ice calorimetry by Lavoisier and Laplace (1783), who weighed the liquid water, and by Bunsen (1870), who measured the change of volume. Dewar (1904) devised an elegant adsorption calorimeter at liquid air temperature the heat was evaluated from the volume of air vaporized. Of course, the temperature of the calorimeter is imposed by the temperature of the phase change. Because these calorimeters lack adaptability and cannot be readily automated, they are mainly of historical interest. 

Heat flow Differential scanning calorimetry (DSC) Phase change, adsorption, absorption, hydrogenation, dehydration, desorption, decomposition, dehydrogenation, reduction, oxidation, catalysis, heat capacity, kinetics,... 

Calorimetry is the basic experimental method employed in thennochemistry and thennal physics which enables the measurement of the difference in the energy U or enthalpy //of a system as a result of some process being done on the system. The instrument that is used to measure this energy or enthalpy difference (At/ or AH) is called a calorimeter. In the first section the relationships between the thennodynamic fiinctions and calorunetry are established. The second section gives a general classification of calorimeters in tenns of the principle of operation. The third section describes selected calorimeters used to measure thennodynamic properties such as heat capacity, enthalpies of phase change, reaction, solution and adsorption. 

In addition to calorimetry, information to establish the mode of adsorption is often obtained spectroscopically. Changes in the optical properties of (groups on) the surface or the adsorptive may be monitored. As an Illustration of the former. Rochester studied adsorption from the gas euid liquid phase on rutile (TiOj) and used infrared spectroscopy to distinguish between attachment at different surface hydroxyls. As an example of an ESR study, McBride investigated the adsorption of fatty acids on amorphous alumina from methanol by labelling them with a spin probe. Relevant information could be... 

Although the heat of adsorption or enthalpy change accompanying adsorption is directly obtained by calorimetry, it can conveniently be evaluated from the adsorption isostere. According to thermodynamics, the relationship between temperature T and pressure P under a state of -(J> phase equilibrium can generally be expressed with the Clausius-Clapeyron equation ... 

In the liquid-flow calorimetry experiment, the purified adsorbent bed remains in contact with a stock solution of constant composition. It is clear that the environment of the liquid phase does not change during the measurement. This is an important advantage of the flow calorimetry, especially in the case of solid-solution systems containing electrified interfaces. The study of ions adsorption from aqueous solutions... 

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