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Abstract

Using special thermogravimetry Q-TG method, physicochemical properties of lunar sample surfaces were investigated. The numerical and analytical procedures for the evaluation of energetic heterogeneous properties on the basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium conditions are presented. The calculations of the adsorption capacity and energy distribution functions of liquids on lunar surfaces on the basis of the thermogravimetry data are presented.

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Determination of liquid adsorption and desorption on and from solids by means of the derivatograph

Part III. Determination of water adsorption and desorption heats on silica gel by derivatographic measurements

Journal of Thermal Analysis and Calorimetry
Author: P. Staszczuk
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Abstract  

A simple method has been adopted to obtain an important information on the heterogeneous properties of materials studied, adsorbed liquid films and liquid-solid interactions. The method utilizes Q-TG mass loss and the first derivative Q-DTG mass loss curves with respect to temperature and time obtained during programmed liquid thermodesorption in quasi-isothermal conditions. The values of the adsorption capacity, total porosity of material, the value of active centers, desorption energy distribution and mesopore-size distribution functions obtained by this method are in good agreement with those estimated on the basis of independent methods. The theoretical and experimental results provided novel and unique data on the heterogeneity of solid surfaces, properties of liquid adsorbed films and thermal stability of the liquid/solid interfaces. This paper presents the more important results obtained so far in the studies the liquid/solid systems by means of the Paulik's classical and quasi-isothermal techniques.

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Determination of liquid vapour adsorption and desorption on and from solids by means of the derivatograph II

Determination of kinetics and isotherms of adsorption and desorption of water vapour on silica gel

Journal of Thermal Analysis and Calorimetry
Author: P. Staszczuk

Studies of water adsorption and desorption on silica gel with a modified derivatograph are described. The dynamic gas chromatography step profile method was used to determine isotherms of adsorption and desorption from the TG curve. The obtained isotherms agree with those from other methods. The properties of surface liquid layers can be investigated by this method.

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Determination of liquid vapour adsorption and desorption on and from solids by means of the derivatograph

Part I. Derivatograph for measurements of adsorption and desorption at a constant temperature

Journal of Thermal Analysis and Calorimetry
Author: P. Staszczuk
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This paper presents investigations of phase and structural transitions occurring in water adsorbed on the surface of bovine serum albumin (BSA) and on the so-called ‘intelligentrs or ‘smart’ silica gel surface covered with a chemically bonded BSA phase. Cyclic changes of heat flow (HF) were observed in the samples studied during cooling and heating of the measuring cell of the differential scanning calorimetry (DSC) apparatus. These cyclic changes reflect structural transitions occurring in the water adsorbed on the surface at subambient and elevated temperatures. This is connected with cyclic changes (decay and reproduction) of ice-like structures existing in the adsorbed water layers. On the basis of quantitative investigations it appears that, depending on the direction of the cooling or heating process of the samples studied, the number of ice-like water structures in the surface film increases or decreases. It has been stated that the observed fluctuations occur spontaneously and suddenly in the whole volume of adsorbed water in different and not regular temperature ranges, especially at the ‘paradoxical effect’ temperatures.

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Controlled-rate thermal analysis

Characterization of heterogeneity of active carbon surfaces and adsorbed water layers

Journal of Thermal Analysis and Calorimetry
Author: P. Staszczuk

Controlled-rate thermal analysis (CRTA) and differential scanning calorimetry (DSC) were used to investigate the adsorbed water layers and the surface properties of different commercial activated carbons. A simple method is proposed to obtain information on the properties of the adsorbed water film and the surface heterogeneity of the materials studied. This method utilizes TG mass loss and the first derivative of the DTG mass loss curves with respect to temperature and time, obtained during programmed liquid thermodesorption. The obtained TG mass loss curves, which reflect the energetic heterogeneity, consisted of steps and inflections which were associated with the mechanism of wetting of the solid surfaces. The heights of these steps and inflections depend on the adsorption capacity, the adsorption potential and the nature and number of the active centers of the carbon samples studied. The values of the total porosity and the surface phase capacity obtained by this method are in good agreement with those estimated on the basis of independent methods. The behaviour of water/carbon samples was studied by means of DSC at subambient and elevated temperatures. The experimental results provided novel data on the structural heterogeneity, the thermal stability of the water/carbon interface and its phase and structural transitions.

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Abstract  

The results of dynamic and quasi-isothermal thermodesorption of water from a silica gel surface at low furnace heating rates in the temperature range 20–125° are presented. From the experimental results, the water film pressure π on silica gel surface, the activation energy ΔE and the evaporation heat ΔH were calculated. An interpretation of π changes in relation to the film thickness and wetting process has been proposed. It is concluded that the characteristic film pressure values correspond to the work of spreading, and immersional, adhesional and adhesional-cohesional wetting. From the determined film pressure values, the average value of the silica gel polar component, γ s P , was calculated to be 114.67 mJ/m2.

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