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Thermodynamic properties and structure of water films in flotation processes

Influence of adsorption of tetradecylammonium chloride (TDAHCl) on barite and marble surfaces

Journal of Thermal Analysis and Calorimetry
Authors: P. Staszczuk and B. Biliñski
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The paper presents possible applications of differential thermal analysis for study of the physicochemical properties of liquid/solid systems, mainly through programmable liquid thermodesorption from the sample under quasi-isothermal conditions. The results prove its applicability in the determination of solid physicochemical properties, and particularly in calculations of adsorption potential distribution, the activation energy of molecules adsorbed on the surface and the surface heterogeneity by means of computer techniques.

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Abstract  

This paper presents the first evaluation of the pore-size distribution and energy distribution of butanol on a silica gel surface on the basis of one experimental run. The Q-TG mass loss and the first derivative Q-DTG mass loss curves of n-butanol thermodesorption from a silica gel sample were made with a Derivatograph Q-1500 D (MOM, Hungary), using an analyser equipped with an automatic ultraslow procedure and a special crucible capable of maintaining the quasi-isothermal heating procedure to increase the resolution of thermal analysis. A numerical procedure was developed for evaluation of the mesopore-size distribution and energy distribution functions of liquids preadsorbed on the mesoporous surfaces from special thermal analysis techniques. This is based on a condensation approximation to treat the kinetics of liquid thermodesorption from solids. A preliminary example is presented of application of the above approach to a quantitative description of the structural and energetic heterogeneities of silica gel surfaces on the basis of a single Q-DTG curve of n-butanol thermodesorption under quasi-isothermal conditions.

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Abstract  

Thermogravimetry (TG) was successfully applied in order to study the heterogeneous properties of solid surfaces and adsorbed liquid films. The method utilized the thermogravimetric mass-loss Q-TG and differential Q-DTG curves with respect to temperature and time for the desorption of liquidus from solid surfaces under quasi-isothermal conditions. Evaluation of the experimental data revealed the heterogeneous properties of the tested samples. It appears that this modern special TG technique is very useful for the study of liquid/solid systems and can be competitive with traditional techniques because of the speed and accuracy with which the data are obtained and the simplicity of the experimental operations.

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Thermodesorption of benzene and water from alumina samples saturated in vacuum dessicator were studied under quasi-isothermal conditions. The Q-TG and Q-DTG curves show multi-step mass losses associated with the evaporation of liquids from pores and physisorbed liquid films from active sites with different energies. The isotherms of adsorption-desorption of nitrogen on porous alumina samples were measured using sorptomatic method and pore size distribution functions have been calculated. The correlation between porosity parameters and the volume of desorbed liquids is presented. A good agreement between above data was obtained.

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Abstract  

Programmed thermodesorption of n-butanol from Na-, La-montmorillonite, natural and commercial zeolite samples in quasi-isothermal conditions made. The new method of fractal dimension calculations from thermogravimetry data has been presented. On the basis of nitrogen adsorption-desorption isotherms from sorptometry and mercury porosimetry data the fractal dimensions of montmorillonites were calculated. The results from above independent and separated techniques were compared and good correlation were obtained.

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Some of the materials used as chromatography packings, adsorbents or catalyst supports are glasses of controlled porosity (CPGs). The chemical structure of these materials can easily be changed by heating the porous glass. Such thermal modification leads to the enrichment of the CPG surface in boron atoms. The long exposure of CPGs to thermal treatment can even cause the formation of borate crystals in the pores of the glasses. This paper considers the application of thermal analysis to the investigation of porous glasses heated for different periods of time.

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