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Abstract  

The new method of diffusion coefficient calculations from thermogravimetry Q-TG data has been presented. Programmed thermodesorption of polar and apolar liquids from aluminium oxide and montmorillonite-Na and -La samples in quasi-isothermal conditions has been made. The result from above method was compared with literature data and good correlation were obtained.

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Abstract  

Calculations based on the fractal geometry in the estimation of surface heterogeneity are superior compared with conventional calculation methods (e.g. from the data of gas adsorption or X-ray radiation scattering) as they can be applied without limitation as far as the range of surface sizes of the studied structures is concerned. This paper presents structural characteristics of carbon and carbon- free nanomaterials based on the determined surface and volumetric fractal coefficients. Fractal coefficients were determined from the data obtained by means of two independent methods: sorptometry and atomic force microscopy (AFM). Correlation between porosity parameters and fractal coefficients is presented.

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Studies of surface properties of Na- and La-montmorillonites

Thermogravimetry Q-TG, sorptometry, porosimetry and AFM methods

Journal of Thermal Analysis and Calorimetry
Authors: P. Staszczuk, J. Bazan, M. Błachnio, D. Sternik, and N. Garcia

Abstract  

This paper presents possible applications of thermal analysis, sorptometry and porosimetry to study physico-chemical properties of Na- and La-montmorillonite samples, especially for determination of total surface heterogeneity. The quasi-isothermal thermogravimetric (Q-TG) mass loss and its first derivative (Q-DTG) curves with respect to temperature and time obtained during programmed liquid thermodesorption under quasi-isothermal conditions have been used to study adsorbed layers and heterogeneous properties of the Na- and La-montmorillonites. Calculations of the desorption energy distribution functions by analytical procedure using mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption under quasi-isothermal conditions of polar and non-polar liquid vapours preadsorbed on a material surface are presented. Parameters relating to porosity of samples were determined by sorptometry, mercury porosimetry and atomic force microscopy (AFM). From nitrogen sorption isotherms from sorptometry and porosimetry methods, the fractal dimensions of montmorillonites have been calculated. Moreover, a new approach is proposed to calculate fractal dimensions of materials obtained from Q-TG curve; this is compared with values obtained by the above methods. The total heterogeneous properties (energy distribution function and pore-size distribution functions) of samples studied were estimated. The radius and pore volume of the tested samples calculated on the basis of thermogravimetry, sorptometry and porosimetry techniques were compared and good correlations obtained.

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Abstract  

Properties relating to porosity of solids (fractal dimensions, surface roughness parameters) were evaluated from atomic force microscopy (AFM) and nitrogen adsorption-desorption isotherms measured at 77 K for selected high-temperature [(RE) Ba2Cu3O7−x, RE=Y, Sm] superconductors. Adsorption capacity, specific surface area, fractal dimensions were determined from adsorption-desorption isotherms. The adsorption isotherms of all samples were S-shaped and belong to type II according to the IUPAC classification. A linear relationship was demonstrated between the fractal coefficients calculated by using the two methods and values of adsorption capacity of monolayer.

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Abstract  

Complex studies of physicochemical properties of pure and modified of aluminia oxides samples are presented. The presence of Mn2+ and Ni2+ modifiers on the aluminium oxide surface causes increase in water adsorption capacity and decrease in benzene and n-octane adsorption. This is due to decrease of specific surface area, volume and radius of pores as a result of surface impregnation and microcrystal formation during modification with manganese and nickel chlorides. Microcrystal formation on the surface and porosity decrease as confirmed by AFM, EDX and powder diffraction studies using automated diffractometer by step scanning. From the Q-TG and Q-DTG data, the energies of liquid desorption from the surface of the samples and the functions of desorption, energy distribution were calculated. High degree of nonlinearity of the functions resulting from great heterogeneity of the studied surface was found. Adsorption of cations creates more homogeneous surface in aluminium oxide, and it is responsible for the change in adsorbate molecule interaction energy and changes mechanism of adsorption and desorption as well as thickness and structure of the adsorbed film. From the experimental data some parameters characterizing adsorption properties and porosity of the studied samples were determined using the complex measuring methods (thermal analysis, sorptometry, porosimetry, AFM and EDX).

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Abstract  

The paper presents the method of preparation and determination of physicochemical properties of silica gels with a chemically bonded BSA phase as well as studies of the effect of support porosity on the synthesis. Wide-porous Z-300 and narrow-porous Z-100 silica gels were studied. The investigations showed a significant effect of pore size on the synthesis of stationary phases with BSA. Modification with protein results in changes of adsorption properties and porosity of adsorbent samples. Changes of physicochemical properties result in significant changes of geometrical and structural heterogeneity of the support (specific surface area, fractal coefficient) as well as energetic heterogeneity of the samples.

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Abstract  

Uniformly carbon-covered alumina (CCA) was prepared via the carbonisation of sucrose highly dispersed on the alumina surface. Using special thermogravimetry and sorptometry methods physicochemical properties of carbon-covered alumina surfaces were investigated. A numerical and analytical procedure for the evaluation of total heterogeneous properties (desorption energy distribution and pore-size distribution functions) on the basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium conditions are presented. The desorption energy distribution was derived from the mass loss Q-TG and the differential mass loss Q-DTG curves of thermodesorption of pre-adsorbed polar and apolar liquid films. For the first time, the evaluation of the fractal dimensions of carbon-covered alumina using the sorptometry, thermogravimetry and AFM data is presented.

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Abstract  

Jntti published in 1970 a method to obtain values of the sorption parameters at an early stage of gravimetric sorption measurements. In the present paper we apply that method to volumetric sorption measurements to discuss its applicability. A method is presented to cope with inaccuracies when using Jntti’s method. This will be of special importance for volumetric measurements where accuracy plays a major part. In the paper a second order regression method is used. We use a computer simulation as well as experimental data on desorption of nitrogen from a silica aerogel at 77 K.

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Abstract  

This paper presents possible applications of thermal analysis and sorptomatic methods to study physico-chemical properties of the high-T csuperconductor Y1Ba2Cu3O7-x and perovskite LaCoO3. It is shown that both Y1Ba2Cu3O7-x and perovskite phase are highly sensitive to water vapour. Mechanism of adsorption of water on LaCoO3depends largely on time activation (t act). When the time of water vapour saturation was 0<t act<180 s, physisorption process was observed. In the case of longer times water vapour action, t act>180 s, chemical decomposition was observed.

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Journal of Thermal Analysis and Calorimetry
Authors: D. Sternik, P. Staszczuk, J. Pękalska, G. Grodzicka, B. Gawdzik, J. Osypiuk-Tomasik, and P. Witer

Abstract  

The adsorption of a polar (water) and a non-polar (n-octane) liquid on silica gels, modified by adsorption of proteins, has been studied by thermal analysis. Silica gels with physically adsorbed BSA and ovalbumin layers were used. Thermodesorption energies were determined from Q-TG and Q-DTG curves recorded under quasi-equilibrium conditions. Significant differences in liquid desorption were observed from the surfaces due to heterogeneous changes (energetic and geometrical) as a result of modification. These results are compared with those obtained for the samples heated at 160C for 1 h.

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