Values Of Surface Fractal Dimension Research Articles

SURFACE FRACTAL DIMENSION OF BENTONITE AND ITS APPLICATION IN CALCULATION OF SWELLING DEFORMATION

The correlation between the void ratio of swelled montmorillonite and the vertical overburden pressure can be expressed as [Formula: see text]. The surface fractal dimension D s of five bentonites were estimated from the swelling deformation tests according to this fractal correlation. The reliability of surface fractal dimension obtained from the swelling deformation test was confirmed by nitrogen adsorption test, with identical values of surface fractal dimension obtained from both tests. The surface fractal dimension can also be used to estimate the swelling deformation of bentonite, after calculating the swelling coefficient K from the parameters of diffuse double layer (DDL) model in the osmotic swelling phase. Comparison of the model predictions with a number of experimental results on swelling deformation of both Na dominant and Ca dominant bentonites suggests that the surface fractal model works excellent in the cases tested.

Characteristics of rapeseed oil cake using nitrogen adsorption

Abstract Adsorption of nitrogen on the rapeseed oil cake and rapeseed oil cake with wheat meal extrudates was investigated. The results are presented as adsorption-desorption isotherms. The Brunauer-Emmet and Teller equation was used to analyse the experimental sorption data. To obtain estimates of the surface area and surface fractal dimension, the sorption isotherms were analyzed using the Brunauer-Emmet and Teller and Frenkel-Halsey-Hill equations. Mesopore analysis was carried out using the Dollimore and Heal method. The properties and surface characteristic of rapeseed oil cake extrudates are related to different basic properties of particular samples and duration of the extrusion process. Extrusion conditions lead to essential differences in particular products. For all kinds of rapeseed oil cakes the amount of adsorbed nitrogen was different, but for the rapeseed oil cake extrudates a large amount of adsorbed nitrogenwas observed. The average surface area of the rapeseed oil cake extrudates was about 6.5-7.0 m2 g-1, whereas it was equal to about 4.0-6.0 m2 g-1 for rapeseed oil cake with the wheat meal extrudates. In the case of non-extruded rapeseed oil cake and wheat meal, the dominant group included ca. 2 and 5 nmpores. The values of surface fractal dimension suggested that the surface of the extrudates was more homogenous than that of the raw material. Duration of the extrusion process to 80 s resulted in a decrease in the specific surface area, surface fractal dimension, and porosity of the extrudates.

Structural characteristics of modified natural zeolite

Natural zeolite of Slovak provenience has been modified with magnetic nanoparticles at selected temperatures of 20, 50 and 85 °C with the aim to enhance its sorption properties. The pore, surface and structural properties of zeolite/iron oxide composite were characterized using nitrogen adsorption measurements, electron probe microanalysis and powder X-ray diffraction. The crystallinity of the host zeolite was strongly influenced by the temperature of iron oxide particles precipitation, but it was still retained. It followed from the nitrogen adsorption measurements that the surface area and the pore volume of zeolite composites have increased in relation to the precipitation temperature, the best sorption properties were revealed at the composite prepared at 85 °C. As followed also from the SEM images, the iron oxide nanoparticles being of size 30 nm are forming mesoporous aggregates adsorbed on the zeolite surface. Fractal analysis used to describe the modified geometry of zeolite composites has given the values of surface fractal dimension between 2.36 and 2.51.

Structure and Adsorption Properties of Nanocrystalline Silicon

The structure of the particles of nanocrystalline silicon synthesized in argon plasma with added oxygen is studied. An amorphous shell composed of silicon oxide is formed on the surface of silicon nanoparticles. The particles form clusters with a fractal structure. The adsorption of nitrogen on a powder of nanocrystalline silicon at 77 K is studied, and adsorption isotherms obtained for nanocrystalline silicon and nonporous silica adsorbents with identical specific surface areas are compared. The values of surface fractal dimension of powdered nanocrystalline silicon are calculated using the Frenkel-Halsey-Hill equation for multilayer adsorption under the dominant contribution of van der Waals or capillary forces. It is shown that surface fractal dimension is a structure-sensitive parameter characterizing both the morphology of clusters and the structure (roughness) of the surface of particles and their aggregates.

Surface Roughness Created by Acidic Dissolution of Synthetic Goethite Monitored with SAXS and N2-Adsorption Isotherms

The development of surface roughness of two synthetic goethites with a high, 176 m2/g, and a low, 7 m2/g, initial specific surface area by acid attack is described in terms of fractal geometry. The dissolution kinetics were influenced by the presence of micropores and small mesopores created during dissolution and leading to an initial increase in surface area causing S-shaped dissolution curves. The fractal dimensions were calculated from the adsorption isotherms obtained with N2as adsorbate. These values of surface fractal dimension agree quite well with the values of the mass and surface fractal dimension obtained with small angle X-ray scattering (SAXS).