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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  

The paper presents evaluation of energy distribution of n-octane and pore-size distribution functions on the alumina oxide surface (e.g. total heterogeneity) of on the basis one experimental run. the Q-TG mass loss and derivative Q-DTG mass loss curves of n-octane thermodesorption from the alumina oxide sample were made using a hungarian derivatograph with an analyser equipped with an automatic ultraslow procedure and a special crucible of maintaining the quasi-isothermal heating procedure to increase the resolution of thermal analysis. a new theoretical and experimental procedure was developed for evaluation of distribution functions of liquid preadsorbed on the mesoporous surface from special thermogravimetry. An example of the approach to quantitative description of the energetic and structural heterogeneities of alumina oxide surface is given.

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Abstract  

The gas adsorption method is the most common means to characterise the topology of solid surfaces with regard to its use as an adsorbent. Adsorption isotherms are determined advanta-geously using a vacuum microbalance: Thermogravimetric techniques allow the observation of sample degassing and its optimization. The dry mass is determined in situ, the mass of gas adsorbed is measured directly and different gases can be used without calibration. From the isotherm the pore size distributions, specific surface area, fractal dimension and density can be derived. Commercially available gravimetric sorption apparata and vacuum balances as well as software for data evaluation are reviewed in tables. The sorption analysis of an aluminum oxide is presented. The porous material was used as a matrix for a slow drug release.

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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  

Colloids play a major role in the transport of trace metals as well as radionuclides in natural waters. These species are of importance for passive take in biota.Radionuclides may form colloids and pseudocolloids during hydrolysis or through interaction with other components present in the water phase, such as clay minerals or humic substances. Furthermore, aggregation and dispersion and other transformation processes, will influence the colloidal fraction, for instance during storage of samples. Fractionation of radionuclides associated with colloids in natural waters should, therefore, take place in situ or shortly after sampling.Different analytical techniques are useful for the fractionation of colloids, pseudocolloids, and particles. In the present paper, the application of hollow fiber ultrafiltration and dialysis is demonstrated for radionuclides in waste waters from the Oscarshamn nuclear installation in Sweden.The results illustrate that hollow fiber ultrafiltration is a more powerful technique than dialysis. The fractionation is rapid, sorption is of minor significance, the pore size distribution is rather narrow, and the filtering capacity is high.

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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  

Thermogravimetry (TG) and mass spectrometry (MS) combined techniques have been used to investigate the thermal degradation and catalytic decomposition of high-density polyethylene (HDPE) over solid acid catalysts as H-ZSM-5, Al-MCM-41 and a hybrid material with a bimodal pore size distribution (H-ZSM-5/Al-MCM-41). The silicon/aluminum ratio of all catalysts is 15. Both thermal and catalytic processes showed total conversion in a single mass loss step. Furthermore, the catalytic conversion presents average reduction of 27.4%, in the onset decomposition temperature. The kinetic parameters were calculated using non-isothermal method. These parameters do not indicate significant differences between the thermal and catalytic processes. Even though, the presence of the catalysts changes the reaction mechanism, from phase boundary controlled reaction to random nucleation mechanism. Important difference in distribution of evolved products was detected when several catalysts were used. However, in all cases the main products were alkanes (C2, C3 and C4), alkenes (C3 and C4), dienes (C4 and C5) and traces of aromatic compounds.

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Abstract  

Application study for the evaluation of sorption characteristics of sawdust as an economical sorbent material used for decontamination of radioisotopes cesium and europium from aqueous solution has been carried out in the present work. In this respect, sawdust (untreated and treated by HNO3) has been prepared from the commercial processing of wood for furniture production. Pore properties of the activated carbon such as BET surface area, pore volume, pore size distribution, and pore diameter were characterized by N2 adsorption and DFT software. Radiotracer method onto sawdust from aqueous solutions was studied in a batch technique with respect to pH, contact time, temperature. The kinetics of adsorption of Eu3+ and Cs+ have been discussed using five kinetic models namely, pseudo-first-order model, pseudo-second-order model, Elovich equation, intraparticle diffusion model, and modified Freundlich equation that have been tested in order to analysis the experimental data. Kinetic parameters and correlation coefficients were determined. It was shown that the second-order kinetic equation could describe the sorption kinetics for two metal ions. The metal uptake process was found to be controlled by intraparticle diffusion. Thermodynamic parameters, such as ΔH, ΔG and ΔS, have been calculated by using the thermodynamic equilibrium coefficient obtained at different temperatures. The obtained results indicated that endothermic nature of sorption process for both 152+154Eu and 134Cs onto sawdust.

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Szabadföldi kísérleteink során azt vizsgáltuk, hogy a különböző talajművelési rendszerek miként hatnak a talaj fizikai tulajdonságaira, különösen a talaj vízforgalmát jelentős mértékben meghatározó víztartóképesség-függvényekre (pF-görbékre). A talaj szerkezetét pórusméret-eloszlása alapján jellemeztük a különböző művelési rendszerekben. E célból egy- és kétpórusú pF-görbéket illesztettünk a talajművelési kezelések talajrétegeinek mért víztartóképesség-értékeire. Igazoltuk, hogy a kétpórusú pF-görbe valamennyi vizsgált kezelésben kisebb hibával illeszkedik a mért értékekre, mint az egypórusú görbe. A kétpórusú pF-görbe alapján jól elkülönült a vízforgalom szempontjából meghatározó makro- és mikropórus-tartomány, amit a művelés hatásainak értékelésére használtunk fel. Tanulmányoztuk a direktvetéses (bolygatás nélküli rendszer), a szántásos, a tárcsás és az egyéb agrotechnológiai beavatkozások hatását a talaj víztartó képességére. A művelés nélküli technológia alig változó makropórus-tartományt mutatott a különböző mélységekben, míg a szántásban a művelési mélység jól nyomon követhető volt a pórustartományok változásával. Az agrotechnológiai eljárások között eltérések voltak mind a pórusméret eloszlásában, mind a talajban található nedvességformákban. Az alkalmazott összetett függvényben a pórustartományok arányát kifejező w-érték tükrözte leginkább a talajművelések egyedi hatásait. Megállapítottuk, hogy a vizsgált termőhelyi feltételek között a mélykultivátoros művelési rendszer hozta létre a legstabilabb szerkezetű, valamint a víz- és levegőforgalmi szempontból legkedvezőbb talajállapotot.

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hydrocarbons. Obviously, the influence of the porous structure of the support was quite complicated [ 7 ]. Recently, mesoporous molecular sieves due to their high surface areas and narrow pore size distribution were used as the support for preparing Co-based FT

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