JSCS Vol 70, No. 1

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Impresum http://www.shd.org.rs/HtDocs/SHD/PDFicon.gif104 KB;  Content of Vol 70, No. 1 http://www.shd.org.rs/HtDocs/SHD/PDFicon.gif38 KB;  Instruction for authors http://www.shd.org.rs/HtDocs/SHD/PDFicon.gif96 KB

J. Serb. Chem. Soc. 70 (1) 1–7 (2005)
UDC 546.763+547.461.2/.3:548.70
JSCS – 3242
Original scientific paper

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The geometrical isomers of oxalato and malonato-(ethylenediAMine-N,N’-di-S,S-2-propionato)-chromate
(III) complexes


Department of Chemistry, Faculty of Science, University of Kragujevac, P. O. Box 60, 34000 Kragujevac, Serbia and Montenegro

(Received 6 February, revised 7 June 2004)
Three octahedral chromium(III) complexes of the general formula Na[Cr(S,S-eddp)L]·2H2O, where eddp = the tetradentate O–N–N–O-type ligand ethylenediAMine-N,N’-di-S,S-2-propionate and L = a bidentate O–O-type ligand, either oxalate or malonate, were prepared. The complexes were synthesized by the reaction of chromium(III) chloride, S,S-eddp and malonic acid or sodium oxalate, at 60 ºC. The complexes were isolated chromatographically and the geometric configuration of the complexes was proposed on the basis of their infrared and electronic absorption spectra.

Keywords: chromium(III) complexes, S,S-eddp, oxalato and malonato ligands.

J. Serb. Chem. Soc. 70 (1) 9–20 (2005)
UDC 546.681'.683':86–034:536.7.001.2
JSCS – 3243
Original scientific paper

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Calculation of the thermodynAMic properties of the Ga–Sb–Tl liquid alloys


Technical Faculty, University of Belgrade, VJ 12, 19210 Bor, Serbia and Montenegro
*Osaka University, Graduate School of Engineering, Department of Materials Science and Processing, 2-1YAMadaoka, Suita, Osaka 565-0871, Japan

(Received 21 April, revised 27 May 2004)

The results of the calculation of the thermodynAMic properties for liquid Ga–Sb–Tl alloys at the temperature 1073 K are presented in this paper. Initially, the most appropriate thermodynAMic model for the investigated system was selected. Based on a comparison of the values calculated by different geometric models (Kohler, Muggianu, Toop, Hillert, Chou) with the existing experimental based data, asymmetric models of calculation were determined to give the best results. The asymmetric nature of the investigated ternary system was additionally confirmed by the Chou similarity coefficient concept. For these reasons, further complete thermodynAMic calculations were performed according to the Hillert model in five sections of the ternary Ga–Sb–Tl system from each corner with the mole ratio of other two components being 9:1; 7:3; 5:5; 3:7 and 1:9. The obtained results include integral excess Gibbs energy dependences on composition for all the investigated sections. The calculated activity values at 1073 K for all components are given in the form of isoactivity diagrAMs. Comparison between the calculated and experimentally obtained gallium activities shows good agreement.

Keywords: thermodynAMics of alloys, Ga–Sb–Tl system, geometric models,

J.Serb.Chem.Soc. 70 (1) 21–31 (2005)
UDC 541.182.64:62–408+546.26
JSCS – 3244
Original scientific paper

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Characterization of carbon cryogels synthesized by sol-gel polycondensation


The Vinca Institute of Nuclear Sciences, P. O. Box 522, 11001 Belgrade and
*Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia and Montenegro

(Received 8 April, revised 2 July 2004)
Resorcinol-formaldehyde (RF) cryogels were synthesized by the sol-gel polycondensation of resorcinol (R) with formaldehyde (F) and freeze-drying was carried out with t-butanol. Carbon cryogels were obtained by pyrolyzing RF cryogels in an inert atmosphere. Characterization by nitrogen adsorption showed that the carbon cryogels were micro and mesoporous materials with high specific surface areas (SBET ~ 550 m2/g). Cyclic voltAMmetry experiments at various scan rates (2 to 200 mV s-1) were performed to study the electrical double-layer charging of carbon cryogel electrodes in 0.5 mol dm-3 HClO4 solution. It has been demonstrated that it is possible to sub-divide the total specific capacitance into the mesoporous and the microporous specific capacitance by analyzing the linear dependence of the charge (q) on the reciprocal of the square root of the potential scan rate (v-1/2), and the linear dependence of the reciprocal charge (1/q) on the square root of the potential scan rate (v-1/2). The specific capacitance was found to be constant over a wide range of sAMple weight (12.5 to 50.0 mg) and a very promising specific capacitance value of 150 F/g, was found for this material operating in an acidic 0.5 mol dm-3 HClO4 solution at room temperature.

Keywords: carbon cryogel, carbonization, porosity, BET specific surface area, cyclic voltAMmetry, impedance, specific capacitance.

J.Serb.Chem.Soc. 70 (1) 33–40 (2005)
UDC 541.183:546.226–325:547.532
JSCS – 3245
Short communication

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Adsorption properties and porous structure of sulfuric acid treated bentonites determined
by the adsorption isotherms of benzene vapor


Faculty of Technology and Mettallurgy, “St. Kiril and Metodij” University, Skopje, R. Macedonia

(Received 2 April, revised 7 July 2004)
In a previous paper adsorption isotherms of benzene vapor on natural bentonite from Ginovci, Macedonia, and forms acid activated with 10 % and 15 % solutions of hydrochloric were interpreted by means of the Dubinin–Radushkevich–Stoeckli and Dubinin–Astakhov equations; the investigation has been continued with bentonites acid activated with 10 % and 15 % solutions of sulfuric acid where X-ray analysis indicates smaller structural changes. Using the above equations, the heterogeneity of the micropores and the energetic heterogeneity of the bentonites were determined from the differential distribution of the micropore volume with respect to the structural parAMeter of the equations characterizing the microporous structure and to the molar free energy of adsorption. Activated bentonites obtain bigger pores but also a certain quantity of new small pores appear during acid activation with the higher concentration of acid. The micropore volumes, determined from the adsorption of benzene vapor, of bentonites activated with 10 % and 15 % solution of hydrochloric acid (144.60 cm3 kg-1 and 110.06 cm3 kg-1, respectively), decrease in comparison with that of natural bentonite (162.55 cm3 kgv).1 In contrast, the values of the micropore volume for bentonities treated with 10 % and 15 % solutions of sulfuric acids increase
(169.19 cm3 kg-1 and 227.74 cm3 kg-1). That is due to the difference in the structural changes occurring during activation with hydrochloric and sulfuric acids. The values of the free energy of adsorption of benzene vapor for natural bentonite are higher than those of the acid acitivated bentonities, what is in accordance with the structural and porosity changes.

Keywords: adsorption, benzene, bentonite, chemical activation, Dubinin–Radushkevich –Stoeckli and Dubinin–Astakhov equations.

J. Serb. Chem. Soc. 70 (1) 41–49 (2005)
UDC 66.097:546.57+541.135.5+547.75
JSCS – 3246
Original scientific paper

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Characterization and electrocatalytic application of silver modified polypyrrole electrodes


ICTM Institute of Chemistry, Technology and Metallurgy, Center for Electrochemistry, Njegoseva 12,
P. O. Box 473, 11001 Belgrade, Serbia and Montenegro

(Received 9 March, revised 29 June 2004)
Silver modified polypyrrole electrodeswere preparedwith the aim of testing them for the electrooxidation of formaldehyde in alkaline solution. The modification of polypyrrole by immersion in aqueous AgNO3 solution was studied by cyclic voltAMmetry and vacuum techniques (AES and XPS). The influence of time of immersion and the thickness of the polypyrrole film, prepared by electrochemical polymerization, on the modification of the polymer were exAMined. The results acquired from both electrochemical and spectroscopic exAMinations show that immersion of a polypyrrole electrode in a AgNO3 solution results in its modificationwith silver, which is deposited in the elemental state on the surface. The quantity of silver deposited depends not only on the immersion time but also on the thickness of the polymer film. A modified PPy/Ag electrode exhibits catalytic activity for the electrooxidation of CH2O in NaOH. In spite of the low quantity of silver, the activity of the electrode for this reaction is comparable to that of a polycrystalline silver electrode.

Keywords: polypyrrole, modification by immersion in AgNO3, AES and XPS techniques, electrooxidation of formaldehyde.

J.Serb.Chem.Soc. 70 (1) 51–61 (2005)
UDC 541.13:546.733:546.26–0.39.5
JSCS – 3247
Original scientific paper

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The effect of heterocyclic S,S’-ligands on the electrochemical properties of some cobalt(III) complexes in acid


Institute of Chemistry, Technology and Metallurgy, Department of Electrochemistry, Njegoseva 12, P. O. Box 473, 11000 Belgrade, Serbia and Montenegro *Faculty of Chemistry, University of Belgrade, P. O. Box 158, 11001 Belgrade, Serbia and Montenegro and
**Rice University, Chemistry DepartmentMS60, 6100 Main Street, Houston, TX 77005, USA

(Received 12 May, revised 29 June 2004)
Eight mixed-ligand cobalt(III) complexes with the macrocyclic AMine 1,4,8,11-tetraazacyclotetradecane (cyclAM) and a heterocyclic dithiocarbAMate (Rdtc-) i.e., morpholine- (Morphdtc), thiomorpholine- (Timdtc), piperazine- (Pzdtc), N-methylpiperazine-(Mepzdtc), piperidine- (Pipdtc), 2-, 3- or 4-methylpiperidine- (2-, 3- and 4-Mepipdtc) carbodithionato-S,S ions, of the general formula [Co(cyclAM)Rdtc](ClO4)2, were investigated in deoxygenated 0.1MHClO4 solutions. Cyclic voltAMmetry data at a glassy carbon (GC) electrode demonstrate a redox reaction of cobalt(III) from the complexes at potentials strongly influenced by the presence of different heterocyclic Rdtc- ligands. In this respect, the complexes were separated into two groups: the first, with a heteroatom O, S or N in the heterocyclic ring, and the second, with a methyl group on the piperidine ring of the Rdtc- ligand. Anodic polarization of an Fe electrode in the presence of the complexes shows their influence not only on the dissolution of iron but also on the hydrogen evolution reactions and on this basis complexes the complexes could be divided into the sAMe two groups. It was found that the weaker the inhibiting effect of the free heterocyclic AMines is, the significantly higher is the efficiency of the corresponding complexes.

Keywords: cobalt(III) complexes, azAMacrocycles and dithiocarbAMate, cyclic voltAMmetry, glassy carbon, iron, perchloric acid.

J.Serb.Chem.Soc. 70 (1) 63–66 (2005)
UDC 541.13:546.733:546.26–033.5
JSCS – 3248
Short communication

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The surface energy of disperse cadmium electrodeposits formations


Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia and Montenegro

(Received 15 April 2004)
The surface energy of disperse cadmium electrodeposits formation was determined by using a procedure described earlier. It was shown that the surface energy strongly depends on the composition of the solution from which the deposition was carried out.

Keywords: electrodeposition, cadmium, disperse cadmium formation, surface energy.

J. Serb. Chem. Soc. 70(1) 67–78 (2005)
UDC 532.614+546.48:541.13
JSCS – 3249
Original scientific paper

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Protolytic equilibria in homogeneous and heterogeneous systems of ketoconazole and its direct spectrophotometric determination in tablets


Faculty of Chemistry, University of Belgrade, Studentski trg 16, P. O. Box 158, 11001Belgrade and
*Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, P. O. Box 146, 11000 Belgrade, Serbia and Montenegro

(Received 13 February, revised 7 June 2004)

The acid-base equilibria of a diprotic, slightly hydrosoluble base ketoconazole were studied in homogeneous and heterogeneous water systems. The determinations were performed at 25 ºC at a constant ionic strength of 0.1M(NaCl). The acidity constant Ka1 was determined by potentiometric (pKa1 3.20) and spectrophotometric (pKa1 3.26) methods. A pKa2 constant of 6.10 was obtained based on the equilibrium constants pKs0 4.84 and pKs1 –1.26, determined in a heterogeneous ketoconazole system. The obtained values of the constants served to calculate the solubility and the distribution of the equilibrium forms of ketoconazole as a function of pH. On the basis of the distribution of the equilibrium forms of ketoconazole, a spectrophotometric method for the determination of its content in commercial tablets was developed. The determinations were performed at 225 nm in 0.1 M HCl. The method is simple and rapid and enables the direct spectrophotometric determination of the content of ketoconazole without previous isolation.

Keywords: ketoconazole, acidity constants, heterogeneous equilibria, spectrophotometric determination, pharmaceuticals.

J. Serb. Chem. Soc. 70 (1) 79–85 (2005)
UDC 666.32+621.039.629:621.385.833
JSCS – 3250
Original scientific paper

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Optical diagnostics of fullerene synthesis in the RF thermal plasma process


Vinca Institute of Nuclear Sciences, P. O. Box 522, 11001 Belgrade, Serbia and Montenegro
*Research Laboratory of Materials and Environmental Chemistry, Chemical Research Center,
Hungarian Academy of Sciences H-1525 Budapest, P. O. Box 17, Hungary,
**Department of Silicate Chemistry and Materials Engineering, Veszprém University, H-8200 Veszprém, Egyetem u. 2, Hungary and
***Faculty of Physics, University of Belgrade, P. O. Box 368, 11001 Belgrade, Serbia and Montenegro

(Received 27 February, revised 25 June 2004)
In this work, the results of an optical emission study of fullerene synthesis in an inductively coupled radio frequency thermal plasma reactor are presented. The emission spectroscopy studies, based on the use of the Swan C2 (0,1) and CN (0,0) vibrational emission spectra, were carried out to determine the plasma temperature. The evaporation process of graphite powderwas observed by scanning electron microscopy.

Keywords: fullerene, otpical emission study, scanning electron microscopy.

J.Serb.Chem.Soc. 70 (1) 87–95 (2005)
UDC 549.517.1:548.2
JSCS – 3251
Original scintefic paper

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The growth of ruby single crystals


Institute of Physics, Pregrevica 118, P. O. Box 68, 11080 Zemun,
*Faculty of Mining and Geology, Djusina 7, P. O. Box 162, 11000 Belgrade,
**Faculty of Technology and Metallurgy, Karnegijeva 4, Belgrade, Serbia and Montenegro

(Received 9 March, revised 2 June 2004)
Ruby (Cr:Al2O3) single crystals were grown by the Czochralski technique in an argon atmosphere. The critical crystal diAMeter dc = 1.0 cm and the critical rate of rotation wc = 20 rpm were calculated by equations of the hydrodynAMics of the melt. The rate of crystal growthwas experimentally obtained to be 2.7 mm/h. For chemical polishing, conc. H3PO4 at 593 K for an exposure of 3 hours was determined. Conc. H3PO4 at 523 K for an exposure of 3 h was found to be a suitable etching solution. The lattice parAMeters a = 0.47627(6) nm and c = 1.301(1) nm were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

Keywords: Czochralski technique, ruby, growth, single crystal, etching.

J. Serb. Chem. Soc. 70 (1) 97–105 (2005)
UDC 66.046.58+66.093.4:539.24
JSCS – 3252
Original scientific paper

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The influence of different parAMeters on the hydration process of binders based on alkali activated slag


Holcim Cement Plant “Novi Popovac”, Paracin, Serebija and Montenegro and
*Center for Multidisciplinary Studies, University of Belgrade, Kneza Viseslava 1a, Belgrade, Serbia and Montenegro

(Received 17 March, revised 28 May 2004)
The influence of certain types of activators (water glass Na2O·nSiO2 and sodium-metasilicate Na2SiO3·5H2O) on the hydration process of alkali activated slag was investigated in this study. The influence of activator concentration, specific surface area of the slag and the modulus n of the water glass (mass ratio between SiO2 and Na2O) on the kinetics of the hydration process i.e., the change of compressive strength were also investigated. Poorly crystallized low base calcium silicate hydrate C–S–H (I) is the main hydration product of alkali activated slag regardless of the activator used. This is the reason for the rapid increase in the strength of alkali activated slag and also of the very high strength values. The strength growth rate and strength values were significantly higher when sodium–metasilicate was used as the activator than when water glass was used. The specific surface area of the slag and the activator concentration are parAMeters which have a closely connected influence on strength and their action is cumulative. The modulus n of water glass does not have an explicit influence on the strength of alkali activated slag.

Keywords: alkali activated slag, microstructure, calcium silicate hydrate, compressive strength.

J. Serb. Chem. Soc. 70 (1) 107–114 (2005)
UDC 547.673:532.7
JSCS – 3253
Original scientific paper

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The concentrating of alizarin using a reverse osmosis process


Chemical Engineering Department, Razi University, Kermanshah, Iran

(Received 11 December 2003, revised 7 June 2004)
Membrane technologies in general and reverse osmosis in particular have been employed for the concentrating of solutions. In this study, the concentrating of a heat sensitive alizarin extracted from madder root was realized using an FT30 reverse osmosis membrane. The effects of cross flow velocity, transmembrane pressure and pH on the flux and rejection were studied. Increasing the transmembrane pressure increased the flux while the rejection was constant. At pH 7–8, the highest flux was achieved. This study showed that reverse osmosis is the process of choice for the concentrating of alizarin solutions. The optimum operating conditions were 1.0 m/s crossflow velocity, 16 bars transmembrane pressure and pH 7. The system was tested for 12 h without severe fouling problems.

Keywords: reverse osmosis, alizarin, FT30 membrane.

J. Serb. Chem. Soc. 70 (1) 115–124 (2005)
UDC 633.811+531.3:547.979.8
JSCS – 3254
Original scientific paper

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An investigation of influence of solvent on the degradation kinetics of carotenoids in oil extracts of Calendula officinalis


Faculty of Tehnology and Metallurgy, Karnegijeva 4, 11000 Belgrade and
*Faculty of Pharmacy, Vojvode Stepe 450, 11000 Belgrade, Serbia and Montenegro

(Received 3 November 2003, revised 21 May 2004)
The stability of carotenoids was studied in marigold oil extracts prepared with following solvents: Myritol 312®, paraffin oil, almond oil, olive oil, sunflower oil, grape seed oil, and soybean oil. The concentration of the carotenoids was determined by spectroscopic measurement at 450 nm. Degradation rate showed a first order dependence on the concentration of carotenoids with a faster first stage (which lasted 35–50 days, depending on the solvent) and a slower second stage. The highest degradation rates were observed in extracts prepared with linoleic acid rich solvents (sunflower oil, soybean oil and grape seed oil), while the lowest were found in oil with saturated fatty acids (Myritol 312®) and paraffin oil. These results confirm the connection between the degradation of carotenoids and lipid autoxidation, and suggest that the influence of the oil solvents on the stability of oil extracts of Calendula officinalis is a factor that must be considered when selecting a solvent for the production of marigold oil extracts.

Keywords: Calenula officinalis, oil extract, carotenoids.

J. Serb. Chem. Soc. 70 (1) 125–136 (2005)
UDC 541.183:546.226–325:547.532
JSCS – 3255
Original scientific paper

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Mathematical modeling and simulation of gel drying with supercritical carbon dioxide


Faculty of Technology and Metrallurgy, University Belgrade, Karnegijeva 4, P. O. Box 3503, 11120 Belgrade, Serbia and Montenegro

(Received 30 June 2003, revised 6 July 2004)
Mathematical models of alumina/silica gel supercritical drying with carbon dioxide were studied using supercritical drying experimental data. An alumina/silica gel with zinc chloride was synthesized and dried with superciritical carbon dioxide, and its weight change wasmonitored as a function of drying time. The pore size distribution of the obtained aerogel was determined using the BET method and nitrogen adsorption/desorption. Themathematical model of the supercritical drying of the wet gel was represented as unsteady and one-dimensional diffusion of solvent through the aerogel pores filled with supercitical carbon dioxide. Parallel pore model and pores in
series model were developed on the basis of the measured porous structure of the aerogel. It was found that these models which use different effective diffusivity value for each pore size were in much better agreement with the experimental data than models which use an overall effective diffusivity. The local effective diffusivity coefficients were calculated using different tortuosity values for each pore size, and they were distributed according to the pore size distribution data. Model simulations of the superciritical drying with carbon dioxide confirmed that the drying temperature and gel particle diAMeter have a significant influence on the drying time.

Keywords: supercritical drying, aerogels, modeling of diffusion.

J. Serb. Chem. Soc. 70 (1) 137–144 (2005)
UDC 66.040.46:519.87
JSCS – 3256
Original scientific paper

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Exchange between the stagnant and flowing zone in gas-flowing solids-fixed bed contactors


Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia and Montenegro

(Received 24 March 2004)
In countercurrent gas – flowing solids – fixed bed contactors, a fraction of the flowing solids is in motion (dynAMic holdup), while the other fraction is resting on the fixed bed elements. In this study it was experimentally proved that the stagnant zone should not be considered as a dead part of the column, but that there is a dynAMic exchange between these two portions of flowing solids particles. Combining a mathematical model with tracer experiments, the rate of exchange was determined and it was shown that only a small part (ca. 20 %) of the stagnant region should be considered as a dead one.

Keywords: gas–flowing solids–fixed bed contactors, gas–solids trickle flow, multiphase contactors, tracers.

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