JSCS Vol 70, No. 1
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Impresum |
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J. Serb. Chem.
Soc. 70 (1) 1–7 (2005) |
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The geometrical isomers of oxalato and
malonato-(ethylenediAMine-N,N’-di-S,S-2-propionato)-chromate
(III) complexes
VERICA V. GLODJOVIC, MILAN D. JOKSOVIC and SRECKO R. TRIFUNOVIC
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.
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J. Serb. Chem.
Soc. 70 (1) 9–20 (2005) |
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Calculation of the thermodynAMic properties of the
Ga–Sb–Tl liquid alloys
DRAGAN MANASIJEVIC, DRAGANA ZIVKOVIC, IWAO
KATAYAMA* and ZIVAN ZIVKOVIC
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,
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J.Serb.Chem.Soc.
70 (1) 21–31 (2005) |
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Characterization of carbon cryogels synthesized by sol-gel polycondensation
BILJANA BABIC, DIVNA DJOKIC and NEDELJKO
KRSTAJIC*
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.
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J.Serb.Chem.Soc.
70 (1) 33–40 (2005) |
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SHORT COMMUNICATION
Adsorption properties and porous structure of sulfuric acid treated bentonites
determined
by the adsorption isotherms of benzene vapor
SNEZANA BREZOVSKA, BILJANA MARINA, DONCO
BUREVSKI, BILJANA ANGJUSHEVA,
VASA BOSEVSKA and LEPA STOJANOVSKA
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.
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J. Serb. Chem.
Soc. 70 (1) 41–49 (2005) |
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Characterization and electrocatalytic application of silver modified
polypyrrole electrodes
V. M. JOVANOViC, S. TERZIC and A. DEKANSKI
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.
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J.Serb.Chem.Soc.
70 (1) 51–61 (2005) |
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The effect of heterocyclic S,S’-ligands on the electrochemical properties of
some cobalt(III) complexes in acid
V. M. JOVANOVIC, K. BABIC-SAMARDZIJA*,**
and S. P. SOVILJ*
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.
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J.Serb.Chem.Soc.
70 (1) 63–66 (2005) |
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SHORT COMMUNICATION
The surface energy of disperse cadmium electrodeposits formations
P. M. ZIVKOVIC and K. I. POPOV
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.
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J. Serb. Chem.
Soc. 70(1) 67–78 (2005) |
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Protolytic equilibria in homogeneous and heterogeneous systems of ketoconazole
and its direct spectrophotometric determination in tablets
MIRJANA P. VOJIC, GORDANA V. POPOVIC*, DUSAN M.
SLADIC and LIDIJA B. PFENDT
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.
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J. Serb. Chem.
Soc. 70 (1) 79–85 (2005) |
To download this article click here 174 KB |
Optical diagnostics of fullerene synthesis in
the RF thermal plasma process
B. TODOROVIC-MARKOVIC, Z. MARKOVIC, I. MOHAI*,
Z. KÁROLY*, Z. FARKAS**, Z. NIKOLIC*** and J. SZÉPVÖLGYI*
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.
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J.Serb.Chem.Soc.
70 (1) 87–95 (2005) |
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The growth of ruby single crystals
ALEKSANDAR GOLUBOVIC, SLOBODANKA NIKOLIC, STEVAN DJURIC* and ANDREJA VALCIC**
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.
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J. Serb. Chem.
Soc. 70 (1) 97–105 (2005) |
To download this article click here 261 KB |
The influence of different parAMeters on the
hydration process of binders based on alkali activated slag
DARKO KRIZAN , MIROSLAV KOMLJENOVIC* and
BRANISLAV ZIVANOVIC*
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.
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J. Serb. Chem.
Soc. 70 (1) 107–114 (2005) |
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The concentrating of alizarin using a reverse
osmosis process
S. S. MADAENI and H. DANESHVAR
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.
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J. Serb. Chem.
Soc. 70 (1) 115–124 (2005) |
To download this article click here 111 KB |
An investigation of influence of solvent on the degradation
kinetics of carotenoids in oil extracts of Calendula officinalis
DEJAN BEZBRADICA, JELA MILIC-ASKRABIC*, SLOBODAN
D. PETROVIC and SLAVICA SILER-MARINKOVIC
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.
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J. Serb. Chem.
Soc. 70 (1) 125–136 (2005) |
To download this article click here 177 KB |
Mathematical modeling and simulation of gel drying
with supercritical carbon dioxide
ALEKSANDAR ORLOVIC, STOJAN PETROVIC and DEJAN
SKALA
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.
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J. Serb. Chem.
Soc. 70 (1) 137–144 (2005) |
To download this article click here 100 KB |
Exchange between the
stagnant and flowing zone in gas-flowing solids-fixed bed contactors
ALEKSANDAR P. DUDUKOVIC, NIKOLAM. NIKACEVIC,
RADA V. PJANOVIC and ZELJKO V. KUZELJEVIC
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.
Copyright &AMp; copy; SHD 2005.
February
20, 2005.
For
more information contact: SHD@tmf.bg.ac.yu