JSCS Vol 66, No. 4

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J.Serb.Chem.Soc. 66(4)213–236(2001)
UDC 536.77:621.929
JSCS–2849
Review

R E V I E W
Mixing rules for excess free energy models

BOJAN D. DJORDJEVIC, MIRJANA LJ. KIJEVCANIN, JADRANKA P. ORLOVIC* and SLOBODAN P. SERBANOVIC

Faculty of Technology and Metallurgy, University of Belgrade, YU-11120, Karnegijeva 4 and
*”Duga” - Paints and Varnishes Industry, Viline vode 6, YU-11000 Belgrade, Yugoslavia

(Received 30 December 2000)
1. Introduction
2. Huron-Vidal mixing rule (HV)
3. MHV1, MHV2 mixing rules
4. Wong-Sandler mixing rule
5. LCVM mixing rule (WS)
6. Huron-Vidal-Orbey-Sandler mixing rule (HVOS)
7. Predictive CEOS/GE models. PSRK model
8. Twu et al. mixing rules
9. VLE calculation in polymer solutions using EOS/GE models
10. Summary
Keywords: cubic equation of state, mixing rule, vapour-liquid equilibria, excess molar properties, correlation, prediction.
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J.Serb.Chem.Soc. 66(4)237–241(2001)
UDC 539.2
JSCS–2850
Original scientific paper

On molecular graphs and digraphs of annulenes and their spectra

IVAN GUTMAN and PETER J. PLATH*

Faculty of Science, University of Kragujevac, P.O. Box 60, YU-34000 Kragujevac, Yugoslavia and
*Institute of Applied and Physical Chemistry, University of Bremen, P.O. Box 330440, D-28334 Bremen, Germany

(Received 25 December 2000)
Amolecular graph, consisting of undirected edges, can be represented as a sum of two digraphs, consisting of oppositely oriented directed edges. In the case of annulenes, the eigenvalue spectrum of the molecular graph is equal to the sum of the eigenvalue spectra of the respective two molecular digraphs.
Keywords: molecular graph, molecular digraph, annulene, spectrum (of graph).
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J.Serb.Chem.Soc. 66(4)243–247(2001)
UDC 547.2
JSCS–2851
Original scientific paper

Narumi-Katayama index of phenylenes

ZELJKO TOMOVIC and IVAN GUTMAN

Faculty of Science, University of Kragujevac, P.O. Box 60, YU-34000 Kragujevac, Yugoslavia

(Received 22 December 2000)
The Narumi-Katayama topological indes S of a hydrocarbon is the product of vertex degrees of the respective molecular graph. If PH is a phenylene and HS is its hexagonal squeeze, then the respective Narumi-Katayama indices are related as S(PH) = 9h–1 S(HS), where h is the number of hexagons of PH and HS, or as S(PH) = S(HS)b , where a = 0.078 and b = 1.613.
Keywords: Narumi-Katayama topological index, phenylenes, hexagonal squeeze, benzenoid hydrocarbons.
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J.Serb.Chem.Soc. 66(4)249–258(2001)
UDC 536.5/546.46
JSCS–2852
Original scientific paper

The improvement of the detection power of a U-shaped DC plasma

MIRJANA TRIPKOVIC, IVANKA HOLCLAJTNER-ANTUNOVIC*, MOMIR MARINKOVIC** and DRAGAN MARKOVIC

Institute of Physics, P.O. Box 57, YU-11000 Belgrade,
*Faculty of Physical Chemistry, University of Belgrade, P.O. Box 157, YU-11000 Belgrade and
**Vinca Institute of Nuclear Sciences, P.O. Box 522, YU-11001 Belgrade, Yugoslavia

(Received 8 December 2000)
Optimization of the operating parameters of U-shpaed DC arc plasma and spectrometer parameters has been undertaken to explore the possibilities of improving its detection power. It is demonstrated, with a U-shaped arc as an example, that the limits of detection, in addition to well-defined parameters as described by Boumans and Winge, depend on the signal integration time. It is shown that with increasing integration time, the limits of detection are decreased within some limits and that the precision and concentration sensitivity are improved as well. A mathematical expression for the dependence of the detection limit on the integration time is presented. To increase the reliability of the measurement of the mentioned parameters, the working conditions were optimized for the following analytes: Ag, Al, Au, Cr, Fe, Mn, Ni, Pb, Pd, Pt, and V. The obtained limits of detection are comparable or better than those obtained by ICP for the elements studied. Itwas estimed that the possibility exists for their further improvement up to 10 times.
Keywords: optical emission spectrometry, signal integration time, detection limits, precision, DC plasma.
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J.Serb.Chem.Soc. 66(4)259–271(2001)
UDC 543.844: :546.76
JSCS–2853
Original scientific paper

Inverse gas chromatography of chromia. Part I. Zero surface coverage

A. E. ONJIA, S. K. MILONJIC and LJ. V. RAJAKOVIC*

The Vinca Institute of Nuclear Sciences, P.O. Box 522, YU-11001 Belgrade and
*Faculty of Technology and Metallurgy, P.O. Box 494, YU-11001 Belgrade, Yugoslavia

(Received 24 November 2000)
The surface properties of the solid obtained from colloidal chromiawere investigated by inverse gas chromatography (IGC), at zero surface coverage conditions. The solid samples I dried at 423 K and II heated at 1073 K in the amorphous and crystalline form, respectively, were studied in the temperature range 383–423 K. The dispersive components of the surface free energies, enthalpies, entropies, and the acid/base constants for the solidswere calculated from the IGC measurements and compared with the data for a commercially available chromia (III). Significantly lower enthalpies and entropies were obtained for cyclohexane on solid II and chloroform, highly polar organic, on solid I. The dispersive contributions to the surface energy of solid II and III were similar, but much greater in the case of solid I. All the sorbents had a basic character, with the KD/KAA ratio decreasing in the order I > II > III. The retention and resolution in the separation of a vapour mixture of C5–C8n-alkanes on the three substrates were different.Arapid separationwas observed on solid II and an enhanced retention on solid I. Generally, the heated chromia (II) exhibited diminished adsorption capacity, and enhanced homogeneity of the surface.
Keywords: inverse gas chromatography, chromia, adsorption, thermodynamics.
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J.Serb.Chem.Soc. 66(4)273–280(2001)
UDC 661.86: :541.124
JSCS–2854
Original scientific paper

The kinetics of the partial dehydration of gibbsite to activated alumina in a reactor for pneumatic transport

LJILJANA ROZIC, TATJANA NOVAKOVIC, NADEZDA JOVANOVIC, ANA TERLECKI-BARICEVIC and ZELJKO GRBAVCiC*

ICTM - Department of Catalysis and Chemical Engineering, P.O. Box 815, Njegoseva 12, Belgrade and
*Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, Belgrade, Yugoslavia

(Received 11 July 2000, revised 12 January 2001)
The dehidration kinetics of gibbsite to activated alumina was investigated at four different temperatures between 883 K and 943 K in a reactor for pneumatic transport in the dilute two phase flow regime. The first order kinetic behavior of this reactionwith respect to the water content of the solid material was proved and an activation energy of 66.5 kJ/mol was calculated. The effect of residence time on the water content is given and compared with theoretical calculations. The water content and other characteristics of the products depend on two main parameters, one is the short residence time and the other is the temperature of the dehydration of gibbsite. The short residence time of the gibbsite particles in a reactor for pneumatic transport prevents crystallization into new phases, as established from XRD analysis data. Reactive amorphous alumina powder, with a specific surface area of 250 m2/g, suitable as a precursor for catalyst supports is obtained.
Keywords: gibbsite, dehydration kinetics, pneumatic transport, activation energy.
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J.Serb.Chem.Soc. 66(4)281–287(2001)
UDC 661.993:66.094.54659
JSCS–2855
Original scientific paper

Carbon monoxide oxidation on a Au(111) surface modified by spontaneously deposited Ru

SVETLANA STRBAC, OLAF M. MAGNUSSEN* and ROLF-JÜRGEN BEHM*

ICTM - Institute of Electrochemistry, P.O. Box 815, YU-11001 Belgrade, Yugoslavia and
*Abteilung für Oberflächenchemie und Katalyze, Univerzität Ulm, D-89069 Ulm, Germany

(Received 25 December 2000)
The spontaneous deposition of Ru on Au(111) was performed in 10-3 M RuCl3 + 0.5 M H2SO4 solution. The obtained surface was characterized by STM under potential control in 0.5 M H2SO4 solution. The coverage of the Au(111) terraces by deposited Ru was estimated by STM to be 0.02 ML. Step decoration could be noticed in the STM images, which indicates that the steps, as lined defects, are active sites for the nucleation of Ru monolayer islands, while the random distribution of Ru nuclei, observed on the terraces indicates point defects as active sites. The electrocatalytic activity of Au(111) surface modified by spontaneously deposited Ru was studied towards CO oxidation. The significant enhancement in the reaction rate compared to CO oxidation on a pure Au(111) surface, indicated that the edges of the deposited Ru islands were the active sites for the reaction.
Keywords: spontaneous deposition, Ru, Au(111), CO oxidation, STM.
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