JSCS - Vol 65, No 9

JSCS Vol 65, No. 9

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J.Serb.Chem.Soc. 65(9) 611-618 (2000)
UDC 546.289 87/.548.55-54-31:535.56
JSCS-2783
Original scientific paper

The optical properties of bismuth germanium oxide single crystals

ALEKSANDAR GOLUBOVIC, RADOS GAJIC, CHANGKANG CHEN* and ANDREJA VALCIC**

Institute of Physics, Pregrevica 118, P. O. Box 57, YU-11001 Belgrade,
*Clarendon Laboratory, Parks Road, Oxford OXI 3PU, United Kingdom, and
**Faculty of Technology and Metallurgy, Karnegijeva 4, YU-11000 Belgrade, Yugoslavia

(Received 1 February, revised 5 June 2000)
Bi₁₂GeO₂₀ single crystals were grown by the Czochralski technique. Suitable polishing and etching solutions were determined. Reflection spectra were recorded in the wave numbers range 20–5000 cm^–1, and compared with the spectra of Bi₁₂SiO₂₀ single crystals to study the position of the phonon modes. The optical constants of the Bi₁₂GeO₂₀ single crystals were obtained using Kramers-Kronig analysis. The obtained results are dicussed and compared with published data.
Keywords: Czochralski technique, bismuth germanium oxide, single crystals, optical properties, optical phonons.

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J.Serb.Chem.Soc. 65(9) 619-630 (2000)
UDC 547.498:543.422:54.03/.04
JSCS-2784
Original scientific paper

A study of the behaviour of some substituted 1,2,4-triazoline-3-thiones in different media

LUCIJANA ARMAN-ZUBIC, NADA PERISIC-JANJIC and MARIJA LAZAREVIC*

Institute of Chemistry, Faculty of Science, Trg D. Obradovica 3, YU-21000 Novi Sad, Yugoslavia and
*Faculty of Technology and Metallurgy, R. Boskovic 16, 91000 Skopje, Macedonia

(Received 30 September 1999, revised 22 May 2000)
The acid-base behaviour of 4-phenyl-5-(4-R-benzyl)-1,2,4-triazoline-3-thione (1(R = OH); 2(R = OC₂H₅)) was studied in aqueous sulfuric acid and sodium hydroxide solutions. Three ionisation equilibria of compound 1 (pK_BH₃⁺ = –4.64, pK_BH₂ = 7.50, pK_BH^– = 10.06) and two ionisation equilibria of compound 2 (pK_BH₂⁺ = –4.82, pK_BH = 7.45) were found. The first equilibrium belongs to the protonation of 1,2,4-triazoline-3-thione, while the second belongs to the dissociation of the same part of the molecule. The third equilibrium represents the dissociation process of the phenolic OH group of compound 1. The kinetics of hydrolysis of compounds 1 and 2 were studied in high concentrated sulfuric acid solutions. The hydrolysis follows an irreversible first-order consecutive reaction path.
Keywords: 1,2,4-triazoline-3-thione derivatives, electonic absorption spectra, dissociation constants, acid hydrolysis.

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J.Serb.Chem.Soc. 65(9) 631-638 (2000)
UDC 541.428.49:549.6:547.814.5:535.243
JSCS-2785
Original scientific paper

A spectrophotometric investigation of the complex between titanyl oxalate and 3-hydroxyflavone in water ethanolic mixtures

MARA ALEKSIC, SLAVICA BLAGOJEVIC, DUSAN MALESEV and ZORICA RADOVIC

Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, P. O. Box 146, YU-11000 Belgrade, Yugoslavia

(Received 26 November 1999, revised 25 May 2000)
It has been established, by the application of suitable spectrophotometric methods and pH-metric measurements, that titanyl oxalate anion and 3-hydroxyflavone (3HF) form a [TiO(C₂O₄)₂(C₁₅H₉O₃)₂]^4– complex. The investigation of the composition and the concentration stability constant of the complex were carried out in a 50 % aqueous ethanol solution at room temperature (20°C), in the pH range from 1.9 to 9.0. The concentration stability constant of the complex, log b2, ranged from 16.65 at pH 5.0 to 13.96 at pH 7.0. The conditions for the spectrophotometric determination of 3HF by means of the complex formation were investigated in the concnetration range from 2.5×10^–5 to 3.0×10^–4 mol dm^–3 3HF.
Keywords: complex, 3-hydroxylflavone (3HF), titanyl oxalate, spectrophotometric methods.

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J.Serb.Chem.Soc. 65(9) 639-643 (2000)
UDC 541.183.123:2.541.128.11
JSCS-2786
Short communication

SHORT COMMUNICATION
Activity of some disiloxanes toward the cation exchange resin-catalyst in the siloxane equilibration reaction

M. N. GOVEDARICA

ICTM, Centre of Chemistry, Department of Polymeric Materials, Njegoseva 12, YU-11000 Belgrade, Yugoslavia

(Received 14 December 1999, revised 5 June 2000)
The relative activities of four disiloxanes toward the cation exchange resin, which was used as an equilibration catalyst, were determined in such a way that the equilibrium initially present in an arbitrary chosen equilibrate was disturbed by adding the respective disiloxanes to it, and then by recording the viscosity of the equilibrating mixtures as a function of reaction time. As a result, a set of different viscosity-reaction time relationships was obtained, which implies different activities of disiloxanes toward the catalyst. In this way the following decreasing order of acitivites was established: 1,3-tetramethyldisiloxane > 1,3-divinyltetramethyldisiloxane > hexamethyldisiloxane > 1,3-bis(3-carboxypropyl)tetramethyldisiloxane.
Keywords: cation exchange resin, catalyzed siloxane equilibration, activities of disiloxanes, acidic equilibration catalyst.

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J.Serb.Chem.Soc. 65(9) 645-648 (2000)
UDC 547.85:535.243:547.923
JSCS-2787
Note

NOTE
Spectrophotometric determination of fluocortolone in tablets using 1,4-dihydrazinophthalazine

OLIVERA CUDINA, SOTE VLADIMIROV, DOBRILA ZIVANOV-STAKIC and DANICA AGBABA

Department of Pharmaceutical Chemistry, Faculty of Pharmacy, P. O. Box 146, Vojvode Stepe 450, YU-11152 Belgrade, Yugoslavia

(Received 4 November 1999, revised 12 May 2000)
The proposed method for the determination of fluocortolone is based on the formation of a stable, yellow coloured hydrazone product with 1,4-dihydrazinophthalazine as the reagent. Heating at 85°C for 2 h was found to be necessary to ensure optimal hydrazone formation in acidified 1-propanol as the solvent. The detection limit was 1.2 µg/ml. This method when applied for the determination of fluocortolone in pharmaceutical formulations gave precise and reproducible results.
Keywords: fluocortolone, 1,4-dihydrazinophthalazine, tablets, spectrophotometry.

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J.Serb.Chem.Soc. 65(9) 649-660 (2000)
UDC 546.96'824''.821'''-/54-88/:541.182.644
JSCS-2788
Original scientific paper

The effect of the presence of alcohol in the dispersing phase of oxide sols on the properties of RuO₂-TiO₄/Ti anodes obtained by the sol–gel procedure

V. PANIC, A. DEKANSKI*, S. MILONJIC**, R. ATANASOSKI*, and B. NIKOLIC

Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P. O. Box 3503, YU-11120 Belgrade (e-mail: bane@elab.tmf.bg.ac.yu),
*ICTM - Center for Electrochemistry, Njegoseva 12, P. O. Box 815, YU-11001 Belgrade and
**Vinca Institute of Nuclear Sciences, P. O. Box 522, YU-11001 Belgrade, Yugoslavia

(Received 2 March 2000)
The effect of the addition of ethanol and 2-propanol to the dispersing phase of TiO₂ and RuO₂ sols mixture on the morphology and, consequently, on the electrochemical properties of the sol-gel obtained activated titanium anodes was investigated. The properties of the obtained anodes were compared to those obtained by the thermal decomposition of appropriate chloride salts. The morphology of the anode coatings was examined by scanning tunneling microscopy. The electrochemical behaviour was investigated by cyclic voltammetry and by polarization measurements. An accelerated stability test was used for the examination of the stability of the anodes under simultaneous oxygen and chlorine evolution reaction. A dependence of the anode stability on the type of added alcohol is indicated.
Keywords: activated titanium anodes, RuO₂ sol, TiO₂ sol, sol-gel procedure, accelerated stability test.

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J.Serb.Chem.Soc. 65(9) 661-670 (2000)
UDC 546.47:543.251:532.517.6
JSCS-2789
Original scientific paper

Zinc electrodeposition from alkaline zincate solution by pulsating overpotentials

MILOS V. SIMICIC and KONSTANTIN I. POPOV*

Chemical Power Sources Institute, Batajnicki put 23, YU-11080 Belgrade (E-mail: IHIS@eunet.yu) and
*Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, YU-11000 Belgrade, Yugoslavia

(Received 22 December 1999, revised 26 April 2000)
It is well known that smooth zinc deposits cannot be obtained from alkaline zincate using constant overpotential and current rate. During prolonged metal deposition, spongy and dendritic deposits are formed. It has been shown that the deposits are less agglomerated in the case of square-wave pulsating overpotentials regime than the ones obtained in case of constant overpotential regime. This is explained in a semiquantitative way by two phenomena: selective anodic dissolution during overpotentials “off” period and decreasing diffusion control. These effects is more pronounced at higher pause-to-pulse ratio. Increasing the pause-to-pulse ratio causes a reduction of the ratio between diffusion and activation overpotential, resulting in a more compact deposit. Confirmation of the proposed semiquantitative mathematical model was obtained by zinc electrodeposition onto a copper wire from a 0.1 M zincate solution in 1.0 M KOH at room temperature.
Keywords: zinc electrodeposition, zincate solution, pulsating overpotential, scanning electron microscopy.

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J.Serb.Chem.Soc. 65(9) 671-680 (2000)
UDC 546.562:547.298.1:541.135.52:531.15
JSCS-2790
Original scientific paper

Electrochemical behaviour of copper in N,N-dimethylformamide + 0.5 M potassium perchlorate solution

V. VOJINOVIC, V. KOMNENIC, M. PJESCIC and S. MENTUS*

Faculty of Metallurgy and Technology, YU-81000 Podgorica and
*Faculty of Physical Chemistry University of Belgrade, Studentski trg 16, YU-11000 Belgrade, Yugoslavia

(Received 26 February 1999, revised 23 March 2000)
The electrochemical deposition and dissolution of copper in 0.0025 M CuSO₄ + N,N-dimethylformamide + 0.5 M KClO₄ solution was examined by the rotating disc and potentiodynamic methods. Both platinum and copper were used as working electrodes. A wide polarization range –1 to +2 V vs. SCE, and several temperatures between 25 and 55°C were encompased. The Cu/electrolyte interface was found to be permanently out of equilibrium, as a consequence of the development of a passivating layer. In accordance with the classic theory of a copper electrode in acidified aqueous solutions, the cathodic and anodic Tafel lines of metallic copper define a unique value of the exchange current density, however, their slopes do not correspond to the classic theory.
Keywords: copper, N,N-dimethylformamide, electrode kinetics, rotating disc electrode, passivation.

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