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Jegdic B.V.,Institut Gosa | Bajat J.B.,University of Belgrade | Popic J.P.,ICTM IEC P.O. Box 815 | Miskovic-Stankovic V.B.,University of Belgrade
Progress in Organic Coatings | Year: 2011

The influence of steel surface pretreatment with different types of iron-phosphate coatings on the corrosion stability and adhesion characteristics of polyester coatings on steel was investigated. The phosphate coating was chemically deposited either from the simple novel plating bath, or with the addition of NaNO 2, as an accelerator in the plating bath. The morphology of phosphate coatings was investigated using atomic force microscopy (AFM). The corrosion stability of polyester coatings on steel pretreated by iron-phosphate coatings was investigated by electrochemical impedance spectroscopy (EIS) in 3% NaCl solution, while "dry" and "wet" adhesion were measured by a direct pull-off standardized procedure. It was shown that greater values of pore resistance, R p, and smaller values of coating capacitance of polyester coating, C c, on steel pretreated with iron-phosphate coating were obtained, as compared to polyester coating on steel phosphated with accelerator, and on the bare steel. The surface roughness of phosphate coating deposited on steel from the bath without accelerator is favorable in forming stronger bonds with polyester coating. Namely, the dry and wet adhesion measurements are in accordance with EIS measurements in 3% NaCl solution, i.e. lower adhesion values were obtained for polyester coating on steel phosphated with accelerator and on the bare steel, while the iron-phosphate pretreatment from the novel bath enhanced the adhesion of polyester coating on steel. © 2010 Elsevier B.V. All rights reserved.

Popic J.P.,University of Belgrade | Jegdic B.V.,Institut Gosa | Bajat J.B.,University of Belgrade | Veljovic D.,University of Belgrade | And 2 more authors.
Applied Surface Science | Year: 2011

The influence of deposition temperature and concentration of NaNO 2 in the phosphating bath on the surface morphology and coverage of iron-phosphate coatings on low carbon steel was investigated. The phosphate coatings were chemically deposited on steel from phosphate bath at different temperatures (30-70 °C) and with the addition of different amounts of accelerator, NaNO2 (0.1, 0.5 and 1.0 g dm-3). The morphology of phosphate coatings was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition of iron-phosphate coatings was determined using energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Surface coverage was evaluated by the voltammetric anodic dissolution (VAD) technique. It was shown that the increase in temperature of the NaNO2-free phosphating bath up to 70 °C caused an increase in surface coverage. The addition of NaNO2 in the phosphating bath significantly increased the surface coverage of phosphate coatings deposited at temperatures lower than 50 °C. The phosphate crystals were of laminated and needle-like structures for deposits obtained at temperatures lower than 50 °C, while at higher temperatures needle-like structure was transformed to laminated structure. The increase in NaNO 2 concentration in the phosphating bath from 0.1 to 1.0 g dm -3 did not significantly increase the surface coverage, but decreased the crystals size, consequently favouring the phosphate nucleation and better packing of the crystals. © 2011 Elsevier B.V. All rights reserved.

Jegdic B.V.,Institut Gosa | Bajat J.B.,University of Belgrade | Popic J.P.,University of Belgrade | Stevanovic S.I.,University of Belgrade | Miskovic-Stankovic V.B.,University of Belgrade
Corrosion Science | Year: 2011

The effect of different type of iron-phosphate coatings on corrosion stability and adhesion characteristic of top powder polyester coating on steel was investigated. Iron-phosphate coatings were deposited on steel in the novel phosphating bath with or without NaNO2 as an accelerator. The corrosion stability of the powder polyester coating was evaluated by electrochemical impedance spectroscopy (EIS), adhesion by pull-off and NMP test, while surface morphology of phosphate coatings were investigated by atomic force microscopy (AFM). The adhesion and corrosion stability of powder polyester coatings were improved with pretreatment based on iron-phosphate coating deposited from NaNO2-free bath. © 2011 Elsevier Ltd.

Holclajtner-Antunovic I.,University of Belgrade | Mioc U.B.,University of Belgrade | Todorovic M.,University of Belgrade | Jovanovic Z.,Vinča Institute of Nuclear Sciences | And 3 more authors.
Materials Research Bulletin | Year: 2010

Potassium salts of 12-tungstophosphoric acid with varying amounts of cation, KxH3 - xPW12O40 (x = 1, 2, 3) have been prepared and their characteristics investigated by thermal analyses, FT-IR and micro-Raman spectroscopy and SEM-EDS analysis. It was found that the number of replaced protons by potassium ions in the 12-tungstophosphoric acid structure has influence on the presence of different protonic species, their dynamic equilibrium and on the conductivity of salts. The results reported in this study have been applied to improve the structural model of insoluble acidic salts. It is shown that an acidic potassium salt presents a mixture of neutral salt and unreacted acid. The nature of this mixture depends on the number of replaced protons-oxonium ions by cations. Preliminary measurements with synthesized compounds as solid electrolytes in fuel cells have been done, too. © 2010 Elsevier Ltd. All rights reserved.

Zivkovic L.S.,Vinča Institute of Nuclear Sciences | Jegdic B.V.,Institut Gosa | Popic J.P.,University of Belgrade | Bajat J.B.,University of Belgrade | Miskovic-Stankovic V.B.,University of Belgrade
Progress in Organic Coatings | Year: 2013

Cerium-based conversion coatings (CeCCs) are one of the most prospective alternatives to the widely used chromate conversion coatings (CCCs) due to their anticorrosion efficiency, environmentally friendly nature and low cost. In this work, the CeCCs on AA6060 were prepared by immersion into aqueous cerium salt solutions at room temperature, and subsequently post-treated in heated phosphate solution. The effect of counter ion (nitrate and chloride) on the coating properties was studied testing CeCCs as sole or conversion layers for the top polyester coating. Since the 60 μm thick polyester coating was applied, an artificial defect of 0.8 mm hole was introduced to faster assess the differences between pretreatments. The system with CCC pretreatment was used as reference. Corrosion properties were investigated in 0.5 M NaCl solution by electrochemical impedance spectroscopy while the adhesion strength was measured by NMPR (N-methyl-2-pyrrolidone) and pull-off tests. As shown, the post-treated chloride-based CeCC offered better protection than crack-free thin nitrate-based CeCC, when used as sole coatings. On the other hand, it was brought to evidence that in combination with top powder polyester coating, the CeCC deposited from nitrate solution exhibited better protection compared to protective system pretreated with chloride-based one. Excellent polyester coating adhesion was found independently on aluminium surface pretreatment. © © 2013 Elsevier B.V. All rights reserved.

Rakic V.,University of Belgrade | Rac V.,University of Belgrade | Krmar M.,Institut Gosa | Otman O.,CNRS Research on Catalysis and Environment in Lyon | Auroux A.,CNRS Research on Catalysis and Environment in Lyon
Journal of Hazardous Materials | Year: 2015

In this study, the adsorption of pharmaceutically active compounds - salicylic acid, acetylsalicylic acid, atenolol and diclofenac-Na onto activated carbons has been studied. Three different commercial activated carbons, possessing ~650, 900 or 1500m2g-1 surface areas were used as solid adsorbents. These materials were fully characterized - their textural, surface features and points of zero charge have been determined.The adsorption was studied from aqueous solutions at 303K using batch adsorption experiments and titration microcalorimetry, which was employed in order to obtain the heats evolved as a result of adsorption. The maximal adsorption capacities of investigated solids for all target pharmaceuticals are in the range of 10-4molg-1. The obtained maximal retention capacities are correlated with the textural properties of applied activated carbon. The roles of acid/base features of activated carbons and of molecular structures of adsorbate molecules have been discussed. The obtained results enabled to estimate the possibility to use the activated carbons in the removal of pharmaceuticals by adsorption. © 2014 Elsevier B.V.

Kozic M.S.,Military Technical Institute Belgrade | Ristic S.S.,Institut Gosa | Puharic M.A.,Institut Gosa | Katavic B.T.,Institut Gosa
Thermal Science | Year: 2011

This paper presents the results of numerical flow simulation in ventilation mill of Kostolac B power plant, where louvers and centrifugal separator with adjustable blade angle are used. Numerical simulations of multiphase flow were performed using the Euler-Euler and Euler-Lagrange approach of ANSYS FLUENT software package. The results of numerical simulations are compared with measurements in the mill for both types of separators. Due to very complex geometry and large number of the grid cells, convergent solution with the Eulerian model could not be obtained. For this reason the mixture model was employed resulting in very good agreement with measurements, concerning the gas mixture distribution and velocity at the main and secondary burners. There was large difference between the numerical results and measurements for the pulverized coal distribution at the burners. Taking into consideration that we analyzed dilute mixture with very low volume fraction of the coal, the only choice was the Euler-Lagrange approach, i. e. discrete phase model limited to volume fraction of the discrete phase less than 10-12%. Obtained distributions of the coal at the burners agree well for both types of separators.

Polic-Radovanovic S.,Central Institute for Conservation in Belgrade | Ristic S.,Institut Gosa | Stasic J.,Vinča Institute of Nuclear Sciences | Trtica M.,Vinča Institute of Nuclear Sciences
Journal of Non-Crystalline Solids | Year: 2012

Application of non-contact and rapid laser technique, which is minimally invasive, non-contaminant and efficient method, for ancient glass investigation and cleaning is highly desirable for restoration purposes. Irradiation of Roman glass dated from 1st to 4th/5th century AD with TEA CO 2 (wavelength 10.6 μm; pulse duration t p = 100 ns), Nd:YAG (wavelength 1064 nm and 532 nm; t p = 150 ps) and ruby laser (wavelength 694 nm; t p = 30 ns) in air ambience was studied. For all three lasers, moderate energy densities (15-30 J/cm 2) induced significant changes of morphology - from superficial exfoliation and occurrence of mosaic structure after few pulses to deep damages and hydrodynamic features after higher number of accumulated shots. Irradiation with moderate energy density, accompanied with plasma appearance in front of the samples, is convenient for numerous potential applications, particularly surface elemental analysis such as laser induced breakdown spectroscopy. On the other hand, lower densities are more suitable for Roman glass cleaning. Calculations of Roman glass surface temperature have shown that pulsed CO 2 laser is favorable for surface cleaning and optimal fluence is ~ 2 J/cm 2. This was confirmed by additional experiments for fluences 1.5 and 3 J/cm 2. Morphological changes on the Roman glass surface induced by lasers were studied by optical microscopy (OM) and scanning electron microscopy (SEM). The composition of Roman glass was determined by energy dispersive X-ray analysis (EDX) and inductively coupled plasma (ICP) method. Chemical analysis confirmed that the investigated glass dates from the Roman period. © 2012 Elsevier B.V. All rights reserved.

Kozic M.,VTI | Ristic S.,Institut Gosa
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2010

Numerical simulations of two-dimensional (2D) flow obtained by solving the Reynolds-averaged Navier-Stokes (RANS) equations served for the design of 2D thrust vectoring nozzles. Thrust is directed by means of deflectors with different heights placed at the end of the bottom wall. The nozzle was manufactured and tested. A series of experiments were performed in a trisonic wind tunnel. The experimental results obtained by optical methods and pressure measurements are compared with the results of a numerical flow simulation. Differences were observed in pressure distribution along the bottom wall. More detailed research revealed that the real flow considerably deviated from the 2D flow. The primary goal of this work is to provide applicability of the used numerical methods in nozzle design. The results show that RANS 2D simulations with turbulent models based on the Boussinesq approximation are not able to predict reliable enough results for 2D thrust vectoring nozzles.

Vasovic I.,Institut Gosa
Hemijska Industrija | Year: 2010

The subject of this work is focused on strength analysis of filament-wound composite tubes made of E glass/polyester under internal pressure. The primary attention of this investigation is to develop a reliable computation procedure for stress, displacement and initial failure analysis of layered composite tubes. For that purpose we have combined the finite element method (FEM) with corresponding initial failure enterions. In addition, finite element analyses using commercial code, MSC/NASTRAN, were performed to predict the behavior of filament wound structures. Computation results are compared with experiments. Good agreement between computation and experimental results are obtained.

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