Технолошки факултет [Научни радови] / Faculty of Technology [Scientific papers]

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Morphology and growth of electrodeposited silver powder particles
(Elsevier, 2007) Maksimović, V. M.; Pavlović, Lj. J.; Tomić, M. V.; Jović, V. D.
The effect of overpotential pulsing and periodic current reversal on the morphology of silver powders was investigated using a scanning electron microscope (SEM). It is shown that the profile of pulses or current reversal determines the micromorphology of the electrodeposited silver particles. Generally, three forms of silver were detected: (1) dendrites, (2) equiaxial crystals (independent and/or agglomerates) and (3) rods. The shape of particle seems to be the result of an interplay between the surface energy and growth kinetics.
INFLUENCE OF PRESSURE AND TIME ON EXTRACTION PROCESS USING SUPERCRITICAL CO2
(Technical Faculty in Bor, Serbia, 2008) Mićić, V.; Lepojević, Ž.; Mandić, B.; Jotanović, M.; Tadić, G.; Tolić, A.
The supercritical fluid extraction (SFE) by carbon dioxide (CO2) of Salvia officinalis L. was investigated. SFE by CO2 was performed at different pressure (80, 100, 150, 200 and 300 bar) and constant temperature of 40ºC (all other extraction conditions, such are flow rate, particle diameter of Salvia officinalis, extraction time were kept constant. The GC – MS method was used for determination of qualitative and quantitative composition of obtained extracts and essential oils.
Lead and silver extraction from waste cake from hydrometallurgical zinc production
(Serbian Chemical Society, 2008) STANOJEVIĆ, DUŠAN, D.; RAJKOVIĆ, MILOŠ, B.; TOŠKOVIĆ, DRAGAN, V.; TOMIĆ, MILANA, A.
This paper presents the experimental results of the extraction of lead and silver from a lead-silver waste cake obtained in the process of hydrometallurgical zinc production. While controlling the pH value, the lead-silver cake was leached at a temperature close to boiling point in different concentrations of aqueous calcium chloride solutions. The experiments were performed applying different ratios between the mass of cake and the volume of the leaching agent under different durations of the process. It was concluded that at the optimal process parameters (pH 2.0-2.5; CaCl2 concentration, 3.6 mol dm-3; temperature, 95°C; solid/liquid ratio, 1:5), the leaching efficiency of lead and silver could reach the approximate value of 94 %. Applying the same optimal process parameters, the method was applied to the leaching of a lead-silver cake in a magnesium chloride solution, but with significantly lower efficiencies. The results show that leaching of lead and silver in a calcium chloride solution could be a prospective method for increasing the recovery of lead and silver during hydrometallurgical zinc production.
IR Resonant Absorption in Molecular Nanofilms
(Polish Academy of Sciences, 2009) Pelemiš, S. S.; Šetrajcic, J. P.; Markoski, B.; Delic, N.V.; Vucenovic, S. M.; Mirjanic, D. Lj.
The paper presents a theoretical research of changes of optical properties of various nanofilm molecular crystals which are caused by the presence of two parallel and close borders. We used combined analytical-numerical calculation to find the allowed energy states of excitons and their spatial distribution (per layers) along the axis perpendicular to surface planes. We determined permittivity for the observed models of these ultrathin dielectric films and explored the influence of boundary parameters on the occurrence of discrete (per frequencies) and selective (per layers) absorption. The conditions for occurrence of smallest number of resonant absorption lines have been found and their localization has been defined.
ANALIZA KRISTALIZACIJE NATRIJUM HLORIDA IZ RASTVORA U VAKUUM KRISTALIZERU SA RECIRKULACIJOM SUSPENZIJE
(Association of the Chemical Engineers of Serbia, 2009) JOTANOVIĆ, MILOVAN B.; SULJKANOVIĆ, MIDHAT S.
U ovom radu je izvedena analiza kristalizacije NaCl iz vodenih rastvora u vakuum kristalizerima sa recirkulacijom suspenzije. Vakuum kristalizer kao objekat projektovanja prikazan je kao skup osnovnih aparativno-procesnih jedinica. Aparativno-procesna jedinica je krupni sastavni dio aparata u kojoj se odvija niz fizičko-hemijskih pojava koje zajedno čine jedinični proces kristalizacije. Analizom teorijskih postavki, literaturnih podataka i rezultata istraživanja opisana je svaka aparativno-procesna jedinica odgovarajućim sistemom matematičkih funkcija. Ovaj rad je doprinos stvaranju jedinstvene metodologije projektovanja vakuum kristalizera.
Selective Absorption in Twolayered Optic Films
(American Scientific Publishers, 2009) Pelemiš, S. S.; Šetrajčić, J. P.; Markoski, B. S.; Delić, N. V.; Vučenović, S. M.
This paper summarizes theoretical investigations of changes in optical properties of smallest symmetrical nanofilm-molecular crystals due to the presence of boundaries and different boundary parameters. Using analytic and numerical calculations, the energy spectrum of excitons was found and relative permittivity of these ultrathin dielectric films was determined. The influence of boundary parameters on the occurrence of discrete (by parameters)and selective (by planes)absor ption of external electromagnetic radiation was also investigated. Because of the symmetric conditions on film boundaries, double resonant peaks appear.
Adaption and application of the Green function method to research on molecular ultrathin film optical properties
(IOP Publishing, 2009) Setrajčić, Jovan P; Ilić, Dušan I.; Markoski, Branko; Setrajčić, Ana J.; Vučenović, Siniša M; Mirjanić, Dragoljub Lj.; Škipina, Blanka; Pelemiš, Svetlana
Interest in the study of the exciton subsystem in crystalline structures (in this case nanostructures, i.e. thin films) occurred because dielectric, optical, photoelectric and other properties of materials can be explained by means of it. The basic question to be solved concerning theoretical research into the spatially strongly bounded structures is the inability to apply the standard mathematical tools: differential equations and Fourier analysis. In this paper, it is shown how the Green function method can also be efficiently applied to crystalline samples so constrained that quantum size effects play a significant role on them. For the purpose of exemplification of this method’s application, we shall consider a molecular crystal of simple cubic structure: spatially unbounded (bulk) and strongly bounded alongside one direction (ultrathin film).
JEDAN MODEL ZA ANALIZU I PRORAČUN POUZDANOSTI PRIMENJEN NA PRIMERU IZ HEMIJSKE INDUSTRIJE
(Association of the Chemical Engineers of Serbia, 2010) PEJOVIĆ, BRANKO B.; TADIĆ, GORAN S.; JOTANOVIĆ, MILOVAN B.; TOMIĆ, MILORAD V.; MIĆIĆ, VLADAN M.
Predmet rada se odnosi na projektovanje pouzdanosti kod procesa polimerizacije koji se odvijaju u reaktorima jedne hemijske industrije. Kroz razvijeni model, određene su karakteristike i pokazatelji pouzdanosti, a time i utvrđeni osnovni faktora koji doprinose lošem odvijanju procesa. S obzirom na mogućnost njihove kontrole, mogu se smanjiti očekivani gubici, i na taj način postići kvalitetnija proizvodnja. Za analizu i proračun pouzdanosti, primenjena je deduktivna metoda zasnovana na konstruisanju šeme stabla otkaza sistema na bazi induktivnog zaključivanja. Pri ovome korišćeni su standardizovani logički simboli, odnosno pravila Bulove algebre i matematičke logike. Rezultati rada kroz kvantitativnu i kvalitativnu analizu pouzdanosti posmatranog procesa, omogućavaju dobijanje potpunih informacija o verovatnoći neželjenog događaja procesa i donošenje objektivnih odluka i alternativnih rešenja.
VIŠEVARIJANTNI SIMULATOR PROCESA HLAĐENJA TROKOMPONENTNOG ELEKTROLITIČKOG SISTEMA U VAKUUMU
(Association of the Chemical Engineers of Serbia, 2010) SULJKANOVIĆ, MIDHAT; JOTANOVIĆ, MILOVAN; AHMETOVIĆ, ELVIS; IBRIĆ, NIDRET
U ovom radu prezentirana je metodologija razvoja viševarijantnog simulatora za procese hlađenja višekomponentnih elektrolitičkih sistema u vakuumu. Metodologija podrazumijeva simulaciju procesa hlađenja, s ciljem korištenja dijela entalpije sistema, a također omogućava utvrđivanje i simulaciju fizički provedivih alternativa za procese hlađenja uz kristalizaciju soli ili smješe soli. Za slučajeve kada parametri polaznog sistema ne obezbjeđuju kristalizaciju ciljne soli, u trivijalnoj strukturi, kreirana metodologija utvrđuje uslove pri kojima se podsistem kondicioniranja, sa podsistemom kristalizacije integriše u acikličnu odnosno cikličnu strukturu. Karakteristike razvijene metodologije i viševarijantnog procesnog simulatora pokazane su na nizu primjera vezanih za hlađenje sistema NaCl–CaCl2–H2O odnosno NaCl–KCl–H2O.
Electrodeposition of Fe Powder from Citrate Containing Electrolytes
(Electrochemical Science Group, Serbia, 2010) Pavlović, Lj. J.; Pavlović, M. M.; Pavlović, M. G.; Nikolić, N. D.; Tomić, M. V.
Polarization characteristics of the electrodeposition processes of Fe powders from different citrate electrolytes and the morphology of the obtained powders were investigated. The effect of complexing agents on the cathodic polarization, the current efficiency and morphology of electrodeposited Fe powders were investigated. The morphology of obtained powders depends on the kind of supporting electrolyte, but not on the current density in investigated range. A characteristic feature of powders deposited from citrate-chloride supporting electrolyte is cauliflower-like compressed structure. On the other side, Fe powders electrodeposited from citrate-sulfate supporting electrolyte appeared in the form of spongy-like agglomerates. Possibility of Fe powders protection from corrosion in the process of production and during long-term storing has been shown.
UTICAJ KVALITETA VODE NA POUZDANOST RADA KOTLOVSKIH POSTROJENJA
(Association of the Chemical Engineers of Serbia, 2010) GAJIĆ, ANTO S.; TOMIĆ, MILORAD V.; PAVLOVIĆ, LJUBICA J.; PAVLOVIĆ, MIOMIR G.
U ovom radu su prikazani osnovi i vrste korozionih procesa cevnog sistema kotla TE „Ugljevik“, R. Srpska. Korozione procese nije moguće u potpunosti zaustaviti, ali se oni mogu usporiti pa i smanjiti posledice koje oni izazivaju. Da bi se korozija vitalne opreme termoenergetskih postrojenja, a naročito kotlova, svela na minimum, neophodno je u svakom pojedinačnom slučaju odrediti delujući mehanizam korozije kao i uzročnike koji ga izazivaju. Oštećenja i njima izazvani zastoji u radu termoenergetskih postrojenja u velikom broju su izazvani odvijanjem različitih tipova korozionih procesa. Posebna pažnja je posvećena pripremi vode, s obzirom na njen uticaj na pojavu korozije. Vizuelnim pregledom su utvrđene sledeće vrste korozije na ekranskim cevima kotla sa strane vode i pare: eroziona, jamasta i naponska sa prslinama. Unutrašnje površine ekranskih cevi sa kojih je uklonjen (“sljušten“) sloj kamenca ukazuju da je usled erozije dolazilo do skidanja kamenca i produkata korozije, odnosno erozione korozije, uz stanjivanje zidova cevi. Prsline (perforacije) na ekranskim cevima koje su zavarene, pokazuju da se odigrala naponska korozija cevi sa obrazovanjem prslina, odnosno da je došlo do pucanja cevi. Rupice (udubljenja) na unutrašnjoj površini ekranskih cevi, vidljive nakon uklanjanja kamenca i produkata korozije, dokaz su da se odigrala tačkasta korozija. Istaknuti su potencijalni uzročnici korozije i dat je predlog mera za njihovo eliminisanje.
Effect of hemicelluloses and lignin on the sorption and electric properties of hemp fibers
(Elsevier, 2010)
This study investigated the influence of hemicelluloses and lignin removal on the sorption and electric properties, as well as fineness of hemp fibers. Hemp fibers with different content of either hemicelluloses or lignin were obtained by chemical treatment with 17.5% sodium hydroxide or 0.7% sodium chlorite. The sorption properties of hemp fibers were evaluated as moisture and iodine sorption, while electric properties were evaluated as volume electric resistance. Hemicelluloses removal increases in higher extent fiber liberation than lignin removal; the modified hemp fibers were finer up to 12 times in relation to unmodified fibers. Furthermore, hemicelluloses removal increased the moisture and iodine sorption, as well as electric resistance of hemp fibers compared to unmodified fibers, while lignin removal decreased both moisture and iodine sorption, and only slightly increased the electric resistance of modified hemp fibers.
Changes in Optical Properties of Molecular Nanostructures
(Polish Academy of Sciences, 2010) Vucenovic, S. M.; Šetrajcic, J. P.; Markoski, B.; Mirjanic, D. Lj.; Pelemiš, S.; Škipina, B.
This paper represents an overview about exciton systems in the molecular nanostructures (ultra thin films and superlattices) and their implications on optical properties, primarily on absorption coefficient, which is given in the form of dielectric permittivity. With utilization of Green’s function method, we have calculated dispersion law, spectral weight of exciton states and dielectric permittivity for every type of nanostructures. All obtained results are compared with optical properties in bulk crystals. Dielectric permittivity in all types of nanostructures shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of the expressed quantum effects, very thin thickness in these structures (or at least one dimension confinement) and boundary conditions.
Modelling the process of Al(OH)3 crystallization from industrial sodium aluminate solutions using artificial neural networks
(Serbian Chemical Society, 2011) SMILJANIĆ, RADENKO; LAZIĆ, DRAGICA; GLIGORIĆ, MILADIN; JOTANOVIĆ, MILOVAN; ŽIVKOVIĆ, ŽIVAN; MIHAJLOVIĆ, IVAN
This paper presents an attempt to define the non-linear correlation dependence between the degree of decomposition of the aluminate solution, the average diameter of the crystallized gibbsite, the total Na2O content in the obtained alumina and the specific utilization level of the process on the one hand and important input parameters of the process on the other. As input parameters having an influence on the process, the concentration of Na2O (caustic), the caustic ratio and the crystallization ratio, the starting and final temperature of the process, the average diameter of the crystallization seed and the duration of the decomposition process were considered. As the result of measurements of these process parameters and the acquisition of the resulting output parameters of the process, a database with 500 data lines was obtained. To define the correlation dependence, with the aim of predicting the process parameters of the decomposition process of the sodium aluminate solution, the artificial neural network (ANN) methodology was applied.
Specifičnosti elektrohemijskog taloženja i morfologija Zn–Mn prevlaka dobijenih iz pirofosfatnog elektrolita
(Association of the Chemical Engineers of Serbia, 2011) Bučko, Mihael M.; Stevanović, Sanja I.; Tomić, Milorad V.; Pavlović, Miomir G.; Bajat, Jelena B.
U proteklih nekoliko godina pokazano je da se alkalni pirofosfatni elektrolit može primeniti za elektrohemijsko taloženje prevlaka Zn−Mn legura na čeliku. U ovom radu je ispitana zavisnost morfologije i hemijskog sastava Zn−Mn prevlaka od primenjene gustine struje taloženja. Karakterizacija prevlaka vršena je mikroskopijom atomskih sila i energetskom disperzionom atomskom analizom. Metodom linearne voltametrije ispitan je uticaj dodatka, askorbinske kiseline, na katodne procese. Utvrđeno je da se iz alkalnog rastvora mogu dobiti prevlake zadovoljavajućeg kvaliteta, ali da gustina struje ima veliki uticaj na homogenost i hrapavost površine Zn−Mn prevlaka. Askorbinska kiselina inhibira redukciju vodonika i povećava iskorišćenje struje za taloženje legure.
Dobijanje prelaznih faza aluminijum-oksida polazeći od natrijum-aluminata primenom Bajerovog postupka
(Association of the Chemical Engineers of Serbia, 2011) Obrenović, Zoran; Filipović, Radislav; Milanović, Marija; Stijepović, Ivan; Nikolić, Ljubica M.
Polazni aluminijum-hidroksidni i aluminijum-oksihidroksidni prahovi za dobijanje prelaznih faza Al2O3 su dobijeni u postupku neutralizacije natrijum-aluminata, dobijenog u klasičnom Bajerovom postupku, 1 M rastvorom sumporne kiseline. U zavisnosti od koncentracije polazog rastvora, trajanja reakcije neutralizacije i pH rastvora, sintetisani su prahovi različitog faznog sastava, uglavnom višefazni, ali sa dominantnom fazom gibsita, bajerita ili bemita. Pored toga, različiti uslovi sinteze uticali su na dobijanje prahova različite morfologije i specifične površine. Posle termičke obrade prahova na 500 oC u trajanju od 30 min, u zavisnosti od njihovog polaznog sastava i morfoloških karakteristika dobijene su prelazne faze aluminijum-oksida i to η- i γ-Al2O3, specifične površine od 264 do 373 m2/g. Pri tome je pokazano da se zagrevanjem bajerit i pseudobemit transformišu u η-fazu, a gibsit u γ-fazu, zadržavajući morfologiju polaznog praha.
Upravljanje korišćenim gumama, dometi u svetu i stanje u Srbiji
(Association of the Chemical Engineers of Serbia, 2011) Stanojević, Dušan D.; Rajković, Miloš B; Tošković, Dragan V.
U radu je razmatrano upravljanje korišćenim gumama u nekim od najrazvijenijih zemalja sveta i Srbiji, sa ciljem da se ukaže na očekivana kretanja u ovoj oblasti u budućnosti. U mnogim zemljama se sa korišćenim gumama nekontrolisano postupa; gume se odlažu na deponije, pa su česti požari sa ozbiljnim posledicama po životnu sredinu. U zemljama gde je pitanje korišćenih guma rešeno na bezbedan način, deo korišćenih guma se direktno ili posle obnavljanja ponovo koristi na vozilima, a ostatak (otpadne gume) prerađuje se u vredne sirovine i proizvode, ili se koristi kao energent. Ovakvim postupanjem rešava se problem odlaganja otpadnih guma i otklanjanju brojni rizici takve prakse. U svetu, u bezbednom upravljanju otpadnim gumama prednjači EU koja sa Norveškom i Švajcarskom zbrinjava 95% otpadnih guma, a slede Japan sa 91% i SAD sa 89%. U Srbiji korišćenim gumama se upravlja na bezbedan način, saobražen sa praksom kakva se primenjuje u razvijenim zemljama. Zbog ubrzanog globalnog iscrpljivanja sirovina, posebno nafte, očekuje se da će otpadne gume u budućnosti imati značaj dragocenog resursa.
Selective IR absorption in molecular nanofilms
(Elsevier, 2011) Škipina, B.; Mirjanić, D. Lj.; Vučenović, S. M.; Šetrajčić, J. P.; Šetrajčić, I. J.; Šetrajčić-Tomić, A. J.; Pelemiš, S. S.; Markoski, B.
We have formulated a microscopic theory of optical properties of ultrathin molecular films (nanofilms), i.e. quasi 2D systems parallel to XY planes bounded by two surfaces. Exposure of nanofilms to the external electromagnetic fields has result in creation of excitons – but different than bulk ones. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green’s functions. It has been shown that two types of optical excitations can occur: bulk and surface exciton states. Exciton energy dispersion law shows discrete behavior with non-zero values. Analysis of the dielectric properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. In addition, permittivity shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of both resonance and quantum size effects. Influences of boundary conditions on optical characteristics (through analyses of dynamical absorption coefficient) of these nanostructures were specially and in details explored.
The effect of glucose on the formation of the nanocrystalline transition alumina phases
(Elsevier, 2011) Obrenović, Zoran; Milanović, Marija; Djenadić, Ružica R.; Stijepović, Ivan; Giannakopoulos, Konstantinos P.; Perušić, Mitar; Nikolić, Ljubica M.
Series of alumina powders were synthesized starting from sodium aluminate solution prepared from Bayer liquor. The neutralisation of sodium aluminate solution was performed with the use of sulphuric acid. The influence of glucose as a non-surfactant additive on the structure of alumina powders at moderate pH was investigated. The results show that the properties of the powders are influenced by the initial pH value of the solution, as well as the duration of the neutralisation step. High pHs lead to the formation of powders with heterogeneous structure with bayerite as a dominant phase, which during calcinations converts to h-alumina with high surface area. Addition of glucose to the starting aluminate solution leads to the formation of nanocrystalline boehmite with estimated average crystallite size less than 3 nm and high surface area (above 300 m2/g). After calcinations, boehmite transforms to g-alumina. The results have shown that during the heat treatment, structural transformations proceeded simultaneously with the significant changes in the textural properties of the obtained mesoporous g- and h-alumina powders
The Effect of Periodically Changing Regimes on the Electrodeposition of Silver Powder
(Electrochemical Science Group, Serbia, 2011) Pavlović, LJ. J.; Pavlović, M. G.; Pavlović, M. M.; Nikolić, N. D.; Tomić, M. V.
The effect of different deposition regimes (constant and reversing currents, constant and pulsating overpotential), on the powdered and dendritic silver electrodeposits morphology were investigated. The morphology of electrodeposited silver powder was studied utilizing a scanning electron microscope. The results obtained in constant regimes were compared with those obtained in pulsating and reversing regimes. The size of dendrites decreased strongly with increased overpotential or current. It was also shown that the agglomeration of silver dendrites in spongy-like agglomerates was strongly decreased by pulsating overpotential electrodeposition or reversing current. The possibility of obtaininig powder particles, with different properties, depending on conditions of electrolysis was demonstrated.

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