bluuebunny/crossref_metadata_2025 huggingface dataset:
Refreshment topics II: Design of distillation columns
Authors: Milojevic Svetomir , Skala Dejan
Published: July 2008

For distillation column design it is necessary to define all the variable parameters such as component concentrations in different streams temperatures, pressures, mass and energy flow, which are used to represent the separation process of some specific system. They are related to each other according to specific laws, and if the number of such parameters exceeds the number of their relationships, in order to solve a problem some of them must be specified in advance or some constraints assumed for the mass balance, the balance of energy, phase equilibria or chemical equilibria. Knowledge of specific elements which are the constituents of a distillation unit must be known to define the number of design parameters as well as some additional apparati also necessary to realize the distilation. Each separate apparatus might be designed and constructed only if all the necessary and variable parameters for such a unit are defined. This is the right route to solve a distilation unit in many different cases. The construction of some distillation unit requires very good knowledge of mass, heat and momentum transfer phenomena. Moreover, the designer needs to know which kind of apparatus will be used in the distillation unit to realize a specific production process. The most complicated apparatus in a rectification unit is the distillation column. Depending on the complexity of the separation process one, two or more columns are often used. Additional equipment are heat exchangers (reboilers, condensers, cooling systems, heaters), separators, tanks for reflux distribution, tanks and pumps for feed transportation, etc. Such equipment is connected by pipes and valves, and for the normal operation of a distillation unit other instruments for measuring the flow rate, temperature and pressure are also required. Problems which might arise during the determination and selection of such apparati and their number requires knowledge of the specific systems which must be separated. The experience of the designer and his creativity for proposing a solution for an industrial unit which enables optimal process operation accompanied with minimal energy consumption, as well as a small number of apparati, and minimal total length of pipes and number of instruments is always a valuable additional effect for minimal investment costs and an optimal production process.
The influence of polyol type on cell geometry and the thermal stability of polyurethane foams
Authors: Prendzov Slobodan , Loncar Kristijan , Dimzoski Bojan , Prendzova Magdalena
Published: July 2008

The aim of this study was to examine the influence of substituting defined amounts of polyol Voranol 3322 by polyol Voranol CP 1055 on the cell geometry and thermal stability of the synthesized flexible polyurethane foams. The influence of the amount of antipyrene on the cell geometry and their thermal stability was also investigated. The following components were used in the synthesis of the polyurethanes: a mixture of two polyols (Voranol 3322 with the hydroxyl number 47 mg KOH/g, mean molecular mass 3400 and Voranol CP 1055 with the hydroxyl number 156 mg KOH/g, mean molecular mass 1000), toluene discarnate as the isocyanate component, a combination of an organic-metallic compound and a tertiary amine as catalysts, surfactant and water as the coreactant. The thermal stability was determined by thermogravimetric analysis (in a nitrogen atmosphere). The cell geometry was analyzed by optical microscopy. Examination of the cell geometry revealed different cell shapes. The form factor as an indicator of cell deviation from spherical shape increased (more round forms were observed) with increasing amount of Voranol CP 1055. The TG examination showed that specimens with 6 and 8 g of Voranol 3322 substituted by Voranol CP 1055 completely degraded at 350 ?C, while foams with 10 and 12 g of Voranol 3322 substituted by Voranol CP 1055 displayed lower mass loss at higher temperatures and had residual masses of 46 % and 43 % at 600?C respectively. The addition of antipyrene in an amount of 1% (based on the amount of polyol) contributed to improved thermal stability, no visible color change of the specimen tested at 210?C for 40 minutes, and to rounder cell forms. Considering the obtained results it can be concluded that an increase in the amount of Voranol CP 1055 yielded more spherically shaped cells and better thermal stability of the synthesized flexible polyurethane foams. The addition of antipyrene improves the thermal stability and the cell geometry.
Investigation of the possibility of binding fly ash particles by elemental sulphur
Authors: Vidojkovic V. , Djordjevic N. , Boljanac T. , Vlahovic M. , Martinovic S.
Published: July 2008

Thermal power plants in Serbia use lignite for electrical power production The secondary product of coal combustion is fly ash in the amount of 17%. Fly ash causes the pollution of air, water and soil, and also cause many human, especially lung diseases. Secondary sulphur is a product of crude oil refining. The aim of this study was to investigate the use of sulphur as a bonding material in ultra fine particle agglomeration (smaller than 63 ?m) in fly ash. The agglomeration should make the ash particles larger and heavy enough to fall without flying fractions. The experiments showed that during the homogenization of the ashes and sulphur from 150 to 170 ?C in a reactor with intensive mixing, an amount of 15% sulphur was sufficient to bond particles and cause agglomeration without visible flying fractions.
Eco-chemical knowledge, behavior and engagement of workers employed in the mineral fertilizer industry in Novi Sad
Authors: Cvjeticanin Stanko , Segedinac Mirjana
Published: July 2008

The level of environmental pollution is influenced by the knowledge, behavior and ecological engagement of both the individual and society. The mineral fertilizer industry represents a potential source of pollution. The issue examined in this study is the level of eco-chemical knowledge, behavior and ecological engagement of the workers employed in the mineral fertilizer industry in Novi Sad. We have concluded that the workers hover low level of knowledge, behavior and engagement. The results obtained could be used for the selection of methods to enhance the eco-chemical knowledge of the employees.
Vinca landfill leachate characteristics prediction by the leaching method
Authors: Calic Natasa , Ristic Mirjana
Published: July 2008

Under the newly implemented waste management policy in European Union countries, sanitary landfilling constitutes the fourth and the least preferred of the alternative management options for the disposal of solid urban wastes. Landfills generate emissions over long periods, often longer than a lifetime. The longest lasting emission is leachate: leachate production and management is now recognized as one of the greatest problems associated with the environmentally sound operation of sanitary landfills. These liquid wastes can cause considerable pollution problems by contacting the surrounding soil, ground or surface waters and, are therefore considered major pollution hazards unless precautionary measures are implemented. Landfill leachate characterization is a critical factor in establishing a corresponding effective management strategy or treatment process. This paper summarizes leachate quality indicators, and investigates the temporal variation of leachate quality from municipal solid waste. The toxicity of leachates from the municipal solid waste landfill "Vinca" in Belgrade, the capital of Serbia, was characterized using toxicity characteristics leaching procedures (TCLP). The "Vinca" landfill was established in 1978 as one of several municipal landfills. Since the 1990-ies the "Vinca" landfill has been the only operating landfill servicing the Belgrade Metropolitan area, the biggest city in Serbia, with 1,576,124 inhabitants in the larger-city area, and 1,273,651 inhabitants in the inner-city area. The total average amount of solid wastes deposited in the landfill is estimated to be 1100 tons/day. The landfill site is not lined and the tributary flows through the centre of the site-in some places directly under the mass of refuse. No consideration has been given to the protection of ground waters, surface runoff or drainage. Local authorities plan to expand the landfill by 0.4 km2 to a total of 1.3 km Chemical analysis was performed on the samples and the temporal variation of several parameters was monitored including pH, COD, chlorides, sulfates, nitrates, ammonia nitrogen, hardness, and heavy metals. The COD and pH were related to the biological activity within the landfill and the results indicated differences between the samples due to waste age. The concentrations of heavy metals, sulfates, nitrates, chlorides and ammonia nitrogen in the leachate were low, indicating their initially low amount in landfilled waste or their flushing with moisture contributing to a reduction in their concentrations.
Environmentally friendly disinfectant: Production, disinfectant action and efficiency
Authors: Cekerevac Milan , Simicic Milos , Rakin Petar , Popovic Negica , Nikolic-Bujanovic Ljiljana , Rakin Dejan
Published: July 2008

Silver is a known disinfectant from ancient times, and it has been widely used for various purposes: for food and water disinfection, curing of wounds and as a universal antibiotic for a wide spectrum of diseases - until the Second World War and the discovery of penicillin. Until recently, it was assumed that silver, being a heavy metal, was toxic for humans and living beings. However, the newest research provides facts that the usage of silver, even for drinking water disinfection, is benign if it is added in small concentrations (in parts per billion). It has been shown in the newer scientific and technical literature that silver in colloidal form is a powerful (secondary) disinfectant for drinking water, that it can be effectively used for the disinfection of water containers including swimming pools, installations in food industry, medicine, etc. Particularly, it has been shown that colloidal silver combined with hydrogen peroxide shows synergism having strong bactericidal and antiviral effects. The combination can be successfully used as a disinfectant in agriculture, food production and medicine. The original electrochemical process of production, the mechanism of physical-chemical reactions in that process and the mechanism of the antiseptic affect of the environmentally friendly disinfectant, based on the synergism of colloidal silver and hydrogen peroxide and the activity of electrochemically activated water, is shown. The starting solution was anolyte, obtained in electrochemical activation by water electrolysis of a highly diluted solution of K-tartarate in demineralized water (5.5-1CT4 M). The problem of electrolysis of very dilute aqueous solutions in membrane cells was particularly treated. It was shown that the efficiency of the electrolysis depends on the competition between the two processes: the rates of the processes of hydrogen and oxygen generation at the electrodes and the process of diffusion of hydrogen and hydroxyl ions through the cell membrane. Relatively strong disinfectant and sterilization action on standard races of gram-positive and gram-negative bacteria, blast spores and spores, as well as the safety of implementation of an environmentally friendly disinfectant was certified in a relevant institution, the Military Academy of Medicine in Belgrade.
An analysis of moist air energy potential during the process of paper band drying
Authors: Valent Vladimir , Krgovic Milorad , Nikolic Srecko
Published: July 2008

The energy potential of moist air venting from the dryer of the installation for drying paper bands was analyzed. The thermodynamic state of air is defined by the air temperature at the outlet of the dryer and the dew temperature of the air. For the temperature at the outlet of the dryer (55-85?C) and selected dew temperatures (45-65?C), the specific consumption of dry air was determined. For selected kinetics of paper band drying, 10-35 kgH2O/(m2h), the modification of energy potential of the air as a function of air temperature at the outlet of the dryer and the temperature of dew air was specified. The air flow through the dryer was also correlated with the operation of the ventilation system and recuperation of energy. An analysis of the thermodynamic state of moist air venting from the dryer and the calculation of its energy potential confirmed that increase of the dew temperature of the air decreases its energy potential. With the intensity of vaporization Ivm,isp = 10 kgH2O/(m2h), the decrease is 6%. With Ivm,isp = 35 kgH2O/(m2h), the decrease is much greater and amounts to 21.6%. With increasing dew temperature, the specific consumption of dry air decreases, as well as the relative humidity of the air.
The analysis of loading losses from tank trucks
Authors: Jovanovic Ana , Stijepovic Mirko , Jovanovic Mica
Published: July 2008

The quantity of loading losses, which are the primary source of evaporative emissions from tank cars and trucks was analyzed in this paper. Loading losses occur as organic vapors in "empty" cargo tanks are displaced to the atmosphere by the liquid being loaded into the tanks. Emissions from loading petroleum liquid were estimated using three methods: the API (American Petroleum Institute) method, the VDI (Verein Deutscher Ingenieure -Association of German Engineers) method and the Yugoslav Standard JUS B.HO.531 method. The mass of evaporative losses from loading operations is a function of the following parameters: the method of loading the cargo, the physical and chemical characteristics of the cargo and the ambient temperature during loading. Evaporation losses from the loading of motor gasoline (MB-95, BMB-95, MB-98 and MB-86) and diesel fuels (D-2, Euro D-2) were calculated. Losses on a monthly and annual basis were presented for an assumed amount of loaded cargo. It was estimated that the highest loading losses occur in the summer period because of high ambient daily temperatures and in the period of higher transporting levels. It should be pointed out that the loading losses of diesel fuel calculated using an empirical coefficient according to JUS B.HO.531 are significantly higher in comparison with the loading losses calculated using emission factors from the EPA and the VDI method. The gasoline loading losses calculated using emission factors derived from the three methods are similar.
Investigation of fly ash properties with purpose of its utilization as a secondary raw material for portland cement clinker production
Authors: Bascarevic Zvezdana , Komljenovic Miroslav , Petrasinovic-Stojkanovic Ljiljana , Jovanovic Natasa , Rosic Aleksandra , Rsumovic Mihailo
Published: July 2008

In this paper the results of the investigated properties of fly ash from four thermal power plants in Serbia are presented. The physical, chemical, mineralogical and thermal characterization of fly ash was carried out, in order to determine the possibility to utilize this material in the building materials industry, foremost in the cement industry. It was determined that, although there are differences concerning the physical, chemical, and mineralogical characteristics of the investigated samples, they are very similar concerning their thermal characteristics. It was concluded that using fly ash as one of the raw components in the mixture for Portland cement clinker synthesis, not only enables the substitution of natural resources, but it might have a positive effect on the lowering of the sintering temperature.
Substitution of the clayey mineral component by lignite fly ash in portland cement clinker synthesis
Authors: Jovanovic Natasa , Komljenovic Miroslav , Petrasinovic-Stojkanovic Ljiljana , Bascarevic Zvezdana , Bradic Violeta , Rosic Aleksandra
Published: July 2008

Fly ash from four power plants in Serbia (PP "Morava" - Svilajnac, PP "Kolubara" - Veliki Grijani, PP "Kostolac" - units B1 and B2 - Kostolac and PP "Nikola Tesla" - units A and B - Obrenovac) was utilized as the starting raw component for Portland cement clinker synthesis. Limestone and quartz sand from the "Holcim - Serbia, a.d." cement factory were the other two starting raw components. Based on the chemical composition of the raw components and from the projected cement moduli, the amounts of raw components in the raw mixtures were calculated. Six different raw mixtures were prepared - each one consisted of limestone, sand and different fly ash. A raw mixture from the industrial production of the "Holcim - Serbia, a.d." cement factory was used as the reference material. The prepared raw mixtures were sintered in a laboratory furnace at 1400?C. The chemical and mineralogical compositions of the synthesized clinkers were determined. The characteristics of clinkers, based on fly ash, were compared to the characteristics of the industrial Portland cement clinker from the "Holcim - Serbia, a.d." cement factory. The results of the investigation showed that fly ash from power plants in Serbia can be suitable for Portland cement clinker synthesis.
Compressed ethylene phase states and their importance for the production of low density polyethylene
Authors: Stoiljkovic Dragoslav , Damjanovic Budimir , Djordjevic Jovica , Spehar Danko , Jovanovic Slobodan
Published: July 2008

In the last three decades the authors have published papers on the concept of the supra-molecular organization and the phase state of compressed ethylene gas and their effects on the mechanism and kinetics of free-radical ethylene polymerization. The effects on the macromolecular structure of low density polyethylene (LDPE) were also explained. The importance of the phase state of compressed ethylene on the industrial process of LDPE production are presented in this paper: The start-up of polymerization, the peak in the polymerization rate curve, the stability of the reaction, the structure and properties of LDPE, the separation of unreacted ethylene and polyethylene and ethylene compression are discussed.
Group contribution methods for estimating the properties of polymer systems
Authors: Bogdanic Grozdana
Published: July 2008

Polymer materials are nowadays used in a wide range of technological applications. Reliable knowledge of the thermo physical properties of pure polymers and their mixtures in the whole composition and a wide temperature and pressure range determines whether a given polymer is suitable for a specific application. On the other hand, accurate knowledge of the thermodynamic properties of the systems is a vital prerequisite for computer-aided syntheses, design, and the optimization of industrial polymer processes. However, the experimental data on polymer solubility are often scarce, and at this point, thermodynamics provide a powerful tool for modeling and extrapolating the experimental data. These models, together with factual data banks, are powerful software tools for the reliable development of chemical processes and other applications of industrial interest. The status of the different approaches and important applications of industrial interest using thermodynamic information derived from data banks or by using predictive thermodynamic models are presented in this review.
The application of macroporous copolymers in the sorption of heavy and precious metals from aqueous solutions
Authors: Nastasovic Aleksandra , Jovanovic Slobodan , Onjia Antonije , Sandic Zvjezdana , Malovic Ljiljana , Jakovljevic Dragica , Vukovic Zorica
Published: July 2008

Macroporous crosslinked poly(GMA-co-EGDMA) was synthesized by the suspension copolymerisation and functionalized by the ring-opening reaction of the pendant epoxy groups with ethylene diamine. The porosity parameters (specific pore volume, specific surface area, and pore diameter, which corresponds to half of the pore volume) for the initial and amino-functionalized copolymer samples were calculated from the cumulative pore volume distribution curves obtained by mercury porosimetry. The selectivity, sorption capacity and sorption rate of amino-functionalized poly(GMA-co-EGDMA)-en were determined under static conditions. The sorption of Cu(ll) and Ag(l) ions on poly(GMA-co-EGDMA)-en was very rapid (ti/2 value about 1 min). Slower sorption was observed for Au(lll) ions with a ti/2 value of 6.5 minutes. The different rates of Au(lll), Cu(ll) and Ag(l) sorption could be applied for gold, copper and silver ion separation from mixed solutions. The sorption of Ni(ll) and Cu(ll) ions from galvanic solution under competitive conditions was also fast, with ti/2 values of 0.5 and 2 min, respectively. However, Zn(ll) sorption was considerably slower (a ti/2 of 10 min). Similar results were obtained for galvanic solution under dynamic conditions, i.e., the metal sorption capacities of poly(GMA-co-EGDMA)-en decreased in the order: Ni(ll) > Cu(ll) >> Zn(ll). The reusability of amino-functionalized poly(GMA-co-EGDMA) for Cu(ll) sorption was tested in four sorption/desorption cycles. Regeneration experiments were performed with 0.1 and 1 M H2SO4 showed a Cu(ll) capacity loss of 50 % in the first sorption/desorption cycle. The sorption capacity increased when additional neutralization with 0.1 and 1 M NaOH was performed after each sorption/desorption cycle.
The adhesion of epoxy cataphoretic coating on phosphatized hot-dip galvanized steel
Authors: Bajat Jelena , Miskovic-Stankovic Vesna , Popic Jovan , Drazic Dragutin
Published: July 2008

The influence of hot-dip galvanized steel surface pretreatment on the adhesion of epoxy cataphoretic coating was investigated. Phosphate coatings were deposited on hot-dip galvanized steel and the influence of fluoride ions in the phosphating plating bath, as well as the deposition temperature of the plating bath, were investigated. The dry and wet adhesion of epoxy coating were measured by a standard pull-off method. The surface roughness of phosphatized galvanized steel was determined, as well as the wettability of the metal surface by emulsion of the epoxy resin in water. The adhesion of epoxy coatings on phosphatized hot-dip galvanized steel was investigated in 3wt.%NaCI.
The influence of filler on the properties of elastomeric materials based on poly(ethylene-co-propylene-co-2-ehylidene-5-norbornene) rubber
Authors: Budinski-Simendic Jaroslava , Milic Jelena , Cvetkovic Ivana , Radicevic Radmila , Korugic-Karasz Ljiljana , Vukov Miodrag , Mirkovic Desa
Published: July 2008

Crosslinked samples based on poly(ethylene-co-propylene-co-2-ehylidene5-norbornene) EPDM rubber, carbon black as active filler and natural chalk as inactive filler were cured with sulphur. The content of carbon black was varied from 100 to 200 pph. The content of chalk was varied from 0 to 100 pph. The content of paraffin oil was also varied in some samples. The compounds were prepared by mixing ingredients on a laboratory two-roll mill. Vulcanizates were prepared by curing at 180?C. Various methods were used for the physical and mechanical characterizations. The dynamic mechanical properties of the elastomers were measured in the temperature range from -120 to 80?C.
Porous poly(methylmethacrylate) and poly(methylmethacrylate-co-acrylamide)
Authors: Nikolic Ljubisa , Nikolic Vesna , Stankovic Miroslav , Todorovic Zoran , Vukovic Zorica
Published: July 2008

The characteristics of two types of porous polymers: poly(methyl methacrylate) and copolymers of methyl methacrylate and acrylamide were investigated in this study. Poly(methyl methacrylate) was synthesized in suspension, using ethylene glycol dimethacrylate as the cross-linking agent, poly(vinyl pyrrolidone) as the protective colloid, and benzoyl peroxide as the initiator. The synthesis of poly(methyl methacrylate-co-acrylamide) was initiated in emulsion in the presence of dioctyl sulfosuccinate sodium salt, followed by a sol-gel process, and completely reacted to the solid state. Potassium persulfate was used as the initiator, and tetramethylol glycoluril as the cross-linking agent. Both types of syntheses were carried out in the presence of ethyl acetate. The porosity, specific surface and distribution of the pore sizes of the obtained polymers were determined by mercury porosimetry. The polymers were used as inert carriers for the immobilization of enzymes and whole cells of Saccharomyces cerevisiae yeast.
System for electrochemical investigations based on a PC and the Lab VIEW package
Authors: Stevic Zoran , Rajcic-Vujasinovic Mirjana
Published: July 2008

This paper describes an electrochemical research system based on the Lab VIEW computer software package. An overview of well known electrochemical methods, such as potential measurements, chronopotentiometry, chronoamperometry, cyclic voltammetry and EIS is given. Electrochemical impedance spectroscopy has been adapted for systems containing large capacitances. For signal generation and recording of the response of the investigated electrochemical cell, a measurement and control system was developed, based on a PC P4 computer. The rest of the hardware consists of a commercially available AD-DA converter and an external interface for analog signal processing. The interface is a result of the authors own research. The software platform for the desired measurement methods is Lab VIEW package, which is regarded as a high standard in the area of modern virtual instruments. The developed system was adjusted, tested and compared with other commercially available systems. One such system is in constant use at the Technical Faculty in Bor.
Photocatalytic degradation of synthetic dye under sunlight
Authors: Mijin Dusan , Jugurdzija Mirko , Jovancic Petar
Published: July 2008

Synthetic dyes are widely used in the textile industry. Dye pollutants from the textile industry are an important source of environmental contamination. The majority of these dyes are toxic, mostly non-biodegradable and also resistant to decomposition by physico-chemical methods. Among new oxidation methods or "advanced oxidation processes", heterogeneous photocatalysis appears as an emerging destructive technology leading to the total mineralization of many organic pollutants. CI Basic Yellow 28 (BY28), commonly used as a textile dye, could be photocatalytically degraded using TiU2 as catalyst under sunlight. The effect of some parameters such as the initial catalyst concentration, initial dye concentration, initial NaCl and Na2CO3 concentrations, pH, H2O2 and type of catalyst on the degradation rate of BY28 was examined in details. The presence of NaCl and Na2CO3 led to inhibition of the photodegradation process. The highest photodegradation rate was observed at high pH, while the rate was the lowest at low pH. Increase of the initial H2O2 concentration increased the initial BY28 photodegradation efficiency. ZnO was a better catalyst than TiO2 at low dye concentrations.
Determination of stoichiometric coefficients by the matrix method
Authors: Tadic Goran , Pejovic Branko , Gligoric Miladin , Micic Vladan
Published: July 2008

The problem of calculating stoichiometric coefficients in a chemical equation can be solved by standard methods and the method of multidimensional vector space, but good knowledge of vector algebra is required. In this paper, the authors proposed a matrix method and other treatment of the problem was given as the authors' own interpretation. A matrix was formed in the form of base using all the elements which take place in a chemical reaction, after which the matrixes of all the chemical compounds were determined based on numerical indexes and element symbols. This approach enables the setting of a principal matrix equation based on a mathematical approach. The solutions of this matrix equation are the desired stoichiometric coefficients that form a balanced equation. A new approach to tabular solving is presented. This method, compared to existing standard methods, is faster, simpler, and more effective, especially for complex chemical equations. The method was tasted on examples from inorganic chemistry and metallurgy.
Shrinking core models applied to the sodium silicate production process
Authors: Stankovic Mirjana , Ρezο Lato , Kovacevic Branimir , Jovanovic Mica , Debeljkovic Dragutin
Published: July 2008

The sodium silicate production process, with the molar ratio SiO2/Na2O = 2, for detergent zeolite 4A production, is based on quartz sand dissolving in NaOH aqueous solution, with a specific molality. It is a complex process performed at high temperature and pressure. It is of vital importance to develop adequate mathematical models, which are able to predict the dynamical response of the process parameters. A few kinetic models were developed within this study, which were adjusted and later compared to experimental results. It was assumed that SiO2 particles are smooth spheres, with uniform diameter. This diameter decreases during dissolving. The influence of particle diameter, working temperature and hydroxide ion molality on the dissolution kinetics was investigated. It was concluded that the developed models are sufficiently correct, in the engineering sense, and can be used for the dynamical prediction of process parameters.
Cordierite ceramics for applications in foundry practice
Authors: Acimovic-Pavlovic Zagorka , Prstic Aurel , Andric Ljubisa
Published: July 2008

The research of new ceramic coatings has an important role in the improvement and development of new casting methods, especially casting with meltable and evaporable patterns. The selection of ceramic materials to be used as refractory fillers, materials for the binding system and additives for maintaining suspension stability, will be carried out in accordance with the casting method selected for the actual alloys and types of castings. The actual importance of these problems is reflected in the fact that the application of quality coatings increases the production efficiency by producing high quality castings, increases the metal yield and eliminates the expensive casting operations-cleaning and machining. Cordierite ceramic are of great importance in modern technology. Standard raw materials, kaolin, talc, MgO, alumina, feldspar were used in the synthesis of cordierite ceramics. Sintered cordierite of the composition 2MgO ? 2Al2O3 ? 5SiO2 was used as a refractory filler in a ceramic coating for evaporative polystyrene patterns in a new casting technology, the EPC Method. Cordierite characterization was carried out by means of X-ray diffraction. The characteristic temperatures for carrying out solid state reactions in the three component system 2MgO ? 2A12O3 ? 5SiO2 were determined by differential thermal analysis in the range from ambient temperature to 1100 ?C. In order to realistically evaluate possible cordierite application in the production of evaporative pattern ceramic coatings, concurrent analyses with a talc-based coating were carried out. Cordierite ceramics have not yet been used in casting.
Analytical model of carrier mobility in a Polymer Field Effect Transistor
Authors: Milosevic Milan , Ramovic Rifat
Published: July 2008

In this paper, the carrier mobility analytical model in a POFET (Polymer Field Effect Transistor) channel is proposed. The model was developed on the basis of existing models and experimental results. The proposed model is universal because it encompasses the carrier mobility dependence on temperature, electric field and trap density in the POFET channel. The model is comparatively simple, easy for application and gives valuable results. According to the presented model, simulations of mobility as a function of the parameters of interest were performed. The obtained results are shown graphically. In comparison to accessible experimental results excellent correspondence was found. This model enables the calculation of simple POFET current-voltage I (V) characteristics.
Interaction of ruby laser with carbon fibrous materials
Authors: Stasic Jelena , Sreckovic Milesa , Kaludjerovic Branka , Ristic Slavica
Published: July 2008

Carbon fibrous materials are interesting because of their good properties and numerous possible applications. The characteristics of these materials can be programmed by careful selection of the modification process parameters. The laser technique can be successfully employed for these purposes. The high temperatures arising in the material during a short laser pulse can cause a number of changes in the material. Carbon fibrous materials with different textile shapes, during different stages of processing, were exposed to laser radiation. A ruby laser (X=694.3 nm) was used to modify the material. The structural changes were examined by scanning electron microscopy and X-ray diffraction. It was established that the radiation of this laser induces structural changes leading to a better arrangement of the turbostratic carbon fiber structure.
Thermal memory effects to photothermal pulse response
Authors: Popovic Marica , Stojanovic Zoran , Galovic Slobodanka
Published: July 2008

An analytical model that describes surface temperature variations of media with thermal memory stimulated by laser pulses was developed. The influence of thermal memory for semi infinite sample was analyzed by comparing our results with classical model results which neglect the thermal memory of materials for different pulse widths and for different pulse shapes. It was shown that this influence was outstanding around steep changes of the incentive flux and for short incident pulses.
Hydrogen desorption from nanostructured magnesium hydride composites
Authors: Brdaric Tanja , Stamenkovic Ljiljana , Novakovic Nikola , Grbovic-Novakovic Jasmina
Published: July 2008

The influence of 3d transition metal addition (Fe, Co and Ni) on the desorption properties of magnesium hydride were studied. The ball milling of MgH2-3d metal blends was performed under Ar. Microstructural and morphological characterization were performed by XRD and SEM analysis, while the hydrogen desorption properties were investigated by DSC. The results show a strong correlation between the morphology and thermal stability of the composites. The complex desorption behavior (the existence of more than one desorption peak) was correlated with the dispersion of the metal additive particles that appear to play the main role in the desorption. The desorption temperature can be reduced by more than 100 degrees if Fe is added as additive. The activation energy for H2 desorption from the MgH2-Fe composite is 120 kJ/mol, implying that diffusion controls the dehydration process.
Synthesis of biomorphaus SiC-ceramics
Authors: Egelja Adela , Gulicovski Jelena , Devecerski Aleksandar , Boskovic Snezana , Matovic Branko
Published: July 2008

The carbothermal reduction processing of partially mineralized fir (Abies alba) samples was used to obtain highly-porous SiC ceramics with cellular structure. The infiltration of TEOS (tetraetilortosilikat, Si(OC2H5)4) as a silica source, was conducted in order to carry out the mineralization process. Synthesis of the SiC was achieved with a C/SiO2 replica annealing at 1723 K in Ar atmosphere. The obtained samples were characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The experimental results revealed that the hierarchical bimorphous wood structure was preserved even after high-temperature treatment. Microstructural characterization of the ceramics revealed the presence of the P-SiC phase and traces of the a-SiC phase.
Aerosol synthesis and characterization of nanostructured particles of Y3Al5O12:Ce3+ and Y2O3:Eu3+
Authors: Marinkovic Katarina , Veselinovic Ljiljana , Gomez Luz , Rabanal Maria , Mancic Lidija , Milosevic Olivera
Published: July 2008

Nanostructured YAG:Ce3+ and Y2O3:Eu3+ were synthesized by low temperature (320?C) aerosol synthesis-LTAS and high temperature (900?C) aerosol synthesis-HTAS, respectively. The synthesis included aerosol generation from a nitrate precursor solution by an ultrasonic atomizer (1.3 MHz). The obtained aerosol was introduced into a tubular flow reactor, using air as the carrier gas, where successively, on a droplet level, evaporation/drying, precipitation and thermolysis occurred. The obtained powders were collected and thermally treated at different temperatures (900-1200?C). The phase development and the morphology were investigated by the X-ray powder diffraction method (XRPD) and scanning electron microscopy combined with energy dispersive spectrometry (SEM/EDS). Structural refinement was performed using the Rietveld method with the Fullprof and Koalariet programs. The average crystallite size for the Y2O3:Eu system was calculated using the Profit program. It was shown that 89 wt.% of Y3Ai5Oi2:Ce was obtained by annealing (1000?C/6 h) the as prepared, amorphous powder, synthesized by the low temperature aerosol method (LTAS). High temperature spray pyrolysis (HTAS) at 900?C led to the formation of the targeted cubic phase of Y2O3:Eu3+. The microstructural parameters of the asprepared samples of the Y2O3:Eu3+ system indicate the formation of nanostructures with crystallite size smallest than 20 nm. The substitution of luminescent centers (Ce3+, Eu3+) into a host lattice (YAG, Y2O3, respectively) was confirmed by changes in the crystal lattice parameters. Also, it was shown in both systems that good morphological characteristics (non-a?gglomerated, spherical, submicron particles) were obtained enabling improved luminescent characteristics.
Dispersion and deagglomerat1on of nano-SiO2 particles with a silane modification reagent in supercritical CO2
Authors: Stojanovic Dusica , Vukovic Goran , Orlovic Aleksandar , Uskokovic Petar , Aleksic Radoslav , Bibic Natasa , Dramicanin Miroslav
Published: July 2008

The supercritical CO2 method was used in order to perform deagglomeration and improve the dispersion of nano-SiO2 particles. ?-Met-hacryloxypropyltrimethoxysilane was used as the surface modification reagent. The conventional method for coating nano-SiO2 particles was used as the comparison method. Considerable improvement of the dispersion and deagglomeration was found using supercritical CO2. Analysis of the TEM micrographs and DLS results showed the reduction of the average size of the agglomerates with the silane coupling reagent. Thermogravimetric analysis (TGA) showed that the particles treated in super?critical CO2 were more thermally stable than particles treated by conventional method. Encapsulation of several particles coated with the silane coupling reagent was observed in certain parts of the primary particles. A chemical reaction takes place between the modification reagent, MEMO silane, and active hydroxyl groups on the surface of the nano-SiO2 particles. A larger quantity of MEMO silane reacted using the con?ventional method instead of the supercritical method. On the other hand, the reacted silane molecules were better arranged around the particle surface in the supercritical method because of the formation of covalent or self-assembled structures. Polycondensed structures were preferentially obtained in the conventional method. This was achieved by using supercritical CO2, which has a high solvating power such as organic solvents and physical properties (low viscosity, low surface tension and high diffusion coefficient) similar to gases on the other side. These properties enable the sufficient and uniform wettability of nano-SiO2 particle surfaces. These results are important for obtaining nanofillers with improved dispersion and polymer wettability. Such nanofillers can be used to obtain composite materials with considerably improved mechanical characteristics.
Influence the of Na-LTA synthesis route on low-carnegieite crystallization and stability
Authors: Radulovic Aleksandra , Dimitrijevic Radovan , Vulic Predrag , Dondur Vera
Published: July 2008

The thermal transformation of zeolite precursor is a relatively novel route for the synthesis of aluminosilicate-based ceramic materials which had found numerous uses in the production of dielectric ceramics, microelectronic packaging electromagnetic windows, high-temperature electrical insulators, glass ceramic materials, etc. The mechanism of a thermally induced transformation strongly depends on the extra framework cations and the type of used zeolites. The sodium form of LTA zeolite transforms to low-carnegieite (lt-Carn) in the temperature range between 800 and 900?C. The formed low-carnegieite transforms to nepheline at >900?C. However, the mechanisms of the thermal transformation of Na-LTA zeolite into the low-carnegieite (lt-Carn) phase are still not completely understood. Different structure transformation mechanisms of Na-LTA zeolite into lt-Carn heve been reported. The carnegieite can be formed by a direct solid-solid topotactic transformation: Na-LTA -> lt-Carn. A two step mechanism: Na-LTA -> Am -> lt-Carn can also take place. Such behavior is probably the consequence of the applied synthesis route in the precursor preparation. Therefore, it is of interest to consider the influence of the zeolite preparation route on the processes of thermal transformation of Na-LTA zeolite into lt-Carn. The present paper deals with a systematic study on the thermally induced phase transformation of sodium LTA zeolites synthesized by the gel route under different reaction conditionss. Different gel compositions Na2O(2.4-3.9):Al2O3(l):SiO2(1.5-2.0):H2O(90-170) were used and several zeolite samples were prepared. The prepared zeolite samples were thermally treated at different temperatures from 600 to 950?C at an interval of 20 ?C and the products were analyzed by X-ray diffraction. The zeolites and formed products were characterized by various methods including XRPD, IR, DTA, SEM. It was shown that the rate of lt-Carn formation is dependent on the composition and conditions of gel preparation. It was determined by X-ray diffraction analysis that all the synthesized Na-LTA zeolites recrystallised into lt-Carn or a new crystalline intermediate phase. The amorphous phase was not present in the investigated system. The mechanism of the direct solid-solid topotactic transformation: Na-LTA -> lt-Carn was confirmed.
Thermal properties of radiolytically synthesized PVA/Ag nanocomposites
Authors: Krkljes Aleksandra , Kacarevic-Popovic Zorica
Published: July 2008

The radiolytic method was used to synthesize two types of nanocomposites with silver, PVA/Ag by film casting and PVA hydrogel/Ag nanocomposites. This method is particularly suitable for generating metal nanoparticles in solution. The radiolytic species (solvated electrons and secondary radicals) exhibit strong reducing properties such that metal ions are reduced at each encounter. Metal atoms then tend to grow into larger clusters. It was found that solid or swollen polymers are able to stabilize small crystallites against spontaneous growth via aggregation. Using differential scanning calorimetry (DSC), the melting behavior and kinetics of the PVA/Ag nanocomposites were investigated and compared to those of pure PVA. The melting as well as crystallization behavior of polymers is crucial because it governs the thermal properties, impact resistance and stress strain properties. Understanding the melting behavior is significant not only to tailor the properties of nanocomposites but to investigate the interactions between the constituents. The DSC curves of pure PVA and prepared nanocomposites show only one melting peak between 175 and 230?C, indicating that the melting behavior of these two systems are analogous. In both cases, with increasing heating rate, the melting peak shifts to a higher temperature, but with increasing Ag content the peak melting temperature is lower. When specimens are heated at high heating rate, the motion of PVA molecular chains cannot follow the heating temperature on time due to the influence of heat hysteresis, which leads to a higher peak melting temperature. When Ag nanoparticles are added they increase the heat transfer among the PVA molecular chains decreasing the melting temperature. The Ag content is a major factor affecting the degree of crystallinity. It was observed that at low nanofiller content, up to the 0.5 wt%, the degree of crystallinity of the nanocomposites increased, while at a higher content the crystallization was retarded. The half time of melting is non-linearly dependent on the amount of nanofiller. In the range from 0.25 to 1 wt% Ag it slightly increases, because at a low Ag content the nanoparticles act as a heterogeneous nucleation agent during the crystallization process. For large amounts of nanofiller, the half time of melting is markedly higher than for pure PVA. At a higher Ag content, the nanoparticles act as a barrier that restricts the thermal motion of PVA molecular chains and the half time of complete melting increases. The significantly lower melting activation energy of the nanocomposites with high amount of nanofiller compared to pure PVA, calculated by the Kissinger method, indicated that nanoparticles reduced the heat barrier for the melting process. .
Electrochemical and microstructural characterization of platinum supported on glassy carbon
Authors: Terzic Sanja , Jovanovic Vladislava , Tripkovic Dusan , Kowal Andrzej , Stoch Jerzy
Published: July 2008

The effect of the electrochemical oxidation of glassy carbon on the deposition of platinum particles and the electrocatalytic activity of platinum supported on oxidized glassy carbon were studied for methanol oxidation in H2SO4 solution. Platinum was potentiostatically deposited from H2SO4 + 6mM H2PtCl6 solution. Glassy carbon was anodically polarized in 1 M NaOH at 1.41 V (SCE) for 35 and 95 s and in 0.5 M H2SO4 at 2V (SCE) for 35; 95 s and 2.25 V for 35 and 95 s. Electrochemical treatment of the GC support leads to a better distribution of platinum on the substrate and has remarkable effect on the activity. The activity of the Pt/GCox electrode for methanol oxidation is larger than that of polycrystalline Pt and by more than one order of magnitude larger than that of a Pt/GC electrode. This increase in activity indicates the pronounced role of the organic residues of the GC support on the properties of Pt particles deposited on glassy carbon.
Photoacoustic spectroscopy investigation of sintered zinc-tin-oxide ceramics
Authors: Ivetic Tamara , Nikolic Vesna , Pavlovic Vladimir , Nikolic Pantelija , Ristic Momcilo
Published: July 2008

In this paper the changes that occurred in differently activated ZnO-SnO2 and sintered samples were investigated using photoacoustic spectroscopy. ZnO and SnO2 powders, mixed in the molar ratio 2:1, were mechanically activated in a planetary ball mill for 10-160 min. The mixtures were pres?sed and isothermally sintered at 1300?C for two hours. X-ray diffraction analysis of the obtained sintered samples was performed in order to investigate changes of the phase composition and confirmed only the presence of a pure zinc stannate (Zn2SnO4) phase in all the sintered samples as a result of the solid state reaction and reaction sintering between the starting ZnO and SnO2 powders. The microstructure of the sintered sam?ples was examined by scanning electron microscopy and showed that mechanical activation leads to the formation of a structure with reduced particle size which accelerates spinel formation. Grain growth of the spinel phase slows down the densification process and together with the agglomerates formed during mechanical activation causes the appearance of a porous microstructure. The photoacoustic (PA) phase and amplitude spectra of the sintered samples were recorded as a function of the chopped frequency of the laser beam used (red laser with a power of 25 mW, ?=632 nm) in a thermal-transmission detection configuration. PA experimental data were analyzed using the Rosenzweig-Gersho thermal-piston model, which enabled determination of the thermal diffusivity, Z)T (m2s-1), diffusion coefficient of the minority free carriers D (m2s-1) and the optical absorption coefficient (m-1). The detected differences of the measured thermal-electrical properties of the obtained Zn2SnO4 ceramics indicate changes in the material induced by the different preparation procedure of the starting powders before the sintering process.