bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyrite oxidation by Acidithiobacillus ferrooxidans bacteria
Authors: Savic Dragisa , Lazic Miodrag , Veljkovic Vlada , Vrvic Miroslav
Published: July 2008

The kinetic model of pyrite particle dissolution by the action of bacteria Acidithiobacillus ferrooxidans in a shaken Erlenmeyer flask was presented. The model agreed well with the experimental data for the extracted iron and the number of cells in the liquid phase. The specific growth rate of the adsorbed cells was evaluated (?A = 1,6 d-1) by fitting the experimental data to the model curve. Also, the relevance of the two proposed mechanisms for the bacterial dissolution of sulphide (direct and indirect) was discussed, indicating that the indirect one was dominant. The adsorption process of A. ferrooxidans to the pyrite surface was well correlated by a Langmuir type isotherm.
Analysis of trace anions in the water-steam cycle in power plants
Authors: Cickaric Dragana , Cuckovic Jagoda , Rajakovic Ljubinka
Published: July 2008

This study offers some insight into the significance of water quality control in thermal power plants. In order to maintain high reliability indices in thermal plants and to realize the expected lifetime of these plants, high water quality should be accomplished. Also, the working tools of the analyst in thermal power plants and the types of problems, which help in solving daily tasks, are discussed. The difficulties the analyst might face are indicated. This review considers the implementation of standard control and diagnostic parameters crucial for water quality in all segments of a water-steam system. The subject of this paper was to analyze anion traces in the water-steam cycle, using a modern, highly sensitive instrumental method the method of ion chromatography (1S). Thus, the possibility of monitoring ionic species that can cause corrosion processes in the water-steam system is examined.
Monolayer capacity and specific surface area of cement pastes determined from benzene adsorption isotherms
Authors: Marina Biljana , Brezovska Snezana , Burevski Donco , Angjuseva Biljana
Published: July 2008

Hydrated cement pastes, prepared from Portland cements with different degrees of dispersity obtained by adding small quantities of triethanol amine and ethylene glycol as a grinding aids were investigated. The adsorption isotherms of benzene vapor on the pastes were interpreted by means of the Brunauer - Emmet - Teller (BET), N - layer Brunauer - Emmet -Teller (N - BET) and Huttig equations. The monolayer capacity and specific surface areas of the pastes after 28 days of hydration were determined. By comparison of the results obtained using different equations, the most suitable equation could be selected and used to determine the monolayer capacity and specific surface area. The influence of the dispersity of the cement on the specific surface area of the cement gel in the pastes could also be analyzed from the obtained results. The investigations were in accordance with the results of the physical mechanical properties of cement plasters.
Coated limestone as a filler for the production of PVC-products
Authors: Mihajlovic Slavica , Sekulic Zivko , Petrov Milan
Published: July 2008

The results of laboratory investigations of the possibility to obtain coated limestone for the production of PVC-products are presented in this paper. Limestone from the "Vencac" deposit (Arandjelovac, Serbia and Montenegro) was used as the raw material. The investigations were carried out in two phases: obtaining the coated limestone and determination of the degree of coating. The results of the investigations showed that successful coating of the surface of the limestone particles with Ca-stearate (Ca-stearate content 3%) was achieved in a vibro mill with rings and the obtained degree of coating was higher than 95%. The coating degree was determined in transmitted light by a polarization microscope applying the immersion method (water immersion).
Biodiesel production by enzyme-catalyzed transesterification
Authors: Stamenkovic Olivera , Lazic Miodrag , Veljkovic Vlada , Skala Dejan
Published: July 2008

The principles and kinetics of biodiesel production from vegetable oils using lipase-catalyzed transesterification are reviewed. The most important operating factors affecting the reaction and the yield of alkyl esters, such as: the type and form of lipase, the type of alcohol, the presence of organic solvents, the content of water in the oil, temperature and the presence of glycerol are discussed. In order to estimate the prospects of lipase-catalyzed transesterification for industrial application, the factors which influence the kinetics of chemically-catalysed transesterification are also considered. The advantages of lipase-catalyzed transesterification compared to the chemically-catalysed reaction, are pointed out. The cost of down-processing and ecological problems are significantly reduced by applying lipases. It was also emphasized that lipase-catalysed transesterification should be greatly improved in order to make it commercially applicable. The further optimization of lipase-catalyzed transesterification should include studies on the development of new reactor systems with immobilized biocatalysts and the addition of alcohol in several portions, and the use of extra cellular lipases tolerant to organic solvents, intracellular lipases (i.e. whole microbial cells) and genetically-modified microorganisms ("intelligent" yeasts).
Modeling of simultaneous ultra filtration and diafiltration with real flux
Authors: Tokos Hela , Zavargo Zoltan , Djuric Mirjana
Published: July 2008

A mathematical model of diafiltration with variable volume is presented in this study. The characteristics of the process were examined, both with constant flux and variable flux. In the case of variable flux, the equations for the flux were taken from the literature, based on different theories. The time dependence of the macro solute concentration, the amount of out-wash liquid, the out-wash degree of the micro solute were studied. The results show that the accomplishment of a high concentration of macro solutes, required more time and out-wash liquid. In order to remove small amounts of micro solutes larger amounts of out-wash liquid must be used. For high degrees of out-washing, the velocity of the process increases and the amount of out-wash liquid decreases. It was observed that the rejection coefficient decreased with macro solute penetration through the membrane causing decrease of the process velocity.
Kinetics of convective drying of the sugar beet pulp
Authors: Jokic Aleksandar , Gyura Julianna , Zavargo Zoltan , Levic Ljubinko
Published: July 2008

Different authors have investigated hot air drying of sugar beet pulp, but no data on drying kinetics can be found in the literature. The aim of this study was to find suitable model for drying kinetics of sugar beet pulp. Of all models applied to drying curves, the best results were obtained for logarithmic equation. Also it was found that pressing of sugar beet pulp reduces time needed for drying by 10%, without any change in drying kinetics or any significant influence on coefficient of rehydration ratio.
The determination of furaldehyde and benzaldehyde in plum brandy
Authors: Rajkovic Milos , Peric Lazar
Published: July 2008

Among all alcohol liqueurs, brandies from drupaceous plants are characterized with the highest level of hydro cyanic acid, benzaldehyde and ethylcarbamate. In fruit brandies ethylcarbamate mainly originates from hydro cyanic acid during the processes of alcohol fermentation of crushed fruit and its preservation, distillation and ripening of the brandy. Hydro cyanic acid and benzaldehyde arise from the hydrolysis of amygdaline that is found exist in the heart of fruit stones and seeds, as well as from the hydrolysis of prunasine from the skin and flesh of drupaceous plants. The content of amygdaline and prunazine depends on the type of fruit, which corresponds to the potential content of hydro cyanic acid and benzaldehyde in the brandy that corresponds the stoichiometric ratio 1:3.94. The content of the aldehydes: furfural and benzaldehyde in plum brandy, strong plum brandy, young brandy, of domestic production in the various regions of Serbia were analyzed in this paper.
Technological and energetic improvement of a propylene distillation column
Authors: Ostrovski Nikolaj , Stamenkovic Predrag , Kenig Franja , Mauhar Sinisa , Barjaktarovic Branislava
Published: July 2008

A multicomponent distillation column for propylene purification was optimized in order to increase its energetic effectively. The ?-method coupled with the Soave-Redlich-Kwong equation of state for generating K-values and enthalpies was used. The optimal combination of pressure, temperature and reflux flow provided the decrease of steam consumption and loss of propylene with bottom flow.
Antifreeze life cycle assessment (LCA)
Authors: Kesic Jelena , Skala Dejan
Published: July 2008

Antifreeze based on ethylene glycol is a commonly used commercial product The classification of ethylene glycol as a toxic material increased the disposal costs for used antifreeze and life cycle assessment became a necessity. Life Cycle Assessment (LCA) considers the identification and quantification of raw materials and energy inputs and waste outputs during the whole life cycle of the analyzed product. The objectives of LCA are the evaluation of impacts on the environment and improvements of processes in order to reduce and/or eliminate waste. LCA is conducted through a mathematical model derived from mass and energy balances of all the processes included in the life cycle. In all energy processes the part of energy that can be transformed into some other kind of energy is called exergy. The concept of exergy considers the quality of different types of energy and the quality of different materials. It is also a connection between energy and mass transformations. The whole life cycle can be described by the value of the total loss of exergy. The physical meaning of this value is the loss of material and energy that can be used. The results of LCA are very useful for the analyzed products and processes and for the determined conditions under which the analysis was conducted. The results of this study indicate that recycling is the most satisfactory solution for the treatment of used antifreeze regarding material and energy consumption but the re-use of antifreeze should not be neglected as a solution.
Separation processes, I: Azeotropic rectification
Authors: Milojevic Svetomir
Published: July 2008

In a series of two articles, the problems of azeotrope separation (part I) and the design of separation units (part II) were analyzed. The basic definition and equations of vapour-liquid equilibria for ideal and non-ideal systems, the importance of the activity coefficient calculation necessary for the analysis of non-ideal equilibrium systems, as well as theoretical aspects of azeotrope rectification and the determination of the optimal third component (modifier or azeotrope agent) are presented in the first part.
Trends in making offset printing forms
Authors: Zivkovic Predrag , Jovanovic Slobodan
Published: July 2008

This paper presents new technologies for making offset printing plates, new materials for inplate manuifacturing and new screening technologies.
Pulp moulding machines for the production of packing paper elements
Authors: Lukic Ljubomir , Krgovic Milorad , Jarakovic Ilija
Published: July 2008

Paper pulp molds are now commonly applied in the technology of modern packing for a wide range of products. The technological process of producing the paper molds has three basic phases: paper pulp preparation, in which water and waste paper are the basic raw materials, the formation of product in tool pulp moulding machines and process drying. The firm "SERVOTEH" from Belgrade has developed various pulp moulding machines for different operating conditions (manual, semiautomatic and automatic operation), different manufacturing capacities and an alternative number of tools. The system of "SERVOTEH" pulp moulding machines covers several construction solutions: a sinking system, veer system and rotation system. This paper presents the technological process, as well as the integral and concept approach to the design of pulp moulding machines and system tools.
Soft roll linings - better conduits: First press of the PS 2, paper machine, Belisce, Croatia
Authors: Dolenc Iztok
Published: July 2008

Paper with demanding technical properties is formed in the press of the paper machine when the paper pulp is passed between the rolls. In order to form paper in the appropriate manner, an elastic lining with particular stiffness is spread over the rolls. In this study a practical example of how softer linings generally give better results concerning the percentage of the dry part and the paper structure is presented. From the rubber roll manufacturers' point of view, the weak side of soft linings lies in greater deformations, which present difficulties in obtaining good adhesion between the lining and metal core of the roll. Only the best manufacturers in the industry can match such high demands.
Thermoradial drying of paper coatings
Authors: Valent Vladimir
Published: July 2008

The thermoradial drying of material (paper) was discussed. The basic and most important parameters of the process of industrial drying were defined. Thermoradial drying provides a relatively large heat flux to the wetted material. It shortens the time of drying and is advantageous for drying liquid coatings on the surface of the paper. The technical solution of the iradiation method must be defined taking into account the structural absorptive and optical characteristics of the formed solid phase of the coating.
Materials processing using supercritical fluids
Authors: Orlovic Aleksandar , Skala Dejan
Published: July 2008

One of the most interesting areas of supercritical fluids applications is the processing of novel materials. These new materials are designed to meet specific requirements and to make possible new applications in Pharmaceuticals design, heterogeneous catalysis, micro- and nano-particles with unique structures, special insulating materials, super capacitors and other special technical materials. Two distinct possibilities to apply supercritical fluids in processing of materials: synthesis of materials in supercritical fluid environment and/or further processing of already obtained materials with the help of supercritical fluids. By adjusting synthesis parameters the properties of supercritical fluids can be significantly altered which further results in the materials with different structures. Unique materials can be also obtained by conducting synthesis in quite specific environments like reversed micelles. This paper is mainly devoted to processing of previously synthesized materials which are further processed using supercritical fluids. Several new methods have been developed to produce micro- and nano-particles with the use of supercritical fluids. The following methods: rapid expansion of supercritical solutions (RESS) supercritical anti-solvent (SAS), materials synthesis under supercritical conditions and encapsulation and coating using supercritical fluids were recently developed.
Microwaves in organic chemistry and organic chemical
Authors: Mijin Dusan , Petrovic Slobodan
Published: July 2008

The usual way of applying heat to a chemical reaction is the use of a Bunsen burner, an oil or some other type of bath, or an electric heater. In inorganic chemistry, microwave technology has been used since the late 1970s while it has been implemented in organic chemistry since the mid-1980s. Microwave heating has been used in the food industry for almost fifty years. The shorter reaction times and expanded reaction range that is offered by microwave technology are suited to the increased demands in industry. For example, there is a requirement in the pharmaceutical industry for a higher number of a novel chemical entities to be produced, which requires chemists to employ a number of resources to reduce time for the production of compounds. Also, microwaves are used in the food industry, as well as in the pyrolysis of waste materials, sample preparation, the solvent extraction of natural products and the hydrolysis of proteins and peptides.
UV protection of cotton: The influence of weaving structure
Authors: Grancaric Ana , Penava Zeljko , Tarbuk Anita
Published: July 2008

Due to the depletion of the ozone layer, shorter but high energy UV-B rays and longer energy UV-A rays causing known skin aging and recently the formation of skin malignant neoplasm are reaching the surface of earth. The paper deals with the influence of different fabric construction on ultraviolet skin protection expressed as the ultraviolet protection factor (UPF). It is well known that clothing provides some protection against damage by ultraviolet radiation, but it highly depends on fabric construction, especially for longer exposure to sun light. Fabric openness or porosity is a key parameter influencing ultraviolet (UV-R) transmission. The effect of fabric density and cover factor using twelve woven fabrics from the same cotton fibres and yarn count, but different in type of weaving and fabric density were investigated. UPF and UV-A and UV-B transmission were measured using a transmission spectrophotometer Gary 50 Solarscreen (Varian) according to the AATCC Test Method 183-2000.
The impact of lactic acid bacteria on sourdough fermentation
Authors: Savic Dragisa , Jokovic Natasa
Published: July 2008

The baking of sourdough breads represents one of the oldest biotechnological processes. Despite traditionality, sourdough bread has great potential because of its benefits. Sourdough is a mixture of flour and water that is dominated by a complex microflora composed of yeasts and lactic acid bacteria that are crucial in the preparation of bread dough. Lactic acid bacteria cause acidification by producing lactic acid that increases the shelf life of bread by preventing the growth of undesirable microorganisms and affects the nutritional value of bread by increasing the availability of minerals. In addition to these advantages, the use of sourdough fermentation also improves dough machinability, breadcrumb structure and the characteristic flavour of bread. Lactic acid bacteria in sourdough fermentation are well known representing both homofermentative and heterofermentative bacteria. They may originate from selected natural contaminants in the flour or from a starter culture containing one or more known species of lactic acid bacteria. Sourdough can be cultivated in bakeries or obtained from commercial suppliers. However, many bakeries in Europe still use spontaneously fermented sourdoughs, which have been kept metabolically active for decades by the addition of flour and water at regular intervals. The impact of lactic acid bacteria on sourdough fermentation and their influence on dough and bread quality was discussed on the basis of research and literature data.
Kinetics of the extraction of pumpkin seed oil (Cucurbita pepo L) by supercritical CO2
Authors: Sovilj Milan , Barjaktarovic Branislava
Published: July 2008

This paper deals with the supercritical carbon dioxide extraction of pumpkin seed oil (Cucurbita pepo L). Supercritical fluid extraction (SFE) has been used to obtain total lipid extracts from other oilseeds, and it has also proved successful in the isolation and enrichment of sterols from oilseeds. The SFE of pumpkin seed oil on a laboratory scale was investigated in thus paper, with special interest in the influence of the extraction pressure on the overall yield of pumpkin seed oil. Extractions were carried out at the pressures of 15, 25 and 30 MPa and at 313 K, and at a pressure of 30 MPa and the temperatures 313, 323, and 333 K. The yield of the extractions conducted at 15 MPa was rather low, 0.1814 g oil per 1g of seed feed (18.4%) for an extraction time of 14 h. However, extractions at higher pressures yielded greater quantities of the oil; at 22.5 MPa for 9 h, 36.3% of the oil and at 30 MPa for 6 h, 41.0% of the oil. For comparison, hexane extraction of the seed material yielded less than 40% of the oil. Temperature did not influence the extraction yield. At a pressure of 30 MPa, the color of the fractions yielded during successive extraction time intervals varied greatly, from pail yellow (the first 2 h), through orange-yellow (from 2-4 h) to red (after 4 h). The experimental results of the oil yields were compared with the data obtained by the mathematical model of Hong et al., presented in the literature.
Amtimicrobial activity of essential oil of Melissa officinalis L, Lamiaceae
Authors: Anicic Nada , Dimitrijevic Suzana , Ristic Mihailo , Petrovic Slobodan , Petrovic Slobodan
Published: July 2008

The antimicrobial activity of the essential oil of Melissa officinalis was investigated in this paper. The essential oil was obtained by the principle of water and steam and analyzed by GC and GC-MS using FID and MSD. The main components of the oil of Melissa officinalis were geranial (17.30%), neral (14.70%) and citronellal (10.70%). The antimicrobial properties were tested against the following bacterial species: B subtilis, B.cereus Bifidobacterium sp., Corynobacterium sp., E. coli, Klebsiella sp., L. acidophilus, L. fermentum, L. plantarum, L. rhamnosus, Listeria monocytogenes, P. vulgaris, P. aerugenosa, S. enteritidis, Shigella sp., S. aureus, and fungi Candida albicans, Alternarija sp. and Aspergillus niger. The diffusion technique was used for testing: the antimicrobial activity, and the MIC was determined by the broth dilution method. The essential oil of M. officinalis showed high antimicrobial activity.
Antimicrobial activity of kombucha made from Rtanj tea
Authors: Cvetkovic Dragoljub , Markov Sinisa , Velicanski Aleksandra
Published: July 2008

Kombucha is a beverage with special therapeutic properties produced by the metabolic activity of yeasts and acetic acid bacteria in sweetened black tea (traditional cultivation medium). The antimicrobial activity of kombucha (for consumption) made from black tea and Rtanj tea, as well as particular control samples, was examined by the modified disc diffusion method. Salmonella enteritidis, Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa Staphylococcus aureus, Bacillus sp., Sarcina lutea, Penicillium aurantiogriseum, Aspergilus niger, Aspergilus flavus, Rhodotorula sp. Candida pseudotropi-calis and Saccharomyces cerevisae have been used as test organisms. Acetic acid and kombucha samples show significant antimicrobial activity against all bacteria except Sarcina lutea. The other control samples (neutralized kombucha, tea and a "model sistem") show less bacteriostatic activity. Kombucha and acetic acid solution show borderline inhibitory activity against some moulds, while was no activity against yeasts.
Determination of total lipids and characterization of marigold flower extracts (Calendula officinalis)
Authors: Novkovic Vesna , Stoiljkovic Zora , Stankovic Mihajlo
Published: July 2008

Bioactive extracts from marigold flower are important ingredients for parapharmaceutical and cosmetic preparations. Their antiflogistic holeretic.antimicrobic, antidermatic and anticancer effects are due to the presence of flavonoids, carotenoids, etheric oils, and terpenoids. This study presents the results of spectrophotometric investigation for the overall carotene content calculated as (3-caroten (442 nm), visual and physico-chemical characteristics according to Ph.Jug. V in oil extracts of marigold flower obtained by maceration (room temperature and 70?C) and percolation (room temperature) with olive oil and sunflower oil by original procedures.The largest content of (3-carotene (57.5 mg/kg of oil extracts) is in the oil extract obtained by maceration for 72 hours with olive oil (solvomodulus 1:5 m/m) at room temperature.
Influence of microwaves on the rate of the distillation and yield of etheric oil from the wooded greenery of conifers
Authors: Marjanovic-Balaban Zeljka , Miletic Predrag
Published: July 2008

It is known that many plants represent valuable raw materials for technological processing and that there has been an increase in the use of medicinal, aromatic and spice plants as raw materials in industry. Our research was directed toward studying the rate of the distillation and yield of etheric oils from the wooded greenery of conifers (fir, spruce, pine juniper and Douglas fir) by using a new procedure. These conifers represent an important raw material basis in this area, which could be used for the industrial production of etheric oil for the pharmaceutical, cosmetic and food industry. Before distillation, the samples were treated with microwaves under laboratory conditions, and the influence of microwaves on the duration of the distillation and yield of etheric oil compared to steam distillation was analyzed. The results showed that less time was required to achieve the same yield during the distillation, if the samples were treated with microwaves, which can be a significant economic factor in the production of this etheric oil.
Characteristics of heat flow in recuperative heat exchangers
Authors: Lalovic Milisav , Radovic Zarko , Jaukovic Nada
Published: July 2008

A simplified model of heat flow in cross-flow tube recuperative heat exchangers (recuperators) was presented in this paper. One of the purposes of this investigation was to analyze changes in the values of some parameters of heat transfer in recuperators during combustion air preheating. The logarithmic mean temperature (Atm) and overall heat transfer coefficient (U), are two basic parameters of heat flow, while the total heated area surface (A) is assumed to be constant. The results, presented as graphs and in the form of mathematical expressions, were obtained by analytical methods and using experimental data. The conditions of gaseous fuel combustions were defined by the heat value of gaseous fuel Qd = 9263.894 J.m-3, excess air ratio ?= 1.10, content of oxygen in combustion air ?(O2) = 26%Vol, the preheating temperature of combustion air (cold fluid outlet temperature) tco = 100-500?C, the inlet temperature of combustion products (hot fluid inlet temperature) thi = 600-1100?C.
Geothermal heat exchanger with coaxial flow of fluids
Authors: Pejic Dragan , Stojiljkovic Dragan , Stojiljkovic Stanisa , Djurovic-Petrovic Maja , Mitic Nebojsa
Published: July 2008

The paper deals with a heat exchanger with coaxial flow. Two coaxial pipes of the secondary part were placed directly into a geothermal boring in such a way that geothermal water flows around the outer pipe. Starting from the energy balance of the exchanger formed in this way and the assumption of a study-state operating regime, a mathematical model was formulated. On the basis of the model, the secondary circle output temperature was determined as a function of the exchanger geometry, the coefficient of heat passing through the heat exchange areas, the average mass isobaric specific heats of fluid and mass flows. The input temperature of the exchanger secondary circle and the temperature of the geothermal water at the exit of the boring were taken as known values. Also, an analysis of changes in certain factors influencing the secondary water temperature was carried out. The parameters (flow temperature) of the deep boring B-4 in Sijarinska Spa, Serbia were used. The theoretical results obtained indicate the great potential of this boring and the possible application of such an exchanger.
Packaging based on polymeric materials
Authors: Jovanovic Slobodan , Zivkovic Predrag , Stoiljkovic Dragoslav
Published: July 2008

In the past two years the consumption of common in the developed countries world wide (high tonnage) polymers for packaging has approached a value of 50 wt.%. In the same period more than 50% of the packaging units on the world market were made of polymeric materials despite the fact that polymeric materials present 17 wt.% of all packaging materials. The basic properties of polymeric materials and their environmental and economical advantages, providing them such a position among packaging materials, are presented in this article. Recycling methods, as well as the development trends of polymeric packaging materials are also presented.
Initiation of MMA polymerization by iniferters based on dithiocarbamates
Authors: Jovanovic Slobodan , Nastasovic Aleksandra , Dzunuzovic Enis , Jeremic Katarina
Published: July 2008

Twelve modified dithiocarbamates and a thiuramdisulfide used for the initiation of methyl methacrylate (MMA) polymerization were synthesized in this study. The polymerization of MMA was followed by determine the yield and molar mass of the obtained PMMA as a function of polymerization time. Four of the synthesized dithiocarbamates S-benzyl-N,N-dibenzyldithiocarbamate, S-allyl-N,N-dibenzyldithiocarbamate S-benzyl-N,N-diisobutyldithiocarbamate and S-benzoyl-N,N-diisobutyldithiocarbamate, as well as N,N,N',N'-tetrabenzylthiuramdisulfide acted as iniferters. They were active as the initiators of the photo and/or thermally initiated radical polymerization of MMA in bulk and inert solvents (benzene and toluene). S Benzyl - N,N - dibenzyldithiocarbamate can be successfully used for the initiation of MMA polymerization in a polar solvent such as dimethylacetamide.
Corrosion behavior of duplex polyaniline/epoxy coating on mild steel in 3% NaCl
Authors: Gvozdenovic Milica , Grgur Branimir , Kacarevic-Popovic Zorica , Miskovic-Stankovic Vesna
Published: July 2008

The corrosion behavior and thermal stability of epoxy coatings electrodeposited on mild steel and on mild steel with electrochemically deposited polyaniline (PANI) film were investigated by electrochemical impedance spectroscopy (EIS) and thermo gravimetric analysis (TGA). The aim of the paper was to present new findings on the corrosion protection of mild steel by a duplex PANI/-epoxy coating in 3% NaCI solution and to determine the effect of thin PANI film on the protective properties of the coating. PANI film was deposited electrochemically on mild steel from an aqueous solution of 0.5 mol dm"3 sodium benzoate and 0.1 mol dm"3 aniline at a constant current density of 1.5 mA cm"2. Non-pigmented epoxy coatings on mild steel and on mild steel with PANI film were obtained by cathodic electrode position at constant voltage and stirring conditions. The resin concentration in the electrode position bath was 10 wt.% solid dispersion in water at pH 5.7. The applied voltage was 250 V, the temperature 26?C and the deposition time 3 min. It was shown that thin PANI film could be used to modify the surface of mild steel prior to epoxy coating deposition, due to the increased corrosion protection of a duplex PANI/epoxy coating comparing to an epoxy coating on mild steel in 3% NaCl solution.
Studies of chemical interactions between chlorosulphonated polyethylene and nit rile rubber
Authors: Markovic Gordana , Marinovic-Cincovic Milena , Radovanovic Blaga , Budinski-Simendic Jaroslava
Published: July 2008

Highly polar rubbers interact with each other through their active functional groups via condensation or substitution reactions at high temperature. Chlorosulphonated polyethylene (CSM) rubber is a highly reactive rubber, the reactivity of with is due to the -SO2CI groups. When CSM reacts with nit rile rubber (NBR), a chemical reaction takes place between the two rubbers at high temperature. Fourier transform infrared (FTIR) studies support that CSM/NBR (50/50 w/w) isothermally induces a self cross-linking blend, when cross-linking takes place via the acrylonitrile groups of NBR and the SO2CI groups or the insitu generated allyl chloride moieties of CSM. There is a loss of some -CN groups during cross-linking. This may be due to an attack on the -CN groups by HCI (produced during the heating of CSM) in the presence of inherent moisture in the polymers. Amid type of linkage is formed due to cross-linking.
The cross linking of EPDM and NBR rubber
Authors: Samardzija-Jovanovic Suzana , Jovanovic Vojislav
Published: July 2008

In the process of macromolecule cross linking, the choice of type and quantity of the components and the experimental conditions are important to obtain the new cross linked materials with better mechanical and chemical characteristics. The cross linking method depends on the rubber type and structure. Intermolecular cross linking results in the formation elastomer network. The basis of the cross linking process, between ethylene propylene diene rubber (EPDM) and acrylonitrile butadiene rubber (NBR), is a chemical reaction. Fillers and other additives are present in different mass ratios in the material. The exploitation properties of the cross linked materials depend on the quantity of additive in the cross linked systems.
Photo degradation of synthetic dyes under visible and solar light
Authors: Mijin Dusan
Published: July 2008

The photo degradation of synthetic dyes under visible and solar light as a method for the removal of synthetic dyes from water and wastewater was reviewed. The mechanisms of photo degradation are presented. The influence of catalysts, inorganic ions and other substances on photo degradation was discussed.
Effect of solid paraffin's on crude oil rheology
Authors: Secerov-Sokolovic Radmila , Bjelovic Zoran , Sokolovic Srdjan
Published: July 2008

Effect of solid paraffin on crude oil rheology was investigated. The experiments were carried out on model-crude oil at constant temperature 30?C. Medical paraffin malting point of 61 ?C different concentration was dissolved in kerosene fraction. Concentration range of paraffin was from 1 to 32% weight. Shear stress strongly depends on paraffin's content only over high shear rate. Shear stress increases exponentially with increasing paraffin concentration for high shear rate. This dependence does not existed for real crude oil investigated in this paper.
The sorption of lead, cadmium and strontium from aqueous solutions on sepiolite
Authors: Lazarevic Slavica , Jankovic-Castvan Ivona , Ilic Miloje , Jovanovic Dusan , Janackovic Djordje , Petrovic Rada
Published: July 2008

The results of the characterization and the sorption properties of sepiolite from the locality Slovici are presented in this paper. X-Ray diffraction analysis, infrared spectroscopy and differential thermal analysis revealed sepiolite as the main phase and small amounts of magnesite as an impurity. The specific surface area of sepiolite, determined by nitrogen adsorption and by applying the BET equation was found to be 339 m2/g. The point of zero charge was determined by the batch equilibration method, under different conditions, and the shift in the point of zero charge, in the presence of Pb2+, Cd2+ and Sr2+ ions, was investigated. It was determined that the point of zero charge changed with modification of the solid/liquid ratio and by washing the powder, which indicated that under the investigated conditions some dissolution of the sepiolite and impurities took place also influencing the position of the point of zero charge. In the presence of Pb2+, Cd2+ and Sr2"1" ions, the point of zero charge was shifted toward lower pH values denoting specific ion sorption. The greatest shift and, therefore the largest specific sorption, appeared in the case of Pb2+ ions, somewhat less with Cd2+, and the least with Sr2"1" ions. The adsorption isotherms were determined for the Pb2+, Cd2+ and Sr2+ ions, as well as the amounts of these ions that were removed from aqueous media by the ion exchange of Mg2+ ions from the sepiolite structure, depending on the equilibrium ion concentrations. In the case of ion exchange, as in the case of specific sorption, the affinity of sepiolite for the investigated ions can be presented in the following order Pb2+ > Cd2+ > Sr2"1". For the removal of Sr2"1" ions from aqueous media by sepiolite, a third mechanism is important probably, the ion exchange of exchangeable ions from the sepiolite structure channels. As the result of the action of all the sorption mechanisms sepiolite is removes mostly Pb2+ ions, then Cd2+ and least of all Sr2"1" ions from the aqueous media.
Hydrolysis of tanned leather wastes under alkaline, acidic and oxidative conditions
Authors: Botic Tatjana , Iliskovic Nadezda
Published: July 2008

Different wastes in large quantities are the outcome or the by-product of processes in the tanning industry. The largest part of solid wastes is collagen based and obtained in the reprocessing steps of tanned and non-tanned products. The quality collagen substance obtained from wastes of the leather industry used as a supporting material in many reprocessing industries. Hydrolysis is the basic step of collagen processing, namely the shortening of its polypeptide chain. The main goal of this investigation was to examine the influence of the following parameters on the extent of collagen hydrolysis: type and quantity of reagent used for hydrolysis temperature of hydrolysis, pH, duration of hydrolysis as well as the dimensions of the "shavings" samples. The change of molar mass during hydrolysis was monitored by UV-spectroscopy. Special attention was paid to the dechroming process of the collagen hydrolysate.
Influence of accompanying substances of hemp fibres on their electric resistance
Authors: Pejic Biljana , Asanovic Koviljka , Kostic Mirjana , Skundric Petar , Mihajlidi Tatjana
Published: July 2008

Hemp fibres belong to the group of natural, cellulose bast fibres. These fibres have exceptional properties such as: antimicrobial effect, absence of allergy effect, extraordinary sorption properties, good electro-physical properties (small static electricity in regard to other cellulose fibres) as well as high values of breaking strength (the natural fibre with the highest strength). However, hemp fibres have some defects: heterogeneous chemical composition, large quantity of accompanying substances (lignin pectins, waxes) and unsatisfactory fineness and eveness. It is possible to a great extent to eliminate or reduce, the defects of hemp fibres by of appropriate modification treatments. In order to determine the appropriate modification treatment of hemp fibres, the dependences between the chemical composition, fineness and electric resistance of hemp fibres were presented in this paper. In the experimental part of the paper, by the application of a procedure for the determination of the chemical composition, the accompanying supstances of hemp fibres were gradually removed. After each phase some fibrous substrates were separated. After that the fineness and electric resistance were determined. This experiment was conducted in order to define the influence of each component of hemp fibres on the fineness and electric resistance. In this paper, hemp fibres were modified by an aqueous solution of sodium hydroxide, under different conditions of modification. The influence of modification conditions on the fineness and electric resistance were studied.
The usage of optical fibers for damage detection in ballistic protection composite laminates
Authors: Zivkovic Irena , Kojovic Aleksandar , Tomic Milos , Brajovic Ljiljana , Aleksic Radoslav
Published: July 2008

This paper describes the procedure of embedding fiber optic sensors in laminar thermoplastic composite material, as well as damage investigation after ballistic loading. Thermoplastic-reinforced composite materials were made for increased material damage resistance during ballistic loading. Damage inside the composite material was detected by observing the intensity drop of the light signal transmitted through the optical fibers. Experimental testing was carried out in order to observe and analyze the response of the material under various load conditions. Different types of Kevlar reinforced composite materials (thermoplastic, thermo reactive and thermoplastic with ceramic plate as the impact face) were made. Material damage resistance during ballistic loading was investigated and compared. Specimens were tested under multiple load conditions. The opto-electronic part of the measurement system consists of two light-emitting diodes as light sources for the optical fibers, and two photo detectors for the light intensity measurement. The output signal was acquired from photo detectors by means of a data acquisition board and personal computer. The measurements showed an intensity drop of the transmitted light signal as a result of the applied loading on composite structure for all the optical fibers. All the diagrams show similar behavior of the light signal intensity. In fact, all of them may be divided into three zones: the zone of penetration of the first composite layer, the bullet traveling zone through the composite material till its final stop, and the material relaxation zone. The attenuation of the light signal intensity during impact is caused by the influence of the applied dynamic stress on the embedded optical fibers. The applied stress caused micro bending of the optical fiber, changes in the shape of the cross-section and the unequal changes of the indices of refraction of the core and cladding due to the stress-optic effect. The main goal of the experiment was to develop a system for thermoplastic composite structure health monitoring during real life exploitation. The results of the experiments confirmed that optical fibers could be applied as intensity sensors in the real-time monitoring of structural changes in thermoplastic laminar composite materials under ballistic loading. The light signal intensity drops in an optical fiber in response to the applied loading on the composite material.
Chemical engineering and chemistry: education in a changing world
Authors: Reijenga Jetse
Published: July 2008

Current trends in science and engineering research are analyzed, together with an inventory of changes in the field of employment and practice in industry. The resulting demands on the university education of chemists and chemical engineers have been translated into a more or less continuous updating of the curriculum at the Department of Chemical Engineering and Chemistry of the Eindhoven University of Technology in the Netherlands. In general it can be said that the emphasis within education will have to shift from the knowledge of facts, towards the ability to apply this knowledge to the process of solving problems in a realistic setting. Two topics will be highlighted. Multidisciplinary project group work was successfully introduced to enable students to apply theoretical knowledge to real life situations in a professional (industrial) context, resulting among others in a sharper focus on communication skills. On the other hand, knowledge of theory and experimental practice are combined and augmented by the increased use of experiment simulations for illustration, demonstration and experimentation purposes. Here, the increased use of information technology facilities and skills is essential.
The use of image analysis for the interaction of 1,3,5-trisubstituted isocyanurates with oxidizer and different binders in composite materials
Authors: Dostanic Jasmina , Barbu Mihela , Jancic-Heinemann Radmila , Volkov-Husovic Tatjana , Uscumlic Gordana , Mljin Dusan
Published: July 2008

Composite propellants are non-homogenous propellants and comprise primarily crystalline oxidizer and metal fuels uniformly suspended in a resin binder. The strength of the bonds between the polymer matrix and the oxidizer determine the mechanical properties of composite propellants. In order to achieve good mechanical properties of the fuel, bonding agents are added to the mixture. The role of the bonding agents is to enable good interactions (interphase) between the polymer matrix and the oxidizer grains. The level of interconnection between the phases could be measured by using the surface obtained by cutting the composite material and observing the resulting surface. A problem in the visualization of such a material is to enable the visibility of the polymer matrix and the grains in the image as both phases are white. There are two possible ways to overcome this problem: to add a pigment into the matrix polymer and to color the matrix and make it different from the grain color. Another possibility is to find a solvent for one of the phases and to dissolve one of the phases in an appropriate solvent so that the remaining phase could be stained, photographed and analyzed using the image analysis program. The morphological characteristics of the image could be established and analyzed. The topic of this study was to establish the conditions of preparation of composite propellants containing ammonium per chlorate and HMX and RDX as oxidizers, and polymer of the polybutadiene type and 1,3,5-trisubstituted isocyanurates as bonding agents. The bonding phenomenon was investigated by optical microscopy. The established procedure of preparation will enable the visualization of the composite structure and the morphological characteristics of the surface will be obtained. From the morphological properties of the obtained composite, it will be possible to select a suitable polymer for the preparation of uniformly distributed composite propellant.
On the asymptotic stability of linear discrete time-delay systems: The Lyapunov approach
Authors: Stojanovic Sreten , Debeljkovic Dragutin , Mladenovic Ilija
Published: July 2008

New conditions for the stability of discrete delay systems of the form x (k+1) = Arjx (k) + Aix (k-h) are presented in the paper. These new delay-independent conditions were derived using an approach based on the second Lyapunov's method. These results are less conservative than some in the existing literature. A numerical example was worked out to show the applicability of the derived results.
Robust stability of linear perturbed discrete systems with multiple time-delay
Authors: Stojanovic Sreten , Debeljkovic Dragutin , Mladenovic Ilija
Published: July 2008

The paper presents some new sufficient conditions, independent of delay, for the asymptotic stability of a particular class of linear perturbed time-delay systems with multiple delays. The proposed criteria introduce a smaller number of assumptions and are expressed in more natural and simpler mathematical forms. Numerical results are presented to support and illustrate the derived results.
The determination of hyperoside in the flower and leaf of hawthorn (Crataegus oxycantha and Crataegus monogyna) by the spectrophotometric method
Authors: Mihajlovic Dusanka , Novkovic Vesna , Bankovic Vladimir
Published: July 2008

The flower and leaf of hawthorn contains many active components, used in the production of pharmaceutical preparations for cardiotonic, anti-hypertonic anti-hypotonic, artherosclerotic, anti-arithmic and anti-anemic groups. According to the ROTTE list (1996), 159 of 1800 pharmaceutical preparations contain components from hawthorn. Due to the remedial action of hyperoside and other flavonoids from hawthorn, their determination is important for the standardization of extract and preparation quality. The extraction of the flavonoids from a mixture of hawthorn (C. oxycantha and C. monogyna) flower and leaf was carried out by percolation with 40% and 70% (v/v) ethanol. In order to determine the content of total flavonoids calculated as hyperoside spectrophotometric method with aluminium(lll) chloride as a colour reagent at 425 nm was applied. The total flavonoid content in the herbal material mixture was 0.483%, in 40% and 70% (v/v) ethanolic liquid extract it was 138 mg/100 cm3 and 157 mg/100 cm, respectively. The extraction degree of total flavonoids with 40% and 70% (v/v) ethanolic solutions was 57.14% and 65.01% respectively. The yield of total flavonoids in the dry extract was 63% in regard to the herbal mixure content.