The method for determing the efficiency of the impressed current system of cathodic protection of the vessels from the corrosion

Korozija podvodnog dela trupa broda je jedan od izuzetno važnih problema u brodogradnji. Pored osnovnog načina zaštite dobijenog organskim premazima, postoji tendencija primene aktivne katodne zaštite pomoću spoljašnjeg izvora jednosmerne struje. Time se obezbeđuje znatno veći stepen zaštite čelika od korozije. U radu su navedeni faktori koji utiču na koroziju kao i njihovo međusobno dejstvo. Predstavljena je električne shema dvojnog električnog sloja i polarizacionih krivih, pri koroziji metala u morskoj i rečnoj vodi. Izvršeno je matematičko modelovanje anode, čelika koji se štiti, kao i sredine u kojoj se obavlja korozija. Prikazani su rezultati merenja oštećenja na brodu usled korozije a koji je proveo preko 20 godina u eksploataciji. Dati su osnovni podaci o sistemu aktivne katodne zaštite. Data su analitička rešenja nekih dvodimenzionalnih i trodimenzionalnih rešenja za idealizovane slučajeve. Prikazan je numerički metod za rešavanje eliptičkih parcijalnih diferencijalnih jednačina koji se koristi za računanje potencijalnog polja oko trupa broda, kao i numerički dobijeni rezultati raspodele potencijala na trupu broda sa jednom, ili obe elektrode. Navedeni su rezultati merenja zaštitnog potencijala na brodu dizalici koji se nalazi u bazenu brodogradilišta "Beograd". Prikazani su rezultati merenja prirodnog potencijala korozije, brzine porasta kao i pada zaštitnog potencijala. Na kraju je data mreža mernih tačaka sa izmerenim potencijalom trupa broda u ustaljenom stanju. Izvršeno je poređenje numeričkih i analitičkih rešenja sa eksperimentalno dobijenim podacima. Istaknut je praktičan značaj primene rezultata istraživanja datih u ovoj disertaciji. Posebno treba istaći činjenicu da je eksperiment izveden na realnom objektu i da su pri tome rešeni gotovo svi praktični problemi prilikom ugradnje i primene ovog sistema zaštite od korozije. Treba istaći anode i okoloanodne ekrane, referentne elektrode, ispravljače za ovu namenu, kablovske prolaze i drugo. Na osnovu ovog rada stvorena je podloga da se ovaj sistem može ugrađivati na realnim objektima i praktično koristiti.The corrosion of the underwater part of the ship hull is one of the very important problems in shipbuilding. Beside the elementary way of protection, made by the organic paint, there is a tendency of applying the impressed current system (active cathodic protection) with help of exterior source of the direct current. There is a way to achieve the higher degree of protecting the steel from the corrosion. The factors that have an influence to the corrosion and their mutual action are presented in this paper. It is also presented an electric scheme of double electric layer an polar curve, by corrosion of the metal in sea and river water. It is made the mathematic model of the anode, the protecting steel and of the water. This paper includes also, the results of measuring the damages on the ship, which is more than 20 years in exploitation, caused by the corrosion. There are also given the elementary data about the impressed current system of cathodic protection. The analytical solutions of some two dimensional or three dimensional solutions for ideal cases are also presented. It is shown the numerical method for elliptical partial differential equations, which serves for calculating the potential field around the ship hull. The numerically received results of the potential distribution on the ship hill with one or both electrodes is also given. There are quoted also the results of measuring the protecting potential on the ship, located in the Shipyard "Beograd". The results of measuring the natural potential of the corrosion, the changing of the protecting potential are presented. It is shown the screen of the measuring potential of the ship hull in steady condition. The numerical and analytical solutions with experimentally received data are compared. It is emphasized the practical importance of the use of researching results, that are presented in this dissertation. The experiment is done on the real object and that way, almost all practical problems about the application of this system are solved. There are anodes, dielectric shield, reference electrode, rectifier for this use, cable coffer dam, etc. This paper shows that, based on the facts that are presented, this system could be built-in on the real objects and it could be practically used

Fast Fourier Transform IR Characterization of Epoxy GY Systems Crosslinked with Aliphatic and Cycloaliphatic EH Polyamine Adducts

The use of fast FT-IR spectroscopy as a sensitive method to estimate a change of the crosslinking kinetics of epoxy resin with polyamine adducts is described in this study. A new epoxy formulation based on the use of polyamine adducts as the hardeners was analyzed. Crosslinking reactions of the different stoichiometric mixtures of the unmodified GY250 epoxy resin with the aliphatic EH606 and the cycloaliphatic EH637 polyamine adducts were studied using mid FT-IR spectroscopic techniques. As the crosslinking proceeded, the primary amine groups in polyamine adduct are converted to secondary and the tertiary amines. The decrease in the IR band intensity of epoxy groups at about 915 cm(-1), as well as at about 3,056 cm(-1), was observed due to process. Mid IR spectral analysis was used to calculate the content of the epoxy groups as a function of crosslinking time and the crosslinking degree of resin. The amount of all the epoxy species was estimated from IR spectra to changes during the crosslinking kinetics of epichlorhydrin

Formiranje cena prirodnog gasa za velike industrijske potrošače u Srbiji prema standardima evropske unije

Natural gas is a primary energy resource with the indicated highest annual growth of global demand and consumption in all recent forecasts. The chemical industry is a leading non-seasonal consumer of natural gas, mainly because it utilizes natural gas both for energy and as a feedstock. Specifically, these major and established gas consumers in chemical industry enjoy worldwide a recognized status of "privileged clients" of gas industry and as such have been granted the most favorable commercial terms. Unfortunately, that is not the case in Serbia. This paper emphasizes the economic logic and rationale of demands of major industrial users regarding harmonization of gas prices with EU standards.Prirodni gas je konvencionalni primarni energent sa projektovanim najdinamičnijim globalnim rastom potrošnje. Vrlo veliki i kontinualni industrijski potrošači prirodnog gasa, a posebno oni iz oblasti bazne hemijske industrije koji gas troše i kao energent i kao sirovinu, svuda u svetu su klijenti kojima industrija gasa posvećuje posebnu pažnju i obezbeđuje najpovoljniji komercijalni status. Nažalost, samo u Srbiji nije taj slučaj. Ovaj rad pokušava da još jednom naglasi ekonomsku logiku opravdanih zahteva vrlo velikih potrošača u srpskoj industriji za harmonizacijom cena prirodnog gasa saglasno standardima EU

Arterijska vaskularizacija mozga malog zelenog majmuna, Cercopithecus aethiops sabeus

Cell cultures from the small green monkey are used for the cultivation of poliovirus in the manufacture of vaccines against poliomyelitis. In addition kidney cultures from the same monkey serve for detection of the virus in biological material. This was the main reason that prompted us to undertake a study of one part of the monkey’s cardiosvascular system and thus contribute to a better understanding of the structure of its body.Glavni krvni sudovi koji dovode arterijsku krv u mozak su A.carotis interna i A. vertebralis. Spajanjem leve i desne kičmene arterije (A. vertebralis sinistra et dextra) nastaje A. basilaris cerebri. A. carotis interna sinistra et dextra pružaju se kroz parafaringealni prostor prema lobanjskoj duplji, u koju ulaze pošto prođu kroz karotidne kanale (canales carotici) piramide slepoočne kosti u kavernozni sinus u kome se povezuju obe Aa. carotides preko A. intercarotica caudalis. Grane A. carotis internae su: A. ophthalmica, A. cerebri media, A. communicans caudalis. A.ophthalmica dovodi krv u optičke i pomoćne delove oka. A. cerebri media daje grane koje ulaze u moždanu masu i dovodi krv u lateralnu površinu moždane hemisfere. A. communicans caudalis povezuje zadnju moždanu arteriju (A. cerebri caudalis) sa unutrašnjom karotidnom arterijom i daje grane za vaskularizaciju hipotalamusa. A.cerebri rostralis je produžetak stabla unutrašnje karotidne arterije. Ona se spaja sa odgovarajućom granom druge strane ispred Chiasma opticum. Iz ovog spoja nastaje A. cerebri rostralis communis. Od A. cerebri rostralis odvajaju se površne i duboke grane koje ulaze u moždanu masu. A. cerebri caudalis, A. communicans caudalis i A. cerebri rostralis obrazuju oko hipofize i raskršća vidnih nerava arterijski krug (Circulus arteriosus Willisi)

Electric Conductivity of Electrolytic Copper Powder Filled Poly(Lactide-co-Glycolide) Composites

This manuscript presents the results of investigating the properties of composite materials having poly(lactide-co-glycolide) (PLGA) matrix filled with electrolytically produced copper powder whose particles have a highly developed branched structure. The volume fraction of the copper powder used as a filler for the preparation of the composite was varied from 0.4 to 7.2 vol. %. The samples were prepared at 140 °C by hot molding injection. The effect of the morphology of electrolytically obtained copper powder on the appearance of the percolation threshold and on the conductivity of the composites was studied. Characterization included impedance spectroscopy (IS) measurement of electric conductivity and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier-transform Infrared Spectroscopy (FTIR) morphological analysis. Electric conductive pathways were formed throughout the entire volume of the composites, where their formation was purely stochastic in all the dimensions. The percolation threshold was 2.72 vol.%, which is significantly lower than the one stated in the literature for similar composites, since these kind of composites are investigated for the first time. This property can be attributed to the use of a filler of different, diverse morphologies

Distinct cytotoxic mechanisms of pristine versus hydroxylated fullerene

The mechanisms underlying the cytotoxic action of pure fullerene suspension (nano-C-60) and water-soluble polyhydroxylated fullerene [C-60(OH)(n)] were investigated. Crystal violet assay for cell viability demonstrated that nano-C-60 was at least three orders of magnitude more toxic than C-60(OH)(n) to mouse L929 fibrosarcoma, rat C6 glioma, and U251 human glioma cell lines. Flow cytometry analysis of cells stained with propidium iodide (PI), PI/annexin V-fluorescein isothiocyanate, or the redox-sensitive dye dihydrorhodamine revealed that nano-C-60 caused rapid (observable after few hours), reactive oxygen species (ROS)-associated necrosis characterized by cell membrane damage without DNA fragmentation. In contrast, C-60(OH)(n) caused delayed, ROS-independent cell death with characteristics of apoptosis, including DNA fragmentation and loss of cell membrane asymmetry in the absence of increased permeability. Accordingly, the antioxidant N-acetylcysteine protected the cell lines from nano-C-60 toxicity, but not C-60(OH)(n) toxicity, while the pan-caspase inhibitor z-VAD-fmk blocked C-60(OH)(n)-induced apoptosis, but not nano-C-60-mediated necrosis. Finally, C-60(OH)(n) antagonized, while nano-C-60 synergized with, the cytotoxic action of oxidative stress-inducing agents hydrogen peroxide and peroxynitrite donor 3-morpholinosydnonimine. Therefore, unlike polyhydroxylated C-60 that exerts mainly antioxidant/cytoprotective and only mild ROS-independent pro-apoptotic activity, pure crystalline C-60 seems to be endowed with strong pro-oxidant capacity responsible for the rapid necrotic cell death

Electrical conductivity of poly (L lactic acid) and poly (3-hydroxybutyrate) composites filled with galvanostatically produced copper powder

This manuscript presents experimental studies of composite materials based on poly (L lactic acid) (PLLA) and poly (3-hydroxybutyrate) (PHB) matrices filled with electrolytic copper powder, having a very high dendritic structure. Volume fractions of the copper powder used as filler in all prepared composites were varied in the range 0.5-6.0 vol.%. Samples were prepared by hot moulding injection at 170 degrees C. Influence of particle size and morphology, as well as the influence of matrix type on conductivity and percolation threshold of the obtained composites were examined. Characterization included: electrical conductivity measurements using AC impedance spectroscopy (IS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier-transform Infrared spectroscopy (FTIR). Presence of three-dimensional conductive pathways was confirmed. The obtained percolation thresholds of 2.83 vol.% for PLLA and 3.13 vol.% for PHB composites were measured, which is about three times lower than the ones stated in the literature for similar composites. This property is ascribed to different morphologies of the filler used in the present investigation

Uticaj morfologije punioca na termijske karakteristike kompozita lignoceluloze punjene metalnim prahovima

In this manuscript the results of experimental studies of the properties of composite materials based on lignocellulosic matrix (LC) filled with electrolytic copper powder and chemically obtained silver powder are presented. Volume fractions of metal fillers in the composite materials in tested samples were varied in the range of 1.6-30% (v/v), and the samples were prepared by compression - cold pressing. Characterization included examination of the influence of particle size and morphology on the conductivity and percolation threshold of the composites using variety of testing techniques: SEM, TGA, DSC, particle size distribution and conductivity measurements. Thermal analysis of the prepared composites showed the improvement of the thermal characteristics of the composites. This was due to the presence of the metallic fillers which are very good thermal conductors, hence accumulating the emitted heat during TGA measurements primary to lignocellulosic matrix. On the other hand, there is no difference in the response with different metallic fillers and particles with different morphologies. Glass transition temperature is improved by 20ºC for all the composites.U ovom radu su prikazani eksperimentalni rezultati istraživanja termijskih svojstava kompozitnih materijala na bazi lignocelulozne matrice (LC) punjenih elektrolitičkim bakarnim prahom i hemijski dobijenim srebrnim prahom. Udeo metalnih punilaca u kompozitnim materijalima u ispitnim uzorcima variran je u opsegu od 1.6-30% (v/v), a uzorci su pripremljeni hladnim presovanjem - kompaktiranjem pri različitim pritiscima. Karakterizacija i ispitivanje uticaja veličine i morfologije čestica na termijske karakteristike dobijenih kompozita. je uključivala različite tehnike ispitivanja: SEM, TGA, DSC, raspodelu veličina čestica i merenja provodnosti. Rezultati termijske analize pripremljenih kompozita pokazuju poboljšanje termalnih karakteristika samih kompozita usled prisustva metalnih punilaca koji su izrazito dobari termički provodnici, tako da se emitovana količina toplote tokom TGA merenja prvobitno akumulira u česticama punioca, pa tek potom dolazi do promene u samoj lignocelulozi. Sa druge strane, nema razlike u odgovoru kompozita sa različitim veličinama i vrstama čestica. Temperatura prelaska u staklasto stanje lignoceluloze kod svih pripremljenih kompozita je povećana za oko 20ºC

Investigating possibilities for synthesis of novel sorbents and catalyst carriers based on ceramics with controlled open porosity

The aim of this study was to investigate a possibility of synthesis of porous ceramics with controlled open porosity, which could be used as sorbents and catalyst supports. Two organic additives were used to obtain open porosity: polystyrene beads and cellulose fibers, which are mixed with kaolin clay powder and the appropriate water content. Samples were sintered at 1050 oC for 1 h. Characterization of the obtained products included X-ray powder diffraction analysis (XRPD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and elemental CHNS analysis. In addition, porosity was examined by quantification of visual information. The specific surface areas were determined by the Brunauer–Emmett–Teller (BET) method. Also, density and compressive strength of the obtained samples were assessed. It was determined that by sintering, the organic component completely leaves the system. For samples prepared with polystyrene beads and with cellulose fibers, satisfactory mechanical properties were obtained: compressive strengths were 1.42 and 1.56 MPa, respectively. It was noted that significantly higher open porosity was obtained by using polystyrene beads as a sacrificial template (porosity of ̴56 %) instead of cellulose fibers (porosity of ̴6 %)