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2.
Characterisation of a new dental alloy with high Au content
Rebeka Rudolf, Tjaša Zupančič Hartner, Ivan Anžel, Primož Mrvar, Jože Medved, Dragoslav Stamenković, 2007, original scientific article

Abstract: The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. This new Au dental alloy is based on the ternary system of Au-Pt-Zn with a nominal composition of 88.5Au-8.7Pt-1.5Zn-0.5In-0.4Ir-0.3Rh. The alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. Casting was followed with subsequent thermo-mechanical treatment (procedures of profile and polish milling, thermal treatment) and cutting-off strips to form a regular shape. The heat treatments of Au alloy samples were carried out in a tube furnace under different temperatures, and over different times. Testing of the new Au dental alloy included examining the initial cast, and the different heat treated conditions of the Au alloy. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done.Osnovo razvoja nove dentalne zlitine z visoko vsebnostjo Au predstavljata pravilna določitev kemijske sestave in tehnologije izdelave. Nova dentalna zlitina temelji na ternarnem sistemu of Au-Pt-Zn z nominalno kemijsko sestavo 88,5Au-8,7Pt-1,5Zn-0,5In-0,4Ir-0,3Rh. Izdelava dentalne zlitine je potekala s pretaljevanjem zelo čistih komponent v vakuumski indukcijski peči v Zlatarni Celje. Temu je sledilo odlivanje taline v ustrezno formo, postopek termo-mehanske obdelave odlitka in razrez zlitine v ustrezno obliko. Toplotna obdelava je bila izvedena pri različnih temperaturah in za različne čase. Testiranje dentalne zlitine je vključevalo določitev lastnosti začetnega stanja in stanja po različnih toplotnih obdelavah. Optične lastnosti dentalne zlitine so bile raziskane s spektro-fotometrično kolorimetrijo. Na novi Au dentalni zlitini so bili narejeni še testi citotoksičnosti z uporabo standardain vitro analize za testiranje biokompatibilnosti z uvajanjem novih, bolj občutljivih in vitro testov na celični liniji.
Keywords: dental alloy, characterisation, microstructure, properties
Published: 31.05.2012; Views: 1365; Downloads: 34
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3.
Internal oxidation of Cu-C and Ag-C composites
Gabrijela Čevnik, Gorazd Kosec, Ladislav Kosec, Rebeka Rudolf, Borut Kosec, Ivan Anžel, 2008, short scientific article

Abstract: The internal oxidation in copper-carbon and silver-carbon composites occurs when they are exposed to air or oxygen at high temperature. Solubility of carbon in copper or in silver is very low. The kinetics of oxidation at high temperature and activation energy were determined and the mechanism of internal oxidation was analysed. The kinetics of internal oxidation was determined for both cases and it is depended from the diffusion of oxygen following parabolic time dependence according to Wagner's theory. The activation energy for Cu-C composite is 70.5 kJ/mol, and for Ag-C composite is 50.1 kJ/mol, what is in both cases close to the activation energy for the volume diffusion of oxygen in copper or in silver. In both cases gas products are formed during the internal oxidation of composites. In the internal oxidation zone pores, bubbles occur. The carbon oxidates directly with the oxygen from solid solution as long there is a contact, which breaks down with the presence of gas products. Then the oxidation occurs over the gas mixture of CO and CO2.Pri visokih temperaturah kompoziti bakra in srebra z ogljikom na zraku ali v kisiku reagirajo po mehanizmu notranje oksidacije. Topnost ogljika v trdnem bakru in trdnem srebru je zelo majhna. Analizirali smo kinetiko oksidacije kompozitov, določili aktivacijsko energijo in mehanizem notranje oksidacije. Kinetika oksidacije je pri obeh skupinah materialov odvisna od difuzije kisika in sledi parabolični odvisnosti od časa v skladu z Wagnerjevo teorijo. Aktivacijska energija procesa je za kompozit Cu-C enaka 70,5 kJ/mol, za kompozit Ag-C pa 50,1 kJ/mol, kar je blizu aktivacijski energiji za volumsko difuzijo kisika v trdnem bakru oziroma srebru. Pri oksidaciji kompozita nastajajo plinski produkti. Oksidacija ogljika poteka neposredno s kisikom iz trdne raztopine, ko pa se zaradi nastanka plinske faze stik prekine, pa preko plinske zmesi CO in CO2.
Keywords: internal oxidation, internal oxidation zone, composite, copper, silver, diffusion, kinetics
Published: 31.05.2012; Views: 1297; Downloads: 19
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4.
Yield strength modelling of formed material using evolutionary computational method
Leo Gusel, Rebeka Rudolf, 2009, original scientific article

Abstract: In this paper we propose an evolutionary computation approach for the modelling of yield strength in formed material. One of the most general evolutionary computation methods is genetic programming, which was used in our research. Genetic programming is an automated method for creating a working computer program from a problemćs high-level statement. Genetic programming does this by genetically breeding a population of computer programs using the principles of Darwinianćs natural selection and biologically inspired operations. During our research, material was cold formed by drawing using different process parameters and then determining yield strengths (dependent variable) of the specimens. On the basis of a training data set, various different genetic models for yield strength distribution were developed during simulated evolution. The accuracies of the best models were proved by a testing data set and comparing between the genetic and regression models. The research showed that very accurate genetic models can be developed by the proposed approach.
Keywords: metal forming, yield strength, genetic programming, modelling
Published: 31.05.2012; Views: 1448; Downloads: 25
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5.
Optical and magnetic properties of PbTe(Ni)
Nebojša Romčević, J. Trajić, M. Romčević, D. Stojanović, T. A. Kuznetsova, D. Khokhlov, W. Dobrowolski, Rebeka Rudolf, Ivan Anžel, 2009, published scientific conference contribution

Abstract: Far-infrared and magnetic properties of Ni doped PbTe (ZNi = 1 £ 1019 at./cm3)single crystal are investigated in a broad range of temperature and magnetic elds. Far-infrared re°ection spectra were analyzed using a tting procedure based on the modi ed plasmon{two phonon interaction model. Together with the strong plasmon{two longitudinal optical phonon coupling we obtained a local mode of Ni at about 180 cm¡1. This mode intensity depends on temperature. Magnetic measurements shows that PbTe alloys doped with Ni reveals weak ferromagnetic interaction between magnetic ions.
Keywords: semiconductor compounds, PbTe(Ni)
Published: 31.05.2012; Views: 1183; Downloads: 64
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6.
Low-frequency Raman scattering from ZnO(Fe) nanoparticles
R. Kostić, Nebojša Romčević, M. Romčević, B. Hadžić, Rebeka Rudolf, I. Kuryliszyn Kudelska, W. Dobrowolski, U. Narkiewicz, D. Sibera, 2009, published scientific conference contribution

Abstract: Nanocrystalline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine the sample composition and the mean crystalline size. Low frequency Raman modes were measured and assigned according to confined acoustic vibrations of spherical nanoparticles. Frequencies of these vibrational modes were analyzed in elastic continuum aproximation, which considers nanoparticle as homogeneous elastic sphere.
Keywords: nanocrystalline samples, Raman modes
Published: 31.05.2012; Views: 1007; Downloads: 73
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7.
Raman spectroscopy of multiphonon emission process in Ni-doped PbTe
Nebojša Romčević, J. Trajić, B. Hadžić, M. Romčević, D. Stojanović, Z. Lazarević, T. A. Kuznetsova, D. Khokhlov, Rebeka Rudolf, Ivan Anžel, 2009, published scientific conference contribution

Abstract: In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1* 1019 at./cm3. Well resolved peaks appear at about 126, 143, 181, 362 and 724 cm-1. The modes at 126 and 143 cm-1, which are also observed in other telluride compounds, originate from vibrations in TeO2. We assume that the mode at about 181 cm-1 is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor Ni3+ state). Modes at about 362 cm-1 and 724 cm-1 are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.
Keywords: crystals, Raman scattering
Published: 31.05.2012; Views: 1176; Downloads: 83
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8.
Ellipsometric measurements of plastically deformed copper
M. Mirić, Rebeka Rudolf, Ivan Anžel, B. Hadžić, M. Romčević, J. Trajić, Nebojša Romčević, 2009, published scientific conference contribution

Abstract: Chemically pure copper (99.99) prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm was extremely plastically deformed with the repeated application of equal channel angular pressing. Equal channel angular pressing was applied as an effective technique for producing bulk nanoscaled structures. It is well known that severe plastic deformation of metallic materials often leads to microstructure with ultrafine grains and cross-sections which remain about equal before and after deformation. Optical properties of the sample were studied using spectroscopic ellipsometry in UV-VIS range. The parameters of the sample like copper oxide and surface roughness overlayer were calculated using two-film model together with the Bruggeman effective medium approximation.
Keywords: hydrometallurgical extraction of metals, copper
Published: 31.05.2012; Views: 1088; Downloads: 93
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9.
Metallographic sample preparation of orthodontic Ni-Ti wire
Lidija Zorko, Rebeka Rudolf, 2009, original scientific article

Abstract: Shape memory alloys (SMA) has been at the forefront of research for the last several decades. In this field especially, Nickel-Titanium (Ni-Ti) alloys have been found to be the most useful of all SMA. The most important applications of SMA Ni-Ti alloys are namely in medicine and dentistry, where they are used as orthodontic wires. In this paper we describe the procedure of preparing metallographic samples of typical orthodontic Ni-Ti wires which are nowadays used in dentistry praxis. We prepared the samples for microstructure observation using a light microscope. Special attention is given to the metallographic preparation, which could result in damages and deformations of the sample surfaces if the procedure is incorrect. Finally, we illustrated the typical metallographic recipe for Ni-Ti SMA alloys for optical observation.
Keywords: shape memory alloys, Ni-Ti wire, metallographic preparation, microstructure
Published: 31.05.2012; Views: 1221; Downloads: 25
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10.
Optical properties of plastically deformed copper
J. Trajić, Rebeka Rudolf, Ivan Anžel, M. Romčević, N. Lazarević, M. Mirić, Z. Lazarević, B. Hadžić, Nebojša Romčević, 2010, published scientific conference contribution

Abstract: Pure copper (99.99), prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm, was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing (ECAP). ECAP was applied as an effective technique for producing bulk nano-scaled structures. Optical properties of the sample were investigated using Raman spectroscopy. Two types of lines: narrow (with width of 7 cm¡1) and wide ( 40 cm¡1) are registered. Existence of two types of lines indicates that in the specimen exists nano-sized crystal structures of both Cu and CuO related with three dimensional amorphous boundary spaces, which indicates that plastic deformation of the sample did not lead to total amorphisation of the specimen.
Keywords: plastically deformed copper, hydrometallurgical extraction of metals
Published: 31.05.2012; Views: 1258; Downloads: 72
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