Recent Developments in Advanced Materials and Processes

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Authors: Vlada D. Jović, V. Maksimović, M.G. Pavlović, B.M. Jović
Abstract: In this paper the morphology of Ni-Co powders electrodeposited from ammonium sulfate-boric acid containing electrolyte is investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni2+/Co2+ concentration is found to influence both, the alloy phase composition and the morphology of Ni-Co alloy powders. At the highest ratio of Ni2+/Co2+ ions concentration, typical 2D fern-like dendritic particles were obtained. With decrease of Ni2+/Co2+ ions ratio among 2D fern-like dendrites, 3D dendrites and different agglomerates of a size of about 100 μm, being either compact (typical for pure Co powder) or composed of a large number of small 3D dendrites on their surface were obtained. According to the X-ray analysis, with decreasing Ni2+/Co2+ concentration ratio the amount of f.c.c. β-Ni phase was found to decrease, while the amount of h.c.p. α-Co phase was found to increase being accompanied by the appearance of the f.c.c. Co phase at Ni2+/Co2+ = 0.33.
Authors: N. Mitrović, Stefan Roth, S. Kane
Abstract: Multistep current annealing (CA) treatments were performed on amorphous FINEMETtype Fe-Cu-V-Si-B, as well as on a novel Fe-Al-Ga-P-C-B alloy with a large supercooled liquid region, in order to optimize their magnetotransport properties. On-line and post-annealing electrical resistivity measurements, DSC, XRD and Mössbauer spectroscopy were used for characterization of structural changes evolved during CA treatments. Results on magnetoresistance (MR) and magnetoimpedance (MI) effects after CA in ribbon samples with relaxed amorphous as well as precipitated nanocrystalline structure are presented. Significant improvement in MI-response after CA up to Z/Z ≈ 50% was recorded at frequencies 2-3 MHz. The highest MI-element sensitivity was found for low magnetic field intensity where values of about 6 %/kA/m for samples of Fe-Al- Ga-P-C-B alloy were attained.
Authors: J. Belošević-Čavor, F. Congiu, V. Koteski, Bozidar Cekić, Giorgio Concas
Abstract: Magnetization M as a function of applied magnetic field H up to 50 kOe was measured at low temperature T = 5K, using an SQUID magnetometer, for HfCo2 and Hf2Co intermetallic compounds. Both samples showed paramagnetic behaviour with a weak ferromagnetic contribution due to impurities (0.01-0.001 wt%). The values of the mass susceptibilities χ were deduced from the measurements. In addition, calculations using full-potential linearized augmented plane wave (FP-LAPW) WIEN 97 programme package were done, in order to check their agreement with the experimental results.
Authors: Ana Umićević, H.E. Mahnke, Bozidar Cekić, Jasna Grbović Novaković, V. Koteski, J. Belošević-Čavor
Abstract: The alloying and phase formation in Ni-Hf samples with 0.2-, 2-, and 5-at.% Hf were studied by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). Both characterization methods, XRD and SEM, reveal the presence of the HfNi5 phase (fcc structure) where the excess Ni atoms are present in the form of Ni or Ni-rich segregations in the sample containing 5-at.% Hf. The sample with 2-at.% Hf is characterized by the presence of the two phases present in the 5-at.% sample and by Hf atoms, which occupy substitutional lattice positions in the Ni lattice. Finally, in the third sample with 0.2-at.% Hf, the Hf atoms mainly substitute the Ni atoms in the lattice. This analysis is being complemented with additional information on the local structure around Hf by extended X-ray absorption fine structure spectroscopy (EXAFS).
Authors: A.R. Tančić, M. Davidović
Abstract: Within the framework of the many-body theory by using the Random Phase Approximation with Exchange (RPAE) method we calculated the frequency dependent polarizability, refractive index, and Verdet coefficient of some atoms. Calculated time-dependent peculiarities of a set of atoms are very significant in the nano-region and might be important for designing new materials.
Authors: I. Popović, M. Zlatanović
Abstract: The electrical and optical signal waveforms of nitrogen/hydrogen glow discharges used for plasma nitriding process were recorded and analyzed. The shape of the discharge voltage and current signals is dependent on the process parameters, pulse plasma generator properties and cathode geometry. It has been found that the dynamic parameters of the electrical signal waveforms contain information related to the charged particles generation, which is relevant to the homogeneity of different gas discharge surface treatment processes. On the other hand, information related to the active species generation responsible for thermochemical processes at the cathode surface is stored in the optical emission waveforms. The generation and quenching of the active ingredients during the voltage pulses switch on and off influence the shape of the emitted light signals. From the optical signal analysis it was found that the thermochemical processes are influenced by the plasma generator properties such as pulse duty cycle, frequency, applied discharge voltage level and process parameters like working gas composition, operating temperature and pressure.
Authors: E.R. Andrievskaya, V.P. Red'ko
Abstract: Phase equilibria in the ternary system ZrO2-Y2O3-La2O3 at 1250 °C have been studied and isothermal section have been developed. Fine chemical technique such as co-precipitation was used to obtain ceramic nanopowders (with average particle size of 8-20 nm) available for nonisothermal sintering as well. The phase compositions of the annealed samples were studied by methods of X-ray analysis at 20 °C, petrographic and electron microprobe X-ray analyses. No ternary compounds were found. The phase equilibria in the system are determined by intermediate phases: La2Zr2O7 and LaYO3 that crystallize in the pyrochlore and perovskite-type structures, respectively. Solid solutions based on the constituent oxides such as tetragonal (T) and cubic fluorite-type structure (F) ZrO2, cubic form of rare-earth oxides (C-type) Y2O3,as well as hexagonal (A) and monoclinic (B) forms La2O3 were found at 1250 °C. The nanocrystalline powders of tetragonal zirconia actively sintered on heating up to 1150-1400 °C and the powders of lanthanum zirconate show active densification on heating up to 1550-1650 °C. The electrical properties (at 600-950 °C) of yttria-doped pyrochlore were measured, the highest conductivity has been revealed at 10 mol % Y2O3.
Authors: J. Radić-Perić
Abstract: The synthesis of solid BN in thermal plasma is investigated theoretically by computing the equilibrium composition of a gas mixture containing boron, nitrogen, hydrogen and argon. The calculations are done for the temperature range between 500 and 6000 K and the total pressure in the system of 1 bar. They are based on the fact that thermal plasma is in local thermodynamic equilibrium, which makes possible theoretical determination (by employing the Gibbs free energy data for the compounds present in the system) of its equilibrium composition. From the calculated compositions of investigated gas systems, the temperature zones with saturated and/or oversaturated vapour of B and B2N are determined and the formation mechanism of BN in solid state is proposed.
Authors: Lj. Budinski-Petković, M. Petković, Z.M. Jakšić, S.B. Vrhovac
Abstract: We perform numerical simulation of a lattice model for the compaction of a granular material based on the idea of reversible random sequential adsorption. Reversible random sequential adsorption of objects of various shapes on a two−dimensional triangular lattice is studied numerically by means of Monte Carlo simulations. The growth of the coverage ρ(t) above the jamming limit to its steady−state value ρ∞ is described by a pattern ρ (t) = ρ∞ − ρEβ[−(t/τ)β], where Eβ denotes the Mittag−Leffler function of order β ∈ (0, 1). For the first time, the parameter τ is found to decay with the desorption probability P− according to a power law τ = A P− −γ. Exponent γ is the same for all shapes, γ = 1.29 ± 0.01, but parameter A depends only on the order of symmetry axis of the shape. Finally, we present the possible relevance of the model to the compaction of granular objects of various shapes.
Authors: Srboljub J. Stanković, R.D. Ilić, M. Petrović, B. Lončar, A. Vasić
Abstract: The use of semiconductor materials in radiation processing, radiation therapy and diagnostics, and detection of cosmic radiation motivated development of numerical methods for its radiological characterization. This paper presents the application of the Monte Carlo method using the FOTELP-2K4 code for radiological characterization of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) dosimeter. The advantages of MOSFET dosimeters include small size, immediate readout, and ease of use for a wide photon energy range. In order to determine the dosimeter response accurately, distribution of the absorbed dose in the MOSFET structure has been investigated. Our results show that the absorbed dose distribution calculated by the presented simulation model compares well with the published data.

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