Research Trends in Contemporary Materials Science

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Authors: D. Stojanović, P. S. Uskoković, I. Balać, V.J. Radojević, R. Aleksić
Abstract: Composites with nano-SiO2 particles and high density polyethylene (HDPE) matrix were produced by hot pressing with various particle contents and particle surface treatment using commercially available silane coupling agents: γ-methacryloxypropyltrimethoxy silane and γ- glycidyloxypropyltrimethoxysilane. The influence of the particle treatment on the mechanical properties of composites was determined by compression and indentation tests. Additionally, numerical analysis was performed in order to calculate Young’s modulus and stress concentrations for various particle contents in order to provide reference data by simulating micro- and macro particle composites with perfect bonding to the matrix.
479
Authors: V.V. Antić, M.P. Antić, M.N. Govedarica, P.R. Dvornić
Abstract: Poly(methylhydrosiloxane) [PMHS], prepared by siloxane equilibration reaction, was used for the hydrosilylation with 1-decene to obtain poly(methyldecylsiloxane) [PMDS]. Pt(0)-1,3- divinyltetramethyldisiloxane complex was used as a catalyst for hydrosilylation reaction. In order to investigate the kinetics of the formation of PMDS, a series of experiments was performed at different reaction temperatures (from 48 to 64 °C) with catalyst concentrations of 7.0 · 10-7 mol of Pt per mol of CH=CH2. All reactions were carried out in bulk, with equimolar amounts of the reacting Si-H and CH=CH2 groups. The course of the reactions was monitored by following the disappearance of the Si-H bands by quantitative infrared spectroscopy. The obtained results show that an induction period occurs at lower reaction temperatures and that the rate of Si-H conversion follows the first-order kinetics.
485
Authors: J. Budinski-Simendić, M. Ilavsky, Jan Šomvarsky, M. Špírková, Lj. Korugić-Karasz, R. Radičević, T. Dikić, K. Dušek
Abstract: The aim of this contribution was to study the rubber elasticity of dry and swollen networks obtained by cyclotrimerization crosslinking reaction of isocyanate groups located at a linear telechelic network precursor. Telechelic diisocyanates were prepared in the undiluted state from 2,4-tolylene diisocyanate, α,ω,dihydroxypoly(oxypropylenes) and different contents of the monool component 2-(2-metoxyetoxy) ethanol. The network synthesis proceeded in a bulk. Detailed network topology was calculated by the theory of branching processes. The equilibrium swelling degree of prepared samples was related to the parameters, which are experimentally accessible for a network arising from an end-linking process using the Flory-Rehner theory. The experimental data for network modulus were compared with those arising from the "affine" model, "phantom’ model" and the model of constrained junctions.
491
Authors: Dejan Miličević, S. Trifunović, N. Ignjatović, E. Suljovrujić
Abstract: Hydroxyapatite/poly L-lactide (HAp/PLLA) is a composite biomaterial which has been widely utilized for substitution and reparation of the hard bone tissue. It is well known that gamma irradiation has been successfully employed in the modification/sterilization of such porous composites and that it has advantages over other procedures. In this study, differential scanning calorimetry (DSC) measurements were made to investigate the influence of the radiation on glass transition behavior and structural relaxation, as well as to estimate the activation energy for this process. The apparent activation energy ΔH* for structural relaxation in the glass transition region was determined on the basis of the heating rate dependence of the glass transition temperature Tg. Furthermore, the results were correlated with those obtained by gel permeation chromatography (GPC). Our findings support the fact that the radiation-induced chain scission in the PLLA phase is the main reason for the decrease of the glass transition temperature and/or activation energy with the absorbed dose.
497
Authors: B. Marjanović, G. Ćirić-Marjanović, A. Radulović, I. Juranić, P. Holler
Abstract: New functional polymeric, semiconducting materials were synthesized by chemical oxidative polymerization of acriflavine hydrochloride in aqueous solution at room temperature, using ammonium peroxydisulfate as an oxidant. Polymerization products were characterized by gelpermeation chromatography (GPC), FTIR spectroscopy, scanning electron microscopy (SEM) and conductivity measurements. The influence of the oxidant/monomer molar ratio on the molecular structure, molecular weight distribution and the electrical conductivity of polyacriflavines was studied. Molecular weights approach a maximum value of ~20000. The polyacriflavine prepared by using oxidant/monomer molar ratio 1.25 shows the conductivity of 2.8 × 10–7 S cm–1. New substitution pattern shown by FTIR spectroscopic analysis combined with MNDO-PM3 semiempirical quantum chemical calculations revealed N─C2 coupling reactions as dominant. The formation of phenazine rings in ladder structured polymerization products was observed by FTIR spectroscopy. The existence of a certain polyacriflavine crystalline structure was suggested from the SEM micrographs.
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Authors: I. Radisavljević, D. Marjanović, N. Novaković, N. Ivanović
Abstract: Effects induced by uniaxial compression and external electric field in P2P to P6P oligophenylene molecules are investigated by versatile calculations. In this way some useful relations between particular values of compression or field directions and intensities to specific changes in molecular structure and properties have been established, enabling estimation of possibilities for tuning the materials characteristics and their spectroscopic analyses. The results are compared to the existing experimental data and similar calculations, and some consequences for applications of oligophenylenes-based materials are discussed.
509
Authors: M.V. Gordić, I.M. Djordjević, D.R. Sekulić, Z.S. Petrović, M.M. Stevanović
Abstract: The paper reports on an experimental study of the Mode I interlaminar fracture of unidirectional carbon fibers/epoxy resin composites. Mode I delamination strain energy release rate GIC was determined in double cantilever beam (DCB) test, before and after gamma irradiation at various doses. Glass transition temperature, Tg of epoxy matrix was determined from dynamic mechanical measurements. The delamination surfaces of tested coupons were observed by scanning electron microscopy. The variations in GIC values were correlated with irradiation doses, Tg values and the features of delamination microfractographs, as well as with the variation under irradiation of matrix or fibre/matrix dominated mechanical properties.
515
Authors: N. Mitrović, B. Čukić, Branka Jordović, Stefan Roth, M. Stoica
Abstract: The rods of Fe-based bulk metallic glasses with the nominal composition Fe65.5Cr4Mo4Ga4P12C5B5.5 were cast by melt injection into 1.5 and 1.8 mm diameter copper molds. The thermal stability, microstructure and crystallization behavior were investigated by differential scanning calorimetry, optical micrography and X-ray diffraction, respectively. The wide supercooled liquid region between crystallization temperature (Tx) and glass transition temperature (Tg) in the as-cast state Tx=Tx-Tg=60 K, as well as the high value of reduced glass transition temperature Trg=Tg/Tl=0.567 (Tl is liquidus temperature) approves enhanced thermal stability of the alloy against crystallization. In the as-cast “XRD-amorphous” state, microhardness HV1=742 was observed. Multistep current annealing thermal treatments were performed for structural relaxation. After applying high enough heating power per square area (PS ≥ 6 W/cm2), intensive crystallization of the samples characterized by appearance of several iron-metalloid compounds (Fe5C2, Fe3Ga4, Fe63Mo37 and Mo12Fe22C10) was observed. The microstructure changes after crystallization bring about differences in the microhardness values. The areas of still present amorphous matrix are with increased value HV1=876, but a remarkable decrease to HV1=323 was observed in precipitated crystallized zone that propagate along inner part of cylinders.
521
Authors: V. Ćosović, A. Grujić, J. Stajić-Trošić, V. Spasojević, N. Talijan
Abstract: Phase transformations and magnetic properties of multiphase Nd4.3Fe76.2B19.5 alloy were investigated in the temperature range of heat treatment 600-700°C. The influence of different heat treatment regimes was observed by correlation of phase composition and measured magnetic properties. The heat treatment regime, which provided the microstructure that improves exchange interactions between grains of soft and hard magnetic phases and consequently enhances magnetic properties, was defined and discussed. For optimized magnetic alloy grain size of the present phases Fe3B, Nd2Fe14B and α-Fe was calculated by size-strain analysis of X-ray powder diffraction data. Calculated mean grain size was on a nanoscale, below 30 nm.
527
Authors: Aleksandra Kalezić-Glišović, N. Mitrović, A. Maričić, R. Simeunović
Abstract: The magnetoimpedance (MI) effect in magnetically soft Fe89.8Ni1.5Si5.2B3C0.5 metallic glass ribbons is studied in this paper. As soft magnetic properties were determined by field induced anisotropy (and therefore by magnetic domain structure), ribbon samples were annealed under tensile stress in order to enhance induction of transverse anisotropy and to improve magnetoimpedance effect. Stress-annealing (SA) technique up to 420 0C/475 MPa/30 min. was used for tailoring electrical resistivity (ρ) and magnetic permeability (μ), i.e. two material properties that in classical skin effect determine the penetration depth δm and therefore have influence on MIeffect. The critical frequency of about 600 kHz was observed as the point with the initial increase of MI. Significant improvement of MI-response reaching the value Z/Z ≈ 25 %, after annealing at 420 0C, was recorded at driving frequency 4 MHz. The highest MI-element sensitivity was found for low magnetic field intensity where values of about 12 % / kA/m were attained.
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