bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study on the Electrical Properties of ZnO Based Transparent TFTs
Authors: Barquinha Pedro , Fortunato Elvira , Gonçalves Alexandra , Pimentel Ana , Marques António , Pereira Luís , Martins Rodrigo
Published: March 2009

The purpose of this work is to present in-depth electrical characterization on transparent TFTs, using zinc oxide produced at room temperature as the semiconductor material. Some of the studied aspects were the relation between the output conductance in the post-pinch-off regime and width-to-length ratios, the gate leakage current, the semiconductor/insulator interface traps density and its relation with threshold voltage. The main point of the analysis was focused on channel
mobility. Values extracted using different methodologies, like effective, saturation and average mobility, are presented and discussed regarding their significance and validity. The evolution of the different types of mobility with the applied gate voltage was investigated and the obtained results are somehow in disagreement with the typical behavior found on classical silicon based MOSFETs, which is mainly attributed to the completely different structures of the semiconductor materials
used in the two situations: while in MOSFETS we have monocrystalline silicon, our transparent TFTs use poly/nanocrystalline zinc oxide with grain sizes of about 10 nm.
Influence of the Deposition Parameters on the Properties of Bis-Triethoxysilylpropyl] Tetrasulphide (BTESPT) Layers on AA2024-T3 – An Ellipsometric Study
Authors: Cabral Ana , Correia Jorge P. , Ferreira Mário G.S.
Published: March 2009

A bis-sulphur silane (BTESPT) was used to produce thin protective layers on AA2024- T3, a structural aluminium alloy widely used in the aeronautic industry, being the coatings analysed ex-situ by ellipsometry. Despite a slight degree of film anisotropy evidenced by measurements at different angles of incidence, an optical model of a single homogeneous phase could be employed to describe the silane based layer. The information obtained allowed to characterize the influence of
the operational deposition parameters on the film thickness and structural organization of the silane phase (evaluated by its optical absorption). It is shown that the silane concentration of the solution and immersion time determine the final thickness of the formed layer while the curing time does not affect significantly this parameter. On the other hand, it was observed a marked decrease of the
optical absorption of the coatings submitted to curing temperatures of at least 100°C, which should be ascribed to a structural reorganization phenomena induced by the removal of water molecules from the film. The data gathered by ellipsometry were successfully corroborated by independent surface profilometry analysis of the films.
The Influence of Austempering Heat Treatment Variables on Dimensional Changes of a Ni-Cu Ductile Iron
Authors: Yazdani Sasan
Published: March 2009

Control and prediction of the dimensional changes (DC) during austempering heat
treatment of ductile iron is difficult because many factors influence this behavior. In the present work cylindrical specimens of ductile iron were used to study the effect of austenitizing temperature, austempering time, temperature, and prior microstructure on DC. The results show that DC increases with increasing austenitizing temperature in the range of 850 to 950°C with a fully
ausferrite microstructure. Evaluation of different combinations of ferrite and pearlite contents in prior microstructure indicates that a fully ferritic structure has the highest DC. In addition, results show that by lowering austempering temperature from 400 to 250°C, DC increases.
Preparation of Dispersion-Strengthened Coppers with Niobium Carbide and Niobium Boride by Mechanical Alloying
Authors: Livramento Vanessa , Marques M.T. , Correia Jose Brito , Almeida Amélia , Vilar Rui
Published: March 2009

The present study examines nanocomposites prepared by mechanical alloying of copper with other transition elements, which will produce a dispersion of stable boride and carbides reinforcement particles within a nanostructured copper matrix, at room temperature. Copper, niobium, boron and graphite powder mixtures were mechanically alloyed for several hours in a planetary ball-mill, in argon atmosphere and using a stainless steel container. The powder mixtures were produced with nominal composition of 10-30 vol.% NbC and 7-10 vol.% NbB2, using
powders of pure elemental Cu, Nb, synthetic graphite and crystalline boron. The microstructural changes during milling of these powder mixtures were studied using X-ray diffraction, optical microscopy, scanning electron microscopy and microhardness measurements.
Lead Hardening by Oxide Dispersion
Authors: Potecasu F. , Potecasu O. , Braz Fernandes Francisco Manuel , Muşat Viorica
Published: March 2009

Lead hardened through oxide scattering is investigated as raw materials for the
fabrication of the support gratings of lead accumulators in order to increase their life service. For the preparation of lead powder hardened through oxide scattering we used air jet pulverisation, a technique specific to powder metallurgy. Two research approaches are presented in the paper: one in which the oxide was introduced through oxidised lead powder, and the other in which additional lead oxide was introduced. Oxide dispersion into metallic matrix was achieved by pronounced
deformation through extrusion of the powder. During extrusion, the particles are compelled to pass through the mould calibration zone and consequently they are considerably deformed. As an effect of this deformation, the particles of fragile oxide which cover the lead powder particles are crashed and carried away to the material flowing through the matrix longitudinally on the extruded semiproduct.
The content of oxide introduced in matrix by the oxidised lead powder depends on the powder particle size. This paper presents the effect of the powder particle size and oxide phase dispersion in the metallic matrix on the mechanical, chemical and electrical properties of the extruded semi-products. The semi-products made from lead powder belonging to the grain size class of < 40 µm and oxide particles allowance have the highest mechanical resistance and the best corrosion behaviour. Using controlled oxidised lead powder better extruded semi-products are
obtained in terms of mechanical resistance, corrosion behaviour and electrical conductivity as compared with lead and Pb-Sb alloy. A higher electrical conductivity represents an important advantage especially for the starting accumulators where the voltage fall should be as low as possible.
Creep Behaviour of Si3N4 Ceramics Sintered with RE2O3
Authors: dos Santos Claudinei , Strecker Kurt , Neto Francisco Piorino , Silva Cosme Roberto Moreira , Almeida Flávia A. , Silva Rui F.
Published: March 2009

The objective of this work was to evaluate the creep behaviour of Si3N4 based ceramics obtained by uniaxial hot-pressing. As sintering additive, an yttrium-rare earth oxide solid solution, designed RE2O3, that shows similar characteristics to pure Y2O3, was used. Samples were sintered using high-purity α-Si3N4 powder, with additive mixtures based on RE2O3/Al2O3 or RE2O3/AlN, at 5 and 20 vol.%, respectively. The sintered samples were characterized by X-ray diffractometry,
scanning electron microscopy and density. Specimens of 3x3x6 mm3 were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 13750C in air. Samples with RE2O3/Al2O3 showed β-Si3N4 as crystalline phase, with grains of high aspect
ratio, and a relative density around 99% of the theoretical density. The Si3N4/RE2O3/AlN samples presented α-Si3N4 solid solution, designed α-SiAlON, with a more equiaxed microstructure and slightly lower relative density (96-98%). The results of creep tests indicated that these ceramics containing α-SiAlON are the more creep resistant, with steady-state creep rates around 10-4 h-1,
with stress exponents (n) in the range 0.67-2.53, indicating grain boundary sliding as the main creep mechanism.
Assessment of Particle Clustering in MMCs by Quantitative Image Analysis
Authors: Silva Nelson , Velhinho Alexandre
Published: March 2009

In the present paper, work of a preliminary nature pertaining to the development of a
simple tool for easy identification of reinforcement clustering in particle-reinforced MMCs is reported. The tool consists of an image processing and analysis routine performed with the aid of a public-domain software. Results obtained were in the form of distribution curves pertaining to the Euclidian distances between particle centroids within sample images. Analysis of that distribution allowed the identification of cluster occurrence. The technique was successfully applied to computer-generated images of virtual MMCs, as well as to micrographs of rheocast MMCs. Apart from particle clustering, the distribution curves were found useful to roughly assess the matrix cell size, for cases where this is significantly higher that the size of the reinforcing particles.
Carrier Transport Investigation on Organic Semiconductor by Electrical DC and AC Measurements: the Case of Alq3
Authors: Silva V.M. , Graça Manuel P.F. , Madaleno Joana Catarina , Costa Luís Cadillon , Pereira Luiz
Published: March 2009

In the present work, the nature of the electrical mechanism for carrier transport in Alq3 is studied by current-voltage measurements and broadband dielectric spectroscopy. The d.c. currentvoltage characteristics at low applied electrical field exhibits a classical “N” shape due to interfacial states located at metal-organic interface, but tend to disappear when successive higher forward bias
is applied. Using dielectric spectroscopy it is possible to observe that the main relaxation peak shifts to a higher frequency with the increase of the applied d.c. voltage (from approximately 100 Hz with 0 V d.c. bias to approximately 400 Hz with 6 V d.c. bias) indicating a semiconductor structure change. The logarithmic Z’’ vs. Z’ plot has a slope about 0.7 that decreases to 0.5 with the increasing applied d.c. voltage, reaching a classic Debye relaxation. An attempt to correlate with
some structural changes is made.
Damage Mechanisms Identification in FRP Using Acoustic Emission and Artificial Neural Networks
Authors: de Oliveira Rui , Marques António Torres
Published: March 2009

In this study is proposed a procedure for damage discrimination based on acoustic
emission signals clustering using artificial neural networks. An unsupervised methodology based on the self-organizing maps of Kohonen is developed considering the lack of a priori knowledge of the different signal classes. The methodology is described and applied to a cross-ply glassfibre/
polyester laminate submitted to a tensile test. In this case, six different AE waveforms were identified. The damage sequence could so be identified from the modal nature of those waves.
Novel Organic Hole Transport Layers for Molecular Electronic Systems
Authors: Burrows Hugh D. , Castro Ricardo , Esteves M. Alexandra , Gigante Barbara , Leitão Luísa , Pauleta Ana
Published: March 2009

Five novel triarylamines based on the bulky dehydroabietic acid unit have been
synthesised, and their potential as hole transport layers tested. This bulky group facilitates film preparation and stability without significantly affecting the chemical or materials properties. Three of these systems present excellent stability, and show considerable potential for device applications.
Dynamic Vulcanisation of EPDM-Based Thermoplastic Vulcanisates during Extrusion: Effect of Processing Conditions
Authors: Machado Ana Vera , van Duin Martin , Covas José A.
Published: March 2009

Dynamic vulcanisation of EPDM/PE blends using the resol/SnCl2 system was studied in a co-rotating twin screw extruder using a series of sampling devices. In order to study the effect of the processing conditions on chemical development along the extruder and on the mechanical properties of the extrudate material, the same recipe (having the same polyolefin/EPDM ratio) was compounded under different processing conditions. The results showed that both chemical
evolution and mechanical properties depend on the processing conditions.
Synthesis and Characterization of New Polyurethane Adhesives
Authors: Correia Cristina Borges , Bordado João C.
Published: March 2009

Polyurethane adhesives provide excellent flexibility, impact resistance and durability.
Polyurethanes are formed through the reaction of an isocyanate component with polyether or polyester polyols or other active hydrogen compounds. This paper refers to polyurethane adhesives made from polyester polyols with long aliphatic chains (up to 36 carbon atoms) and MDI (diphenylmethane-4,4’-diisocyanate). The polyester polyols have been made from dimer acids obtained from renewable sources and short chain diols. The polyols that were used presented different degrees of unsaturation. The influence of the different raw
materials in the adhesives performance is studied. The polyurethanes were produced by reaction between quasi-stoichiometric quantities of polyol and
MDI, at several temperatures. The reaction was carried under inert atmosphere and at temperatures below 100°C. Performance of the adhesives was tested by carrying adhesion, hardness and water absorption tests. Characterization of both the polyester polyols and polyurethane adhesives was carried by Fourier
Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Magnetic Nuclear Resonance (NMR), X-Ray Diffraction (WAXD), Scanning RMN Imaging of 1H of Stray- Field b (MRI) and Brookfield viscometry.
Polyurethane-Polyurea Membranes for Blood Oxygenation
Authors: Pinto M. Isabel , Queiroz Denise P. , Gil M. Helena , Guiomar Antonio Jorge , Norberta de Pinho Maria
Published: March 2009

The structural versatility of polyurethane based membranes is enhanced through the
introduction of two soft segments to obtain new membranes with improved hemocompatibility. Crosslinked polyurethane/urea membranes with two soft segments were prepared by extending a polypropylene oxide-based tri-isocyanate terminated prepolymer (PU) with polybutadiene diol (PBDO). The ratio of PU to PBDO was 100/0 and 90/10. The membranes were characterised in terms of permeation towards O2 and CO2 and their hemocompatibility was evaluated through
hemolysis and thrombosis experiments. It was found that the membrane with PBDO had the highest permeability to O2 and CO2 and it was non-hemolytic and less thrombogenic.
Electroplating of Iron Films: Microstructural Effects of Alkaline Baths
Authors: Poznyak Sergey K. , Kharton Vladislav V. , Frade Jorge R. , Ferreira Mário G.S.
Published: March 2009

Several alkaline baths based on different complexing agents were examined for iron
electroplating. The resultant films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was shown that adherent and smooth iron coatings with uniform microstructure can be obtained using alkaline Fe (II) baths containing pyrophosphate and tartrate ions as complexing agents. The average grain size can be substantially decreased by glycine additions in the pyrophosphate bath. The faradaic efficiency in these electrolytes may achieve up to
40-50%. The tartrate-containing baths are characterized with a higher throwing power and an increased buffer capacity with respect to the pyrophosphate-based electrolytes. The resultant Fe coatings are single-phase, whilst substantial broadening of the XRD peaks indicates nano-scale grain size. The alkaline baths based on EDTA complexes of iron (III) give black dull iron deposits and are characterized by rather low cathodic current efficiencies, especially at low current densities.
Open Cell Polyurethane Foams for New Filters with Supported Adsorbents
Authors: Correia Nuno , Bordado João C. , Pires João , Carvalho Manuela B. , Carvalho Ana P. , Pinto Moisés
Published: March 2009

A flexible foam was developed based on polymeric diphenylmethane diisocyanate (MDI) to be used as support for pre-synthesized adsorbent additives (activated carbon) for air-conditioning filters that provide air purification and improve indoor air quality. Foam for air purification filters must be an open cell foam with low density, air permeability and the adsorbents must retain indoor air pollutants, such as volatile organic compounds (VOCs). To achieve the right structural characteristics different polyether polyols, catalysts and surfactants were used and several tests of pressure drop, apparent volume, real volume and densities were performed.
Another aspect that was studied in this work was the adsorption capacity of several activated carbons and the foam matrix influence in the adsorption. For that purpose room temperature adsorption isotherms of toluene, which is a probe of noxious aromatic VOCs, were determined and compared. For scale up purpose, rise time curves of the foams were measured. This study was made at different starting temperatures and with different types and quantities of catalyst. The relationships
rise time/starting temperature and rise time/quantity of catalyst were obtained and expressed in equations.
Plastic Behaviour of Copper Polycrystal Subjected to Fatigue-Tension Sequential Loading Tests
Authors: Jia Wei Ping , Fernandes José Valdemar
Published: March 2009

Sequences of fatigue-tension tests were performed on copper polycrystal sheet, with
32µm mean grain size. The effect of strain path change on subsequent reloading yield stress as well as work hardening rate has been investigated. Dislocation microstructure was observed by transmission electron microscopy after mechanical tests. Under present conditions, it was found that fatigue prestraining caused the increase of reloading yield stress, larger amplitude of strain path change resulted in higher reloading yield stress and lower work hardening rate. Reloading tensile
curves are independent of predeformation plastic strain amplitudes in both cases. Many isolated dislocation lines between cell walls have been detected for Φ=0° case when the subsequent tension strain amount is 5%, this can be well understood from the microscopic dislocation slip mechanisms. When the reloading tension tests have been done until rupture, dislocation structures become typical of monotonic tension without preloading. The correlation of mechanical properties and microstructural observations was discussed in this paper.
Sorption of Sodium Dodecyl Sulfate by Polyaniline-Cellulose Acetate Blends: Equilibrium and Kinetic Studies
Authors: Valente Artur J.M. , Burrows Hugh D. , Lobo Victor M.M.
Published: March 2009

The interaction between sodium dodecyl sulfate (SDS) and blends of polyaniline (PANi) and cellulose acetate (CA) is discussed. The diffusion coefficients of SDS in the blends show that the transport process is accompanied by interactions between the diffusant and the polymeric matrix. In the visible absorption spectrum, the interaction between SDS and CA-PANi blends results in a red shift of the maximum absorption wavelength. This behaviour is explained on the
basis of alterations in the lamellar phase of the polymer upon SDS sorption. The interactions between SDS and the blend film are of the Langmuir-type. These blends also show an interesting selective behaviour to SDS with respect to a set of similar surfactants.
Cu(In,Ga)Se2 Prepared by a 2 and 3-Stage Hybrid RF-Magnetron Sputtering and Se Evaporation Method: Properties and Solar Cell Performance
Authors: da Cunha António F. , Kurdzesau F. , Salomé Pedro M.P.
Published: March 2009

The potential of RF-magnetron sputtering to achieve high quality Cu(In,Ga)Se2 (CIGS) thin films and efficient solar cells with the goal of using a single technique for all solar cell processing steps is explored. The end point detection method was adapted to RF-magnetron deposition of CIGS in two- or three stages sputtering process. It allows the control of the final composition of the deposited layers in a reproducible way. The influence of substrate temperature and Ar pressure during the deposition on the surface and crossectional morphology of CIGS films was studied for two and three-stage sputtering process sequence. The solar cells prepared with films deposited by two-stage sputtering nave showed a better performance with maximum efficiency above 8 %.
Study of Electrical Properties of Natural Cork and Two Derivative Products
Authors: Carmo Lança M. , Neagu Eugen R. , Silva Paulo C. , Gil Luís , Marat-Mendes José N.
Published: March 2009

Electrical properties of natural cork, commercial cork agglomerates (for floor and wall coverings) and a recently developed composite of cork/TetraPak® were studied. Measurements of isothermal charge and discharge currents were made for natural cork samples in different directions (axial, radial and tangential cuts). The isothermal current characteristics and the samples conductivity were investigated under different conditions (electric field, temperature and environmental conditions: in air at ambient relative humidity (RH), dry air and vacuum), also the
samples could be or not conditioned (dried in vacuum or in a P2O5 atmosphere at room temperature). From these results the influence of water on the electrical properties of natural cork could be seen. In order to compare the three different cork materials a preliminary study was made. Isothermal charge and discharge currents and conductivity after 1h charging were measured and compared for different electric fields and temperature in air at ambient RH.
Push-Pull Tricyanovinyl-Substituted Thienylpyrroles: Synthesis, Solvatochromic and Electrochemical Properties
Authors: Raposo M. Manuela M. , Sousa Ana M. R. C. , Fonseca António Maurício C. , Kirsch Gilbert
Published: March 2009

New tricyanovinyl- derivatives 1 of 1-(alkyl)aryl-2-(2´-thienyl)pyrroles 2 have been synthesized and characterized. Compounds 1 display dramatic reductions in both their optical and electrochemical band gaps in comparison to thienylpyrroles 2. The solvatochomic behavior of tricyanovinyl- derivatives 1 was investigated in a variety of solvents. In agreement with the solvatochromic and the electrochemical studies for push-pull derivatives 1 the new compounds prepared, can find application for manufacturing new materials with notable non-linear optical
properties.
Bone Tissue Engineering Constructs Based on Starch Scaffolds and Bone Marrow Cells Cultured in a Flow Perfusion Bioreactor
Authors: Gomes Manuela E. , Reis Rui L. , Mikos Antonious G.
Published: March 2009

This study aims to investigate the effect of culturing conditions (static and flow perfusion) on the proliferation and osteogenic differentiation of rat bone marrow (RBM) stromal cells seeded on two starch based three-dimensional scaffolds exhibiting distinct porous structures. For this purpose, it was selected: i) a scaffold based on SEVA-C (a blend of starch with ethylene vinyl alcohol) obtained
by extrusion with a blowing agent and ii) a scaffold based on SPCL (a blend of starch with polycaprolactone) obtained by a fiber bonding process.
The obtained results suggest that flow perfusion culture enhances the osteogenic differentiation of RBM cells and improves their distribution in 3-D starch-based scaffolds, by improving nutrients delivery in the interior of the scaffolds and simultaneously by stimulating the seeded cells by exposing
them to fluid shear forces. They also indicate that scaffold architecture and pore interconnectivity affect the homogeneity of the formed tissue.
Bioactive Composite Materials for Bone Tissue Applications
Authors: Leite Ferreira B.J.M. , Duarte M.G.G.M. , Gil M. Helena , Correia Rui N. , Román J. , Vallet-Regí Maria
Published: March 2009

Two materials with potential application in bone tissue repair have been developed: 1) a non-biodegradable composite based in a new methacrylic-co-acrylic matrix; and 2) a biodegradable composite based in a chitosan (Ch) matrix. Both matrices were reinforced with glass-ceramic particles of composition (mol%) 70 SiO2 – 30 CaO. The in vitro bioactivity of composites was assessed by soaking in simulated body fluid (SBF) for periods of up to 7 days at 37º C. X-ray
diffraction (XRD) and scanning electron microscopy coupled with X-ray energy dispersive spectroscopy (SEM-EDS) were used for deposit identification after different soaking periods. Calcium phosphate particulate deposits were detected after 3 days of immersion, followed by growth and maturation towards apatite.
Transport in Cathode of Lithium-Ion Cells
Authors: Hashim Ali Siti Aishah
Published: March 2009

A mathematical model for the transport in cathode of a lithium-ion cell is developed and
analytical solutions to the model equations are obtained. The derived equation is tested by fitting it
to published experimental discharge characteristics. Wherever possible, the values of the relevant
parameters are obtained from the same literature from which the discharge characteristics were
obtained. The agreement between the predicted and the experimental discharge curves are
measured statistically using t-test. Since the discharge characteristics are usually plotted as voltage
versus time or capacity or even state-of-discharge, hence the expression for the cell voltage has
been derived.
Application of Modified Power Law and Arrhenius Relationship in Studying Rheological Behavior of Bio-Oils
Authors: Wan Nik W.S. , Eng Giap S.G. , Masjuki H.H. , Senin H.B.
Published: March 2009

Tribological aspects of bio-oils have to be investigated before they are used as industrial
fluids. In this paper rheological (fluid deformation under shear) properties of four bio-oils are
presented. A Couette type viscometer was used to evaluate flow behavior of the oils at seven
discrete temperatures. Commercial coconut, canola, sunflower and corn oil were used in this study.
For all the oil samples, viscosities were affected by the change of shear rate and temperature. Two
rheological models, temperature dependence and shear rate dependence, were used in the study.
The original power law gives contradict picture of flow curves and flow parameters. Thus,
modified power law model was proposed. The modified model was fitted to experimental data to
obtain the flow behavior index. Arrhenius type equation was fitted to experimental data to obtain
the activation energy due to different temperatures and shear rates. Evaluation of rheological
properties by modified power law model indicates that these bio-oils belong to the pseudo-plastic
group.
A Chemical Sensor Based on AlGaN
Authors: Hudeish A.Y. , Tan C.K. , Aziz Azlan Abdul , Zainuriah Hassan
Published: March 2009

There is a particular interest in the development of wide band gap semiconductor gas
sensor because of their potential for high temperature operation and the ability to integrate them
with power or microwave electrodes or with UV solar-blind detector and emitters fabricated in the
same materials. AlGaN based devices are attractive for gas sensing in automotive exhausts and
flow-gas, because of strong spontaneous polarization of AlGaN (free carrier concentration profiles
inside this material that is very sensitive to any manipulation of surface change). In this report, we
characterized the Ni/AlGaN/Sapphire Schottky barriers as hydrogen gas sensor at temperature
range of 25°C to 500°C. A change in forward current was obtained in response to a change in
ambient from pure N2 to 2% H2/ 98% N2, higher than the change in forward current obtained in
Ni/GaN or Ni/Si Schottky diodes measured under the same conditions. The sensor response time
was independent on the rate of mass transport of gas into the test chamber, while at high
temperature, dissociation of gas controlled by the diffusion of atomic hydrogen through the
metal/AlGaN surface, increased the sensor response time.
The Nanoscience of Fullerenes
Authors: Sheka E.F.
Published: March 2009

A brief review of fascinating properties of fullerene is presented on the basis of the concept of effectively non-paired electrons. A versatile chemistry of fullerenes follows from the regioselectivity of their atoms and the uniqueness of donor-acceptor abilities. Computational synthesis of the fullerene derivatives is discussed. Applications of the basic concepts to medicinal applications of fullerenes as well as their magnetic properties and ability to form technomimetic species are considered.
Structural, Magnetic, and Electrical Characteristics of Metastable Iron Oxide Nano-Sized Powders
Authors: Vulićević Lj. , Ivanović N. , Maričić A. , Vučković A. , Popović N. , Vardić S.
Published: March 2009

Structural, magnetic and electrical properties of iron oxide nano-sized powders synthesised electrochemically under various conditions are presented. The influence of the temperature and current density of synthesis on particular powder characteristics is established. Possibilities for co-existence of various phases and their impact on powder properties, as well as feasible paths of phase relaxation and transition during non-isothermal heating are investigated, too. In this way, optimal procedures for the preparation and stabilisation of iron oxides nano-sized powders of different characteristics are evaluated.
Thermal, Dynamic Mechanical and Dielectric Behavior of Liquid-Crystalline Linear and Crosslinked Polyurethanes with Mesogenic Group in Side Chains
Authors: Ilavsky M. , Valentova H. , Sedlakova Z. , Nedbal J. , Velychko V.
Published: March 2009

This paper describes DSC, dielectric and dynamic mechanical behavior of linear and crosslinked liquid crystalline (LC) polyurethanes based on LC diols with a mesogenic group in the side chain, diisocyanates of various flexibility and two triols. From our investigations it follows: a) Linear polymers prepared from diols with simple end side chain substituents (as hydrogen, nitro and nitril group) exhibit only amorphous behavior regardless of the structure of used diisocyanate; generally, the most pronounced LC behavior exhibited polymers prepared from a diol with phenyl substituent. b) Investigation of the curing reaction showed that rheological power-law parameters, which are characteristic of the structure at the gel point, are dependent on the initial ratio of the reactants (amount of LC diol in EANCs). c) Strong physical interactions between the mesogens support the cyclization in the course of crosslinking reaction. d) Introduction of chemical junctions (amount of triols) suppresses LC ordering in the networks.
Chemical Oxidative Polymerization of 4-Amino-3-Hydroxynaphthalene-1-Sulfonic Acid and Its Salts
Authors: Ćirić-Marjanović G. , Marjanović B. , Juranić I. , Holler P. , Stejskal J. , Trchová M.
Published: March 2009

New functional homopolymeric, semiconducting materials soluble in polar solvents,
were synthesized by chemical oxidative polymerization of 4-amino-3-hydroxynaphthalene-1-
sulfonic acid (AHNSA) and its salts, using ammonium peroxydisulfate as an oxidant, in water at
room temperature. Polymerization products obtained from AHNSA, AHNSA hydrochloride,
AHNSA mono-sodium salt and AHNSA di-sodium salt were characterized by elemental analysis,
gel-permeation chromatography (GPC), infrared spectroscopy (IR) and conductivity measurements.
Polymers of AHNSA salts have increased weight-average molecular weights and polydispersity
index values, compared to AHNSA polymer. Molecular weights approach a maximum value of
~25200 for polymers of AHNSA salts. Elemental analysis data of polymeric samples show a
decrease of the S/C ratio for all polymeric materials in comparison with the monomer, indicating
considerable elimination of sulfonic acid group from the macromolecular structure during the
polymerization process. New substitution patterns shown by IR spectroscopic analysis combined
with MNDO-PM3 semi-empirical quantum mechanical calculations revealed N─C coupling
reactions as dominant, where C belongs to unsubstituted AHNSA ring. Coupling mode N─C1 is
also important. Naphthoquinonoid and benzenoid structures were observed by IR spectroscopy.
Influence of pH on the AHNSA oxidative chemical polymerization mechanism was examined.
Optical Study of Eu3+ Ion Embedded in (1-x)Na2WO4-xP2O5 Glasses Highlighting a Temperature Effect on its Local Environment
Authors: Antić-Fidančev E. , Viana Bruno , Aschehoug P. , Bih L. , Nadiri A. , Taibi M. , Aride J.
Published: March 2009

Tungsten-phosphate glasses doped with trivalent europium ion are synthesized and their spectroscopic properties are analyzed. Following the evolution of the 5D0 → 7F1 electronic transition in a series of various glass compositions via two rank crystal field parameters (cfp’s), a slight modification of the local symmetry is evidenced in the series. Decay lifetimes of 5D1 and 5D0 levels are also analyzed. Optical properties clearly correspond to Eu3+ in the glassy phase. At room as well as at liquid nitrogen temperatures, the emission spectra display comparable features with prominent 5D0 → 7F2 transition. However, at 77 K, the maximum 7F1 splitting exhibits an increase of ≈ 20-23 % for all compounds. This increase is directly connected to a change in local environment around the rare earth ion. The optical properties and the crystal field variation could be correlated with the shortness of the metal-oxygen distances produced by the pressure when cooling.
Synthesis, Structural and Luminescent Properties of Gd2O3-SiO2:Eu3+ Nanopowder Composites
Authors: Dramićanin M.D. , Jokanović V. , Andrić Z. , Viana Bruno , Aschehoug P. , Antić-Fidančev E.
Published: March 2009

In view of the improvement of luminescent intensity in classical phosphors, different new techniques of synthesis have been developed. One of them is the sol-gel technique for nanopowder synthesis. Applied to a binary system Gd2O3-SiO2 doped with trivalent europium ion, very fine powder form samples have been obtained. In that case the emission intensity of 5D0→F2 electronic transition of 4f6 configuration is greatly enhanced compared to the bulk oxide. The lifetime measurements are given too. The size of nanoparticles is of about 10 nm, determined by dynamic light scattering and XRD analysis.
XRD Analysis of Calcium Phosphate and Biocomposite Calcium Phosphate/Bioresorbable Polymer
Authors: Kandić Ljiljana , Mitrić M. , Ignjatović N.
Published: March 2009

Composite biomaterials based on calcium phosphate ceramic due to their high bioactivity are of interest for biological application and bone tissue repair. Structural and microstructural parameters of inorganic constituent of these materials are very important for the synthesis and characterization of composites. Quantitative and qualitative content, crystallite size of phases, as well as the degree of crystallinity have a great influence on the quality of composites, their application and bone tissue repair. X-ray diffractometry was employed to investigate the components of biocomposite materials, calcium phosphate (CaP) ceramic and poly-DL-lactide-coglycolide (DLPLG) polymer, as well as the biocomposite obtained from the mentioned components. Composite biomaterial was obtained by modified emulsion process. Using the Rietveld refinement, we analyzed CaP as an inorganic component of the composite, whence we have determined structural and microstructural properties of ceramic component of the investigated composite. The results obtained by structure refinement show that calcium phosphate ceramic materials synthesized at room temperature contain hydroxyapatite HAp as a predominant phase. The calculated Ca/P ratio is 1.667. The Rietveld analysis revealed lattice parameters a(Å)=9.4324(7) and c(Å)=6.8785(6) that are in agreement with the theoretical values.
Evaluation of Cytotoxic Activity of d-Metal Complexes with Hydrazone Ligands
Authors: Lazić M. , Radulović Siniša , Todorović Tamara R. , Sladić D.M. , Tešić Ž. , Andjelković K.K.
Published: March 2009

Cytotoxic activity of four series of coordinated complexes of Zn(II) and Fe(II) with hydrazone/hydrazide ligands against HeLa and B16 cells was evaluated. The ligands N’,N'2- bis[(1E)-1-(2-pyridyl)ethylidene]ethanedihydrazide (H2L1) and N’,N'2-bis[(1E)-1-(2-pyridyl) ethylidene]propanedihydrazide (H2L2) and their Zn(II) complexes showed IC50 values in the low micromolar range, while the other ligands and complexes were less active or inactive.
Microstructural Factors Affecting Fatigue Initiation in Various Al Based Bearing Alloys
Authors: Ali M.S. , Reed P.A.S. , Syngellakis S. , Moffat Andrew J. , Perrin Carl
Published: March 2009

Microscale fatigue damage mechanisms in various Al-Sn-Si based bearing alloys used as linings of plain
automotive bearings are reported. Extensive work on previously developed alloys has concluded that
secondary phase particles such as Sn and Si are potential fatigue initiation sites with a complex
combination of various particle geometry parameters. A newly developed alloy contains a number of
complex widely scattered intermetallics with much finer and fewer Sn and Si particles. This alloy system
appears to be more resistant to initiate microscale fatigue damage compared to the previous systems.
A Suitable Criterion for Precise Determination of Incipient Necking in Sheet Materials
Authors: Situ Q. , Jain Mukesh K. , Bruhis M.
Published: March 2009

Forming limit diagram (FLD) is a measure of the formability of a sheet material. The
major-minor strain pairs that are closest to the neck on multiple specimens of various strain paths
are utilized to construct a boundary between safe and unsafe zones. The challenge to obtain the
FLD is the determination of incipient necking. Three approaches to determine the limit strains have
been investigated and compared in this research in order to establish the optimal one for
implementation: (1) commonly used Bragard criterion ( 1)e Br with periodic grids; (2) tracking the
region of large local strains from strain history to locate the instance when critical major strain
( 1)e cr happens; (3) post-processing of strain history to locate the inflection in the major strain rate
curve 1 max (e&&) at the onset of localization. The last criterion of inflection in strain rate 1 max (e&&) carries
both a numerical and a physical meaning towards developing an understanding of flow localization,
formability and fracture.
Development of Aluminium Foam Processes and Products
Authors: Bryant J. Daniel , Wilhelmy Deborah , Kallivayalil Jacob , Wang Wei
Published: March 2009

Aluminum foams offer an attractive combination of attributes as engineering materials, such as low density, high rigidity, high energy absorption, and fire resistance. To date, however, metallic foams have achieved only a fraction of the market acceptance enjoyed by polymeric foams, owing largely to size limitations, poor uniformity and, above all, high unit costs. Methods utilizing casting (non-powder) metallurgy, while seemingly offering the potential of economies of scale, often suffer quality issues such as large cell sizes, poor uniformity and insufficient structural integrity. Many of these problems are associated with the rheology of the molten metal itself. While prior efforts to modify melt rheology through extrinsic additions of ceramic particles have been shown to be effective, the costly materials and processing paths used to create such suspensions have limited the economic attractiveness of such products. In this paper, aluminum foams produced through an alternative processing method will be described. The physical and mechanical properties in these fine (< 1 mm) celled aluminum foams will be related to their cellular structure and the properties of the aluminum alloy matrix from which they are produced.
Recently-Developed Aluminium Solutions for Aerospace Applications
Authors: Warner Timothy
Published: March 2009

Two principal approaches are available to materials’ engineers to improve the overall cost-weight balance of metallic airframe structures: improving alloy performance and optimising materials’ utilisation. Although both approaches have been successful in the past, they are most effective when applied concomitantly. The Aluminium industry has a long record of improving aerospace alloys’ performance. Nevertheless, even in apparently well-explored alloy systems such as the 7xxx family, products with improved damage tolerance-strength balances have recently been developed, thanks to an improved understanding of the optimum Zn-Mg-Cu combinations for the required property balances but also to developments in casting capability. Novel dispersoids and dispersoid combinations have enabled further improvements of the performance of existing alloy families. For example, appropriate Sc and Zr additions have a significant impact on the grain structure of 2xxx alloys and thus on performance. Another high potential approach for alloy performance improvements is the optimisation of Al-Cu-Li-(Mg-Ag-Zn) alloys. These so-called “third generation Al-Li alloys” were principally developed for military and space applications; in order to meet the demands of future commercial airframes, more damage tolerant variants are being developed. AA2198 and AA2050 are used to illustrate the potential of these higher damage tolerance Al-Cu-Li alloys. However, materials performance improvements are only part of the potential developments of metallic solutions for airframes. Further gains of a similar magnitude in component weight and cost can be achieved by applying new technologies and new design solutions to metallic structures. The future of metallic airframes will depend on the concomitant application of both these approaches.
Microstructures of Alumina-Aluminium/Magnesium Interpenetrating Composites
Authors: Higginson R.L. , Chang H. , Binner Jon
Published: March 2009

Interpenetrating composites allow a completely 3-dimensional matrix of two phases,
in this case an alumina (ceramic) and aluminium-magnesium alloy (metal), to be
developed. This 3-dimensionality yields a material with mechanical and physical
properties that are superior to either the metal or ceramic individually. The composites
were produced by heating an alumina foam and aluminium-magnesium alloys
together in flowing nitrogen to in excess of 900°C. At these temperatures the alloy is
drawn into the ceramic foam by capillary action. The infiltration process is dependent
on the interaction of the alloy with the nitrogen atmosphere in the furnaces. This
complex interaction and its affect on the microstructural development has been
studied using Electron Backscatter Diffraction (EBSD) coupled with Energy
Dispersive x-ray Spectroscopy (EDS).
Superplasticity in Coarse-Grained Al-Mg Alloys
Authors: Samuel Ehab , Jonas John J. , Samuel F.H. , MacEwen S.R.
Published: March 2009

Superplasticity refers to a high temperature deformation process involving a marked sensitivity of
the flow stress to the imposed strain rate, with resulting enhanced ductility. Although
conventionally associated with fine-grained materials, superplasticity has recently been observed in
coarse-grained alloys. The present research involves the deformation behavior of Al-Mg base
alloys, where superpure Al-3%Mg and Al-5%Mg, and commercial Al 5056 were selected for study.
The results for the Al-5%Mg and Al 5056 alloys are presented in this article. Flat sheet-type
samples were tensile tested to 10% strain at increasing temperatures and at prescribed strain rates
(0.001/s, 0.01/s, and 0.1/s). The dependence of flow stress on temperature was found to display
some unusual characteristics. This behavior is interpreted as resulting from the occurrence of
dynamic strain ageing (DSA). The aim of the overall study is to determine the relation between
DSA and superplasticity in coarse-grained Al-Mg alloys. This will, in turn, lead to the control of the
strain ageing behavior so as to produce the largest possible values of strain rate sensitivity (and,
hence, elongation).
Evolution and Control of 2219 Aluminium Microstructural Features through Electron Beam Freeform Fabrication
Authors: Taminger Karen M. , Hafley Robert A. , Domack Marcia S.
Published: March 2009

Electron beam freeform fabrication (EBF3) is a new layer-additive process that has been
developed for near-net shape fabrication of complex structures. EBF3 uses an electron beam to
create a molten pool on the surface of a substrate. Wire is fed into the molten pool and the part
translated with respect to the beam to build up a 3-dimensional structure one layer at a time. Unlike
many other freeform fabrication processes, the energy coupling of the electron beam is extremely
well suited to processing of aluminum alloys.
The layer-additive nature of the EBF3 process results in a tortuous thermal path producing
complex microstructures including: small homogeneous equiaxed grains; dendritic growth
contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the
deposits. Several process control variables contribute to the formation of these different
microstructures, including translation speed, wire feed rate, beam current and accelerating voltage.
In electron beam processing, higher accelerating voltages embed the energy deeper below the
surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a
low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum
alloy 2219 was processed over a range of different variables to explore the design space and
correlate the resultant microstructures with the processing parameters. This report is specifically
exploring the impact of accelerating voltage. Of particular interest is correlating energy to the
resultant material characteristics to determine the potential of achieving microstructural control
through precise management of the heat flux and cooling rates during deposition.
Physical Simulation of Longitudinal Weld Seam Formation in Aluminium Extrusions
Authors: Edwards S.P. , den Bakker Andrew J. , Zhou Jie , Katgerman Laurens
Published: March 2009

In the present study, a thermomechanical simulator (Gleeble 3500) was used to represent the solid–state bonding of aluminium in hollow dies during the extrusion of AA7020 alloy. The variations in strain, strain rate, temperature and pressure reflected those typically encountered during extrusion. The results showed that to form a good bond, strain was the most influential parameter, along with the time of deformation (bonding time). Temperature and pressure were found to be less influential within the parameter ranges investigated. On the basis of the results obtained, the ‘stretching’ of the interface has been proposed to be a critical parameter to quantify the solid–state bonding phenomenon.
Analysis of Hardness Maps on Aluminium Alloy Processed by ECAP
Authors: Leo Paola , Cerri Emanuela , McQueen H.J. , De Marco P.P.
Published: March 2009

Microhardness and hardness maps have been measured in different sections of samples processed by Equal Channel Angular Pressing (ECAP). In order to investigate the homogeneity of the hardening induced by ECAP as a function of deformation, the hardness maps have been based on samples deformed at different strains (after one and four passes). After one pass the specimen’s outer side, both on its cross and longitudinal planes, is less hard than all other zones. Moreover, after 4 passes via route Bc, the hardening induced on the sample cross section is lower at the surface than in the central area of the billet. The reduced hardness regions are compared to the distributions of plastic equivalent strain generated by finite element analysis.