bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Characterization of Pd-Black Films for Electrocatalysis
Authors: Oliveira Maria Cristina F.
Published: March 2009

Spontaneously-deposited Pd-black films were prepared on a Ni mesh. Characterization of the films morphology was performed by Scanning Electron Microscopy. Cyclic voltammetry in 0.1 M NaOH was used to characterize the voltammetric profile in the H-adsorption/absorption region. Contrasting to smooth Pd, the results revealed that the H-adsorption peak can be detected using this
electrode. It was found that the displacement metal reaction leads to codeposition of Ni during the Pd-black film preparation. The ability of these electrodes to be used on the electrohydrogenation of organic molecules was evaluated using 3-buten-1-ol as a test molecule. It was also analysed the stability of the electrodes upon reusing the same electrode in repetitive electrolysis. It was concluded that the films present a
very good catalytic activity to electrohydrogenation but show poor adherence to the substrate when are re-used.
Electrical Imaging Map on Polycrystalline Diamond Films and Diodes and Structural Relationship Obtained by Micro-Raman
Authors: Madaleno Joana Catarina , Pereira Luiz
Published: March 2009

In this work we present an equipotential surface map with a resolution higher than
100 nm, resulting from conductive atomic force microscopy (AFM). The images, obtained in polycrystalline MPCVD (Microwave Plasma Assisted Chemical Vapor Deposition) diamond devices, are clearly structure dependent. Diamond and non-diamond phases were identified by micro-Raman spectroscopy and correlated with the electrical conduction map. The application of the non-homogeneous contact theory lead to the extraction of two Schottky Barrier Heights (SBH),
one close to 0.6 V with dispersion ~ 0.1 V, attributed to the diamond / metal interface, and the other close to 0.4 V with dispersion ~ 0.04 V, due to the non-diamond phases / metal interface. The diamond / non-diamond phase ratio is about 85:15, taken from the micro-Raman spectra. Combining these results with the electrical conduction map, a general model to predict the macroscopic electrical behavior of polycrystalline diamond based devices is proposed.
Laser Developed Al-Cr Surface Alloys: Microstructure, Mechanical and Wear Behaviour
Authors: Almeida Amélia , Carvalho Patrícia Almeida , Vilar Rui
Published: March 2009

Surface alloys with composition ranging from 10 to 20% Cr were produced by laser
surface alloying. Their microstructure consists of faceted plate-like Al4Cr intermetallic compound particles dispersed in a matrix of α-Al solid solution. During remelting, heterogeneous nucleation of eutectic Al7Cr/α-Al occurred in the undercooled liquid ahead of the columnar solid-liquid interface, followed by equiaxial solidification, resulting in a microstructure formed of equiaxed cells. Al-Cr
alloys present Young’s modulus and hardness values that increase with increasing volume fraction of intermetallic compounds. Wear resistance, measured in dry sliding conditions, increases with increasing load due to the protective effect of a stable mechanically mixed layer that forms at the surface of the samples and the steel counterbody. Alloys formed of equiaxed eutectic cells provide better wear resistance than those formed of large plate-like particles since a thinner, more stable and harder mechanically mixed layer is formed, which offers best protection against wear.
Microstructural Characterization of 5083 Al Alloy Joints Friction Stir Welded
Authors: Reis Mónica , Louro Rui , Morais Paulo J. , Santos Leonel , Gouveia Helena
Published: March 2009

The Friction Stir Welding (FSW) process is a quite recent joining method whose
particular characteristics yield to materials modifications not yet fully understood. This paper aims to present the research results of a study focused on the modifications induced in an aluminium alloy AA5083 – H111, when processed by FSW to build components for structural applications. The welded samples were firstly analysed by optical microscopy in order to define the different joined zones and to identify defects. Further tests included the measurement of the Vickers
microhardness, grain and particle distribution and chemical analysis of the constituents, particularly of the intermetallic second phase particles, by Auger spectroscopy. Special attention has been given to the characterisation of several microstructural “non-homogeneities” like a laminated structure called onion ring and an identified anomaly (in the form of a line), whose presence was evaluated in
order to determine its effects on the final joint properties. The results have shown important new details about the relationship between the microstructure and
the final joint structural properties, contributing to improve the knowledge about the materials behaviour increasing the potential of utilization of the FSW process.
Comparative Study of the Additional Hardening Effects of Three Structural Steels
Authors: Reis Luís G. , Li Bin , de Freitas Manuel
Published: March 2009

For a safe and reliable design of components, it is needed to study the effects of
multiaxial loading and particularly the non-proportional loadings on the fatigue damage. The objective of this paper is to evaluate and compare the additional hardening effects of proportional and non-proportional loading paths. Low-cycle fatigue behaviour of three structural steels: CK45 (ferritic-perlitic microstructure) normalized steel, 42CrMo4 (bainitic microstructure) quenched and tempered steel and stainless steel (austenitic microstructure) X10CrNiS 18 9 are studied under
different proportional and non-proportional loading paths and different levels. A series of tests of biaxial low-cycle fatigue composed of tension/compression with static or cyclic torsion were carried out on a biaxial servo-hydraulic testing machine Instron 8088. The experiments showed that the three materials studied have very different additional hardening behaviour, under multiaxial cyclic loading paths. The local cyclic stress/strain states are influenced by the multiaxial loading paths due
to interactions between the normal stress and shear stress during cyclic plastic deformation. The microstructure is an important key and has a great influence on the additional hardening. The additional hardening effect is dependent of the loading path and also the intensity of the loading.
Texture and Evolution of Recrystallization in Low Carbon Steel Wire
Authors: Zidani Mosbah , Boumerzoug Zakaria , Baudin Thierry , Penelle Richard
Published: March 2009

The effect of cold wire drawing on texture of industrial low carbon steel wire was
investigated. On the other hand, the mechanism of recrystallization of drawn-wire was studied during different isothermal annealing below 723 °C. The structural evolution of wire was studied by optical microscopy, SEM, EBSD and X-Ray diffraction. From this study, a fiber texture was observed in deformed wire. However, a recrystallization reaction occurs after critical temperature
during annealing.
Residual Stress Evaluation on X 36 Cr Mo 17 HSM Finished Mould Steel
Authors: Nobre Joao P. , Batista António Castanhola , Capela Carlos , Gaspar Marcelo Calvete
Published: March 2009

The presented study was carried out in an industrial environment, using existing
equipments, tools and materials. A set of tests was performed based on production demands and restrictions, aiming to achieve the lowest surface roughness and beneficial residual stress state. The experimental test surfaces were obtained using high-speed milling (HSM) and precision surface grinding on a DIN X 36 CrMo 17 steel work piece, widely used in injection moulding industry. The grinded surface was considered as a reference surface in order to evaluate the high-speed milling
performance. For HSM tests, two types of tools were selected: tungsten carbide end mills with and without a TiAlN multilayer coating. The selected HSM main parameters ranged an upper, middle and lower limit value, considering the standard working values. The residual stress state at machined surfaces was evaluated by X-ray diffraction (XRD). Experimental results are discussed in order to achieve a procedure to select the optimal machining parameters that meet manufacturing
specifications.
Fatigue Properties of a Ck45 Steel Coated with a Post-Heat Treated Ni-Cu-P Electroless Deposit
Authors: Yazdani Sasan , Parvini-Ahmadi N. , Saeid Tohid
Published: March 2009

The Fatigue tests under rotating bending conditions have been conducted on samples of a quenched and tempered Ck45 steel in two different conditions: (a) uncoated, (b) coated with an electroless Ni-Cu-P deposit, followed by a post-heat treatment (PHT) at 673 K for 1 h. Such a deposit had a thickness of approximately 10µm, with Cu and P contents of 6wt.% and 13.7wt.%
respectively. The results indicate that plating the base steel with this kind of deposit leads to a reduction of the fatigue life of the material. The reduction in fatigue life has been quantified in terms of the Basquin parameters of the materials tested under different conditions. The microscopic observation of the fracture surfaces of the samples indicates that the reduction in fatigue life is associated with the nucleation of fatigue cracks on the coating-substrate interface and the deposit remains well adhered to substrate during fatigue testing since interfacial cracks have been very
rarely observed. It is therefore concluded that, in the present case, the interface acts as a surface crack source or surface notch, which decreases the fatigue life of the coated material by reducing the crack nucleation stage.
Transverse Rupture Strength of M3:2 High Speed Steel Produced through Conventional Casting and Powder Metallurgy Techniques
Authors: Araujo Filho Oscar O. , Liberati João Franklin , Monteiro Waldemar Alfredo , das Neves Mauricio David Martins , da Silva Luís Carlos Elias , Ambrozio Filho Francisco
Published: March 2009

The main aim of this work is to study the influence of the heat treatment on the
transverse rupture strength of three M3:2 high speed steel obtained by differents techniques. PM Sinter 23 obtained by hot isostatic pressing (HIP) of gas atomized powders, a vacuum sintered high speed steel obtained by uniaxial cold compaction and liquid phase sintering of M3:2 water atomized powders and a conventional (cast to ingot and hot work) VWM3C were submitted to hardening in
order to determine the influence of this treatment on the transverse rupture strength. The two PM high speed steels and the conventional one were submitted to heat treatment of hardening with austenitizing temperatures of 1140, 1160, 1180 and 1200 °C and tempering at 540 and 560 °C. The effectiveness of the heat treatment was determined by hardness tests (Rockwell C hardness). The microstructure was evaluated by scanning eletronic microscopy (SEM). At least five samples of
these three high speed steels were manufactured, austenitized, quenched and tempered as described above and fractured in three point bending tests in order to evaluate the influence of this treatment on the transverse rupture strength (TRS).
Magnesium Removal from TiC-TiB2 SHS-Powders by Controlled Hot Acid Leaching
Authors: Delmas Francisco , Gonçalves Lucinda , Martins Isabel M. , Oliveira Manuela
Published: March 2009

TiC and TiC–TiB2 powder mixtures obtained directly from titanium (TiO2) and boron (B2O3 or B4C) raw-materials by reduction with magnesium by self propagating high temperature synthesis (SHS) contain, as impurity, large quantities of MgO under its periclase form, together in some cases with unreacted magnesium. Several leaching agents, namely hydrochloric acid, sulphuric acid, acetic acid and EDTA were tested aiming at removal of magnesium from these
powders as required characteristic for further work. Several parameters as leachant concentration, pH, reaction time and temperature were evaluated. Alternative leaching methodologies were compared in order to achieve magnesium removal yields over 98% and minimising at the same time the expected high matrix losses due to TiC and/or TiB2 co-solubilisation. As main conclusion it was
established that strong hydrochloric acid (6M) is the most efficient medium to remove magnesium from these particular TiC-TiB2 SHS mixtures. The leaching methodology used (controlled hot acid leaching under close conditions) allowed to minimise TiC and TiB2 solubilisation losses. Sulphuric acid is not an effective leaching medium and contaminates the resulting powder mixture with unfriendly sulphur. Using acetic acid, magnesium removal yield is low and titanium losses are
considerable. On the other hand, low aggressive EDTA complexant leaves TiC-TiB2 matrix unalterable but residual MgO remains over 6%. The proposed process seems to have potential for application in the general field of semi-micro materials purification.
Role of Hydrogen Plasma on the Electrical and Optical Properties of Indium Zinc Transparent Conductive Oxide
Authors: Raniero Leandro , Gonçalves Alexandra , Pimentel Ana , Zhang Shibin , Ferreira Isabel , Vilarinho Paula M. , Fortunato Elvira , Martins Rodrigo
Published: March 2009

In this work we studied the influence of the power density of hydrogen plasma on
electrical and optical properties (Hall mobility, free carrier concentration, sheet resistance, optical transmittance and a.c. impedance) of indium zinc oxide films, aiming to determine their chemical stability. This is an important factor for the optimization of amorphous/nanocrystalline p-i-n hydrogenated silicon (a/nc-Si:H) solar cells, since they should remain chemically highly stable during the p layer deposition. To perform this work the transparent conductive oxide was exposed
to hydrogen plasma at substrate temperature of 473 K, 87 Pa of pressure and 20 sccm of hydrogen flow. The results achieved show that IZO films were reduced for all plasma conditions used, which leads mainly to a decrease on films transmittance. For the lowest power density used in the first minute of plasma exposition the transmittance of the IZO films decreases about 29%.
Intermetallic Hydrides Based on (Zr-Ti)(Fe-Cr)2 Type of Compounds
Authors: Makridis Sofoklis S. , Christodoulou C. , Konstantakou Mary , Steriotis Th.A. , Daniil M. , Ioannidou A. , Kikkinidis E.S. , Stubos Athanasios K.
Published: March 2009

In this work, the (Zr-Ti)(Fe-Cr)2 based compounds have been synthesized while charging-discharging hydrogen ability has been examined. Relatively low hydrogen pressure has been used for the hydrogenation of the samples. After following the discharging procedure, a high desorbed amount of hydrogen ~180 (ml of H2)/(gr of the alloy) has been measured on the first 15 min by using a volumetric device. The crystal structure has been analyzed by means of x-ray
diffraction (XRD) while a Rietveld analysis has been performed on the x-ray diffraction patterns and the characteristic MgZn2 type of structure has found to be the dominant phase in both compounds. The scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) have been used for microstructural studies and quantitative analysis, respectively. Magnetic
measurements have been performed on the samples and a paramagnetic behaviour has found to be at room temperature.
Thermal Cycling Treatment and Structural Changes in Cu-Al-Ni Monocrystalline Alloys
Authors: Silva Rui Jorge C. , Matlakhova L.A. , Pereira E.C. , Matlakhov A.N. , Monteiro Sérgio Neves , Rodríguez R.J.S.
Published: March 2009

In the present work a monocrystalline Cu-13.5Al-4Ni (wt.%) alloy with shape memory effect (SME) submitted to thermal cycling inside the critical range was investigated in terms of number of cycles and resulting structural changes. Attention was paid to the structural changes associated with reversible β1↔γ’1 martensite transformation. The monocrystalline Cu-Al-Ni alloy was produced in Russia, according to a specific technology. The structural characteristic of the
alloys was studied through optical microscopy and X-ray diffraction methods using Cu-Kα radiation. Differential scanning calorimetry permitted the determination of the temperature range as well as a thermal effect due to the β1↔γ’1 martensitic reversible transformations, before and after 100, 200 and 300 thermal cycles.
Laser Cutting of Glass Tubes
Authors: Coelho João M.P. , Alves D. Castro , Abreu Manuel A.
Published: March 2009

This work presents a technique for cutting glass tubes, without the need of pre-heating or any posterior action. Rotating the piece under a laser beam focused on the surface at the zone were it’s to be cut, stresses will not act, and while the material is dissociated at the laser beam irradiated volume, at its frontiers the glass reduces his viscosity allowing that the resulting faces become smoothed.
Laser Drilling of Natural Stones
Authors: Soto R. , Boutinguiza M. , Lusquiños F. , Pou Juan , Quintero F. , Pérez Amor Mariano
Published: March 2009

Following previous work focused on the laser processing of natural stones, we present in this paper the results of the study carried out to verify the feasibility of the lasers to drill slate tiles and granite slabs. The two types of laser equipments most used in the industry (CO2 and Nd:YAG) have been used to fulfil a comparative study. The influence of different parameters involved in the process, such as, average power, stand-off distance, and assist gas pressure, have been studied to
characterise the drilled holes size and geometry. Results from the different tests show that it is possible to obtain holes according to the required dimensions at reasonable powers ( i.e. no more than 400 W for the Nd:YAG and 1 kW for the CO2 laser). Holes up to 2 mm can be achieved in a very reduced time without breaking of the stone plates. The overall results show that the laser drilling technique could be an alternative to mechanical drilling of plates of natural stones to be used in ventilated façades or for roof fixation.
Characterisation of Elastoplastic Behaviour Using Spherical Indentation
Authors: Batista António Castanhola , Marinheiro José P. , Nobre Joao P. , Dias A. Morão
Published: March 2009

An inverse method for the characterisation of the elastoplastic behaviour of materials has been studied. The method is based on spherical indentation test data and numerical analysis of the indentation process, enabling to find a characteristic stress-strain curve. This method will be appropriate for elastoplastic behaviour study, mainly on surface hardened materials, when the standard methods cannot be applied. In this work, the method was applied to annealed and quenched steels, with homogeneous properties over the cross section. The obtained results are in
good agreement with those obtained from the standard tensile tests. However, if the material does not follow a linear hardening law, the elastoplastic characteristics determined by the inverse method will depend on the indentation depth. For these cases a method for the evaluation of the actual behaviour law has been improved.
In-Situ Friction Monitoring of Self-Mated CVD Diamond Coatings Using Acoustic Emission
Authors: Abreu C.S. , Oliveira Filipe J. , Gomes J.R. , Belmonte Manuel , Fernandes A.J.S. , Silva Rui F.
Published: March 2009

In-situ measurements of acoustic emission (AE) in self-mated tribological pairs of CVD diamond coated silicon nitride (Si3N4) were made with the purpose of investigating the relationship between AE signal and friction events. A good correlation is found between the energy dissipation/emission processes, therefore enabling the possibility of monitoring the different friction regimes occurring during the sliding contact of microcrystalline diamond (MCD) coatings. Deposition of MCD on flat and ball-shaped Si3N4 samples was accomplished using microwave
plasma assisted chemical vapour deposition (MPCVD) with H2/CH4 gas mixtures. The friction behaviour of self-mated MCD coatings was assessed using a reciprocating ball-on-flat geometry. The tests were run in ambient atmosphere without lubrication, the frequency (1Hz) and stroke (6mm) were kept constant while the applied normal load varied in the range 10-80N. The microstructure, surface topography and roughness of the MCD coatings were characterised by SEM and AFM techniques. The diamond quality was assessed from micro-Raman spectroscopy. The friction evolution was characterised by a short running-in period where the main feature is a sharp peak reaching values as high as approximately 0.6 followed by a steady-state regime with very low values in the range 0.03-0.04.
On the Evaluation of the Mechanical Behaviour of Structural Glass Elements
Authors: Costa Sandra , Miranda Micaela , Varum Humberto , Teixeira Dias Filipe
Published: March 2009

Glass can be considered to be a high-technology engineering material with a
multifunctional potential for structural applications. However, the conventional approach to the use of glass is often based only on its properties of transparency and isolation. It is thus highly appropriate and necessary to study the mechanical behaviour of this material and to develop adequate methods and models leading to its characterisation. It is evident that the great potential of growth for structural glass applications is an important opportunity of development for the glass
industry and the building/construction sectors. The work presented in this paper is a reflection of this conclusion. The authors shortly present the state-of-the-art on the application of glass as a structural element in building and construction, and refer to other potential fields of application and available glass materials. The experimental procedures and methods adopted in three-point bending tests performed on 500 × 100 [mm2] float, laminated and tempered glass specimens with thicknesses between 4 and 19 mm are thoroughly described. The authors evaluated the mechanical
strength and stiffness of glass for structural applications. This work contributes to a deeper knowledge of the properties of this material.
A Multi-Level Low Cycle Fatigue Damage Model for Forging Die Material
Authors: Gao S. , Werner Ewald
Published: March 2009

The forging die material, a high strength steel designated W513 is considered in this paper. A fatigue damage model, based on thermodynamics and continuum damage mechanics, is constructed in which both the previous damage and the loading sequence are considered. The unknown material parameters in the model are identified from low cycle fatigue tests. Damage evolution under multi-level fatigue loading is investigated. The results show that the fatigue life is closely related to the loading sequence. The fatigue life of the materials with low fatigue loading
first followed by high fatigue loading is longer than that for the reversed loading sequence.
Determination of Elastic Modules in Dependence on Orientation by the Resonant Beam Technique
Authors: Puchegger Stephan , Loidl Dieter , Peterlik Herwig , Kromp Karl
Published: March 2009

A novel procedure, based on the Resonant Beam Technique, and its application to
anisotropic composites is presented. The evaluation of the elastic modules of anisotropic materials from the measurement of the transverse eigenfrequency spectra of resonant beams is performed by a two step process: firstly the beams cut out from the test material in different directions are evaluated in-dependently of each other under the assumption, that they are isotropic, solving Timoshenko´s
equations using an isotropic correction factor for shear. Secondly the beams are evaluated together as representatives of one anisotropic material, using an anisotropic correction factor for shear. The equipment, developed for such measurements is presented. Finally, the procedure is applied to a transversely isotropic carbon fibre-reinforced carbon composite and the relevance of the results is discussed.
Transient Rheological Behaviour of PA6/EPM/EPM-g-MA Blends
Authors: Silva Jorge M. , Machado Ana Vera , Maia João M.
Published: March 2009

In this work the transient shear behaviour, in terms of both flow and stress relaxation, were measured for several blends of PA6/EPM/EPM-g-MA. The results indicate that there is a competition between slip at the interface due to the non-compatibility between the PA6 and the EPM and the action of the compatibilizer. In flow experiments, at low total strains it was observed that the behaviour is characteristic of immiscible polymer blends and gradually changes to that
typical of compatible blends. This suggests that initially the action of the compatibilizer (especially for low compatibilizer contents) is not enough to prevent the lower viscosity PA matrix from slipping around the high viscosity EPM droplets. However, as the droplets are deformed and oriented, the increase in interfacial area enhances the performance of the compatibilizer, thus resulting in a much better interaction between the two phases across the interface.
Novel Multilayer Coatings on Polyethylene for Acetabular Devices
Authors: Santos Veronica , Borges João Paulo , Ranito Cláudia M.S. , Pires Eduardo , Araújo Hugo F. , Marques António , Tomás Luís , Fortunato Elvira , Martins Rodrigo , Nunes Yuri
Published: March 2009

Total hip replacement is a common practice in every day clinical work. Artificial hip
implants consist of a femoral component and an acetabular component. Nowadays the acetabular component is composed of a polymeric cup and a metallic shell. This study focuses the development of an innovative acetabular component substituting the metallic shell by a multilayer coating on the acetabular cup. A titanium coating was deposited onto ultra-high molecular weight polyethylene (UHMWPE) samples by physical vapour deposition (PVD), having an in situ pretreatment with argon ion bombardment in order to optimize the adhesive strength by surface
modification, followed by the deposition of a thin film of hydroxyapatite (HA) using rf magnetron sputtering technique, at room temperature. Results obtained seem to indicate that these multilayer coatings can be a viable alternative to the metallic shell, leading to the substitution of a two part for a one part acetabular component.
The Influence of Material Density on Bipolar Charge Transport in Polymer-Based Electronic Applications
Authors: Ramos Marta M. D. , Correia Helena M.G. , Carmo Hugo
Published: March 2009

Using a mesoscopic modelling approach, the authors performed computer experiments to study the influence of polymer density on bipolar charge evolution through thin layers of polydiacetylene (PDA) exhibiting specific microstructures. We found that the competition between charge transport, trapping and recombination within the polymer layer leads to several general trends, some of them being non-intuitive, as one varies polymer density. Our results show that polymer density mainly affects current and recombination efficiencies in the absence of defects or
impurity states. The overall trends depend both on chain orientation relative to the electrodes and on the strength of the external applied electric field. These results suggest that adequate modelling of charge transport in electronic and optoelectronic devices based on conducting and semiconducting polymers, such as PDA, must include their structure and related key factors at mesoscopic scale. Such models provide the necessary knowledge-base to optimize the polymer film structure for
electronic applications.
Influence of Catalyst Type on Biocompatibility of Polyurethanes
Authors: Ryszkowska Joanna , Bil Monika , Woźniak Piotr , Lewandowska Małgorzata , Kurzydlowski Krzysztof Jan
Published: March 2009

Segmented polyurethanes (PUR) based on poly(ε-caprolactone)diol (PCL) as soft segments and cycloaliphatic diisocyanate were obtained. Two different types of catalysts were used for synthesis: dibutyltin dilaurate (DBTDL) and iron (III) acetylacetonate Fe(acac)3. Structure, thermal analysis, water absorption of obtained polyurethanes were studied. Polyurethanes catalyzed by Fe(acac)3 have lower glass transition temperature (Tg2) and melting temperature (Tm2) of hard domains in comparison with polyurethanes synthesized with DBTDL. Amount of absorbed water is in the range of 1,0-2,0% and is higher for PUR catalyzed by DBTDL. SEM observations show that type of catalyst used in synthesis affect structure of polyurethanes. Biological test XTT was done in order to determine influence of various metallic compounds used as catalyst on viability of human
bone cell culture. The XTT results indicate no influence on viability of human osteoblasts cultured on the obtained PUR.
The Influence of the Ambient Gas Environment on the Non-Isothermal DC Electric Measurements in Polymers
Authors: Marat-Mendes José N. , Neagu Eugen R.
Published: March 2009

The direct current (dc) electric measurements in dielectrics, especially for highly
insulating materials, are strongly influenced by the ambient air, mainly by the water vapors contained by the ambient (humid) air which determine a significant increase of the electric conductivity. Beside this, there is a second effect related to the interaction of the absorbed and adsorbed gas molecules with the polymer matrix that modify both the surface and the bulk conductivities. The aim of the paper is to present the influence of the absorbed and/or adsorbed gas molecules on the electric charge trapping and/or detrapping in polyamide 11. The measurements were carried out under ambient (humid) air, in a vacuum at 8 x 10-3 Torr and in dry nitrogen.
Because the trapping/detrapping processes and the molecule diffusion process in polymeric materials are slow processes, a variant of the thermally stimulated discharge current method, namely the final thermally stimulated discharge current method and the final isothermal discharge current method have been used in the temperature range from 20 to 190 0C. The absorbed/adsorbed gas molecules into polymer matrix results in a perturbation of the thermodynamic equilibrium and consequently a charge transfer could occur speeding up the deep level charge detrapping.
Biomorphic Silicon Carbide Ceramics Coated with Bioactive Glass for Medical Applications
Authors: Borrajo Jacinto P. , González Pio , Serra Julia , Liste Sara , Chiussi Stefano , León Betty , de Carlos Alejandro , Varela-Feria Francisco M. , Martínez-Fernández Julian , de Arellano-López António Ramirez
Published: March 2009

There is a need to develop new tough bioactive materials capable to withstand high loads when implanted in the body and with improved fixation, which led to the production of bioactive coatings on metallic substrates. A new approach, which consists of biomorphic silicon carbide (SiC) coated with bioactive glass, was recently presented. This new material joins the high mechanical strength, lightness and porosity of biomorphic SiC, and the bioactive properties of PLD glass films.
In this work, a multiple evaluation in terms of biocompatibility of this new material was carried out starting from the biomorphic SiC morphology and porosity, following with the bioactivity of the coatings in simulated body fluid, and ending with a deep biocompatibility study with MG-63 cells. Different ranges of porosity and pore size were offered by the biomorphic SiC depending on the starting wood. The PLD glassy coatings had a high bioactivity in vitro and both the biomorphic SiC coated and uncoated presented high levels of biocompatibility.
Scale-up of Poly[(Vinyl Chloride)-b-(n-Butyl Acrylate)-b-(Vinyl Chloride)] prepared by Living Radical Polymerization
Authors: Coelho Jorge F.J. , Alves Patricia , Monteiro Joana , Castro M. Margarida C.A. , Abreu Mariana , Gonçalves Pedro , Gil M. Helena
Published: March 2009

Vinyl Chloride (VCM) based copolymers were synthesised by using Living Radical
Polymerization. The obtained materials were characterized by determining their molecular weight,
glass transition temperature and mechanical properties after processing in industrial equipments.
Their chemical composition was evaluated by using NMR.
Study of the Fosfosal Controlled Permeation through Glutaraldehyde Crosslinked Chitosan Membranes
Authors: Silva Ricardo M.P. da , Mano João F. , Reis Rui L.
Published: March 2009

Fosfosal, a phosphate derivative of salicylic acid, which presents both analgesic and antiinflammatory properties, was used as a model drug to study the potential of recently developed chitosan membranes (with different crosslinking degrees) to be used as drug release rate-controlling membranes. The fosfosal permeation across these membranes was studied using an in-house built developed diffusion cell with online automatic monitoring. Experiments were performed using
phosphate buffer saline (PBS) solution at 37°C. Different flow properties of the detection set up were determined in order to estimate the errors introduced by the automatic online monitoring system. For increasing crosslinking degrees the permeability initially decreased, and then increased, likely as a consequence of the crosslinking influence on a variety of properties like crystallinity and
hydrophilicity that have opposite influence on permeability. In summary, it was possible to control the drug release profile by means of changing the degree of crosslinking of chitosan membranes and to follow the respective release kinetics by means of using the developed diffusion cell.
Enzymatic Degradation Behaviour of Starch Conjugated Phosphorylated Chitosan
Authors: Baran Erkan Turker , Jayakumar Rangasamy , Mano João F. , Reis Rui L.
Published: March 2009

Phosphorylated chitosan (P-chitosan) was synthesized by means of graft
copolymerization technique. The conjugate membranes were prepared from oxidised starch and Pchitosan using reductive alkylation crosslinking. The synthesized membranes were characterised by FT-IR. In order to characterize degradation behaviour of this conjugated system, the membranes were incubated in enzyme solutions of alpha-amylase and lysozyme as well as a physiological
saline solution (PBS) used as control solution. In PBS, low starch containing membranes (0.16-0.38 weight (starch)/weight (P-chitosan), (ws/wc)) and control membranes have not showed significant change in their weight during two months of incubation. High starch containing membranes (0.73-1.04
ws/wc) indicated less than 20 % weight loss after this period. After α-amylase incubation, a distinct degradation behaviour was observed from starch-P-chitosan membranes. The degradation of the conjugate membranes was found to be fast with increasing starch content. Weight losses between 20 to 55 % were detected for the lowest (0.16 ws/wc) starch and highest (1.04 ws/wc) starch containing membranes, respectively. In the lysozyme degradation study, the conjugate membranes were not degraded by enzymatic activity and the weights of membranes were seen to be increased about 20 % because of swelling. The control membranes showed gradual weight loss in enzyme solutions. These results indicated the lysozyme degradation of starch-free P-chitosan membranes and inhibition of degradation P-chitosan by highly conjugated starch molecules.
Microstructure of Solder Joint Interconnect in Used Mobile Phone
Authors: Shahdan Shahrul Nizam , Jalar Azman , Hamid Muhammad Azmi Abd
Published: March 2009

A tin-lead solder is generally used to mount an electronic package on to a printed circuit
board (PCB) of an electronic devices. In this study, we investigated the microstructure of the solder
joint from a four years old used mobile phone. Microstructure and morphology of the joint was
obtained using optical and scanning electron microscopy (OM and SEM) respectively. Cracks and
voids can clearly be seen in the solder area for the most of the sample observed. Crack up to 10 μm
wide appeared to be propagating along the solder line between Cu lead and Cu substrate. Energy
dispersive X-ray (EDX) analysis revealed that cracks occurred at the richer tin content. It was not
clear the exact mechanism that leads to the existence of the crack. However we believe that
thermomechanical cause such as thermal fatigue, void formation and the thicker layer of
intermetallic compound contributed to the failure of the solder joint.
Concentration Effects on n-GaN Schottky Diode Current-Voltage (i-v) Characteristics
Authors: Munir Tarriq , Aziz Azlan Abdul , Abdullah Mat Johar , Mahmoud Ahmed Naser
Published: March 2009

We focus on the epi layer carrier concentration variation effects to improve the current –
voltage (I-V) characteristics of an n-GaN schottky diode. The carrier concentration of 1×10 15cm-3,
1×1016 cm−3, 1×1017 cm−3 were employed. The simulated current was obtained by forward biasing
the device of up to 2Volt at room temperature using Pt electrode. The study was conducted by
using Atlas/Blaze using various models such as Consrh (Concentration Dependent Shockley Read
Hall), Cvt (Lombardi Model), Fermi (Fermi Dirac), Bgn (Bandgap Narrowing), Conmob
(Concentration Dependent Mobility), Auger (Auger). We found that as the concentration increases
the value of forward current also increase linearly when biased at maximum of 2 volts. The reverse
bias characteristics at the same concentration of the simulated diode up to 100Volt were also
determined. We found that at low carrier concentration the reverse leakage current is minimum and
breakdown voltage is maximum. As the carrier concentration increases there is a linear relationship
between reverse leakage current and epi layer doping carrier concentration. By analyzing the
forward and reverse characteristics we conclude that in forward bias for low carrier concentration
the diode shows schottky rectifying behavior while for higher carrier concentration the diode shows
ohmic behavior. For higher carrier concentration there is a linear relationship between carrier
concentration (n) and forward current. The reverse leakage current is minimum approaching an
ideal value at n≤1×1015cm-3 and breakdown voltage is maximum at these values of concentration.
Increasing the concentration from n≤1×1015cm-3 the value of reverse leakage current is approaching
to the maximum value as a result breakdown voltage decreases. We conclude that for n-GaN
schottky diode the ideal schottky rectifying behavior of I-V characteristics is obtained at carrier
concentration of n≤ 1×1015cm-3 for the simulated diodes at different carrier concentration.
Effects of Ho3+ Substitution on Ultrasonic Attenuation in Hoba2-xHoxCu3O7-δ Superconductors
Authors: Yahya Ahmad K. , Ishak A. , Hamadned I. , Abd-Shukor R.
Published: March 2009

Longitudinal and shear ultrasonic attenuation measurements were performed at 10
MHz in HoBa2-xHoxCu3O7-δ (x=0.0 and 0.15) polycrystalline ceramics between 80 K and 285
K. Longitudinal attenuation profiles showed a large peak around 200 K for superconducting
HoBa2Cu3O7-δ but not for oxygen-reduced non-superconducting HoBa2Cu3O7-δ. Two
longitudinal attenuation peaks at 190 K and 250 K were observed for Ba-substituted
HoBa1.85Ho0.15Cu3O7-δ. The high temperature (∼190 K-200 K) peaks are due to absorption of
sound energy during interaction of ultrasound wave with mobile oxygen atoms involved in an
oxygen rearrangement process involving Cu-O chains of the materials.
Optimization of InGaN Based Light Emitting Diodes
Authors: Zainal N. , Haslan Abu Hassan , Zainuriah Hassan , Hashim M. Roslan , Mahmoud Ahmed Naser
Published: March 2009

The performance of InGaN quantum well based Light Emitting Diodes; (LEDs) had been
numerically investigated by using standard industrial software, Silvaco. In this work, we found that
InGaN single quantum well (SQW) LEDs gives better performance than InGaN triple quantum
wells LEDs. The simulation results suggest that the inhomogeneity of electron and hole
distributions in quantum wells active region plays an important role in the LEDs performance. The
threshold current per μm also increases as the number of quantum well is increased.
Response Mechanism of Pd-GaN Schottky Barriers Comparative to Pd-Si Gas Sensors
Authors: Hudeish A.Y. , Tan C.K. , Aziz Azlan Abdul , Zainuriah Hassan
Published: March 2009

In this paper we report on the characteristics of Pd/GaN and Pd/Si Schottky barriers
exposed to different gases at various temperature range from 25°C to 500°C. The characteristics of
Pd/GaN and Pd/Si Schottky barriers as gas sensors were measured as a function of temperature and
ambient. Both types of sensor show changes in forward current upon introduction of different gases
(N2, air, H2) into the ambient. The devices can be operated at large forward current, leading to large
signal size for current at short response time for switching from one gas ambient to another such as
N2 to H2 (2%) in N2. The signal size increases with the increase in measurement temperature due to
more efficient cracking of the gas molecules. Both types of devices appear well suited to
combustion control and leak detection.
Structural, Electrical Properties and Magnetoresistive Effect in the (La1-xDyx)0.67Sr0.33MnO3 Compound
Authors: Lee O.J. , Halim S.A. , Lim K.P. , Talib Z.A. , Huda A. , Priscilla I.
Published: March 2009

The significant influences of substituting low concentration Dy at La- site for
La0.667Sr0.333MnO3 perovskites compounds in structural, electrical and magnetoresistance properties
have been studied. The polycrystalline samples (La1-xDyx)0.667Sr0.333MnO3 with x= 0.00, 0.02 and
0.10 were synthesized via conventional solid-state reaction in bulk. This work measured their
resistivity properties with (below 1 Tesla) and without the presence of magnetic field (0 Tesla) as a
function of temperature, microstructure and particle distribution and structural distortion using four
point probe resistivity technique, X- ray diffractometer (XRD) and Atomic Force Microscope
(AFM). The resistivity in applied magnetic field or so-called magnetoresistance ratio is defined as
MR% = (Ro – RH)/RH x 100 was measured at 90K, 100K, 150K, 200K, 250K, 270K and 300K.
The highest MR% values for x=0.00, 0.02 and 0.10 are 15.3%, 15.5% and 20.6% at 1 Tesla
respectively. The metal- insulator transition temperature, TMIT correspond to >300K, 298K and
230K of sample with x= 0.00, 0.02 and 0.10 respectively were observed from resistivitytemperature
(R-T) curve.
Immittance Studies of DBP Plasticized Salicylic Acid Doped PMMA Based Gel Electrolytes
Authors: Isa M.I.N. , Majid S.R. , Arof A.K.
Published: March 2009

A gel electrolyte system was prepared by dissolving poly(methyl methacrylate) in ethylene carbonate and propylene carbonate doped with salicylic acid and plasticized with dibutylphthalate (DBP). The gel was heated to 70 0C before it was cast into glass dishes. The composition of the electrolytes was 35 wt% EC, 30 wt% PC, 5 wt% SA, 5wt% DBP and 25 wt% PMMA. The gel electrolyte was sandwiched between two stainless-steel blocking electrodes and impedance measurements were conducted. The conductivity of the gel electrolyte was 2.03 x 10-4 S cm-1 at room temperature. The conductivity activation energy was obtained from the log σ versus 103/T graph. Loss tangent was calculated at every frequency for all temperatures. From the tan δ versus frequency plot, the activation energy of relaxation of the ion was calculated and plotted as ln τ versus 103/T. The conductivity activation energy value was (0.21 ± 0.04) eV and the activation energy of relaxation was (0.24±0.07) eV. The similarity between these activation energies imply that the protons ‘hop’ from one electronegative oxygen site in DBP to another.
Studies of the Dynamics of Thin Ion Exchange Films by Spectroscopic Ellipsometry and Attenuated Total Reflectance Spectroscopy
Authors: Pantelić N. , Piruska A. , Seliskar Carl J.
Published: March 2009

A chemically selective film, usually of optical quality, is a key component of optical and
electrochemical sensors. We have examined the dynamics of various thin selective films by
spectroscopic ellipsometry and attenuated total reflectance (ATR) spectroscopy. Spectroscopic
ellipsometry provided a non-invasive method for measurement of optical constants (n(λ), refractive
index; k(λ), extinction coefficient) and thicknesses of thin selective films which were conditioned in
time by solvent and penetrant mass transport. The methods we have developed allowed us to
characterize film dynamic response, stability, and chemically specific mass transport even to the
point of quantitatively modeling both transport and structural changes. The ATR spectra of thin,
highly absorbing films are distorted both by reflectance and interference phenomena. Enhanced
absorbance was observed under film leaky mode conditions.
Static and Fatigue Characterization of Sandwich Panels
Authors: Abbadi Ahmed , Azari Z. , Belouettar Salim , Gilgert J. , Pluvinage G.
Published: March 2009

Problems for load carrying elements reside mainly in buckling, embrittlement and corrosion. These problems can be mainly solved by introduction of composite materials of a sandwich type. These materials ally lightness, rigidity and resistance to the corrosion. For the design of a large number of applications, static and cyclic properties are necessary. In this paper, first static and fatigue tests on four points bending of four types sandwich panels have been performed. Load/displacement and S-N fatigue curves are presented and analysed. Fatigue failure and damage modes are observed with an electronic microscope and are discussed. Numerical simulation applied to the static tests is compared to the experimental results. The second is to address such fatigue behaviour by using a damage model and check it by experimentation. This fatigue damage model is based on stiffness degradation, which is used as a damage indicator. Four non-linear cumulative damage models derived from the chosen stiffness degradation equation are examined with assumption of linear Miner’s damage summation. Predicted results are compared with available experimental data.
A Study of Water Influence on Carbon Monoxide Adsorption and Oxidation on Nanocrystals of: γ-Fe2O3, Au/Fe2O3 and MnxZn1-xFe2O4
Authors: Dondur V. , Radić Nenad , Grbić Boško , Drofenik Miha
Published: March 2009

In this paper the adsorption and oxidation of CO on nanocrystalline Au/γ-Fe2O3, Au/α-
Fe2O3, γ-Fe2O3 and a series of mixed ferrite with MnxZn1-xFe2O4 composition are investigated. The
catalysts were prepared by co-precipitation method and characterized using X-ray diffraction
(XRPD), specific surface (BET), transition electron spectroscopy (TEM) and magnetization
measurements. A temperature programmed desorption (TPD) study of the water and CO interaction
with nanocrystalline adsorbents is presented. The catalytic activities towards CO oxidation
increased in the following order: γ-Fe2O3 < MnxZn1-xFe2O4 < Au/γ-Fe2O3 .
Creep of Al-Sc Microalloys with Rare-Earth Element Additions
Authors: Karnesky Richard A. , Seidman David N. , Dunand David C.
Published: March 2009

Cast and aged Al-Sc microalloys are creep-resistant to 300, due to the blocking of dislocations by nanosize, coherent Al3Sc (L12) precipitates. Rare-earth elements substitute for Sc in these precipitates, leading to a higher number density of smaller precipitates, which have a greater lattice-parameter mismatch with Al than in the Al-Sc binary microalloy. This leads to an improvement in both ambient temperature microhardness and high temperature creep. Creep threshold stresses of Al-Sc-RE (RE = Y, Dy, or Er) at 300 are higher than for Al-Sc and Al-Sc-M (M = Mg, Ti, or Zr) microalloys. This is in agreement with a dislocation climb model that includes the elastic stress fields of the precipitates.