bluuebunny/crossref_metadata_2025 huggingface dataset:
Standardized Investigation Methods of Self Compacting Concrete and Effect of Sand Content on Properties in Fresh State
Authors: Sugár Viktória , Takács Márton
Published: November 2012

Investigation methods of self-compacting concrete (SCC) in fresh state in virtue of the new Hungarian standard are summarized. The referenced testing methods of former technological guidance were finally replaced by the MSZ EN 12350:2010 standards, part 8, 9, 10, 11 and 12, however momentarily these are only available in English. Besides testing methods, the requirements of MSZ EN 206-9:2010 Additional rules for self-compacting concrete reference titled standard are precedent. Neither of the currently used and standardized testing methods is suitable for collective evaluation of each special feature of SCC, thus these should be used coinstantaneously. Results of recent research work regarding change of SCC features by adding different amount of sand aggregate are presented in this article, too.
Structural and Mechanical Properties of Milled Si3N4/CNTs Composites by Spark Plasma Sintering Method
Authors: Balázsi Csaba , Tapasztó Orsolya , Károly Zoltán , Kun Peter , Balázsi Katalin , Szépvölgyi János
Published: November 2012

Multiwall carbon nanotubes were dispersed with a concentration of 3wt% in silicon nitride ceramic host. A high efficiency attritor mill has been used for an effective dispersion of the filler phase in the matrix. In this work we have developed a spark plasma sintering process (SPS) suitable to consolidate and tailor the microstructure of CNT-reinforced silicon nitride-based ceramic composites. Mechanical measurements, micro-indentation investigations of the hardness and fracture toughness have been performed. Scanning electron microscopy has been involved in order to reveal the microstructure of the resulting composites.
Investigation of Mixing Processes of Polymer Composites
Authors: Dogossy G. , Sági E. , Ronkay Ferenc
Published: November 2012

Three ultrahigh molecular weight polyethylene (UHMWPE) composites of differing composition, reinforced with multiwalled carbon nanotubes (MWCNT) were prepared. The homogeneous distribution of MWCNT has been attempted by two dry blending methods and one melt-mixing process. The efficiency of the various methods was characterized by their effects on the quasi-static and dynamic physical properties of the composites. In the case of composites manufactured by ball milling the effects of various adhesion promoter additives (compatibilizers) has also been studied by analyzing the tensile, flexural, Charpy impact and wear properties of the composites.
Effects of the Cooling Rate on the Acoustic Properties of Pb-10Sn Solder
Authors: Harkai Endre , Hurtony Tamás , Gordon Péter
Published: November 2012

Microhardness and sound velocity were measured in case of differently prepared solder samples. The used Pb-10Sn solder samples were melted then cooled down applying different cooling rates. These procedures caused variant microstructure thus different microhardness and sound velocity values. The sound velocity was measured by means of scanning acoustic microscopy. Characterization of solder materials by acoustic microscopy gives the possibility to non-destructively estimate mechanical and reliability parameters of the given material.
Surface Modification of PDMS Based Microfluidic Systems by Tensides
Authors: Holczer E. , Fekete Z. , Fürjes P.
Published: November 2012

The material aspects of a polymer based microfluidic structure were characterised considering the compatibility of the system with bioanalytical applications. The polydimethylsiloxane (PDMS) based channel system is to be integrated in a full polymer photonic biosensor device developed within the European Union project P3SENS (FP7-ICT4-248304).
This work is intended to define a modified material composition, which is appropriate to improve both the wettability and the non-specific protein binding characteristics of the PDMS significantly. Triton X-100 (Sigma-Aldrich) surfactant was added to the raw PDMS before polymerisation. The influence of the tenside was studied considering the polymerisation reaction, the surface characteristics and the functional applicability. To test the hydrodynamic behaviour and non-specific protein adsorption on the surfaces, phosphate buffered saline (PBS) solution and fluorescent labelled human serum albumin (HSA) was applied in a microfluidic capillary system.
Microstructure Comparison of Soldered Joints Using Electrochemical Selective Etching
Authors: Hurtony Tamás , Bonyár Attila , Gordon Péter
Published: November 2012

The microstructure of the commonly used SnAgCu (SAC) lead free solder alloy was investigated. SAC solder bumps were soldered by two different soldering techniques (Vapor Phase Soldering (VPS), Laser reflow). Since the soldering profile of the VPS method is considerably different from the temperature profile of the laser reflow soldering, the created microstructures are expected to be diverse. Selective electrochemical etching was applied on cross sectional samples in order to extract the tin from the cross sectioning plane. In this manner the spatial structure of Cu6Sn5 and the Ag3Sn intermetllic compounds (IMCs) was highlighted. The microstructures of the samples were analyzed with optical microscopy and Scanning Electron Microscope (SEM) on cross-section samples. The composing elements were identified by SEM-EDS.
Glass Forming Ability of Bulk Amorphous Materials in Cu-Zr-Ag Ternary Alloy Systems
Authors: Janovszky Dóra , Tranta F. , Sólyom J. , Roósz A.
Published: November 2012

The glass forming ability (GFA) of the Cu-Zr-Ag alloy system was investigated on the basis of the thermal stability, and the structural, thermodynamic and kinetic properties of the material. We changed the concentration of the alloys, as we departed from the Cu58Zr42 composition and produced three different eutectic points in the Cu-Zr-Ag ternary system, in accordance with the results published in the respective literature. We produced various test pieces of Cu-Zr-Ag amorphous alloys with different Ag contents (0-70%), by casting the material into wedge-shaped copper moulds. In such ternary alloy system there is only a limited concentration range where amorphous materials can be produced: in the event that the Ag content of the material exceeds 35 at%, no amorphous material structure will develop. In our experiment the maximum temperature range of the supercooled liquid region (ΔTx) was 75 K. The calculated four GFA parameter values are not in perfect harmony and fail to point out the optimal composition available; however, based on γ and the reciprocal value of ω, the best compositions from the GFA aspect are Cu42.5Zr37.5Ag20 and Cu40Zr37.5Ag22.5. The decrease of the maximum thickness of the bulk metallic glasses is influenced more by the oxygen content than the composition changes within the Cu-Zr-Ag system.
Evaluation of XRD Analysis of Amorphous Alloys
Authors: Kőrösy G. , Tomolya Kinga , Janovszky Dóra , Sólyom Jenő
Published: November 2012

There is an active research work in the field of amorphous alloys since the discovery of metallic glasses, half a century ago [. In contrast with crystalline alloys, amorphous one have unique material properties, e.g. high yield strength, superior elastic limit, high corrosion resistance, unique acoustical properties [2,. Producing amorphous alloys, it is first necessary to quantify the forming of structure and define the amorphous amount. All of the methods to determine the structure have advantages and disadvantages. An accurate determination of amorphous volume fraction can be accomplished by transmission electron microscopy (TEM), this observation is much localized [ and the evaluation is difficult. The most common techniques to determine the amorphous fraction are XRD and DSC methods, which reflect the entire sample [. However, XRD has a detection limit depending on the type of equipment. Apart from this fact, it is an admitted method in researches, if the XRD reflexion shows an amorphous halo. Amorphous fraction transformed to crystalline can be measured by DSC. This method is much sensitive to impurities, especially oxygen, which can influence on the results.
Observer Based Leakage Detection of Hydraulic Cylinder Applied in Rolling Mills Electro-Hydraulic Gap Adjustment System
Authors: Kővári Attila
Published: November 2012

Hydraulic system is commonly used in the modern strip rolling mills to adjust the gap between the work rolls. Automatic gauge control based on the hydraulic systems is commonly used in modern strip rolling mills to adjust the gap between work rolls. The dynamic control of rolling gap and force is achieved by using electro-hydraulic servo actuators so-called hydraulic capsules which can adjust the rolling gap dynamically for high rolling force. The basic aim of the paper is to define an observer which could forecast the required maintenance of hydraulic cylinder using parameter estimation of the mill model.
Advanced Hetero-Modulus and Hetero-Viscous Complex Materials
Authors: Gömze László A. , Gömze Ludmila N.
Published: November 2012

To obtain advance hetero-modulus and hetero-viscous complex materials with extreme high dynamic strength, wear and thermal shock resistances a novel approach was applied by the authors. The developed new hetero-modulus and hetero-viscous composites were reinforced with nanoparticles and submicron fibers and whiskers of Si2ON2, SiAlON, AlN, Si3N4 as well as with special additives, which had turned into amorphous phases during sintering. These types of materials have several Youngs modulus and viscosities simultaneously and have high damage tolerance and ability to absorb and dissipate the elastic energy during crack propagation. Understanding the energy engorgement of high speed collision processes, the material structures and rheological properties of such a complex hetero-modulus and hetero-viscous material the authors could mathematically describe the mechanical shear stresses in these complex materials.
Analytical methods applied in this research were scanning electron microscopy (SEM), X-ray diffraction, and energy dispersive spectrometry, digital image analysis was applied to microscopy results, to enhance the results of transformations.
Evaluation Methods of Antimicrobial Activity of Plastics
Authors: Kun Eva , Marossy Kalman
Published: November 2012

There are several methods to evaluate the antimicrobial efficiency of the plastics. In recent work we intended to collect these methods together and compare. There are some methods, which are basically used in the microbial practice for testing antibiotics, and give a good ground for testing other materials. Some other simple methods exist, which can also be used, so the contact between the sample and the inoculums can be solved in many ways.
Investigation of the Microstructure of Al/SiC(Ni)p Composites
Authors: Pázmán Judit , Mádai Viktor , Tóth József , Gácsi Zoltán
Published: November 2012

Al/SiC composites are used especially in automotive and aerospace industry due to the numerous advantageous mechanical properties. These end-products can be produced by casting or powder metallurgical techniques. High strength with high toughness can be reached only by perfect interfacial bonds between the matrix and reinforcing phase. To improve the interfacial bond, one of the methods is the surface coating of the SiC particles. But the metal layer of the reinforcing phase reacts with the matrix due to the high sintering temperature and long sintering time. In our research work the formation of Al-Ni intermetallic phase was investigated by Scanning electron microscopy (SEM) and X-ray diffraction measurements (XRD).
Effect of Processing Conditions on Microstructure and Mechanical Behaviour of Metals Sintered from Nanopowders
Authors: Gubicza Jenő , Dirras Guy , Ramtani Salah
Published: November 2012

The influence of the consolidation conditions on the microstructure and plastic behavior of ultrafine-grained Ni and Al sintered from nanopowders was studied. It was found that the smaller initial Ni powder particle size yielded a smaller grain size and a larger oxide content in the as-consolidated sample resulting in a higher strength and lower ductility. When the Ni nanopowder was in contact with air (instead of an inert atmosphere) during the short handling time before sintering, the oxide content increased without a considerable change of the grain size that also decreased the ductility. The reduced time and temperature in Spark Plasma Sintering compared to Hot Isostatic Pressing led to a smaller grain size that resulted in a higher strength of Ni. In the case of an Al nanopowder processed by Hot Isostatic Pressing at 450 °C, the consolidation was hindered by the strongly limited diffusion due to the presence of a rigid amorphous layer on the surface of particles. However, at the sintering temperature of 550 °C, the crystallization and the fragmentation of the layer occurred that yielded a better densification.
Preparation and Study of Li6Y(Bo3)3 and Li6Gd (Bo3)3 Double Borates
Authors: Tichy-Rács É. , Péter Á. , Horváth V. , Polgár K. , Lengyel K. , Kovács L.
Published: November 2012

Li6Y(BO3)3 and Li6Gd (BO3)3 powders were synthesized using wet chemical method. Lithium-nitrate, yttrium-/gadolinium-nitrate and boric acid solutions were mixed in stoichiometric composition, and a colloidal precipitate was obtained by adjusting the pH of the mixture. Li6Y(BO3)3/Li6Gd (BO3)3 phase formation was achieved by annealing the precursors in the 650700 °C temperature range. The reaction steps were monitored by FTIR and Raman-spectroscopy, and the final products were characterized by X-ray powder diffraction and scanning electron microscope. XRD assessment shows that we obtained LYBO/LGBO as dominant phases after a 24 h treatment at 650 °C.
Design of Trussed Steel Towers According to the Eurocodes
Authors: Tomka Pál , Katula Levente , Bagi István
Published: November 2012

The paper deals with the towers of electric high voltage overhead lines. The target is a relatively simple suspension tower (tension support) made of hot rolled angles. The main aspects of structural design and the structural details are given due to the newly introduced design codes and the former Hungarian ones. The fundamental aim of the paper is to point out the changes according to the new developments. As an important design aid, a set of interactive programs developed by the authors is also shortly introduced.
Complex Study of H-Induced Structural Rearrangements in FeZr Glasses
Authors: Vehovszky Balázs , Kamasa Pável , Kováč Jozef , Fogarassy Zsolt
Published: November 2012

Microstructural changes and relaxation processes were examined in Fe-Zr based rapidly solidified samples. These phenomena occur far below crystallization temperature in the course of heat treatment, or even at room temperature, induced by absorbed hydrogen.
Examination of the Microstructure of the Findings from Cannon Foundry Sárospatak
Authors: Ringer István , Barkóczy Péter , Kovács Árpád , Pásztor Lilla
Published: November 2012

The Rákóczi Museum of the Hungarian National Museum revealed a cannon casting foundry in the territory of the castle of Sárospatak. The excavation started in the summer of 2006. A great amount of findings were revealed from the metallurgical, alloying and casting processes of the foundry. The Archeometallurgical Research Group of the University of Miskolc examines the microstructure and the chemical composition of these findings. The aim of this research work is to complete the knowledge of the contemporary literature and reconstruct the technological processes of the foundry. In this article the current status of the examination is introduced.
Ni-S(uper)O(xide)D(ismutase) Inspired Ni(II)-Amino Acid Complexes Covalently Grafted onto Merrifield’s Resin - Synthesis, Structure and Catalytic Activity
Authors: Csendes Zita , Kiss Janos T. , Kutus Bence , Sipos Pal , Pálinkó Istvan
Published: November 2012

In this work the syntheses of covalently grafted Ni(II)-complexes formed with various N- or C-protected amino acid ligands (L-histidine, L-tyrosine, L-cysteine and L-cystine) inspired by the active site of the Ni-SOD enzyme are presented. Merrifield’s resin was used as support to mimic the proteomic skeleton of the enzyme. Conditions of the syntheses were altered and the structural features of the substances obtained were studied by infrared spectroscopy. It was found that the preparation of covalently anchored Ni(II)−amino acid complexes was successful in all cases. In many cases the structures of the anchored complexes and the coordinating groups substantially varied upon changing the conditions of the syntheses. The obtained materials were studied by energy dispersive X-ray fluorescence coupled to scanning electron microscope (SEM−EDX). All the covalently anchored materials displayed superoxide dismutase (SOD) activity and some proved to be exceptionally efficient in the biochemical test reaction.
Fabrication of La-Doped Bi4Ti3O12 Ceramics
Authors: Lisińska-Czekaj Agata , Bernard Henryk , Osinska Katarzyna , Dzik Jolanta , Czekaj Dionizy
Published: November 2012

La-modified Bi4Ti3O12 is a typical ferroelectric, piezoelectric and electro-optic material, having relatively low coercive field, low dielectric constant, high Curie temperature and high breakdown strength. Goal of the present research was to apply mixed oxide method for fabrication of BiTLax ceramics, study its chemical composition, crystalline structure and microstructure. The compound BiTLax for x=0, 0.25, 0.5, 0.75 ceramic powders were prepared from mixture of oxides by a solid state reaction at T=1000°C for t=3h. Ceramic powders of BiTLax were next press and the compacts were sintered by the free sintering at temperature T=1000°C with the soaking time t=2h. A crystal structure Bi-layered structured of ferroelectrics was confirmed by a X-ray diffraction. It was found that La-doped BiT ceramics sintered at T=1000°C adopted the monoclinic symmetry. Influence of La-doping on chemical composition and microstructure of BiTLa ceramics was studied by scanning electron microscopy HITACHI S-4700 and energy dispersion spectroscopy.
Optic and Piezoelectric Coupling in the Sol-Gel PLZT Electroceramics
Authors: Kozielski Lucjan , Plonska Malgorzata
Published: November 2012

PZT ceramic system with presence of La contents, have been proposed and prepared using sol gel sintering method for practical application of photostriction, which is the superposition of photovoltaic and piezoelectric effects. Such a ceramics produced by conventional mixing oxide method does not exhibit photostrictive properties due to the defects and inhomogeneous distribution of grains and pores. In this study, an investigated lanthanium(III) doped PZT ceramics were obtained by sol-gel technique from the organometallic precursors. It was found that fabricated material were effective in the enhancement of photovoltaic and photostrictive properties. Consequently, lanthanium influence deviation of piezoelectric parameters were studied as a function UV light illumination. For the determination lighting dependancy of the transformation parameters the resonant and antiresonant method was implemented. The improved Piezoelectric Transformer structure successfully changed gain characteristics proportionally to light intensity. The authors invention of a light driven output gain adjustment in Piezoelectric Transformers (PT) yields a novel “smart” multifunctional wireless device. This new created application area can be utilized in self-adopting shutters in photo cameras due to improved sensitivity to surrounding illumination conditions.
Phase and Microstructural Characterization of Lime-MK Blended Mixes
Authors: Gameiro André , Silva António Santos , Veiga R. , Velosa Ana
Published: November 2012

Metakaolin (MK) is nowadays a well-known pozzolanic material used in cement-based materials. Its benefits are related to its great pozzolanic reactivity when compared with some others pozzolanic materials, like fly ash or ground-granulated blast furnace slag. When MK reacts with calcium hydroxide, cementitious products are formed. It is known that the main phases produced during its pozzolanic reaction at ambient temperature are calcium silicate hydrates (CSH), stratlingite (C2ASH8) and calcium aluminate hydrate (C4AH13). However, in literature there are several discrepancies regarding these phases stability, namely the transformation of stratlingite and C4AH13 into hydrogarnet (C3AH6) at long term. The consequences of that instability are a reduction in the porosity and a loss of microstructural strength that can induce a complete material degradation. The MK is a material with great potential in Portugal, since there is a large abundance of kaolinitic clays, however its development is not yet achieved. In order to answer this demand a research project was initiated with the aim of optimizing the production of MK in Portugal and enhancing the durability of aerial calcitic lime mortars, to be mainly used in conservation and restoration of historical buildings. With the objective of studying the compounds formed in lime/MK and their stability during time, we have prepared different lime/MK ratio pastes (molar ratios). These lime/MK pastes were stored at saturated conditions (RH > 95%) and 23 ± 2 °C temperature being analysed at several ages by TGA-DTA, XRD and SEM-EDS. In this paper the results obtained are presented and discussed.
Synthesising Carbo-Nitrides of some D-Group Transition Metals Using a Solar Furnace at PSA
Authors: Shohoji Nobumitsu , Oliveira Fernando A. Costa , Rosa Luis Guerra , Fernandes José Cruz , Magalhães Teresa , Coelho Manuel Caldeira , Rodríguez José , Cañadas Inmaculada , Ramos Carlos , Martínez Diego
Published: November 2012

Carbo-nitride synthesis was undertaken using a solar furnace at PSA in flowing N2/Ar gas mixture under total pressure 1 atm and processing temperature T = 1600°C for some d-group transition elements (Ti; Zr, V, Nb, Mo, W) starting from 1.5G/M (graphite/metal powder mixture with mole ratio 1.5:1) compact to ensure co-presence of free carbon with the reaction product. Clear X-ray diffraction (XRD) evidence of formation of carbo-nitride was detected for Ti (IVa group metal) showing higher N content in the carbo-nitride synthesised in N2 gas environment at partial pressure p(N2) = 1 atm than that at p(N2) = 0.5 atm. For M = V and Nb (Va group metals), formation of mono-carbide MC single-phase was detected in the N2 environment showing no evidence of formation of carbo-nitride in spite of presence of N2 in the environment. For M = Mo and W (VIa group metals), formation of higher carbide, among several options of carbide phases, appeared to be promoted in the N2 gas environment although, like in cases with the Va group metals, no evidence of dissolution of N into the reaction product was detected. As such, at T = 1600°C in N2 gas environment up to p(N2) = 1 atm under concentrated solar beam, carbo-nitride formed from the 1.5G/M mixture only for IVa group metal (Ti) but not for Va and VIa group metals. Anyway, it seemed certain that N2 gas affected somehow the reaction path between G and M to yield the carbide phase for M = V, Nb, Mo and W.
Thermoelectric Power of Gd4(Co-A)3 Compounds (A = Cu, Pt)
Authors: Seixas Teresa M. , da Silva Manuel A. Salgueiro , Braun Hans F. , Eska Georg
Published: November 2012

We report on a comparative study of thermoelectric power measurements (S(T)) in ferrimagnetic Gd4(Co1-xAx)3 compounds with A = Cu, Pt, in the temperature range 8 K – 300 K. Whereas in Gd4Co3S(T) is always negative, for x > 0 the substitution of Co for Cu/Pt gives rise to the appearance of a low temperature positive maximum in S(T) at around 30 K. Based on our previous study of Gd4(Co1-xCux)3 compounds, we argue that this maximum in S(T) originates from electron-magnon scattering and is sensitive to electron band structure changes resulting from the substitution of Co for Cu/Pt and the accompanying reduction in the ratio between the electron-magnon and the electron-phonon scattering strengths. The decreasing role of Co 3d electrons with the progressive substitution of Co for Cu/Pt, evidenced by a strong reduction in the spin disorder resistivity and the Co magnetic moment, is seen to be crucial for the existence of such low temperature maximum in S(T) for x > 0. It is seen that the substitution of Co for Pt leads to higher values of the amplitude and temperature of the positive maximum in S(T) than the substitution of Co for Cu.
XRD, SEM and Petrologic Characterization of a L4-L5 Ordinary Chondrite Meteorite
Authors: Seixas Teresa M. , Almeida Bruno , Mendes Maria H. , da Silva Manuel A. Salgueiro , Santos José F. , Almeida Fernando , Diogo Zenaida , Lopes Augusto B. , Vieira Joaquim M.
Published: November 2012

In this work, a meteorite sample recovered in Morocco is characterized by detailed petrographic observations in transmitted and reflected light optical microscopy and by using XRD and SEM and it is tentatively classified. VIS/NIR spectral analysis of the same meteorite in a previous study suggested that it is seemingly related to the HAMLET meteorite, which was classified as LL4 chondrite. From the obtained results in the refinement of the analysis of the present study, this meteorite is classified as L4 to L5 chondrite. Composition maps across selected chondrules and in the matrix are presented.
Composite Thin Film Obtained Using Tetraethoxysilane and Aimed at VOCs Detection
Authors: Hernandez Leonardo F. , Lima Roberto R. , Pecoraro Edson , Rosim-Fachini Esteban , da Silva Maria L.P.
Published: November 2012

The aim of this work was production of tetraethoxysilane (TEOS) plasma polymerized thin films and optimization of their physical-chemical characteristic for sensor development. The films were analyzed using several techniques. It was possible to produce composites (graphite clusters imbibed by silicon oxide film) made from only one reactant (TEOS). Deposition rate can vary significantly, reaching a maximum of 30 nm/min; cluster formation and their size widely depending on deposition parameters. The film surface was hydrophobic but can be wetted by organic compounds, probably due to carbon radicals. These films are good candidates for sensor development.
Effect of Oxide Stabilizers and Surface Metallization on the Wetting Behaviour of Silver Based Brazing Alloys onto Zirconia Substrates for Oil Well Drill Bits Application
Authors: Pereira Jorge Carlos , Santos Poliana Rochele , Silva João Moreno , Nascimento Rubens Maribondo , Martinelli Antonio Eduardo
Published: November 2012

Tricone drill bits with hard ceramic inserts are often used in oil well drilling operations. However, the cutting action and breakdown of the rock formation produces failures on the tricone bits, which mainly are related to wear, partial or total rupture of the drill bit body or ceramic inserts, thermal shock, and corrosion. Brazing is a well established technique to joint metal-metal, ceramic-ceramic and ceramic-metal materials. Wetting phenomena plays an essential role in the production of metal/ceramic interfaces if a liquid phase is present. Stabilized zirconia with yttria and magnesia can be an interesting material for hard ceramic inserts application on drill bits when oil well or the drilling fluid has acid characteristics. In this work, silver based brazing alloys were melted onto zirconia substrates under high vacuum. The effect of oxide stabilizers and the metallized surface on the wetting behaviour were studied. Better results were found for the yttria stabilized zirconia system using AgCu with 3% Ti as filler alloy.
Influence of Substrate Temperature and Post-Annealing Treatment on the Microstructure and Electric Properties of ZnO:Al Thin Films Deposited by Sputtering
Authors: Garcia Cibeli B. , Ariza Edith , Tavares Carlos J.
Published: November 2012

In this work, it is reported the characterization of the microstructure and electric properties of ZnO:Al thin films produced by magnetron sputtering. An AZOY sputtering target (98 wt% ZnO + 2 wt% Al2O3) was used as source material. The microstructure, optical and electrical properties of ZnO:Al thin films were investigated and correlated with substrate deposition temperature and post-annealing temperature. It is demonstrated that the microstructural, electrical and optical properties of the as-deposited thin films are dependent on the substrate temperature. The crystalline texture of ZnO:Al was improved with temperature deposition as shown in the EBSD analysis and X-ray diffraction. ZnO:Al thin film deposited at 250 °C exhibited very good electrical conductivity, as high as 200 S.cm-1 with an activation energy of 5.4 meV. As substrate temperature or heat treatment temperature is increased there is an apparent blue-shift on the absorption edge of the transmittance spectra, which can be explained by the Burnstein-Moss effect.
Morphology Control of Thin P3HT-Si-NCs Composite Films for Hybrid Photovoltaic Cells
Authors: Cunha Mara , Bernardo Gabriel , Hilliou Loic , Wiggers Hartmut , Pereira Rui N.
Published: November 2012

This work deals with an experimental investigation of the microstructure/morphology of spin-casted composite thin films of poly(3-hexylthiophene) (P3HT) and silicon nanocrystals (Si-NCs), in the weight proportion 1:1, which develop under different deposition conditions. The experimental parameters considered were the following: i) solvent quality; ii) spinning rate; iii) spinning time and iv) solution concentration. The developed morphologies were characterized by means of optical microscopy and X-ray diffraction (XRD) measurements. The present work aims at a) establishing the relationship between processing conditions and resultant morphology and b) defining the most relevant processing parameters that govern and are of significance for the induced morphology.
Electric Field Distribution around the Deep Brain Stimulation Electrode Inferred from Dielectric Measurements
Authors: Neagu Bogdan , Neagu Eugen R. , Igreja Rui , Dias C.J.
Published: November 2012

Information about the spatial distribution of the electric field can be obtained by measuring the electrode impedance as a function of the diameter of the electrolyte surrounding the electrode. The non-uniform distribution of the electric field around the electrode is supported by the variation of the geometry factor (GF) with the electrical conductivity and geometry of the volume conductor. A comparison of the values obtained for the GF from experimental data, from model calculations and simulations help to understand the non-uniform distribution of the electric field. The GF calculated from four-electrode-measurements is significantly higher. GF should be used with caution in calculations of the deep brain stimulation (DBS) electrode impedance.
Assessment of Materials for Fuselage Panels Considering Fatigue Behavior
Authors: Tavares S.M.O. , Camanho Pedro P. , de Castro P.M.S.T.
Published: November 2012

Minimum-weight designs are frequently too costly to manufacture, whereas less expensive and easy to fabricate and assemble designs are often much heavier. The most efficient design on the basis of both cost and weight often lies between these two extremes. The current trend in structural materials selection consists of the extensive use of composite materials in the airframe. Composite materials have high specific strength, are less prone to fatigue crack initiation and provide enhanced flexibility for structural optimization compared to the aluminum alloys. On the other hand, aluminum alloys display higher toughness and better damage tolerance in the presence of defects. A simple methodology for the weight assessment based on the specific weight for different damage scenarios for an exemplary, simplified fuselage panel, will be presented, in order to quantify the savings under different conditions. The results show that the composites have advantages over the aluminum alloys, although due to low ductility, in parts that are exposed to external damages the aluminum alloys can have better performance due to the better damage tolerant properties.
Characterization of Epoxy/Steel Fibres Composites for Hybrid Injection Moulds
Authors: Leite Janaina L. , Salmoria Gean V. , Ahrens Carlos H. , Pouzada António Sergio
Published: November 2012

Metallic fibres in polymeric matrix are used for mouldings blocks of hybrid injection moulds improving the mechanical and thermal properties. This paper reports on the characterization of epoxy resin/short steel fibres (SSF) composites. The effect of the concentration of 2,4,6-tris (dimethylamino-methyl) phenol as accelerator in the epoxy system was evaluated by viscosity and dynamical mechanical analyses. The composites were characterized by compression and microhardness tests. The fibres dispersion into the epoxy matrix was analysed by optical microscopy. It was found that the best accelerator concentration for this type of composite was 5,0 parts by weight
Characterization of Raw and Treated Curaua Fibers to be Applied as Reinforcement in Composites
Authors: d'Almeida Ana.L.F.S. , Melo Filho João A. , d'Almeida José R.M.
Published: November 2012

Lignocellulosic fibers present several advantages over synthetic fibers, such as low cost and biodegradability. In this work the tensile mechanical behavior of as-received and surface treated curaua fibers was analyzed. Mercerization and three different enzyme surface treatments were used. The tensile stress data were analyzed using the Weibull statistical distribution, and SEM was used to characterize the surface modifications caused by the treatments. The results show that mercerization causes an increase of the deformation capacity of the fibers. This result was attributed to the removal of hemicellulose, and to an increase of mobility of the internal fibrils. The increase of NaOH concentration at the alkali solution affects both the surface characteristics and the tensile properties. Solutions with more than 5%wt NaOH degraded the fibers. The enzyme treatments increase the tensile mechanical properties, but also increase their brittleness.
Fractographic Observation of Various Loading Modes of Fibre Reinforced Laminates
Authors: Marat-Mendes Rosa , de Freitas Manuel
Published: November 2012

One of the major disadvantages of laminated composites is their tendency to delaminate. Unidirectional glass/epoxy laminates have been tested under static conditions by the use of fracture mechanics. Mode I, mode II, mixed mode I-II, mode III and mixed mode II-III tests were performed. Double cantilever beam (DCB), end-notched flexure (ENF), mixed-mode bending (MMB) and edge crack torsion (ECT) specimens were used. Scanning electron microscopy technique was used to identify distinguishing fractographic features and to establish the differences between the various modes of fracture after specimens testing. The propagated orientation of the delamination could be specified from the patterns of fracture surface. Scanning electron micrographs of fractured surfaces showed that the most predominant fractographic features in mode I and mode II are the large amount of fibre pull-out and the cusps markings respectively. In the MMB specimen the fracture surfaces are characterized by fibre breakage under shearing with fractures localized in the resin with cusps having an orientation of 90º (mode II) and also fractures localized in the resin and along the resin/fibre interface (mode I). Mode III characterization concluded that some limited mixed mode II-III seems to be present for ECT specimen on delamination initiation and growth, but a large majority of mode III delamination is present.
Hybrid Fibre-Reinforced Cement Composite
Authors: Silva Elisabete R. , Ferreira Humberto E. , Coelho Jorge F.J. , Bordado João C.
Published: November 2012

This paper reports the results of a series of experiments carried out to investigate the effectiveness of newly hybrid polyethylene/polypropylene (PP/PE) fibres inclusion in the mechanical performance of cement matrices, with regard to fibres properties and content. The results indicate that, compared with plain cement matrix, the PP/PE fibre-reinforced cement matrices (FRC) revealed improvements on their mechanical performance. Increases of 37 ± 1% on compressive (40.2 MPa) and flexural strengths (8.1 MPa) were obtained for 24 mm fibre length composites containing a rather low fibre’s content (1 wt.%). These mechanical improvements were achieved after optimisation of the mortar workability by the addition of a superplasticizer. FRC mechanical behaviours also evidenced that despite the compressive strengths increasing with fibre length, a flexural strength effect is only noticeable for a 24 mm length fibre-reinforced composite and for fibres volume higher than 2.9 %. Morphological observations showed a strong interaction between fibres and cement matrix, evidenced a crack arrest role (bridge effect) on fibre/cement interfacial zone and revealed a typical multiple fracture cracking mechanism.
Mechanical Behavior of Gypsum and Cork Based Composite Material
Authors: Vasconcelos Graca , Martins Andreia , Cunha Sandra , Camões Aires , Lourenço Paulo B.
Published: November 2012

The main aim of this work is the mechanical characterization of a composite material resulting from the combination of three by-products coming from industry, namely, flue gas desulfurization (FGD) gypsum, granulated cork and textile fibers from tire recycling. The material is considered as a green material as the raw material are considered by-products and it is intended to be used as a building material for non-structural purposes in civil engineering construction. The mechanical characterization includes uniaxial compressive tests and bending tests for characterization of the fracture behavior. Additionally, ultrasonic pulse velocity is measured to evaluate its variation with time of curing.
Self-Sensing Hybrid Composite Rod with Braided Reinforcement for Structural Health Monitoring
Authors: Rosado Mérida Katherine P. , Rana Sohel , Gonilho-Pereira Cristiana , Fangueiro Raul
Published: November 2012

Enhancing the performance and lightness of different structures has already been achieved by the employment of fibre reinforced composite materials. Nowadays, a new challenging perspective is being given to these materials by the inclusion of non-metallic conductive components. This emerging technology will lead to multifunctional composites with possible applications in structural health monitoring and traffic monitoring. The aim is to avoid corrosion problems from metallic components, as well as to eliminate the need of expensive equipments used for the health monitoring of large infrastructures. In the present research, the strain-sensing capability of a core-reinforced hybrid carbon fibre/glass fibre braided composite has been investigated in order to develop continuous monitoring system. The characterization of sensing behaviour was performed with the help of an instrumental set-up capable of measuring the change in electrical resistance with mechanical stresses applied to the samples. The effect of core composition (carbon fibre/glass fibre weight ratio) on the strain sensitivity of the braided composites has been studied in order to find out the optimum composition for best sensing capability. Among the three compositions studied (23/77, 47/53 and 100/0), composites with lowest amount of carbon fibre showed the best strain sensitivity with gauge factors up to 23.4 at very low flexural strain (0.55%). Attempts have also been made in this research to develop a piezoresistive matrix for the braided composites in order to further enhance their strain sensitivity. For this purpose, the strain sensing capability of an unsaturated polyester matrix dispersed with chopped carbon fibres (1mm and 3 mm lengths) at various weight % (0.5, 0.75 and 1.25%) was evaluated in order to find out their optimum length and concentration. It was observed that chopped fibres with different lengths showed similar strain sensitivity, which however, improves with the decrease in their concentrations.
Alkali-Aggregate Reactions in Concrete: Methodologies Applied in the Evaluation of Alkali Reactivity of Aggregates for Concrete
Authors: Santos Silva António , Soares Dora , Matos Lina , Fernandes Isabel , Salta Maria Manuela
Published: November 2012

The alkali-aggregate reaction (AAR) in concrete is a group of chemical reactions that involves the reaction of certain minerals present in the aggregates with alkali and hydroxyl ions in the interstitial solution of cement paste in concrete. These reactions form an alkaline hygroscopic gel that absorbs water and expands causing internal stresses with cracking [1]. The AAR mitigation measures oblige the correct evaluation of the alkali reactivity of the aggregates. This is normally assessed by petrographic, chemical or expansion test methods. Several studies regarding alkali reactivity of aggregates for concrete structures in Portugal, including bridges and dams, indicated that their field performance does not correspond to the previously performed evaluation. Presently, Portuguese methodology is based on the LNEC Specification E461-2007, which shows some limitations regarding rock types such as granitoids [2]. This situation motivated the development of a research project, involving medium and long term expansion tests in different conditions, under accelerated and natural exposure conditions, as well as petrographic evaluation of the main Portuguese aggregates used/to be used in concrete. This paper presents the preliminary results of this research.
Behaviour of Glass in Cement-Based Materials: Its Role on ASR
Authors: Serpa D. , Santos Silva António , Soares D. , Santos M. Barreto , de Brito J.
Published: November 2012

One of the most worrying degradation mechanisms in hardened concrete is the occurrence of chemical expansive reactions, namely due to alkali-silica reactions (ASR). This pathology involves the formation of expansive products inside the material. This situation is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by ASR. Hence, there is an urgent need to find preventive methods that may inhibit these reactions in new concrete structures. Nowadays, the use of pozzolanic mineral additions is recommended to mitigate this type of degradation. Moreover, their effect depends on their chemical and mineralogical composition and also on the cement content replacement ratio. Glass is a common material with some environmental problems regarding recycling and landfilling. Some studies exist about its use as fine powder, like a pozzolan, in cement-based materials. However, there are also some problems related to its use as coarse aggregate in cement–based materials due to ASR development. This paper presents the results obtained in mortars exposed to 1M NaOH solution prepared with crushed glass as aggregate and as addition in cement substitution. The results reveal that ASR is reduced with the incorporation of glass as aggregate or addition, and its efficiency depends on its replacement content. This study shows that an incorporation of glass aggregates up to 20% in mass will generate no significant expansion when compared with concrete made with natural aggregates.
Comparative Study of the Chemical Degradation Effects on Polymer Concrete with Limestone Aggregates
Authors: Galán-Marín Carmen , Rivera-Gómez Carlos
Published: November 2012

The objective of this paper is to investigate the influence of chemical degradation effects on polyester polymer mortar (PM). For this purpose, different dosages of siliceous and limestone PMs and natural stone specimens were exposed to representative degradation agents. Since the motivation for the research was to determine the durability of polymer mortar, it was considered important to simulate the types of aggressive environments that could conceivably be brought into contact with the material in domestic and industrial environments. In this paper, the possible variation of the surface aspect, water absorption and mass of the tiles after being immersed the specimens in different solutions, was measured and considered by visual observation and optical microscopy. As a conclusion PMs stability is strongly affected by the adhesion between matrix and aggregates at interface, and it is also dependent of the nature and packing level of aggregates.
Concrete Retrofitting Using CFRP and Geopolymer Mortars
Authors: Vasconcelos Eduardo , Fernandes Sérgio , de Aguiar Barroso , Pacheco-Torgal F.
Published: November 2012

A new development in the repair and strengthening of reinforced concrete systems is the use of carbon fiber reinforced polymers (CFRP) strips bonded to concrete substrate with epoxy resins. It has been reported that epoxy adhesive are extremely sensitive to high temperatures. Some authors conclude that the epoxy temperature should not exceed 70 °C in order to safeguard the adhesiveness of the epoxy and, thus, the integrity and adequate functioning of CFRP. It is noted that even frequently exposure to direct sunlight causes temperatures higher than 70 °C. Since geopolymers are known to possess high stability at high temperature, these materials can be an alternative to epoxy resins. This papers presents results about the use of metakaolin based geopolymers mortars to insure the adhesion between the CFRP and the concrete substrate. Several compositions of geopolymer mortars were executed by varying the percentage of binder, sand/binder ratio and the concentration of sodium hydroxide. It was found that geopolymer mortars demonstrate very promising performances, having obtained a high mechanical resistance and a good adhesion to concrete. On the other hand the adhesion between CFRP and geopolymer mortars proved to be smaller than expected which could be due, to the fact that the composition of the mortar was not optimized or even to the nature of the CFRP.
Influence of the Parameters of Formulation on the Fresh Properties of Cementing Materials with Admixtures
Authors: Boudchicha Abdelaziz , Cheikh Zouaoui Mustapha , Gallias Jean Louis
Published: November 2012

The use of mineral admixtures in cementing materials can generate significant modifications in the fresh and hardened mixes, which can depend on the parameters of formulation. To study the influence of the parameters of formulation on the rheological properties of cementing materials with admixtures, we used seven admixtures different by their mineralogical natures, their fineness, and their morphological characteristics, two types of cements and two types of superplasticizers. The experimental methodology used is based on the volume substitution of the cement by admixtures in mixtures whose the absolute volume of the solid phases and workability are preserved constant. The main results achieved showed that the rheological properties of the fresh mortars with admixtures are very influenced by the amount and the properties of admixtures, and the nature of the superplasticizer, but depended rather on the nature of the cement used.
Performance of Stones Under Different Conditions: A Study of Metro Stations
Authors: Alves Carlos , Figueiredo Carlos , Maurício António , Figueiredo Paula , Aires-Barros Luís
Published: November 2012

The study of stone alterations in the Lisbon Metro stations allowed the discussion of the influence in the development of these alterations of stones characteristics and the actual conditions to which the stones are subjected. Alterations occur under what can be considered the usual conditions of use but also under abnormal situations that must be taken into account given its frequency. The diverse situations identified are considered in the discussion of possible recommendations bearing in mind the actual situations found at the stations.