bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Characterization of Dense Hydroxyapatite Blocks
Authors: Ranito Cláudia M.S. , Oliveira Fernando A. Costa , Borges João Paulo
Published: March 2009

Bioactive dense HAp ceramics possess a unique set of properties, which make them
suitable as bone substitute. However, both physical and mechanical properties of HAp have to be evaluated in order to produce new materials that match the bone stiffness. This paper highlights the influence of both porosity and grain size on the four-point flexural strength and the indentation fracture toughness of pure dense HAp blocks sintered at 1300°C. Both discs and rectangular bars were produced by uniaxial pressing at 40MPa and sintered in static air at temperatures between 1150 and 1325°C for 1 h in order to assess the densification behaviour of the P120S medical grade HAp powder used. After sintering, both the density and the open
porosity were measured. In addition to FT-IR, XRD and SEM, the mechanical properties of the dense HAp blocks, including Young´s modulus, flexural strength, Vicker´s hardness and fracture toughness, were characterized and whenever possible these properties were compared to those reported for cortical bone. Pressureless sintering to full density at temperatures below 1300°C does
not occur for the stoichiometric powder used. The results obtained underline the importance of full mechanical characterisation of dense HAp so that new implant materials can be developed. There is a need to improve the microstructure and thus enhance mechanical strength of HAp ceramics, as it was found that flexural strength is closely related to the micropores present in the sintered samples.
Terbiumpolyoxotungstate Anions as Building Units to Fabricate Nanostructured Films
Authors: Sousa Filipa L. , Soares-Santos Paula C.R. , Nogueira Helena I.S. , Ferreira Rute A. Sá , Cavaleiro Ana M.V. , Carlos Luís D. , Trindade Tito
Published: March 2009

A layer-by-layer assembly method was employed to fabricate multilayered films
containing the terbium heteropolyanions K6[Tb(BW11O39)(H2O)3]·32H2O and
Ky[Tb(XW11O39)2]·nH2O (X = Si and P) and the polyelectrolytes poly(4-styrenesulfonate) and poly(allylamine hydrochloride). A comparative study on the optical properties of the films containing distinct polyoxometalates and different types of multilayers was carried out. The photoluminescence of the solid polyoxometalates and of the resulting films was investigated.
Short-Range Effects and Magnetization Reversal in Co80 Fe20 Thin Films: A MOKE Magnetometry/ Domain Imaging and AMR Study
Authors: Teixeira José M. , Silva Rui F.A. , Ventura João , Pereira A. , Araújo João P. , Amado M. , Carpinteiro Francisco , Sousa João Bessa , Cardoso S. , Ferreira R. , Freitas Paulo
Published: March 2009

A MOKE magnetometry unit simultaneously sensitive to both in-plane magnetization
components, based on an intensity differential detection method, allows us to observe the uniaxial anisotropy impressed during CoFe-deposition and to discriminate the magnetization processes under a magnetic field parallel and perpendicular to such axes. Our MOKE imaging unit, using a CCD camera
for Kerr effect domain visualization provides direct evidence on the dominant M-processes, namely domain wall motion and moment rotation. Further magnetic information was obtained by AMR measurements due to the dependence of the electrical resistivity on the short-range spin disorder and also on the angle between the electrical current direction (I) and the spontaneous magnetization (MS).
New Polyoxotungstates with Ln(III) and Co(II) and Their Immobilization in Silica Particles
Authors: Balula M.Salete S. , Nogueira Helena I.S. , Cavaleiro Ana M.V.
Published: March 2009

New lanthanotungstocobaltates with the Keggin structure and general formula
KxHy[Ln(CoW11O39)(H2O)3]⋅nH2O or KxHyLn[Ln(CoW11O39)(H2O)3]⋅nH2O, LnIII = Ce, La, Eu,
Sm, Tb, were prepared and characterized for the first time. Hybrid silica materials, with the
polyoxoanions anchored to spherical silica particles, were also prepared and characterised. Their
study by IR spectroscopy and EDS suggested that the structure of the Keggin-type polyanions is
maintained when they are immobilized in the silica material.
Influence of the Microwave Radiation on the Thermal Properties of Ni,Al Hydrotalcite-Like Compounds
Authors: Benito Patricia , Labajos Francisco Martin , Rives Vicente
Published: March 2009

The thermal stability of Ni,Al-CO3 hydrotalcite-like compounds synthesized by the
coprecipitation method and aged upon microwave-hydrothermal treatment for different periods of
time was studied. The samples prepared were characterized by Elemental Analysis, PXRD, Thermal
analyses (DTA and TG) and Temperature Programmed Reduction (TPR). The results show that the
use of microwave radiation as a source of heating during the ageing treatment leads to an increase
in the crystallinity of the solids, which determines their thermal stability.
Effect of Deposition and Processing Conditions for LaNiO3 Bottom Electrodes on the Properties of Pb(Zr,Ti)O3 Thin Film Capacitors Made by RF Magnetron Sputtering
Authors: Mardare Cezarina C. , Mardare Andréi I. , Savu Raluca
Published: March 2009

Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si
substrates: LaNiO3 (LNO), Pt/Ti and LNO/Pt/Ti. The effect of different deposition and processing
conditions for the LNO films on the ferroelectric properties of sputtered Pb(Zr0.52Ti0.48)O3 (PZT)
capacitors was investigated. The LNO films were either deposited at room temperature and heattreated
in O2 flow in the furnace at 500 or 600°C or made in situ in the range of 200-500°C. Other
deposition parameters under study were the pressure, the RF power and the Ar:O2 ratio. The
resistivity of the LNO films was measured and on some of the films with the lower values,
amorphous PZT was deposited and then crystallized in the furnace. X-ray diffraction results show
that the PZT films deposited over Pt/Ti had a preferential (100) orientation, while those deposited
over LNO made in situ are strongly (100) oriented and the ones deposited over amorphous LNO do
not exhibit any preferential orientation. The remanent polarization of the capacitors was around
28μC/cm2 when amorphous LNO or Pt/Ti electrodes were used and around 20μC/cm2 with LNO
made in situ. Leakage currents were improved when LNO electrodes made in situ was used; a good
ferroelectric fatigue performance of the capacitors when subjected to 1010 switching cycles was also
observed
Ferroelectric Properties of Pb(Zr,Ti)O3 Thin Film Capacitors Made by RF Magnetron Sputtering and Heat-Treated by the Bottom Electrode Crystallization Method
Authors: Mardare Andréi I. , Mardare Cezarina C. , Savu Raluca
Published: March 2009

The bottom electrode crystallization (BEC) method was applied to the crystallization of Pb(Zr,Ti)O3 (PZT) thin films deposited by RF magnetron sputtering on Pt/Ti/SiO2/Si substrates. Using a proportional-integral-differential controller, the current flowing in the Pt/Ti films provided accurately controlled Joule heating for the crystallization of the PZT films. The temperature uniformity of the heat treatments was investigated by measuring the ferroelectric properties of PZT. Platinum and tungsten wires were alternatively used as electrical contacts. Scanning electron microscopy (SEM) images were used to inspect the electrical contact regions between the platinum films and different contact wires. The PZT films showed higher remanent polarizations and lower leakage currents near the electrical contacts when Pt wires were used; the ferroelectric properties were more uniform on the PZT films heat-treated with W contact wires. The BEC method can successfully replace the more conventional means for thin film crystallization, having the advantage of being a very precise, low cost and low power consumption technique.
Characterization of n-Type:ZnO:Al Films Grown by Magnetron Sputtering
Authors: Chaabouni F. , Costa Luís Cadillon , Abaab Mohamed , Monteiro Jorge
Published: March 2009

ZnO is a wide band gap semi-conductor that has attracted tremendous interest for its
potential applications in optoelectronic, solar cell, gas detection …
In this work, aluminium doped zinc oxide (ZnO:Al) films were deposited by RF magnetron
sputtering on glass substrates with different RF power densities of 1.2, 2.5, 3.7 and 4.9 W/cm2. We
notice that the films grown at 1.2 W/cm2 were very thin and their physical properties were not
precisely determined. The electrical properties of ZnO films were investigated using the impedance
spectroscopy technique in the frequency range from 5 Hz to 13 MHz. The impedance data,
represented by Nyquist diagrams showed that the resistivity of the films changed during the first
three months after deposition.
The deposited films show good optical transmittance (over 80 %) in the visible and near infrared
spectra. The band gap is around 3 eV and decreases with the increasing of the RF power density
(from 3.35 to 3.05 eV).
The results of this study suggest that the variation of the RF power density used for deposition allow
the control of the electrical and optical properties of the films
The Sodium Loss and Transport through the Walls of the Ceramic Discharge Tube of High Pressure Sodium Lamps
Authors: Lovas Henriett , Josépovits Vargane Katalin , Tóth Zoltán , Madarász János
Published: March 2009

In this work we present the investigations on the blackening of the outer jacket of the
High Pressure Sodium (HPS) lamps. For this purpose ceramic arc tubes and their glass outer jackets
taken from lamps burned for different times (0h-10000h) were examined by X-ray Photoelectron
Spectroscopy (XPS) and Secondary Ion Mass Spectroscopy (SIMS) in order to determine the
composition of the deposit on the internal wall of glass outer jacket. In the case of the several
thousand hours burned lamps the outer bulb was found to be covered by aluminium, which comes
to a black deposit on the glass surface. XPS identified Al on the glass surface can be found in two
different chemical state (elemental Al, Al2O3). The assumed evaporation of aluminium-oxide
ceramic tube might be described by a dissociative mechanism of the alumina evaporation. This
papers described the possible mechanism of the alumina evaporation. Na was also found in the
black deposit, whose cause of this in the case of the several thousand hours burned lamps is
probably related to the sodium transport through the walls of the arc tube
Modified Titania in the Photo-Assisted Oxidation of Chloroform
Authors: Gouveia R. , Silva Raquel A. , Rangel Carmen M.
Published: March 2009

Degussa P-25 TiO2 powder was used as a catalyst in the photocatalytic oxidation of
organics. With the objective of promoting a more effective electron-hole separation upon
irradiation, the catalyst was modified with small amounts of platinum. Characterisation of the
powders was done by X-Ray diffraction and SEM. Chloroform was used as a model molecule and
its degradation followed using selective electrodes, with excellent results for the modified titania.
Langmuir-Hinselwood kinetic was used to describe the heterogeneous oxidation of chloroform on
TiO2, for low solute concentrations.
Precise Characterization of Selected Silica-Based Materials from Grand Canonical Monte Carlo Simulations
Authors: Herdes Carmelo , Santos Miguel A. , Medina Francisco , Vega Lourdes F.
Published: March 2009

We present results concerning the characterization of selected silica-based materials from
a molecular modeling approach, together with some physical and mathematical tests to check the
reliability of the obtained results. The experimental adsorption data is used in combination with
Monte Carlo simulations and a regularization procedure in order to propose a reliable Pore Size
Distribution (PSD). Individual adsorption isotherms are obtained by Monte Carlo simulations
performed in the Grand Canonical ensemble. The methodology is applied to M41S materials,
chosen due to their well defined pore geometry and pore size distribution, obtainable from
alternative procedures. Our results are in excellent agreement with previous published results,
demonstrating the reliability of this methodology for the characterization of other materials, with
less well-defined structural properties.
Modelling of Mixing in Single Screw Extruders
Authors: Domingues Natália , Gaspar-Cunha António , Covas José A.
Published: March 2009

Polymer extrusion is one of the most important polymer processing techniques.
Modelling of the phenomena developing inside single screw extruders enabled the development of
commercial software which can be used to study the performance of existing systems and to define
the equipment characteristics for new applications.
Although mixing is one of the most important performance measures of extrusion, it is usually
disregarded in the available programs. Consequently, in this work mathematical models for
quantifying mixing in single screw extruders are developed and subsequently inserted in a global
computer modelling program of single screw extrusion. The mixing model quantifies distributive
and dispersive mixing and coalescence mechanisms in a liquid-liquid system. This is accomplished
by calculating the variation of the thickness of drops considered to be suspended in the polymeric
matrix, taking into account the rate and drop break-up time and the coalescence probability.
The influence of several parameters, such as viscosities, initial drop dimension, screw speed and
barrel temperature, are examined
Quantitative Characterization of Pore Arrangement in Pore Bands in Pressure Die Cast AZ91 Magnesium Alloy by Image Processing
Authors: Prakash D. G. Leo , Regener Doris
Published: March 2009

Microporosity is the major processing defect in pressure die cast AZ91 magnesium alloy.
There is a big difference in the arrangement of pores in different regions of the castings. The present
work explains the pore arrangement in pore bands and other regions. Quantification and
characterization of pores in pore bands is expected to be useful to understand the process-propertymicrostructure
correlation. A computational microstructural (image) analyzing technique has been
developed by a programming language to quantify and analyze the micropores in pore bands. The
pore band regions and the rest were separated and quantified. In addition, image analyzing
technique was used to measure the clustering tendency of porosity in pore bands and it was
compared with other regions.
Effect of Membrane Pore Size and Membrane-Solute Interactions on Lysozyme Ultrafiltration
Authors: Magueijo Vitor , Semião Viriato , Norberta de Pinho Maria
Published: March 2009

A model based on steric hindrance mechanisms [1] is used to determine the pore sizes of two
ultrafiltration (UF) membranes. The lysozyme rejection coefficients of those membranes are
predicted through the same model after modification of the pore size and solute radius by taking
into account the development of electric double layers. Two asymmetric cellulose acetate
membranes M1 and M2 were prepared and characterized. Membrane M1 has an hydraulic
permeability of 2.1x10-6 m/s/bar, a molecular weight cut-off (MWCO) of 30,000 Da and an average
pore radius of 2.6 nm. Membrane M2 has an hydraulic permeability of 5.9x10-6 m/s/bar, a
molecular weight cut-off (MWCO) of 60,000 Da and an average pore radius of 5.3 nm. Aqueous
solutions of lysozyme containing a NaCl concentration of 0.1M were ultrafiltrated through
membranes M1 and M2. The predicted lysozyme rejections considering the development of electric
double layers on the protein and membrane pore surfaces, are in good agreement with the
experimental results.
A 5 GHz Resonant Cavity for Complex Permittivity Measurements: Design, Test Performances and Application
Authors: Costa Luís Cadillon , Devesa Susana , Henry François
Published: March 2009

The theoretical treatment of a cavity resonator consists of solving the Maxwell equations
in that cavity, respecting the boundary conditions. The resonance frequencies appear as conditions
in the solutions of the differential equation involved and are not significantly affected by the fact
that the cavity walls have a finite conductivity. Solutions for rectangular cavities and for the lowest
resonant mode, where the probability of mistaking one mode from another is slight, are readily
obtained.
The measurement of the complex permittivity, ε* = ε´-iε´´, can be made using the small
perturbation theory. In this method, the resonance peak frequency and the quality factor of the
cavity, with and without a sample, can be used to obtain the complex dielectric permittivity of the
material. We measure the shift in the resonant frequency of the cavity, f, caused by the insertion of
the sample, which can be related to the real part of the complex permitivitty, ε´, while the change in
the inverse of the quality factor of the cavity, (1/Q), gives the imaginary part, ε´´.
In this work we report the construction details, the performance tests of the cavity to confirm the
possibility of the use of the small perturbation theory, and the application of the technique to
measure the complex permittivity of a reinforced plastic.
Stress and Texture Analysis in Thin Films and Coatings by X-Ray Diffraction
Authors: Pina J.C.P. , Marques Maria José , dos Santos J.M.M. , Dias A. Morão
Published: March 2009

The thin and textured coatings present a double difficulty for characterization by
conventional X-ray diffraction. Their shallow depth reduces the diffracted intensity and allows the
interference of the underlying material. Frequently they present a crystallographic texture which
limits the number of orientations that provide good intensity and induces anisotropy effects on their
mechanical behavior. Reliable results can be determined using diffraction geometry of lowincidence
angle. This paper describes the application of the technique to several films, characterized
by thicknesses of the order of 1 μm and crystallographic textures. Examples are proposed of
chromium films applied by PVD on molybdenum substrates, decorative electroplated coatings, and
aluminum coatings used for interconnections in microelectronic circuits. The Cr films are 1.5 μm
thick and exhibit a strong <100> fiber texture. The decorative coatings were studied both on the
nickel undercoat and in the Cr top layer. Results are presented for chromium where tensile stresses
and a <110> fiber texture were observed. The Al films are 1.0 μm thick. Some samples were heattreated
at different annealing temperatures. Tensile stresses were always observed, which increase in
the annealed samples.
Structural Grades of Timber by Bending and Compression Tests
Authors: Branco Jorge M. , Varum Humberto , Cruz Paulo
Published: March 2009

This paper presents the results obtained in a series of tests on Pinus Pinaster Ait. timber
specimens, using the prEN408:2000, to estimate the local and global Young’s modulus and strength
both in bending and compression parallel to the grain. The results obtained are compared with the
values presented in the Portuguese Nationally Determined Parameters of Eurocode 5, for the quality
classes assign by Portuguese Standard NP4305:1994 by visual grading.
Evaluation of Physical Processing in the Recycling of Spent Domestic Batteries
Authors: Cabral Marta , Climaco Nuno , Ribeiro João P. , Pessoa Paulo. A. , Nogueira Carlos A. , Margarido Fernanda
Published: March 2009

Domestic-type batteries sample was tested aiming at its characterization and the
evaluation of the feasibility of physical separation of its main components. The sample was
essentially constituted by saline and alkaline types (Zn-MnO2 based systems, >90% w/w) and
cylindrical shape (> 90% w/w). The mass balance of alkaline battery samples indicated as main
battery components the steel case materials (25 %), the electrodes (71%) and the connector and
separator/insulating materials (4 %), while the corresponding values to the saline type are 16%,
72% and 12% respectively. Despite electrochemical principles are similar, internal constitution of
saline and alkaline batteries is different. Differences in electrolytes are also relevant (KOH in
alkaline type and chloride salts in saline type) affecting therefore the mass balances in the chemical
treatment.
Fragmentation of batteries was done aiming at to evaluate the efficiency of the liberation of
different components, namely scrap and electrodes. Results obtained are very promising
considering the good efficiency reached on the physical separation treatment and consequently the
chemical step will be necessarily improved.
Development of an Ultrasonic Motor Based on a Piezoelectric Ceramic Sandwiched between Two Laminate Composite Plates
Authors: Basílio A. , Igreja Rui , Inácio Paulo , Dias C.J. , Marat-Mendes José N.
Published: March 2009

Ultrasonic motors are of great interest since their operation is not affected by a magnetic field. On this work the development of a prototype of a smart ultrasonic motor and its characteristics will be presented. The stator of the motor is formed by a cantilever made of PZT ceramic plate sandwiched between two unidirectional CFRP composite sheets. The composite sheets are oriented to 45º and -45º in the longitudinal direction. By application of a sinusoidal electric field to the piezoelectric ceramic plate, it vibrates. The anisotropy of the CFRP composite sheets induces an expansion/torsion movement. This effect is transformed into rotation by friction.
The study of adequate voltages and frequencies of the applied electric field allows the optimization of the rotating motor performance.
Study of the High Frequency Dielectric Properties of SrBi2 Ta2O9 Ferroelectric Thin Films
Authors: Delmonte Nicola , Watts Bernard Enrico , Leccabue Fabrizio , Cova Paolo , Chiorboli Giovanni
Published: March 2009

In recent years several ferroelectric thin films have been studied at microwave
frequencies; lead zirconate titanate (PZT) and barium-strontium titanate (BST) has been widely investigated. However, the microwave dielectric properties of strontium-bismuth tantalate (SBT) have not yet been investigated so widely [1]. The purpose of this work is the microwave characterization of the dielectric properties of an SBT thin film biased at different DC voltages. The dielectric properties of SBT make it a good material for the production of FERAM memories.
Microwave characterizations may show other properties that could promote the SBT as good candidate for capacitors to be employed also in microwave circuits (e.g. resonators and filters). In this work a study of high frequency dielectric properties has been performed and equivalent circuit model has been used to correct the measurements.
TEM and XRD Investigation of MnO2 Microstructure and its Influence on ESR of Ta Capacitors
Authors: Dias Décio , Monteiro Rui , Carvalho Patrícia Almeida , Ferro Alberto C. , Lohwasser Werner
Published: March 2009

The development of solid electrolytic tantalum capacitors with MnO2 as counter electrode has been carried out in order to decrease the equivalent series resistance (ESR). Capacitor samples produced under different pyrolysis conditions have been characterized in terms of equivalent circuit parameters. The Ta/Ta2O5/MnO2 system has also been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). X-ray powder diffraction patterns obtained were inconclusive due to the MnO2 complex structure and to the presence of highly intense tantalum peaks that shadow interesting MnO2 diffraction peaks. Electron diffraction TEM results enabled the characterization of the microstructure and furthermore revealed the complex crystalline structure that affects the electrical properties of the semiconductor layer. A relation between the calculated circuit parameters and microstructure of MnO2 is discussed.
Heat Generation in Tunnel Junctions for Current-Written Pinned Layer Switching
Authors: Ventura João , Pereira A. , Teixeira José M. , Araújo João P. , Carpinteiro Francisco , Sousa João Bessa , Liu Y. , Zhang Z. , Freitas Paulo
Published: March 2009

To commute between the different resistance states of a magnetic tunnel junction (TJ) one can use a thermally-induced pinned layer switching mechanism. When a sufficiently high electrical current flows through the insulating barrier, local temperatures inside the tunnel junction can increase above the blocking temperature of the antiferromagnetic layer used to pin the magnetization of the adjacent ferromagnet. Then, it is possible to switch the magnetization of the pinned layer with a small magnetic field H and thus revert the magnetic state of the TJ. Here we
demonstrate thermally-induced pinned layer switching in thin magnetic tunnel junctions. We further present numerical results that suggest that heating is small when one takes into consideration the uniform current density flowing through the tunnel junction and that one must conclude that nanoconstrictions concentrate most of the current, increasing local current densities and temperature. Simulation of heating and cooling times demonstrates that current-induced pinned layer switching is a competitive mechanism for actual technological applications.
The Growth of SiC Crystals from CoSi Molten Alloy Fluxes
Authors: Gao Ming Xia , Pan Yi , Oliveira Filipe J. , Yang G.Y. , Vieira Joaquim M.
Published: March 2009

The growth of SiC single crystals from SiC saturated Co-Si molten alloy fluxes is
reported. Experiments were performed by two routes: liquid phase sintering of CoSi/SiC and Si/Co/SiC powder compacts and melt infiltration of CoSi alloy into porous SiC powder preforms. Results showed that euhedral SiC crystals, many of which appeared as polygonal or plate shaped single crystals, grew from the SiC saturated CoSi molten alloy. The largest SiC crystals exceed half
millimetre in size, after 25h of isothermal dwelling at 1700°C in the melt infiltration process. The nature of the growth mechanism, the crystal defects and the effects of constituent materials, temperature and time on the abnormal grain growth of SiC single crystals are further discussed.
Three-Dimensional Dispersion of Nano-Fillers in Soft Composite as Revealed by Transmission Electron Microscopy/Electron Tomography (3D-TEM)
Authors: Kohjiya Shinzo
Published: March 2009

. Generally rubber products are a typical soft material, and a composite of a nano-filler (typically, carbon black or particulate silica) and a rubber (natural rubber and various synthetics are used). The properties of these soft nano-composites have been well known to depend on the dispersion of the nano-filler in the rubbery matrix. The most powerful tool for the elucidation of it has been transmission electron microscopy (TEM). The microscopic techniques are based on the projection of 3-dimensional (3D) body on a plane (x, y plane), thus the structural information along the thickness (z axis) direction of the sample is difficult to obtain. This paper describes our recent results on the dispersion of carbon black (CB) and particulate silica in natural rubber (NR) matrix observed by TEM combined with electron tomography (3D-TEM) technique, which enabled us to obtain images of 3D nano-structure of the sample. Thus, 3D images of CB and silica in NR matrix are visualized and analyzed in this communication. These results are precious ones for the design of soft nano-composites, and the technique will become an indispensable one in nanotechnology.
Oxygen Evolution on Perovskite-Type Cobaltite Anodes: An Assessment of Materials Science-Related Aspects
Authors: Kovalevsky Andréy V. , Sviridov D.V. , Kharton Vladislav V. , Naumovich E.N. , Frade Jorge R.
Published: March 2009

Ceramic anodes, made of perovskite-type rare-earth and strontium cobaltites substituted in both sublattices, exhibit a high electrocatalytic activity towards oxygen evolution in alkaline media. This work analyzes the relationships between cation composition, defect structure, electronic conductivity and electrochemical performance for a wide group of perovskite-like cobaltites, including Ln1-yAyCoO3-δ (Ln= Pr, Nd, Sm; A= Sr, Ca; y= 0-0.4), La1-x-ySrxBiyCoO3-δ (x= 0-0.6, y=
0-0.1), La0.7-xSr0.3CoO3-δ (x= 0-0.10), Sr1-xBaxCoO3-δ (x= 0.1-0.2) and SrCo1-yMyO3-δ (M=Fe, Ni, Ti, Cu; y= 0.1-0.6). The materials were prepared by the standard ceramic technique and characterized employing XRD, TGA, iodometric titration, and total conductivity measurements. A relatively high electrochemical performance in alkaline solutions was observed for (La,Sr)CoO3-based
compositions with a moderate A-site deficiency. For SrCoO3-based materials, an increase in the oxygen evolution rate was found when co-substituting cobalt with several transition metal cations, such as Fe3+/4+ and Cu2+/3+. The results show that, in general, the key composition-related factors influencing electrochemical activity in alkaline media include the oxygen vacancy concentration, the average positive charge density in the crystal lattice, and possible blocking of active sites on the electrode surface.
Oxygen Nonstoichiometry and Ion-Electron Transport in SrFe0.9M0.1O3-δ (M=Cr, Ti, Al)
Authors: Patrakeev Mikhail V. , Leonidov I.A. , Kozhevnikov V.L. , Kharton Vladislav V.
Published: March 2009

The total conductivity and oxygen deficiency of partially substituted strontium ferrite,
SrFe0.9M0.1O3-δ (M=Cr, Ti, Al), at 700-950°C were measured depending on oxygen partial pressure varying in ranges 10-19-0.5 and 10-5-0.5 atm. The partial contributions of n- and p-type electronic charge carriers and oxygen ions to the electrical transport were determined analyzing the total conductivity vs. oxygen pressure dependencies. Additions of all dopants studied in this work are found to extend the cubic perovskite phase stability range and to improve oxygen transport in the intermediate-temperature range. The behavior of hole mobility suggests a polaron conduction mechanism. Doping with aluminum has a weak influence on the mobility level, while the incorporation of Cr and Ti cations into the ferrite lattice decreases hole mobility up to four times.
Hydrophobic Porous Benzene-Silica Hybrid Clay Heterostructure and Its Application in the Adsorption of Volatile Organic Compounds
Authors: Ferreira P. , Nunes C.D. , Pires João , Carvalho Ana P. , Brandão P. , Rocha João
Published: March 2009

A new porous benzene-silica hybrid clay heterostructure has been prepared by a
template-assisted method. The synthesis of Hybrid Porous Clay Heterostructures (HPCH) has been performed via the intercalation of a quaternary ammonium cation surfactant (cetyltrimethylammonium bromide) and a neutral amine (octylamine) as cosurfactant, in a Portuguese clay, to direct the interlamellar hydrolysis and condensation polymerisation of neutral inorganic etraethylorthosilicate (TEOS) together with an organic precursor, the 1,4-
bis(triethoxysilyl)benzene (BTEB). The material has been characterised by elemental analysis, powder X-ray diffraction, nitrogen adsorption, 13C CP MAS, 29Si MAS and CP MAS NMR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermal analyses. The hydrophobicity of the material was tested by water adsorption. Its potential application as adsorbent of volatile organic compounds was studied by the adsorption of methanol,
methyl ethyl ketone, toluene and trichloroethylene.
Joining of Gamma-Based Titanium Aluminides – A Review
Authors: Ramos Ana Sofia , Vieira Maria-Teresa Freire , Vieira Manuel F. , Viana Filomena
Published: March 2009

The optimisation of joining technologies is essential to the application of advanced
materials in the design of parts and devices. The development of intermetallic compounds, as structural materials, inevitably requires a new approach to join these compounds to themselves or to other materials. Among different intermetallic classes, titanium aluminides are one of the most studied. However, the industrial application is far from being proportional to the research, due to different problems, where joining processes have an important role. The present paper highlights
the state of art on joining γ-TiAl alloys. A review is presented with special emphasis on solid-state diffusion bonding process, because it seems to be the most suitable technique to produce high quality joints of advanced materials. The influence of the bonding conditions on the physical and mechanical properties of the joints is highlighted and the introduction of single or multiple interlayers to assist in the bonding process is discussed. A novel approach developed by the authors
to the solid-state diffusion bonding of γ-TiAl alloys using Ti/Al multilayer thin films as bonding materials is proposed. The improvement of the solid-state diffusion bonding will induce sound joints at lower temperatures or pressures.
Electrical Performances of Low Temperature Annealed Hafnium Oxide Deposited at Room Temperature
Authors: Pereira Luís , Barquinha Pedro , Fortunato Elvira , Martins Rodrigo
Published: March 2009

In this work, HfO2 was deposited by r.f. sputtering at room temperature and then
annealed for different times at 200°C in a forming gas atmosphere. After annealing for 2 hours the HfO2 layers present a reduction on the flat band voltage of about 1 V, relatively to the as deposited film, decreasing from -2.23V down to -1.28 V. This means an improvement of the interface properties and a reduction on the oxide charge density from 1.33×1012 cm-2 to 7.62×1011 cm-2. The dielectric constant reaches a maximum of 18.3 after 5h annealing due to film’s densification. When
annealing for longer times such as 10h a small degradation of the electrical properties is observed. After 10h annealing the dielectric constant, flat band voltage and fixed charge density are respectively, 14.9, -2.96 V and 1.64 ×1012 cm-2 and the leakage current also increases due to film’s crystallization.
Effect of the Ni Chemical Distribution on the Reactivity and Densification of WC-(Fe/Ni/Cr) Composite Powders
Authors: Fernandes Cristina M. , Senos Ana Maria R. , Castanho José M. , Vieira Maria-Teresa Freire
Published: March 2009

The objective of this work was to study the effect of the Ni distribution on the reactivity and densification of WC-(Fe/Ni/Cr) composite powders. For such, stainless steel AISI 304, was used as a binder base composition which was enriched with Ni by three different processing methods: WC sputter deposition using a target of stainless steel with Ni discs, conventional wet milling of commercial powders (WC, stainless steel and Ni powders) and a previous coating of the
WC particles with Ni, followed by the conventional mixing of this coated powder with stainless steel powder. The reactive sintering of these composite powders with identical compositions was investigated. The powder compacts were characterized by scanning electron microscopy and X-ray diffraction with Rietveld analysis to quantify de crystalline phases present.
Shrinkage Behaviour of Borosilicate Glass-Al2O3 Composites during Isothermal Sintering
Authors: Lima M.M.R.A. , Monteiro Regina da Conceição Corredeira
Published: March 2009

The effect of rigid inclusions on the densification during isothermal sintering of glass
matrix composites was investigated. Mixtures containing borosilicate glass powder and 0, 5, 10 and 25 vol. % alumina (Al2O3) particles were prepared and powder compacts isostatically pressed at 200 MPa have been used. The sintering behaviour of the samples heated at 800°C during various times was investigated through density measurement, axial and radial shrinkage measurements. The
microstructure was analysed by SEM and the crystalline phases present in the sintered composites were identified by XRD. The relative density of the isothermally treated borosilicate glass-Al2O3 composites decreased significantly with the increase in Al2O3 content because the presence of rigid inclusions retarded the densification of the compacts. The borosilicate glass exhibited anisotropic
shrinkage behaviour, showing a radial shrinkage higher than the axial shrinkage and isotropic shrinkage was favoured by Al2O3 additions. Sintered glass showed a dense microstructure with some spherical closed pores. The microstructure of composites with 5 vol. % Al2O3 revealed that most of the pores were filled by capillary flow of the glass. The microstructure of composites with
higher Al2O3 additions showed dense areas together with interconnected pores, which appeared at the sites of large glass particles in the green compacts.
The Oxidation Behaviour of TiC Matrix Ni3Al and Fe40Al Toughened Composites at High Temperatures
Authors: Gao Ming Xia , Oliveira Filipe J. , Pan Yi , He Y. , Jiang E.B. , Baptista J.L. , Vieira Joaquim M.
Published: March 2009

High temperature oxidation of TiC ceramic matrix Fe40Al and Ni3Al toughened
composites (Fe40Al/TiC, Ni3Al/TiC) of different TiC contents, made by pressureless melt infiltration, was investigated. Oxidation experiments were conducted in air for up to 65 hours at 700-1100°C. Weight gains of the composites showed that Fe40Al/TiC is more oxidation resistant than Ni3Al/TiC ones. SEM/EDS and X-ray diffraction showed that the dense oxidation layers of the two types of composites are mainly composed of crystalline TiO2. The growth of the oxidation layer follows parabolic passive oxidation kinetics, the calculated values of the activation energy of the oxidation mechanism being 270-280kJ.mol-1 and 240-250kJ.mol-1 for Fe40Al/TiC and Ni3Al/TiC, respectively. Al2O3 and Ni-rich phases were also detected in the oxidation layer of Fe40Al/TiC and Ni3Al/TiC, respectively.
Mechanical Performance of Unsaturated Polyester Resins Modified with Powder from Scrap Tyre Rubber
Authors: Nóvoa Paulo J.R.O. , Ferreira Antonio , Marques António Torres
Published: March 2009

Unsaturated polyester resins are extensively used in the automotive industry as matrix for polymer based composite materials, but have poor impact resistance. Toughness can be improved dispersing a softer phase in brittle polymers. Scrap tyres constitute a significant waste problem and are a low-cost source for rubber. The objective of this work is the mechanical characterization of matrix systems containing solid rubber particles obtained from scrap tyres. Several pre-treatments
were tested based on contact time and temperature. The flexural and Charpy impact behaviour of the modified resins showed a decrease in performance. Dynamic mechanical tests did not result in clear evidence of phase mixing. Optical microscopy showed the presence of contaminant particles, which were considered the cause for the low performance. Among the modified resins, a positive
shift in flexural behaviour occurred when pre-heating was used. It is thought the strategy may prove effective in enhancing resin toughness, if the waste rubber is purified prior to its utilization.
Microstructure and Mechanical Properties of Friction Stir Welds in Aluminium Alloys 2024-T3, 5083-O and 6063-T6
Authors: Leal Rui M. , Loureiro Altino
Published: March 2009

The aim of this research is to study the effect of the welding process on the
microstructure and mechanical properties of friction stir welded joints in aluminium alloys 2024- T3, 5083-O and 6063-T6. A small loss of hardness and strength was obtained in welds in alloys 2024-T3 and 5083-O as opposed to welds in alloy 6063-T6, where a substantial softening and a drop of strength were observed. In alloy 6063-T6 a strength efficiency of only 45 to 47% was obtained.
Laser Cladding of Ni Based Cermets
Authors: Tobar Maria José , Amado José Manuel , Álvarez Carlos , Rodríguez German , Yáñez Armando
Published: March 2009

The self fluxing NiCrBSi alloys can produce coating layers by means of laser processing techniques. Main procedures are the laser post-treatment of previously thermal or plasma sprayed coats and the laser cladding, for which preplaced or continuously delivered powder (in this case aided by powder feeders) can be used. NiCrBSi alloys have an interesting property due to the presence of boron and silicon in its composition: they exhibit a relatively low melting point, making
the laser cladding process easier. The layers obtained on metallic based materials are resistant to high temperature erosion wear and corrosion. However, if additional abrasive wear resistance is needed, the feeding with ceramic powders such as tungsten carbides (WC) is required. The high melting point of ceramics makes the laser cladding process complicated as the melt pool is made up of liquid metal plus not totally melted ceramic particles and the whole suffers the effect of the
shielding and carrying gas flows, producing undesired instabilities. In this paper several combination of WC and NiCrBSi powders were tested. It is shown that the WC fraction in the mixture has a major influence on the obtention of pore and crack free clad layers. Bellow a certain ratio the meltpool appears to be more stable and less affected by the different gas flows used in the process, yielding dense NiCrBSi coatings with rather evenly distributed WC particles. In these conditions, the analysis and characterization of the produced coatings shows that the microstructure gains homogeneity without decreasing too much microhardness if compared with the pure ceramic layers.
Thermoreactivity of Sol-Gel Precursor for ZnO-Based Thin Films
Authors: Muşat Viorica , Vilarinho Paula M. , Monteiro Regina da Conceição Corredeira , Fortunato Elvira , Segal E.
Published: March 2009

The thermoreactivity of a zinc acetate non-alkoxide solution used for the preparation of ZnO-based thin films was investigated in the temperature range 20-600°C by TG-DTA, XRD and SEM data. We found that the formation in air of ZnO crystallites from the sol-gel precursor occurs above 150°C simultaneously with the decomposition of an intermediary compound, most probably carbonate hydroxide (sclarite and/or hydrozincite). At 200 °C, the crystalline structure is well defined in terms of ZnO hexagonal lattice parameters, although residual organic compounds and water were not yet fully removed and an amorphous phase coexists. A kinetic investigation on the thermal decomposition of sol-gel precursor from DTA data using Kissinger differential equation is also presented. Apparent activation energy values of about. 100 kJ mol-1 corresponding to the nonisothermal decomposition of solid precursors in the temperature range 170-250oC have been found.
Thermal Shock Behaviour of Open-Cell Cordierite Foams
Authors: Oliveira Fernando A. Costa , Dias Susana , Fernandes Jorge Cruz
Published: March 2009

Open-cell ceramic foams are being considered for a variety of applications owing to their high permeability and low weight, including molten metal filters, catalytic substrates and radiant burners. In these applications, foams are exposed to high temperatures and thermal gradients and thus the materials used require resistance to severe thermal stresses during service. Unfortunately, little is known about the thermal shock behaviour of cordierite foams when subjected to sudden
changes in temperature. The objective of the present study was to investigate the thermal shock behaviour of two kinds of cordierite-based ceramic foams manufactured by the replication process. Thermal shock experiments were carried out by rapidly transferring the heated samples from a resistance furnace to
a quenching bath containing distilled water followed by measuring of the retained flexural strength. Unlike dense cordierite samples that showed a sudden decrease in flexural strength at quench temperature differences above 325 K, the strength retained after thermal shock by open-cell cordierite foams decreased gradually with increasing quench temperatures. This suggests a cumulative damage mechanism reflecting an increase in damage throughout the material rather than sudden failure owing to propagation of pre-existing cracks.
Evaluation of Welding Residual Stresses Using the Incremental Hole-Drilling Technique
Authors: Nobre Joao P. , Loureiro Altino , Batista António Castanhola , Dias A. Morão
Published: March 2009

In this work the reliability of the hole-drilling technique (HDT) for measuring welding residual stresses was analysed. HDT residual stress results were systematically compared with those determined by X-ray diffraction. A systematic overestimation of the residual stresses determined by HDT was observed, which was mainly attributed to the possibility of the so-called plasticity effect occurring. Experimental results were discussed taking the measurement principles of both
techniques into consideration. In addition, preliminary results of a numerical study, using the finite element method, will be presented for a better understanding of the plasticity effect on HDT residual stress results.
Influence of the Interaction Potential Parameters on the Mechanical Response of Simulated Semi-Crystalline Polymeric Materials
Authors: Simões Ricardo , Viana Julio , Dias Gustavo R. , Cunha António M.
Published: March 2009

The tensile deformation of a semi-crystalline lamellar structure was simulated using
coarse-grain molecular dynamics. Interactions between statistical segments are described by Lennard-Jones potentials, with two types of interactions (primary and secondary bonds) defined for the amorphous and crystalline phases. The choice of the correct interaction potentials in coarsegrain simulations requires an understanding of the influence of each interaction potential parameter
on the mechanical response. The present paper reports results from that study, following a design of experiments approach. It was found that the apparent modulus is mainly determined by the width of the secondary bond potential. The yield stress and the extent of deformation of the material at a fixed force level are influenced both by the width of the secondary bond potential and the depth of the potential well of the amorphous region. Thus, the tensile mechanical properties and behaviour of
the specific lamellar structure under study seems to be mainly determined by the secondary interactions in the amorphous region.
Study of Electrochromic Devices Incorporating a Polymer Gel Electrolyte Component
Authors: Gonçalves Alexandra , Gonçalves Gonçalo , Fortunato Elvira , Marques António , Pimentel Ana , Martins Rodrigo , Silva Manuela A. , Smith Michael J. , Bela João , Borges João Paulo
Published: March 2009

Electrochromic materials have attracted considerable attention during the last two
decades as a consequence of their potential application in several different types of optical devices. Examples of these devices include intelligent windows and time labels. In this paper the authors describe results obtained with thin tungsten oxide films produced at room temperature by rf magnetron sputtering under an argon and oxygen atmosphere on transparent conductive oxide coated glass substrates. To protect the surface of the electrochromic film, prevent water absorption and obtain a good memory effect under open circuit voltages, a layer of Ta2O5 was deposited over the WO3 films. In this study, the effect of different electrolyte compositions on the open circuit memory of optical devices has been characterized. The best results were obtained for electrochromic devices with polymer gel p(TMC)3LiClO4 and p(TMC)8LiClO4 electrolytes. These prototype devices present an
overall transmittance of ~75% in their bleached state and after coloration 40.5 and 52.5% respectively. These devices also show memory effect and an optical density considered satisfactory for some electrochromic applications.