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Materials Research, Volume: 11, Número: 1, Publicado: 2008
  • Materials Research - Ibero-american Journal of Materials: judicious, fair and educative!

    Zanotto, Edgar Dutra
  • Influence of cathodic current density and mechanical stirring on the electrodeposition of Cu-Co alloys in citrate bath

    Farias, Leandro Trinta de; Luna, Aderval Severino; Lago, Dalva Cristina Baptista do; Senna, Lilian Ferreira de

    Resumo em Inglês:

    Cathodic polarization curves of Cu-Co alloys were galvanostatically obtained on a platinum net, using electrolytes containing copper and cobalt sulfates, sodium citrate and boric acid (pH values ranging from 4.88 to 6.00), with different mechanical stirring conditions. In order to evaluate quantitatively the influence of the applied current density and the mechanical stirring on the cathodic efficiency, the alloy composition for the Cu-Co alloy deposition process, and the average deposition potential, an experimental central composite design 2² was employed, and three current density intervals (0.11 to 0.60, 0.50 to 1.98 and 2.44 to 9.94 mA.cm-2) were chosen from the polarization curves for this purpose. The results indicated that the current density (mainly in the range between 0.11 and 0.60 mA.cm-2) affected significantly all the studied variables. In the intermediate range (0.50 to 1.98 mA.cm-2), only the average potential was influenced by the current density. On the other hand, the mechanical stirring had a significant effect only on the copper content, for both the lowest (0.11 to 0.60 mA.cm-2) and the highest current density range (2.44 to 9.94 mA.cm-2). Indeed, in the last range, none of the studied deposition parameters presented significant influence on the studied variables, except for the copper content. This could probably be explained by the direct incorporation of Cu-Citrate complexes in the coating, which was enhanced at high current values.
  • Sintered eutectoid P/M steel behaviour during cold upsetting

    Kannan, A. Rajesh; Pandey, K.S.; Shanmugam, S.; Narayanasamy, R.

    Resumo em Inglês:

    Cold upsetting experiments were carried out on sintered Fe-0.8%C steel preforms in order to evaluate the technical relationship that exist between the applied stresses against continuous deformation and densification. Powder preforms of 86% theoretical density and 0.40 of initial aspect ratio were subjected to incremental compressive loading of 0.04 MN under three different friction conditions such as dry, graphite and zinc stearate employed during deformation until fracture appears at free surfaces. Experimental results revealed that the response of applied stresses with induced strain and attained densification exhibits a continuous enhancement but with three different stages. Irrespective of friction conditions the first and third stage shows steep rise, which offers high resistance to deformation, whereas the second stage shows virtually steady state; deformation needed gradual increase in applied stresses but with high rate of densification. Further, preform deformed under without lubricant exhibited maximum strain hardening as well as an enhanced rate of strain hardening through out the deformation in comparison with lubricants employed conditions.
  • Microstructure and composition of rare earth-transition metal-aluminium-magnesium alloys

    Zarpelon, Lia Maria Carlotti; Galego, Eguiberto; Takiishi, Hidetoshi; Faria, Rubens Nunes

    Resumo em Inglês:

    The determination of the microstructure and chemical composition of La0.7-xPr xMg0.3Al 0.3Mn0.4Co0.5 Ni3.8 (0 < x < 0.7) metal hydride alloys has been carried out using scanning electron microscopy (SEM), energy dispersive X ray analysis (EDX) and X ray diffraction analysis (XRD). The substitution of La with Pr changed the grain structure from equiaxial to columnar. The relative atomic ratio of rare earth to (Al, Mn, Co, Ni) in the matrix phase was 1:5 (LaNi5-type structure). Magnesium was detected only in two other phases present. A grey phase revealed 11 at.% Mg and the concentration ratios of other elements indicated the composition to be close to PrMgNi4. A dark phase was very heterogeneous in composition, attributed to the as-cast state of these alloys. The phases identified by XRD analysis in the La0.7Mg0.3Al0.3Mn0.4Co 0.5Ni3.8 alloy were: La(Ni,Co)5, LaAl(Ni,Co)4, La2(Ni,Co)7 and AlMn(Ni,Co)2. Praseodymium favors the formation of a phase with a PuNi3-type structure. Cobalt substituted Ni in the structures and yielded phases of the type: Pr(Ni,Co)5 and Pr(Ni,Co)3.
  • Empirical models for end-use properties prediction of LDPE: application in the flexible plastic packaging industry

    Costa, Maria Carolina Burgos; Jardini, André Luiz; Maciel, Maria Regina Wolf; Embiruçu, Marcelo; Maciel Filho, Rubens

    Resumo em Inglês:

    The objective of this work is to develop empirical models to predict end use properties of low density polyethylene (LDPE) resins as functions of two intrinsic properties easily measured in the polymers industry. The most important properties for application in the flexible plastic packaging industry were evaluated experimentally for seven commercial polymer grades. Statistical correlation analysis was performed for all variables and used as the basis for proper choice of inputs to each model output. Intrinsic properties selected for resin characterization are fluidity index (FI), which is essentially an indirect measurement of viscosity and weight average molecular weight (MW), and density. In general, models developed are able to reproduce and predict experimental data within experimental accuracy and show that a significant number of end use properties improve as the MW and density increase. Optical properties are mainly determined by the polymer morphology.
  • Ultrasonic study of structural instabilities in nickel induced by magnetic fields

    Moreno-Gobbi, Ariel; Moreno, Daniel; Zamir, Gabriel

    Resumo em Inglês:

    The ultrasonic phase velocity was measured on a high purity nickel single crystal with a bias magnetic field in cooling and heating runs over the interval of temperatures from approximately 100 to 325 K. An evident anomaly of the phase velocity was observed in both branches of the temperature cycle. The temperature of the anomaly in the heating run was always greater than that in the cooling run, indicating the presence of a hysteretic mechanism. The observed changes are attributed to dimensional alignment of the nickel single crystal twins which are able to distort the crystalline network. The temperature of the anomalies and its hysteretic behavior depend on the synergy between the direction and strength of the magnetic field, the direction of the ultrasonic wave propagation, the internal friction between the domains and the crystallographic orientation. The frictions between magnetic domains that do not contribute to the velocity anomaly produce a hysteretic loop. The process can be easily inhibited by disorientation of the magnetic field.
  • Thermal properties of WC-10 wt. (%) Co alloys

    Machado, Francisco de Assis Léo; Rodrigues, Márcio Ferreira; Vargas, Helion; Filgueira, Marcello; Faria Júnior, Roberto da Trindade

    Resumo em Inglês:

    In this article, photothermal techniques were used in order to determine some thermal properties: diffusivity, conductivity, effusivity and specific heat capacity of WC-10 wt. (%) Co six samples subjected to different sintering processes. The samples were sintered using high pressure - high temperature (HPHT) sintering system. The open cell photoacoustic (OPC) used to measure thermal diffusivity is described in detail. The values of thermal properties here measured and evaluated are consistent to those previously reported in the literature.
  • Oxidation and erosion-oxidation behavior of steels

    Fernandes, Stela Maria de Carvalho; Correa, Olandir Vercino; Ramanathan, Lalgudi Venkataraman

    Resumo em Inglês:

    The high temperature oxidation and erosion-oxidation (E-O) behavior of steels AISI 1020, 304, 310, and 410 were determined. These steels were selected to evaluate the effect of chromium content on its E-O resistance. The oxidation behavior was determined in a thermogravimetric analyzer. A test rig in which a specimen assembly was rotated through a fluidized bed of erodent particles was used to determine the E-O behavior. Alumina powder (200 µm) was used as the erodent. The E-O tests were carried out in the temperature range 25-600 °C, with average particle impact velocities of 3.5 and 15 ms-1 and impact angle of 90°. The oxidation resistance of the steels increased with chromium content. The E-O behavior of the steels was determined as wastage. The E-O wastage of the steels exposed to particle impact at low velocity was low but increased with temperature above 300 °C. The E-O wastage of the different steels exposed to particle impact at high velocity was quite similar. The wastage increased with increase in temperature above 500 °C. The increases in E-O wastage of the steels observed at temperatures above 300, 400 or 500 °C, depending on the steel, were due mainly to a transition in the dominant wastage process, from 'erosion' to 'erosion-oxidation'.
  • Hydroxyapatite coating on silicon nitride surfaces using the biomimetic method

    Silva, Cecilia Chaves Guedes e; Rigo, Eliana Cristina da Silva; Marchi, Juliana; Bressiani, Ana Helena de Almeida; Bressiani, José Carlos

    Resumo em Inglês:

    Silicon nitride based ceramics are promising candidates for biomedical applications due to their chemical and dimensional stability associated to suitable mechanical strength and relatively high fracture toughness. However, the bioinert characteristics of these ceramics limit their application to situations where the formation of chemical bonds between the material and the tissue are not essential. A way to broaden the application field of these ceramics in medicine is promoting their bioactivity by means of a hydroxyapatite coating. Therefore, in this paper, samples of silicon nitride were coated with apatite using the biomimetic method. The treated silicon nitride surface was characterized by diffuse reflectance infrared Fourier transformed, X ray diffraction and scanning electron microscopy. The results showed that a layer of hydroxyapatite could be deposited by this method on silicon nitride samples surface.
  • Influence of grain size and additions of Al and Mn on the magnetic properties of non-oriented electrical steels with 3 wt. (%) Si

    Cardoso, Rodrigo Felix de Araujo; Brandao, Luiz; Cunha, Marco Antônio da

    Resumo em Inglês:

    The influence of hot-band grain size and additions of aluminum and manganese on the magnetic properties of non-oriented grain (NOG) low-carbon electrical steel with about 3 wt. (%) Si were investigated using optical microscopy and X ray diffraction. The addition of manganese resulted in larger grains after final annealing. Coarse grains in the hot-band and addition of Mn led to a Goss orientation component after final annealing, which resulted in an increase in the magnetic permeability.
  • Influence of ultrasonic setting on compressive and diametral tensile strengths of glass ionomer cements

    Barata, Terezinha Jesus Esteves; Bresciani, Eduardo; Adachi, Akimi; Fagundes, Ticiane Cestari; Carvalho, Carlos Augusto Ramos; Navarro, Maria Fidela Lima

    Resumo em Inglês:

    The aim of this study was to assess the influence of ultrasonic wave propagation on the compressive (CS) and diametral tensile (DTS) strengths of glass ionomer cements (GICs). Three variables were evaluated: conventional GICs, ultrasonic excitation and storage time (1 hour, 24 hours and 7 days). Bovine teeth molds were used for simulating a clinical ultrasonic excitation. The data were submitted to three-way ANOVA and Tukey tests (P < 0.05). All the tested conventional GICs presented an increase in strength from 1 hour to 7 days for CS and DTS. Ultrasonic excitation resulted in a statistically significant increase in the CS, but showed no statistically significant difference in the DTS. Regardless the GICs tested the increase in strength was maturation time-dependent for all groups.
  • Grain size effect on the structural parameters of the stress induced epsilonhcp: martensite in iron-based shape memory alloy

    Nascimento, Fabiana Cristina; Mei, Paulo Roberto; Cardoso, Lisandro Pavie; Otubo, Jorge

    Resumo em Inglês:

    The aim of this work was to study the effect of austenitic grain size (GS) reduction on the structural parameters of the epsilonhcp - martensite in stainless shape memory alloy (SMA). Rietveld refinement data showed an expansion in c-axis and a reduction in a and b-axis with thermo-mechanical cycles for all samples analyzed. Samples with 75 < GS (µm) < 129 were analyzed. It was also observed an increase of the unit cell volume in this phase with GS reduction. The smallest grain size sample (GS = 75 µm) presented a c/a ratio of 1.649, and approximately 90% of total shape memory recovery.
  • Influence of light-curing unit systems on shear bond strength and marginal microleakage of composite resin restorations

    Sassi, Juliano Fernandes; Batista, Andrigo dos Reis; Ciccone-Nogueira, Juliane Cristina; Corona, Silmara Aparecida Milori; Palma-Dibb, Regina Guenka

    Resumo em Inglês:

    The aim of the present study was to evaluate the influence of different photopolymerization (halogen, halogen soft-start and LED) systems on shear bond strength (SBS) and marginal microleakage of composite resin restorations. Forty Class V cavities (enamel and dentin margins) were prepared for microleakage assessment, and 160 enamel and dentin fragments were prepared for the SBS test, and divided into 4 groups. Kruskal-Wallis and Wilcoxon tests showed statistically significant difference in microleakage between the margins (p < 0.01) with incisal margins presenting the lowest values. Among the groups, it was observed that, only at the cervical margin, halogen soft-start photo polymerization presented statistically significant higher microleakage values. For SBS test, ANOVA showed no statistical difference (p > 0.05) neither between substrates nor among groups. It was concluded that Soft-Start technique with high intensity end-light influenced negatively the cervical marginal sealing, but the light-curing systems did not influence adhesion.
  • Effect of salt leaching on PCL and PLGA(50/50) resorbable scaffolds

    Barbanti, Samuel Hilsdorf; Zavaglia, Cecília Amélia Carvalho; Duek, Eliana Aparecida de Rezende

    Resumo em Inglês:

    The use of porous bioresorbable scaffolds in the field of tissue engineering represents an alternative for the treatment of lesions and losses of biological tissues. This work evaluates the leaching salt effect of two different processes and polymers. Dense and porous scaffolds were prepared with poly(epson-caprolactone) (PCL) and poly(D,L-lactic acid-co-glycolic acid) (50/50) (PLGA50) by casting and melting compression process. Sodium citrate with particles sizes of 180-250 µm of diameter was used as porogen. The dense and porous samples were immersed in distilled water for 30 hours and evaluated for pH and mass variations, by scanning electronic microscopy (SEM), differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA). The results of the analyses showed that the inclusion of the salt and leaching process did not affect the properties of the scaffold, indicating that the method is useful to make porous scaffolds to be potentially used in tissue engineering.
  • Characterization of ground SBR scraps from shoe industry

    Massarotto, Marinês; Crespo, Janaina da Silva; Zattera, Ademir José; Zeni, Mara

    Resumo em Inglês:

    Expanded poly(butadiene-co-styrene) (SBR), a residue of the shoe industry of Rio Grande do Sul, is a crosslinked material. For further utilization in recycling and reclaiming processes this residue was ground under ambient conditions. The obtained powder (SBR-r) was physically, thermally and chemically characterized and the results were analyzed as for its suitability for reuse methods. This characterization provides a better understanding of the SBR residue components, which may lead to economic and environmental advantages. The SBR-r (3548 mesh) is composed by 22.2% of SBR and 77.8% of filler. The elastomeric fraction has 71.4% of crosslinked material. The results demonstrate that SBR can be recycled for use in microcellular composites.
  • Dielectric behaviour of CaCu3Ti4O12-epoxy composites

    Ramajo, Leandro Alfredo; Ramírez, Miguel Angel; Bueno, Paulo Roberto; Reboredo, María Marta; Castro, Miriam Susana

    Resumo em Inglês:

    The dielectric behavior of composite materials (epoxy resin - barium titanate and epoxy - CCTO) was analysed as a function of ceramic amount. Composites were prepared by mixing the components and pouring them into suitable moulds. In some compositions, the matrix was reduced by tetrahydrofuran (THF) incorporation. Samples containing various amounts of ceramic filler were examined by TG/DTA and scanning electron microscopy analysis. Dielectric measurements were performed from 20 Hz to 1 MHz and 30 to 120 °C. It was demonstrated that the epoxy - CCTO composites possessed higher permittivity than classic epoxy - BaTiO3 composites. However, the low resin permittivity prevailed in the composite dielectric performance.
  • Performance of 3Y-TZP bioceramics under cyclic fatigue loading

    Souza, Renato Chaves; Santos, Claudinei dos; Barboza, Miguel Justino Ribeiro; Baptista, Carlos Antonio Reis Pereira; Strecker, Kurt; Elias, Carlos Nelson

    Resumo em Inglês:

    In this work, the static mechanical properties and cyclic fatigue life of 3 mol. (%) Y2O3-stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramics were investigated. Pre-sintered samples were sintered in air at 1600 °C for 120 minutes, and characterized by X ray diffraction and scanning electronic microscopy. Hardness and fracture toughness were determined by Vicker's indentation method, and Modulus of Rupture was determined by four-point bending testing. Fully dense sintered samples, near to 100% of theoretical density, presented hardness, fracture toughness and bending strength of 13.5 GPa, 8.2 MPa.m½ and 880 MPa, respectively. The cyclic fatigue tests were also realized using four-point bending testing, within a frequency of 25 Hz and stress ratio R of 0.1. The increasing of load stress lead to decreasing of the number of cycles and the run-out specimens number. The tetragonal-monoclinic (t-m) ZrO2-transformation observed by X ray diffraction contributes to the increasing of the fatigue life. The 3Y-TZP samples clearly presents a range of loading conditions where cyclic fatigue can be detected.
  • Characterization of antiseptic apatite powders prepared at biomimetics temperature and pH

    Belouafa, Soumia; Chaair, Hassan; Loukili, Hayate; Digua, Khalid; Sallek, Brahim

    Resumo em Inglês:

    Antiseptic apatite-based calcium phosphates were prepared as the single-phase powders. Phosphocalcic oxygenated apatites were synthesized from calcium salts and orthophosphate dissolved in oxygenated water solution at 30%, under the biomimetic conditions of 37 °C and pH 7.4. The characterization and chemical analysis of the synthesized biomimetic apatite powders were performed by scanning electron microscopy (SEM), powder X ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR) and chemical analysis. The obtained materials are a calcium deficient apatites with different morphologies.
  • Evaluation of the transformation mechanisms and mechanical properties of ferrite: martensite microalloyed steels

    Henry, Ovri; Monde, Kamma Celestine

    Resumo em Inglês:

    The influence of starting point microstructures on the transformation mechanisms and mechanical properties of a micro alloyed steel after annealing in the alpha + gamma region have been investigated. Three different microstructures: austenite, pearlite in a ferrite matrix and martensite were used as starting point microstructures for the production of dual (alpha + <IMG SRC="/img/revistas/mr/v11n1/18s1.gif">) phase structures in the test steel. Photomicrographs obtained from metallographic examination of the heat treated samples were used as criteria for the assessment of results obtained from impact toughness and hardness testing. The results obtained showed that the transformation mechanisms and hence the morphology of ferrite - martensite microalloyed steels are strongly influenced by their initial microstructural details. Ferrite - martensite structures produced via the intercritical quench (IQ) treatment, with martensite as the starting point microstructure, have the best combination of hardness and impact energy.
  • Formal analysis of isothermal martensite spread

    Rios, Paulo Rangel; Guimarães, José Roberto Costa

    Resumo em Inglês:

    A formal kinetic approach was applied to the spread of isothermal martensite over the neighboring austenite grains in a Fe-23.2 wt. (%) Ni-2.8 wt. (%) Mn alloy. The number of grains in a spread event changed with parent austenite grain size. However, isothermal martensite spread formed from fine-grained parent austenite and athermal martensite from a Fe-31 wt. (%) Ni-0.02 wt. (%) C alloy studied in a previous work followed the same microstructural path. The number of grains per spread- event found in the present study was shown to be consistent with the number of neighbors of the grain originating the spread event by means of a simple geometrical model of the parent austenite grain network. The study of the kinetics of isothermal martensite spread showed that the nucleation rate of the spread-event in isothermal martensite remained constant during the transformation. This result parallels the constant nucleation rate of the spread-event also found using the same methodology in athermal martensite formed in a Fe-31 wt. (%) Ni-0.02 wt. (%) C alloy studied in a previous work.
  • Simulation of recrystallization in iron single crystals

    Salazar, Tatiana Caneda; Assis, Weslley Luiz da Silva; Rios, Paulo Rangel

    Resumo em Inglês:

    Recrystallization of an iron single crystal was reported in detail by Vandermeer and Rath (V&R). We present predictions of recrystallization based on cellular automata (CA) simulations, and compare them with the data and analysis from V&R's study. Agreement is found between our CA simulations and V&R's results, provided that the CA simulations were carried out using a sufficient dynamic range for time, precision spatial dimensionalization, and accommodation of grain shape effects inherent in CA techniques.
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