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Materials Research, Volume: 11, Número: 4, Publicado: 2008
  • Materials Research - Ibero-american Journal of Materials: Judicious, fair and educative! Editorial

    Zanotto, Edgar Dutra
  • Microstructure and mechanical properties of gypsum composites reinforced with recycled cellulose pulp Regular Articles

    Carvalho, Magaly Araújo; Calil Júnior, Carlito; Savastano Junior, Holmer; Tubino, Rejane; Carvalho, Michele Tereza

    Resumo em Inglês:

    The use of waste fibers for the reinforcement of brittle matrices is considered opportune for the sustainable management of urban solid residues. This paper examines the microstructure and mechanical properties of a composite material made of gypsum reinforced with cellulose fibers from discarded Kraft cement bag. Two different kinds of gypsum were used, natural gypsum (NG) and recycled gypsum (RG), both with an addition of 10% by mass of limestone. For the production of samples, slurry vacuum de-watering technique followed by pressing was evaluated revealing to be an efficient and innovative solution for the composites under evaluation. The composite was analyzed based on flexural strength tests, scanning electron microscopy (SEM) imaging, secondary electron (SE) detection, and pseudo-adiabatic calorimetry. The morphology of the fractured surfaces of flexural test samples revealed large gypsum crystals double the original size surrounding the fibers, but with the same overall aspect ratio. Natural fibers absorb large amounts of water, causing the water/gypsum ratio of the paste to increase. The predominance of fiber pullout, damaged or removed secondary layers and incrusted crystals are indicative of the good bonding of the fiber to the gypsum matrix and of the high mechanical resistance of composites. This material is a technically better substitute for the brittle gypsum board, and it stands out particularly for its characteristics of high impact strength and high modulus of rupture.
  • Characterization of compression strength of granite-epoxy composites using design of experiments Regular Articles

    Piratelli-Filho, Antonio; Shimabukuro, Frank

    Resumo em Inglês:

    This paper presents a processing study of the polymer matrix composite (PMC) developed with an epoxy polymeric matrix reinforced with particulate ceramic granite. This PMC composite has been reported to be used as structural parts of machine tools and Coordinate Measuring Machines due to its superior vibration damping characteristics and reduced processing cycle over cast iron. The investigated processing variables were epoxy content and particle size and the mechanical characterization was carried out by compressive tests. Rejects of granite with particle size smaller than 500 µm were prepared by crushing, milling and classification operations. The powder was mixed with different compositions of epoxy resin, between 15 and 20% in weight. An experiment was planned and executed according to the Factorial design technique using two variables at two levels. The obtained cylindrical samples were submitted to compressive strength tests and the results showed a maximum resistance of 114.23 MPa at 20 wt. (%) epoxy, value close to that of the literature.
  • Characterization of manganese alloy residues for the recycling of FeSiMn and high-carbon FeMn fines Regular Articles

    Faria, Geraldo Lúcio de; Reis, Érica Linhares; Araújo, Fernando Gabriel da Silva; Vieira, Cláudio Batista; von Krüger, Fernando Leopoldo; Jannotti Jr., Nelson

    Resumo em Inglês:

    Crushing residues of FeSiMn and high-carbon (HC) FeMn alloys were characterized in order to evaluate their recycling possibility. Particle size determination was performed by screening, followed by chemical analysis of each particle size range using plasma spectrometry (ICP-AES). The slag content was identified and quantified by optical microscopy. All of the fines with grain sizes above 1.18 mm presented alloy contents in excess of 99 wt. (%) and were determined to need no further concentration prior to recycling. However the contents of Mn, Fe, Si and P in the fraction below 1.18 mm did not meet the chemical specifications for commercial manganese alloys, except for phosphorous. Optical microscopy of the fraction below 1.18 mm, showed that 87.95% of the FeSiMn corresponded to the alloy and that the slag content was 12.05%. For the HC-FeMn sample, 95.07% corresponded to the alloy and only 4.93% to the slag. These results revealed potential for gravity concentration and recycling, reducing the residues in about 95% and improving the process productivity.
  • Natural gas storage in microporous carbon obtained from waste of the olive oil production Regular Articles

    Solar, Cecilia; Sardella, Fabiana; Deiana, Cristina; Lago, Rochel Montero; Vallone, Andrea; Sapag, Karim

    Resumo em Inglês:

    A series of activated carbons (AC) were prepared from waste of the olive oil production in the Cuyo Region, Argentine by two standard methods: a) physical activation by steam and b) chemical activation with ZnCl2. The AC samples were characterized by nitrogen adsorption at 77 K and evaluated for natural gas storage purposes through the adsorption of methane at high pressures. The activated carbons showed micropore volumes up to 0.50 cm³.g-1 and total pore volumes as high as 0.9 cm³.g-1. The BET surface areas reached, in some cases, more than 1000 m².g-1. The methane adsorption -measured in the range of 1-35 bar- attained values up to 59 V CH4/V AC and total uptakes of more than 120 cm³.g-1 (STP). These preliminary results suggest that Cuyo's olive oil waste is appropriate for obtaining activated carbons for the storage of natural gas.
  • Hydrophobicity classification of polymeric materials based on fractal dimension Regular Articles

    Thomazini, Daniel; Gelfuso, Maria Virginia; Altafim, Ruy Alberto Corrêa

    Resumo em Inglês:

    This study proposes a new method to obtain hydrophobicity classification (HC) in high voltage polymer insulators. In the method mentioned, the HC was analyzed by fractal dimension (fd) and its processing time was evaluated having as a goal the application in mobile devices. Texture images were created from spraying solutions produced of mixtures of isopropyl alcohol and distilled water in proportions, which ranged from 0 to 100% volume of alcohol (%AIA). Based on these solutions, the contact angles of the drops were measured and the textures were used as patterns for fractal dimension calculations.
  • Characterization of interference thin films grown on stainless steel surface by alternate pulse current in a sulphochromic solution Regular Articles

    Junqueira, Rosa Maria Rabelo; Loureiro, Célia Regina de Oliveira; Andrade, Margareth Spangler; Buono, Vicente Tadeu Lopes

    Resumo em Inglês:

    The aim of this work was to characterize thin interference films grown on the surface of AISI 304 stainless steel for decorative purposes. Films were grown in a sulphochromic solution at room temperature by an alternating pulse current method. The morphology and chemical state of the elements in the films were investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), glow discharge optical emission spectrometry (GDOES), and infrared Fourier transform spectroscopy (FTIR). Depth-sensing indentation (DSI) experiments and wear abrasion tests were employed to assess the mechanical resistance of the films. The coloration process resulted in porous thin films which increased the surface roughness of the substrate. The interference films mainly consisted of hydrated chromium oxide containing iron. Increasing film thickness produced different colors and affected the mechanical properties of the coating-substrate system. Thicker films, such as those producing gold and green colors, were softer but more abrasion resistant.
  • Portland cement hydration in the presence of admixtures: black gram pulse and superplasticizer Regular Articles

    Dwivedi, Viveka Nand; Das, Shiva Saran; Singh, Nakshatra Bahadur; Rai, Sarita; Gajbhiye, Namdev Shriram

    Resumo em Inglês:

    Effect of admixtures such as black gram pulse (BGP) and sulfonated naphthalene based superplasticizer (SP) on the hydration of Portland cement has been studied. The hydration characteristics of OPC in the presence of BGP and SP were studied with the help of non evaporable water content determinations, calorimetric method, Mössbauer spectroscopic and atomic force microscopic techniques. Results have shown that both BGP and SP get adsorbed at the surface of cement and its hydration products. The hydration of Portland cement is retarded in the presence of both the admixtures and nanosize hydration products are formed.
  • Physico-chemical analysis of flexible polyurethane foams containing commercial calcium carbonate Regular Articles

    Sant'Anna, Sabrina Sá e; Souza, Denilson Arlindo de; Araujo, Danielle Marques de; Carvalho, Cornélio de Freitas; Yoshida, Maria Irene

    Resumo em Inglês:

    Calcium carbonate (CaCO3) is a filler often utilized by the Brazilian mattress factories in the production of polyurethane foams. The filler allows the substitution of part of the polymeric agents, conferring dimensional stability and hardness to the foams. However, in agreement with experimental data, it is observed that the excess of commercial CaCO3 utilized in industry causes the increase of hysteresis, possibly causing permanent deformations and damaging the quality of the final product. In the present work, the physico-chemical analyses of the flexible polyurethane foams with different contents of CaCO3 were performed. The foams are submitted to the morphological, mechanical and positron analyses to verify the alterations provoked by the progressive introduction of this filler.
  • Using lithium glass infiltration to enhance the properties of alumina bodies Regular Articles

    Acchar, Wilson; Queiroz, José Renato Cavalcanti de

    Resumo em Inglês:

    The use of an infiltration process to improve the properties of sintered materials has been widely investigated. This work describes the research carried out in the manufacturing of lithium glass-infiltrated alumina. The infiltration material consisted of a mixture of elements such as Li2O, ZrO2, SiO2 Al2O3, CaO and La2O3. Alumina specimens were sintered in air at 1400 °C for 2 hours. A number of samples were then submitted to the infiltration process at 1400 °C for 15 minutes. Sintered and infiltrated specimens were characterized by X ray diffraction, apparent density, open porosity, flexural strengths and scanning electron microscopy. The results showed that the infiltration process considerably improves the properties of alumina bodies.
  • Synthesis of mesoporous silica microsphere from dual surfactant Regular Articles

    Narayanan, Venkatathri

    Resumo em Inglês:

    A new procedure is reported to synthesis mesoporous silica micro sphere for the first time. In these method two surfactants namely Span 80 and Tween 80 were used. Small angle X ray diffraction and N2 adsorption analysis shows the synthesized material has mesoporous property. The material has spherical morphology with 1-10 µm particle size. Beside the material found to have microcapsule property as observed from the Transmission electron microscopy. The Fourier transform Infrared spectroscopic analysis reveals that the materials are similar to other mesoporous materials. We also encapsulated an UV-absorber Ibuprofen inside the microcapsule, by mixing it before the synthesis. This shows a possibility of the materials in cosmetic applications.
  • Properties of SBS and sisal fiber composites: ecological material for shoe manufacturing Regular Articles

    Verney, José Carlos Krause de; Lima, Martha Fogliato Santos; Lenz, Denise Maria

    Resumo em Inglês:

    The worldwide trend toward using cheap, atoxic and durable materials from renewable resources contributes to sustainable development. Thus, the investigation of the potential use of vegetal fibers as reinforcing agent in polymeric composites has gained new significance. Sisal fiber has emerged as a reinforcing material for polymers used in automobile, footwear and civil industries. In this work, properties such as hardness, tensile strength and tear strength of polymer composites composed by block copolymer styrene-butadiene-styrene (SBS) and 5, 10 and 20% by weight of sisal fiber were evaluated. The influence of conventional polymer processing techniques such as single-screw and double-screw extrusion, as well as the addition of coupling agent on the composite mechanical performance was investigated. Also, the morphology and thermal stability of the composites were analyzed. The addition of 2 wt. (%) maleic anhydride as coupling agent between sisal fiber and SBS has improved the composite mechanical performance and the processing in a double-screw extruder has favored the sisal fiber distribution in the SBS matrix.
  • Analysis of the relative rib area of reinforcing bars pull out tests Regular Articles

    Barbosa, Maria Teresa Gomes; Sánchez Filho, Emil de Souza; Oliveira, Thais Mayra de; Santos, White José dos

    Resumo em Inglês:

    The good performance of reinforced concrete structures is ensured by the transfer of stress linking a reinforcing bar and the surrounding concrete. The bond steel-concrete is a very complex phenomenon. This paper presents the experimental results of a program with specimens used in the pull out test with concrete strength of 20, 40, 60, 80 and 100 MPa and four different steel diameters: 12.5, 16.0, 20.0 and 25.0 mm. The test results indicated that the bond stress varied with the bars rib face angle, rib spacing, and rib height. The trends of the results were independent of the concrete strength with the test results, and design recommendations made as regards optimum rib geometries of deformed bars with high bond-slip characteristics.
  • Virtual analysis of stresses in human teeth restored with esthetic posts Regular Articles

    Amarante, Martha Vasconcellos; Pereira, Marcos Venicius Soares; Darwish, Fathi Aref Ibrahim; Camarão, Arnaldo Freitas

    Resumo em Inglês:

    The use of intra-radicular posts for rebuilding of damaged teeth is a normal practice in contemporary dentistry. However, dental roots restored with posts are subjected to the risk of failure under occlusal loads, particularly in cases of small dentin thickness. This study adopted the finite element analysis to compare the elastic stress distribution in simulated endodontically treated maxillary central incisor restored with two different esthetic posts, a ceramic post and a prefabricated fiber glass post. Under masticatory load, the shear stress and von Mises equivalent stress were determined for the different regions of the two models. The results demonstrated that stress concentrations occurred mainly in the cervical dentin in the prefabricated fiber glass post model. The ceramic post model presented stress concentration in a region limited to the proper post adjacent to its apical end, thus preserving the root dentin.
  • Characterization of thiol-functionalised silica films deposited on electrode surfaces Regular Articles

    Cesarino, Ivana; Cavalheiro, Éder Tadeu Gomes

    Resumo em Inglês:

    Thiol-functionalised silica films were deposited on various electrode surfaces (gold, platinum, glassy carbon) by spin-coating sol-gel mixtures in the presence of a surfactant template. Film formation occurred by evaporation induced self-assembly (EISA) involving the hydrolysis and (co)condensation of silane and organosilane precursors on the electrode surface. The characterization of such material was performed by IR spectroscopy, thermogravimetry (TG), elemental analysis (EA), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV).
  • Evaluation and modelling of integral capacitors produced by interdigitated comb electrodes Regular Articles

    Ramajo, Leandro Alfredo; Ramajo, Damian Enrique; Reboredo, María Marta; Santiago, Diego Hernan; Castro, Miriam Susana

    Resumo em Inglês:

    Integral capacitors (IC) of one or two-layer printed wiring board (PWB) circuits were produced using comb electrodes fixtures and dielectric composites as the inter-electrode material. ICs were fabricated at laboratory scale, using copper comb electrodes and BaTiO3-epoxy composite materials deposited on a glass-Epoxy FR4 board. They were experimentally tested in order to obtain their electrical response. Furthermore, ICs behaviour was modelled through 2-dimensional models applying finite element method (FEM). Results showed that by this laboratory technique it was possible to obtained integral capacitors with low dielectric losses. Moreover, acceptable agreement was found between numerical and experimental capacitance results for all the different analysed ICs. In conclusion, 2D FEM models are a suitable tool to predict electric response of IC devices.
  • Chemsensor of NO2 gas based on porphyrin of 5, 10, 15, 20-tetraphenylporphyrin LB films and LS films Regular Articles

    Sales, Nelício Faria de; Mansur, Herman Sander

    Resumo em Inglês:

    The sensitivity of 5, 10, 15, 20-tetraphenylporphyrin (H2TPP) to the presence of NO2 gas in diluted solutions and in Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) films was investigated by UV-visible spectroscopy. The shift of Soret and Q bands were analyzed and the energies involved were calculated. The exposure of LB porphyrin films deposited onto glass slides to NO2 has performed as an active chemsensor with 7000 ppm gas concentration. Furthermore, the UV-vis dichroism absorption results associated with the Soret bands have given evidence of the tilt angle of the macrocycle related to the substrate. H2TPP in LB film was tilted by an angle of 51 ± 5° and in the LS film was tilted by an angle of 36° ± 5° indicating the formation of a preferential organization of the molecular films depending on the deposition method.
  • Evaluation of PHB/Clay nanocomposite by spin-lattice relaxation time Regular Articles

    Bruno, Mariana; Tavares, Maria Inês Bruno; Motta, Leandro Medeiros; Miguez, Eduardo; Preto, Monica; Fernandez, Amanda Oliveira Rodriguez

    Resumo em Inglês:

    Poly(3-hydroxybutyrate) (PHB) based on nanocomposites containing different amounts of a commercial organically modified clay (viscogel B7) were prepared employing solution intercalation method. Three solvents, such as: CHCl3, dimethylchloride (DMC) and tetrahydrofuran (THF) were used. The relationship among the processing conditions; molecular structure and intermolecular interaction, between both nanocomposite components, were investigated using a nuclear magnetic resonance (NMR), as a part of characterization methodology, which has been used by Tavares et al. It involves the hydrogen spin-lattice relaxation time, T1H, by solid state nuclear magnetic resonance, employing low field NMR. X ray diffraction was also employed because it is a conventional technique, generally used to obtain the first information on nanocomposite formation. Changes in PHB crystallinity were observed after the organophilic nanoclay had been incorporated in the polymer matrix. These changes, in the microstructure, were detected by the variation of hydrogen nuclear relaxation time values and by X ray, which showed an increase in the clay interlamelar space due to the intercalation of the polymer in the clay between lamellae. It was also observed, for both techniques, that the solvents affect directly the organization of the crystalline region, promoting a better intercalation, considering that they behave like a plasticizer.
  • Thermoplastic polyolefins as formaldehyde free binders in highly filled lignocellulosic panel boards: using glycerine as a processing aid in kenaf fiber polypropylene boards Regular Articles

    Sanadi, Anand Ramesh; Caulfield, Daniel

    Resumo em Inglês:

    A new technique was developed to make highly loaded (up to 95%) formaldehyde free natural fiber boards. The purpose of the paper is to report a broad study on 85% kenaf boards using linear thermoplastic polymers as the binder in preparing the boards to determine if these materials have potential in commercial applications by comparing them to other commercial materials. In these materials, linear thermoplastic polymer chains act as an adhesive and the product resembles a typical wood based panel (e.g., phenol formaldehyde fiber board). The process involved the use of small amount of glycerine in the fiber to enhance processibility in a thermo-kinetic mixer followed by hot pressing. In this paper, we report the properties of 85% by weight kenaf fiber boards using polypropylene as the adhesive. A maleated polypropylene was used to improve the adhesion and stress transfer between the adhesive and kenaf fiber. The addition of 2% by weight of glycerine based on the dry weight of kenaf fiber resulted in the best properties of the boards. Differential scanning calorimetric studies suggested that the glycerine had a little effect on the percent crystallinity of the matrix. Dynamic mechanical tests of the 85% boards showed some differences compared to conventional 60% by weight kenaf-PP composites. The 85% kenaf boards had a flexural strength of 75 MPa and a flexural modulus of 6.8 GPa with a specific gravity of 1.24. These properties are comparable to standard formaldehyde free high density hardboards with flexural strengths of 48.3 MPa and flexural modulus of 5.5 GPa, and a specific gravity of 1.28. This paper gives a broad overview of an initial study of these new materials.
  • Easy synthesis of CaB2O4 via pyrolysis of calcium fructoborate Letters To The Editor

    Wagner, Claudia Cecilia; Baran, Enrique José

    Resumo em Inglês:

    The investigation of the thermal behavior of calcium fructoborate samples of composition Ca(C6H10O6BO)2.3.5H 2O showed that CaB2O4 is generated as the final solid pyrolysis residue. On the basis of these observations a new, very easy, synthetic procedure for the preparation of high purity samples of this calcium borate is proposed. The material was characterized by X ray powder diffractometry and IR spectroscopy.
  • A simple model to estimate the optimal doping of p - Type oxide superconductors Letters To The Editor

    Luiz, Adir Moysés

    Resumo em Inglês:

    Oxygen doping of superconductors is discussed. Doping high-Tc superconductors with oxygen seems to be more efficient than other doping procedures. Using the assumption of double valence fluctuations, we present a simple model to estimate the optimal doping of p-type oxide superconductors. The experimental values of oxygen content for optimal doping of the most important p-type oxide superconductors can be accounted for adequately using this simple model. We expect that our simple model will encourage further experimental and theoretical researches in superconducting materials.
ABM, ABC, ABPol UFSCar - Dep. de Engenharia de Materiais, Rod. Washington Luiz, km 235, 13565-905 - São Carlos - SP- Brasil. Tel (55 16) 3351-9487 - São Carlos - SP - Brazil
E-mail: pessan@ufscar.br