Scielo RSS <![CDATA[Materials Research]]> http://www.scielo.br/rss.php?pid=1516-143920140001&lang=es vol. 17 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>Preparation and characterization of PbTi0<sub>3</sub> ceramics modified by a natural mixture of rare earth oxides of xenotime</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100001&lng=es&nrm=iso&tlng=es Lead titanate ceramics modified by xenotime (Xm) with nominal composition (Pb, Xm)TiO3, Xm 10 or 15 mol %, were prepared by the conventional oxide mixture technique. Xenotime is a natural mineral consisting of a mixture of rare earth oxides. Thermal, structural and electric properties were investigated through differential and gravimetric thermal analysis, X-ray diffraction and dielectric measurements as a function of temperature. The results of both compositions revealed a higher density and free of cracks ceramic body, compared to pure PbTiO3 prepared by the same procedure. On the other hand, the structural characteristics and Curie temperature are nearly the same as those of pure PbTiO3. The hysteresis loop measured at room temperature revealed a hard ferroelectric material with coercive field of 10.7 kV/cm and a remanent polarization of 0.2 ∝C/cm². These finding reveal a material with properties that highlight potential to be used as electronic devices that operate at high temperature and high frequencies. <![CDATA[<b>Lithograph-moulded poly-L-co-D,L lactide porous membranes for osteoblastic culture</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100002&lng=es&nrm=iso&tlng=es Pore size, shape, wall morphology, porosity, and interconnectivity are important characteristics of the scaffolds. Lithography is a manufacturing technique that allows the production of tridimensional scaffolds with a controllable and reproducible inner architecture. The aim of this study was to use lithography to create a poly-L-co-D,L lactide (PLDLA) scaffold with symmetrical pore size and distribution, and to evaluate its biocompatibility with osteoblasts in vitro. Lithographic moulds were used to produce porous PLDLA membranes by a casting procedure. Osteoblasts were removed from calvarial bones and seeded onto porous and smooth PLDLA membranes after which cell viability and adhesion assays, cytochemical analysis and scanning electron microscopy were used to characterize the cells. Cell viability and adhesion assays, cytochemical analysis, and scanning electron microscopy were carried out. Cell viability was similar on porous and smooth PLDLA membranes but higher than on a polystyrene substrate (positive control). Although osteoblasts adhered to the surface of all the materials tested, cell adhesion to lithographed PLDLA was greater than to smooth PLDLA membranes. In conclusion, osteoblasts interacted well with PLDLA membranes, as shown by the viability and adhesion assays and by the enhanced collagen production. <![CDATA[<b>Doping technique in the interfacial transition zone between paste and lateritic aggregate for the production of structural concretes</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100003&lng=es&nrm=iso&tlng=es This paper discusses the use of doping technique in the interfacial transition zone (ITZ) between Portland cement paste and lateritic aggregates with the objective of promoting the implementation of structural concrete. Doping technique consists of establishing the initial impregnation of the aggregate with a high performance paste in order to improve its binding to the matrix. A Scanning Electron Microscope (SEM) equipped with an energy dispersive X-ray (EDX) analysis system is used to observe the results of the technique in the ITZ. The results are observed through an analysis of the cement hydration products formed in the ITZ. An ITZ with high concentration of large crystals of calcium hydroxide (CH) is observed in plain concrete, whereas in concrete prepared with doping technique the ITZ is rich in calcium silicate hydrate (CSH). This result confirms the possibility of using this material, which has no commercial value nowadays, as an alternative aggregate for elaborating structural concrete. <![CDATA[<b>Utilization of teflon and aluminum oxide for wheel cleaning in Minimum Quantity Lubrication (MQL) grinding</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100004&lng=es&nrm=iso&tlng=es Researches concerning cooling-lubrication optimization in grinding have been conducted to contribute to a more sustainable process. An alternative to flood coolant is minimum quantity lubrication (MQL), which spray oil droplets in a compressed air jet. However, problems related to wheel cleaning were reported, due to wheel loading by a mixture of chips and oil, resulting in worsening of surface quality. This work aims to evaluate the viability of Teflon and aluminum oxide for wheel cleaning, compared to MQL without cleaning and MQL with cleaning by compressed air, through the following output variables: surface roughness, roundness, wheel wear, grinding power and acoustic emission. Vickers microhardness measurements and optical microscopy were also carried out. The results showed that both materials were efficient in cleaning the wheel, compared to MQL without cleaning, but not as satisfactory as compressed air. Much work is to be done in order to select the right material for wheel cleaning. <![CDATA[<b>Synthesis of Cu<sub>x</sub>O(x = 1,2)/amorphous compounds by dealloying and spontaneous oxidation method</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100005&lng=es&nrm=iso&tlng=es Cu xO(x = 1,2)/amorphous compounds have been successfully synthesized by chemical free dealloying and spontaneous oxidation method. Technological parameters, such as the acid concentration and dealloying time strongly influence the crystal type, size and morphology of coppery oxide. The further study shows that with the increase of HCl concentration, the surface coverage rate of Cu2O micro-flowers increases and the sizes of Cu2O micro-flowers get bigger. Moreover, it is observed that cracks are formed on the etched ribbon surface and plentiful Cu2O/CuO particles grow up from these crack walls if the dealloying time extends to long enough. Considering many fascinating properties of Cu2O/CuO particles and the amorphous alloy carrier, potential application fields of these amazing compounds will be developed in future. <![CDATA[<b>Compressive stress-strain behaviour of cement mortar-composites reinforced with short sisal fibre</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100006&lng=es&nrm=iso&tlng=es To design building elements using sisal fibre reinforced mortar composites, the stress-strain curves of the composites both under tensile and compression load is needed. In this study short sisal fibre-cement based composites were developed and their stress-strain behaviour under compression characterized experimentally. The composites consisted of two mortar matrices, one self-compacting and one of normal consistency, reinforced with randomly distributed short sisal fibre (25 and 50 mm long) in volume fractions ranging from 2% to 6%. Based on the experimental results a compressive constitutive law for the composites was proposed based on the damage theory developed by Mazars (1986). This theory was used to model the ascending branch of the stress-strain curve and a damage parameter associated to the fibre-reinforcing index is proposed to allow the modelling of the post-peak behaviour of the composites. The modified model was then validated using results available in the literature. The experimental results obtained in the study indicated that the addition of short sisal fibres to cement matrices tends to reduce its elastic modulus, peak stress and strain and to increase its toughness. However, the use of a self-compacting matrix allowed better sisal fiber dispersion and composites with superior performance were obtained. The modified analytical model was able to predict with good accuracy the ascending and descending branch of the stress-strain curves of the sisal fiber-mortar composites and allowed evaluating the effect of fibre reinforcing index on material damage. In the ascending branch, an increase in the damage from 40% to 70% is recorded for fiber volume ranging from 2 to 6%. In the descending branch, on the other hand, the variation of fiber volume allowed a reduction of the damage from 65% to 60%. <![CDATA[<b>Characterization and three-dimensional reconstruction of pores of self-reducing pellets done by EAF dust</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100007&lng=es&nrm=iso&tlng=es This work focused on the characterization physical and microstructural of the self-reducing pellet made of Electric Arc Furnace (EAF) dust using different low cost techniques. The serial sectioning technique was used to evaluate detailed measurements of pore connections, tortuositiy of pores and porosity distribution. The chemical analysis using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES), Scanning Electron Microscopy (SEM), Optical Microscopy (OM) and X-ray diffraction were carried out to identify the common phases presented in EAF dust agglomerate. It was observed that the pellet phase composition is formed by iron as magnetite, metallic iron, wustite, and zinc ferrite. The visualization of the reconstructed 3D microstructure provided average qualitative and quantitative analysis of the porosity (41.61%), a consistent result and in accordance with that obtained by pycnometry technique (41.53%). As expected, these results are more precise when compared with the result obtained by two-dimensional technique (23.41%). In addition, it was calculated the value of the tortuosity parameter (0.84) that suggested a morphological structure closest to cylindrical shape. <![CDATA[<b>Experimental analysis of indentation morphologies after spherical indentation</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100008&lng=es&nrm=iso&tlng=es Indentation morphologies depend on the mechanical properties of materials, especially the strain-hardening exponent and yield strength-to-elastic modulus ratio. Hernot et al.¹ described a model that can be used to obtain the indentation morphology index from properties determined in tensile tests. The model is used here with two aluminum alloys and 1020 steel tested under spherical indentation with different loads and ball diameters. There was good agreement between the values predicted by the model and the experimental findings for all the materials tested except partially recovered AA1350 aluminum alloy (H24 condition). This exception is discussed and a possible explanation for it is sought in other experimental deviations and in microstructural inhomogeneities. <![CDATA[<b>Electrochemical characterization of chromate free conversion coatings on electrogalvanized steel</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100009&lng=es&nrm=iso&tlng=es The chromate conversion treatment is widely used, but it requires highly toxic chromic acid solutions with the consequent effluent disposal and ecological problems. The removal of these toxic chemicals is considered a priority within European Union. The corrosion resistance of three alternative treatments applied on electrogalvanised steel, and immersed in aerated 0.3 M Na2SO4 solution, pH 10, at 25 °C, was investigated using electrochemical techniques. Their performance was compared with the obtained using the traditional Cr6+-based treatment in the same conditions. The achieved results show that the alternative coatings exhibited discrete protective properties in the sulphate solution. The nitro-cobalt chemical conversion treatment showed similar protective properties than the traditional Cr6+-based treatment, while with the Cr3+-based treatment those were very poor. The phosphate treatment initially performed acceptably but as the time elapsed, its protective properties decreased. <![CDATA[<b>Photo-assisted electrochemical copper removal from cyanide solutions using porous TiO<sub>2</sub> thin film photo-anodes</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100010&lng=es&nrm=iso&tlng=es TiO2 porous films were prepared on ITO coated glass slides by the sol-gel dip-coating method assisted with Polyethylene glycol (PEG). The films were used as photo-anodes in the photo-assisted electrolytic removal of cuprous ions in cyanide media. These were characterized by SEM, UV-Visible spectroscopy and XRD. The PEG modified films were free of cracks and developed a porous structure after heat treatment at 500 ºC, due to the thermal decomposition of the structure associated PEG. It was demonstrated that the photo-assisted electrochemical reduction of copper is promoted by the use of modified TiO2 films as photo-anodes, thanks to the greater surface area given by the PEG decomposition. However, the film thickness was found to be a critical factor in the process, to such an extent that films composed of 5 layers were completely inefficient, meaning that despite the open porosity, multilayered films acted as a barrier within the photo-electrolytic process. <![CDATA[<b>Effect of hyperbranched polyesters on HTPB polyurethane curing kinetic</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100011&lng=es&nrm=iso&tlng=es Effects of hyperbranched polyesters on kinetics of the reaction between hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI) were investigated. HTPB and IPDI were in-situ cured in the presence of two different hyperbranched polyesters, stearic acid ester-terminated hyperbranched polyester (SHPE) and acetate-terminated hyperbranched polyester (AHPE). The curing processes were monitored by quantitative Fourier transform infrared (FTIR) spectroscopy. The results showed the stearic acid ester-terminated hyperbranched polyester had catalytic effects on the reaction between HTPB and IPDI, while acetate-terminated hyperbranched polyester did not have an influence on the reaction between HTPB and IPDI. <![CDATA[<b>A systematic study on electrolytic production of hydrogen gas by using graphite as electrode</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100012&lng=es&nrm=iso&tlng=es Alkaline water electrolysis is one of the easiest methods for hydrogen production that has the advantage of simplicity. The major challenges in the water electrolysis are the reduce energy consumption, cost and maintenance and to increase reliability, durability and safety. In this regard, the electrolytic production of hydrogen is systematically studied by commercially available graphite electrode at room temperature. The experimental results showed the rate of production of hydrogen gas was significantly affected when the reaction parameters such as effect of electrolyte concentration, temperature, applied voltage and reaction time are varied. From the experimental results, it has been found that graphite is a good choice for the production of maximum hydrogen compared to various other electrodes. <![CDATA[<b>Utilization of minimum quantity lubrication (MQL) with water in CBN grinding of steel</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100013&lng=es&nrm=iso&tlng=es The use of cutting fluids is fundamental to machining processes, mainly when it comes to high heat generation, which is the case of grinding. Thus, lubrication and cooling provided by cutting fluids improve the final quality of the workpiece. However, cutting fluid usage provide some drawbacks concerning environmental, costs and health issues. Therefore, new methods for application and optimization of cutting fluids are being researched aiming to reduce the amount of fluid used, as well as the minimization of cutting fluid hazards. The present study analyzes the behavior of a recently proposed optimization method, up to now only tested in turning, which consists of adding water to minimum quantity lubrication (MQL). Three different proportions were tested in this study: 1/1, 1/3 and 1/5 parts of oil per parts of water. The following output variables were evaluated: surface roughness, roundness errors, grinding power and diametric wheel wear. Also, optical microscopy and microhardness measurements were conducted, in order to detect burns and surface alterations. The obtained results were also compared to conventional (flood coolant) cooling-lubrication and traditional MQL (without water). MQL with water (1/5) presented better results of surface roughness and roundness errors, when compared to traditional MQL, and the results are very close to when using flood coolant. For grinding power and wheel wear, the results for MQL with water (1/5) were the best among the tested conditions. <![CDATA[<b>Mechanical and morphological properties of LDPE/ PHB blends filled with castor oil pressed cake</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100014&lng=es&nrm=iso&tlng=es Blends of PHB and LDPE were prepared by melt mixing in a twin screw extruder. Castor oil cake (CC) was used as filler for the blends. The design of experiments (DOE) technique was used to evaluate the effect of the components proportion on the materials properties. The mechanical properties and morphology of the materials were evaluated. The LDPE Young's modulus increases but the other tensile properties and impact resistance deteriorate with the addition of PHB or CC. The tensile strength values of binary mixtures of LDPE lie in the range from 8.9 to 10 MPa. As some commercial grades of LDPE have mechanical strength in this range, it may be inferred that the addition of a certain amount of PHB or CC to LDPE may be considered as a possibility for obtaining LDPE based materials with increased susceptibility to biodegradation. The poor interfacial adhesion between the phases became visible in all samples. <![CDATA[<b>Designing of CK45 carbon steel and AISI 304 stainless steel dissimilar welds</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100015&lng=es&nrm=iso&tlng=es Gas tungsten arc welding of CK45 and AISI304 stainless steel was performed through preparation of different types of samples using ER308L and ERNi-1 wires. Welded samples were studied by different techniques including optical metallography, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction, hardness measurements and impact test. It was observed that in the buttered specimen, the structure of the weld metal was completely austenitic while the microstructure of unbuttered sample was duplex ferritic-austenitic. M23C6-type carbides were observed within the weld metal of both as-weld specimen types. Effects of different post-weld heat treatments (PWHTs) were investigated. The experimented results concluded that simultaneous grain growth and carbides precipitation were competitive during PWHT. Also, there were not any indication related to sigma-phase in as-welded and PWHTed specimens due to their lower Cr/Ni ratios and insufficient preservation times. <![CDATA[<b>Correlation between morphological properties and ionic conductivity in an electrolyte based on poly(vinylidene fluoride) and poly (2-hydroxyethyl methacrylate)</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100016&lng=es&nrm=iso&tlng=es Materials based on a mixture of poly(vinylidene fluoride) (PVDF), poly(2-hydroxyethyl methacrylate) (PHEMA) and LiClO4 were produced to evaluate their ionic behavior and morphological structure to determine if they can be used as an electrolyte in electrical devices. FTIR chemical analysis results indicated the presence of interactions between PVDF, PHEMA and LiClO4. MDSC results showed that the transition temperatures of the polymers shifted to higher temperatures for systems containing high concentrations of each polymer. SEM images indicated that there was some miscibility between the polymers especially for the 25 and 75 wt. % compositions. In terms of the electrical performance, the ionic conductivity level of the electrolyte could be controlled by changing the composition of the system. <![CDATA[<b>Study of hygral behavior of non-asbestos fiber cement made by similar hatschek process</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100017&lng=es&nrm=iso&tlng=es Fiber cement, similarly to all cementitious materials, undergoes dimensional and volumetric changes when it is exposed to dry and wet environments. When exposed to natural weathering, cement-based materials absorbs and may also release water to their surroundings via a very complex inherent pore structure. In this work initialized a few years ago, some properties of asbestos-free fiber cement composites were studied, such as density, porosity and loss or absorption of water. For the understanding of the behavior of this material, modifiers were employed in the cement matrix such as styrene- acrylic, styrene-butadiene and vinyl acetate-versatic vinylester copolymers to verify their influence on the variables described above. All composites were analyzed by mercury intrusion porosimetry (MIP). For monitoring the expansion/shrinkage movements, the specimens were exposed inside a controlled environmental chamber with constant temperature and relative humidity (RH) during the test time. The results showed no interference on hygral behavior because particular casting process of these composites but, as showed by literature, increase of toughness. Also, it was possible to verify that moisture movement within the asbestos-free fiber cement can be very complex and the variables density and porosity (pore structure) play a very important role in the expansion/shrinkage properties of these composites. <![CDATA[<b>Influence of calcium carbonate and slip agent addition on linear medium density polyethylene processed by rotational molding</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100018&lng=es&nrm=iso&tlng=es In this paper, the influence of calcium carbonate and slip agent on linear medium density polyethylene (LMDPE) processed by rotational molding was evaluated. LMDPE was dry blended with different CaCO3 masterbatch ratios, erucamide slip agent and then extruded, micronized and rotomolded. The powder samples were characterized using MFI (Melting flow index), dry flow and bulk density. The characterization of rotomolded samples properties was performed by DSC (Differential scanning calorimetry), microscopy analysis, izod impact and tensile test. The results pointed out that the CaCO3 addition modifies the bulk density compared to neat LMDPE, but did not significantly affect the dry flow and MFI. The erucamide addition decreased the dry flow and increased the bulk densities. The porosity degree data showed that CaCO3 addition in the LMDPE increased the quantity of pores. The DSC results showed no significant difference in the crystallinity degree. The behavior of porosity led to a decrease in the mechanical properties of LMDPE with the CaCO3 addition. <![CDATA[<b>Density profile as a tool in assessing quality of new composite</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100019&lng=es&nrm=iso&tlng=es This paper present a study to apply the X-ray densitometry technique in obtaining density profiles, along the thickness of new composites made from eucalyptus fibers and sugarcane bagasse particles. Experimental panels were made in treatments with different percentages of both raw materials and bonded with two urea formaldehyde resin percentages, 13% and 16%, with target density of 750 kg m-3, obtaining density profiles and qualitative variables of maximum, medium and minimum densities. The results indicated that the dosage of resin at 16% promoted greater homogeneity in the profile formats and statistical similarity between the minimum density values in the different treatments, which refers to performance as to the internal bond. The density profiles along the thickness showed variations of the panel frame and provided important quality information, applied to the press cycle setting and indications of its technological performance, expanding the possibilities of raw material parameter diagnosis and the panel manufacturing processes. <![CDATA[<b>Influence of local raw materials on the mechanical behaviour and fracture process of PVA-SHCC</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100020&lng=es&nrm=iso&tlng=es This paper addresses the results of an investigation on the influence of the Brazilian raw materials on the mechanical performance of Strain Hardening Cementitious Composites (SHCC). The mixtures were produced with variations of fly ash/cement and sand/cement proportions and with different maximum sand particle. Mechanical properties were evaluated by direct tension, bending and compression tests. Crack formation under direct tension and bending loads was also investigated. The results indicate that the use of high quantities of fly ash with low quantities of fine sand is the ideal combination to obtain strain hardening composites with tensile strain capacity superior to 3% using local materials. The increase in the sand content and particle size affects the behavior of the composites and tended to reduce the strain capacity of the specimens by up to 30%. Keeping constant the fly ash/cement and sand/cement rates it was found that the crack density and width measured under direct tension are only affected by the diameter of the sand for tensile strains in the range of 2%. The same general trends were observed for specimens submitted to compressive and bending loads. <![CDATA[<b>Starch consolidation of red clay-based ceramic slurry inside a pressure-cooking system</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100021&lng=es&nrm=iso&tlng=es The consolidation of red clay-based slurry by gelatinization of starch in a domestic pressure cooker was presented. Aqueous ceramic slurries were prepared consisting of a ternary powder mixture of red clay, quartz, feldspar, and different starch types. The starch slurries with and without the presence of ceramic particles demonstrated the same gelling mechanism and heating time inside the pressure cooker. The gel strengths of pressure-cooked samples were higher than samples heated conventionally. Subsequently, the shaping of large ceramic prototypes is possible using a calculated heating time based on best pressure cooking conditions. The physical characterizations disclosed that the pressure-cooked ceramic samples in dried and fired states exhibited better physical properties depending upon the type of starch added in the ceramic slurry. Specifically, the compressive strengths of fired ceramic bodies shaped in the pressure cooker ranged from 82 ± 2 to 255 ± 9 MPa with bulk porosities of 29.0 ± 0.8-18.7 ± 0.2%, whereas the conventionally shaped bodies possessed compressive strengths ranging from 138 ± 8 to 164 ± 11 MPa with bulk porosities of 25.6 ± 0.1-28.5 ± 0.2%. <![CDATA[<b>Using fine recycled concrete aggregate for mortar production</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100022&lng=es&nrm=iso&tlng=es This research assessed the performance of mortars in which recycled concrete aggregates (RCA) was a component. It replaced natural sand but kept the same particle size distribution. Three mortars were produced with replacement ratios of 20%, 50% and 100% as well as a reference mortar containing no recycled aggregate. The compressive and flexural strength, water absorption by capillarity, drying capacity and susceptibility to cracking of these mortars were analyzed first. Then, based on these results, the most satisfactory replacement ratio was chosen and the following properties were analyzed: water retentivity, shrinkage, adhesive strength, modulus of elasticity, and water vapor permeability. Somewhat surprisingly the best results in the first stage occurred for 20% and 100% replacement ratios, leading to a cautious choice of the 20% ratio for the second stage. Generally the mortar with 20% replacement ratio performed better than the reference mortar, except for adhesive strength and dimensional stability. <![CDATA[<b>Impact of vibrations on the final characteristics of normal and self-compacting concrete</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100023&lng=es&nrm=iso&tlng=es The quality and durability of normal concrete directly depends on the number and the shape of voids, so, in order to produce durable concrete, it is necessary to reduce the amount of air that is trapped inside the concrete, which is usually done by vibrating the concrete in the mixing stage or the casting stage. Self-compacting concretes are concretes that, in principle, don't require vibrating during casting. Such concretes possess enough compactness and flowability through gravity that during pouring they fill all the space in the formwork. However, it is frequently the case that the ideal self-compacting concrete that is produced in a laboratory cannot be produced on a construction site so such concretes require additional vibrations. The work examines the impact that the introduction of vibrations during mixing and during casting has on the final appearance and the compressive strength of normal and self-compacting concretes. Achieved results confirm that vibrating during the mixing stage can improve the workability of fresh concrete but not its final strength, especially for self-compacting concretes, while vibrating in the casting stage significantly contributes to the final strength of the concrete. <![CDATA[<b>Giant reversible magnetocaloric effect in flower-like </b><b>β</b><b>-Co(OH)<sub>2</sub> hierarchical superstructures self-assembled by nanosheets</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100024&lng=es&nrm=iso&tlng=es A facile hydrothermal strategy is proposed to synthesize flower-like β-Co(OH)2 hierarchical microspherical superstructures with a diameter of 0.5-1.5 μm, which are self-assembled by β-Co(OH)2 nanosheets with the average thickness ranging between 20 and 40 nm. The magnetocaloric effect associated with magnetic phase transitions in Co(OH)2 superstructures has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a filed-induced transition from the antiferromagnetic to the ferromagnetic state below the Néel temperature. The large reversible magnetic-entropy change -ΔSm (13.4 J/kg K at 15 K for a field change of 5 T) indicates that flower-like Co(OH)2 superstructures is a potential candidate for application in magnetic refrigeration in the low-temperature range. <![CDATA[<b>Optimization and non-destructive test analysis of SS316L weldments using GTAW</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100025&lng=es&nrm=iso&tlng=es This work aims at optimization and analysis of SS316L weldments using TIG Welding, SS316L is selected over other grades because of its lower carbon content and its weldability properties. The welding parameters are being assessed by means of Taguchi's L9 orthogonal array with varying gas flow, current and bevel angle with the predictions achieved the sample is welded. The level of importance of welding parameters for tensile strength is determined by using analysis of variance (ANOVA) and it was concluded that gas flow played the prominent role and the bevel angle was least contributor. The optimization of power and the gas flow is made analytically so some confirmatory tests were performed to check the efficiency of the predictions found. The Radiography inspection and microstructure test were performed on samples which showed low, medium and high tensile strength in order to view the changes occurred after welding. <![CDATA[<b>Some aspects on geometric and matrix work-hardening characteristics of sintered cold forged copper alloy preforms</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100026&lng=es&nrm=iso&tlng=es Powder metallurgy (P/M) material subjected to plastic deformation results into densification, however the extended deformation would not only enhance the densification also supplements the strain hardening. Unlike fully dense material that would only undergo strain hardening while plastic deformation, the P/M material leads to pore closure as well; this phenomenon complicates the work hardening mechanism. The present study revealed that both strain and density configures strengthening of P/M preform, which respectively termed as matrix and geometric work hardening. An attempt has been made to delineate some aspects of work hardening behaviour with the influence of different aspect ratios of sintered and cold deformed copper alloy preforms. The preforms were initially prepared through conventional P/M route and finally subjected to cold upsetting under dry friction condition. A statistical analysis has also been introduced to study the quantitative impact of strain and density in the presence of aspect ratio on work hardening rate characteristics. <![CDATA[<b>LDPE/PHB blends filled with castor oil pressed cake</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100027&lng=es&nrm=iso&tlng=es Blends of PHB and LDPE were prepared by melt mixing in a twin screw extruder. Castor oil pressed cake (CC) was used as filler for the blends. The mixture design technique was used to evaluate the effect of the components proportion on the materials flexural properties. The results show that superior LDPE flexural properties may be obtained by the addition of PHB or castor oil cake to LDPE. Biodegradation was evaluated burying the samples in simulated soil for different periods of time. The ternary mixtures with higher content of PHB showed more pronounced degradation. Under the experimental conditions studied the LDPE/CC compositions presented no degradation. However, the loss of mass of the LDPE/PHB/CC ternary mixtures was higher than the loss of mass of the corresponding LDPE/PHB binary mixture. This result suggests that the castor oil cake accelerates the degradation of the LDPE/PHB mixtures. <![CDATA[<b>Synthesis of high value-added zeolitic materials using glass powder residue as a silica source</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100028&lng=es&nrm=iso&tlng=es In this work, zeolite A was obtained using alkaline fusion followed by a hydrothermal treatment of glass powder residue derived from the manufacturing of glass. The following parameters were evaluated: leaching of the stock material (silica source), mineralizing agent, alumina source, and the alkaline fusion and crystallization temperatures. The synthesized materials were characterized by chemical analysis using energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD and SEM results showed that zeolite A was obtained under almost all of the evaluated parameters. The use of pseudoboehmite as an aluminum source led to the formation of zeolite X as a secondary phase and a change in the temperature of fusion, which at 500 °C, there was formation of zeolite A, hydrated sodalite and zeolite X. <![CDATA[<b>Influence of the oxidation step on the behaviour and the performances of an oxygen carrier in fixed bed reactor</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100029&lng=es&nrm=iso&tlng=es Chemical Looping Combustion is a promising technology for clean power generation with integrated CO2 capture. In this process the oxygen required for combustion is provided by a metal oxide. This work deals with the development of an experimental procedure to study performances of an oxygen carrier during oxidation/reduction cycles and the influence of the oxidation step on its behaviour. Tests were performed in a laboratory fixed bed reactor, with NiO/NiAl2O4, a promising oxygen carrier, and CO as fuel. Two different protocols of oxidation were studied. Results reveal that the oxidation step conditions can change the performances of the oxygen carrier. A significant decrease in total reduction capacity was observed using the regeneration step at high temperature due to structural changes in particles. SEM analysis reveals that particle surface contains different crystallites according to this procedure. With the second procedure (oxidation in temperature ramp), nickel is partially agglomerated. <![CDATA[<b>Evaluation of decomposition kinetics of poly (ether-ether-ketone) by thermogravimetric analysis</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100030&lng=es&nrm=iso&tlng=es The non-isothermal thermogravimetric methods have been used extensively for the determination of kinetic parameters in polymers. The poly (ether ketones) are used as matrix in advanced high performance composites due its high thermal stability, excellent environmental performance and superior mechanical properties. In this work, the non-isothermal decomposition kinetics of the polymer poly (ether ether ketone) (PEEK) was evaluated in nitrogen and synthetic air atmospheres, using the Flynn-Wall-Ozawa and Coats Redfern models. The results showed that the necessary time for the material decomposes in 5% is approximately 216 years if it is submitted to temperatures of 350 °C in nitrogen atmosphere. On the other hand, if the material is submitted to air atmosphere, this decomposition time drops to about 1,05 years in the same temperature and for the same conversion rate. The decomposition kinetics study by Coats Redfern showed that the D3 mechanism (three-dimensional diffusion (Jander equation)) had better adjustment to the decomposition kinetics of the material in nitrogen atmosphere, while in synthetic air the R1 mechanism (phase boundary controlled reaction (one-dimensional movement)) has better adjustment to the decomposition kinetics of the material. <![CDATA[<b>Processing of a LLDPE/HDPE pressure vessel liner by rotomolding</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100031&lng=es&nrm=iso&tlng=es Biaxial rotational molding is a low-pressure process that uses a polymer powder to produce large and/or complex-shaped hollow thermoplastic goods using low cost molds, being very suitable for prototype production. In the present work, liner prototypes (F 78 × 280 mm) made of linear low density (LLDPE) and high density polyethylene (HDPE) blends were produced aiming to later use them as compressed natural gas type IV cylinders. The LLDPE/HDPE blend composition and the process parameters (temperature/time cycle, and rotation speed) were varied to evaluate their effect on blend miscibility and liner final properties, such as density and crystallization behavior. Blend composition and process parameters were found vital for the production of a homogeneous wall and for the liner to reach adequate characteristics for the intended product. <![CDATA[<b>Current developments of mixed conducting membranes on porous substrates</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100032&lng=es&nrm=iso&tlng=es The fabrication of mixed ionic-electronic conducting (MIEC) ceramic-based membranes for oxygen separation has extensively increased in the last three decades as a promising alternative of clean energy delivery. In recent years, the interest on supported MIEC membranes has increased due to their attractive properties such as higher mechanical strength and oxygen flux compared to self-supported membranes. This work presents a literature review on the development of supported MIEC membranes of perovskite structure. The concepts and transport mechanism of those membranes are explained and recent works on supported MIEC membranes are presented. Finally, manufacturing methods of self-supported membranes and their influence on oxygen permeation are discussed. <![CDATA[<b>Effect of salt-water fog on fatigue crack nucleation of Al and Al-Li alloys</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100033&lng=es&nrm=iso&tlng=es Fatigue and corrosion-fatigue tests were performed to quantify the fatigue properties of AA2524-T3 and AA2198-T851 Al alloys. High cycle axial fatigue tests were carried out under air and salt-water fog conditions. In air, the specimens were fatigue tested at a frequency of 50 Hz, using specimens with and without preconditioning in a salt spray chamber, and for the corrosion fatigue condition, the tests took place at a frequency of 30 Hz in a salt-water fog condition. In all cases it was used a sinusoidal waveform and a stress ratio (R) of 0.1. The results indicate that the saline environment had a deleterious effect on the fatigue life of the two aluminum alloys. AA2524-T3 exhibited a better fatigue strength than AA2198-T851 when fatigue tested in air. However, considering the corrosion fatigue test in a saline fog environment an inverse behavior was observed with the AA2198-T851 exhibiting higher fatigue strength. <![CDATA[<b>The inhibition effect of mad Honey on corrosion of 2007-type aluminium alloy in 3.5% NaCl solution</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100034&lng=es&nrm=iso&tlng=es The inhibition effect of mad honey on corrosion of 2007-type aluminium alloy in 3.5% NaCl solution was investigated by Tafel extrapolarisation (TP), electrochemical impedance spectroscopy (EIS) and dynamic electrochemical impedance spectroscopy (DEIS). All the studied parameters exhibited good anti-corrosive properties against corrosion of 2007-type aluminium alloy in the test solution; the corrosion rates decreased with the increase of the mad honey concentration. The surface morphology of the alloy was examined under scanning electron microscopy (SEM) in the absence and presence of the inhibitor. The inhibitory adsorption processes of mad honey on the 2007-type aluminium alloy surfaces conformed to the Langmuir adsorption isotherm. <![CDATA[<b>Thermal properties of poly (methyl methacrylate)/organomodified montmorillonite nanocomposites obtained by <i>in situ</i> photopolymerization</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100035&lng=es&nrm=iso&tlng=es The organoclay/poly(methyl methacrylate) (PMMA) nanocomposites were prepared by in situ photopolymerization method using two solvents, ethanol and acetonitrile. The influences of organoclay loading, solvent nature and length of attached surfactant (C8 or C16) on thermal and mechanical properties were studied by thermogravimetric analysis and dynamic mechanical analysis. Alkylammonium surfactants with C8 and C16 chain lengths were evaluated as clay modifiers. All the nanocomposites prepared in acetonitrile exhibited improvement in their thermal stability, mainly due to the interaction between the clay and the polymer which is maximized by the exfoliated clay structure. In the case of PMMA and nanocomposites synthesized in ethanol, the thermal stability of polymer and nanocomposites remained practically the same once the clay structure is predominantly of the intercalated type. In comparison with pure PMMA, glass transition temperature and storage modulus of polymer are notably increased by the presence of clay. It was found that the chain length of surfactant attached to the SWy-1 clay affects the Tg values. Glass transition temperatures of nanocomposites SWy-1-C16/PMMA were significantly higher than the values obtained for nanocomposites SWy-1-C8/PMMA. This can be attributed to the modifying agent C16, which has a greater hydrophobic chain length. The organic tail can provide a better dispersion of the MMA monomer in the organoclay, resulting in a nanocomposite with predominant exfoliated structure. Another significant factor to be considered was the effect of solvent used in the nanocomposite preparation. Considering nanocomposites with the same chain length (C8 or C16), Tg values obtained for nanocomposites prepared with ethanol is higher than those observed for those prepared in acetonitrile. This was attributed to the influence of the average molecular weight; once the nanocomposites prepared in ethanol exhibited higher polymeric chains. <![CDATA[<b>On the use of capsaicin as a natural preservative against fungal attack on <i>Pinus</i> sp. and <i>Hymenaea</i> sp. woods</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100036&lng=es&nrm=iso&tlng=es Capsaicin (capsicum oleoresin) extracted from two peeper species, Capsicum frutescens and Capsicum baccatum, was investigated as a natural preservative against fungal (Paecilomyces variotti) attack on Pinus sp. and Hymenaea sp. Static contact angle measurements were performed as a function of time in order to investigate the wetting properties of the wood samples treated with capsicum oleoresin. As revealed by X-ray diffraction analysis, photographs, and angle contact measurements, Hymenaea sp is more sensitive to the presence of capsicum oleoresin, which can inhibit, or retard, the growth of Paecilomyces variotti. Structures of filaments called hyphae, occurring typically in multicellular fungi, were observed on the sample surfaces studied by using an electronic scanning microscope. The capsicum oleoresin extracted from Capsicum frutescens showed to be more effective as a preservative due to its greater degree of pungency (higher capsaicin content) and better penetration into the cellular structure of the woods. <![CDATA[<b>Behavior in simulated soil of recycled expanded polystyrene/waste cotton composites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100037&lng=es&nrm=iso&tlng=es Composites consisting of waste cotton yarn (CF) from the textile industry and postconsumer expanded polystyrene (EPS) was followed during 90 days of exposure in simulated soil. The mechanical properties, morphologies and chemical natures of the composites were determined before and after exposure in simulated soil. The composites were made using a single-screw extrusion, a twin-screw extrusion and injection molding. The composites showed an increase of the mechanical properties nearly 50% in relation to the recycled expanded polystyrene (rEPS). After exposure in simulated soil the composites presented losses of mechanical properties. Evidence of the oxidation of the samples was demonstrated by the increase in the values of the carbonyl index after 30 days of exposure in simulated soil. Changes in the color of the surface of the sample were observed after 90 days of exposure and are due to the fungi and bacteria colonization on the surface. <![CDATA[<b><i>In situ</i> </b><b>α</b><b>-alumina hydrophobization dynamics at acid pH</b>: <b>effectiveness limitations of short-chain amphiphilic molecules</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000100038&lng=es&nrm=iso&tlng=es The present work highlights that α-alumina hydrophobicity (attained by the in situ modification of its surface properties with water soluble organic monoacids) cannot be increased by using molecules with low acidity (pKa) values due to the alumina zeta potential profile at pHs below approximately 4. In order to certify this statement, the effects of short-chain fatty acids and fluorinated ones on the alumina contact angle (θe) with water were analyzed. It is also pointed out that the θe values derived from the experiments carried out using fluorinated acids are the highest possible when monoacid surfactants are added in α -alumina suspensions in acidic pH. This result indicates that there is another constraint to the in situ hydrophobization procedure, which was not previously elucidated or fully settled in literature.