Scielo RSS <![CDATA[Materials Research]]> vol. 9 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<B>Materials Research - Ibero-american Journal of Materials</B>: <B>judicious, fair and educative!</B>]]> <![CDATA[<B>A review on the development and properties of continuous fiber/epoxy/aluminum hybrid composites for aircraft structures</B>]]> Weight reduction and improved damage tolerance characteristics were the prime drivers to develop new family of materials for the aerospace/aeronautical industry. Aiming this objective, a new lightweight Fiber/Metal Laminate (FML) has been developed. The combination of metal and polymer composite laminates can create a synergistic effect on many properties. The mechanical properties of FML shows improvements over the properties of both aluminum alloys and composite materials individually. Due to their excellent properties, FML are being used as fuselage skin structures of the next generation commercial aircrafts. One of the advantages of FML when compared with conventional carbon fiber/epoxy composites is the low moisture absorption. The moisture absorption in FML composites is slower when compared with polymer composites, even under the relatively harsh conditions, due to the barrier of the aluminum outer layers. Due to this favorable atmosphere, recently big companies such as EMBRAER, Aerospatiale, Boing, Airbus, and so one, starting to work with this kind of materials as an alternative to save money and to guarantee the security of their aircrafts. <![CDATA[<B>Investigation of sintered cobalt-zinc ferrite synthesized by coprecipitation at different temperatures</B>: <B>a relation between microstructure and hysteresis curves</B>]]> The magnetic properties of sintered samples of cobalt-zinc ferrites produced from the corresponding coprecipitate were calculated based on hysteresis curves (Hc). The Hc values confirmed that soft ferrites were obtained by the procedure. A possible relation between the magnetic hysteresis curves and the microstructure of the sintered samples was investigated. X ray diffraction, thermal analysis and scanning electron microscopy were used to characterize the microstructure and the phases present in the sintered ceramic pieces, as well as those of their coprecipitated tri-metallic hydroxide precursor powders. It was found that sintering of Co0.5Zn0.5Fe2O4 at 1400 &deg;C led to "honeycombing" of the ferrite grains and that there was no single phase in the microstructure of a sample sintered at 1400 &deg;C. Thus, a more complete study was made of the behavior of the microstructure at lower sintering temperatures, i.e., in the 1100-1350 &deg;C range. <![CDATA[<B>Fiberglass-reinforced glulam beams</B>: <B>mechanical properties and theoretical model</B>]]> The glued-laminated lumber (glulam) technique is an efficient process for making rational use of wood. Fiber-Reinforced Polymers (FRPs) associated with glulam beams provide significant gains in terms of strength and stiffness, and also alter the mode of rupture of these structural elements. In this context, this paper presents a theoretical model for designing reinforced glulam beams. The model allows for the calculation of the bending moment, the hypothetical distribution of linear strains along the height of the beam, and considers the wood has a linear elastic fragile behavior in tension parallel to the fibers and bilinear in compression parallel to the fibers, initially elastic and subsequently inelastic, with a negative decline in the stress-strain diagram. The stiffness was calculated by the transformed section method. Twelve non-reinforced and fiberglass reinforced glulam beams were evaluated experimentally to validate the proposed theoretical model. The results obtained indicate good congruence between the experimental and theoretical values. <![CDATA[<B>Surface characterization of alumina reinforced with niobium carbide obtained by polymer precursor</B>]]> Active filler controlled pyrolysis of polymers (AFCOP) is a recent method for obtaining near-net shaped ceramic bodies. Alumina based composites have been developed for use as cutting tools, so knowledge of the surface composition is extremely important because it is directly related to the hardness and wear resistance Samples containing a fixed concentration of 60 wt. (%) of polysiloxane and a mixture of metallic niobium and alumina powder were homogenized, uniaxially warm pressed at 80 &deg;C and subsequently pyrolyzed in flowing argon at 1200, 1400 and 1500 &deg;C. Analysis of the surface composition was carried out by X ray photoelectron spectroscopy, infrared spectroscopy, X ray diffraction and scanning electron microscopy. The results have indicated that the formation of the phases on the surface depends strongly on the niobium/carbon ratio in the raw materials. <![CDATA[<B>Effect of exposure time <I>vs.</I> irradiance on knoop hardness of dental composites</B>]]> A comparison was made of the hardness of Z250 and Esthet-X composites light cured with different light sources. Cavities (3 mm diameter x 6 mm deep) were prepared in 240 bovine incisors. The composite was bulk inserted and light-cured using halogen light, LED or xenon plasma arc (PAC) with different irradiances and exposure times, maintaining the same energy density. The specimens were stored in an incubator at 37 &deg;C for 24 hours prior to sectioning for hardness measurements. Three measurements were taken at each depth: surface, 1, 2, 3, 4 and 5 mm. The data were analyzed by ANOVA and Tukey's test (p < 0.05). No statistically significant differences were found for LED up to 2 mm, for PAC up to 3 mm, and for halogen light up to 5 mm. Photoactivation with intermediate power density and exposure time resulted in the highest Knoop hardness values. <![CDATA[<B>Comparison of the corrosion resistance of DIN W. Nr. 1.4970 (15%Cr-15%Ni-1.2%Mo-Ti) and ASTM F-138 (17%Cr-13%Ni-2.5%Mo) austenitic stainless steels for biomedical applications</B>]]> The resistance to localised corrosion of the full austenitic 15%Cr-15%Ni-1.2%Mo titanium stabilized stainless steel (DIN W. Nr. 1.4970) was investigated by electrochemical methods including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiostatic polarization measurements in a phosphate-buffered solution (PBS). The low carbon and non-stabilized austenitic stainless steel, AISI 316L (ASTM F-138), widely used for surgical implants, was also tested for comparison. The tests were conducted at room temperature after a stable potential had been reached. After the electrochemical measurements, the surfaces of the specimens were observed using SEM to evaluate the presence of pits. Potentiodynamic polarization results showed that both steels are prone to localized corrosion. Larger pits were found on the surface of AISI 316L specimens after the electrochemical tests. EIS response has indicated the duplex structure of the passive oxides. The results showed that the electrochemical behaviour of the DIN W. Nr. 1.4970 is better than of AISI 316L steel. Therefore, their application as an implant material may be considered. <![CDATA[<B>Use of castor oil-based polyurethane adhesive in the production of glued laminated timber beams</B>]]> Researchers from the Polymer Technology and Analytical Chemistry (LQATP) group at the São Carlos Institute of Chemistry, University of São Paulo, developed a polyurethane adhesive based on castor oil. In addition to deriving it from a renewable source, this adhesive is nonaggressive to humans and the environment. The purpose of this study is to investigate the feasible use of polyurethane adhesive based on castor oil in the production of 12 beams of Glulam, using the species Pinus caribea hondurensis and Eucaliptus grandis. The structural performance of the beams of Glulam was evaluated through static bending tests. The results obtained enabled to conclude good efficiency of the polyurethane adhesive based on castor oil, for use in Glulam. <![CDATA[<B>Electronic ceramics based on polycrystalline SnO<SUB>2</SUB>, TiO<SUB>2</SUB> and (Sn<SUB>x</SUB>Ti<SUB>1-x</SUB>)O<SUB>2</SUB> solid solution</B>]]> In the present text we discuss on electronic properties arising from polycrystalline semiconductor ceramics of SnO2, TiO2 and (Sn xTi1-x)O2 solid solution rutile-type structure. This is intended to be a short overview of the most recent papers in this area. One of the most important content discussed in this text is based on sinterability of these polycrystalline ceramics, which depends on the target application used to project porous or highly dense microstructure. The majority of discussion is focused in two main applications: varistor and sensor. In both applications there are similarities involved in the control of the sensor and varistor properties, which can mainly ascribed to the grain boundary structure and composition. The similarities found are consistently explained by the fact that all of these n-type semicondutor ceramics have the tendency to establish a grain boundary region with a "p-type semiconductor nature" (due to metal transition atoms segregated at the grain boundary region and then favors negative charged species to adsorb and enrich this region). This configuration enables electrons to become localized on the surfaces, giving rise to a negative surface and, as a result, electron depletion layers are formed, acting as potential barriers which control the properties of the mentioned devices. <![CDATA[<B>Remarks on orthotropic elastic models applied to wood</B>]]> Wood is generally considered an anisotropic material. In terms of engineering elastic models, wood is usually treated as an orthotropic material. This paper presents an analysis of two principal anisotropic elastic models that are usually applied to wood. The first one, the linear orthotropic model, where the material axes L (Longitudinal), R( radial) and T(tangential) are coincident with the Cartesian axes (x, y, z), is more accepted as wood elastic model. The other one, the cylindrical orthotropic model is more adequate of the growth caracteristics of wood but more mathematically complex to be adopted in practical terms. Specifically due to its importance in wood elastic parameters, this paper deals with the fiber orientation influence in these models through adequate transformation of coordinates. As a final result, some examples of the linear model, which show the variation of elastic moduli, i.e., Young&acute;s modulus and shear modulus, with fiber orientation are presented. <![CDATA[<B>Effect of tire rubber particles on crack propagation in cement paste</B>]]> Tire rubber particles (NaOH-treated and untreated) were investigated as possible crack stabilizer and toughness enhancer when added to cement paste through in situ crack propagation measurements using two different types of cement, type I/II and an Interground polypropylene Fiber Cement (IFC). Crack deflection and crack bridging were observed in specimens with untreated rubber in cement type I/II. Crack tip mechanisms associated with crack pinning and acrack arrest were present in type I/II cement and IFC with treated rubber particles. Crack tip mechanisms in IFC with treated rubber lead to the increase in CMOD at the ultimate load level. Crack wake mechanisms in IFC with untreated or treated rubber lead to strain hardening and strain softening behavior. Crack wake bridging mechanisms were replaced by multiple cracking mechanisms in the IFC specimens with treated rubber. The IFC specimens with untreated rubber inclusions provided the best results with respect to toughness enhancement. <![CDATA[<B>Thermogravimetric analyses and mineralogical study of polymer modified mortar with silica fume</B>]]> Mineral and organic additions are often used in mortars to improve their properties. Microstructural investigation concerning the effects of styrene acrylic polymer and silica fume on the mineralogical composition of high-early-strength portland cement pastes after 28 days of hydration are presented in this paper. Thermogravimetry and derivative thermogravimetry were used to study the interaction between polymers and cement, as well as the extent of pozzolanic reaction of the mortars with silica fume. Differential scanning calorimetry and X ray diffraction were used to investigate the cement hydration and the effect of the additions. The results showed that the addition of silica fume and polymer reduces the portlandite formation due to delaying of Portland cement hydration and pozzolanic reaction. <![CDATA[<B>Compression tests of castor oil biopolymer</B>]]> Many methods have been developed to test and evaluate the mechanical properties of the biopolymer from castor oil employed in implants and osteo-repositions, among other things. Most of the methods are performed under quasi-static and cyclic loads (creep and relaxation tests) and under high strain rate, uniaxial compression conditions. This paper presents and discusses the development and applicability of a simple load-application apparatus, devised to reduce shear and barrelling effects on specimens and allow for conventional strain around 45%. Besides contributing valuable information on the mechanical behavior of the castor oil polyurethane, the results of this research point to multiple biomedical applications for this material. <![CDATA[<B>Conversion of rice hull ash into soluble sodium silicate</B>]]> Sodium silicate is used as raw material for several purposes: silica gel production, preparation of catalysts, inks, load for medicines, concrete hardening accelerator, component of detergents and soaps, refractory constituent and deflocculant in clay slurries. In this work sodium silicate was produced by reacting rice hull ash (RHA) and aqueous sodium hydroxide, in open and closed reaction systems. The studied process variables were time, temperature of reaction and composition of the reaction mixture (expressed in terms of molar ratios NaOH/SiO2 and H2O/SiO2). About 90% silica conversion contained in the RHA into sodium silicate was achieved in closed system at 200 &deg;C. The results showed that sodium silicate production from RHA can generate aggregate value to this residue. <![CDATA[<B>Evaluation of rare earth oxides doping SnO<SUB>2</SUB>.(Co<SUB>1/4</SUB>,Mn<SUB>3/4</SUB>)O-based varistor system</B>]]> The present paper aims to verify the inuence of rare earth oxide such as lanthanum (La2O3) and neodymium (Nd2O3) doping SnO2 + 0.25%CoO + 0.75%MnO2 + 0.05%Ta2O5 system. The analysis focus on microstructural inuence on electrical properties. Microstructural analysis were made by using Transmission Electron Microscopy (TEM) at different regions of the samples. From such analysis it was found that La2O3 and Nd2O3 oxides cause heterogeneous segregation and precipitation at grain boundary concerning cobalt and manganese, decreasing the nonohmic electrical properties, as discussed, likely due to the increasing of grain boundary non-active potential barriers. <![CDATA[<B>The effect of cyclic torsion on the dislocation structure of drawn mild steel</B>]]> Cold forming is usually associated with the "work hardening" of the material being formed. The work hardening behavior of metals subject to complex processing paths is different from that in monotonic deformation. The results show that, after some initial hardening, there is a possibility that further deformation will cause softening in the material ("work softening"). Recent work showed that cyclic torsion applied to drawn products causes changes in the subsequent tensile behavior of low carbon steel, and that the effect will depend on the previous "history" of the material. For annealed samples, the cyclic torsion leads to an increase in the yield strength, but does not affect the tensile strength and elongation. For the case of previously drawn bars, the cyclic deformation caused a decrease in the yield and tensile strength and an increase in the total elongation. The present paper discusses the dislocation structure changes associated with different strain paths in mild steel.