Resumo em Inglês:

In Part I of this study, quasi-static and impact bending properties of four aeronautical grade carbon-epoxy laminates have been determined and compared. Materials tested were unidirectional cross-ply (tape) and bidirectional woven textile (fabric) carbon fiber lay-up architectures, impregnated with standard and rubber-toughened resins, respectively, giving rise to 1.5 mm-thick laminates. Quasi-static mechanical properties assessed in transversal mode loading were modulus of elasticity, flexural strength and tenacity at the maximum load, whereas the net absorbed energy was determined under translaminar impact conditions. Two-dimensional woven carbon fiber reinforcements embedded in a rubber-toughened matrix presented the best mechanical performance under static loading. Under dynamic loading conditions, woven fiber fabric pre-forms were favorably sensitive to increasing impact energies regardless the nature of the employed epoxy resin. However, it was concluded that great care should be taken with this material within the low energy impact regimen.

Resumo em Inglês:

In Part II of this work, quasi-static tensile properties of four aeronautical grade carbon-epoxy composite laminates, in both the as-received and pre-fatigued states, have been determined and compared. Quasi-static mechanical properties assessed were tensile strength and stiffness, tenacity (toughness) at the maximum load and for a 50% load drop-off. In general, as-molded unidirectional cross-ply carbon fiber (tape) reinforcements impregnated with either standard or rubber-toughened epoxy resin exhibited the maximum performance. The materials also displayed a significant tenacification (toughening) after exposed to cyclic loading, resulting from the increased stress (the so-called wear-in phenomenon) and/or strain at the maximum load capacity of the specimens. With no exceptions, two-dimensional woven textile (fabric) pre-forms fractured catastrophically under identical cyclic loading conditions imposed to the fiber tape architecture, thus preventing their residual properties from being determined.

Resumo em Inglês:

The production of metallic powder by precipitation from solution was studied in laboratory scale as an alternative to the conventionally adopted processes, based on the atomization of molten material, for producing metal powders with small particle size. The process is based on the precipitation of metals from aqueous solutions by reduction under controlled conditions. Results of laboratory scale experiments are presented for the production of copper particles from aqueous solutions of copper sulfate, using formaldehyde as reducing reactant, and EDTA as complexing agent. The effect of the presence of nuclei was studied. Metallic particles with average sizes in the range from about 0.3 µm to about 15 µm were obtained. In the process, large particles are formed mainly by aggregation of submicrometric particles, indicating that the particle size distribution of the product depends on the control of particle agglomeration rate.

Resumo em Inglês:

This work presents a study on the influence of national heavy petroleum in the corrosion of the AISI 444 and AISI 304 stainless steels in simulated refining operation conditions. The petroleum was first characterized through physicochemical analysis (density, fluidity point, viscosity, sulfur concentration). In an attempt to understand the corrosion effect of temperature and of the type of heating the referred types of steel thermal treatments were carried out at three levels of temperature (200, 300 and 400 °C). The procedure was done in conditions close to those in the distillation column. Heat was gradually increased from room temperature, and directly heated to working temperature. Each treatment took 4 hours to be completed. Scanning electronic microscopy (SEM) and the analysis of X rays dispersive energy (EDX) were used after the trials to characterize the samples. The results show that treatment temperature, as well as the type of heating, has distinct influences on each type of steel.

Resumo em Inglês:

This present work evaluates the influence of microstructure on the fracture toughness of two types of silicon nitride. The two microstructural types of silicon nitride were processed using the gas pressure sintering (GPS) and hot pressing (HP) pathways. The fracture toughness was measured using the Single Edge V-Notch Beam (SEVNB) and Chevron Notch Beam (CNB) methods. The results from both methods for the two forms were in close agreement (with a maximum variation of 5.8%); the K Ic of the material processed by HP was 35% higher than that of GPS and the grain length had a direct influence on the fracture toughness.

Resumo em Inglês:

Electrochemical response of ferri/ferrocyanide redox couple is discussed for a system that uses reticulated vitreous carbon (RVC) three dimensional electrodes prepared at five different Heat Treatment Temperatures (HTT) in the range of 700 °C to 1100 °C. Electrical resistivity, scanning electron microscopy and X ray Diffraction analyses were performed for all prepared samples. It was observed that the HTT increasing promotes an electrical conductivity increasing while the Bragg distance d002 decreases. The correlation between reversibility behavior of ferri/ferrocyanide redox couple and both surface morphology and chemical properties of the RVC electrodes demonstrated a strong dependence on the HTT used to prepare the RVC.

Resumo em Inglês:

This article presents a literature overview and discusses a practical case involving the effect of in service weld repair on the performance - behavior under creep conditions and remanent life - of low alloy CrMo steel steam pipelines with longstanding use. According to the specialized literature, several authors argue that the in service weld repair of low alloy CrMo steel steam pipes can be done successfully, while others disagree, reporting a reduction of up to 30% or more in the remanent life. According to the case analyzed here, which involves the weld repair of a 1¼Cr½Mo ferrite-pearlite steel steam pipe operating for 20 years at 480 °C, in service weld repair leads to the intragranular precipitation of Fe2MoC-type carbides and decreases the solute concentration of the ferrite in the base metal adjacent to the welded joint, thereby considerably reducing the pipeline's remanent life, since the estimated rupture time for the service-aged material is 3.6 times that estimated for the weld-repaired joint.

Resumo em Inglês:

The nanoindentation technique allows the determination of mechanical properties at nanometric scale. Hardness (H) and elastic modulus (E) profiles are usually determined by using the Oliver-Pharr method from the load/unload curves. This approach is valid only for flat surfaces, or at least, when a very low degree of asperity is present (lower than 30 nm). The basic statement is the determination of the zero tip-surface contact point. If a rough surface is present, errors can occur in determining this contact point and, as a consequence, the surface hardness and elastic modulus profiles are drastically altered resulting in under evaluated values. Surfaces with different roughness were produced by controlled nitrogen glow discharge process on titanium. The changed nitriding parameters were different N2/H2 atmospheres and temperatures (600 °C-900 °C). The most correct H and E profiles were obtained by using the contact stiffness analysis method, proposed here, that overcomes the surface roughness. The obtained results were compared with available literature data.

Resumo em Inglês:

The effect of non-random nuclei location and the efficiency of microstructural descriptors in assessing such a situation are studied. Cellular automata simulation of recrystallization in two dimensions is carried out to simulate microstrutural evolution for nuclei distribution ranging from a periodic arrangement to clusters of nuclei. The simulation results are compared in detail with microstrutural descriptors normally used to follow transformation evolution. It is shown that the contiguity is particularly relevant to detect microstructural deviations from randomness. This work focuses on recrystallization but its results are applicable to any nucleation and growth transformation.

Resumo em Inglês:

Recent studies published in the literature have focused on reinforcing alumina with different refractory carbides and nitrides in order to improve hardness, fracture toughness and wear resistance. The incorporation of hard particles as WC, (Ti,W)C and NbC on alumina matrix has shown to be a good alternative in improving the mechanical properties of the composite material. The present work reports some preliminary results obtained reinforcing alumina with 20 wt. (%) (Ti,W)C and 10 wt. (%) NbC. Alumina, (Ti,W)C and NbC powders were homogenized and mixed in a planetary ball mill and subsequently hot-pressed at 1650 °C under 20 MPa in flowing argon. Specimens were characterized by Vicker's microhardness (H V), fracture toughness (K IC), X ray diffraction and scanning microscopy. The composite material showed hardness values of 19.5 GPa and fracture toughness values <FONT FACE=Symbol>»</FONT> 5.2 MPa.m½. The high fracture toughness encountered in this work is related to the crack deflection mechanism.

Resumo em Inglês:

The aim of the present study was to evaluate histologically the pulp response of anionic lyophilized collagen matrix with or without hydroxyapatite as a biomaterial pulp-capping agent in pulpotomy of dogs' teeth. Sixty pre-molar roots from three dogs were used. After pulpotomy, the remaining pulp tissue was capped with one of the following materials: Group I (20 roots): anionic lyophilized collagen matrix; Group II (20 roots): anionic lyophilized collagen matrix associated with hydroxyapatite; Group III (10 roots): calcium hydroxide (p.a.) paste in saline; Group IV (10 roots): zinc oxide eugenol cement. After 90 days the animals were killed by anesthetic overdose and the teeth were removed and submitted to histological processing. According to the histopathological results, we concluded that the zinc oxide eugenol cement and anionic lyophilized collagen matrix with or without hydroxyapatite did not present satisfactory pulp response and that calcium hydroxide is the suitable material for pulpotomy.

Resumo em Inglês:

Al2O3 and H3PO4/Al2O3 catalysts were investigated in the conversion of oleic acid to biofuels and biolubricant at 1 atm and at 623 K. The catalytic tests were performed in a fixed bed and continuous flow reactor, using an oleic acid-catalyst ratio of 4 and N2 as the carrier gas. The reaction products were analyzed by gas chromatography and acidity measurements. N2 adsorption-desorption, X ray diffraction, 31P nuclear magnetic resonance and FT-IR spectroscopy were also employed to evaluate the textural, structural and acidic properties of the catalysts. The results showed that phosphoric acid impregnation improved the alumina decarboxylation activities, generating hydrocarbons in the range of gasoline, diesel oil and lubricant oil. The best catalytic performance was achieved with the highest surface area alumina impregnated with H3PO4, which was the solid that allied high total acidity with a large quantity of mesopores.

Resumo em Inglês:

Polyvinyl alcohol (PVA), PVA crosslinked with glutaraldehyde hydrogels (PVA/GA), PVA with tetraethylorthosilicate (PVA/TEOS) and PVA/GA/TEOS hybrids with recombinant MPB70 protein (rMPB70) incorporated were chemically characterized by Fourier transform infrared spectroscopy (FTIR). FTIR spectra of PVA hydrogel samples showed the absorption regions of the specific chemical groups associated with poly(vinyl alcohol) (-OH, -CO, -CH2) and PVA/GA confirming the formation of crosslinked hydrogel (duplet -CH). It was observed C-H broad alkyl stretching band (n = 2850-3000 cm-1) and typical strong hydroxyl bands for free alcohol (nonbonded -OH stretching band at n = 3600-3650 cm-1), and hydrogen bonded band (n = 3200-3570 cm-1). The most important vibration bands related to silane alcoxides have been verified on FTIR spectra of PVA/TEOS and PVA/GA/TEOS hybrids (Si-O-Si, n = 1080 and n = 450 cm-1; Si-OH, n = 950 cm-1). FTIR spectra of f PVA hydrogel with rMPB70 incorporated have indicated the specific groups usually found in protein structures, such as amides I, II and III, at 1680-1620 cm-1, 1580-1480 cm-1 and 1246 cm-1, respectively. These results have given strong evidence that recombinant protein rMPB70 was successfully adsorbed in the hydrogels and hybrids networks. These PVA based hydrogels and hybrids were further used in immunological assays (Enzyme-Linked Immunosorbent Assay - ELISA). Tests were performed to detect antibodies against rMPB70 protein in serum samples from bovines that were positive in the tuberculin test. Corresponding tests were carried out without PVA samples in microtiter plates as control. Similar results were found for commercially available microplates and PVA based hydrogels and hybrids developed in the present work regarding to immunoassay sensitivity and specificity response.

Resumo em Inglês:

The main objective of this work was to obtain the damping factor (xi ) as well as the elasticity modulus (E) of two kinds of synthetic graphite (HLM and ATJ), using the modal analysis technique. Prismatic beams of square section (~ 11 x 11 mm) and length over thickness ratio (L/t) of about 22.7 were tested in the free - free boundary condition. The first four modes of vibration were taken into account in the non-destructive evaluation of the materials. In addition, numerical simulations were also carried out in this investigation. The agreement between the theoretical and the experimental results was quite good. The average values of E and xi for the HLM graphite were 20% and 90% higher, respectively, than those presented by the ATJ graphite, indicating that the HLM graphite has, proportionally, more damping mechanisms than the ATJ graphite.

Resumo em Inglês:

Rare earths have been used to increase high temperature oxidation resistance of many chromium dioxide and alumina forming alloys. These rare earths can be added as elements (or as oxide dispersions) to the alloys or applied as an oxide coating to the alloy surface. The sol-gel technique is considered to be very efficient to apply fine oxide particle coatings. Oxide gel coatings of various rare earths such as lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, yttrium, erbium and ytterbium have been applied to an iron-chromium alloy to determine their influence on the cyclic oxidation behavior (RT-900 °C) of the alloy. The morphology and coverage of the rare earth oxide gels varied with the type of rare earth. The cyclic oxidation resistance of the alloy increased with increase in time at temperature required to reach a specific chromium dioxide layer thickness and this in turn was influenced by the rare earth ion radius and characteristics of the rare earth oxide coating such as morphology, stability, coverage, resistance to thermal stresses and consequently adhesion.

Resumo em Inglês:

Nanostructured magnetic materials have great interest because of their applications in high-density magnetic information storage and for magnetic sensors. The electrodeposition of materials into porous alumina arrays is a suitable technique to produce nanomaterials, since highly ordered uniform nanomaterials can be obtained simply and cheaply. In this work, template-assisted Co nanowire arrays were prepared by electrodeposition into nanometer-sized pores of an alumite film using a two-electrode electrochemical cell. The Co nanowires were electrodeposited from a solution of 400 g/L of CoSO4.7H2O and 40 g/L of H3BO3. The morphology of the samples was investigated by means of TEM and AFM. The structural characteristic of the samples was examined using XRD, EDX and FTIR, which confirm the cobalt nanowire formation.

Resumo em Inglês:

Several electrochemical techniques can be used to monitor corrosion, among them are open circuit potential (OCP) and eletrochemical impedance spectroscopy (EIS). Monitoring OCP is the most typical procedure for routine inspection of reinforced concrete structures and can be easily carried out, however it only gives an approximate idea of the corrosion process. EIS is a more complete technique, which supplies information regarding the mechanism and kinetics of reaction electrochemistries, but only used in the laboratory. Based on these two techniques, this study is related to the steel corrosion in high-performance concrete with silica fume and silica from rice husk. The acceleration of the corrosion was carried out using immersion cycles in a 3.5% NaCl solution. As well as high compressive strength values, the addition of silica fume presented low corrosion risks and high impedance module values and significant increases of the concrete resistivity after 22 months of alternate immersion/drying cycles were obtained.

Resumo em Inglês:

The deformation response of magnesium based metal matrix composite was investigated by means of hot compression tests. The flow curves were obtained in the temperature and strain rate range of 300-500 °C and 0.001-1 s-1 respectively in order to obtain the processing maps of the studied material and interpreting them on the basis of the dynamic material model. Micro-structural characterization studies conducted on the deformed composite samples, using optical and scanning electron microscopy, revealed a recrystallized grain morphology, debonding of Titanium particles, particle breakage and cracking of the matrix. The observations were performed in order to describe the behavior of the material under hot forming operation in terms of material damage and micro- structural modification.

Resumo em Inglês:

Microstructural evolution in three dimensions of nucleation and growth transformations is simulated by means of cellular automata. Two types of nucleation are considered: site-saturated nucleation and constant nucleation rate. The simulated microstrutural evolution agrees very well with exact analytical expressions. The simulated data also gives very good agreement with expressions derived to describe the evolution of the interfaces between transformed grains.

Resumo em Inglês:

Polycrystalline structure is of paramount importance to materials science and engineering. It provides an important example of a space-filling irregular network structure that also occurs in foams as well as in certain biological tissues. Therefore, seeking an accurate description of the characteristics of polycrystals is of fundamental importance. Recently, one of the authors (MEG) published a paper in which a method was devised of representation of irregular networks by regular polyhedra with curved faces. In Glicksman's method a whole class of irregular polyhedra with a given number of faces, N, is represented by a single symmetrical polyhedron with N curved faces. This paper briefly describes the topological and metric properties of these special polyhedra. They are then applied to two important problems of irregular networks: the dimensionless energy 'cost' of irregular networks, and the derivation of a 3D analogue of the von Neumann-Mullins equation for the growth rate of grains in a polycrystal.

Resumo em Inglês:

The purpose of this study was to compare the effect of casting temperature and atmosphere on the castability of three Ni-Cr alloys against direct flame casting method. Vera Bond (VB), Vera Bond 2 (VB2) and Wiron 99 (W99) were cast at three temperatures: VB and VB2 (1310 °C, 1340 °C and 1370 °C); W99 (1400 °C, 1430 °C and 1460 °C) in atmosphere, vacuum and direct flame. Each alloy was cast in seven different conditions. Castability was assessed by the method that verifies the alloy potential to reproduce a nylon mesh. Kruskal-Wallis test demonstrated for VB, while there was no influence in the temperature range, castability was greater by vacuum (99.3%) than by direct flame (96.2%) and atmosphere (93.06%). For VB2, castability was greater at evaluated temperatures (1370 °C = 94.4%, 1340 °C = 91.15% and 1310 °C = 87.9%) than direct flame (77.8%); related vacuum (97.33%) obtained better values than atmosphere (84.6%) and direct flame. For W99, while atmosphere had no influence, castability was higher at 1460 °C (84.3%) than at other temperatures (1430 °C = 70.3%, 1400 °C = 37.05%) and direct flame (62.5%). Comparison among interactions showed that for all alloys it was possible to significantly increase the filling percentage of the mold in a comparative manner with the direct flame cast method.

Resumo em Inglês:

Nanocrystalline powder of tripotassium sodium sulfate (K3Na(SO4)2 - KNS) was successfully obtained by mechanical alloying a mixture of potassium sulfate (K2SO4) and sodium sulfate (Na2SO4) with a proportion of 3:1 in a planetary mill. X ray powder diffraction (XRPD) was used to characterize this material. Powders produced with high milling times: 15, 30, 45 and 60 hours, have shown a single phase. For 60 hours of milling time, the powder was formed with very small grains (60 nm in average). We also prepared several samples with low milling times: 30, 60, 120, 150 and 180 minutes. The results for this series show that 120 minutes of milling is enough to produce a single crystalline phase of KNS. Therefore, we showed that a nanocrystalline powder of tripotassium sodium sulfate is easily obtained by mechanical alloying and that the grain size can be controlled by the amount of milling time.