Resumo em Inglês:

Abstract Biodegradable films were prepared using regular and waxy starch and reinforced with cellulose nanofibers (CNF) from eucalyptus. Both films were characterized by their optical, structural, barrier, thermal and mechanical properties. The films presented a homogeneous, smooth surface without bubbles or cracks and good handling characteristics. Both films showed a mixture of B and V-type diffraction patterns. The water solubility of the samples decreased after the incorporation of nanocellulose. The water vapor permeability for both sources significantly reduced after incorporating nanocellulose at 0.5% and 1%. It is possible to observe that the addition of CNF increased the thermal stability of the starch films. On the other hand, the incorporation of nanocellulose improved either the mechanical resistance of the starch films.

Resumo em Inglês:

Abstract Vegetable fibers are widely used as reinforcement in the production of composites. In this work, the photodegradative potential of polymer composites containing babassu fiber was characterized and evaluated. The fibers were extracted manually and immersed in a 10% NaOH solution (Mercerization). After drying, they were crushed and incorporated into the low-density polyethylene matrix in proportions of 5%, 10%, and 20% of the total mass of the composite. The composites were subjected to Scanning Electron Microscopy analysis (showed the incorporation of fibers into the polymeric matrix), Infrared Spectroscopy (the presence of fiber was observed with peaks at 3200-3600 cm-1, and 1596 cm-1-1036 cm-1), Mechanical Tests (with 20% fiber, there is a 44% decrease in tension, 48% in strain and 12% in Young's modulus) and Thermogravimetric Analysis (inicial fiber degradation starts between 220-337 °C, and matrix degradation between 333-550 °C). The composites were subjected to degradation processes by solar radiation and under artificial UV-B. Samples of oxy-biodegradable plastic bags were also degraded under the same degradation conditions of the composites. These results show that the materials used in the research, besides presenting an excellent degree of compatibilization, also reveal an improvement in the photodegradation potential of composites.

Resumo em Inglês:

The pitting corrosion of supermartensitic stainless steel (SMSS) was studied in an aqueous solution of 0.1 mol/L NaCl using the scanning vibrating electrode technique (SVET) and cyclic voltammetry. The SMSS showed 0.9% of retained austenite, as verified by Mössbauer spectroscopy. Cuboidal TiN particles were identified on the steel surfaces, by using optical, scanning electron, and transmission microscopy, associated to Mg-Ca-Al rich precipitates. Pit nucleation was slow and only verified after 24 h, associated to TiN/CaO·MgO·Al2O3 complex inclusions, thus on original interdendritic spaces, where lower Cr content and the presence of inclusions are expected.

Resumo em Inglês:

Hot compression tests for 2219/TiB2 Al-matrix composite were conducted on a Gleeble-3500 isothermal simulator in the temperature range of 300~500°C and strain rates of 0.01, 0.1, 1, 10s-1 to obtain true stress strain curves. The original Johnson-Cook model was calculated and used to describe the constitutive relationship of hot deformation behavior of this composite. After precision evaluation and analysis, a new modified Johnson-Cook model was proposed. Comparing with the original model, the new model has a lower absolute average relative error (AARE) of 6.4415% and a higher relative error (R) of 0.9852, which indicates better prediction precision. Meanwhile, to understand the intrinsic workability of this composite, processing map based on dynamic materials model was constructed. Two stable regions locating at 300~400°C&0.01~0.1s-1 and 420~500°C &0.01~1s-1 were identified by the processing map and the instable microstructure in the instability region validated the reliability of the processing map. Furthermore, the microstructure evolution was analyzed and the results revealed that the θ-phase reduced with the increasing temperature.

Resumo em Inglês:

Magnesium phosphate cements (MPCs) are formed when an aqueous solution of ammonium dihydrogen phosphate (ADP, NH4H2PO4) and magnesium oxide (MgO) react in the presence of other aggregates for filling or reinforcement (e.g., fibers, waste, and sand). Therefore, understanding how the MgO/ADP ratio influences phase formation to produce cementitious matrices with better performance is essential. MgO dissolved in an acid solution undergoes numerous transformations because of which different opinions exist regarding the mechanisms by which the setting reactions and formation of hydrated phases occurs in MPCs. In this study, the effect of different MgO/ADP ratios on the properties of MPCs was evaluated regarding phase formation using X-ray diffraction, setting time, and pore size distribution. Increased ADP concentration was found to increase the concentration of hydrated phases, however, this increases the pore content while decreasing the apparent density of MPCs. Compared with compositions with lower MgO/ADP ratios, the composition with the highest MgO/ADP ratio required higher setting time due to the lower concentration of hydrated phases.

Resumo em Inglês:

Abstract Wood offers a good combination of high strength and low density, but its complete characterization takes a long time. This study aimed to correlate apparent density, chemical component and porosity parameters with the physical and mechanical properties of the wood as an alternative route to reduce the time spent proposing equations to estimate each mechanical property. Ten tropical wood species were characterized in accordance with Brazilian Standards and chemical components were determined by the Klason method, and the porosity using mercury intrusion. Multivariate regression models were applied to the results of each species to find the relationships. Good results were obtained, such as the coefficient of determination and the analysis of variance, which indicated that the equations for 10 out of the 16 properties are significant. Therefore, the apparent density, chemical component and porosity parameters used reduce the time intervals much lower than the time test stipulated by the standard.

Resumo em Inglês:

Abstract The use of continuous cooling bainitic steels can provide a more energy efficient manufacturing route. However, for their use in mechanical components like gears, it is necessary to improve their surface properties without impacting the core properties to guarantee reliable mechanical performance. The effect of temperature and time on the plasma nitriding response of a DIN 18MnCrSiMo6-4 steel was investigated. The plasma nitriding was performed for 3, 6 and 9 hours, at 400, 450, 500 and 550 °C, using a gas mixture composed of 76 vol.% nitrogen and 24 vol.% hydrogen. Samples were characterized before and after plasma nitriding concerning the microstructure, hardness and microhardness, fracture toughness, phase composition and residual stress states. Based on the results presented, layer growth constants (k) for different temperatures was determined. Moreover, it could be found that 500 °C gave the best results investigated here, as higher temperature took to core and surface hardness decrease. The nitrided samples with thicker compound layers presented a fracture behavior dominated by the formation of Palmqvist cracks. X-ray phase analysis indicated the formation of biphasic compound layer on the surface of all nitrided samples. The diffusion zone presented compressive residual stresses with highest values near the surface.

Resumo em Inglês:

RESUMO Polyols as solvents are widely and successfully used in various methodologies to obtain zinc oxide nanostructures. One of the main reasons of using polyols is related to its capacity to prevent the agglomeration of ZnO nanoparticles during the synthesis and to promote a more stable colloidal solution of it. In this work it is presented, for the first time, the obtaining of nanostructured ZnO by a polyol mediated solvothermal synthesis using zinc nitrate as precursor. The combination of the zinc source with sodium hydroxide in a polyol medium with PVA as dispersing agent provided a simple process for obtaining nanostructured ZnO. The zinc oxide nanostructures obtained were characterized by UV-visible, XRD, FESEM, TEM, DLS and BET. As result, was obtained a wurtzite phase with hexagonal structure with crystallite size of 12 nm and, according to TEM micrographs, an average size of 14 nm, which was corroborated to other analyses.

Resumo em Inglês:

Abstract Silicon nanotubes (SiNTs) have been successfully synthesized recently. Despite the wide potential applications of SiNTs, their mechanical properties are rarely reported. In this study, as the first step, the mechanical behavior of clamped-free single-walled silicon nanotubes (SWSiNTs) for both armchair and zigzag structures is investigated by using molecular dynamics (MD) simulations while the inter-atomic forces are described by the Tersoff-Brenner many-body potential energy function. Meanwhile, the results of the total strain energy are used to establish an expression for predicting Young’s modulus of the nanotubes. Afterward, the free vibrational analysis including torsional, longitudinal and transverse vibrations behavior of SWSiNTs with different diameters and lengths are investigated to report the corresponding fundamental frequencies as a significant design parameter. In this study, also, an important stress-strain parameter ratio is defined for vibration analyses named dynamic Young’s modulus. Thereafter, the natural frequencies that are obtained using the current atomistic model are successfully compared with those evaluated by the continuum mechanics model. It is concluded that the utilized approach can predict the frequencies with reasonable accuracy. Furthermore, the effects of geometry on the natural frequencies for both armchair and zigzag structures are examined. The obtained results provide valuable insights into the vibrational behavior of silicon-based nanotubes.

Resumo em Inglês:

Ionic trace elements such as Mg2+, Mn2+ and Sr2+ are very difficult to stabilize in the hydroxyapatite lattice, and they can induce phase transformations when subjected to thermal treatments. The effects of the ions themselves are often confused with the effects of the newly formed phases. Therefore, the objective of this work was to evaluate the effects of the ions isolated from the effects caused by the inherent phase transformations observed in these systems. WDXRF, XRD, FTIR and biological assays using mouse preosteoblastic cells (MC3T3-E1) showed the Mg2+ ions can stimulate cell differentiation even when segregated from the HA structure in the form of MgO. However, the presence of MgO considerably retards cell proliferation. At the same time, Mn2+ ions are able to increase cell proliferation and induce the production of high levels of ALP, regardless of whether they are inserted into the HA structure or segregated in the form of Mn3O4. Finally, the presence of Sr2+ in the HA lattice does not appear to directly affect cell behavior, since both the proliferation and production of ALP are comparable to those observed in the nondoped HA sample.

Resumo em Inglês:

Bismuth (Bi) alloying in Aluminum (Al) alloys is considered of importance in special applications requiring improvements in the alloy machining. Despite that, the influence of Bi either on evolution of the solidification or on resulting microstructure of hypereutectic Al-Si alloys is still to be determined. The present research work is devoted to these requirements. In the present study, Al-15wt.% Si hypereutectic alloy is modified with 1.0 wt.% Bi. The effects of this addition on the morphology of the phases forming the microstructure and on the tensile/wear properties are investigated. Various samples characterized by distinct cooling rates are generated by transient directional solidification of the ternary Al-Si-Bi alloy. Microstructure is examined by optical microscopy and scanning electron microscopy (SEM) analyses, segregation by energy-dispersive X-ray spectroscopy (EDS) whereas wear and tensile properties have been characterized by standardized tests. The experimental variations of the eutectic spacing are compared to each other based on their trends. It is found that the addition of minor Bi content (~1 wt. %) permitted tensile strength and ductility of 195 MPa and 14%. Furthermore, wear resistance is improved by up to 20% due to the Bi addition. The reasons for that will be outlined.

Resumo em Inglês:

Abstract The clay minerals have characteristics and properties that allow their applicability in the cosmetic area, being incorporated into formulations as an active principle. Therefore, the aim of this work is characterizing and evaluating the influence of a clay from Miracema do Norte, Tocantins, Brazil, named Clay V, on the physicochemical characteristics of a hydrophilic gel of Aristoflex®, a copolymer of the neutralized acryloyldimethyltaurate and vinylpyrrolidone sulphonic acid. Clay V was decontaminated and characterized through microbiological evaluation, crystalline phases present by X-Ray Diffraction (XRD), chemical composition by X-Ray Fluorescence (XRF), thermogravimetric analysis (TGA) and granulometric distribution by sieving. Gels were prepared using Clay V with particles in the range ≤ 180 μm in three different concentrations: 1%, 3% and 5% (w/w) and a standard gel without clay. The formulations were evaluated according to organoleptic characteristics, pH, viscosity, spreadability and the centrifugation test. The microbiological evaluation showed that the clay sample is in compliance with the parameters established by the legislation. The following mineral phases were identified by XRD: kaolinite, illite, vermiculite and quartz, mainly composed of silica and alumina according to XRF. Thermal analysis showed that the clay has two thermal decomposition reactions, the largest being 547.6°C. The granulometric analysis identified that the largest fraction (63.22%) was of particles with sizes greater than 710 μm. The organoleptic characteristics presented by the formulations were suitable, with characteristic gel odor, homogeneous appearance, soft and refreshing texture and staining based on the concentration of Clay V used. The obtained pH values were within the range between 5.5 and 6.5, and it was verified that the gel has high spreadability, distributing evenly on the skin. The values obtained for viscosity showed that the formulations are non-Newtonian fluids with pseudoplastic behavior. The centrifugation test showed that the formulations are stable, with no phase separation. The results obtained with the tests showed that the natural clay V material is beneficial in cosmetic products and can be used for incorporation in cosmetic gel formulations of Aristoflex® type.

Resumo em Inglês:

Abstract In this work, CoCrMo-base alloys specimens were produced by additive manufacturing using selective laser melting (SLM) as well as CAD/CAM milling. For SLM specimens, spherical particles were laser processed at 1320°C under argon atmosphere and submitted to thermal stress relieving at 750°C–45min. Specimens from CoCrMo blocks were milled by CAD/CAM machining and sintered at 1300°C–60min. The materials from both techniques were characterized by relative density, dilatometry, SEM/BSE, OM and XRD analysis. The mechanical properties were determined by Vickers hardness and tensile tests. The specimens from both techniques exhibited single phase γCo (FCC) and CTE of 14 x10-6 °C-1. Relative density of 95.4%/ 85.6%, hardness values near 400HV/ 350HV and UTS of 905MPa/ 780MPa were measured for SLM and CAD/CAM specimens, respectively. Higher relative density is the main factor for increased mechanical properties of SLM specimens. On the other hand, both SLM and CAD/CAM specimens present properties in accordance with ISO-22674 recommendations, compatible with dental applications such as bridges containing four or more elements as well as fully dense pontics.

Resumo em Inglês:

Abstract Despite the experimentation of bainitic and martensitic microstructures in wheel-rail steels, pearlitic microstructure remains dominant in railway track. The wear resistance behavior of bainitic and pearlitic microstructures is still a matter of controversy. In this study, pin-on-disc sliding wear tests were performed to analyze the effects of the microstructure on wear resistance. The AISI 1080 steel was isothermally treated at five temperatures using a dilatometer in order to obtain pearlite, bainite and martensite structures. After these treatments, bainitic and martensitic samples were tempered at 500°C. It was possible to achieve pearlitic specimens with interlamellar spacing ranging from 70 ± 4 nm to 243 ± 9 nm. It was found that the wear resistance increases with decreasing the interlamellar spacing, fine pearlite showed 30% lower mass loss than coarse pearlite. The severe deformation and dislocation accumulation in different depth from the contact surface were analyzed by electron backscattered diffraction technique. The results showed that the first 10 µm depth from the contact surface was severely deformed and a high number of random high-angle boundaries developed due to the large compressive force. Fine pearlitic structure tends to present a better wear performance when compared to bainitic or martensitic structures.

Resumo em Inglês:

Abstract In this paper the production and characterization of compacted graphite iron alloys in ten chemical compositions is presented. The specimens were obtained through a foundry process performed by a gating system model developed in order to allow the incorporation of silicon, copper and tin. Hardness and tensile tests were performed, as well as microstructural evaluation. Additionally, the results related to the experimental investigation were compared to those obtained from a finite element method analysis. The results showed a correlation between the addition of silicon and the increase of ferrite and graphite count per mm2. Regarding copper and tin additions, the percentage increase of pearlite was associated with the reduction of graphite average size. Changes in chemical composition led to different values of ultimate tensile strength, yield strength and hardness, whose magnitude was mainly related to the amount of ferrite. Computer simulation was considered efficient in predicting these results.

Resumo em Inglês:

Abstract This study aimeds at investigating the mechanical behavior of an E-glass fiber-reinforced epoxy resin of a laminated composite sandwich with honeycomb core and a central hole, used in the aeronautics industry submitted to bending loading. Three analytical failure models applied to laminated composites were compared in order to study the influence of stress concentration due to a central hole. The following criteria were assessed: Average Stress Criterion (ASC), Point Stress Criterion (PSC) and the Inherent Flaw Model (IFM). These models were applied to experimental data obtained in a four-point bending test in samples of the sandwich laminate. Finally, modifications on failure prediction models were proposed and appied in sandwich laminates with a central hole. The results obtained showed the applicability of the proposed formulation and that the suggested changes to the model more adequately fit it to the experimental data.

Resumo em Inglês:

Abstract Environmental friendliness and cost demand the development of lignin-modified phenolic (LPF) resins for application as a binder for carbon-containing refractories (CCRs) production. Moreover, the in-situ graphitization of such resins can produce crystalline carbon, which is an essential component of CCRs. Consequently, this study investigated LPF resins graphitization using ferrocene, boron oxide and boric acid. The modified resins were synthesized using thermally treated kraft lignin based on 1.5 formaldehyde to phenol molar ratio and with up to 30 wt.% lignin as phenol replacement. The resins chemical composition and the structural organization and oxidation resistance of carbons derived from the plain resins and those containing the graphitizing additives were determined. The results showed that ferrocene and the boron compounds could induce graphitic carbon generation when carbonizing LPF resins at 1500 °C for 5 hours. The best graphitization level (73%) was achieved when 10 wt.% boric acid was added to the resin produced with 20 wt.% lignin. Regarding the formulations containing ferrocene, the highest amount of graphitic carbon (48%) was generated when 5 wt.% of this additive was added to the resin synthesized with 10 wt.% lignin. The carbons derived from the formulations containing boron oxide presented the best oxidation resistance.

Resumo em Inglês:

Abstract The inhibitory effect of Oxethazaine drug, 2,2'-(2-Hydroxyethylimino)bis[N-(alphaalpha-dimethylphenethyl)-N-methylacetamide] on corrosion of mild steel in 1M HCl solution was studied by weight loss measurements, electrochemical impedance spectroscopy and potentiodynamic polarization methods. The results of gravimetric and electrochemical methods demonstrated that the inhibition efficiency increased with an increase in inhibitor concentration in 1M HCl solution. The results from electrochemical impedance spectroscopy proved that the inhibition action of this drug was due to adsorption on the metal surface. Potentiodynamic polarization studies revealed that the molecule was a mixed type inhibitor. The adsorption of the molecule on the metal surface was found to obey Langmuir Adsorption isotherm. Potential of zero charge at the metal-solution interface was measured to provide the inhibition mechanism. The temperature dependence of the corrosion rate was also studied in the temperature range from 30 to 50 °C. Quantum chemical calculations were applied to correlate electronic structure parameters of the drug with its inhibition performance. The obtained theoretical results have been adapted with the experimental data.

Resumo em Inglês:

Abstract The projections for the global energy demand have been one of our society’s greatest challenges, which has contributed significantly to the search for new sources of energy, among which biodiesel stands out and, consequently, the development of methods for quality assurance is essential to ensure its technological demand. In this context, a stable sensor based on graphene oxide and gold nanoparticles was developed for glycerol analysis. The electrochemically deposited gold nanoparticles presented the best results with a peak current (Ip) four times greater than the chemically produced gold nanoparticles. The combination of glassy carbon electrode with electrochemically reduced graphene and electrochemically deposited gold nanoparticles (GCE-ErGO-EAuNp) resulted in an efficient sensor to detect glycerol, promoting an Ip increase. The proposed non-enzymatic method showed a linear response in the concentration range of 1.0 x 10-3 to 1.0 x 10-2%(w/w) with a good determination coefficient (r2 = 0.9989), limits of detection and quantification at 1.2 x 10-4% and 4.0 x 10-4%(w/w), respectively, with a repeatability of (RSD% ranged from 0.36% to 2.78%), intermediate precision and recovery of (99.3% to 104.4%) and excellent stability of 700 continuous analysis cycles.

Resumo em Inglês:

Abstract Laser power influences the range of dilution with the substrate and thus, the microstructure and properties of the coatings. This work evaluated the effect of laser power on the dilution, microstructure, hardness and wear behavior of Hastelloy C276TM alloy coatings deposited on AISI 304L stainless steel and GGG40 ductile iron. The microstructure was comprised of γ (Ni-FCC) dendrites and molybdenum-rich interdendritic regions containing carbides. The coatings showed similar second phase nature and fraction and equivalent hardness and wear behavior for the lowest laser power condition. Otherwise, higher power on 304L induced to a lower fraction of blocky-like M23C6/MC carbides; whilst on GGG40 led to a higher fraction of a predominantly lamellar M6C type carbide. Largely diluted coatings on ductile iron entailed differences in the strengthening mechanisms which led to higher hardness and lower wear rate. Moreover, wear tracks showed surface oxidation which in turn negatively influenced the performance of specimens with low dilution on both substrates. On the other way, with high dilution, this feature was only observed on stainless steel.

Resumo em Inglês:

Abstract In this paper, Rheo-Die Cast (RDC) Al-Si alloy with 7.5 wt % Si and 0.3 wt %Mg and Metal Matrix Composites (MMC’s) of RDC Al-Si composites with 5 to 20 vol. % of SiCp were produced by an in-house fabricated RDC machine. Microstructure and wear behavior of both RDC alloy and composites were investigated. Results indicated that the RDC samples have significantly refined microstructure with fine and uniform non-dendritic grains resulting increased hardness and enhanced wear resistance. Wear resistance is three times higher for sample with 20% SiCp than those without SiCp additions. Surfaces of wear test samples were investigated by SEM to study the effect of both grain structure and SiCp particulates on the wear mechanism. It was also observed that reinforced RDC samples showed improved hardness and wear resistance due to the presence of SiCp in the matrix of non-dendritic grains, obtained without modification treatment.

Resumo em Inglês:

Abstract The analysis of structure, defect substructure, elemental and phase compounds and friction properties of Al-11wt%Si alloy surface layer of subjected to complex treatment was carried out by methods of scanning and transmission electron microscopy. Complex treatment includes the electroexplosion influence by Al-Y2O3 compound and subsequent electron beam irradiation. The surface layer ≈ 80 μm thick is formed by high-velocity crystallization cells of 0.8-1.3 μm in dimension. Interlayers 50–75 nm thick located along the cells of high-velocity crystallization are enriched by atoms of silicon and yttrium. Complex surface treatment leads to the increase by 18 times in wear resistance and decrease by 1.6 times in the friction factor of the modified layer.

Resumo em Inglês:

Abstract The paper reviews the events that led to the understanding of the recrystallisation of metals throughout history, covering the timeline from 3500 BC until the 1950s and dealing mainly with the misconceptions related to the “recrystallisation” and “amorphisation”. This history begins with the thermomechanical processing of native metals in pre-Columbian America (3,000 BC), and the production of brass coins in Rome (100 BC). The analysis of the fracture surfaces of metals, commonly used between the 16th and 18th centuries in Europe for the quality control of metallic products, is briefly discussed. The observation of crystalline and fibrous fractures lead to the common misconception of the 19th century that “recrystallisation” takes place during the heating of “amorphous” cold-worked metals. The use of reflecting optical microscopy in the late 19th century indicated, however, that the plastic deformation only promotes a morphological change in the microstructure of the metals without any “amorphisation”. In the early 20th century, the plastic deformation of metals by crystal plane slipping and twinning was well documented by metallographic observation during tensile testing. Nevertheless, in 1915, Prof. Rosenhain advocated that the “crystal” inside the slip bands of a plastically deformed metal was “amorphous” and responsible for the work hardening. The discovery of the X-ray diffraction technique, in 1913, allowed to resolve the ongoing dispute of the “amorphisation” of metals during plastic deformation. Between the 1920s and 1950s, X-ray diffraction was practically the only means of studying the internal structure of metals to explain the nature of their plasticity, confirming many aspects of the dislocation theory. This technique was crucially important to understand the atomic crystal structure of metals in the annealed and cold-work states. Our history finishes in the 1950s when the transmission electron microscopy finally revealed the first images of dislocation in metals. Up to that date, most of the understanding of the dislocations’ distribution and organisation in cold-work and annealed states had already been derived from X-ray diffractograms, which gave birth to the modern physical metallurgy.

Resumo em Inglês:

Abstract Carbon nanostructures have been extensively studied due to combination of properties they present. With different geometries and reactivities, carbon nanotubes, graphene and fullerene were oxidized and modified with octadecylamine (ODA) in order to decrease van der Waals’s interaction and consequently improve the polymer-carbon nanostructures affinity for use in nanocomposites. Nanostructures were characterized as morphology, chemical structure, molecular conformation and thermal properties. All nanostructures showed results that confirm the modification with ODA, without geometry being altered. Modified nanostructures showed different percentages of ODA: graphene 86%, carbon nanotubes 83% and fullerene 63%. It was attributed to distinct reactivities, shapes and specific surface area available, due to different amounts of reactive terminals obtained before oxidation reactions. However, they showed a lower interfacial interaction, which is highly favorable for use in polymer nanocomposites.

Resumo em Inglês:

Abstract In this research, a Metal Matrix hybrid composite (MMHC) is prepared by reinforcing the following reinforcements like Graphite, Aluminium oxide, silicon carbide and boron carbide at a percentage of 4 and 5 is added with A6061. This preparation is carried out by using the stir casting method. In particular, the corrosion properties of the untreated A6061 reinforced composites samples were evaluated using in 3.5% NaCl solution and immersion tests in 1% HCl acidic water solution. The highest percentage of depicts the positive result. In addition to that the SEM, wear, hardness tests are carried out to bring out the positive impact of the newly prepared samples. In accordance with that the fundamental spotlight is given on Aluminum network composites on account of its novel blend of good corrosion protection, wear properties and outstanding mechanical properties.

Resumo em Inglês:

Abstract High-purity SAPO-34 was synthesized using industrial kaolin waste produced in the Amazon region as the main source of silicon and aluminium. The hydrothermal method was applied to investigate the effect of the Si/Al ratio and crystallization time on the phase formation and purity. The materials were characterized by X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy, which demonstrated that SAPO-34 with greater purity was obtained only for the composition whose Si/Al ratio was approximately 1, which was obtained by inserting Al2O3 into the synthesis gel.

Resumo em Inglês:

Abstract The four-layer Aurivillius CaBi4Ti4O15 with introducing of La3+ on the A-site and Mn3+ on the B-site with the formula Ca1-xBi3+xLaTi4-xMnxO15 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) were synthesized by molten salt method using the mixture of sulfate salts K2SO4/Na2SO4 as the flux. XRD data confirmed the formation of single-phase Aurivillius with A21am orthorhombic structure for x = 0, 0.2, 0.4, and 0.6, whereas for x = 0.8 and 1, the impurity phases were observed. SEM analysis shows the anisotropic plate-like grains, which are a typical grain of Aurivillius phases. The cell volume decreases with increasing x, indicating a presence of mixed valences of Mn3+ and Mn4+. The dielectric constants increased with x, strongly correlated with the higher distortion of the structure, the 6s2 lone pair electrons of Bi3+ cation increase. The presence of Mn3+ unpaired electrons results in the increase of dielectric loss as increasing x.

Resumo em Inglês:

Abstract Cemented carbides (WC-Co) are difficult to be processed by conventional machining processes. Electrical discharge machining (EDM) appears as an efficient technology to manufacture WC-Co products with high accuracy. In EDM literature no research works investigating the influences of different grades of CuW electrodes on geometrical characteristics when ED-machining the same cemented carbide was found. This work presents an investigation on ED-Machining of cemented carbide (WC-Co) with 10% Co using two grades of coper-tungsten (CuW) electrodes with 65% and 85% of tungsten. ED-Machining experiments were carried out under rough, semifinish and finish regimes with input variables discharge current ie, discharge duration te and pulse interval time to using analysis of variance (ANOVA) based on design of experiments with complete factorial 32. Output variables evaluated were WC-Co workpiece geometrical characteristics 3D surface roughness and round cavities circularity measures. Results showed that ED-Machining regime is the most significant parameter on both WC-Co workpiece circularity and surface roughness measures. Electrodes grades CuW65 and CuW85 presented similar results on workpiece circularity and 3D surface roughness.

Resumo em Inglês:

Abstract Electrospun fibers find a number of biomedical applications, like scaffolds for tissue engineering, as polymer nanofiber mats can mimic the extracellular matrix (ECM) of the body. In this research, non-woven mats composed of poly(L-lactic acid) (PLLA) fibers were obtained by low voltage (6 kV) electrospinning of PLLA/chloroform (CL)/sodium lauryl ether sulfate (SLES) solution. Tests were performed in two different collector/capillary distances and the produced fibers were evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and cell viability. The results show the formation of three dimensional mats composed of porous fibers created by the addition of small amounts of aqueous solution of SLES surfactant; a higher crystallinity degree for longer collector/capillary electrospun distance and positive cell proliferation.

Resumo em Inglês:

In this research work, Inconel 718 specimens are fabricated by Direct Metal Laser Sintering process in the closed chamber which is filled with argon gas environment from a pre-alloyed powder. The process contains the high intensity of the laser source to melt the powder material, and the segment is placed on the top of the previous layer. Plates were vertically fabricated systematically (i.e., z-axis) and columnar grains are exhibited perpendicular to the build direction (i.e., x-axis). Test specimens are stress-relieved at 980°C for 2 hours and the recrystallized zone are found to be spheroid structure precipitates. The Ni-Cr matrix in the recrystallized interface and grain boundaries is observed in the samples, the micro hardness of the as-fabricated material is found as 340-350 VHN. Also, correspondingly mechanical properties are comparable with the wrought inco-718 alloy material. Further, the as build condition specimens are used for making butt joint configuration using Tungsten Inert Gas (TIG) welding process and Mechanical and microstructural properties are studied. The studies on welding of additive manufactured component will ensure the weldability of the AM material for the research community and industry.