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Materials Research, Volume: 16, Número: 1, Publicado: 2013
  • A semi-analytical model for deflection analysis of laminated plates with the Newton-Kantorovich-Quadrature method Regular Articles

    Khandan, Rasoul; Noroozi, Siamak; Sewell, Philip; Vinney, John; Koohgilani, Mehran

    Resumo em Inglês:

    A semi-analytical approach for analysis of laminated plates with general boundary conditions under a general distribution of loads is developed. The non-linear equations are solved by the Newton-Kantorovich-Quadrature (NKQ) method which is a combination of well-known Newton-Kantorovich method and the Quadrature method. This method attempts to solve a sequence of linear integral equations. The convergence of the proposed method is compared with other semi-analytical methods. The validation of the method is explored through various numerical examples and the results compared with finite element method (FEM) and experimental tests. Good agreement between the NKQ model, FEM and experimental results are shown to validate the model.
  • Effect of calcium content on the microstructure, hardness and in-vitro corrosion behavior of biodegradable Mg-Ca binary alloy Regular Articles

    Harandi, Shervin Eslami; Mirshahi, Mohammad; Koleini, Shahriar; Idris, Mohd Hasbullah; Jafari, Hassan; Kadir, Mohammed Rafiq Abdul

    Resumo em Inglês:

    Effect of calcium addition on microstructure, hardness value and corrosion behavior of five different Mg-xCa binary alloys (x = 0.7, 1, 2, 3, 4 wt. (%)) was investigated. Notable refinement in microstructure of the alloy occurred with increasing calcium content. In addition, more uniform distribution of Mg2Ca phase was observed in a-Mg matrix resulted in an increase in hardness value. The in-vitro corrosion examination using Kokubo simulated body fluid showed that the addition of calcium shifted the fluid pH value to a higher level similar to those found in pure commercial Mg. The high pH value amplified the formation and growth of bone-like apatite. Higher percentage of Ca resulted in needle-shaped growth of the apatite. Electrochemical measurements in the same solution revealed that increasing Ca content led to higher corrosion rates due to the formation of more cathodic Mg2Ca precipitate in the microstructure. The results therefore suggested that Mg-0.7Ca with the minimum amount of Mg2Ca is a good candidate for bio-implant applications.
  • A characterization for the flow behavior of as-extruded 7075 aluminum alloy by the improved Arrhenius model with variable parameters Regular Articles

    Quan, Guo-zheng; Li, Gui-sheng; Wang, Yang; Lv, Wen-quan; Yu, Chun-tang; Zhou, Jie

    Resumo em Inglês:

    In order to perform the numerical simulations of forging response and establish the processing parameters for as-extruded 7075 aluminum alloy, the compressive deformation behavior of as-extruded 7075 aluminum alloy were investigated at the temperatures of 573 K, 623 K, 673 K and 723 K and the strain rates of 0.01 s-1, 0.1 s-1, 1 s-1 and 10 s-1 on a Gleeble1500 thermo-mechanical simulator. Based on the analysis of the effect of strain, temperature and strain rate on flow stress, dynamic recrystallization (DRX) type softening characteristics of the stress-strain curve with single peak were identified. The traditional Arrhenius type model is in favor of the prediction for the flow stress at a fixed strain, and can not satisfy the need of the numerical simulations of various hot forming processes due to the lack of the effect of strain on flow stress. Lin et al. improved Arrhenius type model with a series of variable coefficients as functions of true strain (including activation energy of deformation Q, material constants n and a, and structure factor A) to predict the flow stress during the hot compression. The application has been demonstrated in this work for as-extruded 7075 aluminum alloy. The comparisons between the predicted and experimental results show that, for the worst case, the error in the flow stress estimate is 5.63%, and the max mean error is 3.6%. The developed model provides fast, accurate and consistent results, making it superior to the conventional Arrhenius type model. In further it can be used in computer code to model the forging response of 7075 aluminum alloy mechanical part members under the prevailing loading conditions.
  • Characterization of poly (L-co-D,L Lactic Acid) and a study of polymer-tissue interaction in subcutaneous implants in wistar rats Regular Articles

    Ciambelli, Giuliano Serafino; Perez, Mariana Ortega; Siqueira, Guilherme Vasconcelos; Candella, Marco Aurélio; Motta, Adriana Cristina; Duarte, Marcia Adriana Tomaz; Alberto-Rincon, Maria do Carmo; Duek, Eliana Aparecida de Rezende

    Resumo em Inglês:

    Poly (L-co-D,L lactic acid) (PLDLA) is an important biomaterial because of its biocompatibility properties that promote cellular regeneration and growth. The aim of this study was to evaluate the polymer-tissue interaction of PLDLA implants in the dorsal subcutaneous tissue of male Wistar rats at various intervals (2, 7, 15, 30, 60 and 90 days) after implantation. Physical properties such as the glass transition point (Tg), degradation behavior and other mechanical properties were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), scanning electron microscopy (SEM) and tension tests. Analysis of the degradation of PLDLA membranes in vitro showed that the polymer became crystalline as a function of the degradation time. Mechanical tension tests showed that the polymer behaved like a ductile material: when subjected to constant tension it initially suffered deformation, then elongation and finally ruptured. TGA/MEV provided evidence of PLDLA membrane degradation. For histological analysis, samples from each group were processed in xylol/paraffin, except for the 60 - and 90 - day samples. Each of the latter samples was divided in two: one half was treated with xylol/paraffin and the other with historesin. Light microscopy showed the adhesion of cells to the biomaterial, the formation of a conjunctive capsule around the implant, the presence of epithelioid cells, the formation of foreign body giant cells and angiogenesis. During degradation, the polymer showed a 'lace' - like appearance when processed in xylol/paraffin compared to the formation of "centripetal cracks in the form of glove fingers" when embedded in historesin.
  • Zeolite A synthesis employing a brazilian coal ash as the silicon and aluminum source and its applications in adsorption and pigment formulation Regular Articles

    Bieseki, Lindiane; Penha, Fábio Garcia; Pergher, Sibele Berenice Castellã

    Resumo em Inglês:

    Zeolite A was synthesized using the coal ash from Siderópolis/RS - Brazil. The synthesis was based on a standard IZA synthesis using coal ash as the Si and Al source. XRF analysis showed that the coal ash has a Si/Al ratio of 1.52, which is close to the Si/Al ratio required to produce zeolite A (1.0). The synthesized materials were analyzed by XRD, SEM and N2 adsorption. More crystalline materials were obtained during synthesis when an additional treatment was applied at a temperature of 353 K at the dissolution of NaOH step. The product formed after 4 hours was the most crystalline, but even the product formed after 1 hour proved to be better than that formed using the standard 4 hours IZA synthesis. The zeolites synthesized by this method had an adsorption capacity of 120 mg.g-1 for Ca2+, half the capacity of commercial zeolite A (300 mg.g-1). It was not possible to obtain blue or green pigments using the synthesized zeolite A.
  • Novel morphology of needle-Like nanoparticles of Na2Mo2O7 synthesized by using Ultrasonic spray pyrolysis Regular Articles

    Validžić, Ivana Lj.; Mitrić, Miodrag

    Resumo em Inglês:

    Low-temperature method for the synthesis of novel morphology of needle-like nanoparticles of disodium dimolybdate (Na2Mo2O7) in the process of ultrasonic spray pyrolysis (USP) using aqueous solutions of thermodynamically stable molybdenum (VI) oxide clusters as precursor is described. Needle-like Na2Mo2O7 particles were obtained and collected in toluene, while centrifugation was employed to isolate solid material from solution. The scanning electron microscopy (SEM) confirmed that the morphology of the synthesized Na2Mo2O7 particles is needle-like collected into bundles. The X-ray Powder Diffraction (XRPD) analysis revealed appearance of orthorhombic Na2Mo2O7, synthesized at 300 °C. By comparing the XRPD pattern of the synthesized needle-like Na2Mo2O7 powder obtained in the process of USP with the XRPD pattern simulated for randomly-distributed crystallites by planes, the most prefered growth plane of needle-like nanoparticles were found.
  • Corrosion evaluation of orthodontic wires in artificial saliva solutions by using response surface methodology Regular Articles

    Barcelos, Arianne Madureira; Luna, Aderval Severino; Ferreira, Nancy de Assis; Braga, Antônio Vitor Castro; Lago, Dalva Cristina Baptista do; Senna, Lilian Ferreira de

    Resumo em Inglês:

    In the present work, stainless steel and Ni-Ti commercial orthodontic wires were immersed in artificial saliva solutions, containing or not F- ions, in different pH values, during 30 days. The weight loss and the Ni2+ content in the solutions at 15 and 30 days of exposition were evaluated using a composite design 2³ and response surface methodology. The open circuit potential (OCP) was measured over the same period of time. Polarization curves and morpHological analysis of the wires before and after the corrosion experiments were also carried out. The results showed that corrosion of the studied metal alloys depended on a combination among saliva pH, the exposition time, and the concentration of F- ions in the solution. The critical condition was observed for Ni-Ti wires at pH = 3.0, and high concentration of F- ions, causing a decrease in the OCP values and an increase in Ni dissolution and corrosion current density.
  • Evaluation of the properties of iron oxide-filled castor oil polyurethane Regular Articles

    Mussatti, Eleonora; Merlini, Claudia; Barra, Guilherme Mariz de Oliveira; Güths, Saulo; Oliveira, Antonio Pedro Novaes de; Siligardi, Cristina

    Resumo em Inglês:

    The aim of this study was to obtain and evaluate the electrical, thermal and mechanical properties of iron oxide-filled castor oil polyurethane (PU/Fe2O3). The iron oxide used in this study was a residue derived from the steel pickling process of a Brazilian steel rolling industry. Polymeric composites with different iron oxide volume fractions (2.5, 5.0, 7.5, 10.0 and 12.5%) were prepared through the casting process followed by compression molding at room temperature. The composites were analyzed by FTIR, XRD and densities, tensile strength, Young's modulus, electrical and thermal conductivities measurements. By increasing the iron oxide content, the apparent density, tensile strength, Young's modulus and electrical conductivity values of the composites were also increased. The iron oxide additions did not change significantly the value of thermal conductivity (from 0.191 W.mK-1 for PU up to 0.340 W.mK-1 for PU enriched with 12.5% v/v of iron oxide). Thus, even at the higher iron oxide concentration, the compounds as well as the pure polyurethane can be classified as thermal insulators.
  • Age-hardenability and related microstructural changes during and after phase transformation in an Au-Ag-Cu-based dental alloy Regular Articles

    Kim, Hyung-Il; Kim, Tae-Wan; Kim, Young-Oh; Cho, Su-Yeon; Lee, Gwang-Young; Kwon, Yong Hoon; Seol, Hyo-Joung

    Resumo em Inglês:

    The aim of this study was to clarify how the microstructural changes during and after phase transformation determine the age-hardenability of an Au-Ag-Cu-based dental alloy. The rapid increase in hardness in the initial stage was the result of rapid atomic diffusion by spinodal decomposition into metastable Ag-rich' and Cu-rich' phases. The constant hardening after apparent initial hardening was the result of a subsequent transformation of the metastable Ag-rich' and Cu-rich' phases to the stable Ag-rich α1phase and AuCu I phase through the metastable AuCu I' phase. During the increase in hardness, fine block-like structure with high coherency formed in the grain interior, which changed to a fine cross-hatched structure. A relatively coarse lamellar structure composed of Ag-rich α1and AuCu I phases grew from the grain boundaries, initiating softening before the grain interior reached its maximum hardness. As a result, the spinodal decomposition attributed to rapid hardening by forming the fine block-like structure, and the subsequent ordering into AuCu I, which is a famous hardening mechanism, weakened its hardening effect by accelerating the lamellar-forming grain boundary reaction.
  • Surface cellulose modification with 2-aminomethylpyridine for copper, cobalt, nickel and zinc removal from aqueous solution Regular Articles

    Silva Filho, Edson Cavalcanti; Santos Júnior, Luiz Sousa; Silva, Marcia Maria Fernandes; Fonseca, Maria Gardênnia; Santana, Sirlane Aparecida Abreu; Airoldi, Claudio

    Resumo em Inglês:

    Cellulose was first modified with thionyl chloride, followed by reaction with 2-aminomethylpyridine to yield 6-(2'-aminomethylpyridine)-6-deoxycellulose. The resulting chemically-immobilized surface was characterized by elemental analysis, FTIR, 13C NMR and thermogravimetry. From 0.28% of nitrogen incorporated in the polysaccharide backbone, the amount of 0.10 ± 0.01 mmol of the proposed molecule was anchored per gram of the chemically modified cellulose. The available basic nitrogen centers attached to the covalent pendant chain bonded to the biopolymer skeleton were investigated for copper, cobalt, nickel and zinc adsorption from aqueous solution at room temperature. The newly synthesized biopolymer gave maximum sorption capacities of 0.100 ± 0.012, 0.093 ± 0.021, 0.074 ± 0.011 and 0.071 ± 0.019 mmol.g-1 for copper, cobalt, nickel and zinc cations, respectively, using the batchwise method, whose data was fitted to different sorption models, the best fit being obtained with the Langmuir model. The results suggested the use of this anchored biopolymer for cation removal from the environment.
  • Microstructure Evolution of Electron Beam Physical Vapour Deposited Ni-23.5Cr-2.66Co-1.44Al Superalloy Sheet During Annealing at 600 °C Regular Articles

    Mingwei, Li; Gang, Zeng; Yesheng, Zhong; Fei, He; Xiaodong, He

    Resumo em Inglês:

    Microstructure evolution of electron beam physical vapour deposited (EB-PVD) Ni‑23.5Cr‑2.66Co‑1.44Al superalloy sheet during annealing at 600 °C was investigated. The results showed that the as-deposited alloy was composed of only g phase. After annealing at 600 °C, the locations of diffraction peaks were still the same. The (220) diffraction peak of the deposition side increased with annealing time. The sheet on deposited side had a tendency toward forming (220) texture during post-annealing. No obvious texture was observed at as-deposited and annealed sheet at 600 °C in substrate side. The count and size of "voids" decreased with time. The size of grains increased obviously with annealing time. The ultimate tensile strength of EB-PVD Ni-23.5Cr-2.66Co-1.44Al alloy sheet increased from 641 MPa to 829 MPa after annealing at 600 °C for 30 hours.
  • Preparation of ZnO film on p-Si and I-V characteristics of p-Si/n-ZnO Regular Articles

    Mondal, Shampa; Kanta, Kalyani Prasad; Mitra, Partha

    Resumo em Inglês:

    Zinc oxide (ZnO) thin films were deposited on p-silicon (Si) substrate from ammonium zincate bath following a chemical dipping technique called SILAR. Films in the thickness range 0.5-4.5 µm could be prepared by varying the number of dipping for a fixed concentration (0.125 M) of zincate bath and fixed pH (11.00-11.10). Higher values of dipping produced nonadherent and poor quality films. Structural characterization by X-ray diffraction (XRD) indicates the formation of polycrystalline single phase ZnO with strong c-axis orientation. The structural characteristics of the films were found to be a sensitive function of film thickness. The degree of orientation was found to be a function of film thickness and a maximum was found at around 2.2 µm. Scanning electron microscopy (SEM) reveals the formation of sub-micrometer crystallites on silicon substrate. The coverage of crystallites (grains) on substrate surface increases with number of dipping. Dense film containing grains distributed throughout the surface is obtained at large thicknesses. The ohmic nature of silver (Ag) on ZnO and Aluminum (Al) on p-Si was confirmed by I-V measurements. I-V characteristic of the p-Si/n-ZnO heterojunction was studied and rectification was observed. The maximum value of forward to reverse current ratio was ~15 at 3.0 V.
  • Influence of the pH on Al2O3:CuO pigments prepared by a polymeric precursor method Regular Articles

    Marques, Carolina Hernandes; Mesquita, Alexandre; Araújo, Vinicius Dantas; Bernardi, Maria Inês Basso

    Resumo em Inglês:

    Copper (II) aluminate, CuAl2O4, which is known to be an inverse spinel contains a d9 metal ion and possesses interesting electronic, magnetic and catalytic properties and is used in industry as ceramic pigments, coatings and catalysts. Al2O3 with 10 mol% Cu (AlCu10) was synthesized by the polymeric precursor method varying the pH of the precursor solution with addition of ammonium hydroxide and ethylenediamine. It was shown that the pyrolysis of the polymeric chain occurs in higher temperatures for samples prepared in higher values of pH. The colorimetric coordinates exhibit dependence with pH and with the increase of annealing temperature. AlCu10 samples prepared with higher values of pH present lower values of colorimetric coordinates, indicating alterations in its color. The luminosity parameters L* increase also as a function of pH.
  • The use of PLDLA/PCL-T scaffold to repair osteochondral defects in vivo Regular Articles

    Esposito, Andrea Rodrigues; Bonadio, Angelo Carneiro; Pereira, Nathaly Oliveira; Cardoso, Túlio Pereira; Barbo, Maria Lourdes Peris; Duek, Eliana Aparecida de Rezende

    Resumo em Inglês:

    The physiological repair of osteochondral lesions requires the development of a scaffold that is compatible with the structure of the damaged tissue, cartilage and bone. The aim of this study was to evaluate the biological performance of a PLDLA/PCL-T (90/10) scaffold for repairing osteochondral defects in rabbits. Polymeric scaffolds containing saccharose (75% w/v) were obtained by solvent casting and then implanted in the medial knee condyles of 12 New Zealand rabbits after osteochondral damage with a trephine metallic drill (diameter: 3.3 mm) in both medial femoral condyles. Each rabbit received the same treatment, i.e., the polymeric scaffold was implanted on the right side while no material was implanted on the left side (control). Four and 12 weeks later histological examination revealed bone neoformation in the implant group, with the presence of hyaline cartilage and mesenchymal tissue. In contrast, the control group showed bone neoformation with necrosis, exacerbated superficial fibrosis, inflammation and cracks in the neoformed tissue. These findings indicate that the PLDLA/PCL-T scaffold was biocompatible and protected the condyles by stabilizing the lesion and allowing subchondral bone tissue and hyaline cartilage formation.
  • Investigating the rheological properties of crumb rubber modified bitumen and its correlation with temperature susceptibility Regular Articles

    Mashaan, Nuha Salim; Karim, Mohamed Rehan

    Resumo em Inglês:

    There is substantial evidence on the advantages of using crumb rubber in enhancing conventional bitumen properties, gaining environmental protection and boosting industrial-economical benefits. Thus, the use of this ingenious additive in bitumen modification through sustainable technology is highly advocated.The main objective of this research is to investigate the effects of different blending conditions (of time and temperature) and various crumb rubber contents on the properties of bitumen binders. Testing was conducted using the Dynamic shear rheometer (DSR) test and softening point test. The results showed that differing crumb rubber contents and blending temperature have significant effects on modified binder properties whereas the blending time showed an insignificant effect. Higher blending temperature and crumb rubber content were found to influence the interaction of bitumen-rubber blends and also increased the swelling rate of rubber particles, resulting in an increase in complex shear modulus (G*), storage modulus (G'), loss modulus (G") and softening point as well as a decrease in phase angle (δ). Thus, the modified bitumen became less susceptible to deformation after stress removals. The study also presented a considerable relationship between rheological parameters (G*, G', G' and δ) and softening point in terms of predicting physical-mechanical properties regardless of blending conditions. Thus, in terms of elasticity for the softening point data, the storage modulus and phase angle were found to be good indicators of binder elasticity. When softening point is made available, a prediction about binder ability to recover its original shape after stress removals can be done.
  • A kinetic and equilibrium study of zinc removal by Brazilian bentonite clay Regular Articles

    Araujo, Ana Lucia Pereira de; Gimenes, Marcelino Luiz; Barros, Maria Angelica Simões Dornellas de; Silva, Meuris Gurgel Carlos da

    Resumo em Inglês:

    This paper aimed to study the removal of zinc using bentonite clay from the Northeastern Brazil, as an adsorbent. A study of the clay subjected to thermal and chemical treatment was performed in order to evaluate the optimization of the adsorption capacity of this material. For the evaluation of the kinetic equilibrium of the process, experimental tests were carried out in a finite bath system. The maximum amount of metal adsorbed was 0.151 mEq of metal per gram of calcined clay and 0.257 mEq of metal per gram of sodium saturated clay. The kinetic models of pseudo-first order, pseudo-second order and intraparticle diffusion were fitted to experimental data, and the pseudo-second order model provided the best result. The Langmuir and Freundlich models were used for the adsorption equilibrium analysis, and the Langmuir model provided the best fit for sorption isotherms. The physicochemical characterization of clay involved X-ray diffraction, scanning electron microscopy, chemical analysis by energy-dispersive X-ray spectroscopy, helium pyconometry and thermogravimetric analysis. The modified clay has potential use for removing Zn2+ ions replacing more expensive adsorbents, since good adsorption properties will be also associated with great availability and low cost.
  • Influence of thermal treatment on porosity formation on carbon fiber from textile PAN Regular Articles

    Marcuzzo, Jossano Saldanha; Otani, Choyu; Polidoro, Heitor Aguiar; Otani, Satika

    Resumo em Inglês:

    Activated carbon fibers (ACFs) are known as an excellent adsorbent material due to their particular characteristics such as their high speed adsorption rate and for being easy to handle. The ACFs are commercially manufactured from carbon fibers (CF) which receive an additional activation process and can be produced from celluloses, phenolic resin, pitch and Polyacrylonitrile (PAN). In the present work, the oxidized 5.0 dtex textile PAN fiber was carbonized to CFs formation. During the carbonization process in different heating rates, the topographic features changes on fibers were monitored in order to determine the best carbonization condition for CFs production to be used as raw material for ACF. Different heating rates and maximum temperature of treatment were tested and the results indicated that it is possible to produce poorly activated carbon fiber, directly from oxidized textile PAN fiber, by one single step production process.
  • Control of chilling tendency in grey cast iron reuse Regular Articles

    Seidu, Saliu Ojo; Ogunniyi, Iyiola Olatunji

    Resumo em Inglês:

    In grey cast iron remelt and recycling, white iron can result in the cast product if careful control of the chilling tendency is not ensured. Many jobbing foundries are constrained in furnace types and available foundry additives that the operation always results in white irons. This study is towards ensuring grey iron is reproduced from cast iron scrap auto engine blocks, when using a diesel fired rotary furnace and a FeSi alloy for structural modification (inoculation). With varying addition rate of the FeSi alloy to the tapped molten metal, chill wedge tests were performed on two different wedge samples of type W (according to ASTM A367- wedge test) with cooling modulus of 0.45 cm (W3½) and 0.54 cm (W4). The carbon equivalents for the test casts were within hypoeutectic range (3.85 wt. (%) to 4.11 wt. (%)). In the W4 wedge sample, at 2.0 wt. (%) addition rate of the FeSi alloy, the relative clear chill was totally reduced to zero from 19.76%, while the relative mottled chill was brought down to 9.59% from 33.71%. The microstructure from the cast at this level of addition was free of carbidic phases; it shows randomly oriented graphite flakes evenly distributed in the iron matrix. Hardness assessment shows that increasing rate of FeSi addition results in decreasing hardness, with maximum effect at 2.0 wt. (%) addition. With equivalent aspect ratio (cooling modulus) in a target cast product, this addition rate for this FeSi alloy under this furnace condition will attain graphitized microstructure in the cast product.
  • Relation of transverse air permeability with physical properties in different compositions of sugarcane bagasse particleboards Regular Articles

    Bufalino, Lina; Mendes, Lourival Marin; Tonoli, Gustavo Henrique Denzin; Scatolino, Mário Vanoli; Silva, José Reinaldo Moreira da; Mori, Fábio Akira

    Resumo em Inglês:

    Studies concerning the production of particleboards with sugarcane bagasse as an alternative fibrous material have been carried out as an attempt to provide a sustainable and viable destination for this residue. This work aimed to evaluate the influence of several processing variables related to the microstructure of sugarcane bagasse particleboards (mat type, adhesive type and adhesive content) on their permeability and water sorption properties. Air permeability data was collected by the rotameter method. Superficial air permeability (kg), Darcian constant (k1) and non-Darcian constant (k2) were measured. kg was related to sorption behavior of the particleboards. 1-layer particleboards presented significantly higher kg values than the 3-layer particleboards. In general, adhesive type, position and content did not influence kg of particleboards. However, these processing variables influenced interactions between fluid and material and tortuosity of the porous media. Particleboards produced with urea-formaldehyde with high kg presented higher water absorption and thickness swelling after 24 hours. Such relations were not observed in particleboards produced with melamine-urea-formaldehyde.
  • Nanostructured MgH2 obtained by cold rolling combined with short-time high-energy ball milling Regular Articles

    Floriano, Ricardo; Leiva, Daniel Rodrigo; Deledda, Stefano; Hauback, Bjørn Christian; Botta, Walter José

    Resumo em Inglês:

    MgH2 was processed by short time high-energy ball milling (BM) and cold rolling (CR). A new alternative processing route (CR + BM) using the combination of CR followed by short time BM step was also applied. The effects on the final morphology, crystalline structure and H-sorption properties were evaluated. The CR + BM processing (compared to BM and CR process) resulted in an inhomogeneous particle size distribution and the biggest crystallite size of MgH2, showing that there is a clear dependence between the size/shape of the particles which compose the starting material and the efficiency of crystallite size reduction during the BM process. On the other hand, we observed that a short BM step improved the kinetic properties of the cold rolled material. It shows that the particle size reduction of MgH2 obtained by CR combined with the increase in specific surface area attained by short BM step could be key factors to allow the use of the CR + BM route.
  • Investigation about the copper adsorption on the chloropropylsilica gel surface modified with a nanostructured dendrimer DAB-Am-16: an analytical application for determination of copper in different samples Regular Articles

    Carmo, Devaney Ribeiro do; Paim, Leonardo Lataro

    Resumo em Inglês:

    The third generation (G-3) poly(propyleneimine)hexadecaamine dendrimer (DAB-Am-16) was grafted onto the chloropropylsilica gel surface (DPPIPS). The modified silica (DPPIPS) was characterized by Electronic (Uv-Vis), vibrational and Electron Paramagnetic Resonance (EPR), spectrocopies, surface area (331.07 m².g-1) and porosity analyses (pore diameter of 41.9 nm) and cyclic voltammetry technique. The copper adsorption studies were performed using a batchwise process and the DPPIPS showed adsorption capacities of 16.3, 47.8 and 659.5 mol.g-1 in aqueous, ethanol and acetone medium, respectively, with recoveries close to 100% after percolation with HCl 1.0 mol.L-1. The results suggest that the sorption of copper ions on DPPIPS occurs mainly by surface complexation and a Langmuir model allowed describing the sorption of the metal ions on DPPIPS. As an application of this chemically modified material, copper was determined in real samples of distilled spirits and fuel alcohol.
  • Polyvinyl pyrrolidone-assisted synthesis of crystalline manganese vanadate microtubes Regular Articles

    Pei, Li-Zhai; Pei, Yin-Qiang; Xie, Yi-Kang; Yuan, Chang-Zhou; Li, Dian-Kai; Zhang, Qian-Feng

    Resumo em Inglês:

    Manganese vanadate microtubes have been synthesized by a facile polyvinyl pyrrolidone-assisted hydrothermal route. X-ray diffraction pattern confirms that the microtubes are composed of monoclinic MnV2O6, tetragonal V2O5 and orthorhombic MnO2 phases. The outer diameter and inner diameter of the microtubes are about 300 nm-3 µm and 200 nm-1 µm, respectively. The tube wall thickness of the microtubes is about 50 nm-1 µm. The possible formation process of the manganese vanadate microtubes has been proposed as a polyvinyl pyrrolidone-assisted growth mechanism.
  • A novel vanadium n-propylamino phosphate catalyst: synthesis, characterization and applications Regular Articles

    Anumula, Rajini; Nookaraju, Muralasetti; Selvaraj, Kaliaperumal; Reddy, Ingala Ajit Kumar; Narayanan, Venkatathri

    Resumo em Inglês:

    A novel, lamellar type Vanadium n-propylamino phosphate catalyst is synthesized and characterized by using various physicochemical techniques such as Powder X-ray diffraction, Scanning electron microscopy/Energy dispersive X-ray analysis, Thermogravimetry/Differential thermal analysis, Fourier transform Infrared analysis, Electron spin resonance spectroscopy, Ultraviolet - Visible Diffuse reflectance spectroscopy, X-ray Photoelectron spectroscopy, 31P Magic angle spinning Nuclear Magnetic Resonance spectroscopy and Catalytic applications toward Octahydroquinazolinone synthesis. It is found that the n-propylamine is present as sandwich between Vanadyl phosphate layers. Most of the Vanadium is present as V4+ ions in tetrahedral co-ordination. Vanadium n-propylamino phosphate catalyses Octahydroquinazolinone synthesis more effeciently and the optimum conditions required for Octahydroquinazolinone synthesis are, Benzaldehyde (2 mmol), Dimedone (2 mmol), Urea (4 mmol), Methanol + Water (1:1, 5 mL) and Catalyst (0.05 g). A plausible mechanism is also proposed.
  • Effect of heat treatment on some mechanical properties of 7075 aluminium alloy Regular Articles

    Isadare, Adeyemi Dayo; Aremo, Bolaji; Adeoye, Mosobalaje Oyebamiji; Olawale, Oluyemi John; Shittu, Moshood Dehinde

    Resumo em Inglês:

    This paper reports the effects of annealing and age hardening heat treatments on the microstructural morphology and mechanical properties of 7075 Al alloy. The material was cast in the form of round cylindrical rods inside green sand mould from where some samples were rapidly cooled by early knockout and others gradually cooled to room temperature. From the samples that were gradually cooled some were annealed while others were age hardened. Both the as-cast in each category and heat treated samples were subjected to some mechanical tests and the morphology of the resulting microstructures were characterised by optical microscopy. From the results obtained there is formation of microsegregations of MgZn2 during gradual solidification which was not present during rapid cooling. It was also found out that age hardening and annealing heat treatment operation eliminated these microsegregations and improve mechanical properties of 7075 Al alloy. It is concluded that microsegregation can be eliminated by rapid solidification and appropriate heat treatment process.
  • The effect of gamma radiation on mechanical properties of biodegradable polymers poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Regular Articles

    Oliveira, Leticia Maria; Araujo, Patricia Lopes Barros; Araujo, Elmo Silvano

    Resumo em Inglês:

    Brazilian poly(3-hydroxybutyrate), P(3-HB), and its copolymer, poly (3-hydroxybutyrate-co-3-hydroxyvalerate), P(3-HB-co-3-HV) were irradiated with gamma radiation (60Co) at room temperature and in the presence of oxygen. The viscosity-average molar mass (Mv) was analyzed by viscometry using an Ostwald-type capillary viscometer. Both polymers showed a decrease in molar mass with the increase in dose, reflecting that random main chain scissions occurred. The value G (scissions/100 eV of energy transferred to the system) and the parameter α (scissions per original molecule) were also determined. Mechanical properties decrease with the increase in dose, revealing that P(3-HB) underwent significant changes, especially at doses higher than 50 kGy. Tensile at break and impact resistance properties were the most affected by radiation, while the elastic modulus remained virtually unaltered up to 100 kGy dose.
  • Influence of the microstructure on the electrochemical properties of Al-Cr-N coatings deposited by co-sputtering method from a Cr-Al binary target Regular Articles

    Quintero, Oscar Mauricio Sánchez; Chaparro, Willian Aperador; Ipaz, Leonid; Barco, Jaime Eduardo Sánchez; Beltrán, Francisco Espinoza; Zambrano, Gustavo

    Resumo em Inglês:

    In the present paper, aluminum chromium nitride (Al-Cr-N) films were deposited onto AISI H13 steel substrates by a reactive d.c magnetron co-sputtering system in an atmosphere of Ar/N2 (90/10) gas mixture from a binary target composed of chromium (99.95%) and aluminum (99.99%). Different powers (40, 50, 60, and 70 W) were applied to the target, in order to study the effect of this parameter and the sputtering yield of binary target, on the microstructure and the electrochemical properties of the Al-Cr-N coatings. The corrosion behavior in 3.5 wt. (%) NaCl solution was investigated by electrochemical corrosion tests (Tafel polarization curves and Electrochemical Impedance Spectroscopy (EIS)), and the chemical composition, microstructure and the absorption bands by means of Energy Dispersive X-ray Spectroscopy (EDX), X-ray diffractometry (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), respectively. EIS results showed that the Al-Cr-N coating deposited at 40 W, exhibited the lower porosity and the highest polarization resistance, and subsequently, when the power applied to the binary target increased, the corrosion rate and the porosity increase.
  • Efficacy of a combination of simvastatin and poly(DL-lactic-co-glycolic acid) in stimulating the regeneration of Bone Defects Regular Articles

    Assaf, Kyl; Duek, Eliana Aparecida de Rezende; Oliveira, Newton Maciel

    Resumo em Inglês:

    The proper healing of bone defects requires a bone graft or bone substitute and synthetic materials have been developed as alternatives to autografts and allografts. Poly(DL-lactic-co-glycolic acid) (PLGA) is a synthetic polymer widely used for bone healing because of its biocompatibility and biodegradability. PLGA scaffolds have also been used in drug delivery devices, such as in combination with simvastatin, to stimulate bone growth. In this work, we examined the usefulness of a combination of PLGA with simvastatin for treating bone defects. For this, two defects were created in rat calvaria and in half of the animals the right sides were filled with PLGA scaffolds while the other half received PLGA plus simvastatin; the left sides remained empty. The rats were killed for histological analysis after four and eight weeks. There was a significant increase in the amount of bone formation in the treated lesions, particularly those that received PLGA plus simvastatin.
  • In vitro degradation of Poly-L-co-D, L-lactic acid membranes Regular Articles

    Baraúna, Grazielle; Coraça-Huber, Débora Cristina; Duek, Eliana Aparecida de Rezende

    Resumo em Inglês:

    Poly-L-co-D.L-lactic (PLDLA) is a bioresorbable polymer whose properties have been studied for degradation sensitivity and its application in medicine. In this study, the potential of PLDLA membranes for temporary implantation was evaluated. PLDLA membranes were prepared with the solvent evaporation technique and characterized by differential scanning calorimetry, gel permeation chromatography, thermogravimetric analysis, scanning electron microscopy and traction tests. The glass transition temperature of the membranes was 59 ºC. Degradation started around 340 ºC during the second week showing pores and fissures on the broken surface. Evident degradation was observed after 16 weeks. Microscopy showed that before degradation PLDLA membranes presented no pores. PLDLA properties of resistance to traction and elasticity module were maintained until the 8th week, and after the 16th week there was a sharp reduction of these properties due to degradation. PLDLA membranes present excellent potential as temporary implantation given their degradation characteristics.
  • Electrochemical corrosion behavior of X52 and X60 steels in carbon dioxide containing saltwater solution Regular Articles

    Rihan, Rihan Omar

    Resumo em Inglês:

    X52 and X60 high strength low alloy (HSLA) steels are widely used in the construction of petroleum pipelines. This paper discusses the corrosion resistance of X52 and X60 steels in CO2 containing saltwater at pH 4.4 and 50 ºC. A circulating flow loop system inside an autoclave was used for conducting the experimental work. The rotating impeller speed was 2000 rpm. The corrosion rate was monitored using in situ electrochemical methods such as potentiodynamic sweep, linear polarization resistance, and electrochemical impedance spectroscopy (EIS) methods. Results indicated that the corrosion rate of X60 steel is relatively higher than that of X52 steel.
  • Facile synthesis of inverse spinel NiFe2O4 nanocrystals and their superparamagnetic properties Regular Articles

    Tan, Jie; Zhang, Wei; Xia, Ai-Lin

    Resumo em Inglês:

    Spinel NiFe2O4 nanocrystals have been obtained by means of a novel composite-hydroxide-salt-mediated approach, which is based on a reaction between metallic salt and metallic oxide in the solution of composite-hydroxide-salt eutectic at ~225 ºC and normal atmosphere without any organic dispersant or capping agent. The obtained products are characterized by an X-ray diffraction (XRD), a transmission electron microscopy (TEM) and an alternating gradient magnetometer (AGM). The formation process of NiFe2O4 nanosheet is proposed to begin with a ‘‘dissolution-recrystallization’’ which is followed by an ‘‘Ostwald ripening’’ mechanism. The NiFe2O4 nano-octahedrons can be obtained through adjusting the reaction water content in the hydroxide melts at constant temperature. At 300 K, magnetic hysteresis loops at an applied field of 15 kOe show zero coercivity, indicating the superparamagnetic behavior of the as-prepared NiFe2O4 nanocrystals.
  • Production of struvite from beverage waste as phosphorus source Regular Articles

    Foletto, Edson Luiz; Santos, Wilson Roberto Barreto dos; Mazutti, Marcio Antonio; Jahn, Sérgio Luiz; Gündel, André

    Resumo em Inglês:

    In this work was investigated the influence of pH on the synthesis of struvite using cola beverage waste as source of phosphorus. The process was operated in a batch reactor. The reaction time was 20 minutes, and the chemicals MgCl2.6H2O and NH4Cl were used in the experiment, with a molar ratio of Mg+2:NH4+:PO4(3-) = 1:1:1. The products were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), surface area (BET), thermogravimetric analysis (TGA) and infra-red (IR). From the results was verified the formation of a crystalline phase at pH 9.5, with a surface area of 6.59 m² g-1 and a particle size of about 0.25 µm.
  • The effect of different pH levels on conventional vs. super-force chain elastics Regular Articles

    Santos, Rogério Lacerda dos; Pithon, Matheus Melo; Romanos, Maria Teresa Villela

    Resumo em Inglês:

    The aim of this in vitro study was to evaluate the influence of pH levels on force decay and cytotoxicity of elastic chains submersed in artificial saliva. The samples were divided into two groups: Group SF (Polyurethane elastic, super force) and Group C (Polyurethane elastic, conventional), which were stretched to 100% of their initial length. They were kept in artificial saliva solutions at pH levels of 5.0, 6.0 and 7.5 for time intervals of 10 seconds, 1, 14 and 28 days. Cytotoxicity assay was performed in cells (L929-fibroblast), subjected to "dye-uptake" test. ANOVA, Sidak method and Tukey’s test were used. The pH did not interfere directly in force decay results of tested elastics. Cytotoxicity test showed that Group SF presented similar cell viability when compared with Group C. There was gradual reduction in cell viability from beginning to 28th day. The pH had no significant influence on force decay and cytotoxicity. Time had more influence and contributed to variability in results.
  • Preliminary viability studies of fibroblastic cells cultured on microcrystalline and nanocrystalline diamonds produced by chemical vapour deposition method Regular Articles

    Rodrigues, Ana Amélia; Baranauskas, Vitor; Ceragioli, Helder Jose; Peterlevitz, Alfredo Carlos; Santos Junior, Arnaldo Rodrigues dos; Belangero, William Dias

    Resumo em Inglês:

    Implant materials used in orthopedics surgery have demonstrated some disadvantages, such as metallic corrosion processes, generation of wear particles, inflammation reactions and bone reabsorption in the implant region. The diamond produced through hot-filament chemical vapour deposition method is a new potential biomedical material due to its chemical inertness, extreme hardness and low coefficient of friction. In the present study we analysis two samples: the microcrystalline diamond and the nanocrystalline diamond. The aim of this study was to evaluate the surface properties of the diamond samples by scanning electron microscopy, Raman spectroscopy and atomic force microscopy. Cell viability and morphology were assessed using thiazolyl blue tetrazolium bromide, cytochemical assay and scanning electron microscopy, respectively. The results revealed that the two samples did not interfere in the cell viability, however the proliferation of fibroblasts cells observed was comparatively higher with the nanocrystalline diamond.
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