Navegando por Palavras-chave "Microstructure"
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- ItemSomente MetadadadosCorrelation between microstructure and bioequivalence in Anti-HIV Drug Efavirenz(Elsevier B.V., 2015-04-01) Fandaruff, Cinira; Segatto Silva, Marcos Antonio; Galindo Bedor, Danilo Cesar; Santana, Davi Pereira de; Antunes Rocha, Helvecio Vinicius; Rebuffi, Luca; Azanza Ricardo, Cristy Leonor; Scardi, Paolo; Cuffini, Silvia Lucia [UNIFESP]; Universidade Federal de Santa Catarina (UFSC); Universidade Federal de Pernambuco (UFPE); Inst Tecnol Farmacos Farmanguinhos FIOCRUZ; Univ Trento; Elettra Sincrotrone Trieste; Universidade Federal de São Paulo (UNIFESP)Polymorphism and particle size distribution can impact the dissolution behaviour and, as a consequence, bioavailability and bioequivalence of poorly soluble drugs, such as Efavirenz (EFV). Nevertheless, these characteristics do not explain some failures occurring in in vitro assays and in in vivo studies. EFV belongs to Class II and the High Activity Antiretroviral Therapy (HAART) is considered the best choice in the treatment of adults and children. EFV is a drug that needs bioequivalence studies for generic compounds. in this work, six raw materials were analyzed and two of them were utilized with human volunteers (in vivo assays or bioequivalence). All the routine pharmaceutical controls of raw materials were approved; however, the reasons for the failure of the bioequivalence assay could not be explained with current knowledge. the aim of this work was to study microstructure, a solid-state property of current interest in the pharmaceutical area, in order to find an explanation for the dissolution and bioequivalence behaviour. the microstructure of EFV raw materials was studied by Whole Powder Pattern Modelling (WPPM) of X-ray powder diffraction data. Results for different EFV batches showed the biorelevance of the crystalline domain size, and a clear correlation with in vitro (dissolution tests) and in vivo assays (bioequivalence). (C) 2015 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosDirectionally solidified dilute Zn-Mg alloys: Correlation between microstructure and corrosion properties(Elsevier Science Sa, 2017) Vida, Talita Almeida; Conde, Ana; Freitas, Emmanuelle Sá; Arenas, Maria Angeles; Cheung, Noe; Brito, Crystopher Cardoso de [UNIFESP]; Damborenea, Juan José de; Garcia, Amauri; Universidade Federal de São Paulo (UNIFESP)ZinceMagnesium (Zn-Mg) alloys have been addressed as potential biodegradable biomaterials. These alloys enable to overcome the main drawbacks of Mg, its high corrosion rate and hydrogen evolution. Moreover, homogeneous corrosion degradation is also an interesting issue to ensure the success of load-bearing biodegradable implants. In this work, two directionally solidified dilute alloys, Zn-0.3wt-% Mg and Zn-0.5wt-%Mg were studied. Both alloys having different microstructural morphologies (cellular and dendritic arrays) depending of the distance to the cooling bottom were evaluated to correlate their microstructural features with corrosion properties. Kinetics and corrosion mechanism have been evaluated by means of DC and AC electrochemical techniques in low chloride containing solution, 0.06 M NaCl. Coarser microstructures are shown to promote higher corrosion rate. Like Zn the corrosion mechanism occurs throughout a multistep dissolution process involving the formation of intermediate monovalent Zn-I, and soluble zinc hydroxychloride compounds resulting of the reaction of zincate ions with chloride ions. (C) 2017 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosEstudo do efeito do níquel na microestrutura, na dureza e na corrosão de ligas de alta entropia AlCoCrFeNiX(Universidade Federal de São Paulo (UNIFESP), 2020-02-17) Zemanate, Ana Maria [UNIFESP]; Cardoso, Kátia Regina [UNIFESP]; Universidade Federal de São PauloHigh entropy alloys (HEAs), a new concept in metal alloys have been developed with the aim of producing new materials with unique properties for advanced applications. HEAs are defined as metallic alloys composed of multiple main elements in equimolar or quasi-equimolar atomic proportions, and which form simple solid solutions body-centered cubic (BCC), fase-centered cubic (FCC) or hexagonal close-pack (HCP), due to their high mixing entropies. In this work, three high entropy alloys were obtained: AlCoCrFeNi, AlCoCrFeNi1.5 and AlCoCrFeNi2, by electric arc melting under argon protection, to understand the effects of nickel (Ni) variation on the microstructure, and on the hardness and corrosion resistance. The composition of the alloys were defined based on the calculation of the empirical parameters that defined the HEAs and in computer simulations with the thermo-calc software, which it allowed predicting the equilibrium phase in the alloys depending on the temperature and the variation in the composition. The HEAs were characterized in three conditions: in the as-cast condition, after remelting and after heating treatment at 1125 °C during 5h. The HEAs microstructures were characterized by x-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The three alloys have a much-differentiated microstructures; the equimolar alloy has a dendritic microstructure with fine precipitates, while the interdendritic region has a tissue-like structure with thicker precipitates. The AlCoCrFeNi1.5 alloy has a structure in the form of needles of the Widmanstätten type that grows from the grain boundaries to the center indicating the growth of the CFC phase, while the AlCoCrFeNi2 alloy has a microstructure of the eutectic type that alternates the CFC/B2 phases. With the heat treatment at 1125 °C, the microstructure of the alloys, despite of being essentially they were the same coarser and growth of grains and precipitates were observed. Differential scanning calorimetry (DSC) tests made it possible to evaluate the transition temperature of the phases especially those related to the transformation from the (BCC) phase to the (CFC) phase. The hardness of the alloys were determined, indicating that the increase in the nickel (Ni) content led to a reduction in the hardness from 461 HV in the equimolar alloy to 303 HV in the AlCoCrFeNi2 alloy due to the increased in the fraction of the CFC phase with the nickel content. The remelting of the alloys were followed by casting in a refrigerated mold, which resulted in a higher cooling rate with consequent microstructural refining and increased hardness; the equimolar alloy, for example, it reached a hardness of 520 HV in this condition. With the homogenization heat treatment, the hardness values decreased, which varied from 400HV for the equimolar alloy to 270 HV for the alloy with the highest Ni content. The corrosion resistance of the alloys were evaluated by using the potentiodynamic polarization technique in a 3.5% NaCl solution. In general, the three alloys presented corrosion potentials (Ecorr) in order to -0.31V and low corrosion current densities (Icorr) with the lowest values obtained for the alloy with the highest content of Ni, AlCoCrFeNi2, 41.5 mA/cm2 in the as-cast condition and 55.7 mA/cm2 after the homogenization heat treatment. Preferential corrosion of the B2 phase was observed due to the lower Cr content in this phase.
- ItemSomente MetadadadosHigh Strength AA7050 Al alloy processed by ECAP: Microstructure and mechanical properties(Elsevier B.V., 2011-07-15) Cardoso, K. R. [UNIFESP]; Travessa, D. N. [UNIFESP]; Botta, W. J.; Jorge, A. M.; Universidade Federal de São Paulo (UNIFESP); Univ Vale do Paraiba; Universidade Federal de São Carlos (UFSCar)Commercial AA7050 aluminium alloy in the solution heat-treated condition was processed by ECAP through routes A and B-C. Samples were processed in both room temperature and 150 degrees C, with 1, 3, and 6 passes. the resulting microstructure was evaluated by optical microscopy (OM) and transmission electron microscopy (TEM). Only one pass was possible at room temperature due to the low ductility of the alloy under this condition. in all cases, the microstructure was refined by the formation of deformation bands, with dislocation cells and subgrains inside these bands. the increase of the ECAP temperature led to the formation of more defined subgrain boundaries and intense precipitation of spherical-like particles, identified as eta' and eta phases. After the first pass, an increase in the hardness was observed, when compared with the initial condition. After 3 passes the hardness reached a maximum value, higher than the values typically observed for this alloy in the overaged condition. the samples processed by route B-C evolved to a more refined microstructure. ECAP also resulted in significant strength improvement, compared to the alloy in the commercial overaged condition. (C) 2011 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosImpacto Das Condições De Cristalização Sobre Polimorfismo, Morfologia, Microestrutura Do Efavirenz(Universidade Federal de São Paulo (UNIFESP), 2017-02-21) Guimaraes, Renata [UNIFESP]; Cuffini, Silvia Lucia [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Efavirenz (EFV) is an antiretroviral used for the treatment of HIV infection, which causes Acquired Immunodeficiency Syndrome (AIDS). In 2013 in Brazil, it was estimated that approximately 800,000 people living with HIV (Human Immunodeficiency Virus). EFV shows proper characteristics that make it an antiretroviral most commonly used against the virus as high power viral suppression, proven long-term efficacy and low risk of adverse effects. However, its low solubility is a constraining factor in the pharmaceutical industry. There are different approaches to improve the properties of the solid crystalline forms of poorly soluble drugs. Crystallization is one of the strategies that impacts on these properties. However, there are no studies on the impact of crystallization conditions on the polymorphism, morphology and crystalline domain of EFV solid forms and their correlation with dissolution properties. This project prepared different EFV samples, controlling the polymorphism and morphology through the crystallization conditions (type of solvent, nucleation temperature and cooling rate). The samples obtained under different conditions were characterized for polymorphism, morphology, microstructure and dissolution. It was observed that the temperature has greater influence on the obtained polymorph. Polymorph I can only be obtained at high temperatures. Mixtures are favored at intermediate temperatures and agitation hinders the formation of pure polymorphs. The agitation also impacts the microstructure, but is more intrinsically bound to the type of polymorph, so that polymorph II is more crystalline than the I. Likewise, the type of polymorph also has great influence on the final morphology, with each polymorph has a characteristic morphology. However, high agitation also impacts the final external shape of the crystal.
- ItemSomente MetadadadosMagnetic and structural studies on nanostructured Gd/Cr multilayer films(Elsevier B.V., 2013-10-31) Gadioli, G. Z.; Rouxinol, F. P.; Gelamo, R. V.; Cardoso, L. P.; Gama, S. [UNIFESP]; Moraes, M. A. Bica de; Universidade Estadual de Campinas (UNICAMP); Inst Ciencias Tecnol & Exatas; Universidade Federal de São Paulo (UNIFESP)Investigations of magnetic phases, transition temperatures and coercivity were performed inmultilayered Gd/Cr films as a function of the crystalline state and morphology of the Gd layers. the films were deposited by dc magnetron sputtering at three substrate temperatures, T-s, (room temperature, 300 and 500 degrees C). the Gd and Cr thicknesses were of 10 and 30 nm, respectively. Two series of three films were prepared. in one of the series, the films had a single Gd/Cr bilayer; in the other, 15 bilayers. the discontinuous or granular nature of the Gd layers was revealed by scanning electron microscopy Grazing incidence angle x-ray diffraction was used to investigate the crystalline state of the Gd and Cr layers. These techniques revealed that grain average size and crystalline order increase with increasing T-s. From dc magnetic measurements, the co-existence of ferromagnetic and superferromagnetic phases in the Gd layers was observed, and Curie transition temperatures, T-C, were determined. High coercive fields at low temperature (2 K) were measured in hysteresis cycles. Field-cooled and zero field-cooled magnetizations as functions of temperature curves exhibited, for some of the samples, a low temperature peak suggesting a freezing transition to a cluster glass state. This was confirmed by complementary ac-susceptibility measurements carried out as a function of temperature, for various frequencies of the ac field. Some results of this work - the decline in TC for decreasing Gd grain size, the high coercive field and its dependence on particle size, and the behavior of the magnetization at low temperatures for the sample deposited at room temperature - are discussed in terms of finite size and surface effects in nanosized particles. Published by Elsevier B.V.
- ItemSomente MetadadadosMicrostructure characterization of a directionally solidified Mg-12wt.%Zn alloy: Equiaxed dendrites, eutectic mixture and type/morphology of intermetallics(Elsevier Science Sa, 2018) Verissimo, Nathalia Carolina; Brito, Crystopher Cardoso de [UNIFESP]; Afonso, Conrado Ramos Moreira; Spinelli, José Eduardo; Cheung, Noe; Garcia, Amauri; Universidade Federal de São Paulo (UNIFESP)Over the last years, magnesium and its alloys have deserved special attention due to their good mechanical properties and promising biomedical applications. In the present investigation the Mg-12 wt.% Zn alloy has been directionally solidified (DS) under an extensive range of cooling rates. Based on the scarceness of characterization works related to both the morphology of the eutectic mixture and the development of equilibrium and non-equilibrium intermetallic particles (IMCs) in Mg-Zn alloys, a number of analyses are performed emphasizing and discussing such aspects. Rod and lamellar eutectic spacings are experimentally correlated with the growth rate and the cooling rate. The volume fraction of rod-like eutectic is shown to increase with the decrease in cooling rate during solidification. The characterization on the DS Mg-12 wt.%Zn samples is carried out using X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopies, which allowed the identification of two different non equilibrium IMCs, MgZn2 and Mg4Zn7, which are distributed as nanoparticles throughout the alpha-Mg matrix. The Mg-Zn eutectic morphologies (lamellar and rod-like) are found to be constituted by alpha-Mg/Mg21Zn25 phases, the latter being formed by the decomposition of the eutectic IMC Mg51Zn20 through a eutectoid reaction. (C) 2017 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosSpark plasma sintering of doped (k-x na1-x)nbo3 piezoceramics(Wiley-Blackwell, 2016) Souza, C. A. [UNIFESP]; Eiras, J. A.; Lente, M. H. [UNIFESP]In this work, pure and doped (K-0.48 Na-0.52)NbO3 ceramics (KNN) were prepared by using Spark Plasma Sintering (SPS) method. In order to investigate the influence of doping elements on the microstructural, structural and dielectric properties of KNN, Cu2+ and Li1+ doping elements were added. The results revealed the viability to produce highly dense pure and doped KNN ceramics with good crystallization in the perovskite phase. Densities around 96% and 99% of the theoretical one were reached. In relation to pure KNN, it was verified that Cu2+ addition reduced significantly the sintering temperature, revealing a better microstructure with a more homogeneous grain size distribution and structure with well-defined splitting of the XRD peaks. In comparison to pure KNN, the addition of both doping elements decreased both the dielectric constant the dielectric losses as well.
- ItemSomente MetadadadosStructural and surface functionality changes in reticulated vitreous carbon produced from poly(furfuryl alcohol) with sodium hydroxide additions(Elsevier Science Bv, 2017) Oishi, Silvia Sizuka; Botelho, Edson Cocchieri; Rezende, Mirabel Cerqueira [UNIFESP]; Ferreira, Neidenei GomesThe use of sodium hydroxide to neutralize the acid catalyst increases the storage life of poly(furfuryl alcohol) (PFA) resin avoiding its continuous polymerization. In this work, a concentrated sodium hydroxide solution (NaOH) was added directly to the PFA resin in order to minimize the production of wastes generated when PFA is washed with diluted basic solution. Thus, different amounts of this concentrated basic solution were added to the resin up to reaching pH values of around 3, 5, 7, and 9. From these four types of modified PFA two sample sets of reticulated vitreous carbon (RVC) were processed and heat treated at two different temperatures (1000 and 1700 degrees C). A correlation among cross-link density of PFA and RVC morphology, structural ordering and surface functionalities was systematically studied using Fourier transform infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, Xray diffraction, and X-ray photoelectron spectroscopy techniques. The PFA neutralization (pH 7) led to its higher polymerization degree, promoting a crystallinity decrease on RVC treated at 1000 degrees C as well as its highest percentages of carboxylic groups on surface. A NaOH excess (pH 9) substantially increased the RVC oxygen content, but its crystallinity remained similar to those for samples from pH 3 and 5 treated at 1000 degrees C, probably due to the reduced presence of carboxylic group and the lower polymerization degree of its cured resin. Samples with pH 3 and 5 heat treated at 1000 and 1700. degrees C can be considered the most ordered which indicated that small quantities of NaOH may be advantageous to minimize continuous polymerization of PFA resin increasing its storage life and improving RVC microstructure. (C) 2016 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosUpward and downward unsteady-state directional solidification of a hypoeutectic Al-3wt.% Mg alloy(Elsevier Espana S I, 2017) Brito, Crystopher Cardoso de [UNIFESP]; Bertelli, Felipe; Castanho, Manuel Antonio Pires; Goulart, Pedro Roberto; Cheung, Noe; Spinelli, José Eduardo; Garcia, AmauriSolidification thermal parameters, such as growth rate, cooling rate and dendrite arm spacing (lambda), have been measured in a hypoeutectic Al-Mg alloy directionally solidified under upward and downward transient heat flow conditions. The experimental setup used in this work consists of a water-cooled mould with heat being extracted from the bottom or the top, promoting upward and downward directional solidification, respectively. It is shown that the dendritic arm spacing are not significantly affected by interdendritic convection for both solidification configurations and single growth laws are proposed for both cases. The Bouchard-Kirkaldy model is shown to overestimate the experimental primary dendritic arm spacing, despite fitting properly the secondary dendrite arm spacing. (C) 2017 Portuguese Society of Materials (SPM). Published by Elsevier Espana, S.L.U. All rights reserved.