RENE RAMOS DE OLIVEIRA

RENE RAMOS DE OLIVEIRA

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Cement-based composites incorporating pseudoboehmite nanomaterials
2023 - PACHECO, CAROLINE V.; PERES, RENATO M.; CARRIERI, GABRIELA; MINUSSI, GIULIA R.; ZAMBRANA, GUIDO P.; KANG, JESSICA S.H.; OLIVEIRA, RENE R. de; LIMA, NELSON B. de; BERNUSSI, AYRTON; WARZYWODA, JULIUSZ; MUNHOZ, ANTONIO H.
Pseudoboehmite is a hydrated aluminum oxyhydroxide obtained from inorganic precursors by the sol-gel process. It is used as a precursor to alumina and as a reinforcement in obtaining nanocomposites. Cement-reinforced composites with this nanomaterial were obtained in concrete and mortar. Pseudoboehmite with sodium polyacrylate was used to promote a deflocculation of pseudoboehmite particles, which tend to agglomerate in the material. The obtained material was added to the concrete to improve its workability and strength. The new concrete was characterized by slump tests and mechanical tests. Our results revealed that the incorporation of pseudoboehmite with sodium polyacrylate significantly increased the compressive strength and improved the workability of the concrete. Multiple experiments evaluated compressive strength, ultrasound speed, and nanomaterial characterization. Using the Weibull method in mortars, we verified that the pseudoboehmite brought visible benefits as the characteristic stress increased by 17.5%. This increase was observed with the addition of 3% by weight of pseudoboehmite.
Synthesis of pseudoboehmite nanoparticles and use in simvastatin drug delivery
2022 - VICENTE, MARCOS A.A.H.; SILVA, LEONARDO G.A.; LIMA, NELSON B.; OLIVEIRA, RENE R.; BERNUSSI, AYRTON; SARMENTO, BRUNO; BARBOSA, ISABELLA T.F.; MUNHOZ JUNIOR, ANTONIO H.
Pseudoboehmite is an aluminium compound with a structure similar to that of boehmite. The unit cell of the pseudoboehmite is slightly larger than that of the boehmite because of the greater incorporation of water in the same structure [1]. It has particles of nanometric dimensions and can be synthesized with extremely high purity. Several papers published in the literature show the potential of using this material in the controlled release of drugs, including cancer treatment [2,3]. Using drugs in complexes incorporated into polymer matrices and ceramic gels can lead to adequate control of gastrointestinal absorption when administered orally. Consequently, there is the possibility of promoting a gradual action through the progressive release of the drug, thus increasing its efficiency and reducing dose and toxicity. Previous studies have shown that pseudoboehmite is non-toxic and can be used for drug delivery. During the tests to determine the toxicity of this material, it was observed that the blood glucose content was reduced in mice that took pseudoboehmite by gavage. Since pseudoboehmite is obtained via low-cost inorganic synthesis, different physicochemical characteristics can be incorporated into this high purity medium. The formed structure was evaluated as a drug delivery system to establish a profile of the influence of the physicochemical properties of a molecule in the process of interaction with pseudoboehmite, a drug with recognized pharmacological activity, simvastatin (IUPAC name (1S,3R,7S,8S,8aR)-8-{2-[(2R,4R)-4-hydroxy-6-oxooxan-2-yl]ethyl}-3,7-dimethyl-1,2,3,7,8,8a-hexahydronaphthalen-1-yl 2,2-dimethylbutanoate) was choose. It also emphasizes the importance of pseudoboehmite as a drug carrier, serving as a precursor to new therapeutic systems. The synthesis of pseudoboehmite from ammonium hydroxide and aluminium nitrate was optimized to release simvastatin in vitro. After absorption and hydrolysis in the liver to form the active β-hydroxy acid metabolite, simvastatin acts as a potent reversible, competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, an early and rate-limiting enzyme in the biosynthesis of cholesterol.
Pseudoboehmite as a drug delivery system for acyclovir
2021 - PERES, RENATO M.; SOUSA, JESSICA M.L.; OLIVEIRA, MARIANA O. de; ROSSI, MAURA V.; OLIVEIRA, RENE R. de; LIMA, NELSON B. de; BERNUSSI, AYRTON; WARZYWODA, JULIUSZ; SARMENTO, BRUNO; MUNHOZ JUNIOR, ANTONIO H.
Herpes simplex virus is among the most prevalent sexually transmitted infections. Acyclovir is a potent, selective inhibitor of herpes viruses and it is indicated for the treatment and management of recurrent cold sores on the lips and face, genital herpes, among other diseases. The problem of the oral bioavailability of acyclovir is limited because of the low permeability across the gastrointestinal membrane. The use of nanoparticles of pseudoboehmite as a drug delivery system in vitro assays is a promising approach to further the permeability of acyclovir release. Here we report the synthesis of high purity pseudoboehmite from aluminium nitrate and ammonium hydroxide containing nanoparticles, using the sol–gel method, as a drug delivery system to improve the systemic bioavailability of acyclovir. The presence of pseudoboehmite nanoparticles were verified by infrared spectroscopy, transmission electron microscopy, and X-ray diffraction techniques. In vivo tests were performed with Wistar rats to compare the release of acyclovir, with and without the addition of pseudoboehmite. The administration of acyclovir with the addition of pseudoboehmite increased the drug content by 4.6 times in the plasma of Wistar rats after 4 h administration. We determined that the toxicity of pseudoboehmite is low up to 10 mg/mL, in gel and the dried pseudoboehmite nanoparticles.
The occurrence of a peripheral coarse grain zone (PCGZ) in extruded bars of AA 7108
2021 - SOUZA, SAUL H. de; PLAUT, RONALD L.; LIMA, NELSON B. de; OLIVEIRA, RENE R. de; PADILHA, ANGELO F.
Industrial-scale extruded profiles of AA 7108 with a rectangular section (25.60 mm x 15.95 mm) were used in this investigation. Some complementary microstructural analysis techniques, such as polarized light microscopy, EBSD (Electron Backscatter Diffraction) and X-ray diffraction were used to characterize the microstructure, focusing on the PCG zone. It was observed that the extruded profiles presented a totally recrystallized microstructure and a 300 μm layer of peripheral coarse grains. Additionally, the results showed that the PCGZ predominant grain orientation {311} <110> differs from the texture below the PCGZ (Goss and Cube components).
Synthesis of pseudoboehmite
2020 - SILVA, MATHEUS F.B. da; PACHECO, CAROLINE V.; PERES, RENATO M.; MIRANDA, LEILA F. de; LIMA, NELSON B. de; OLIVEIRA, RENE R. de; BERNUSSI, AYRTON; MUNHOZ JUNIOR, ANTONIO H.
Pseudoboehmite (AlOOH.xH2O) is one of the precursors of alumina. Its calcination produces different phases of alumina and at 1200º C the most stable phase, α-alumina, is formed. The synthesis of pseudoboehmite by the sol-gel process results in a product with high purity, high specific surface area, and high reproducibility. The aging of the pseudoboehmite at temperatures above room temperature results in pseudoboehmites with distinct properties. In this work we report the synthesis of pseudoboehmite by the sol-gel process, using aluminum nitrate and aluminum chloride as precursors, and investigate the effect of acetate ion on crystallinity, adsorption capacity, particle morphology, thermal properties and specific surface area. The X-ray diffraction data of the synthesized pseudoboehmites in the presence of the acetate ion revealed high quality nanoparticles.
The effect of plasma nitriding on the fatigue behavior of the Ti-6Al-4V alloy
2019 - CASTRO, MICHELE C.B. de; COUTO, ANTONIO A.; ALMEIDA, GISELE F.C.; MASSI, MARCOS; LIMA, NELSON B. de; SILVA SOBRINHO, ARGEMIRO da; CASTAGNET, MARIANO; XAVIER, GLEICY L.; OLIVEIRA, RENE R.
The Ti-6Al-4V alloy is widely used in the manufacture of components that must have low density and high corrosion resistance and fatigue strength. The fatigue strength can be improved by surface modification. The aim of this study was to determine the influence of plasma nitriding on the fatigue behavior of a Ti-6Al-4V alloy with a lamellar microstructure (Widmanstätten type). Nitriding was executed at 720 C for 4 h in an atmosphere with N2, Ar, and H2. Microstructure characterization of the samples was carried out by X-ray diffraction analysis, optical microscopy, and scanning electron microscopy. The average roughness of the specimens was determined, and fatigue tests were executed in a bending–rotating machine with reverse tension cycles (R = 􀀀1). X-ray diffraction analysis of the nitrided alloy revealed the following matrix phases: , , "-Ti2N, and -TiN. A nitrogen diffusion layer was formed between the substrate and the titanium nitrides. Plasma nitriding resulted in an increase in low-cycle fatigue strength, whereas at high cycles of 200 MPa, both conditions exhibited similar behaviors. The fracture surface of the fatigue-tested specimens clearly revealed the lamellar microstructure. The fracture mechanism in the non-nitrided specimens appears to be due to cracking at the interface of the and phases of the lamellar microstructure.
Evaluation of 3YTZP films deposited by electrophoretic deposition on titanium and irradiated with Nd:YAG laser
2018 - XAVIER, G.L.; USSUI, V.; OLIVEIRA, R.R.; ROSSI, W. de; LIMA, N.B.; CASTRO, M.C.B. de
Titanium is widely used in chemical, power generation, aerospace and biomedical industries because of its good mechanical properties, corrosion resistance and good biocompatibility. However, when is used, for example, in steam turbines is necessary increase the corrosion resistance at high temperature, or when is used in dentistry, when the metallic gray color compromise the aesthetics rehab, it becomes interesting to coat the titanium with a ceramic layers, and 3YTZP (Yttria-stabilized tetragonal zirconia) is suitable for this application, because it has good mechanical properties, good resistance to thermal cycles and good biocompatibility. The electrophoretic deposition is a suitable technique to obtain theses coatings. After deposition, is necessary achieve out the sintering of coating, but the sintering temperature of zirconia is about 1500 °C, and submit metal/ceramic joint to this temperature, cam bring on the degradation of metal. The solution to these problems is performing the sintering using a laser radiation. In this work it was studied the laser irradiation of zirconia ceramic coating deposited on titanium by electrophoretic deposition. Three series of irradiation tests were carried out using Nd:YAG (wavelength 1.06 μm) pulsed laser, energy of 0.5 J, pulse duration of 10 ms and rate of 10 Hz. During the tests, it was studied the influence of fluency, scanning speed and repetition of laser incidence. The repetition covered a range of 1 to 27 times. Prepared samples were characterized by optical and scanning electron microscopy, X-ray diffraction and scratch microindentation. The Xray results showed presence of tetragonal and monoclinic phases in the irradiated coatings. The optical and SEM results showed that densification increases with the increasing of number of laser incidence repetition and the scratch results showed that the irradiated samples presented more scratch resistance than non-irradiated samples.
Influência da nitretação por plasma sobre as propriedades de fadiga da liga TI-6AL-4V
2018 - CASTRO, M.C.B. de; COUTO, A.A.; ALMEIDA, G.F.C.; LIMA, N.B.; CASTAGNET, M.; OLIVEIRA, R.R.
As falhas por fadiga na liga Ti-6Al-4V ocorrem pela aplicação de tensões flutuantes, onde as tensões responsáveis pela falhasendo estas são menores do que a tensão de escoamento da liga. , caracterizando essas falhas como catastróficas e sem aviso prévio. A fadiga é responsável por pelo menos 90% das falhas por causas mecânicas, cCom o objetivo de aumentar a resistência a fadiga, foi realizada ao o tratamento termoquímico de nitretação por plasma. A nitretação por plasma é caracterizada pela formaçãoforma de uma camada superficial de nitretos na superficie da liga constituída (pelas fases δ-TiN e Ɛ-Ti2N). A formação dessas fases além de aumentar a sua dureza superficial, cria uma alta tensão superficial de compressão, fazendo com que as tensões trativas necessárias para ocorrer a formação de trincas sejam superiores. Testes de fadiga do tipo flexo rotativas foram realizados nos corpos de prova nitretados e não nitretados, a fim de se comparar a eficiência do tratamento termoquímico. O ensaio de fadiga foi realizado a uma frequência de 50 hz, e razão de carregamento R=-1, variando tensões de 610 a 203 MPa. Foram contados o número de ciclos necessários para as fraturas dos corpos de prova, e os resultados foram plotados em uma curva S-N. Após a fratura dos corpos de prova, suasAs superfícies de fratura foram analisadas em um microscópio eletrônico de varredura (MEV).O comportamento em fadiga das ligas nitretadas foi superior ao das ligas não nitretadas. Conclui-se que quanto após a nitretação por plasma, quanto maior a tensão aplicada ao ensaio, maior é a diferença de resistência entre a liga nitretada e a não nitretada, sendo esta diferença diminuída com a redução da tensão. Para altas tensões a liga nitretada apresentou cerca de 5x mais resistência à fadiga. Palavras chave: Liga Ti-6Al-4V, fadiga, nitretação por plasma.
Efeito da tensão residual na microdeformação da rede cristalina em aço Cr-Si-V jateado por shot peening
2018 - OLIVEIRA, R.R.; LIMA, N.B.; XAVIER, G.L.; CASTRO, M.C.B. de
No presente trabalho foram estudados os efeitos causados pelo shot peening com a avaliação do perfil de tensão residual na região de tensão compressiva. Um efeito anômalo em relação ao perfil característico da distribuição de tensão residual foi notado pela perda de compressão próxima à superfície. Foi observada a região deformada plasticamente permitindo o estudo do mecanismo que infere este efeito. Os resultados fornecem as informações necessárias para comparar os efeitos que a microdeformação influenciam na tensão residual. Esta relação foi comprovada pela sobreposição dos resultados da distribuição da microdeformação com a tensão residual ao longo da espessura na região plasticamente deformada. Os resultados mostraram a existência de anisotropia de tensões entre os planos geradas pela densidade de discordâncias. O método aplicado foi o Williansom-Hall modificado.
Effect of plasma nitriding on fatigue behavior of Ti-6Al-4V alloy
2018 - CASTRO, MICHELE C.B. de; COUTO, ANTONIO A.; ALMEIDA, GISELE F.C.; MASSI, MARCOS; LIMA, NELSON B. de; SILVA SOBRINHO, ARGEMIRO da; CASTAGNET, MARIANO; XAVIER, GLEICY L.; OLIVEIRA, RENE R.
The Ti-6Al-4V alloy is widely used in the manufacture of components that should have low density, high corrosion resistance, and fatigue strength. The fatigue strength can be improved by surface modification. The aim of this study was to determine the influence of plasma nitriding on the fatigue behavior of Ti-6Al-4V alloy with a lamellar microstructure (Widmanstätten type). Nitriding was executed at 720 °C for 4 hours in an atmosphere with N2, Ar and H2. Samples microstructure characterization was carried out by X-ray diffraction analysis, optical microscopy and scanning electron microscopy. The average roughness of the specimens was determined, and fatigue tests were executed in a bending-rotating machine with reverse tension cycles (R= -1). X-ray diffraction analysis revealed the matrix phases α and β, and the phases Ɛ-Ti2N and δ-TiN in the nitrided alloy. A nitrogen diffusion layer was formed between the substrate and the titanium nitrides. Plasma nitriding resulted in an increase in low cycle fatigue strength, whereas at high cycles, both conditions exhibit similar behavior. The fracture surface of the fatigue tested specimens clearly revealed the lamellar microstructure. The fracture mechanism appears to be due to cracking at the interface of α and β phases of the lamellar microstructure.