Browsing by Author "Macedo, Waldemar Augusto de Almeida"

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    About the role of chromium and oxygen ion diffusion on the growth mechanism of oxidation films of the AISI 304 austenitic stainless steel.
    (2012) Sabioni, Antônio Claret Soares; Ramos, Roberto Paulo Barbosa; Ji, Vincent; Jomard, François; Macedo, Waldemar Augusto de Almeida; Gastelois, Pedro Lana; Trindade, Vicente Braz
    To study the role of ion diffusion on the oxidation process of the AISI 304 austenitic stainless steel, chromium diffusion coefficients were determined in oxide films grown on this steel at 750, 800 and 850 C, in air. The isotope 54Cr was used as a chromium tracer and the diffusion profiles were established by SIMS. The bulk diffusion coefficients are five orders of magnitude smaller than the grain boundary diffusion coefficients. It was found that the values of the chromium diffusivities are lower than the corresponding oxygen diffusivities obtained in previous work. Parabolic oxidation constants calculated as a function of the chrome and oxygen diffusivities, using Wagner0 s theory, are close to those determined experimentally, which shows that the growth rate of chromia is controlled by ion diffusion, but inward oxygen diffusion plays the main role on the growth kinetics of chromia formed by the oxidation of the AISI 304 steel.
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    Aplicação de espectroscopia de fotoelétrons ao estudo de processos de corrosão e oxidação de superfícies metálicas : Inconel 182, Fe/Cu(100) e U-Zr-Nb.
    (Programa de Pós-Graduação em Engenharia de Materiais. Rede Temática em Engenharia de Materiais, Pró-Reitoria de Pesquisa e Pós-Graduação, Universidade Federal de Ouro Preto., 2011) Mendonça, Renato de; Macedo, Waldemar Augusto de Almeida
    Neste trabalho é apresentado um estudo do processo de corrosão/oxidação de três sistemas constituídos de materiais metálicos por espectroscopia de fotoelétrons. No primeiro sistema foi investigada a corrosão do Inconel 182 em ambiente simulado de um reator de água pressurizada. Amostras com e sem tratamento químico superficial foram expostas ao ambiente simulado por um período de até 8 semanas. O óxido formado na superfície das amostras em diferentes condições foi caracterizado por microscopia eletrônica de varredura e espectroscopia de fotoelétrons excitados com raios X (X-Ray Photoelectron Spectroscopy - XPS). As comparações entre os resultados obtidos para os filmes de óxidos formados nas amostras tratadas e não tratadas apontaram diferenças, sendo as principais, o crescimento de uma camada de óxido menos espessa, e relativamente rica em Cr na amostra tratada quimicamente. No segundo sistema foi estudada a oxidação inicial em temperatura ambiente de filmes epitaxiais de Fe cfc e de Fe ccc crescidos sobre Cu (100). Os filmes foram depositados em duas diferentes espessuras para se obter as superfícies cfc Fe (100) e ccc Fe (110). Os resultados, obtidos utilizando espectroscopia de fotoemissão na linha TEMPO do Syncronton de Soleil, mostraram a formação de distintos filmes de óxido. As superfícies também apresentaram diferentes cinéticas de oxidação e a superfície ccc Fe (110) mostrou maior reatividade. A análise dos dados sugeriu a formação de Fe1-xO e Fe3O4 na superfície ccc Fe (110) e Fe1-xO na superfície cfc Fe (100). No último sistema foi investigada a oxidação inicial de ligas U-Zr-Nb em temperatura ambiente. Para isto, as ligas foram expostas a oxigênio em atmosfera de ultra alto vácuo. A análise do pico U 4f mostrou a rápida formação de UO2 na superfície, e uma similar cinética de oxidação entre o U e as ligas U-Zr-Nb. Os elementos de liga apresentaram lenta oxidação, e vários compostos foram observados na análise dos espectros Zr 3d e Nb 3d. O pico Zr 3d sugeriu a formação ZrO2, ao passo que o pico Nb 3d apresentou um aumento significativo na sua largura, apontando a necessidade de um ajuste que sugeriu a formação de NbO, NbO2 e Nb2O5 após os diferentes ciclos de exposição.
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    Chitosan grafted into mesoporous silica nanoparticles as benznidazol carrier for Chagas diseases treatment.
    (2018) Nhavene, Egídio Paulo Francisco; Silva, Wellington Marcos da; Trivelato Junior, Roberto Reis; Gastelois, Pedro Lana; Venâncio, Tiago; Nascimento, Regiane; Batista, Ronaldo Junio Campos; Machado, Carlos Renato; Macedo, Waldemar Augusto de Almeida; Sousa, Edésia Martins Barros de
    The use of chitosan functionalized silica for benznidazole delivery in the treatment of neglected disease such as Chagas disease is one of the forms not yet explored, but with great potential for this therapy, as little is known about nanoformulations for the treatment of Chagas disease. In this work, we used chitosan-succinate covalently attached to the surface pore of MSNs to act as anchor for benznidazole as a delivery system. The samples were characterized structurally and chemically with multiple techniques. The applicability of functionalized MSNs as platforms for benznidazole delivery into T. cruzi parasites was assessed. The results demonstrate that the proposed system is a potential promising nanoplatform for drug and gene delivery targeting neglected diseases such as Chagas disease.
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    Ion diffusion study in the oxide layers due to oxidation of AISI 439 ferritic stainless steel.
    (2014) Sabioni, Antônio Claret Soares; Malheiros, Emiliane Advíncula; Ji, Vincent; Jomard, François; Macedo, Waldemar Augusto de Almeida; Gastelois, Pedro Lana
    Chromium diffusion coefficients were determined in thermally grown chromia layers on the AISI 439 ferritic stainless steel oxidized at 750, 800, 850 and 900 C in synthetic air. The stable isotope 54Cr was used as chromium tracer and the diffusion profiles were established by SIMS analysis. The chromium ion bulk diffusion coefficients evaluated numerically from experimentation were around five orders of magnitude smaller than the chromium ion diffusion coefficients at grainboundary regions. The values of the chromium ion diffusivities in chromia grown on the AISI steel were lower than the corresponding oxygen ion diffusivities obtained in a previous study. Comparison of experimental and calculated parabolic oxidation constants, for the oxidation of the AISI 439 steel, showed that the chromia scale growth mechanism is controlled not only by inward oxygen ion diffusion from atmosphere, but also by outward chromium diffusion from the metallic substrate. However, the role of the oxygen ion diffusion appears to be more important than that of the chromium ion diffusion.
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    Measurement of iron self-diffusion in hematite single crystals by sims and comparison of cation self-diffusion in corundum-structure oxides.
    (2005) Sabioni, Antônio Claret Soares; Huntz, Anne Marie; Daniel, Antônio Márcio J. Mucci; Macedo, Waldemar Augusto de Almeida
    Iron bulk self-diffusion coefficients were measured in Fe2O3 single crystals using an original methodology based on the utilization of 57Fe stable isotope as iron tracer, and depth profiling by secondary ion mass spectrometry (SIMS). The iron self-diffusion coefficients were measured along and perpendicular to c-axis direction, between 900 and 1100o C, in oxygen atmosphere. Along caxis they can be described by D//c (cm2/s)= 5.2x106 exp [-510 (kJ/mol)/RT], and are close to reliable data available in the literature, obtained by means of radioactive techniques. Perpendicular to c-axis, D⊥c (cm2/s)= 83 exp [-430 (kJ/mol)/RT], and the coefficients are smaller than coefficients along caxis. The results are compared with previously obtained results of cation bulk self-diffusion in Cr2O3 and in Al2O3 single crystals.
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    Nanostructured system based on hydroxyapatite and curcumin : a promising candidate for osteosarcoma therapy.
    (2023) Marinho, Jéssica Pauline Nunes; Neme, Natália Paz; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Macedo, Waldemar Augusto de Almeida; Gastelois, Pedro Lana; Gomes, Dawidson Assis; Rodrigues, Michele Angela; Cipreste, Marcelo Fernandes; Sousa, Edésia Martins Barros de
    Osteosarcoma is the most common type of bone cancer. Despite therapeutic progress, survival rates for meta- static cases or that do not respond well to chemotherapy remain in the 30% range. In this sense, the use of nanotechnology to develop targeted and more effective therapies is a promising tool in the fight against cancer. Nanostructured hydroxyapatite, due to its biocompatibility and the wide possibility of functionalization, is an interesting material to design nanoplatforms for targeted drug delivery. These platforms have the potential to enable the use of natural substances in the fight against cancer, such as curcumin. Curcumin is a polyphenol with promising properties in treating various types of cancer, including osteosarcoma. In this work, hydroxyapatite (n- HA) nanorods synthesized by the hydrothermal method were investigated as a carrier for curcumin. For this, first-principle calculations based on the Density Functional Theory (DFT) were performed, in which the modi- fication of curcumin (CM) with the coupling agent (3-aminopropyl) triethoxysilane (APTES) was theoretically evaluated. Curcumin was incorporated in n-HA and the drug loading stability was evaluated by leaching test. Samples were characterized by a multi-techniques approach, including Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), X-ray diffraction (XRD), X-ray fluorescence spectrometry (FRX), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), zeta potential analysis (ζ), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that n-HAs with a 90 nm average size were obtained and successful incorporation of curcumin in the nanostructure was achieved. Cell viability and the number of osteosarcoma cells were decreased by CMAP-HA treatment. Furthermore, the stability test suggests that hydroxyapatite nanoparticles present great potential for the trans- portation of curcumin in the bloodstream, crediting this system for biological performance evaluations aiming at the treatment of osteosarcomas. Keywords: nanostructures, curcumin, hydroxyapatite, osteosarcoma.
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    A new theranostic system for bone disorders : functionalized folate-MDP hydroxyapatite nanoparticles with radiolabeled copper-64.
    (2020) Cipreste, Marcelo Fernandes; Mussel, Wagner da Nova; Silva, Juliana Batista da; Marques, Maria Betânia de Freitas; Batista, Ronaldo Junio Campos; Gastelois, Pedro Lana; Macedo, Waldemar Augusto de Almeida; Sousa, Edésia Martins Barros de
    Hydroxyapatite nanoparticles have been investigated as biological agents for the treatment and diagnosis of bone diseases due to their properties, providing high affinity to bone tissues and also due to the possibility to chemically modify the surfaces of these nanoparticles to provide active targeting to bone tumors or other bone disorders. In this work, synthetic hydroxyapatite nanoparticles and their surface modifications with folic and medronic acid were studied. Copper-64 was produced by neutron irradiation in a TRIGA MARK I nuclear reactor, and the functionalized nanoparticles radiolabeled with this radioisotope. The multi-technique characterization includes FTIR, PXRD, TGA, DSC, CHN, Zeta potential, XPS, SEM, TEM, and Gamma spectroscopy. Furthermore, the evaluation of the chemical interaction stability was through leaching tested for efficiency. The results indicate that folic and medronic acids can be covalently bonded to HA surface, producing a new material not yet described in the literature, been stably attached to hydroxyapatite nanoparticle surfaces, able to provide active targeting for bone disorders. The complexation of copper-64 provides high radiochemistry purity, although the specific activity must be improved.
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    Preparação e caracterização de cerâmicas do sistema ZnO:Mn.
    (2021) Lage, Viviane Maciel de Almeida; Carvalho, Hugo Bonette de; Carvalho, Hugo Bonette de; Jesus, Lilian Menezes de; Manhabosco, Taíse Matte; Lima Júnior, Maurício Morais de; Macedo, Waldemar Augusto de Almeida
    Neste trabalho apresentamos os estudos relacionados à preparação e caracterização estrutural do sistema ZnO:Mn. A utilização de novas rotas de síntese desse material tem levado a obtenção de materiais apresentando formas anisotrópicas, que podem dar origem a novas propriedades e aplicações. Neste contexto, este trabalho descreve a síntese de amostras preparadas via moagem mecânica, e o estudo do limite de solubilidade do Mn na matriz do ZnO, as melhores condições de incorporação dos diferentes precursores e melhor atmosfera de sinterização, bem como o estudo da natureza dos modos vibracionais de defeitos com o aumento da concentração do dopante (Mn) na matriz do ZnO. A caracterização estrutural dos materiais preparados se deu via difração de raios X, espectroscopia de espalhamento Raman, microscopia eletrônica de varredura, espectroscopia de raios X por dispersão em energia, espectroscopia de absorção de raios X e magnetometria SQUID (Superconducting Quantum Interference Device). Conjugando os resultados dessas diferentes técnicas, confirmou-se que o limite de solubilidade do Mn está abaixo de ~ 5,4 at.% (porcentagem atômica) com a substituição do Zn pelo Mn na estrutura wurtzita do ZnO, sem alteração significativa da mesma. As análises confirmam também que com o aumento da concentração de dopantes há um aumento da concentração de defeitos estruturais provocados pela sua inserção à matriz, sendo possível identificar modos vibracionais locais específicos associados aos dopantes utilizados. Apesar dos defeitos induzidos, a caracterização magnética revela a existência da fase paramagnética com acoplamento antiferromagnético entre os íons Mn. Sob a óptica do modelo Bound Magntic Polaron, conclui-se que as vacâncias de oxigênio não são o defeito necessário para promover o ferromagnetismo desejado à temperatura ambiente. Ainda, através do estudo dos modos vibracionais de defeitos com diferentes comprimentos de onda de excitação, observamos que estes modos aumentam a intensidade com a diminuição do comprimento de onda de excitação, em consequência do aumento da interação elétron/fônon, que se dá em função do aumento frequência de vibração dos átomos e consequentemente aumento da quantidade de elétrons na banda de condução. Nas condições alcançadas o material preparado apresenta potencial aplicação em sistemas de fotocatálise, termoeletricidade e spintrônicos.