Navegando por Autor "Batista, Ronaldo Junio Campos"
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Item Ab initio molecular dynamics simulation of methanol and acetonitrile : the effect of van der Waals interactions.(2019) Resende, Rafael Fanni Dias; Costa, Cleidinéia Cavalcante da; Manhabosco, Taíse Matte; Oliveira, Alan Barros de; Matos, Matheus Josué de Souza; Soares, Jaqueline dos Santos; Batista, Ronaldo Junio CamposWe employed PBE and BLYP semi-local functionals and the van der Waals density functional of Dion et al. (2004) (vdW-DF) to investigate structural properties of liquid acetonitrile and methanol. Among those functionals the vdW-DF is the only one that correctly predicts energy minima in inter-molecular interactions between acetonitrile molecules. We found that van der Waals interactions have a negligible effect on H-bonds in methanol chains. However, it significantly increases chain packing resulting in a more dense liquid in comparison to the other two functionals. The overall trend is that the vdW-DF tends to overestimate density and bulk modulus, meanwhile the semi-local functionals tend to underestimate density. Thus, van der Waals interactions play an important role in the properties of liquids in which much stronger dipole-dipole interactions are present.Item Apparent softening of wet graphene membranes on a microfluidic platfor.(2018) Ferrari, Gustavo Arrighi; Oliveira, Alan Barros de; Almeida, Ive Silvestre de; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Fernandes, Thales Fernando Damasceno; Meireles, Leonel Muniz; Silva Neto, Eliel Gomes da; Chacham, Helio; Neves, Bernardo Ruegger Almeida; Lacerda, Rodrigo GribelGraphene is regarded as the toughest two-dimensional material (highest in-plane elastic properties) and, as a consequence, it has been employed/proposed as an ultrathin membrane in a myriad of microfluidic devices. Yet, an experimental investigation of eventual variations on the apparent elastic properties of a suspended graphene membrane in contact with air or water is still missing. In this work, the mechanical response of suspended monolayer graphene membranes on a microfluidic platform is investigated via scanning probe microscopy experiments. A high elastic modulus is measured for the membrane when the platform is filled with air, as expected. However, a significant apparent softening of graphene is observed when water fills the microfluidic system. Through molecular dynamics simulations and a phenomenological model, we associate such softening to a water-induced uncrumpling process of the suspended graphene membrane. This result may bring substantial modifications on the design and operation of microfluidic devices which exploit pressure application on graphene membranes.Item Characterization of magnetic tailings from phosphate-ore processing in Alto Paranaíba.(2022) Silva, Fernando Brandão Rodrigues da; Araújo, Fernando Gabriel da Silva; Krüger, Fernando Leopoldo von; Silva, Guilherme Jorge Brigolini; Batista, Ronaldo Junio Campos; Manhabosco, Taíse MatteThe characterization studies of tailings from mining are crucial for the development of its reuse processes and the reduction of impacts caused by its conditioning on the earth’s surface. This study characterizes the magnetic tailings from phosphate-rock processing using X-ray diffraction, X-ray fluorescence spectrometry and quantitative electron microscopy techniques. Samples were obtained from the magnetic tailings deposit of a mining company in the Alto Paranaíba region, Minas Gerais. The tailings are mainly composed of hematite/magnetite (74.92%), ilmenite (8.91%), fluorapatite (8.8%), anatase (3.07%), calcite (1.67%), goethite (1.62%), and quartz (1.02%). The particle size of the tailings is smaller than that specified for the production of sinter feed. The hematite/magnetite phase is strongly associated with ilmenite and fluorapatite. New stages of comminution and separation are needed due to the low degree of liberation of these minerals for a possible reuse of the components.Item Characterization of magnetic tailings from phosphate-ore processing in Alto Paranaíba.(2023) Silva, Fernando Brandão Rodrigues da; Araújo, Fernando Gabriel da Silva; Krüger, Fernando Leopoldo von; Silva, Guilherme Jorge Brigolini; Batista, Ronaldo Junio Campos; Manhabosco, Taíse MatteThe characterization studies of tailings from mining are crucial for the development of its reuse processes and the reduction of impacts caused by its conditioning on the earth’s surface. This study characterizes the magnetic tailings from phosphate-rock processing using X-ray diffraction, X-ray fluorescence spectrometry and quantitative electron microscopy techniques. Samples were obtained from the magnetic tailings deposit of a mining company in the Alto Paranaíba region, Minas Gerais. The tailings are mainly composed of hematite/magnetite (74.92%), ilmenite (8.91%), fluorapatite (8.8%), anatase (3.07%), calcite (1.67%), goethite (1.62%), and quartz (1.02%). The particle size of the tailings is smaller than that specified for the production of sinter feed. The hematite/magnetite phase is strongly associated with ilmenite and fluorapatite. New stages of comminution and separation are needed due to the low degree of liberation of these minerals for a possible reuse of the components.Item Charge and spin current rectification through functionalized boron nitride bilayers.(2022) Moraes, Elizane Efigenia de; Pinto, Alysson Alves; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Chacham, HelioRecent experiments have reported the transformation of few-layer hexagonal boron nitride (h-BN) into sp3 -bonded c-BN layers through the application of pressure. A proposed mechanism, based on calculations and experiments, is that the phenomenon is facilitated by BN surface functionalization with OH or H radicals. In the present work, we perform ab initio calculations of ballistic electron transport, between Au electrodes, across such functionalized structures. We find that the stabilization of sp3 binding at zero pressure occurs for partial H coverage (≈58%), whereas large OH coverages (>75%) are necessary. Regarding transport properties, we find that all functionalized BN bilayer films present current rectification, consistent with the experimental findings. Maximum rectification occurs for partial OH and H coverages. The films also show spin-dependent transport, where, for a window of values of applied bias, a single spin component contributes to the total current, characterizing a spin filter behavior. Our results indicate that functionalized BN bilayer films are promising materials for the development of electronic devices where both charge and spin degrees of freedom might be manipulated.Item 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 deThe 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.Item A coarse-grained model based on core-oftened potentials for anomalous polymers.(2017) Batista, Ronaldo Junio Campos; Torres, Evy Augusto Salcedo; Oliveira, Alan Barros de; Barbosa, Marcia Cristina BernardesStarting from an anomalous monomeric system, where particles interact via a two-scale coresoftened potential, we investigate how the system properties evolve inasmuch as particles are put together to form polymers whose chain size varies from 4 up to 32 monomers. We observed that the density and diffusion anomaly regions in the pressure versus temperature phase diagram of the monomeric system is smaller in the monomeric system when compared with the polymers. We also found that the polymers do not fold into themselves to form solid spheres instead they tend to maximize the chain-fluid contact.Also, Rouse and Reptation models can be employed to describe the polymers diffusive behaviour. But, in contrast to results of simulations where mere interacts via Lennard-Jones potentials, our results shown a much shorter entanglement length of atmost 8 monomers.Item Comparison between hydroxyapatite/soapstone and hydroxyapatite/ reduced graphene oxide composite coatings : synthesis and property improvement.(2021) Nicomedes, Daniel Nilson Nunes; Mota, Laureana Moreira; Vasconcellos, Rebecca; Medrado, Nathanael Vieira; Oliveira, Michelle de; Alvarenga, Érika Lorena Fonseca Costa de; Juste, Karyne Ramos de Campos; Righi, Ariete; Manhabosco, Sara Matte; Silva, Guilherme Jorge Brigolini; Araújo, Fernando Gabriel da Silva; Oliveira, Alan Barros de; Batista, Ronaldo Junio Campos; Soares, Jaqueline dos Santos; Manhabosco, Taíse MatteEconomic viability and eco-friendliness are important characteristics that make implants available to the pop- ulation in a sustainable way. In this work, we evaluate the performance of a low-cost, widely available, and eco- friendly material (talc from soapstone) relative to reduced graphene oxide as reinforcement to brittle hy- droxyapatite coatings. We employ a low-cost and straightforward technique, electrodeposition, to deposit the composite coatings on the titanium substrate. Corrosion, wear, and biocompatibility tests indicate that the reduced graphene oxide can be effectively replaced by talc without reducing the mechanical, anticorrosion, and biocompatible composite coatings properties. Our results indicate that talc from soapstone is a promising ma- terial for biomedical applications.Item Compression induced modification of boron nitride layers : a conductive two-dimensional BN compound.(2019) Barboza, Ana Paula Moreira; Matos, Matheus Josué de Souza; Chacham, Helio; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Mazzoni, Mario Sergio de Carvalho; Neves, Bernardo Ruegger AlmeidaThe ability of creating materials with improved properties upon transformation processes applied to conventional materials is the keystone of materials science. Here, hexagonal boron nitride (h-BN), a large bandgap insulator, is transformed into a conductive two-dimensional (2D) material – bonitrol – that is stable at ambient conditions. The process, which requires compression of at least two h-BN layers and hydroxyl ions, is characterized via scanning probe microscopy experiments and ab initio calculations. This material and its creation mechanism represent an additional strategy on the transformation of known 2D materials into artificial advanced materials with exceptional propertiesItem Controlling the electrical behavior of semiconducting carbon nanotubes via tube contact.(2011) Barboza, Ana Paula Moreira; Carara, Sabrina Silva; Batista, Ronaldo Junio Campos; Chacham, Helio; Neves, Bernardo Ruegger AlmeidaItem Corrosion and cell viability studies of graphite-like hydrogenated amorphous carbon films deposited on bare and nitrided titanium alloy.(2014) Santos, Adélia Moreira Marques dos; Batista, Ronaldo Junio Campos; Martins, Leo Anderson Meira; Ilha, Mariana; Vieira, Moema Queiroz; Miquita, Douglas Rodrigues; Guma, Fátima Costa Rodrigues; Muller, Iduvirges Lourdes; Manhabosco, Taíse MatteThis work presents a study of corrosion resistance and cell viability of carbon films on bare and nitride Ti–6Al–4V. Films deposited on bare alloy significantly improve the corrosion resistance. Unexpectedly, films deposited on nitrided alloy present delamination and cracking after 16 days. We associate film failure with the presence of pores combined with a weak film/substrate interaction that allows diffusion of ions at the interface. We found that films tend to diminish the osteoblastic cell viability and the observed variations on film roughness do not improve cell viability.Item Corrosion, wear and wear–corrosion behavior of graphite-like a-C:H films deposited on bare and nitrided titanium alloy.(2013) Manhabosco, Taíse Matte; Barboza, Ana Paula Moreira; Batista, Ronaldo Junio Campos; Neves, Bernardo Ruegger Almeida; Muller, Iduvirges LourdesThis work presents a comparative wear, corrosion and wear–corrosion (the last one in a simulated physiological solution) study of graphite-like a-C:H (GLCH) films deposited on bare and nitrided Ti6Al4V alloy. Films, deposited by r.f. PACVD, presented low porosity and promoted high corrosion resistance. The friction coefficient of the films was very lowwith appreciablewear resistance at roomconditions. However, due to the simultaneous action of both load and the corrosive environment in wear–corrosion tests a marked reduction in the coating lifetime was observed. Unexpectedly, films deposited on the nitrided alloy presented a lifetime at least ten times shorter than that of films on bare alloy. We explain such a result in terms of film/substrate interaction. The weak GLCH/nitride alloy interaction facilitates fluid penetration between the film and the substratewhich leads to a fast film delamination. Such an interpretation is supported by force curve measurements, which show that the interaction between GLCH and nitrided alloy is four times weaker than that between GLCH and bare alloy.Item Crystal-oriented wrinkles with origami-type junctions in few-layer hexagonal boron nitride.(2015) Oliveira, Camilla Karla Brites Queiroz Martins de; Gomes, Egleidson Frederik do Amaral; Prado, Mariana C.; Souza, Thonimar Vieira de Alencar; Nascimento, Regiane do; Moreira, Leandro Malard; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Chacham, Helio; Paula, Ana Maria de; Neves, Bernardo Ruegger AlmeidaUnderstanding layer interplay is the key to utilizing layered heterostructures formed by the stacking of different two-dimensional materials for device applications. Boron nitride has been demonstrated to be an ideal substrate on which to build graphene devices with improved mobilities. Here we present studies on the morphology and optical response of annealed few-layer hexagonal boron nitride flakes deposited on a silicon substrate that reveal the formation of linear wrinkles along well-defined crystallographic directions. The wrinkles formed a network of primarily threefold and occasionally fourfold origami-type junctions throughout the sample, and all threefold junctions and wrinkles formed along the armchair crystallographic direction. Furthermore, molecular dynamics simulations yielded, through spontaneous symmetry breaking, wrinkle junction morphologies that are consistent with both the experimental results and the proposed origami-folding model. Our findings indicate that this morphology may be a general feature of several two-dimensional materials under proper stress-strain conditions, resulting in direct consequences in device strain engineering.Item Deposição e caracterização de revestimentos de diamond-like carbon (DLC) sobre substrato de titânio.(2017) Araújo, Mário Almeida; Batista, Ronaldo Junio Campos; Manhabosco, Taíse Matte; Batista, Ronaldo Junio Campos; Vasconcelos, Cláudia Karina Barbosa de; Soares, Jaqueline dos SantosBiomateriais metálicos devem apresentar uma combinação de propriedades como resistência à corrosão, biocompatibilidade e resistência mecânica. O titânio e suas ligas aliam essas propriedades. No entanto, são susceptíveis ao desgaste. No presente trabalho, aplicamos sobre o titânio revestimentos obtidos por meio eletrodeposição, utilizando diferentes potenciais, afim de aumentar sua resistência ao desgaste. O filme depositado foi de carbono tipo diamante (DLC). Esses materiais têm alta dureza e resistência ao desgaste, além de biocompatibilidade intrínseca, característica altamente desejada para biomateriais. A caracterização morfológica do titânio revestido com DLC foi realizada por microscopia de força atômica (AFM). O titânio apresentou uma superfície pouco rugosa, resultante do processo de eletropolimento, a qual foi copiada pelo filme. A espectroscopia Raman mostrou a formação das bandas D e G, características de filmes DLC, e possibilitou a determinação do teor de hidrogênio presentes nos filmes. Além das bandas D e G foi encontrado um pico T, atribuído ao diamante nanocristalino. A presença de carbono na superfície do titânio contribuiu para uma melhoria significativa da sua resistência ao desgaste. Em relação ao comportamento corrosivo, o filme mostrou um comportamento mais resistente à corrosão quando comparado ao substrato. A ação simultânea de desgaste-corrosão levou uma falha prematura do filme. Assim, a presença do filme na superfície do titânio contribuiu para uma melhoria significativa da sua resistência ao desgaste e a corrosão, todavia, os revestimentos DLC falham em situações em que a carga e o ambiente corrosivo estão agindo em conjunto.Item Deposição e caracterização de revestimentos de hidroxiapatita com incorporação de óxido de grafeno.(2017) Nicomedes, Daniel Nilson; Manhabosco, Taíse Matte; Batista, Ronaldo Junio Campos; Manhabosco, Taíse Matte; Vasconcelos, Cláudia Karina Barbosa de; Cazati, ThiagoBiomateriais são substâncias de origem natural ou sintética que podem ser utilizados para substituição total ou parcial de tecidos vivos danificados. Dentre os biomateriais utilizados em aplicações médicas, temos as cerâmicas a base de fosfato de cálcio. Um exemplo deste tipo de cerâmica é o mineral Hidroxiapatita HA (Ca5(OH)(PO4)3) que apresenta bastante similaridade com a fase mineral presente em nossos ossos e dentes. O uso desse mineral em implantes tem se mostrado de grande sucesso devido ao seu comportamento in vivo e por apresentar propriedades bioativas e osteocondutivas que favorecem o crescimento ósseo. Entretanto, a Hidroxiapatita, por ser um material cerâmico, é um biomaterial frágil e susceptível a falha por fadiga. Seguindo a linha de outras pesquisas que têm incorporado uma segunda fase de reforço (nanotubos de carbono, talco, etc.), este trabalho propõe, realiza e analisa a incorporação de óxido de grafeno aos revestimentos de Hidroxiapatita depositados sobre titânio com o objetivo de melhoria nas propriedades mecânicas da HA sem prejudicar a biocompatibilidade. Os resultados mostram que a Hidroxiapatita obtida por eletrodeposição pulsada com incorporação de óxido de grafeno apresenta uma melhor resistência ao desgaste comparada à Hidroxiapatita pura sem comprometimento da biocompatibilidade, apresentando resistência à corrosão um pouco melhor quando comparado ao titânio puro.Item Desenvolvimento de substratos cerâmicos de dióxido de titânio com alta permissividade para utilização em antenas.(2020) Freitas, Antonio Evangelista de; Araújo, Fernando Gabriel da Silva; Costa, Adilson Rodrigues da; Araújo, Humberto Xavier de; Araújo, Fernando Gabriel da Silva; Solé, Rubén Antonio Llobell; Mendes, Jefferson Januário; Bernardes, Américo Tristão; Batista, Ronaldo Junio Campos; Costa, Adilson Rodrigues daÉ investigado o dióxido de titânio (TiO2) como substrato dielétrico para aplicações em dispositivos de telecomunicações, em especial antenas de microfita. A escolha foi baseada no baixo preço do TiO2 e seu comportamento inofensivo à saúde humana. Os substratos foram fabricados pela sinterização por estado sólido. Esta técnica produz cerâmicas de qualidade a baixo custo, o que favorece a viabilidade econômica para as futuras antenas. Devido às propriedades dielétricas, o substrato torna-se importante para a miniaturização e eficiência das antenas. Neste sentido uma completa caracterização da microestrutura torna-se necessária, bem como uma detalhada caracterização das propriedades eletromagnéticas. Os substratos de dióxido de titânio foram sintetizados em temperaturas que variaram de 1150 °C a 1350 °C. O tempo de sinterização também foi investigado, obtendose amostras com tempos de 4 e 12 horas. A difração de raios X e a microscopia eletrônica de varredura (MEV) foram utilizadas para investigar a estrutura cristalina, o tamanho dos grãos e a porosidade das amostras resultantes. As cerâmicas obtidas são tetragonais (fase rutilo), com tamanhos médios de grãos variando de 2,94 µm a 5,81 µm. A variabilidade dos tamanhos de grãos, evidenciada pelo erro médio padrão, não foi muito grande para cada temperatura/tempo de sinterização, o que confirma que não houve crescimento anormal de grão. O tamanho médio dos grãos das amostras aumenta com o aumento da temperatura, enquanto a porosidade total diminui, bem como o tamanho médio das porosidades. O mesmo comportamento, de tamanho de grão e porosidade, é observado quando se mantém a temperatura constante e incrementa-se o tempo de sinterização. O efeito da microestrutura nas propriedades dielétricas dos substratos cerâmicos também foi estudado. Densidades relativas obtidas entre 0.66 e 0.86 indicam a evolução do processo de densificação à medida que tempo/temperatura aumentaram. A densificação, evidenciado pela redução da porosidade e crescimento dos grãos, das amostras aumentam as suas permissividades dielétricas relativas. Um modelo analítico inovador foi desenvolvido, permitindo que se estime a permissividade do material sem poros. Os valores obtidos para a permissividade dielétrica foram elevados se comparados com substratos comerciais usualmente utilizados em componentes de telecomunicações. Isso indica que os substratos cerâmicos obtidos podem ser úteis na miniaturização de dispositivos de telecomunicações, especialmente as antenas de microfita. As tangentes de perdas foram próximas de zero, o que garante uma boa eficiência para os futuros equipamentos construídos sobre os substratos cerâmicos desenvolvidos.Item Determination of current maps by svet of hot-dip galvanized steel under simultaneous straining.(2015) Manhabosco, Sara Matte; Batista, Ronaldo Junio Campos; Silva, Sabrina Neves da; Dick, Luís Frederico PinheiroA new experimental procedure was used to analyse the corrosion behaviour of hot-dip Zn coated steel based on the association of the scanning vibrating electrode technique (SVET) and uniaxial tensile strain applied up to 3.1% in 0.01 M NaCl solutions without release of the elastic strain during the test. The nucleation of localized corrosion sites on the coating occurs at very low strain values around the yield point and the maximum current densities increase continuously with the increase of the applied strain. The nucleation of localized corrosion on the Zn surface was favoured by the rupture of the passive film in contact with the solution by the action of slip steps and fine intergranular cracks, rather than by the exposure of the steel substrate. Straining of the Zn coating immersed in the solution was comparatively a much more aggressive condition than straining the sample in air before the corrosion tests.Item Development and characterization of titanium dioxide ceramic substrates with high dielectric permittivities.(2020) Freitas, Antonio Evangelista de; Manhabosco, Taíse Matte; Batista, Ronaldo Junio Campos; Rêgo Segundo, Alan Kardek; Araujo, Humberto Xavier de; Araujo, Fernando Gabriel da Silva; Costa, Adilson Rodrigues daTitanium dioxide substrates have been synthesized by means of solid-state reactions with sintering temperatures varying from 1150 ◦C up to 1350 ◦C. X-ray diffraction and scanning electron microscopy (SEM) where employed to investigate the crystal structure, grain size and porosity of the resulting samples. The obtained ceramics are tetragonal (rutile phase) with average grain sizes varying from 2.94 µm up to 5.81 µm. The average grain size of samples increases with increasing temperature, while the porosity decreases. The effect of microstructure on the dielectric properties has been also studied. The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectric permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.Item Diffusion behaviour of water confined in deformed carbon nanotubes.(2019) Mendonça, Bruno Henrique da Silva e; Freitas, Débora Nazaré de; Kohler, Mateus Henrique; Batista, Ronaldo Junio Campos; Barbosa, Márcia Cristina Bernardes; Oliveira, Alan Barros deWe use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of eccentricity at 300 K. We found a water structural transition between tubular-like to single-file for (7,7) nanotubes associated with change from a high to low mobility regimes. Water is frozen when confined in a perfect (9,9) nanotube and it becomes liquid if such a nanotube is deformed above a certain threshold. Water diffusion enhancement (suppression) is related to a reduction (increase) in the number of hydrogen bonds. This suggests that the shape of the nanotube is an important ingredient when considering the dynamical and structural properties of confined water.Item Dinâmica ab initio de líquidos polares : acetonitrila e metanol.(2014) Costa, Cleidinéia Cavalcante da; Batista, Ronaldo Junio Campos; Manhabosco, Taíse Matte; Oliveira, Alan Barros de; Mota, Vinícius Cândido