Papers by Luis Rogerio de Oliveira Hein
Practical Metallography, 2001
Protection of Metals and Physical Chemistry of Surfaces, 2016
This study examines the effect of film thickness ranging from 230 to 404 nm on the corrosion resi... more This study examines the effect of film thickness ranging from 230 to 404 nm on the corrosion resistance of Nb2O5 thin films grown by chemical solution deposition. The films were characterized to obtain the relationships between the deposition parameters and the most relevant physical properties (structural, surface morphology and corrosion resistance). From X-ray diffraction and XPS analyses we can conclude that the films were stoichiometric Nb2O5 and crystalline. The internal strain and morphology of the film changes as the number of layers increases indicating a thickness dependent grain size. The surface roughness, corrosion resistance were also affected by the film thickness. Electrochemical impedance spectroscopy (EIS) shows that the thicker film have higher passive and charge transfer resistance than the control samples. These results coating layer of Nb2O5 improves the corrosion resistance on an API 5L X80 steel alloy due to the formation of a film on the surface.
Polymers
A conical-shaped atmospheric pressure plasma jet (CS-APPJ) was developed to overcome a standard l... more A conical-shaped atmospheric pressure plasma jet (CS-APPJ) was developed to overcome a standard limitation of APPJs, which is their small treatment area. The CS-APPJs increase the treatment area but use the same gas flow. In the present work, polypropylene samples were treated by CS-APPJ and characterized by scanning electron microscope (SEM), the contact angle, Fourier-transformed infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). It was observed that the treatment co-occurs on the face directly in contact with the plasma and on the opposite face (OF) of the samples, i.e., no contact. However, the treatment changed the chemical composition on each side; the OF is rougher than the direct contact face (DCF), probably due to the oxygen groups in excess at the DCF and nitrogen in quantity at the OF. Although simultaneous treatment of both sides of the sample occurs for most atmospheric plasma treatments, this phenomenon is not explored in the literature.
IEEE Transactions on Plasma Science, 2012
The specific properties of an atmospheric pressure plasma make it an attractive tool for the surf... more The specific properties of an atmospheric pressure plasma make it an attractive tool for the surface treatment of various materials. With this in mind, this paper presents the results of experimental investigations of a polycarbonate (PC) material surface modification using this new type of argon microwave (2.45 GHz) plasma source. The uniqueness of the new plasma source lies in the shape of the generated plasma-in contrast to other microwave plasma sources, which usually provide a plasma in the form of a flame or column, the new ones provides a plasma in the shape of a regular plasma sheet. The influence of the absorbed microwave power and the number of scans on the changes of the wettability and morphological and mechanical properties of the plasma-treated PC samples was investigated. The mechanical properties and changes in roughness of the samples were measured by the use of atomic force microscopy (AFM). The wettability of the plasma-modified samples was tested by measuring the water contact angle. In order to confirm the plasma effect, each of the above-mentioned measurements was performed before and after plasma treatment. All experimental tests were performed with an argon of flow rate up to 20 L/min and the absorbed microwave power ranged from 300 to 850 W. The results prove the capability of the new atmospheric pressure plasma type in modifying the morphological and mechanical properties of PC surfaces for industrial applications.
Cadernos UniFOA, Feb 4, 2019
Os efeitos da pre-deformacao a frio sobre o comportamento mecânico em tracao da liga Ti-15V-3Cr-3... more Os efeitos da pre-deformacao a frio sobre o comportamento mecânico em tracao da liga Ti-15V-3Cr-3Sn-3A1 sao analisados em funcao das modificacoes microestruturais decorrentes da aplicacao de tratamentos termicos em amostras com diferentes niveis de estiramento uniaxial ...Observacao: O resumo, na integra, podera ser visualizado no texto completo da tese digital Abstract
Surface and Coatings Technology, 2013
In this work, air dielectric barrier discharge (DBD) operating at the line frequency (60 Hz) or a... more In this work, air dielectric barrier discharge (DBD) operating at the line frequency (60 Hz) or at frequency of 17 kHz was used to improve the wetting properties of polypropylene (PP). The changes in the surface hydrophilicity were investigated by contact angle measurements. The plasma-induced chemical modifications of PP surface were studied by X-ray photoelectron spectroscopy (XPS) and Fourier-transformed infrared spectroscopy (FTIR). The polymer surface morphology and roughness before and after the DBD treatment were analyzed by atomic force microscopy (AFM). To compare the plasma treatment effect at different frequencies the variation of the contact angle is presented as a function of the deposited energy density. The results show that both DBD treatments leaded to formation of water-soluble low molecular weight oxidized material (LMWOM), which agglomerated into small mounts on the surface producing a complex globular structure. However, the 60 Hz DBD process produced higher amount of LMWOM on the PP surface comparing to the 17 kHz plasma treatment with the same energy dose. The hydrophilic LMWOM is weakly bounded to the surface and can be easily removed by polar solvents. After washing the DBD-treated samples in de-ionized water their surface roughness and oxygen content were reduced and the PP partially recovered its original wetting characteristics. This suggested that oxidation also occurred at deeper and more permanent levels of the PP samples. Comparing both DBD processes the 17 kHz treatment was found to be more efficient in introducing oxygen moieties on the surface and also in improving the PP wetting properties.
Materials Science and Engineering: A, 2003
Metallographic techniques and digital image processing have been used to investigate heat-treated... more Metallographic techniques and digital image processing have been used to investigate heat-treated Ti–6Al–4V pitting corrosion, often used as aircraft components. LM and SEM metallography of ‘as received’, annealed (heating up to 800°C/30 min and cooling furnace) and aged (heating up to 900°C/30 min, quenching in water, heating up to 540°C/240 min and again water-quenched) microstructures reveal pitting sites at primary
Scanning, 2012
The methodology for fracture analysis of polymeric composites with scanning electron microscopes ... more The methodology for fracture analysis of polymeric composites with scanning electron microscopes (SEM) is still under discussion. Many authors prefer to use sputter coating with a conductive material instead of applying low-voltage (LV) or variablepressure (VP) methods, which preserves the original surfaces. The present work examines the effects of sputter coating with 25 nm of gold on the topography of carbon-epoxy composites fracture surfaces, using an atomic force microscope. Also, the influence of SEM imaging parameters on fractal measurements is evaluated for the VP-SEM and LV-SEM methods. It was observed that topographic measurements were not significantly affected by the gold coating at tested scale. Moreover, changes on SEM setup leads to nonlinear outcome on texture parameters, such as fractal dimension and entropy values. For VP-SEM or LV-SEM, fractal dimension and entropy values did not present any evident relation with image quality parameters, but the resolution must be optimized with imaging setup, accompanied by charge neutralization. SCANNING 00: 1-9, 2012.
Materials Letters, 2002
Jet impingement erosion test rig has been used to erode titanium alloy specimens (Ti-4Al-4V). Ero... more Jet impingement erosion test rig has been used to erode titanium alloy specimens (Ti-4Al-4V). Eroded surface profiles have been obtained by vertical sectioning method for light microscopy observation. Mixed fractals have been measured from profile images by a digital image processing and analysis technique. The use of this technique allows glimpsing a quantitative correlation among material properties, fractal surface topography and erosion phenomena.
biblioteca.univap.br
Resumo: Este trabalho teve como objetivo o desenvolvimento de uma técnica alternativa para caract... more Resumo: Este trabalho teve como objetivo o desenvolvimento de uma técnica alternativa para caracterizar a evolução da corrosão por pites, visando a classificação, tamanho ea determinação dos parâmetros morfológicos que governam o crescimento dos pites. Neste caso o ...
Advanced Materials Research, 2016
An experimental investigation of the resistance welding of PPS/carbon fiber is presented in this ... more An experimental investigation of the resistance welding of PPS/carbon fiber is presented in this manuscript. Currently, one of the main problems of the structural polymer composites consists in its effective integration of the components. The electrical resistance welding has been considered as one of the promising techniques for bonding composites, because it is a quick process with easy surface preparation. To improve the process to welding poly-(phenylene sulfide) (PPS) reinforced with carbon fiber laminates, it was used a full factorial design (23). Considering the factors pressure, electrical current and time, the more appropriate conditions for welding were evaluated based on a criterion of maximum lap shear strength, according to ASTM D1002-10. A comparison between welded and non-welded specimens in terms of analysis dynamic mechanical (DMA), thermomechanical analysis (TMA) and vibration tests was performed. It was demonstrated that large-scale DMA presented a similar results...
Univ Estadual Paulista, Dept Mat & Tecnol, Fac Engn Guarantingueta, BR-12516410 Guaratingueta, SP... more Univ Estadual Paulista, Dept Mat & Tecnol, Fac Engn Guarantingueta, BR-12516410 Guaratingueta, SP, Brazil
Practical Metallography, 2008
Porosity in starch consolidation casting technique is rightly related to original size and morpho... more Porosity in starch consolidation casting technique is rightly related to original size and morphology of starch granules, leaving a pore structure after burning out. This work reports the results for the addition of different native potato and corn starch proportions in suspensions with TiO2 (rutile) powder. Gelling temperature have been defined after observation under light microscopy using a heating stage. Analysis of porous network and isolated pores have been done from images of samples surfaces obtained by depth from focus reconstruction, revealing a qualitative correlation of pores characteristics and starches additions in suspensions, suggesting that the presence of isolated or interconnected pores can be handled by starches selection to control the amylopectin and amylose contents in slurries. Also, the analysis of porous fraction distribution shows no consistent pattern through specimens’ volume according to starches in mixtures.
Materials Research, 2011
The direct three-dimensional characterization of opaque materials through serial sectioning makes... more The direct three-dimensional characterization of opaque materials through serial sectioning makes possible to visualize and better quantify a material microstructure, using classical metallographic techniques coupled with computer-aided reconstruction. Titanium alloys are used as biomaterials for bone implants because of its excellent mechanical properties, biocompatibility and enhanced corrosion resistance. The Ti-6Al-4V alloy (in wt. (%)) with porous microstructure permits the ingrowths of new-bone tissues improving the fixation bone/implant. This is important to understand connectivity, morphology and spatial distribution of pores in microstructure. The Ti-6Al-4V alloy compacts were produced by powder metallurgy and sintered at three distinct temperatures (1250, 1400 and 1500 °C) to obtain distinct microstructures in terms of residual porosity. The visualization of the reconstructed 3D microstructure provides a qualitative and quantitative analysis of the porosity of Ti6Al4V alloy (volume fraction and pore morphology).
Journal of the European Ceramic Society, 2004
A method has been developed to obtain quantitative information about grain size and shape from fr... more A method has been developed to obtain quantitative information about grain size and shape from fractured surfaces of ceramic materials. One elaborated a routine to split intergranular and transgranular grains facets of ceramic fracture surfaces by digital image processing. A commercial ceramic (ALCOA A-16, Al2O3–1.5% of CrO) was used to test the proposed method. Microstructural measurements of grain shape and
Surface and Coatings Technology, 2017
Non-thermal atmospheric pressure plasma jets (APPJs) are capable of generating cold plasma plumes... more Non-thermal atmospheric pressure plasma jets (APPJs) are capable of generating cold plasma plumes that are not confined by electrodes, which makes them very attractive for bio-medical applications. In the present work, the inactivation efficiency of cold APPJ was evaluated against three pathogenic microorganisms with different cell wall characteristics. The Gram-positive bacterium Enterococcus faecalis (ATCC 29212), the Gram-negative bacterium Pseudomonas aeruginosa (ATCC 15442) and the fungus Candida albicans (SC 5314) were plated on standard Petri dishes filled with specific culture media. The plasma jet with mean power of 1.8 W was directed perpendicularly on agar plates and the system was flushed with pure helium at two different flows, 2.0 and 4.0 SLM. During the treatments, time and distance between nozzle and agar were varied. The presence of excited reactive species was confirmed by optical emission spectroscopy. Scanning electron microscopy (SEM) was applied for investigation of cell morphology. The microbicidal efficiency was evaluated by measuring the area of inhibition zone (where there was no cell growth). For different flows of helium, no significant difference of inhibition zone size was noted for the same microbial species. However, high flows led to formation of non-homogenous inhibition zones, presenting microcolonies distributed through the inactivated region. The Gram-positive bacterium was more susceptible to the plasma antimicrobial effects than the other microorganisms.
Microscopy and Microanalysis, 2015
This work evaluates the use of light microscopes (LMs) as a tool for interlaminar fracture of pol... more This work evaluates the use of light microscopes (LMs) as a tool for interlaminar fracture of polymer composite investigation with the aid of correlative fractography. Correlative fractography consists of an association of the extended depth of focus (EDF) method, based on reflected LM, with scanning electron microscopy (SEM) to evaluate interlaminar fractures. The use of these combined techniques is exemplified here for the mode I fracture of carbon–epoxy plain-weave reinforced composite. The EDF-LM is a digital image-processing method that consists of the extraction of in-focus pixels for eachx-ycoordinate in an image from a stack ofZ-ordered digital pictures from an LM, resulting in a fully focused picture and a height elevation map for each stack. SEM is the most used tool for the identification of fracture mechanisms in a qualitative approach, with the combined advantages of a large focus depth and fine lateral resolution. However, LMs, with EDF software, may bypass the restric...
O estudo das relacoes entre a zona de estiramento e a tenacidade a fratura dos materiais para uso... more O estudo das relacoes entre a zona de estiramento e a tenacidade a fratura dos materiais para uso em estruturas mecânicas tem encontrado grande interesse no meio cientifico e tecnologico. Entretanto, grandes restricoes vem sendo encontradas quanto a adocao de tecnicas para sua avaliacao, o que tem implicado em uma pequena quantidade de trabalhos sobre a geometria dessa regiao. Desta forma, este trabalho visa o desenvolvimento de um metodo para analise da superficie da zona de estiramento, baseado nos conceitos das medicoes de paralaxe e em tecnicas de processamento digital de imagens, buscando estabelecer criterios mais precisos para a definicao de seus limites naturais e estudar a evolucao de sua geometria, atraves da analise de perfis. O algoritmo para reconstrucao tridimensional foi inteiramente desenvolvido dentro do ambiente grafico do programa KHOROS, criado por pesquisadores da New Mexico University. Empregando-se tecnicas de observacao em microscopio eletronico de varredura especialmente adaptadas para este trabalho, foram fotografados pares estereoscopicos de zonas de estiramento formadas em superficies de fratura de amostras da liga AI 7050, obtidas em ensaios mecânicos para determinacao do CTOD critico, seguindo orientacoes do metodo EGF PI-87-D. Assim, foram obtidos perfis de elevacao que permitiram realizar medicoes de parâmetros como a largura e a altura da zona de estiramento, bem como estudar a evolucao de sua geometria. A zona de estiramento apresenta relevo muito acidentado, o que provoca uma dispersao natural dos resultados, apesar do emprego de uma definicao consistente para a identificacao de seus limites. Conclui-se que os perfis da regiao, desde que sob estado de deformacao plana, podem ter sua geometria media descrita pela forma de uma semi-parabola. Esses resultados levaram a concluir que a metodologia e o algoritmo desenvolvidos tem aplicacao viavel na fractografia quantitativa Abstract
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Papers by Luis Rogerio de Oliveira Hein