Papers by Clodomiro Alves
Journal of Materials Research and Technology
Cutting tools, such as machining inserts, which in addition to having a complex geometry need to ... more Cutting tools, such as machining inserts, which in addition to having a complex geometry need to handle different demands on more than one face during their application, stimulate investigation for new coating techniques. Even though many hard film deposition techniques are well accepted or even established among researchers and industries, these processes still need to meet a limitation that requires the repositioning of the sample for new treatments in order to cover all of its surfaces. This paper proposes a new methodology for coating deposition on complex geometry pieces, through a structure for threedimensional plasma treatment, using a Rotary Cathodic Cage Plasma Nitriding (RCCPN). TiN films were deposited on cemented carbide inserts applied in machining processes using the RCCPN technique. The plasma parameters were kept constant and deposition time was the only variable input. The deposited films were characterized by SEM, EDS, XRD, and Vickers microhardness. It was observed that the RCCPN technique was useful in producing a uniform TiN layer in all insert surfaces, with a thickness proportional to deposition time.
Materials Chemistry and Physics, 2021
Camadas de nitretos de ferro foram depositadas sobre amostras de vidro em gaiola catodica sob con... more Camadas de nitretos de ferro foram depositadas sobre amostras de vidro em gaiola catodica sob condicoes variadas de pressao, temperatura, tempo de tratamento e razao da mistura N 2 -H 2 , com objetivo de analisar a influencia da deposicao nesta tecnica de nitretacao. Em todas as condicoes de trabalho foram depositadas uma camada de filme metalico, como evidenciado atraves das imagens de microscopia optica e MEV e tambem pela analise dos difratogramas de raios-X, confirmando a eficiencia desta tecnica que utiliza o efeito de catodo oco nos furos da gaiola para obter elevada taxa de deposicao.
The osseointegration of Ti implants is significantly affected by their surface composition and to... more The osseointegration of Ti implants is significantly affected by their surface composition and topography. Recent studies have revealed that the growth of oxide surface layers potentially improve the wettability of implants with respect to physiological fluids thereby reducing the osseointegration time. The objective of the present study was to evaluate the effect of hollow-cathode plasma oxidation parameters on the surface properties of titanium pellets, aiming at the application of this novel technology to commercially available implants. The composition and morphology of the oxide layer as well as their effect on the contact angle between substrate and a synthetic organic fluid were mainly evaluated. Titanium pellets were plasma oxidized between 400 and 500°C using the hollow cathode configuration. The partial pressure of oxygen was adjusted between 2 and 20% and the total pressure set to values ranging from 2.2 to 4.0 mbar. The results suggested that the temperature range invest...
O titânio e um dos materiais mais utilizados para a fabricacao de dispositivos biomedicos e por i... more O titânio e um dos materiais mais utilizados para a fabricacao de dispositivos biomedicos e por isso, passa por uma serie de processos termicos e/ou mecânicos que visam solucionar problemas frequentemente associadas ao processo de fabricacao. Os tratamentos termicos podem alterar de maneira significativa suas propriedades criando ou aliviando tensoes residuais no material e consequentemente alterando a resposta biologica destes. Sabe-se da literatura que o crescimento e proliferacao celular sao fortemente influenciados pelas caracteristicas da superficie a qual a cultura foi realizada. No presente trabalho, foram realizados diferentes tratamentos termicos no titânio comercialmente puro a fim de estudar sua influencia sobre o comportamento de celulas pre-osteoblasticas MC373-E1, quando cultivadas sobre a superficie dos mesmos.
Revista Tecnica De La Facultad De Ingenieria Universidad Del Zulia, 2014
La hidroxiapatita sintetica en polvo ha sido utilizada durante anos para aplicaciones ortopedicas... more La hidroxiapatita sintetica en polvo ha sido utilizada durante anos para aplicaciones ortopedicas, en forma de recubrimientos bioceramicos. En este estudio, fue utilizada una hidroxiapatita, de origen natural, obtenida mediante una reaccion hidrotermal, a partir de corales marinos porites. La hidroxiapatita fue proyectada por plasma termico atmosferico sobre titanio grado II, para explorar el efecto de la temperatura del sustrato y el modo de proyeccion en la cristalinidad, humectabilidad y biocompatibilidad del recubrimiento. La composicion de fase y cristalinidad del recubrimiento fueron determinadas por difraccion de rayos x; la humectabilidad fue medida por el metodo de la gota de contacto y la proliferacion celular fue evaluada por MTT [(bromuro de 3-(4,5-dimetiltiazol-2-il)-2,5)difenil tetrazolio]. Los resultados sugieren que los recubrimientos obtenidos con precalentamiento del sustrato, aseguran mayor cristalinidad; las superficies obtenidas con el sustrato rotando, presenta...
Este trabalho apresenta os resultados de um estudo comparativo da sinterizacao a plasma em duas c... more Este trabalho apresenta os resultados de um estudo comparativo da sinterizacao a plasma em duas configuracoes: catodo oco e catodo planar. Para tal comparacao utilizou-se os seguintes recursos: analise da porosidade e tamanhos de poros por meio de um software, ensaio de molhabilidade e microdureza a fim de definir qual configuracao de sinterizacao a plasma e mais eficiente na confeccao de biomateriais para uso em arcaboucos.
Materials Science and Engineering: C, 2020
We evaluated the effects of titanium plasma nitriding and oxidation on live endothelial cell visc... more We evaluated the effects of titanium plasma nitriding and oxidation on live endothelial cell viscoelasticity. For this, mechanically polished titanium surfaces and two surfaces treated by planar cathode discharge in nitriding (36N 2 and 24H 2) and oxidant (36O 2 and 24H 2). Surfaces were characterized regarding wettability, roughness and chemical composition. Rabbit aortic endothelial cells (RAECs) were cultured on the titanium surfaces. Cell morphology, viability and viscoelasticity were evaluated by scanning electron microscopy (SEM), methyl thiazolyl tetrazolium (MTT) assay and atomic force microscopy (AFM), respectively. Grazing Incidence X-ray Diffraction confirmed the presence of TiN 0,26 on the surface (grazing angle theta 1°) of the nitrided samples, decreasing with depth. On the oxidized surface had the formation of TiO 3 on the material surface (Theta 1°) and in the deeper layers was noted, with a marked presence of Ti (Theta 3°). Both plasma treatments increased surface roughness and they are hydrophilic (angle < 90°). However, oxidation led to a more hydrophilic titanium surface (66.59°± 3.65 vs. 76.88°± 2.68; p = 0.001) due to titanium oxide films in their stoichiometric varieties (Ti 3 O, TiO 2 , Ti 6 O), especially Ti 3 O. Despite focal adhesion on the surfaces, viability was different after 24 h, as cell viability on the oxidized surface was higher than on the nitrided surface (9.1 × 10 3 vs. 4.5 × 10 3 cells; p < 0.05). This can be explained by analyzing the viscoelastic property of the cellular cytoskeleton (nuclear and peripheral) by AFM. Surface oxidation significantly increased RAECs viscoelasticity at cell periphery, in comparison to the nucleus (2.36 ± 0.3 vs. 1.5 ± 0.4; p < 0.05), and to the RAECs periphery in contact with nitrided surfaces (1.36 ± 0.7; p < 0.05) and polished surfaces (1.55 ± 0.6; p < 0.05). Taken together, our results have shown that titanium plasma treatment directly increased cell viscoelasticity via surface oxidation, and this mechanobiological property subsequently increased biocompatibility.
Journal of Physics D: Applied Physics, 2020
Crystallization of salts in droplets of hypersaline solution placed on a glass slide was monitore... more Crystallization of salts in droplets of hypersaline solution placed on a glass slide was monitored and evaluated under controlled conditions of temperature and humidity. Pulsed corona discharge (PCD) was applied over sessil droplets on a glass surface, and its effect in the crystallization is demonstrated for the first time. These results were compared with natural evaporation. Under natural evaporation, crystals are firstly formed on surface, near edges of the drop and grow towards the center, eventually acquiring a pyramidal morphology. Under PCD, a Taylor cone is formed between electrode and droplet surface and then, 4 s after the beginning of the discharge, small crystals were formed on the cone besides a dense crystal film around the discharge incidence point in the droplet. These results are discussed considering existing knowledge about plasma–liquid interaction (PLI) and dynamical of crystal growth. This paper explores an interesting aspect of PLIs, which has both fundamenta...
Journal of Food Protection, 2019
The enzymatic oxidation process that causes black spots on shrimp, named melanosis, leads to spoi... more The enzymatic oxidation process that causes black spots on shrimp, named melanosis, leads to spoilage and economic losses. Therefore, there is an urgent need for strategies to reduce melanosis in the food industry. Cold plasma is an emerging nonthermal food processing technology. This work explores a novel application of cold plasma for the preservation of shrimp quality. This study aimed to evaluate the effects of cold plasma on the quality attributes of Pacific white shrimp (Litopenaeus vannamei). The shrimp samples were divided in two groups: the control group and the plasma group. Samples were exposed to nonthermal plasma for 10 min at a frequency of 500 Hz. Microbiological assays, including total counts of mesophilic and psychrotrophic bacteria, Staphylococcus spp., and Salmonella sp., were performed along with investigations of physicochemical parameters, such as pH, color, water-holding capacity, cooking loss, and shear force. In addition, sensory (quality index method) tests...
Artificial organs, 2018
Bacterial adhesion on three different surfaces: untreated Ti, plasma nitriding, and plasma carbon... more Bacterial adhesion on three different surfaces: untreated Ti, plasma nitriding, and plasma carbonitriding Ti substrates were investigated. The samples were placed in bacterial cultures of Pseudomonas aeruginosa to assess biofilm formation. The correlation between the amount of bacteria attached to the surface after a lapse of time with nanotopography and physicochemical properties was performed. TiN showed the highest capacity to avoid bacterial adhesion, while presenting intermediate roughness and wettability. Although the surface of TiCN had the highest surface roughness and low contact angle (high wettability), bacterial adhesion was intermediate on this sample. Untreated Ti, even though presenting a smooth surface and low wettability, had the highest tendency to form biofilms.
Industrial Crops and Products, 2015
The use of residual sisal fiber is becoming more frequent as reinforcement element in organic or ... more The use of residual sisal fiber is becoming more frequent as reinforcement element in organic or inorganic matrix due to its low cost, high abundance in some countries and constitutes a renewable material. However, a significant loss in the mechanical performance in long term has been observed in fibercement composites after natural aging. These alternative fibers can be utilized in a hybrid fiber-cement in order to decrease the content of traditionally used synthetic fibers. The objective of this work was to evaluate the potential of the methane cold plasma treatment of 10 min duration on structural and physical properties of the residual sisal fibers to mitigate the degradation mechanisms when applied to cementitious matrices. Moisture sensitivity evaluation by capacitance method, dielectric measurements, X-ray diffraction, Fourier transform infrared (FTIR), spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), angle contact and pullout test were carried out in order to follow the effect of the proposed treatment. Besides, mechanical behavior of untreated and treated sisal fibers was evaluated before and after accelerated aging in cementitious solution at 60 • C by 72 h. The results obtained in all these tests confirmed the high potential of the methane cold plasma treatment to delay the degradation of the residual sisal fibers in the presence of a Portland cement environment and these fibers present the higher pullout load and shear stress than one untreated.
Journal of Materials Processing Technology, 2017
Highly-porous titanium was produced by metal injection molding (MIM) of feedstock containing pota... more Highly-porous titanium was produced by metal injection molding (MIM) of feedstock containing potassium chloride particles as a space holder. Macroporosity was generated by dissolving the potassium chloride particles in water. Challenges for MIM of highly-porous parts include shape retention during debinding and sintering and achieving open surface porosity. This study demonstrates that plasma treatment can remedy both these effects for highly-porous titanium. Plasma treatment of unsintered MIM samples enables attaining porosities of up to 64% in combination with good dimensional accuracy. The effect of plasma treatment on the uptake of interstitial impurities, dimensional accuracy, sintered microstructure and porosity, as well as the interaction of the plasma with partially-debinded MIM samples, was investigated. Highly-porous titanium produced by MIM and plasma treatment is attractive for biomedical implants due to its low impurity content, good dimensional accuracy and shape stability in combination with enhanced open porosity, the latter contributing to bone ingrowth and implant fixation.
Encyclopedia of Iron, Steel, and Their Alloys, 2016
Artificial Organs, 2015
To evaluate the effect of topography in nanoscale, titanium surfaces were bombarded by argon ions... more To evaluate the effect of topography in nanoscale, titanium surfaces were bombarded by argon ions (a chemically inert gas), in an atmosphere of plasma. The effects of surface parameters on morphology, adhesion, proliferation, and MC3T3-E1 preosteoblasts differentiation were analyzed. Nontreated (smooth) surfaces were used as a control. The levels of average roughness (Ra) observed in bombarded and smooth titanium surfaces were of 95 and 14 nm, respectively. The wettability increased on treated surfaces. The number of attached cells (30 and 60 min) was significantly higher on the bombarded surface. The cell proliferation after 3 and 7 days was also significantly higher on the ion-bombarded surface. In addition, the ALP activity and expression of osteocalcin were higher in cells grown on the treated surface. The results showed that bombardment with argon ions increased the roughness and the wettability of the Ti surface, promoting a significant increase in the adhesion, proliferation, and differentiation of preosteoblasts.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2015
Cathodic cage plasma deposition (CCPD) was used for growing titanium nitride (TiN) and titanium d... more Cathodic cage plasma deposition (CCPD) was used for growing titanium nitride (TiN) and titanium dioxide (TiO 2) thin films on silicon substrates. The main advantages of the CCPD technique are the uniformity, tridimensionality, and high rate of the film deposition that occurs at higher pressures, lower temperatures, and lower treatment times than those used in conventional nitriding treatments. In this work, the influence of the temperature and gas atmosphere upon the characteristics of the deposited films was investigated. The TiN and TiO 2 thin films were characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy to analyze their chemical, structural, and morphological characteristics, and the combination of these results indicates that the low-cost CCPD technique can be used to produce even and highly crystalline TiN and TiO 2 films.
Applied Surface Science, 2015
Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry a... more Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry and present a good balance between the necessary physical and chemical properties and financial costs. Certain applications, such as in extreme corrosive and abrasive environments, demand improvements in the surface properties of these steels. In the present work, HP13Cr SMSS with a fully martensitic microstructure were plasma nitrided in the 350-450 • C range. The high diffusivity and low solubility of nitrogen in the martensitic structure allowed the production of thick layers (16-61 m) containing-Fe 2-3 N, ␥-Fe 4 N and expanded phase (␣ N) in all the temperatures. In addition, anisotropic sputtering rate and N-diffusion were observed for different grain orientations. Mechanical properties were measured by instrumented indentation, appropriately corrected from roughness effects on the results. Hardness profiles increased from 3.8 GPa (bulk) to ∼14 GPa (near surface region) in all the working temperatures, whereas the elastic modulus was 230 GPa, presenting no statistically significant differences with respect to the bulk value. Nanoscratch tests revealed a hardened-ductile like behavior of these nitride layers. The surface tribo-mechanical behavior was correlated with elastic-plastic responses of the precipitatecontaining texturized layers. Results are interpreted in light of the effectiveness of plasma nitriding to modify the surface properties of SMSS.
Surface and Coatings Technology, 2015
ABSTRACT The mechanical and tribological properties of martensitic AISI 420 (MSS) and supermarten... more ABSTRACT The mechanical and tribological properties of martensitic AISI 420 (MSS) and supermartensitic HP13Cr (SMSS) stainless steels plasma nitrided using the cathodic cage design were investigated. Nitride compounds were produced in the plasma from the cage´s sputtered ions, which eventually deposited on the electrically isolated sample. Prior to nitriding, samples were austenitized and oil quenched in order to attain a fully martensitc microstructure. Nitriding was carried out at different temperatures (350-450 °C) for 6 h. Mechanical properties and scratch resistance were characterized by instrumented indentation and nanoscratch, and were correlated with morphological and microstructural changes by using atomic force microscopy, scanning electron microscopy, X-ray diffraction and profilometry. Both nitrided MSS and SMSS comprised two distinct regions: (i) an outermost nitride layer (300-800 nm thick) containing deposited ε-Fe2 -3N and γ´-Fe4N nitrides and (ii) a diffusion zone composed of N-expanded martensite phase αN. At 450 °C, diffusion zones thicknesses were 4 μm (MSS) and 6 μm (SMSS). Nitride layers presented intense brittleness under normal and tangential loadings. Critical loads for nitride layer detachment were 49 mN and 127 mN for MSS and SMSS, respectively. However, after removal of the thin nitride layers, the toughened diffusion zones were revealed, being uniformly distributed through the entire sample area. Its hardness was 11 GPa. Such value corresponds to a twofold and threefold increase from the hardness of MSS and SMSS substrates, respectively, which are comparable with other plasma nitrided steels at similar temperature conditions.
Matéria (Rio de Janeiro), 2011
Superfícies de TiCxNy foram produzidas por tratamento termoquímico auxiliado por mistura de plasm... more Superfícies de TiCxNy foram produzidas por tratamento termoquímico auxiliado por mistura de plasma N2 - Ar - CH4. A influência da concentração do metano, bem como a inserção de átomos C e N na rede cristalina do Ti foram investigadas através da caracterização das propriedades tribomecânicas desse material. Para tanto, amostras de titânio comercialmente puro (grau II) foram carbonitretadas em plasma com mistura de x N2 - y Ar - z CH4 (onde x e y = 4 sccm e z variando de 2,3 e 4 sccm) a 500°C, durante 1 h. Os perfis de concentração de C e N após o tratamento foram analisados por reação nuclear (NRA). As fases na superfície foram identificadas por difração de raios-X com incidência rasante (GIXRD). Foi utilizado ensaio de pino sobre disco para determinação do coeficiente de atrito, cujas áreas desgastadas foram avaliadas por perfilometria e microscopia eletrônica de varredura (MEV). Foi observado que tanto o coeficiente de atrito quanto o mecanismo de desgaste do titânio foram fortemen...
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Papers by Clodomiro Alves