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Search Results: 1 - 10 of 53398 matches for " Roberto Z. Nakazato "
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Electrochemical Behavior and Corrosion Study of Electrodeposits of Zn and Zn-Fe-Co on Steel  [PDF]
Concei??o A. M. Dutra, Eduardo N. Codaro, Roberto Z. Nakazato
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.36050
Abstract: From industrialized baths, free of cyanide, the corrosion behavior of electrodeposits of zinc and zinc alloys was studied by means of electrochemical tests in aerated solution of 3.5% (0.6 M) NaCl at pH 8.2. In literature, several studies are found about zinc coatings and zinc alloys, for example, Zn-Ni and Zn-Co, nevertheless there is little about the ternary alloy Zn-Fe-Co. The Fe presence in the alloy results in a good adhesion to the substrate and allows application of these materials at higher temperatures. The electrochemical tests were carried out by obtaining open circuit potential curves with immersion time, potentiodynamic polarization curves and cyclic voltammetry. From the obtained results, the large potential differences observed between the steel and the electrodeposits showed that the last protect the substrate, acting as a sacrifice metal. The tests disclosed similar behaviors in both the current densities and the corrosion potential for electrodeposits of Zn and Zn-Fe-Co. After chromate passivation process, a significant decrease in corrosion density was noted for Zn and when the system was de-aerated there was change in the cathodic process mechanism.
Corrosion Resistance of Zn and Zn-Ni Electrodeposits: Morphological Characterization and Phases Identification  [PDF]
Concei??o A. M. Dutra, José W. J. Silva, Roberto Z. Nakazato
Materials Sciences and Applications (MSA) , 2013, DOI: 10.4236/msa.2013.410079

Zinc alloys coatings formed with elements of group VIIIB are promising because they display similar properties and protect steel by galvanic action. The Zn-Ni alloy is remarkable by showing improved mechanical properties and better corrosion resistance when compared to zinc coatings of similar thickness, also can be applied at higher temperatures. In this work, electrodeposits of Zn, Zn-12%Ni, obtained upon SAE 1010 steel from commercial alkali baths, were treated by blue chromatization and characterized according to mechanical properties and morphology. Studies were carried out by using measures of hardness, roughness, SEM, EDS and XRD. Among the studied electrodeposits, alloys treated by chromatization showed higher corrosion resistance and Zn-Ni electrodeposits showed higher value of roughness and hardness, while zinc coating had results similar to the steel substrate By means of XRD, it was found that electrodeposits are crystalline, being identified in Zn-Ni alloy the presence of the phases g(Ni5Zn21) and d(Ni3Zn22), which are responsible for its higher corrosion resistance.

Electrochemical and Microstructural Study of Ni-Cr-Mo Alloys Used in Dental Prostheses  [PDF]
José W. J. Silva, Lucíola L. Sousa, Roberto Z. Nakazato, Eduardo N. Codaro, Hamilton de Felipe
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.21006
Abstract: Ni-Cr-Mo alloys have been widely used as fixed dental prostheses. Recast process influence on corrosion behavior of Ni-Cr-Mo dental alloy in simulated physiological serum has been investigated using chemical and electrochemical techniques. Ni-Cr-Mo alloy recast by induction (induction) or by blowtorch (torch) has exhibited similar dendritic structures with wide and precipitate grains in their boundaries. The torch alloy has presented good corrosion resistance in physiological serum. Passivation process provides this corrosion resistance. Passivation of Ni-Cr-Mo alloy is often attributed to the formation of a thin and compact layer of chromium oxide (Cr2O3). This film is self-limiting because it acts as a barrier to the oxygen transport and metal ions. This film stability will depend on its solubility to the working temperature. Different recast procedures change electrochemical parameters as stabilizing potential in open circuit, current density and passivation interval.
Influence of Ni and Cr Content on Corrosion Resistance of Ni-Cr-Mo Alloys for Fixed Dental Prostheses in 0.05% NaF Aqueous Solution  [PDF]
Nilo A. S. Sampaio, José W. J. Silva, Heloisa A. Acciari, Roberto Z. Nakazato, Eduardo N. Codaro, Hamilton de Felipe
Materials Sciences and Applications (MSA) , 2010, DOI: 10.4236/msa.2010.16053
Abstract: The Ni-Cr-Mo alloys have been used as dental prostheses because they own a good mechanical strength, high corrosion resistance and even to be economically viable. These alloys corrosion protection against in salt solutions typical of physiological media is due to passivation phenomenon with an oxide surface layer formation, mainly chromium oxides. This protective film, subjected to a mechanical stress in a corrosive environment, can partially dissolve by releasing ions, which have deleterious effects in a human body. Fluoride ions, existing in hygiene products, change the buccal environment and their presence may enable a localized corrosion process initiation. The aim of this work has been to investigate the chemical composition influence of three alloys in corrosion resistance to: A (Ni-73% Cr-14% Mo-8.5% Be-1.8% Al-1.8%), B (Ni-61% Cr-25% Mo-10.5% Si-1.5%) and C (Ni-65% Cr-22.5% Mo-9.5%) in media containing fluorides that simulate mouthwashes solution. The study has been done in a 0.05% NaF solution, pH 6, at 37°C using electrochemical techniques. The alloy with the highest nickel and the lowest chromium content is not passive in the middle studied, showing a continuous increase in current density with the potential increasing, while the other alloys show passivation range of 600 mV and passive current density of about 10-6 A/cm2.
Formation of TiO2 Nanotube Layer by Anodization of Titanium in Ethylene Glycol-H2O Electrolyte  [PDF]
Alain Robin, Michele Bernardes de Almeida Ribeiro, Jorge Luiz Rosa, Roberto Zenhei Nakazato, Messias Borges Silva
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2014, DOI: 10.4236/jsemat.2014.43016

In orthopaedics and orthodontics, the growth of nanotubes of titanium oxide on titanium implants is a promising route for improving the osseointegration. Among the fabrication routes to produce nanotubes, anodization was generally preferred due to its simplicity and low cost. TiO2 nanotubes are formed by the simultaneous anodic reaction and chemical dissolution due to the fluoride species present in the anodization bath. In this work, the formation of TiO2 nanotubes was studied in stirred ethylene glycol-H2O electrolyte (90 - 10 v/v) containing NH4F at room temperature. In order to study the effect of NH4F concentration, voltage and anodization time, and to reduce the number of experiments, a design of experiments (DOE) based on a 2k factorial design with four replicates at the center point was used. The analysis of variance (ANOVA) was used to evaluate the effects of the factors of control and their interactions on the percentage of the titanium surface coated by nanotubes. The dimensions of nanotubes (length and diameter) were also evaluated using field emission gun scanning electron microscopy. The cristallinity and phase composition of the oxide layers was investigated by X-ray diffractometry. The electrochemical behavior of as-received and anodized titanium specimens was studied in Ringer’s solution. The statistical analysis showed that fluoride concentration is the most significant factor. The best condition according to the response surface analysis is the center point (1% NH4F, 20 V, 2 h). The nanotubular oxide layers presented an amorphous structure. Electrochemical tests showed that TiO2 nanotubes coated titanium is less corrosion resistant than

Corrosion resistance enhancement of SAE 1020 steel after Chromium implantation by nitrogen ion recoil
Gomes, Geraldo Francisco;Ueda, Mario;Beloto, Antonio Fernando;Nakazato, Roberto Zenhei;Reuther, Helfried;
Materials Research , 2005, DOI: 10.1590/S1516-14392005000400005
Abstract: sae 1020 construction steel is widely used as mortar reinforcement and small machine parts, but aside good surface properties as high ductility, hardness and wear resistance, its surface is prone to severe corrosion. as it is known, chromium in amount over 12%-13% in the fe alloys renders them resistance to several corrosive attacks. sae 1020 samples were recovered with chromium film and then bombarded either by nitrogen ion beam (ib) or plasma immersion ion implantation (piii) to recoil implant cr atoms in the fe matrix. samples treated by 100 kev n+ ib showed irregular, thin cr profile, remaining a part of the film on the surface, to about 10 nm. samples treated by 40 kv n piii presented cr layer of about 18% at., ranging to around 90 nm. cr of the film was implanted in the fe matrix in an almost flat profile. results of corrosion test showed good performance of the piii treated sample. the ib treated sample showed some enhancement over the non-treated reference and the only cr film deposited sample showed no modification on the corrosion behavior as compared to the non-treated reference sample.
Estudo Microestrutural e Eletroquímico de Ligas Ni-Cr-Mo Usadas em Próteses Dentárias Depois de Diferentes Processos de Refundi??o
Sousa,Lucíola Lucena de; Felipe,Hamilton de; Codaro,Eduardo Norberto; Nakazato,Roberto Zenhei;
Corros?o e Protec??o de Materiais , 2010,
Abstract: ni-cr-mo alloys are widely used as fixed dental prostheses, and different procedures for remelting are used which can change the mechanical properties and corrosion resistance. the main aim of this study was to analyze the electrochemical behavior, microstructures and hardness of two remelted alloys by the open flame process (oxy-glp torch) and by induction in high frequency furnace. metallography analysis showed dendritic structures with large grains and precipitates in their contours. alloys recast by induction displayed a lower corrosion resistance in physiologic serum, at 37 °c and higher hardness values.
Dutra,C. A. M; Pereira,M. C; Codaro,E. N; Nakazato,R. Z;
Revista Latinoamericana de Metalurgia y Materiales , 2002,
Abstract: neste trabalho se caracterizou o comportamento eletroquímico da liga de alumínio 2024-t351 em solu??o de nacl 5%(m/m) ph=6,0. o estudo morfológico e microestrutural da liga permitiram uma melhor interpreta??o da resistência à corros?o em meios aquosos contendo cloretos. em meio aerado, a velocidade de corros?o está determinada pela difus?o de oxigênio através da solu??o para os sítios catódicos. estes sítios podem ser partículas intermetálicas que constituem melhores cátodos para a redu??o de oxigênio que os óxidos e/ou hidróxidos formados sobre a superfície da liga. em meio desaerado, a etapa determinante da velocidade é o processo de dissolu??o do filme, o qual pode ser considerado como soma de processos de dissolu??o localizada.
C. A. M Dutra,M. C Pereira,E. N Codaro,R. Z Nakazato
Revista Latinoamericana de Metalurgia y Materiales , 2002,
Abstract: Neste trabalho se caracterizou o comportamento eletroquímico da liga de alumínio 2024-T351 em solu o de NaCl 5%(m/m) pH=6,0. O estudo morfológico e microestrutural da liga permitiram uma melhor interpreta o da resistência à corros o em meios aquosos contendo cloretos. Em meio aerado, a velocidade de corros o está determinada pela difus o de oxigênio através da solu o para os sítios catódicos. Estes sítios podem ser partículas intermetálicas que constituem melhores cátodos para a redu o de oxigênio que os óxidos e/ou hidróxidos formados sobre a superfície da liga. Em meio desaerado, a etapa determinante da velocidade é o processo de dissolu o do filme, o qual pode ser considerado como soma de processos de dissolu o localizada. En este trabajo se caracterizó el comportamiento electroquímico de la aleación de alumínio 2024-T351 en solución de NaCl 5%(p/p) pH=6,0. El estudio morfológico y microestructural de la aleación permitió una mejor interpretación de la resistencia a la corrosión en medios acuosos que contienen cloretos. En medio aerado, la velocidad de corrosión está determinada por la difusión de oxígeno através de la solución hacia los sítios catódicos. Estos sítios pueden ser partículas intermetálicas que constituyem mejores cátodos para la redución de oxígeno que los óxidos y/o hidróxidos formados sobre la superfície de la aleación. En medio desaerado, la etapa determinante de la velocidad es el proceso de disolución de la película, el cual puede ser considerado como suma de procesos de disolución localizada.
An Integrated ISFET Sensor Array
Kazuo Nakazato
Sensors , 2009, DOI: 10.3390/s91108831
Abstract: A monolithically integrated ISFET sensor array and interface circuit are described. A new high-density, low-power source-drain follower was developed for the sensor array. ISFETs were formed by depositing Au/Ti extended-gate electrodes on standard MOSFETs, then thin silicon nitride layers using catalytic chemical vapor deposition and/or SU-8 protective layers were formed on the extended-gate electrodes. Applications for the array include: (1) pH detection by statistical distribution observing time and space fluctuations; (2) DNA detection using thiol-modified or silane-coupled oligonucleotides; (3) bio-image sensing by converting photons to electrons using Photosystem I of Thermosynechococcus elongatus, and sensing the converted electric charges by ISFETs.
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