OLANDIR VERCINO CORREA
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Artigo IPEN-doc 28904 Enhancement of the RE-boronizing process through the use of La, Nd, Sm, and Gd compounds2021 - SANTAELLA, CESAR R.K.; COTINHO, SAMUEL P.; CORREA, OLANDIR V.; PILLIS, MARINA F.Rare-earth elements have been used in the thermochemical treatment of boronizing to enhance boron diffusion. In order to further investigate the effect of these elements on the process, neodymium-, samarium-, and gadolinium were utilized for the treatment of AISI 1045 samples carried out at the temperature of 1173 K for 4 h. The resulting boride layers formed were characterized through optical microscopy, microhardness test, and X-ray diffraction (XRD). The comparison of the layers showed that the addition of neodymium increased the depth by 48%, with samarium by 54%, and with gadolinium by 76%.Artigo IPEN-doc 28127 Surface properties enhancement by sulfur-doping TiO2 films2021 - BENTO, RODRIGO T.; CORREA, OLANDIR V.; ANTUNES, RENATO A.; PILLIS, MARINA F.TiO2 films were sulfur-doped through an alternative route based on the decomposition of H2S at low temperatures. MOCVD technique was used to grown the films on borosilicate glass substrates at 400 °C. The doping was carried out at 50, 100 and 150 °C under a mixture of H2-2%v.H2S. SO42− groups were observed in the surface revealing the substitution of Ti4+ by S6+. Superficial roughness and wettability were also modified by the formation of these sulfate groups on the surface. Photocatalytic experiments of methyl-orange dye decolorization under visible light indicated that the 8 at.% S-TiO2 film exhibited the highest photocatalytic activity, with 72.1% of dye decolorization. The results suggest that the exposition of TiO2 films to the mixture H2-H2S at low temperatures is an efficient method of doping. These films allow the decolorization of the dye under visible light irradiation, which enable its practical use under sunlight or even indoor.Artigo IPEN-doc 28071 Structural characterization, global and local electrochemical activity of electroless Ni–P-multiwalled carbon nanotube composite coatings on pipeline steel2021 - OLIVEIRA, MARA C.L. de; CORREA, OLANDIR V.; SILVA, REJANE M.P. da; LIMA, NELSON B. de; OLIVEIRA, JEFFERSON T.D. de; OLIVEIRA, LEANDRO A. de; ANTUNES, RENATO A.In this work, composite Ni–P-multiwalled carbon nanotube films were produced by electroless deposition. The main goal was to investigate the influence of multiwalled carbon nanotube loading on the local electrochemical behavior of the composite films, as probed by scanning electrochemical microscopy (SECM). The coatings were also characterized with respect to their crystalline structure, surface, and cross-section morphologies. Adhesion strength was examined by scratch tests. The global electrochemical behavior was evaluated by potentiodynamic polarization. The local electrochemical activity was investigated by probing the Fe2+ oxidation in the surface generation/tip collection mode of the SECM. The results revealed that multiwalled carbon nanotubes increased the adhesion strength and reduced the electrochemical activity on the surface of the coated samples.Artigo IPEN-doc 27737 On the surface chemistry and the reuse of sulfur-doped TiO2 films as photocatalysts2021 - BENTO, RODRIGO T.; CORREA, OLANDIR V.; PILLIS, MARINA F.The surface chemistry and recyclability of sulfur-doped titanium dioxide (TiO2) films was evaluated. The photocatalysts were grown by metalorganic chemical vapor deposition (MOCVD) at 400 ◦C. The films were sulfur-doped at 50 ◦C by using hydrogen sulfide (H2S) as sulfur source. The photocatalytic behavior of the films was measure by monitoring the methyl orange dye decolorization under visible light for several cycles. The films are formed only for the anatase crystalline phase. The results demonstrated that no structural modifications or significant differences in the morphology of the films occurred after their use. The sulfur-doped TiO2 films presented good photocatalytic activity, with an efficiency of 72.1% under visible light in its first use. The durability experiments suggest that even with the dye impregnation on the catalyst surface, the photocatalytic activity of the S-doped TiO2 films remained around 70% in the first 3 cycles, which allows their practical application for water treatment and purification under sunlight.Artigo IPEN-doc 27557 Visible-light photocatalytic activity and recyclability of N-doped TiO2 films grown by MOCVD2020 - OLIVEIRA, E.C. de; BENTO, R.T.; CORREA, O.V.; PILLIS, M.F.Nitrogen-doped TiO2 films were grown on borosilicate glass substrates at 400 °C by the metallorganic chemical vapor deposition (MOCVD) for removing dye from water under visible light. The effect of N-doping on the structural, surface, and photocatalytic properties of films was evaluated. X-ray photoelectron spectroscopy (XPS) analyses revealed that 1.56 and 2.44 at% of nitrogen were incorporated into the films by varying the NH3 flux during the growth. Methyl orange dye degradation experiments showed that the N-doped films presented photoactivity under visible light. The film containing 2.44 at% of nitrogen exhibited the best photocatalytic behavior, with 55% of efficiency. Recyclability tests under visible light showed that the film efficiency dropped gradually after each test. N-TiO2 films grown by MOCVD have the potential to be used in environmental applications by removing pollutants using a green method under sunlight or even under internal illumination, although its reuse is limited.Artigo IPEN-doc 27389 Surface chemistry and semiconducting properties of passive film and corrosion resistance of annealed surgical stainless steel2020 - OLIVEIRA, RODRIGO K. de; CORREA, OLANDIR V.; OLIVEIRA, MARA C.L. de; ANTUNES, RENATO A.ASTM F-139 surgical stainless steel was subjected to annealing treatments at 700 °C for different times. The effect of annealing on the chemical composition of the passive film was evaluated by x-ray photoelectron spectroscopy. The correlation of the surface chemistry with the corrosion behavior and semiconducting properties of the passive film was also investigated. Potentiodynamic polarization tests were conducted in phosphate-buffered solution at 37°C. The semiconducting character of the passive film was assessed by the Mott–Schottky approach. The microstructure of the annealed samples was characterized by optical microscopy. The grain size increased after annealing, but the differences between each annealing condition were not significant and could not be associated with the corrosion behavior of the annealed samples. The corrosion resistance was improved depending on the heat treatment condition due to compositional changes of the passive film upon annealing. The best corrosion properties were observed after annealing for 8 h which was ascribed to Cr2O3, MoO3 and FeO enrichment in the passive film.Artigo IPEN-doc 27162 Effect of growth parameters on the photocatalytic performance of TiO2 films prepared by MOCVD2020 - MARCELLO, BIANCA A.; CORREA, OLANDIR V.; BENTO, RODRIGO T.; PILLIS, MARINA F.The present study evaluated the main factors that influence the photocatalytic activity of titanium dioxide (TiO2) films grown by metalorganic chemical vapor deposition (MOCVD) at 400 and 500 °C, in different growth times. The photocatalytic behavior was analyzed by measuring the methyl orange dye degradation at different pH values. Structural and morphological characteristics, and the recyclability of the catalysts for several cycles were also investigated. Anatase phase was identified in all films. The higher photodegradation performances were obtained at acidic pH. The results demonstrated that the photocatalyst thickness is an important parameter in heterogenous photocatalysis. The best photocatalytic result occurred for the 395 nm-thick TiO2 film grown at 400 °C, which presented 65.3% of the dye degradation under UV light. The recyclability experiments demonstrated that the TiO2 films grown by MOCVD present a great stability after several photocatalytic cycles, which allows their practical application for water treatment with high efficiency.