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  • Artigo IPEN-doc 28071
    Structural characterization, global and local electrochemical activity of electroless Ni–P-multiwalled carbon nanotube composite coatings on pipeline steel
    2021 - 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 26509
    Structural, adhesion and electrochemical characterization of electroless plated Ni-P-carbon black composite films on API 5L X80 steel
    2019 - 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-carbon black coatings were obtained by electroless deposition on API 5L X80 substrates. The effect of carbon black on structural, adhesion and electrochemical properties of the plated samples was evaluated. Scanning electron microscopy analyses were carried out to examine the top surface and cross section of the films. Scratch tests were employed to evaluate coating adhesion properties. Potentiodynamic polarization tests were carried out to investigate the global electrochemical behavior of the deposited layers. Scanning electrochemical microscopy (SECM) was employed to measure local electrochemical activity over the coated surfaces. The carbon black concentration markedly affects the morphology, adhesion and electrochemical properties of the Ni-P-carbon black layers. The results point to an optimum carbon black content to achieve the best performance against corrosion. The coatings obtained at a carbon black concentration of 0.25 g L21 provided the best protection ability. The results are discussed with respect to coating morphology, adhesion and electrochemical activity.
  • Resumo IPEN-doc 25348
    Effect of processing parameters on hydrotalcite (HTC) coating microstructure and the corrosion behavior of HTC coated AA 6061 alloy
    2018 - RAMANATHAN, L.V.; FERNANDES, S.C.; CORREA, O.V.; SOUZA, J.A.B.; ANTUNES, R.A.; LIMA, N.B.
    Pitting corrosion of the aluminium cladding of spent nuclear fuels stored in light water pools has been observed. To prevent this, coating of the Al cladding with hydrotalcite (HTC) was proposed. This paper presents the effect of various processing parameters on HTC microstructure and the corrosion behavior of HTC coated AA 6061 specimens. The HTC coating from the high temperature nitrate bath was homogeneous, thicker and consisted of well-defined intersecting platelets than that formed from the room temperature carbonate bath. Electrochemical polarization measurements as well as long term exposure to aggressive aqueous media of HTC coated AA 6061 specimens revealed that specimens coated with HTC from the nitrate bath and further treated in a cerium salt solution were the most resistant to corrosion. The mechanism by which the HTC coating and cerium protect the Al alloy is discussed.
  • Artigo IPEN-doc 24819
    Influence of the tungsten content on surface properties of electroless Ni-W-P coatings
    2018 - OLIVEIRA, MARA C.L. de; CORREA, OLANDIR V.; ETT, BARDIA; SAYEG, ISAAC J.; LIMA, NELSON B. de; ANTUNES, RENATO A.
    Ternary Ni-W-P films were produced by electroless deposition using baths with different tungsten concentrations. After deposition, the coated surfaces were annealed at 400°C for 1h. Surface morphology and film composition in the as-plated condition were assessed by SEM and EDS analyses, respectively. The crystalline phases after annealing were investigated by X-ray diffraction (XRD). Nanoindentation tests were performed to assess the mechanical properties of the deposited films. Surface roughness was determined by confocal laser scanning microscopy (CLSM). Friction coefficient was evaluated by reciprocating were tests in a nanotribometer. The corrosion behavior was evaluated by potentiodynamic polarization curves. The results showed that the surface morphology, crystallization behavior and corrosion resistance were affected by the tungsten content in the film. The best corrosion performance was obtained for the ternary films after annealing. Hardness, surface roughness and friction coefficient were dependent of the tungsten concentration in the film.
  • Artigo IPEN-doc 23968
    Structural and thermodynamic properties of nanocrystalline Cr3C2-25(Ni20Cr) composite powders produced by high-energy ball milling
    2016 - CUNHA, CECILIO A.; CORREA, OLANDIR V.; SAYEG, ISSAC J.; LIMA, NELSON B.; RAMANATHAN, LALGUDI V.
    Nanostructured coatings have been used to protect components exposed to severe service conditions. High energy milling is widely used to produce nanocrystalline feedstock of coating materials such as chromium carbide and tungsten carbide. This paper presents the structural and thermodynamic properties of Cr3C2-25(Ni20Cr) powders that were high energy milled for different times. During the high energy milling of Cr3C2-25(Ni20Cr) powder, severe plastic deformation takes place. A small part of the energy spent in this process is stored in the crystal lattice as deformation energy. The crystallite size and microstrain in nanocrystalline Cr3C2-25(Ni20Cr) powders milled for different times were determined by X-ray diffraction measurements. Differential scanning calorimetric (DSC) studies of the milled powders revealed a broad transformation, characteristic of a large exothermic reaction in the nanostructured powder. The enthalpy variation measured by DSC permitted determination of the deformation energy stored in the Cr3C2-25(Ni20Cr) powders milled for different times. These measurements also enabled calculation of the specific heat variation of the milled powders.
  • Artigo IPEN-doc 23608
    Preparation and characterization of hydrotalcite coatings to protect aluminium alloys
    2016 - FERNANDES, S.M.C.; CORREA, O.V.; SOUZA, J.A.; ANTUNES, R.A.; LIMA, N.B. de; RAMANATHAN, L.V.
    Pitting corrosion of the aluminium alloy cladding of spent research reactor fuels during wet storage is the main form of degradation. To prevent this, hydrotalcite (HTC) based coatings were proposed. This paper presents the effect of chemical bath parameters on the microstructure of HTC coatings and the corrosion behavior of HTC coated AA 6061 specimens. The HTC coating formed at 98 °C from nitrate baths and referred to as HT-HTC was homogeneous and consisted of intersecting blade-like crystallites. Electrochemical tests revealed that HT-HTC coated specimens that were treated in a cerium salt solution were the most resistant to corrosion. Field tests in which un-coated and HTC coated AA 6061 alloy coupons as well as full-size plates were exposed to the IEA-R1 reactor’s spent fuel basin for 23 months corroborated the high corrosion resistance imparted by the HT-HTC + Ce coating. The mechanism by which the HTC coating and cerium protect the Al alloy is discussed.
  • Artigo IPEN-doc 22600
    Development of electrodeposited Fe-Cr-P amorphous metallic alloys
    1999 - KUNIOSHI, C.T.; CORREA, O.V.; LIMA, N.B. de; RAMANATHAN, L.V.
  • Artigo IPEN-doc 21711
    Effect of processing on microstructure and corrosion mitigating properties of hydrotalcite coatings on AA 6061 alloy
    2015 - FERNANDES, STELA M. de C.; CORREA, OLANDIR V.; SOUZA, JOSE A.B. de; ANTUNES, RENATO A.; LIMA, NELSON B. de; RAMANATHAN, LALGUDI V.
  • Artigo IPEN-doc 21603
    Efeito da temperatura de recozimento sobre a resistência à corrosão de revestimentos de Ni-W-P obtidos por deposição química
    2015 - CORREA, OLANDIR V.; LIMA, NELSON B. de; ETT, BARDIA; OLIVEIRA, MARA C.L. de; ANTUNES, RENATO A.
  • Resumo IPEN-doc 20357
    Síntese e caracterização de hidroxiapatita dopada com európio: influência do tamanho médio do cristalito da HA na emissão e no sítio de ocupação da Eu3+
    2014 - SILVA, FLAVIA R.O.; GOUVEIA, DEIBY S.; LIMA, NELSON B.; FERREIRA, NILDEMAR A.M.; USSUI, VALTER; SILVA, ANTONIO A.; CORREA, OLANDIR V.; COURROL, LILIA C.; BRESSIANI, ANA H.A.