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  • Artigo IPEN-doc 27107
    Efeito de tratamentos de envelhecimento sobre a resistência à corrosão da liga de magnésio AZ91D
    2012 - PEREIRA, VIVIAM S.M.; ANTUNES, RENATO A.; OLIVEIRA, MARA C.L. de; CORREA, OLANDIR V.
    O efeito de tratamentos térmicos de envelhecimento (T6) sobre a resistência à corrosão da liga de magnésio AZ91D foi estudado. Amostras solubilizadas a 445°C por 24 h foram envelhecidas a 200 °C por tempos de 8 h, 16 h e 24 h. Todos os tratamentos foram realizados em forno mufla, sob atmosfera inerte (argônio), seguidos de resfriamento em água. Para observação das alterações microestruturais, utilizaram-se as técnicas de microscopia óptica e de MEV. O comportamento eletroquímico foi avaliado por ensaios de espectroscopia de impedância eletroquímica e de polarização potenciodinâmica, utilizando-se solução de Hanks, a 37 °C como eletrólito. O período de imersão foi de 7 dias. Com o tratamento de solubilização, ocorreu a dissolução do constituinte eutético, restando somente a matriz (fase α-Mg) saturada com alumínio, juntamente de resquícios de β- Mg17Al12. Com o tratamento de envelhecimento foram observados precipitados ricos em alumínio (β-Mg17Al12) sobre a matriz. A amostra envelhecida por 8 h foi a que mostrou menor valor de resistência à corrosão; as amostras tratadas por 16 h e 24 h apresentaram valores de impedância semelhantes, sendo que a amostra envelhecida por 16 h apresentou o melhor desempenho.
  • Artigo IPEN-doc 26995
    Coatings for safe long term wet storage of spent Al-clad research reactor fuels
    2015 - RAMANATHAN, L.V.; FERNANDES, S.M.C.; CORREA, O.V.; SOUZA, J.A. de; ANTUNES, R.A.; OLIVEIRA, M.C.L. de
    Pitting corrosion of the aluminium cladding of spent research reactor (RR) fuels in wet storage has been observed and the use of conversion coatings to protect the cladding was proposed. A coating prepared by conventional chemical processing as opposed to electrochemical processing is the only option due to constraints related to the shape of the fuel and its high radioactivity. Hence, hydrotalcite (HTC) and boehmite were considered. This paper presents: (a) preparation of hydrotalcite (HTC) coatings from different baths followed by post-coating treatments; (b) corrosion behavior of HTC coated AA 6061 alloy; (c) results of field studies in which uncoated and HTC coated AA 6061 alloy coupons and plates, the latter assembled as a dummy fuel element, were exposed to the IEA-R1 reactor spent fuel basin for extended periods. The laboratory and field tests revealed marked improvements in the corrosion resistance of HTC coated specimens, coupons and plates. The mechanism of corrosion protection is presented.
  • Artigo IPEN-doc 26954
    Estudo da influência do tamanho de grão sobre o comportamento de corrosão da liga de magnésio AZ91D
    2016 - GONÇALES, LETICIA dos R.; FERRAZ, LUCAS C. de C.; CORREA, OLANDIR V.; ANTUNES, RENATO A.
    A liga AZ91D apresenta 9%pAl e 1%pZn e pode ser submetida a tratamento térmico de solubilização seguido de envelhecimento para melhoria de propriedades mecânicas por meio de precipitação da fase beta-Mg17Al12. Esta fase, porém, pode ter efeitos distintos sobre o comportamento de corrosão da liga. Buscando estudar a influência do tamanho de grão da matriz alfa e a presença de precipitados beta sobre a resistência à corrosão da liga AZ91D, este trabalho utilizou lingotes com estrutura bruta de fusão na obtenção de amostras solubilizadas, laminadas a frio e então envelhecidas, para subsequente análise microestrutural e do comportamento de corrosão. A solubilização ocorreu a 445ºC por 24h e foi efetiva em dissolver quase completamente a fase beta. A laminação levou a uma redução de 20% da espessura das amostras e de 400 para 130 μm o tamanho de grão médio, após envelhecimento. O envelhecimento feito a 200ºC em 2 e 24h permitiu a precipitação de fase beta em maior quantidade e melhor distribuição por contornos de grão em relação às amostras fundidas ou solubilizadas. Ensaios de imersão foram realizados, apontando uma leve queda na taxa média de corrosão quando se lamina a amostra, enquanto as amostras solubilizadas (sem fase beta) mostraram maior susceptibilidade à corrosão. Assim, é possível indicar que o refinamento de grãos é benéfico ao formar uma rede de proteção em ligas de magnésio AZ91D, apesar de introduzir defeitos gerados pela laminação.
  • Artigo IPEN-doc 26899
    Propriedades das camadas termodifundidas de boro e lantânio no aço AISI 1045
    2019 - SANTAELLA, CESAR R.K.; CORREA, OLANDIR V.; COTINHO, SAMUEL P.; PILLIS, MARINA F.
    A boretação é um processo termoquímico de difusão de boro no estado sólido que tem por objetivo aumentar a resistência ao desgaste através da formação de uma camada dura de boretos de ferro na superfície do aço. As propriedades dessas camadas podem ser alteradas com a difusão combinada de boro com outros elementos químicos simultaneamente, como por exemplo o alumínio, para elevar a resistência à oxidação, ou o vanádio, para elevar a resistência ao desgaste superficial. Neste trabalho são apresentados os resultados obtidos com a difusão combinada de boro e lantânio.
  • Resumo IPEN-doc 26842
    Tribological evaluation of CoCrMo alloy for biomedical applications
    2019 - PIERETTI, EURICO F.; NEVES, MAURICIO M. das; CORREA, OLANDIR V.; ANTUNES, R.A.
    The tribological behavior of the CoCrMo alloy was evaluated in the air in a nanotribometer. The chemical composition, microstructure and mechanical properties of CoCrMo alloys makes them potential materials for use as implantable medical or dental devices [1]. This work has a specific focus on covering the possible in vitro wear modes seen on metal-on metal surfaces. Ballcratering wear test was carried out for 10 min with a solid sphere of WC as counterbody, at a frequency of 75 rpm [2]. The CoCrMo samples’ citotoxicity was analyzed in order to determine if the alloy casting process and its surface finishing, current used in industry, affects the biomaterial’s biocompatibility. All tested surfaces were prepared according to the recommendations for clinical use. The results address the potential detrimental effects of hard particles in vivo such as increased wear rates (debris generation), which is greatly influenced by the normal force, and corrosion (metal-ion release). None sample was considered cytotoxic.
  • Resumo IPEN-doc 26828
    Effect of mixed nanocrystalline rare earth oxide coatings on high temperature oxidation of a ferritic stainless steel AISI 409
    2019 - RAMANATHAN, LALGUDI V.; FERNANDES, STELA M.C.; CORREA, OLANDIR V.
    Rare earths (RE) have been used to improve the high temperature oxidation resistance of chromium dioxide and alumina forming alloys. The RE can be added to the alloy as elements or as oxide to form dispersions. It can also be applied as a RE oxide coating on the surface of the alloy. In this investigation the sol-gel technique was used to prepare sols of the RE oxides as it produces nanocrystalline oxide particles. In an effort to increase further the oxidation resistance of high temperature alloys, optimization of RE oxide additions to the alloy surface was attempted. This paper presents the effect of nanocrystalline oxide gel coatings of CeO2, Nd2O3, Pr2O3, CeO2 + Nd2O3, CeO2 + Pr2O3 and Pr2O3 + Nd2O3 on the oxidation behavior of a ferritic stainless steel AISI 409 at 1000 °C in air using a thermogravimetric balance. The morphology of the pure oxides was studied and the following formats were observed: CeO2 – rods; Nd2O3 – platelets; Pr2O3 – needles; La2O3 – cuboids. The average oxide particle sizes and the average crystallite sizes were also determined. The oxidation rate of the coated steel specimen was significantly less than that of the uncoated steel specimen, due to formation of a fine layer of chromium dioxide at the steel/oxide interface. The oxidation rates of the different REO coated steel specimens varied with the type of REO. The mixed oxide containing Pr2O3 increased significantly the oxidation resistance of the steel. The CeO2 + Nd2O3 mixture did not increase oxidation resistance of the steel further, compared to those with either one of these two rare earth oxides. The differences in the influence of a specific rare earth oxide or a mixture are attributable to differences in the ionic radii of the RE and the morphology as well as the crystallite sizes of the RE oxides.
  • Resumo IPEN-doc 26533
    Influence of the heat treatment on the photodegradation efficiency of the supported TiO2 catalysts obtained by a facile airbrush spray-coating
    2019 - BORAZANIAN, TATYANA C.F.; CORREA, OLANDIR V.; BENTO, RODRIGO T.; PILLIS, MARINA F.
    One of the main topics of thin films processing routes based on sol-gel is the need for low-cost and simple techniques [1]. Airbrush spray-coating method has been applied to coat materials, due to its cost-effective, large area and versatile characteristics [2]. However, this technique is not yet sufficiently explored for supported catalysts employed on the water treatment. In this work, titanium dioxide (TiO2) films were successfully deposited on borosilicate substrates by a facile airbrush spray-coating technique, at room temperature, from a solution of titanium (IV) isopropoxide diluted in isopropanol. The angle of the cold spray was fixed in 45°, and the feed rate was 17 mm.s-1. The coated specimens were dried at 100 °C for 60 min, and then heat treated at 300, 450 and 500 °C for 30 min to evaluate the influence of the temperature process on the methyl orange dye degradation under UV light. The catalysts obtained showed a great surface covering, highly porous surface, and good adherence to substrate. The films presented the formation of TiO2-anatase phase. Methyl orange dye degradation experimental results indicated that the TiO2 film heat treated at 500 °C presented a higher photocatalytic behavior, that exhibited 68.3 % of the dye degradation for 300 minutes under UV radiation – around 18.5 % more efficient than the supported catalysts prepared at 300 and 450 °C, with a photocatalytic efficiency of 31.6 % and 57.7 %, respectively. The study of the influence of heat treatment on the photocatalytic activity suggests the existence of an ideal temperature in which the photocatalyst exhibits the better photodegradation performance. The results suggest that the supported TiO2 catalysts deposited by the airbrush spraycoating method have a promising practical application for the green treatment of organic pollutants.
  • Resumo IPEN-doc 26532
    Effect of the thickness of TiO2 films on the photodegration of methyl orange dye
    2019 - MARCELLO, BIANCA A.; CORREA, OLANDIR V.; BENTO, RODRIGO T.; PILLIS, MARINA F.
    The increase of the disposed of azo dyes such as methyl orange (MO) by textile and allied industries in the wastewater results in a significant increase of pollutants, which requires the development of new degradation materials and techniques to purify the effluents [1]. Heterogeneous photocatalysis using titanium dioxide (TiO2) films is a highly efficient oxidative process for water treatment [2]. The TiO2 films were grown on borosilicate substrates by metalorganic chemical vapor deposition (MOCVD) at 500°C, and the growth time was controlled in order to obtain films with the thickness of 400, 600 1100 and 2100 nm. MO dye degradation was evaluated by using anatase-TiO2 as photocatalyst under UV light. The pH of the solutions was set on 2. The TiO2 films presented uniform thickness and well-defined columnar structure that grow perpendicular to the substrate surface. The increasing of the growth time increases both the thickness and the mean grain size of the films. All the films presented the formation of anatase-TiO2 crystalline phase grown preferentially oriented at (112). The results showed that the photocatalytic behavior of the films decreased with increasing the film thickness. The photocatalytic efficiency for the 400, 600, 1100 and 2100 nm films tested at pH 2 are respectively 39.2%, 30.2 %, 24.4 % and 12.2 %. When the thickness of the films augments, the mobility of the electrons is impaired due to the increase of the film opacity, which limits the light penetration through the catalyst, and difficults the diffusion of charge carriers required to activate the semiconductor surface. TiO2 catalysts grown by MOCVD technique is a practical promising application for the water treatment.
  • Resumo IPEN-doc 26552
    Synthesis and characterization of reduced graphene oxide-modified anatase TiO2 photocatalysts grown by MOCVD
    2019 - BENTO, RODRIGO T.; SILVA FILHO, JORGE C.; CORREA, OLANDIR V.; TAKIISHI, HIDETOSHI; PILLIS, MARINA F.
    Inadequate disposal of industrial waste, such as textile dyes and emerging contaminants, have been caused several environmental hazards. Titanium dioxide (TiO2) photocatalysis is an efficient green method for water treatment by solar energy. However, due to its large band gap of 3.2 eV, TiO2 absorbs mostly the UV radiation, which represents only 5-8% of the sunlight spectrum. Recent studies indicate that the surface modification of TiO2 results in an increase in photocatalytic efficiency. In this way, the present paper aims to evaluate the effects of TiO2 surface modification by reduced graphene oxide (rGO). The 470 nm thick anatase-TiO2 films were grown by MOCVD process in a conventional horizontal homemade reactor, on borosilicate substrates at 400 °C. The TiO2 films obtained were dipped into an alkoxide solution including 0.5, 1.5 and 3.0 mg of rGO and 30 mL isopropanol, ultrasonic-treated at room temperature for 40 min, and then dried in an oven at 100 and 150 °C for 24 h. The photocatalytic activity of rGO-TiO2 composites were evaluated by the methylene blue degradation under UV and visible light. The chemical, structural and morphological properties were also characterized. It was observed the presence of rGO agglomerates completely adhered to TiO2 surface. The diffraction peaks identified correspond to anatase phase. Peaks of graphene were also found. The results suggest that the rGO-TiO2 composites have a great potential to be used in water treatment under sunlight.
  • Resumo IPEN-doc 26538
    Performance of nitrogen-doped TiO2 films grown by MOCVD for water treatment under visible light
    2019 - OLIVEIRA, EDUARDO C. de; BENTO, RODRIGO T.; CORREA, OLANDIR V.; PILLIS, MARINA F.
    Titanium dioxide is a semiconductor employed as catalyst in the photodegradation of organic pollutants and bacteria. However, due to its large band gap TiO2 only can be excited by UV light. Recently, TiO2 doping with metals or nonmetals elements has been extensively exploited to allow its use under visible light. In the present work, nitrogen-doped and undoped TiO2 films were grown on borosilicate substrates at 400 ° C for 60 minutes by metallorganic chemical vapor deposition (MOCVD). Titanium isopropoxide IV was used as precursor of titanium and oxygen, and ammonia as nitrogen source. Ammonia was incorporated into the films in three different quantities during the growth. The effect of nitrogen contents on the structural and surface properties of TiO2 catalysts was evaluated. Both doped and undoped films presented rounded well-defined anatase grains. XPS analyses revealed that values of 1.6; 2.4 and 7.3 at% of nitrogen were incorporated into the films by varying the ammonia flux during the growth. Degradation assays have shown that nitrogen-doped TiO2 films exhibited high photocatalytic activity under visible light irradiation. Undoped films did not present activity in this condition. The better catalytic performance under visible light, 55% of dye degradation, was attributed to the film containing 2.4 at% of nitrogen. The results suggest that nitrogen-doped TiO2 catalysts grown by MOCVD have great potential to be used in the treatment of water under sunlight.