The research in this thesis aims to develop new mechanistic knowledge for coating processes at 2024-Al alloy surfaces, ultimately to aid the design of new protective coatings. Coatings formed by phosphating, chromating, and permanganating were characterized especially by scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy, and scanning electron microscopy . The objective was to learn about growth (nm level) as a function of time for different coating baths, as well as a function of lateral position across the different surface microstructural regions, specifically on the μm-sized Al-Cu-Mg and Al-Cu-Fe-Mn particles which are embedded in the alloy matrix . The research characterizes coating thickness, composition, and morphology. The thesis emphasizes learning about the effect of different additives in zinc phosphating baths . It was found that the Ni²⁺ additive has two main roles : first, the rate of increase in local solution pH is limited by the slower kinetics of reactions involving Ni²⁺ compared to Zn²⁺, leading to thinner zinc phosphate (ZPO) coatings when Ni²⁺ is present. Second, most Ni²⁺ deposition occurs during the later stages of the coating process in the form of nickel phosphate and a Ni-Al oxide in the coating pores on the alloy surface, increasing the corrosion resistance. Aluminum fluoride precipitates first during the initial stages of the coating process, followed by aluminum phosphate, zinc oxide, and finally ZPO. When Ni²⁺ is present in the coating solution at 2000 ppm, ZnO predominates in the coating above the A-Cu-Fe-Mn particle while ZPO dominates on the rest of the surface. The Mn²⁺ additive gives a more even coating distribution (compared with Ni²⁺) across the whole surface. The Mn²⁺ -containing ZPO coating is similar to the chromate coating in terms of evenness, while there is more coating deposition at the second-phase particles for permanganate coatings. The oxides on the Al-Cu-Fe-Mn and matrix regions are similar before coating, thereby confirming that a variety of observed differences in ZPO coating characteristics at these regions arise from the different electrochemical characteristics of the underlying metals. Upon exposure to a corrosive solution, the ZPO coating provides more protection to the second-phase particles compared to the matrix.

The research in this thesis aims to develop new mechanistic knowledge for coating processes at 2024-Al alloy surfaces, ultimately to aid the design of new protective coatings. Coatings formed by phosphating, chromating, and permanganating were characterized especially by scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy, and scanning electron microscopy . The objective was to learn about growth (nm level) as a function of time for different coating baths, as well as a function of lateral position across the different surface microstructural regions, specifically on the μm-sized Al-Cu-Mg and Al-Cu-Fe-Mn particles which are embedded in the alloy matrix . The research characterizes coating thickness, composition, and morphology. The thesis emphasizes learning about the effect of different additives in zinc phosphating baths . It was found that the Ni²⁺ additive has two main roles : first, the rate of increase in local solution pH is limited by the slower kinetics of reactions involving Ni²⁺ compared to Zn²⁺, leading to thinner zinc phosphate (ZPO) coatings when Ni²⁺ is present. Second, most Ni²⁺ deposition occurs during the later stages of the coating process in the form of nickel phosphate and a Ni-Al oxide in the coating pores on the alloy surface, increasing the corrosion resistance. Aluminum fluoride precipitates first during the initial stages of the coating process, followed by aluminum phosphate, zinc oxide, and finally ZPO. When Ni²⁺ is present in the coating solution at 2000 ppm, ZnO predominates in the coating above the A-Cu-Fe-Mn particle while ZPO dominates on the rest of the surface. The Mn²⁺ additive gives a more even coating distribution (compared with Ni²⁺) across the whole surface. The Mn²⁺ -containing ZPO coating is similar to the chromate coating in terms of evenness, while there is more coating deposition at the second-phase particles for permanganate coatings. The oxides on the Al-Cu-Fe-Mn and matrix regions are similar before coating, thereby confirming that a variety of observed differences in ZPO coating characteristics at these regions arise from the different electrochemical characteristics of the underlying metals. Upon exposure to a corrosive solution, the ZPO coating provides more protection to the second-phase particles compared to the matrix.

The research in this thesis aims to develop new mechanistic knowledge for coating processes at 2024-Al alloy surfaces, ultimately to aid the design of new protective coatings. Coatings formed by phosphating, chromating, and permanganating were characterized especially by scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy, and scanning electron microscopy . The objective was to learn about growth (nm level) as a function of time for different coating baths, as well as a function of lateral position across the different surface microstructural regions, specifically on the μm-sized Al-Cu-Mg and Al-Cu-Fe-Mn particles which are embedded in the alloy matrix . The research characterizes coating thickness, composition, and morphology. The thesis emphasizes learning about the effect of different additives in zinc phosphating baths . It was found that the Ni²⁺ additive has two main roles : first, the rate of increase in local solution pH is limited by the slower kinetics of reactions involving Ni²⁺ compared to Zn²⁺, leading to thinner zinc phosphate (ZPO) coatings when Ni²⁺ is present. Second, most Ni²⁺ deposition occurs during the later stages of the coating process in the form of nickel phosphate and a Ni-Al oxide in the coating pores on the alloy surface, increasing the corrosion resistance. Aluminum fluoride precipitates first during the initial stages of the coating process, followed by aluminum phosphate, zinc oxide, and finally ZPO. When Ni²⁺ is present in the coating solution at 2000 ppm, ZnO predominates in the coating above the A-Cu-Fe-Mn particle while ZPO dominates on the rest of the surface. The Mn²⁺ additive gives a more even coating distribution (compared with Ni²⁺) across the whole surface. The Mn²⁺ -containing ZPO coating is similar to the chromate coating in terms of evenness, while there is more coating deposition at the second-phase particles for permanganate coatings. The oxides on the Al-Cu-Fe-Mn and matrix regions are similar before coating, thereby confirming that a variety of observed differences in ZPO coating characteristics at these regions arise from the different electrochemical characteristics of the underlying metals. Upon exposure to a corrosive solution, the ZPO coating provides more protection to the second-phase particles compared to the matrix. / Science, Faculty of / Chemistry, Department of / Graduate

Camadas de fosfato tricatiônico são largamente utilizadas na indústria automotiva como proteção contra corrosão e adesão de revestimentos orgânicos ao substrato de aço. A combinação do fosfato e revestimento proporciona à superfície metálica, alta durabilidade à corrosão. Porém a camada cristalina obtida com este tipo de fosfato apresenta poros entre os cristais, expondo o substrato metálico ao ambiente corrosivo, tornando importante um tratamento de passivação após fosfatização. O tratamento comercial de fosfatização tricatiônico e subsequente passivação envolvem o uso de elementos tóxicos, tais como níquel e cromo hexavalente, produzindo resíduos que são prejudiciais ao ambiente e seu uso têm sido cada vez mais proibido. O objetivo do presente estudo é investigar o efeito da troca do níquel, no processo de fosfatização, pelo composto de nióbio (oxalato de nióbio e amônio) com relação à resistência à corrosão do aço fosfatizado. Esta investigação foi realizada através de métodos eletroquímicos, utilizando-se principalmente ensaios de polarização potenciodinâmica e técnicas de espectroscopia de impedância eletroquímica (EIE); como também ensaios de névoa salina. Para caracterização superficial das camadas de fosfato foram adotadas, entre outras, as análises por microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS) e difração de raios-X. Foram adotados dois tipos de banho de fosfato tricatiônico. Inicialmente utilizou-se uma composição de banho preparada em laboratório baseada em formulação usada por indústria de eletrodomésticos. Posteriormente foi adotado um banho com composição típica da indústria automotiva, especialmente preparado para estudos sem a presença do níquel. Os resultados dos testes eletroquímicos mostraram que a camada de fosfato obtida em solução contendo nióbio (zinco, manganês e nióbio) produziu melhor proteção contra corrosão do substrato, comparativamente àquela obtida em banho contendo níquel (zinco, manganês e níquel). O ensaio de névoa salina, por outro lado, sugeriu um desempenho similar com relação à corrosão para estes dois tipos de camadas de fosfato. O oxalato de nióbio e amônio parece apresentar um efeito de passivação mesmo quando usado em banhos de fosfatização. Mas como agente de passivação para aço carbono fosfatizado, os resultados apontaram para a necessidade de se realizar novas pesquisas. / Tricationic phosphate layers are largely used in the automotive industry for corrosion protection and coatings adhesion to the steel substrate. The combination of phosphate and coating provides to the metallic surface long life protection against corrosion. The crystalline phosphate layer however presents porosities that exposes the metallic substrate to the corrosive environment and, consequently, a passivating treatment subsequent to phosphating is advisable. The commercial treatments of tricationic phosphating and subsequent passivation involve the use of toxic elements, such as nickel and hexavalent chromium, producing residues that are harmful to the environment and their use is being increasingly prohibited. The aim of the present study is to investigate the effect of replacement of nickel in the phosphating process by a niobium compound (ammonium niobium oxalate) on the corrosion resistance of the phosphated steel. The corrosion resistance evaluation of the phosphated steel was investigated by electrochemical methods, mainly polarization tests and electrochemical impedance spectroscopy (EIS), and salt spray tests. Characterization of the phosphate layer was also carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction. Two types of tricationic phosphate baths were adopted. Initially, a laboratory prepared type based on the composition used in the electro domestic industry was utilized. Subsequently, another bath with a composition typical of the automotive industry, but specially prepared for this study with no nickel, was used. The results from electrochemical tests showed that the phosphate layer obtained in the niobium containing solution (zinc, manganese and niobium) produced better corrosion protection of the substrate comparatively to that produced in the nickel containing one (zinc, manganese and nickel). The salt spray tests, on the other hand, suggested similar corrosion performance for the samples with the two types of phosphate layers. The oxalate of niobium and ammonium seems to present a passivating effect when it is used in the phosphating bath. But to passivating effect the results pointed out to the need to carry out further research on the effect of niobium compound as a passivating agent for phosphated carbon steel.

Sendo a cana-de-açúcar uma das culturas mais importantes hoje no contexto de agroindústria, sua expansão cresce de acordo com o aumento de consumo de açúcar e etanol no Brasil e no mundo. Muitas vezes, estas expansões são realizadas em área de baixa fertilidade e/ou degradadas, tendo pouca disponibilidade de fósforo. De maneira geral, os solos no Brasil apresentam baixos teores de fósforo. A cultura da cana-de-açúcar considerada semi perene, a aplicação principal de fósforo é realizada na reforma ou implantação do canavial, como fosfatagem e/ou localizado dentro do sulco do plantio. O fósforo é crucial no metabolismo das plantas, em que as limitações na disponibilidade de P no início do ciclo vegetativo podem resultar em restrições no desenvolvimento, das quais a planta não se recupera posteriormente, mesmo aumentando o suprimento de P a níveis adequados. Com a mecanização da colheita, a produtividade passou a andar na contramão da pesquisa, reduzindo a produtividade dos canaviais mesmo com altos potenciais genéticos e técnicas avançadas para o cultivo da cana-de-açúcar. Foram surgindo novas fontes de fósforo (P) como opção para utilização na cana-de-açúcar. Neste sentido, o objetivo desse trabalho foi avaliar qual a melhor forma de aplicação de fósforo no plantio da cana-de-açúcar e o melhor resultado em diferentes fontes de fósforo, auxiliando assim em expansões na instalação do canavial em áreas com baixo teor de fósforo (P). Utilizando a variedade CTC 4, conduzimos em São João da Boa Vista/SP, o trabalho de pesquisa com 25 tratamentos, divididos em parcelas e sub parcelas, sendo as parcelas aplicação de 150 kg de P2O5 de fosfatagem em área total: Controle; MAP; FAPs P28; Super Triplo; Termofosfato; e as sub parcelas adubação de 150 kg de P2O5 no sulco: Controle, FAPs P28 100%; FAPs P28 50% + MAP 50%; FAPs P28 25% + MAP 75%; MAP 100%;. As aplicações das parcelas foram realizadas antes do preparo do solo e as aplicações das sub parcelas na sulcação do plantio. Foram realizadas avaliações de perfilhos, retirado amostra de folhas e solo aos 284 dias após plantio e na colheita , aos 13 meses após plantio, avaliando perfilho, peso de colmo, produtividade, e qualidade tecnológica. Verificou-se que o Termofosfato Magnesiano em área total obteve melhores resultados para fertilidade do solo em todos os elementos na análise de solo, análise foliar e para produtividade. Para a qualidade tecnológica, não houve diferenciação dos tipos e formas de aplicação de adubação com fósforo. Para implantação do canavial (cana planta) é essencial a aplicação de fertilizante fosfatado. / Since sugarcane is one of the most important crops pre4sent by in the context of agribusiness, its expansion grows according to the increase of consumption of sugar and ethanol in Brazil and in the world. Often, these expansions are execute in an area of low fertility and / or degraded, having less availability of phosphorus. In general, soils in Brazil have low levels of phosphorus. On sugarcane crops, considered semi-perennial, the main application of phosphorus is execute in the reforestation or implantation of the sugarcane, as phosphatic and / or located within the furrow\'s plantation. Phosphorus is crucial in plant\'s metabolism, where the limitations on the availability of P at the beginning of the vegetative cycle can result limitation in the development, from which the plant does not recover later, even increasing the P supply at appropriate levels. With the harvest\'s mechanization, the productivity started to move against the research, reducing the productivity of sugarcane\'s plantations even with high genetic potential and advanced for sugarcane\'s plantation. New sources of phosphorus (P) have been as an option for use in sugarcane. In this sense, the objective of this work was to evaluate the best way of applying phosphorus in sugarcane plantation and the best result in different sources of phosphorus, then helping in the expansion of sugarcane\'s plantation in areas with low phosphorus content (P). Using the CTC 4 variety, we conducted the research work with 25 treatments, divided into plots and subplots, in the plots of 150 kg of P2O5 in total area: Control, MAP; FAPs P28; Super Triple; Thermophosphate; and the sub plots fertilization of 150 kg of P2O5 in the furrow: Control, FAPs P28 100%; FAPs P28 50% + MAP 50%; FAPs P28 25% + MAP 75%; 100% MAP . The plots applications were executed before the soil preparation and the subplot\'s application in the furrow. Tiller evaluations were performed, leaves and soil samples were collected at 284 days after plantation and harvest, 13 months after the plantation, evaluating tiller, stem weight, productivity, and technological quality. It was verified that the Magnesian Termophosphate in total area obtained better results for soil fertility in all the elements in the soil analysis, leaf analysis and for productivity. For the technological quality, there was no differentiation of the types and forms of application of fertilization with phosphorus. For implantation of the sugarcane (cane plant) is essential the application of phosphate fertilizer.

Sendo a cana-de-açúcar uma das culturas mais importantes hoje no contexto de agroindústria, sua expansão cresce de acordo com o aumento de consumo de açúcar e etanol no Brasil e no mundo. Muitas vezes, estas expansões são realizadas em área de baixa fertilidade e/ou degradadas, tendo pouca disponibilidade de fósforo. De maneira geral, os solos no Brasil apresentam baixos teores de fósforo. A cultura da cana-de-açúcar considerada semi perene, a aplicação principal de fósforo é realizada na reforma ou implantação do canavial, como fosfatagem e/ou localizado dentro do sulco do plantio. O fósforo é crucial no metabolismo das plantas, em que as limitações na disponibilidade de P no início do ciclo vegetativo podem resultar em restrições no desenvolvimento, das quais a planta não se recupera posteriormente, mesmo aumentando o suprimento de P a níveis adequados. Com a mecanização da colheita, a produtividade passou a andar na contramão da pesquisa, reduzindo a produtividade dos canaviais mesmo com altos potenciais genéticos e técnicas avançadas para o cultivo da cana-de-açúcar. Foram surgindo novas fontes de fósforo (P) como opção para utilização na cana-de-açúcar. Neste sentido, o objetivo desse trabalho foi avaliar qual a melhor forma de aplicação de fósforo no plantio da cana-de-açúcar e o melhor resultado em diferentes fontes de fósforo, auxiliando assim em expansões na instalação do canavial em áreas com baixo teor de fósforo (P). Utilizando a variedade CTC 4, conduzimos em São João da Boa Vista/SP, o trabalho de pesquisa com 25 tratamentos, divididos em parcelas e sub parcelas, sendo as parcelas aplicação de 150 kg de P2O5 de fosfatagem em área total: Controle; MAP; FAPs P28; Super Triplo; Termofosfato; e as sub parcelas adubação de 150 kg de P2O5 no sulco: Controle, FAPs P28 100%; FAPs P28 50% + MAP 50%; FAPs P28 25% + MAP 75%; MAP 100%;. As aplicações das parcelas foram realizadas antes do preparo do solo e as aplicações das sub parcelas na sulcação do plantio. Foram realizadas avaliações de perfilhos, retirado amostra de folhas e solo aos 284 dias após plantio e na colheita , aos 13 meses após plantio, avaliando perfilho, peso de colmo, produtividade, e qualidade tecnológica. Verificou-se que o Termofosfato Magnesiano em área total obteve melhores resultados para fertilidade do solo em todos os elementos na análise de solo, análise foliar e para produtividade. Para a qualidade tecnológica, não houve diferenciação dos tipos e formas de aplicação de adubação com fósforo. Para implantação do canavial (cana planta) é essencial a aplicação de fertilizante fosfatado. / Since sugarcane is one of the most important crops pre4sent by in the context of agribusiness, its expansion grows according to the increase of consumption of sugar and ethanol in Brazil and in the world. Often, these expansions are execute in an area of low fertility and / or degraded, having less availability of phosphorus. In general, soils in Brazil have low levels of phosphorus. On sugarcane crops, considered semi-perennial, the main application of phosphorus is execute in the reforestation or implantation of the sugarcane, as phosphatic and / or located within the furrow\'s plantation. Phosphorus is crucial in plant\'s metabolism, where the limitations on the availability of P at the beginning of the vegetative cycle can result limitation in the development, from which the plant does not recover later, even increasing the P supply at appropriate levels. With the harvest\'s mechanization, the productivity started to move against the research, reducing the productivity of sugarcane\'s plantations even with high genetic potential and advanced for sugarcane\'s plantation. New sources of phosphorus (P) have been as an option for use in sugarcane. In this sense, the objective of this work was to evaluate the best way of applying phosphorus in sugarcane plantation and the best result in different sources of phosphorus, then helping in the expansion of sugarcane\'s plantation in areas with low phosphorus content (P). Using the CTC 4 variety, we conducted the research work with 25 treatments, divided into plots and subplots, in the plots of 150 kg of P2O5 in total area: Control, MAP; FAPs P28; Super Triple; Thermophosphate; and the sub plots fertilization of 150 kg of P2O5 in the furrow: Control, FAPs P28 100%; FAPs P28 50% + MAP 50%; FAPs P28 25% + MAP 75%; 100% MAP . The plots applications were executed before the soil preparation and the subplot\'s application in the furrow. Tiller evaluations were performed, leaves and soil samples were collected at 284 days after plantation and harvest, 13 months after the plantation, evaluating tiller, stem weight, productivity, and technological quality. It was verified that the Magnesian Termophosphate in total area obtained better results for soil fertility in all the elements in the soil analysis, leaf analysis and for productivity. For the technological quality, there was no differentiation of the types and forms of application of fertilization with phosphorus. For implantation of the sugarcane (cane plant) is essential the application of phosphate fertilizer.

Camadas de fosfato tricatiônico são largamente utilizadas na indústria automotiva como proteção contra corrosão e adesão de revestimentos orgânicos ao substrato de aço. A combinação do fosfato e revestimento proporciona à superfície metálica, alta durabilidade à corrosão. Porém a camada cristalina obtida com este tipo de fosfato apresenta poros entre os cristais, expondo o substrato metálico ao ambiente corrosivo, tornando importante um tratamento de passivação após fosfatização. O tratamento comercial de fosfatização tricatiônico e subsequente passivação envolvem o uso de elementos tóxicos, tais como níquel e cromo hexavalente, produzindo resíduos que são prejudiciais ao ambiente e seu uso têm sido cada vez mais proibido. O objetivo do presente estudo é investigar o efeito da troca do níquel, no processo de fosfatização, pelo composto de nióbio (oxalato de nióbio e amônio) com relação à resistência à corrosão do aço fosfatizado. Esta investigação foi realizada através de métodos eletroquímicos, utilizando-se principalmente ensaios de polarização potenciodinâmica e técnicas de espectroscopia de impedância eletroquímica (EIE); como também ensaios de névoa salina. Para caracterização superficial das camadas de fosfato foram adotadas, entre outras, as análises por microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS) e difração de raios-X. Foram adotados dois tipos de banho de fosfato tricatiônico. Inicialmente utilizou-se uma composição de banho preparada em laboratório baseada em formulação usada por indústria de eletrodomésticos. Posteriormente foi adotado um banho com composição típica da indústria automotiva, especialmente preparado para estudos sem a presença do níquel. Os resultados dos testes eletroquímicos mostraram que a camada de fosfato obtida em solução contendo nióbio (zinco, manganês e nióbio) produziu melhor proteção contra corrosão do substrato, comparativamente àquela obtida em banho contendo níquel (zinco, manganês e níquel). O ensaio de névoa salina, por outro lado, sugeriu um desempenho similar com relação à corrosão para estes dois tipos de camadas de fosfato. O oxalato de nióbio e amônio parece apresentar um efeito de passivação mesmo quando usado em banhos de fosfatização. Mas como agente de passivação para aço carbono fosfatizado, os resultados apontaram para a necessidade de se realizar novas pesquisas. / Tricationic phosphate layers are largely used in the automotive industry for corrosion protection and coatings adhesion to the steel substrate. The combination of phosphate and coating provides to the metallic surface long life protection against corrosion. The crystalline phosphate layer however presents porosities that exposes the metallic substrate to the corrosive environment and, consequently, a passivating treatment subsequent to phosphating is advisable. The commercial treatments of tricationic phosphating and subsequent passivation involve the use of toxic elements, such as nickel and hexavalent chromium, producing residues that are harmful to the environment and their use is being increasingly prohibited. The aim of the present study is to investigate the effect of replacement of nickel in the phosphating process by a niobium compound (ammonium niobium oxalate) on the corrosion resistance of the phosphated steel. The corrosion resistance evaluation of the phosphated steel was investigated by electrochemical methods, mainly polarization tests and electrochemical impedance spectroscopy (EIS), and salt spray tests. Characterization of the phosphate layer was also carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction. Two types of tricationic phosphate baths were adopted. Initially, a laboratory prepared type based on the composition used in the electro domestic industry was utilized. Subsequently, another bath with a composition typical of the automotive industry, but specially prepared for this study with no nickel, was used. The results from electrochemical tests showed that the phosphate layer obtained in the niobium containing solution (zinc, manganese and niobium) produced better corrosion protection of the substrate comparatively to that produced in the nickel containing one (zinc, manganese and nickel). The salt spray tests, on the other hand, suggested similar corrosion performance for the samples with the two types of phosphate layers. The oxalate of niobium and ammonium seems to present a passivating effect when it is used in the phosphating bath. But to passivating effect the results pointed out to the need to carry out further research on the effect of niobium compound as a passivating agent for phosphated carbon steel.

This work deals with phosphating technology of steel. In theoretical part are summarized facts about conventional phosphating process, including steel surfaces pretreatment. In the next chapter the latest contemporary technology of phosphating is discussed, i.e. electrolytic phosphating. This chapter contains principles and characteristics of this technique. Than follow comparisons of electrolytic phosphating and conventional process, concerning economical and ecological aspects. In experimental part is firstly stated nowaday situation of process analyses of phosphating bath for electrolytic phosphating. Intention of experimental part is finding of analytical technique which can be used in operating conditions of phosphating production line. Next chapter render an account of all analytical techniques – measuring of density, refractive index, conductance, reduction potential, pH, turbidity and determination of sulphate, iron and phosphate by indicator papers. Discussion of all results leads to conclusions on tested techniques in connection with practical use in operating conditions of phosphating production line and recommendations for use of individual analytical techniques.

Made available in DSpace on 2014-10-09T12:46:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:32Z (GMT). No. of bitstreams: 1 07616.pdf: 6459739 bytes, checksum: 6032bfb27763f826fa1eef8e9dacd71f (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Submitted by Maria Eneide de Souza Araujo (mearaujo@ipen.br) on 2015-02-20T18:11:07Z No. of bitstreams: 0 / Made available in DSpace on 2015-02-20T18:11:07Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP