Inicialmente, é feita uma revisão bibliográfica dos principais métodos de obtenção de vanádio metálico, comparando-se os resultados obtidos com os diversos redutores empregados. Também os métodos de purificação usualmente empregados são revistos, e mostra-se a eficácia de alguns deles. A seguir, analisa-se o processo aluminotérmico de obtenção de vanádio metálico a partir de pentóxido de vanádio, compreendendo estudos termodinâmicos, cinéticos e de transporte de calor. É mostrada a influência de diversas variáveis sobre a recuperação do metal. Desenvolve-se na parte experimental o estudo sobre a aluminotermia de pentóxido de vanádio, utilizando-se para isto reatores abertos revestidos com argamassa refratária. Estuda-se a influência das variáveis de processo sobre a recuperação de vanádio, incluindo a adição de fluxantes, a granulometria dos reagentes, o tamanho da carga, a pureza dos reagentes, o uso de excesso de redutor e o modo de ignição da carga. Os resultados experimentais obtidos são apresentados e discutidos. O trabalho apresenta conclusões e sugestões para pesquisas futuras. / A literature survey on the processes of vanadium reduction was carried out having in mind the behavior of the reducing agents used. The refining methods for crude metallic vanadium were also covered in the review. The aluminothermic process for the reduction of vanadium pentoxide was particularly considered. Its thermochemistry features were studied, as well as the heat transfer and the rate phenomena concerning such a reaction system discussed. It was pointed out the effect of the processes parameters on the recovery of metallic vanadium. The experiments were designed to investigate the effects of the harge composition, the purity level of the reactants, the size of the solid particles of the reacting mixture and the ignition method on the recovery of vanadium. The aluminothermic reaction was carried out in an open reaction vessel. The experimental results are presented and discussed. The research work done has reached conclusive trends which allows the proposal for further interesting research.

Inicialmente, é feita uma revisão bibliográfica dos principais métodos de obtenção de vanádio metálico, comparando-se os resultados obtidos com os diversos redutores empregados. Também os métodos de purificação usualmente empregados são revistos, e mostra-se a eficácia de alguns deles. A seguir, analisa-se o processo aluminotérmico de obtenção de vanádio metálico a partir de pentóxido de vanádio, compreendendo estudos termodinâmicos, cinéticos e de transporte de calor. É mostrada a influência de diversas variáveis sobre a recuperação do metal. Desenvolve-se na parte experimental o estudo sobre a aluminotermia de pentóxido de vanádio, utilizando-se para isto reatores abertos revestidos com argamassa refratária. Estuda-se a influência das variáveis de processo sobre a recuperação de vanádio, incluindo a adição de fluxantes, a granulometria dos reagentes, o tamanho da carga, a pureza dos reagentes, o uso de excesso de redutor e o modo de ignição da carga. Os resultados experimentais obtidos são apresentados e discutidos. O trabalho apresenta conclusões e sugestões para pesquisas futuras. / A literature survey on the processes of vanadium reduction was carried out having in mind the behavior of the reducing agents used. The refining methods for crude metallic vanadium were also covered in the review. The aluminothermic process for the reduction of vanadium pentoxide was particularly considered. Its thermochemistry features were studied, as well as the heat transfer and the rate phenomena concerning such a reaction system discussed. It was pointed out the effect of the processes parameters on the recovery of metallic vanadium. The experiments were designed to investigate the effects of the harge composition, the purity level of the reactants, the size of the solid particles of the reacting mixture and the ignition method on the recovery of vanadium. The aluminothermic reaction was carried out in an open reaction vessel. The experimental results are presented and discussed. The research work done has reached conclusive trends which allows the proposal for further interesting research.

No description available.

Made available in DSpace on 2014-12-17T14:07:20Z (GMT). No. of bitstreams: 1 RoseaneAB.pdf: 1493954 bytes, checksum: 6a4a785122e4795a117a7d18bbd1666c (MD5) Previous issue date: 2007-03-26 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Metallic tantalum has a high commercial value due to intrinsic properties like excellent ductility, corrosion resistance, high melt and boiling points and good electrical and thermal conductivities. Nowadays, it is mostly used in the manufacture of capacitors, due to excellent dielectric properties of its oxides. In the nature, tantalum occurs in the form of oxide and it is extracted mainly from tantalite-columbite ores. The tantalum is usually produced by the reduction of its oxide, using reductants like carbon, silicon, calcium, magnesium and aluminum. Among these techniques, the aluminothermic reduction has been used as the industrial method to produce niobium, tantalum and their alloys, due to the easy removal of the Al and Al2O3 of the system, easing further refining. In conventional aluminothermic reduction an electrical resistance is used to trigger the reaction. This reaction self-propagates for all the volume of material. In this work, we have developed a novel technique of aluminothermic reduction that uses the hydrogen plasma to trigger the reaction. The results obtained by XRD, SEM and EDS show that is possible to obtain a compound rich in tantalum through this technique of aluminothermic reduction in the plasma reactor / O t?ntalo ? um metal de elevado valor comercial devido suas propriedades intr?nsecas como excelente ductilidade, resist?ncia ? corros?o, elevados pontos de fus?o e ebuli??o e boas condutividades t?rmica e el?trica. Atualmente sua maior aplica??o tem sido na produ??o de capacitores, devido ?s excelentes propriedades diel?tricas de seus ?xidos. Na natureza o t?ntalo ocorre na forma de ?xido e ? extra?do principalmente do min?rio tantalita-columbita. O p? de t?ntalo met?lico ? normalmente produzido pela redu??o do seu ?xido, utilizando agentes redutores tais como carbono, sil?cio, c?lcio, magn?sio e o alum?nio. Dentre estas t?cnicas, a aluminotermia vem sendo utilizada como m?todo industrial para a produ??o do ni?bio, t?ntalo e suas ligas, em virtude da f?cil remo??o do alum?nio (Al) e da alumina (Al2O3) do sistema, o que facilita a etapa de refino. No processo de aluminotermia convencional ? utilizado um elemento resistivo como ignitor da rea??o, que se auto-propaga para todo o volume de material. No presente trabalho foi desenvolvida uma t?cnica de aluminotermia que utiliza o plasma de hidrog?nio como ignitor da rea??o. Os resultados obtidos por DRX, MEV e EDS mostram que ? poss?vel a obten??o de um concentrado rico em t?ntalo pela t?cnica de redu??o aluminot?rmica a plasma

Made available in DSpace on 2014-12-17T14:58:10Z (GMT). No. of bitstreams: 1 MarcioWDM.pdf: 1222615 bytes, checksum: 363df5ee1daf20ddbc955155e60347ed (MD5) Previous issue date: 2006-05-19 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The aluminothermic reduction consists in an exothermic reaction between a metallic oxide and aluminum to produce the metal and the scum. The extracted melted metal of that reaction usually comes mixed with particles of Al2O3 resulting of the reduction, needing of subsequent refine to eliminate the residual impure as well as to eliminate porosities. Seeking to obtain a product in powder form with nanometric size or even submicrometric, the conventional heat source of the reaction aluminothermic , where a resistor is used (ignitor) as ignition source was substituted, for the plasma, that acts more efficient way in each particle of the sample. In that work it was used as metallic oxide the niobium pentoxide (Nb2O5) for the exothermal reaction Nb2O5 + Al. Amounts stoichiometric, substoichiometric and superestoichiometric of aluminum were used. The Nb2O5 powder was mixed with aluminum powder and milled in planetarium of high energy for a period of 6 hours. Those powders were immerged in plasm that acts in a punctual way in each particle, transfering heat, so that the reaction can be initiate and spread integrally for the whole volume of the particle. The mixture of Nb2O5 + Al was characterized through the particle size analysis by laser and X-ray diffraction (DRX) and the obtained product of reaction was characterized using the electronic microscopy of sweeping (MEV) and the formed phases were analyzed by DRX. Niobium powders with inferior sizes to 1 mm were obtained by that method. It is noticed, through the analysis of the obtained results, that is possible to accomplish the aluminothermic reduction process by plasma ignition with final particles with inferior sizes to the original oxide / A redu??o aluminot?rmica consiste na rea??o exot?rmica de um ?xido met?lico com alum?nio para produzir o metal e a esc?ria. O metal fundido extra?do dessa rea??o vem normalmente misturado com part?culas de alumina resultante da redu??o, necessitando de um refino posterior tanto para eliminar as impurezas residuais como tamb?m para eliminar porosidades. Visando obter um produto em forma de p? e com tamanho nanom?trico ou at? mesmo submicrom?trico, foi substitu?da a fonte convencional de calor da rea??o aluminotermica, onde se utiliza um resistor (ignitor) como fonte de igni??o, pelo plasma, que atua de forma mais eficiente em cada part?cula da amostra. Nesse trabalho foi utilizado como ?xido met?lico o pent?xido de ni?bio (Nb2O5) para a rea??o exot?rmica Nb2O5 + Al. Foram utilizadas quantidades estequiom?tricas, subestequiom?tricas e superestequiom?tricas de alum?nio. O p? de Nb2O5 foi misturado com p? de alum?nio e mo?dos em planet?rio de alta energia por um per?odo de 6 horas. Esses p?s foram imersos em plasma que age de forma pontual em cada part?cula, transferindo calor, de modo que a rea??o possa ser iniciada e propagada integralmente para todo o volume da part?cula. A mistura de Nb2O5 + Al foi caracterizada atrav?s da granulometria a laser e difra??o de raios X (DRX) e o produto da rea??o obtido foi caracterizado utilizando a microscopia eletr?nica de varredura (MEV) e as fases formadas foram analisadas por DRX. Nota-se, atrav?s da an?lise dos resultados obtidos, que ? poss?vel realizar o processo de redu??o aluminot?rmica por igni??o a plasma com part?culas finais com tamanhos inferiores ao do ?xido original

Aluminium is usually added to the continuous hot-dip galvanizing bath to improve coating ductility and adhesion through the rapid formation of a thin Fe-Al intermetallic layer at the substrate-liquid interface, thereby inhibiting the formation of brittle Fe-Zn intermetallic compounds. On the other hand, Mn is essential for obtaining the desired microstructure and mechanical properties in advanced high strength steels, but is selectively oxidized in conventional continuous galvanizing line annealing atmospheres. This can deteriorate reactive wetting by the liquid Zn(Al,Fe) alloy during galvanizing and prevent the formation of a well developed Fe-Al interfacial layer at the coating/substrate interface, resulting in poor zinc coating adherence and formability. However, despite Mn selective oxidation and the presence of surface MnO, complete reactive wetting and a well developed Fe-Al interfacial layer have been observed for Mn-containing steels. These observations have been attributed to the aluminothermic reduction of surface MnO in the galvanizing bath. According to this reaction, MnO is reduced by the bath dissolved Al, so the bath can have contact with the substrate and form the desired interfacial layer. Heat treatments compatible with continuous hot-dip galvanizing were performed on four different Mn-containing steels whose compositions contained 0.2-3.0 wt% Mn. It was determined that substrate Mn selectively oxidized to MnO for all alloys and process atmospheres. Little Mn surface segregation was observed for the 0.2Mn steel, as would be expected because of its relatively low Mn content, whereas the 1.4Mn through 3.0Mn steels showed considerable Mn-oxide surface enrichment. In addition, the proportion of the substrate surface covered with MnO and its thickness increased with increasing steel Mn content.A galvanizing simulator equipped with a He jet spot cooler was used to arrest the reaction between the substrate and liquid zinc coating to obtain well-characterized reaction times characteristic of the timescales encountered while the strip is resident in the industrial continuous galvanizing bath and short times after in which the Zn-alloy layer continues to be liquid (i.e. before coating solidification). Two different bath dissolved Al contents (0.20 and 0.30 wt%) were chosen for this study. The 0.20 wt% Al bath was chosen as it is widely used in industrial continuous galvanizing lines. The 0.30 wt% Al bath was chosen to (partially) compensate for any dissolved Al consumption arising from MnO reduction in the galvanizing bath.The Al uptake increased with increasing reaction time following non-parabolic growth kinetics for all experimental steels and dissolved Al baths. For the 0.20 wt% dissolved Al bath, the interfacial layer on the 1.4Mn steel showed the highest Al uptake, with the 0.2Mn, 2.5Mn and 3.0Mn substrates showing significantly lower Al uptake. However, increasing the dissolved bath Al to 0.30 wt% Al resulted in a significantly increased Al uptake being observed for the 2.5Mn and 3.0Mn steels for all reaction times. These observations were explained by the combined effects of the open microstructures associated with the multi-phase nature of an oxide-containing interfacial layer and additional Al consumption through MnO reduction. For instance, in the case of the 1.4Mn steel, the more open interfacial layer structure accelerated Fe diffusion through the interfacial layer and increased Al uptake versus the 0.2Mn substrate for the same bath Al. However, in the case of the 2.5Mn and 3.0Mn substrates and 0.20 wt% Al bath, additional Al consumption through MnO reduction caused the interfacial layer growth to become Al limited, whereas the very open structure dominated growth in the case of the 0.30 wt% Al bath and resulted in the changing the growth kinetics from mixed diffusion-controlled to a more interface controlled growth mode. A kinetic model based on oxide film growth (Smeltzer et al. 1961, Perrow et al. 1968) was developed to describe the Fe-Al interfacial layer growth kinetics within the context of the microstructural evolution of the Fe-Al interfacial layer for Mn-containing steels reacted in 0.20 wt% and 0.30 wt% dissolved Al baths. It indicated that the interfacial layer microstructure development and the presence of MnO at the interfacial layer had significant influence on the effective diffusion coefficient and interfacial layer growth rate. However, in the cases of the 2.5Mn and 3.0Mn steels in 0.20 wt% Al bath, the kinetic model could not predict the interfacial layer Al uptake, since the Fe-Al growth was Al limited. In fact, in these cases, additional Al was consumed for reducing their thicker surface MnO layer, resulted in limiting the dissolved Al available for Fe-Al growth. / Dissertation / Doctor of Science (PhD)

Made available in DSpace on 2014-12-17T14:07:06Z (GMT). No. of bitstreams: 1 RoseaneAB_TESE.pdf: 2502276 bytes, checksum: 8d0bea579c9b9da8a192feccb392ae6a (MD5) Previous issue date: 2011-04-29 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this study it was used two metallic oxides, Ta2O5 and TiO2, in order to obtain metallic powders of Ta and Ti through aluminothermic reduction ignited by plasma. Ta2O5 and TiO2 powders were mixed with Al in a planetary mill, using different milling times. A thermal analysis study (DTA and TG) was carried out, in order to know the temperature to react both the mixtures. Then, these mixtures were submitted to a hollow cathode discharge, where they were reacted using aluminothermic reduction ignited by plasma. The product obtained was characterized by XRD and SEM, where it was proven the possibility of producing these metallic particles, different from the conventional process, where metallic ingots are obtained. It was verified that the aluminothermic reduction ignited by plasma is able to produce metallic powders of Ta and Ti, and a higher efficiency was observed to the process with Ta2O5-Al mixtures. Among different microstructural aspects observed, it can be noted the presence of metallic nanoparticles trapped into an Al2O3 matrix, besides acicular structures (titanium) and dendritic structures (tantalum), which are a product characteristic from a fast cooling / No presente estudo foram utilizados dois ?xidos met?licos, Ta2O5 e TiO2, visando a obten??o de part?culas de Ta e Ti met?licos, por meio da redu??o aluminot?rmica com igni??o a plasma. P?s de Ta2O5 e TiO2 foram misturados com p? de Al e mo?dos em um moinho planet?rio por diferentes per?odos. Um estudo de an?lise t?rmica (DTA e TG) foi realizado, visando se conhecer a temperatura de rea??o para ambas as misturas. Conhecidas essas temperaturas, as misturas foram submetidas a uma descarga em c?todo oco, onde foram reagidas pelo processo de redu??o aluminot?rmica com igni??o a plasma. O material obtido foi caracterizado por DRX e MEV, onde se comprovou a possibilidade da obten??o de um produto na forma de p?, algumas vezes de dimens?es nanom?tricas, diferentemente do processo convencional, onde o produto final ? obtido na forma de lingote. Verificou-se que a redu??o aluminot?rmica com igni??o a plasma ? capaz de produzir p?s de Ta e Ti met?licos, com uma efici?ncia maior para a rea??o da mistura Ta2O5-Al. Dentre os diferentes aspectos microestruturais observados, destaca-se a presen?a de nanopart?culas do metal de interesse embebidas em uma matriz de Al2O3, al?m de estruturas acicular (tit?nio) e dendr?tica (t?ntalo), que s?o caracter?sticas de um resfriamento r?pido

Made available in DSpace on 2014-12-17T14:07:05Z (GMT). No. of bitstreams: 1 MarcioWDM_TESE.pdf: 5811012 bytes, checksum: feda974076398f5c8fbcb84ae56af460 (MD5) Previous issue date: 2010-09-17 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Metal substrates were coated by thermal spraying plasma torch, they were positioned at a distance of 4 and 5 cm from the nozzle exit of the plasma jet. The starting materials were used for deposition of tantalum oxide powder and aluminium. These two materials were mixed and ground into high-energy mill, then immersed in the torch for the production of alumina coating infused with particles of tantalum with nano and micrometric size. The spraying equipment used is a plasma torch arc not transferred, which operating in the range of 250 A and 80 V, was able to produce enough heat to ignite aluminothermic between Ta2O5 and aluminum. Upon reaching the plasma jet, the mixing powders react with the heat of the blaze, which provides sufficient energy for melting aluminum particles. This energy is transferred through mechanisms of self-propagating to the oxide, beginning a reduction reaction, which then hits on the surface of the substrate and forms a coating on which a composite is formed by a junction metal - ceramic (Ta +Al2O3). The phases and quantification of each were obtained respectively by X-ray diffraction and the Rietveld method. Morphology by scanning electron microscopy and chemical analysis by energy dispersive spectroscopy EDS. It was also performed measurements of the substrate roughness, Vickers microhardness measurements in sprays and determination of the electron temperature of the plasma jet by optical emission spectroscopy EEO. The results confirmed the expectation generated around the end product of spraying the mixture Ta2O5 + Al, both in the formation of nano-sized particles and in their final form. The electron excitation temperature was consistent with the purpose of work, in addition, the thermodynamic temperature was efficient for the reduction process of Ta2O5. The electron excitation temperature showed values of 3000, 4500 and 8000 K for flows10, 20 and 30 l / min respectively, these values were taken at the nozzle exit of the plasma jet. The thermodynamic temperature around 1200 ? C, was effective in the reduction process of Ta2O5 / Substratos met?licos de a?o inox 416 foram revestidos por aspers?o t?rmica em tocha de plasma. Eles foram posicionados a uma dist?ncia de 4 e 5 cm em rela??o ao bocal de sa?da do jato de plasma. Os materiais de partida utilizados para as deposi??es foram p?s de ?xido de t?ntalo e alum?nio. Esses dois p?s foram misturados e mo?dos em moinho de alta energia, em seguida, imersos na tocha para produ??o de revestimento de alumina impregnada com part?culas de t?ntalo com tamanho nano e microm?tricos. O equipamento de aspers?o utilizado foi uma tocha de plasma de arco n?o transferido que opera na faixa de 250 A e 30 V. Ao atingirem o jato de plasma, os p?s da mistura aquecem at? a temperatura de igni??o da rea??o aluminot?rmica. O calor gerado fornece energia suficiente para a fus?o do produto da rea??o. Esse produto fundido ao chocar-se na superf?cie do substrato forma um revestimento composto por uma jun??o metal cer?mica (Ta + Al2O3). A identifica??o das fases e sua quantifica??o foram obtidas respectivamente por difra??o de raios X e pelo m?todo de Rietveld. Para determina??o da morfologia e composi??o das part?culas foram utilizados microscopia eletr?nica de varredura e an?lise qu?mica por espectroscopia de energia dispersiva EDS, respectivamente. Tamb?m foram executadas medidas de rugosidades no substrato, medi??es de microdureza Vickers nas aspers?es e determina??o da temperatura eletr?nica do jato de plasma por espectroscopia de emiss?o ?tica EEO. Os resultados obtidos confirmaram a expectativa gerada em torno do produto final da aspers?o da mistura Ta2O5 + Al, tanto na forma??o de part?culas nanom?tricas de t?ntalo quanto no formato final delas. A temperatura de excita??o dos el?trons apresentou valores de 3000, 4500 e 8000 K para fluxos de 10, 20 e 30 l/min respectivamente, esses valores foram tomados na sa?da do bocal do jato de plasma. A temperatura termodin?mica, em torno de 1200 ?C mostrou-se eficiente para o processo de redu??o do Ta2O5

Made available in DSpace on 2014-12-17T14:07:22Z (GMT). No. of bitstreams: 1 AntonioCPS.pdf: 2085220 bytes, checksum: 8e64ae2c2f5ffe8a64dd3420c9c87327 (MD5) Previous issue date: 2007-03-23 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this work was used a plasma torch of non transferred arc with argon as work gas, using a power supply with maximum DC current of 250 A and voltage of 30 V to activate the plasma and keep it switched on. The flame temperature was characterized by optical emission spectroscopy, through Boltzmann-plot-method. The torch has been used like igniter in the aluminothermic reduction of the mixture tantalum oxide and aluminum, seeking to obtain metallic tantalum. In heating of the reagents only one particle will be considered to study interactions between plasma-particle, seeking to determinate its fusion and residence time. The early powders were characterized by laser granulometry, scanning electron microscopy (SEM) and X-ray diffraction analysis. The final product of this reaction was characterized by SEM and X-ray diffraction. Crystallite size was calculated by the Scherrer equation and microdeformation was determined using Willamsom-Hall graph. With Rietveld method was possible to quantify the percentile in weight of the products obtained in the aluminothermic reaction. Semi-quantitative chemical analysis (EDS) confirmed the presence of metallic tantalum and Al2O3 as products of the reduction. As was waited the particle size of the metallic tantalum produced, presents values in nanometric scale due the short cooling time of those particles during the process / Neste trabalho foi utilizada uma tocha de plasma de arco n?o transferido com arg?nio como g?s de trabalho, utilizando uma fonte de pot?ncia com corrente m?xima de 250 A e tens?o m?xima de sa?da de 30 V fornecida pelo fabricante. A temperatura da tocha foi caracterizada atrav?s da espectroscopia de emiss?o ?ptica, utilizando a curva de Boltzmann. A tocha foi usada como ignitor para a rea??o de redu??o aluminot?rmica do ?xido de t?ntalo mais alum?nio para a produ??o de t?ntalo met?lico. No aquecimento dos reagentes apenas uma part?cula ser? considerada para o estudo da intera??o tocha-part?cula, com o objetivo de determinar seu tempo de fus?o e resid?ncia. Os p?s de partida foram caracterizados atrav?s da granulometria a laser, microscopa eletr?nica de varredura (MEV) e difra??o de raios X. O produto final desta rea??o foi caracterizado por MEV e difra??o de raios X. O tamanho de cristalito foi calculado atrav?s da equa??o de Scherrer e a microdeforma??o foi determinada utilizando o gr?fico de Willamsom-Hall. Com o m?todo de Rietveld foi poss?vel quantificar o percentual em peso do produto da rea??o aluminot?rmica. An?lise qu?mica semiquantitativa (EDS) confirmou a presen?a do Ta met?lico e Al2O3 como produtos da redu??o. Como era de se esperar, o tamanho das part?culas do t?ntalo met?lico produzida apresenta valores na faixa de nan?metro devido pequeno tempo de resfriamento durante o processo