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Redu??o in situ de NIO durante a sinteriza??o de misturas NI/NIO produzidas por metalurgia do p?Dantas, Elis?ngela Barros 04 June 2012 (has links)
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Previous issue date: 2012-06-04 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPq / As ligas de n?quel s?o largamente utilizadas na produ??o de diversos materiais,
sobretudo, aqueles que necessitam de resist?ncia mec?nica associada ? resist?ncia
? corros?o, como por exemplo, os a?os inoxid?veis. Outro uso do n?quel ? a
produ??o de ligas sinterizadas a partir de p? de n?quel met?lico. Uma alternativa
promissora ? produ??o de componentes sinterizados de n?quel com importante
redu??o de custos do material de partida ? o emprego de misturas de p?s do tipo NiNiO.
Este trabalho teve por objetivo o estudo da redu??o in situ de NiO durante a
sinteriza??o de misturas Ni/NiO produzidas por metalurgia do p?. As misturas foram
processadas pela t?cnica de metalurgia do p? e pr?-sinterizadas em atmosfera
redutora de hidrog?nio. As amostras Ni+15%NiO, Ni+25%NiO e Ni+35%NiO foram
estudadas e comparadas com amostras sinterizadas apenas a partir de Ni met?lico.
Foram realizados ensaios dilatom?tricos para estudo das condi??es de sinteriza??o
das misturas. O material consolidado foi analisado quanto ? sua microestrutura e
microdureza. As curvas de dilatometria mostraram que a adi??o de ?xido de n?quel
em todas as composi??es ativa a sinteriza??o das misturas estudadas. Nos testes
de microdureza foram realizadas indenta??es em pontos distintos da superf?cie das
amostras. Todas as composi??es apresentaram valores de microdureza pr?ximos ao
do material consolidado a partir de n?quel met?lico. Contudo, as amostras contendo
Ni+35%NiO, apresentaram grande dispers?o desses valores. A an?lise
microestrutural do material mostrou uma maior concentra??o de vazios e presen?a
de ?xidos residuais nas misturas da composi??o Ni+35%NiO. As amostras contendo
Ni+15%NiO apresentaram caracter?sticas microestruturais e propriedades
mec?nicas semelhantes ao n?quel met?lico consolidado sob as mesmas condi??es
das composi??es estudadas neste trabalho e, portanto, apresentaram grande
potencial para produ??o de ligas sinterizadas de n?quel / The nickel alloys are widely used in the production of various materials, especially
those that require mechanical strength characteristics associated with resistance to
corrosion, for example, the stainless steel. Another use is the production of
nickel alloy sintered from powder of metallic nickel. A promising alternative for the
production of sintered components of nickel with an important reduction in costs of
starting material is the use of mixtures of powders of Ni-NiO. This work aimed to
study in situ reduction of NiO during sintering mixtures of Ni / NiO produced by
powder metallurgy. The nickel mixtures have been processed by the technique of
powder metallurgy and were pre-sintered in an oven under plasma reducing
atmosphere of hydrogen. Mixtures Ni +15%NiO, Ni +25%NiO and Ni +35%NiO were
studied and compared with samples consisting only of metallic Ni. Dilatometric tests
were performed to study the sintering conditions of the mixtures. The consolidated
material was analyzed for their microstructure and microhardness. Dilatometry
graphs showed that the addition of nickel oxide in all compositions the active
sintering the mixtures studied. In tests of microhardness indentations were made at
different points of the sample surface. All compositions showed microhardness
values close to the consolidated material from metallic nickel. However, sample
containing Ni+35% NiO, showed a large dispersion of the values of microhardness
tests performed at different points of the sample surface. Microstructural analysis of
the material showed a higher concentration of voids and the presence of oxides in
the waste composition of the mixtures Ni 35% NiO. The samples containing
Ni+15%NiO showed microstructural characteristics and mechanical properties similar
to metallic nickel consolidated under the same conditions of the compositions studied
in this work and therefore had great potential for production of sintered nickel alloys
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S?ntese, estudo cin?tico e an?lise microestrutural do sistema c?rio-n?quel obtido pelo m?todo pechiniChaves, Alexsandra Cristina 10 December 2008 (has links)
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Previous issue date: 2008-12-10 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The cerium oxide has a high potential for use in removing pollutants after combustion, removal of organic matter in waste water and the fuel-cell technology. The nickel oxide is an attractive material due to its excellent chemical stability and their optical properties, electrical and magnetic. In this work, CeO2-NiO- systems on molars reasons 1:1(I), 1:2(II) e 1:3(III) metal-citric acid were synthesized using the Pechini method. We used techniques of TG / DTG and
ATD to monitor the degradation process of organic matter to the formation of the oxide. By
thermogravimetric analysis and applying the dynamic method proposed by Coats-Redfern, it was possible to study the reactions of thermal decomposition in order to propose the possible mechanism by which the reaction takes place, as well as the determination of kinetic parameters as activation energy, Ea, pre-exponential factor and parameters of activation. It was observed that
both variables exert a significant influence on the formation of complex polymeric precursor. The model that best fitted the experimental data in the dynamic mode was R3, which consists of nuclear growth, which formed the nuclei grow to a continuous reaction interface, it proposes a spherical symmetry (order 2 / 3). The values of enthalpy of activation of the system showed that the reaction in the state of transition is exothermic. The variables of composition, together with the variable temperature of calcination were studied by different techniques such as XRD, IV and SEM. Also a study was conducted microstructure by the Rietveld method, the calculation routine was developed to run the package program FullProf Suite, and analyzed by pseudo-Voigt function. It was found that the molar ratio of variable metal-citric acid in the system CeO2-NiO (I), (II), (III) has strong influence on the microstructural properties, size of crystallites and microstrain network, and can be used to control these properties / O ?xido de c?rio tem um alto potencial em uso para remo??o de p?s poluentes de combust?o, remo??o de mat?rias org?nicas de ?guas residuais e na tecnologia de c?lulas a combust?vel. O ?xido de n?quel ? um material atraente devido a sua excelente estabilidade qu?mica, bem como suas propriedades ?pticas, el?tricas e magn?ticas. Neste trabalho, sistemas de CeO2-NiO nas raz?es molares 1:1(I), 1:2(II) e 1:3(III) metal-?cido c?trico foram sintetizados
utilizando o m?todo Pechini. Foram utilizadas t?cnicas de TG / DTG e DTA para monitorar o processo de degrada??o da mat?ria org?nica at? a forma??o do ?xido. Atrav?s da an?lise termogravim?trica e aplicando-se o m?todo din?mico proposto por Coats-Redfern, foi poss?vel realizar estudos das rea??es de decomposi??o t?rmica com o intuito de propor o poss?vel mecanismo pelo qual a rea??o se processa, como tamb?m, a determina??o de par?metros
cin?ticos como energia de ativa??o, Ea, fator pr?-exponencial e par?metros termodin?micos de
ativa??o. Foi observado que ambas as vari?veis exercem grande influ?ncia na forma??o do complexo polim?rico precursor. O modelo que melhor ajustou-se aos dados experimentais no modo din?mico foi o R3, que consiste de crescimento nuclear, onde, os n?cleos formados
crescem at? atingirem uma interface de rea??o cont?nua, este, prop?e uma simetria esf?rica (ordem 2/3). Os valores de entalpia de ativa??o do sistema evidenciaram que a rea??o no estado de transi??o ? exot?rmica. As vari?veis de composi??o, juntamente com a vari?vel temperatura de
calcina??o foram estudadas por diferentes t?cnicas, tais como: DRX, IV e MEV. Tamb?m foi realizado um estudo microestrutural pelo m?todo de Rietveld, cuja rotina de c?lculo foi desenvolvida para ser executada no pacote do programa Fullprof Su?te, e analisada pela fun??o pseudo-Voigt. Verificou-se que a vari?vel raz?o molar metal-?cido c?trico no sistema CeO2-NiO (I),(II),(III) tem forte influ?ncia nas propriedades microestruturais, tamanho de cristalito e
microdeforma??o de rede, e podem ser usados para controlar estas propriedades
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