| Summary: | Made available in DSpace on 2014-12-17T14:07:00Z (GMT). No. of bitstreams: 1
AlexsandraCC.pdf: 2480283 bytes, checksum: 5ee60db44e31addafb5e193c9292f73e (MD5)
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
|
|---|
