Effect of calcium oxide microstructure on the diffusion of isotopes

Detalhes bibliográficos
Autor(a) principal: Ramos, João Pedro Fernandes
Data de Publicação: 2012
Tipo de documento: Dissertação
Idioma: eng
Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
Texto Completo: http://hdl.handle.net/10773/8187
Resumo: Calcium oxide (CaO) powder targets have been successfully used at CERN-ISOLDE to produce neutron deficient exotic argon and carbon isotopes under proton irradiation at high temperatures (>1000oC). These targets outperform the other related targets for the production of the same beams. However, they presented either slow release rates (yields) from the beginning or a rapid decrease over time. This problem was believed to come from the target microstructure degradation, justifying the material investigation. In order to do so, the synthesis, reactivity in ambient air and sintering kinetics of CaO were studied, through surface area determination by N2 adsorption, X-ray diffraction for crystalline phase identification and crystallite size determination, and scanning and transmission electron microscopy to investigate the microstructure. The synthesis studies revealed that a nanometric material is obtained from the decarbonation of CaCO3 in vacuum at temperatures higher than 550oC, which is very reactive in air. This reactivity was studied, and it was observed that the CaO powder microstructure is changed through the reaction with air (hydration and carbonation of the oxide) and that this change is not completely reversible after thermal decomposition of the reaction products. Therefore, special care was taken in the target handling at CERN-ISOLDE. From the sintering kinetics, studied in the range of 1000-1200oC, it was determined that this material’s microstructure degrades, with the reduction of the specific surface area and decrease of the powder porosity. At 1200oC, the specific surface area reduction is accentuated, reaching values of 50% of surface area reduction in 10h. These results suggest that the use of high temperatures, equal or higher than 1000oC must be avoided, if the microstructural characteristics of the targets are to be preserved. At CERN-ISOLDE, selected conditions for synthesis, handling of the target and target operation temperatures were chosen, based on the previous material research, and the obtained target material was tested under proton irradiation. From the online studies, the newly developed target proved to show better initial and stable over time release rates of almost all isotopes investigated and especially the exotic ones. These results are essentially due to the nanometric characteristics of the produced target and to the use of operation and handling conditions that decreased the degradation of the microstructural characteristics. Diffusion studies of Ar and Ne were also done in CaO through the application of a mathematical model, to the release curves of the respective isotopes at different temperatures, which enables the determination of the respective diffusion coefficients and activation energies.
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spelling Effect of calcium oxide microstructure on the diffusion of isotopesEngenharia de materiaisÓxido de cálcioFeixes de iõesCalcium oxide (CaO) powder targets have been successfully used at CERN-ISOLDE to produce neutron deficient exotic argon and carbon isotopes under proton irradiation at high temperatures (>1000oC). These targets outperform the other related targets for the production of the same beams. However, they presented either slow release rates (yields) from the beginning or a rapid decrease over time. This problem was believed to come from the target microstructure degradation, justifying the material investigation. In order to do so, the synthesis, reactivity in ambient air and sintering kinetics of CaO were studied, through surface area determination by N2 adsorption, X-ray diffraction for crystalline phase identification and crystallite size determination, and scanning and transmission electron microscopy to investigate the microstructure. The synthesis studies revealed that a nanometric material is obtained from the decarbonation of CaCO3 in vacuum at temperatures higher than 550oC, which is very reactive in air. This reactivity was studied, and it was observed that the CaO powder microstructure is changed through the reaction with air (hydration and carbonation of the oxide) and that this change is not completely reversible after thermal decomposition of the reaction products. Therefore, special care was taken in the target handling at CERN-ISOLDE. From the sintering kinetics, studied in the range of 1000-1200oC, it was determined that this material’s microstructure degrades, with the reduction of the specific surface area and decrease of the powder porosity. At 1200oC, the specific surface area reduction is accentuated, reaching values of 50% of surface area reduction in 10h. These results suggest that the use of high temperatures, equal or higher than 1000oC must be avoided, if the microstructural characteristics of the targets are to be preserved. At CERN-ISOLDE, selected conditions for synthesis, handling of the target and target operation temperatures were chosen, based on the previous material research, and the obtained target material was tested under proton irradiation. From the online studies, the newly developed target proved to show better initial and stable over time release rates of almost all isotopes investigated and especially the exotic ones. These results are essentially due to the nanometric characteristics of the produced target and to the use of operation and handling conditions that decreased the degradation of the microstructural characteristics. Diffusion studies of Ar and Ne were also done in CaO through the application of a mathematical model, to the release curves of the respective isotopes at different temperatures, which enables the determination of the respective diffusion coefficients and activation energies.Alvos de pós de oxido de cálcio (CaO) têm sido usados, com sucesso, no CERN-ISOLDE para produzir isótopos de Árgon (com défice de neutrões) e de carbono, sob irradiação com protões a alta temperatura (>1000oC). Estes alvos têm mostrado um desempenho superior a outros alvos usados para produzir os mesmos feixes. Contudo, apresentam baixas taxas de libertação de isótopos desde o início de operação ou uma redução rápida com o tempo. Suspeitou-se que este problema se devia à degradação da microestrutura do material, justificando a sua investigação. Assim, a síntese, reatividade em ar ambiente e a cinética de sinterização do CaO foram estudadas, nomeadamente através da determinação da área superficial especifica por adsorção de N2, difração de raios-X para identificação de fases e determinação do tamanho de cristalite e microscopia eletrónica de varrimento e transmissão para o estudo da microestrutura. Os estudos de síntese do CaO revelaram que um material nanométrico, e muito reativo em ar, é obtido através da descarbonatação do CaCO3 em vácuo a temperaturas superiores a 550oC. Esta reatividade foi estudada e observou-se que a microestrutura do pó de CaO é alterada por reação com o ar (hidratação e carbonatação do óxido) e que esta alteração não é totalmente reversível após decomposição térmica dos produtos de reação. Assim, foram tomados cuidados especiais no manuseamento dos alvos de CaO. Da cinética de sinterização, estudada na gama de 1000-1200oC, foi concluído que a microestrutura deste material se degrada com redução da área superficial específica e diminuição da porosidade do pó. A 1200oC, a redução da área superficial específica é acentuada, atingindo-se valores de 50% de redução em cerca de 10h. Estes resultados indicam que a utilização de temperaturas elevadas, iguais ou superiores a 1000oC, devem ser evitadas se se pretendem preservar as características microestruturais dos alvos. No CERN-ISOLDE, as condições de síntese, de manuseamento do material e temperatura de operação do alvo foram escolhidas, com base nos estudos anteriores, e o material resultante foi testado sobre irradiação de protões. Dos estudos online, o alvo desenvolvido provou ter melhores taxas de libertação iniciais e que se mantêm ao longo do tempo de libertação, comparativamente a outros alvos de CaO previamente usados no CERN-ISOLDE. Isto verificou-se em praticamente todos os isótopos estudados, especialmente nos exóticos. Estes resultados foram atribuídos às caraterísticas nanométricas do alvo produzido e à utilização de condições de manuseamento e de operação, tais que a degradação das características microestruturais do alvo é reduzida. Estudos de difusão de Árgon e Néon foram feitos no CaO através da aplicação de um modelo matemático às curvas de libertação dos respetivos isótopos a diferentes temperaturas de operação, que permitiram a determinação dos respetivos coeficientes de difusão e energias de ativação.Universidade de Aveiro2012-04-18T11:58:33Z2012-01-01T00:00:00Z2012info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/masterThesisapplication/pdfhttp://hdl.handle.net/10773/8187engRamos, João Pedro Fernandesinfo:eu-repo/semantics/openAccessreponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãoinstacron:RCAAP2024-02-22T11:13:59Zoai:ria.ua.pt:10773/8187Portal AgregadorONGhttps://www.rcaap.pt/oai/openaireopendoar:71602024-03-20T02:45:30.750967Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) - Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãofalse
dc.title.none.fl_str_mv Effect of calcium oxide microstructure on the diffusion of isotopes
title Effect of calcium oxide microstructure on the diffusion of isotopes
spellingShingle Effect of calcium oxide microstructure on the diffusion of isotopes
Ramos, João Pedro Fernandes
Engenharia de materiais
Óxido de cálcio
Feixes de iões
title_short Effect of calcium oxide microstructure on the diffusion of isotopes
title_full Effect of calcium oxide microstructure on the diffusion of isotopes
title_fullStr Effect of calcium oxide microstructure on the diffusion of isotopes
title_full_unstemmed Effect of calcium oxide microstructure on the diffusion of isotopes
title_sort Effect of calcium oxide microstructure on the diffusion of isotopes
author Ramos, João Pedro Fernandes
author_facet Ramos, João Pedro Fernandes
author_role author
dc.contributor.author.fl_str_mv Ramos, João Pedro Fernandes
dc.subject.por.fl_str_mv Engenharia de materiais
Óxido de cálcio
Feixes de iões
topic Engenharia de materiais
Óxido de cálcio
Feixes de iões
description Calcium oxide (CaO) powder targets have been successfully used at CERN-ISOLDE to produce neutron deficient exotic argon and carbon isotopes under proton irradiation at high temperatures (>1000oC). These targets outperform the other related targets for the production of the same beams. However, they presented either slow release rates (yields) from the beginning or a rapid decrease over time. This problem was believed to come from the target microstructure degradation, justifying the material investigation. In order to do so, the synthesis, reactivity in ambient air and sintering kinetics of CaO were studied, through surface area determination by N2 adsorption, X-ray diffraction for crystalline phase identification and crystallite size determination, and scanning and transmission electron microscopy to investigate the microstructure. The synthesis studies revealed that a nanometric material is obtained from the decarbonation of CaCO3 in vacuum at temperatures higher than 550oC, which is very reactive in air. This reactivity was studied, and it was observed that the CaO powder microstructure is changed through the reaction with air (hydration and carbonation of the oxide) and that this change is not completely reversible after thermal decomposition of the reaction products. Therefore, special care was taken in the target handling at CERN-ISOLDE. From the sintering kinetics, studied in the range of 1000-1200oC, it was determined that this material’s microstructure degrades, with the reduction of the specific surface area and decrease of the powder porosity. At 1200oC, the specific surface area reduction is accentuated, reaching values of 50% of surface area reduction in 10h. These results suggest that the use of high temperatures, equal or higher than 1000oC must be avoided, if the microstructural characteristics of the targets are to be preserved. At CERN-ISOLDE, selected conditions for synthesis, handling of the target and target operation temperatures were chosen, based on the previous material research, and the obtained target material was tested under proton irradiation. From the online studies, the newly developed target proved to show better initial and stable over time release rates of almost all isotopes investigated and especially the exotic ones. These results are essentially due to the nanometric characteristics of the produced target and to the use of operation and handling conditions that decreased the degradation of the microstructural characteristics. Diffusion studies of Ar and Ne were also done in CaO through the application of a mathematical model, to the release curves of the respective isotopes at different temperatures, which enables the determination of the respective diffusion coefficients and activation energies.
publishDate 2012
dc.date.none.fl_str_mv 2012-04-18T11:58:33Z
2012-01-01T00:00:00Z
2012
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dc.publisher.none.fl_str_mv Universidade de Aveiro
publisher.none.fl_str_mv Universidade de Aveiro
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