Improvement of the ageing resistance of 2YSZ ceramic

Detalhes bibliográficos
Autor(a) principal: Macedo, Tânia Sofia Oliveira
Data de Publicação: 2016
Tipo de documento: Dissertação
Idioma: eng
Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
Texto Completo: http://hdl.handle.net/10773/21896
Resumo: Zirconia is a widely studied ceramic and it is applied in several areas such as engineering (solid oxide fuel cells, thermal barrier coatings) and biomedicine, in areas such as orthopedic and odontology. This material can be applied with the purpose to restore a body function that was compromised by a degenerative disease (orthopedic implants), in dental area and sensors due to its excellent mechanical properties, aesthetic characteristics and biocompatibility. However, this ceramic is sensitive to ageing and has a low hardness. To overcome these limitations, samples of Yttria Stabilized Zirconia doped with different oxides were developed and the goal was to improve the ageing resistance and mechanical properties of un-doped 2 mol% Yttria Stabilized Zirconia (2YSZ). A careful selection of the dopants and respective concentrations was performed. According to the literature, ceria (CeO2), silica (SiO2), alumina (Al2O3), lanthana (La2O3), ytterbia (Yb2O3) and manganese oxide (MnO2) improve the ageing resistance and/or the mechanical properties of Yttria Stabilized Zirconia (YSZ). In this study, thirteen different doped 2YSZ compositions were developed. For each selected dopant, three to four compositions were performed with different dopant concentrations. After a wet milling stage, the doped stabilized zirconia powders were obtained by spray-drying, from stabilized suspensions with a controlled nanometric particle size distribution. The obtained doped sprayed powders were characterized through several techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), density and specific surface area (SSA). Green bodies of all doped compositions were obtained by uniaxial pressing (70 MPa). High density ceramics (with relative density between 90% and approximately 99%) were achieved at low sintering temperatures (1350 °C and 1400 °C). The grain size of the sintered samples was measured by SEM images, and a dispersed microstructure with a nanometric grain size was observed for all 2YSZ doped samples. The crystallographic phases present in the doped samples were identified by XRD. In order to assess their thermal ageing resistance, the samples were subjected to a thermal treatment at low temperatures (200 °C) during a period of 36 hours. After this treatment, the fracture toughness of the aged samples was evaluated. From all the starting samples, those with better resistance to thermal ageing and fracture toughness were afterwards selected: samples of 2YSZ doped with CeO2 (0.50 wt%) and with SiO2 (0.25 wt%) and La2O3 (1.07 wt%). Cylindrical bodies of the selected doped 2YSZ compositions were obtained by two pressing stages - uniaxial and cold isostatic pressing - and sintered at 1350 ºC for 3 hours. The behaviour of the sintered samples was investigated in terms of hydrothermal ageing resistance, according to the specifications mentioned in ISO 13356:2008 (134 ± 2 ºC and 0.2 MPa), and mechanical properties: Vickers’ hardness along with fracture toughness and flexural strength. The amount of monoclinic zirconia, indicative of degradation, was determined by XRD after 5 hours of ageing test. Afterwards the mechanical behaviour (Vickers hardness, fracture toughness and flexural strength) of the aged samples was assessed. The results obtained in the present study demonstrate that adequate doped 2YSZ samples, with improved hydrothermal degradation resistance (9.87 % of monoclinic zirconia for SiO2 with La2O3 doped 2YSZ sample while un-doped 2YSZ presented a monoclinic phase higher than 15 %) can be obtained. The mechanical properties of the sample of 2YSZ doped with both oxides (SiO2 and La2O3), before and after the hydrothermal ageing, were practically maintained (1159 vs 1141 HV (hardness), 9.68 vs 9.15 MPa.m1/2 (fracture toughness) and 700 vs 698 MPa (flexural strength)). Nevertheless, a decrease of the mechanical properties was observed for both selected doped 2YSZ samples in relation to un-doped sample.
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spelling Improvement of the ageing resistance of 2YSZ ceramicMateriais e dispositivos biomédicosBiocerâmica - Propriedades mecânicasÓxido de zircónio - Resistência à degradaçãoMateriais biocompatíveisPrótesesZirconia is a widely studied ceramic and it is applied in several areas such as engineering (solid oxide fuel cells, thermal barrier coatings) and biomedicine, in areas such as orthopedic and odontology. This material can be applied with the purpose to restore a body function that was compromised by a degenerative disease (orthopedic implants), in dental area and sensors due to its excellent mechanical properties, aesthetic characteristics and biocompatibility. However, this ceramic is sensitive to ageing and has a low hardness. To overcome these limitations, samples of Yttria Stabilized Zirconia doped with different oxides were developed and the goal was to improve the ageing resistance and mechanical properties of un-doped 2 mol% Yttria Stabilized Zirconia (2YSZ). A careful selection of the dopants and respective concentrations was performed. According to the literature, ceria (CeO2), silica (SiO2), alumina (Al2O3), lanthana (La2O3), ytterbia (Yb2O3) and manganese oxide (MnO2) improve the ageing resistance and/or the mechanical properties of Yttria Stabilized Zirconia (YSZ). In this study, thirteen different doped 2YSZ compositions were developed. For each selected dopant, three to four compositions were performed with different dopant concentrations. After a wet milling stage, the doped stabilized zirconia powders were obtained by spray-drying, from stabilized suspensions with a controlled nanometric particle size distribution. The obtained doped sprayed powders were characterized through several techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), density and specific surface area (SSA). Green bodies of all doped compositions were obtained by uniaxial pressing (70 MPa). High density ceramics (with relative density between 90% and approximately 99%) were achieved at low sintering temperatures (1350 °C and 1400 °C). The grain size of the sintered samples was measured by SEM images, and a dispersed microstructure with a nanometric grain size was observed for all 2YSZ doped samples. The crystallographic phases present in the doped samples were identified by XRD. In order to assess their thermal ageing resistance, the samples were subjected to a thermal treatment at low temperatures (200 °C) during a period of 36 hours. After this treatment, the fracture toughness of the aged samples was evaluated. From all the starting samples, those with better resistance to thermal ageing and fracture toughness were afterwards selected: samples of 2YSZ doped with CeO2 (0.50 wt%) and with SiO2 (0.25 wt%) and La2O3 (1.07 wt%). Cylindrical bodies of the selected doped 2YSZ compositions were obtained by two pressing stages - uniaxial and cold isostatic pressing - and sintered at 1350 ºC for 3 hours. The behaviour of the sintered samples was investigated in terms of hydrothermal ageing resistance, according to the specifications mentioned in ISO 13356:2008 (134 ± 2 ºC and 0.2 MPa), and mechanical properties: Vickers’ hardness along with fracture toughness and flexural strength. The amount of monoclinic zirconia, indicative of degradation, was determined by XRD after 5 hours of ageing test. Afterwards the mechanical behaviour (Vickers hardness, fracture toughness and flexural strength) of the aged samples was assessed. The results obtained in the present study demonstrate that adequate doped 2YSZ samples, with improved hydrothermal degradation resistance (9.87 % of monoclinic zirconia for SiO2 with La2O3 doped 2YSZ sample while un-doped 2YSZ presented a monoclinic phase higher than 15 %) can be obtained. The mechanical properties of the sample of 2YSZ doped with both oxides (SiO2 and La2O3), before and after the hydrothermal ageing, were practically maintained (1159 vs 1141 HV (hardness), 9.68 vs 9.15 MPa.m1/2 (fracture toughness) and 700 vs 698 MPa (flexural strength)). Nevertheless, a decrease of the mechanical properties was observed for both selected doped 2YSZ samples in relation to un-doped sample.A zircónia é um cerâmico amplamente estudado e aplicado em diversas áreas da engenharia (células de combustível, revestimentos de barreiras térmicas) e biomedicina, em áreas como a ortopedia e a odontologia. Este material tem sido aplicado com o propósito de restaurar funções corporais que foram comprometidas por uma doença degenerativa (implantes ortopédicos), na área dentária e em sensores, devido às suas excelentes propriedades mecânicas, características estéticas e biocompatibilidade. Atualmente, existe a necessidade de desenvolver novos dispositivos com elevadas taxas de sucesso para as aplicações médicas mencionadas. O aumento da longevidade dos dispositivos protéticos para uma população jovem, mais ativa, com maior esperança de vida, requer o desenvolvimento de novos produtos, com desempenhos e designs fiáveis. O uso de Yttria Tetragonal Zirconia Polycrystal (Y-TZP) abriu possibilidades para desenvolver novos e promissores implantes, com novas e mais complexas geometrias, que não eram possíveis com outros cerâmicos, como por exemplo a alumina (mais frágil). Contudo, a zircónia cerâmica apresenta algumas limitações de trabalho: é sensível ao envelhecimento e apresenta baixa dureza. Devido a estas limitações, foram desenvolvidas várias amostras de zircónia estabilizada com 2 mol% de ítria (2YSZ), dopadas com diferentes óxidos, com o objetivo de avaliar e melhorar a resistência ao envelhecimento e propriedades mecânicas, quando comparadas com as amostras não dopadas. Para este efeito, foi realizada uma seleção criteriosa dos dopantes e respetivas concentrações. De acordo com a literatura, a céria (CeO2), sílica (SiO2), alumina (Al2O3), lantana (La2O3), íterbia (Yb2O3) e óxido de manganês (MnO2) melhoram a resistência ao envelhecimento e/ou as propriedades mecânicas da zircónia estabilizada com ítria (YSZ).Neste estudo, foram desenvolvidas treze diferentes composições dopadas, de zircónia estabilizada com 2 mol% de ítria (2YSZ). Por cada dopante selecionado foram preparadas três a quatro composições. Após uma etapa de moagem, os pós dopados de zircónia foram obtidos por atomização, a partir de suspensões estabilizadas, com uma distribuição de tamanho de partícula nanométrico controlado. Os pós atomizados foram caracterizados recorrendo a várias técnicas tais como microscopia eletrónica de varrimento (SEM), difração de raios-X (DRX), fluorescência de raios-X (FRX), densidade real, e área superficial específica (SSA). Os corpos em verde de todas as composições foram obtidos por prensagem uniaxial (70 MPa). Foram obtidos corpos cerâmicos com densidade elevada (com densidade relativa entre 90% e aproximadamente 99%) a uma temperatura de sinterização relativamente baixa (1350 ºC e 1400 ºC). O tamanho de grão das amostras sinterizadas foi medido através de imagens SEM, sendo verificado em todas as amostras de 2YSZ dopadas, uma microestrutura dispersa, com um tamanho de grão nanométrico. As fases cristalográficas presentes nas amostras dopadas foram identificadas por DRX. A fim de avaliar a resistência ao envelhecimento, as amostras sinterizadas foram submetidas a um tratamento térmico a baixas temperaturas (200 ºC) durante um período de 36 horas. Após este tratamento foi avaliada a tenacidade à fratura das amostras envelhecidas. Com base nestes resultados selecionaram-se as amostras que apresentavam melhor resistência ao envelhecimento térmico e tenacidade à fratura: 2YSZ dopada com CeO2 (0.50 wt%) e SiO2 (0.25 wt%) com La2O3 (1.07 wt%). Os pós das composições selecionadas foram sujeitos a prensagem uniaxial seguida de prensagem isostática a frio e sinterizadas a 1350 ºC durante 3 horas. Após sinterização, o comportamento destas amostras foi investigado em termos de resistência ao envelhecimento hidrotérmico e propriedades mecânicas: dureza de Vickers, tenacidade à fratura e resistência à flexão. Os testes de envelhecimento hidrotérmico foram realizados de acordo com as especificações mencionadas na norma ISO 13356:2008 (134 ± 2 ºC e 0.2 MPa). A percentagem de zircónia monoclínica, indicador de degradação, foi determinada por difração de raios-X após 5 horas de teste de envelhecimento hidrotérmico. Posteriormente, avaliou-se o comportamento mecânico (dureza de Vickers, a tenacidade à fratura e resistência à flexão) das amostras envelhecidas. O presente estudo demonstra que podem ser obtidas amostras cerâmicas de 2YSZ dopadas adequadas, com resistência à degradação hidrotérmico melhoradas (9.87 % de zircónia monoclínica para a amostra de 2YSZ dopada com SiO2 e La2O3, enquanto que a amostra de zircónia não dopada apresenta uma percentagem de fase monoclínica superior a 15 %). As propriedades mecânicas da amostra dopada com ambos os óxidos (SiO2 e La2O3), antes e após o envelhecimento hidrotérmico, foram praticamente mantidas (1159 vs 1141 HV (dureza), 9.68 vs 9.15 MPa.m1/2 (tenacidade à fratura) e 700 vs 698 MPa (resistência à flexão)). Porém, uma diminuição das propriedades mecânicas foi observada para ambas as amostras dopadas de 2YSZ selecionadas em relação à amostra de zircónia não dopada.Universidade de Aveiro2016-10-282016-10-28T00:00:00Z2018-10-28T13:00:00Zinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/masterThesisapplication/pdfhttp://hdl.handle.net/10773/21896TID:201935910engMacedo, Tânia Sofia Oliveirainfo: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:RCAAP2024-02-22T11:42:57Zoai:ria.ua.pt:10773/21896Portal AgregadorONGhttps://www.rcaap.pt/oai/openaireopendoar:71602024-03-20T02:56:12.899766Repositório 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 Improvement of the ageing resistance of 2YSZ ceramic
title Improvement of the ageing resistance of 2YSZ ceramic
spellingShingle Improvement of the ageing resistance of 2YSZ ceramic
Macedo, Tânia Sofia Oliveira
Materiais e dispositivos biomédicos
Biocerâmica - Propriedades mecânicas
Óxido de zircónio - Resistência à degradação
Materiais biocompatíveis
Próteses
title_short Improvement of the ageing resistance of 2YSZ ceramic
title_full Improvement of the ageing resistance of 2YSZ ceramic
title_fullStr Improvement of the ageing resistance of 2YSZ ceramic
title_full_unstemmed Improvement of the ageing resistance of 2YSZ ceramic
title_sort Improvement of the ageing resistance of 2YSZ ceramic
author Macedo, Tânia Sofia Oliveira
author_facet Macedo, Tânia Sofia Oliveira
author_role author
dc.contributor.author.fl_str_mv Macedo, Tânia Sofia Oliveira
dc.subject.por.fl_str_mv Materiais e dispositivos biomédicos
Biocerâmica - Propriedades mecânicas
Óxido de zircónio - Resistência à degradação
Materiais biocompatíveis
Próteses
topic Materiais e dispositivos biomédicos
Biocerâmica - Propriedades mecânicas
Óxido de zircónio - Resistência à degradação
Materiais biocompatíveis
Próteses
description Zirconia is a widely studied ceramic and it is applied in several areas such as engineering (solid oxide fuel cells, thermal barrier coatings) and biomedicine, in areas such as orthopedic and odontology. This material can be applied with the purpose to restore a body function that was compromised by a degenerative disease (orthopedic implants), in dental area and sensors due to its excellent mechanical properties, aesthetic characteristics and biocompatibility. However, this ceramic is sensitive to ageing and has a low hardness. To overcome these limitations, samples of Yttria Stabilized Zirconia doped with different oxides were developed and the goal was to improve the ageing resistance and mechanical properties of un-doped 2 mol% Yttria Stabilized Zirconia (2YSZ). A careful selection of the dopants and respective concentrations was performed. According to the literature, ceria (CeO2), silica (SiO2), alumina (Al2O3), lanthana (La2O3), ytterbia (Yb2O3) and manganese oxide (MnO2) improve the ageing resistance and/or the mechanical properties of Yttria Stabilized Zirconia (YSZ). In this study, thirteen different doped 2YSZ compositions were developed. For each selected dopant, three to four compositions were performed with different dopant concentrations. After a wet milling stage, the doped stabilized zirconia powders were obtained by spray-drying, from stabilized suspensions with a controlled nanometric particle size distribution. The obtained doped sprayed powders were characterized through several techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), density and specific surface area (SSA). Green bodies of all doped compositions were obtained by uniaxial pressing (70 MPa). High density ceramics (with relative density between 90% and approximately 99%) were achieved at low sintering temperatures (1350 °C and 1400 °C). The grain size of the sintered samples was measured by SEM images, and a dispersed microstructure with a nanometric grain size was observed for all 2YSZ doped samples. The crystallographic phases present in the doped samples were identified by XRD. In order to assess their thermal ageing resistance, the samples were subjected to a thermal treatment at low temperatures (200 °C) during a period of 36 hours. After this treatment, the fracture toughness of the aged samples was evaluated. From all the starting samples, those with better resistance to thermal ageing and fracture toughness were afterwards selected: samples of 2YSZ doped with CeO2 (0.50 wt%) and with SiO2 (0.25 wt%) and La2O3 (1.07 wt%). Cylindrical bodies of the selected doped 2YSZ compositions were obtained by two pressing stages - uniaxial and cold isostatic pressing - and sintered at 1350 ºC for 3 hours. The behaviour of the sintered samples was investigated in terms of hydrothermal ageing resistance, according to the specifications mentioned in ISO 13356:2008 (134 ± 2 ºC and 0.2 MPa), and mechanical properties: Vickers’ hardness along with fracture toughness and flexural strength. The amount of monoclinic zirconia, indicative of degradation, was determined by XRD after 5 hours of ageing test. Afterwards the mechanical behaviour (Vickers hardness, fracture toughness and flexural strength) of the aged samples was assessed. The results obtained in the present study demonstrate that adequate doped 2YSZ samples, with improved hydrothermal degradation resistance (9.87 % of monoclinic zirconia for SiO2 with La2O3 doped 2YSZ sample while un-doped 2YSZ presented a monoclinic phase higher than 15 %) can be obtained. The mechanical properties of the sample of 2YSZ doped with both oxides (SiO2 and La2O3), before and after the hydrothermal ageing, were practically maintained (1159 vs 1141 HV (hardness), 9.68 vs 9.15 MPa.m1/2 (fracture toughness) and 700 vs 698 MPa (flexural strength)). Nevertheless, a decrease of the mechanical properties was observed for both selected doped 2YSZ samples in relation to un-doped sample.
publishDate 2016
dc.date.none.fl_str_mv 2016-10-28
2016-10-28T00:00:00Z
2018-10-28T13:00:00Z
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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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