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Previous issue date: 2016-03-30 / P?s de c?ria dopada com 0% (CeO2); 10% (CGO10) ou 20% (CGO20) em mol de gadol?nia foram sintetizados pelo m?todo Pechini. Os p?s calcinados, como-sintetizados e mo?dos/peneirados foram caracterizados por DRX, BET, TG e DTG. Pastilhas de materiais particulados mo?dos/peneirados e como-sintetizados foram prensadas uniaxialmente com 210 MPa, e em seguida sinterizadas at? 1400 ?C com taxa de aquecimento de 5 ?C/min em dilat?metro sem e com a a??o de campo el?trico DC. Os campos el?tricos aplicados foram de 0; 10; 30 e 50 Vcm-1. Os valores da intensidade de corrente el?trica e diferen?a de potencial el?trico foram registrados em fun??o da temperatura. As densidades das pastilhas, a verde e sinterizada, foram calculadas pelo m?todo geom?trico. A caracteriza??o microestrutural das amostras sinterizadas foi realizada por microscopia eletr?nica de varredura (MEV), com o tamanho m?dio de gr?o avaliado por an?lise de imagem no software ImageJ. Os valores de densidades alcan?ados sugerem que a moagem/peneiramento proporciona maior taxa de sinteriza??o independentemente da composi??o e do valor do campo el?trico aplicado. Os resultados obtidos sugerem que a aplica??o de campo el?trico durante a sinteriza??o promove maior densifica??o, p? mo?do/peneirado ou p? sem moer, independentemente da composi??o, e, que quanto maior ? o valor do campo el?trico, maior ? a densifica??o do material. A dopagem da c?ria retardou o crescimento dos gr?os durante a sinteriza??o convencional no dilat?metro, pastilhas com p? mo?do/peneirado ou com p? sem moer. Este retardo no crescimento de gr?o foi atribu?do ao fen?meno ?drag solute?. A sinteriza??o das pastilhas prensadas com p? mo?do/peneirado, sob a a??o de um campo el?trico, proporcionou retardo no crescimento de gr?o para todas as composi??es. Apesar da a??o do campo el?trico retardar significativamente a taxa de crescimento de gr?o, os diferentes valores de campo el?trico n?o causaram diferen?as significativas a esta taxa. Este fen?meno n?o foi observado quando p? sem moer foi usado. Ao retardo no crescimento de gr?o, quando da sinteriza??o sob efeito do campo el?trico, foi atribu?do ? maior temperatura nos contornos de gr?o que reduz a energia livre de difus?o de contorno de gr?o. A a??o conjunta moagem/peneiramento e aplica??o de campo el?trico DC se mostrou eficiente para retardar o crescimento de gr?o das composi??es e aumentar a taxa de densifica??o, em rela??o ? sinteriza??o convencional. A sinteriza??o de p?s ? base de c?ria (mo?dos/peneirados) com aplica??o de um campo el?trico DC (em condi??es n?o isot?rmicas entre 30 e 1400 ?C) mostrou-se um alternativa bastante promissora para a obten??o de cer?micas com reduzido tamanho de gr?o e densidades relativas superiores a 90%. / Ceria powders doped with 0% (CeO2); 10% (CGO10) or 20% (CGO20) of gadolinia mol were synthesized by the Pechini method. The calcined powders, as-synthesized and ground / sieved were characterized by XRD, BET, TG and DTG. materials tablets particulate ground / sieved and as-synthesized were pressed uniaxially at 210 MPa, and then sintered to 1400 ? C with a heating rate of 5 ? C / min in dilatometer with and without DC electric field action. The applied electric fields were 0; 10; 30 and 50 Vcm-1. The values of the intensity of electric current and electric potential difference was recorded as a function of temperature. The densities of the pellets, the green and sintered, were calculated using the geometric method. Microstructural characterization of sintered samples was performed by scanning electron microscopy (SEM), with the average grain size measured by image analysis in ImageJ software. The achieved densities values suggest that the milling / sieving provides enhanced sintering rate regardless of the composition and the value of the applied electric field. The results suggest that the application of the electric field during sintering promotes greater densification, ground / sieved powder or powder without grinding, regardless of composition, and that the greater the value of the electric field, the greater the densification of the material. The delayed doping of ceria grain growth during sintering in conventional dilatometer, tablets with milled powder / or sieved powder without milling. This delay in grain growth was attributed to the phenomenon "drag solute." The sintering of pressed pellets of ground / sieved powder, under the action of an electric field, provided delayed grain growth for all compositions. Despite the electric field action significantly slow the grain growth rate, different electric field values did not cause significant differences in the rate. This phenomenon was not observed when powder without grinding was used. To delayed grain growth when sintering under the influence of the electric field, it was attributed to the higher temperature at the grain boundaries which reduces the free energy of the grain boundary diffusion. The joint action grinding / sieving and application of DC electric field was efficient for retarding grain growth of the compositions and increase the densification rate, as compared to conventional sintering. The powder sintering of ceria (ground / sieved) by applying a DC electric field (in non-isothermal conditions between 30 and 1400 ? C) proved to be a promising alternative for obtaining ceramic with reduced grain size and relative densities exceeding 90%.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/21783 |
| Date | 30 March 2016 |
| Creators | Fernandes, Ednaldo Silva |
| Contributors | 80732810400, Martinelli, Antonio Eduardo, 15724520800, Miranda, Auristela Carla de, 03501789416, Macedo, Daniel Ara?jo de, 01152094416, Menezes, Romualdo Rodrigues, 02664019457, Nascimento, Rubens Maribondo do |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM CI?NCIA E ENGENHARIA DE MATERIAIS, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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