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Título: EVOLUTION OF POINT DEFECTS IN AL2W3O12 DURING CALCINATION IN AIR AND THE EFFECTS OF DIFFERENT SINTERING METHODS ON ITS DENSITY, MICROSTRUCTURE, AND HARDNESS
Autor: MARIANNE DINIZ ROCHA HENRIQUES
Colaborador(es): BOJAN MARINKOVIC - Orientador
Catalogação: 02/SET/2024 Língua(s): ENGLISH - UNITED STATES
Tipo: TEXT Subtipo: THESIS
Notas: [pt] Todos os dados constantes dos documentos são de inteira responsabilidade de seus autores. Os dados utilizados nas descrições dos documentos estão em conformidade com os sistemas da administração da PUC-Rio.
[en] All data contained in the documents are the sole responsibility of the authors. The data used in the descriptions of the documents are in conformity with the systems of the administration of PUC-Rio.
Referência(s): [pt] https://www.maxwell.vrac.puc-rio.br/projetosEspeciais/ETDs/consultas/conteudo.php?strSecao=resultado&nrSeq=67809&idi=1
[en] https://www.maxwell.vrac.puc-rio.br/projetosEspeciais/ETDs/consultas/conteudo.php?strSecao=resultado&nrSeq=67809&idi=2
DOI: https://doi.org/10.17771/PUCRio.acad.67809
Resumo:
This work consists of two complementary studies regarding Al2W3O12-based materials. Therefore, the aim of this work was to i) produce dense Al2W3O12 ceramics by different sintering routes and evaluate its effects on densification and microstructure, and ii) evaluate the evolution of point defects on Al2W3O12 after temperature variations during the calcination process in air atmosphere. Al2W3O12 amorphous powder was produced via coprecipitation synthesis followed by calcination to induce crystallization. The influence of the different calcination temperatures in ambient air atmosphere was assessed while the calcination time remained the same, by various techniques, such as X-ray Powder Diffraction (XRPD), Raman, and Electron Paramagnetic Resonance (EPR) Spectroscopies to understand the formation of point defects into Al2W3O12 crystal structure. Different concentrations of oxygen vacancies were formed while altering the calcination temperature from 500 – 620 degrees C. It was observed that the oxygen vacancy concentration increases with the decrease of the calcination temperature. Interestingly, the highest oxygen vacancy content occurs while the powder is still amorphous at 500 degrees C. Therefore, the crystallization process of orthorhombic Al2W3O12 is highly affected by the formation of oxygen vacancies. The best Al2W3O12 powder, calcined at 570 degrees C, was selected and used to consolidate the pellets for sintering. It was determined that due to the presence of agglomerates, further milling was necessary to break the agglomerates and increase the specific surface area of the powder. After ball-milling the specific surface area went from 26.4 m(2)g(-1) to 31.4 m(2)g(-1). The milled and non-milled calcined powders were used to produce sintered bodies and is densification, microstructure, and mechanical properties compared. The sintering routes consisted of Rapid Pressure-Less Sintering (RPLS) technique and Spark Plasma Sintering method (SPS). RPLS technique produced dense cylinders of 96 percent density at its best setting, while SPS produced pellets as dense as 98.8 percent TD. The process of milling the calcined powder did not show much improvement in either densification or microstructure, forming samples slightly denser than those without milling.
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