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 |
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Colaborador(es): |
BOJAN MARINKOVIC - Orientador |
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Catalogação: | 02/SET/2024 | Língua(s): | ENGLISH - UNITED STATES |
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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. |
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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 |
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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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