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Abstract(s)
Numa aeronave há componentes sujeitos a condições de serviço de grande
exigência mecânica, térmica e química. Estes componentes são chamados de sistemas de
proteção térmica. Quando um sistema está sujeito a forças elevadas, em particular à
compressão, flexão e desgaste, a ambientes agressivos, como temperaturas elevadas,
contacto com gases poluentes e choque de partículas, os materiais cerâmicos surgem
como a primeira opção. Tipicamente um sistema de proteção térmica é constituído por
um material cerâmico que funciona como barreira ou escudo exterior sobre um substrato
metálico responsável pela estrutura do veículo. O fabrico de revestimentos tipo TBC são
caracterizados pela pequena espessura (~ 100 µm), e as partículas de matéria-prima são
de escala submicra. Mas num escudo a espessura pode alcançar alguns centímetros e a
sua viabilidade estrutural e económica é conseguida com o uso de distribuições de
tamanhos de partículas até ao milímetro.
Neste trabalho parte-se da composição cerâmica CaO-ZrO2-MgO, com grande
potencial para aplicações enquanto revestimento termomecânico de partículas finas e
promove-se o seu reforço com partículas grossas de Al2O3. Os resultados mostram que o
MgO se associa com a Al2O3 e forma-se espinela de aluminato de magnésio e a porosidade
é elevada. Para pequenos teores de Al2O3 as propriedades ficam gravemente
prejudicadas, mas para maiores frações mássicas de 60% de Al2O3 a porosidade diminui
e a melhoria das propriedades mecânicas permitem propor o compósito para condições
de serviço mais exigentes como um sistema de proteção térmica de uma aeronave.
In an aircraft there are components subject to severe conditions of operation with higher mechanical, thermal and chemical requirements. These components are called thermal protection systems or thermal shields. When a system is subjected to high stresses, in particular to compression, bending and wear, to aggressive environments, such as high temperatures, contact with exhausting gases and particle shock, ceramic materials appear as the first option. Typically, a thermal shield consists of a ceramic material that acts as a barrier or outer shield over a metallic substrate responsible for the vehicle's structure. The manufacture of coatings (type TBC) is characterized by its small thickness (~ 100 µm), and the starting raw material particles are from a sub-micron scale. But in a shield the thickness can reach a few centimetres and its structural and economic viability is achieved with the use of particle size distributions up to a millimetre. This work starts with the ceramic composition CaZrO3-MgO, with great potential for applications as a thermomechanical coating of fine particles, and its reinforcement with coarse Al2O3 particles is promoted. The results show that MgO is associated with Al2O3 and magnesium aluminate spinel is formed, and the porosity is high. For small contents of Al2O3 the properties are severely impaired, but for higher mass fractions of 60% of Al2O3 the porosity decreases and the improvement of the mechanical properties allows to propose the composite for more demanding service conditions such as an aircraft thermal protection system.
In an aircraft there are components subject to severe conditions of operation with higher mechanical, thermal and chemical requirements. These components are called thermal protection systems or thermal shields. When a system is subjected to high stresses, in particular to compression, bending and wear, to aggressive environments, such as high temperatures, contact with exhausting gases and particle shock, ceramic materials appear as the first option. Typically, a thermal shield consists of a ceramic material that acts as a barrier or outer shield over a metallic substrate responsible for the vehicle's structure. The manufacture of coatings (type TBC) is characterized by its small thickness (~ 100 µm), and the starting raw material particles are from a sub-micron scale. But in a shield the thickness can reach a few centimetres and its structural and economic viability is achieved with the use of particle size distributions up to a millimetre. This work starts with the ceramic composition CaZrO3-MgO, with great potential for applications as a thermomechanical coating of fine particles, and its reinforcement with coarse Al2O3 particles is promoted. The results show that MgO is associated with Al2O3 and magnesium aluminate spinel is formed, and the porosity is high. For small contents of Al2O3 the properties are severely impaired, but for higher mass fractions of 60% of Al2O3 the porosity decreases and the improvement of the mechanical properties allows to propose the composite for more demanding service conditions such as an aircraft thermal protection system.
Description
Keywords
Cazro3 – Mgo - Al2o3 Cerâmica Avançada Distribuição Granulométrica Sistema de Proteção Térmica