Obtenção de compósitos de alumina reforçados com nanopartículas de aluminossilicatos de lítio e niobato de alumínio
[EN] In the search for materials with greater resistance to ballistic impacts, alumina ceramics have gained increased attention due to their cost-effectiveness and favorable properties such as high elastic modulus, high hardness, and high refractoriness. However, their fracture toughness is lower co...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión aceptada para publicación |
| Fecha de publicación: | 2024 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/384467 |
| Acceso en línea: | http://hdl.handle.net/10261/384467 |
| Access Level: | acceso abierto |
| Palabra clave: | Aluminum niobate lithium aluminosilicate fracture toughness alumina Niobato de alumínio aluminossilicato de lítio tenacidade à fratura |
| Sumario: | [EN] In the search for materials with greater resistance to ballistic impacts, alumina ceramics have gained increased attention due to their cost-effectiveness and favorable properties such as high elastic modulus, high hardness, and high refractoriness. However, their fracture toughness is lower compared to carbides. Consequently, there is a significant effort within the scientific community to improve this property using new alumina-based technologies for ballistic applications. The use of alumina matrices with the addition of additives to enhance properties is an alternative for increasing fracture toughness. The aluminum niobate phase, used as an additive in alumina matrices, has the potential to both lower the sintering temperature and improve mechanical properties. Lithium aluminosilicate phases, such as eucryptite and β-spodumene, with low thermal expansion coefficients, can improve the fracture toughness of alumina by forming compressive stresses around the grains. In this context, this research aimed to develop an alumina composite with the addition of aluminum niobate, eucryptite, and β-spodumene phases to improve fracture toughness. The nanostructured aluminum niobate phase was obtained via colloidal synthesis followed by a solid-state reaction, with an average size of 19 nm. The nanostructured β-spodumene and eucryptite phases were obtained via heterocoagulation colloidal synthesis followed by solid-state reaction, with average sizes of 24 and 44 nm, and CET of 0.52×10⁻⁶ °C⁻¹ and 0.46×10⁻⁶ °C⁻¹, respectively. The addition of these phases reduced the sintering temperature by up to 300 °C while maintaining 95% densification. The alumina matrix composites were produced using the slip casting method in plaster molds. The formulations analyzed contained a 5 vol.% addition of each of the three produced phases, as well as a formulation containing 95 vol.% alumina with a 2.5 vol.% addition of aluminum niobate and 2.5 vol.% addition of eucryptite, and another containing 95 vol.% alumina with a 2.5 vol.% addition of aluminum niobate and 2.5 vol.% addition of β-spodumene. All composites exhibited a reduction in grain size. The main results showed that the addition of the AlNbO4 phase promoted transgranular fracture, with the best result obtained in the alumina sample with a 5 vol.% addition of the AlNbO4 phase, sintered at 1400 °C for 35 min. The fracture toughness improved by 63%, increasing from 3.25 MPa·m0.5 to 5.34 MPa·m0.5 and the 2.5EU/NB.13 sample has an elastic modulus of 350 GPa, flexural strength of 270 ± 4 MPa, hardness of 12.2 ± 1.4 GPa, and fracture toughness of 5.0 ± 0.3 MPa·m⁰·⁵, showing itself as the best formulation and potential for use in ballistic protection, suggesting the continuation of studies for practical validation. |
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