Surface Modification of Zirconia for dental implants
Tutor / director / evaluatorCamposilvan, Erik
Document typeMaster thesis (pre-Bologna period)
Rights accessRestricted access - author's decision
Zirconia doped with 3% molar of yttria (3Y-TZP) has been widely used in the manufacturing of medical implants during the last decades, especially thanks to its unique balance of toughness and strength. At room temperature, these properties are mostly related to toughening by the stress assisted transformation of the metastable tetragonal phase into stable monoclinic one in front of a crack tip under stress. This transformation is accompanied by a volume expansion of 5%, which contributes to prevent material failure by reducing crack propagation and increasing toughness. The weak point of 3Y-TZP resides in its environmental sensibility. Indeed, it is prone to Low Temperature Degradation (LTD), an ageing phenomenon which occurs under humid atmosphere at relatively low temperatures, being faster around 200°C. Therefore, this project consists in designing a novel methodology for LTD prevention through Cerium infiltration into pre-sintered 3Y-TZP porous blanks prior to sintering. The purpose is to limit the treatment to superficial regions in order to increase the resistance to LTD without affecting significantly the initial mechanical properties. The control of the infiltration is performed on specimens by adjusting three parameters: solution viscosity, immersion time and penetration mechanism (by diffusion or capillarity). Cerium infiltration appears efficient in regard to LTD prevention, since it is shown that it prevents degradation after 30h of artificial ageing. Besides, the influence of Cerium on mechanical properties, such as hardness and fracture toughness, is determined by the amount and penetration depth of Cerium in 3Y-TZP. By using short immersion times, high solution viscosities and diffusive penetration mechanisms, the mechanical properties of 3YTZP are maintained, without significant reduction on hardness or fracture toughness. Finally, it is proposed another new method to prevent LTD which is based on Cerium infiltration in combination with sandblasting.
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