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Development of three - dimensional structures of yttria stabilized zirconia (YSZ) by lyophilization for biomedical applications
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Over the last decade, zirconia has been widely used in biomedical applications, particularly in dentistry, because it exhibits an unique combination of advantageous properties: mechanical strength, low thermal conductivity, high density, low corrosion potential, biocompatibility, low cytoxicity and minimal bacterial adhesion. In particular, 3 mol% yttrium partially stabilized tetragonal zirconia (3YSZ) is known for presenting the highest strength and exhibiting transformation toughening which enhances fracture toughness. Additionally, in the recent years, nanocrystalline materials have received a great deal of attention, since they display unusual properties including higher strength and hardness.
Hence, in this study, a 3YSZ nanosized crystalline powder, provided by Innovnano, was applied as the starting material to produce quality solid foams using a freeze drying process followed by sintering. However, when dealing with nanopowders, processing problems rise due to nanoparticles agglomeration tendencies. This problem was mitigated by carrying out rheology studies to the powder’s suspensions to determine the optimal viscosity for homogenous suspensions to be made.
Porous samples with densities between 1.95 g/cm3 and 2.65 g/cm3 and open porosities between 52.10% and 67.60% using a low sintering temperature (1350ºC) were obtained. These values lie above what is normal to obtain since it is difficult to manufacture highly porous foams of yttria-stabilized zirconia with porosity percentages greater than about 40 % to 50%. The morphological analysis of the samples was carried out using SEM and by means of X-ray diffraction, it was detected that the main crystallographic phase present in the porous samples is tetragonal (no T-M transformation occurred). By performing compression tests, porous samples with Young’s modulus between 19.20 and 35.60 GPa and collapse stress between 62.60 and 73.20 MPa were obtained.
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3YSZ nanocrystalline porous samples lyophilization rheology