Development of translucent zirconia by robocasting

Partially translucent zirconia for dental applications was developed by robocasting using aqueous-based inks of zirconia doped with 5 mol.%Y2O3 as feedstock and a printing nozzle with 0.25 mm diameter. The manufactured samples were sintered at 1600 °C-2 h and characterized by crystalline phases, microstructure, mechanical properties and opacity. The sintered samples presented ≈94 % relative density, 12.7 ± 0.3 GPa as Vickers hardness, 3.91 MPa.m1/2 as fracture toughness and, 285 ± 57 MPa as flexural strength. The contrast ratio optical parameter varied in the range of 0.5 to 0.9, according to the material thickness. These optical outcomes are determined by the relative density and the microstructure, namely the presence of sub-micrometre tetragonal grains (26.4 %) and cubic phase grains (73.6 %) with sizes in the order of 1.5 μm, that justified the improved translucency obtained when compared to opaque tetragonal 3Y-TZP ceramics.publishe

Direct ink writing of ATZ composites based on inks prepared by colloidal or hydrogel route: linking inks rheology with mechanical properties

The Direct Ink Writing (DIW) technique stands out due to its fast processing, low amounts of additives demanded for the ink’s preparation and, consequently, the relatively quickly thermal post-processing cycles. On this behalf, the development of inks for DIW is usually based on colloidal or hydrogel-based processing routes, which derive from interparticle interactions or gel-particle interactions, respectively. The aim of this work was to evaluate the impact of colloidal or hydrogel-based ceramic inks processing routes in the properties of Alumina Toughened Zirconia (ATZ) composites prepared by DIW. It was found that the alumina grains were homogeneously dispersed into the zirconia matrix on samples derived from the colloidal ink, while big agglomerates could be found on those derived from the hydrogel ink. The good homogeneity observed on the colloidal route is related with the particle-particle (electrosteric) stabilization mechanism that induced an efficient dispersion of the starting powders, in contrast with the hydrogel route where the steric stabilization mechanism is dominant. Given the high interest of these composites as biomaterials, the achievements here attained open future opportunities for the near-net-shape processing of geometrically complex and customized dense and tough prosthesis and implants by DIW with mechanical performance comparable with conventional processing routes.publishe

Nanostructured transparent solutions for UV-shielding: recent developments and future challenges

Ultraviolet (UV) radiation is known to promote health concerns that can manifest over both short and long terms. Aging, sunburn, skin cancer, and other conditions are related to UV radiation. Medication can also be negatively affected by this radiation. Moreover, UV radiation modifies the taste, colour, and texture of food, and may compromise its suitability for human consumption. Therefore, the development of UV-shielding materials attracts considerable research interest for numerous applications, such as UV-light resistant packaging, sunscreens, contact lenses, coatings, and even clothes. UV-shielding materials arise from the dispersion of a UV-absorber of inorganic (such as ZnO, TiO2, CeO2) or organic (such as lignin, nanocellulose) nature into a matrix of high transparency (usually polymer or glass based). The most common types of UV-absorbers are semiconductor particles, quantum dots, or a hybrid approach combining both. However, inhomogeneous dispersion and large size distributions of the absorbing agent usually compromise the transparency of the UV-shielding material. The goal of the current study is to present the newest and most innovative approaches regarding the development of nanostructured transparent solutions for UV-shielding.publishe