In one of the leading journals for biomaterials, we have contributed to the understanding of the effect of yttrium segregation on t–m transformation of 3Y-TZP bioceramics. By careful design of the sintering strategy, it was possible to fabricate 3Y-TZP with identical grain size distributions but with different yttrium concentrations. The influence of phase partitioning on stability and structure of different phases present in 3Y-TZP and on the formation of residual stresses were investigated. It is shown that yttria-rich phases are under compressive stresses in the 3Y-TZP matrix since a systematic relaxation after ageing was observed and explained for the first time. It puts additional perspective on the understanding of the t–m transformation mechanism ultimately governing both the ageing and fracture behaviour of 3Y-TZP.
COBISS.SI-ID: 30688295
We showed how primary crystallites can be used as building blocks for homogenous packing and rapid sintering. Namely, the ordered agglomeration of zirconia primary crystallites into secondary particle assemblies ensured their homogeneous packing, while also preserving the high surface energy to higher temperatures, increasing the sintering activity. When exposed to intense electromagnetic radiation activated by the SPS set-up providing rapid heating, the assembled crystallites were subjected to further agglomeration, coalescence and sliding, leading to rapid densification in the absence of extensive diffusional processes, cancelling out the grain growth during the initial sintering stages and providing a zirconia nanoceramic in only 2 minutes at 1300 °C. The work was published in Scientific Reports and announced in the renowned Ceramic Tech Today portal of the American Ceramic Society.
COBISS.SI-ID: 30524455
The published work resembles on a fruitful collaboration between researchers from IFE (Norway), IMDEA-Nanociencia (Spain) and JSI (Slovenia). The paper deepened the knowledge about the influence of processing on the magnetic properties of cobalt ferrite, which is the only ceramic-based spinel magnet that has hard magnetic properties. Furthermore, the impact of ultra-short milling at liquid nitrogen temperatures on structural and magnetic properties of cobalt ferrite (CoFe2O4) powders has been explored for the first time. Cryomilling for only up to 9 min increases the coercivity of the isotropic powder from 139 to 306 kA/m (1.74 to 3.85 kOe) and results in its modifications comparable with milling for hours at room temperature. Thermal treatment of processed CoFe2O4 enables further optimization of powder magnetic properties and leads to a high value of energy product (13.5 kJ/m3 ) for the sample treated at 600 °C. Systematic studies, comprising analysis of structural and microstructural properties, based on synchrotron powder X-ray diffraction, scanning and transmission electron microscopy demonstrate the high efficiency of cryomilling in the reduction of crystallite sizes and formation of lattice strain in the processed cobalt ferrite samples.
COBISS.SI-ID: 30525223
In collaboration with the University of Szeged, Hungary, we prepared a highly photocatalytic and antibacterial ceramic-based hybrid material by combining semiconductor photocatalyst (TiO2) and a highly lamellar structure (hydroxyapatite – HAp). Immobilization of the photocatalyst is achieved by the addition of a polymer binder. Polymers are often used as photocatalyst matrices due to their flexibility, low weight, impact resistance, and low cost. The presence of biocompatible ceramic HAp microlamellae in the TiO2/polymer hybrid layers results in an incompact structure of the thin films with enhanced photocatalytic surface accessibility. Specific surface values of the TiO2/Hap composites were much higher (140 m2 g−1) than those of the pure HAp (116 m2 g−1) and TiO2 (53 m2 g−1) components. Due to this structure opening effect of the HAp lamellae, the hybrid film consists of 36/24/40 wt% TiO2/HAp/polyacrylate showed the same antibacterial activity as the film with 60/40 wt% TiO2/polyacrylate composition. Moreover, the presence of inert HAp lamellae in the TiO2/polyacrylate matrix has significantly decreased the undesired photodegradation of the polymer binder.
COBISS.SI-ID: 30653479
We have studied the combined effects of alumina airborne-particle abrasion and prolonged in vitro ageing, at 134 °C for up to 480 h, on the flexural strength of popular bioceramic - 3Y-TZP, which is known for its susceptibility to low-temperature degradation (LTD). The results were published in the top ranked dental materials journal. For the first time, it was shown that 10 μm thick altered zone under the abraded surface was involved in both the surface strengthening and the increased ageing resistance. When the zone was annihilated by the LTD, the strength of the ceramic specimens and the speed of LTD returned to the values measured before abrasion. Even at prolonged ageing times, the strength of abraded groups was not lower than that of as-sintered groups. Airborne-particle abrasion was not harmful to 3Y-TZP ceramics.
COBISS.SI-ID: 33233881