By employing advanced materials engineering high-performance thermally insulating materials from renewable resources were prepared aimed improving the energy efficiency of buildings. We showed that freeze casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fireretardant and strong anisotropic highly porous, foams that perform better than traditional polymer-based insulating materials. The porous foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m-1 K-1, which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale advanced materials engineering is a promising strategy for producing porous structures with excellent properties using cellulose and other renewable nanosized fibrous materials. Publication is at the moment ranked as highly cited paper collecting ?170 citations in less than 3 years.
COBISS.SI-ID: 28072487
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
The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics was investigated in collaboration with respected professor Micheal Swain. The results showed that the minor alumina and/or silica additions did not drastically change the densities, grain sizes on mechanical properties of 3Y-TZP, but they did significantly reduce ageing. The co-doped ceramics exhibited predominantly transgranular fracture, reflecting strong grain boundaries (limiting microcracking of the transformed layer), for alumina doping, and rounded grains with a glassy phase at multiple grain junctions (reducing internal stresses) for silica-doped material. These two additives evidently have different dominant mechanisms associated with the deceleration of LTD of 3Y-TZP, but their combination increases resistance to ageing, importantly, without reducing the fracture toughness of this popular biomaterial.
COBISS.SI-ID: 28092455
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
Long-term (480 h) in vitro accelerated ageing was employed to monitor the relationships between ageing, strength and subsurface microstructure. Long-term ageing revealed important new information on the impact of air-particle abrasion (APA; sandblasting) on the mechanical properties. In the initial stages of accelerated ageing, the strength of APA specimens was decreased but then stabilised to match the strength of as-sintered groups. Thinner specimens exhibited similar mechanical behaviour, with the exemption of spontaneous fracturing after 480 h which did not occur in thicker specimens. The ageing in intact specimens exhibited a uniformly increasing linear trend. Upon APA, two-step linear ageing kinetics were observed, matching the approximately 10 µm thick altered zone under the abraded surface. When this zone was annihilated by ageing, the strength and the ageing speed returned to the values measured before abrasion.
COBISS.SI-ID: 33233881
Head of the programme published with co-authors one of the last parts of his studies from PhD dissertation serving as basis for present project, i.e., the evolution of aluminum hydroxides in diluted aqueous aluminum nitride (AlN) powder suspensions in the temperature range 22-90°C, where the a general mechanistic model over a broad temperature range was set up, uniting previously observed hydrolysis reactions at room temperature and at elevated temperatures into a single scheme for the first time. We showed the temperature-dependent formation of various aluminum hydroxides in the following sequence: amorphous aluminum hydroxide gel, aluminum monohydroxide (boehmite), and aluminum trihydroxides (bayerite, nordstrandite, and gibbsite). The unique interdependency between the temperature and the pH of the hydrolyzing AlN powder suspension, governed by the ammonia’s solubility and the exothermic hydrolysis reactions producing Al(OH)4- species, is the driving force for several evolution paths of these aluminum hydroxides exhibiting numerous morphologies.
COBISS.SI-ID: 25586727
The so-called rare-earth crisis has been a trigger for researchers to »discover« ferrite magnets once again. Namely, the increase in the energy product of ferrites would lead to incorporation of ferrite magnets in some applications, which at the moment use Nd-Fe-B magnets. In our work we investigated exchange-coupled hard (SrFe12O19) and soft (CoFe2O4) magnetic phase magnets. To exploit exchange interaction between the hard and the soft magnetic phase, it is necessary to fulfil certain conditions. One of the most important conditions is the size of the soft magnetic phase, which should not exceed 28 nm (if the hard magnetic phase is SrFe12O19). It is known that during the spark plasma sintering (SPS) grain growth is almost negligible when compared to the conventional sintering. Therefore, we used SPS as a densification method. Furthermore, we have determined the optimal sintering conditions (1900 °C, 5 min, 90 MPa), measured magnetic properties, and explained them by means of the microstructural analysis. Results have shown that SPS sintered SrFe12O19-CoFe2O4 composites exhibited 22% higher energy product as a single phase SrFe12O19 used as a hard phase material and prepared following the same procedure.
COBISS.SI-ID: 29371943
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
Relevant conditions for electrophoretic (infiltration) deposition (EPID) of thick conductive fibre preforms were investigated. Modified electrophoretic deposition cell was used to fabricate conductive fibre-reinforced composites from an aqueous suspension. 3D woven fibre preform had to be separated from the depositing electrode, thus enabling the penetration of migrating particles through the porous structure. Infiltration of conductive preforms proceeds in a similar manner as for non-conductive fibre reinforcements, by deposition at the electrode and backfilling of the fibre preform.
COBISS.SI-ID: 28767527
Combination of an Au-based 4-arms thiol terminated poly(ethylene glycol) [Au-(PEGSH)4] dynamic hydrogel exhibiting self-healing ability with 100 nm bioactive glass (BAG) nanoparticles agglomerated in 10 mm clusters, produced via a particulate sol–gel method, resulted in the formation of hydrogel nanocomposites [Au-(PEGSH)4–BAG] with enhanced properties. Compression tests demonstrated the major drawbacks of each individual material, i.e. brittleness for BAG nanoparticles and weak consistency for Au-(PEGSH)4, were suppressed to result in a material composite with high resistance to stress and relatively large deformation ability. Moreover, the slow diffusion inside the 3D matrix allowed the degradation of the BAG nanoparticles to be delayed as well as the pH to be maintained around physiological values. For the same reason, the incorporation of those BAG nanoparticles into the dynamic hydrogel proved to reduce the cytotoxicity of the organic particles. Finally, in vitro degradation of BAG nanoparticles embedded in the dynamic hydrogel led to the formation of hydroxyapatite. As a result, osteoinductive properties could be anticipated for the Au(PEGSH)4–BAG hydrogel nanocomposite which allows this new injectable and self-healing dynamic biomaterial to be considered as a scaffold to induce and promote bone self-repair.
COBISS.SI-ID: 29648679