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.
COBISS.SI-ID: 28072487
The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics was investigated. In order to differentiate between the distinct contributions of two dopants to the overall resistance to low-temperature degradation (LTD), specimens were prepared by infiltration of silica sol into pre-sintered 3Y-TZP pellets, produced from commercially available powders, which were alumina-free or contained 0.05 and 0.25 wt.%. The results howed 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 LTD. The addition of either alumina or silica has the potential to influence both the nucleation and the propagation of moisture-induced transformation, but in different ways and to different extents. 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
This study was designed to explore the complex relationships between the sintering-temperature-dependent grain size, airborne-particle abrasion, ageing and strength of 3Y-TZP ceramics. The low-temperature-sintered, fine-grained ceramic exhibited an excellent ageing resistance, while the high- temperature-sintered, coarse-grained ceramic experienced a higher surface strengthening and a substantially improved ageing resistance with respect to the airborne-particle abrasion. Our results show that the sintering temperature has a minor effect on the flexural strength, but it plays a crucial role in the surface strengthening and the ageing behaviour of 3Y-TZP dental ceramics.
COBISS.SI-ID: 29163303
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
We have merged the benefits of coarsegrained and nanocrystalline powders by the consolidation and sintering of coarse, yet nanostructured, mesoporous zirconia powder. The powder was composed of loosely aggregated, nanoscale crystallites, which can be seen as secondary particles or agglomerates. Their homogeneous, defect free packing proved to be a viable pathway for the pocessing f zirconia nanoceramics. The powder consolidation yielded omogeneous green bodies with hierarchical heterogeneities in terms of intraand interparticle pore packing. The hierarchical heterogeneities had a pronounced effect on the densification and grain growth. The intraparticle pore coalescence along with a “frozen” interparticle porosity, prolonged the porepinning effect, separating the densification and graingrowth mechanisms. Increased heating rates promoted the grain growth and densification via a competitive mechanism of primary crystallite ordered coalescence, while by applying pressure, the crystallite growth was completely prevented, making such a coarse powder suitable for the fabrication of zirconia nanoceramics.
COBISS.SI-ID: 28124455