Translucent, high-performance, mullite ceramics with anisotropic grains were prepared by the spark plasma sintering (SPS) of a powder mixture consisting of commercial mullite powder, which already contained small amounts of alumina and silica, to which 2 and 1 wt% of yttria and amorphous silica was admixed, respectively. The combination of low-viscosity Y2O3–Al2O3–SiO2 transient liquid formation and SPS sintering provided enhanced densification, also provoking anisotropic grain growth at a relatively low sintering temperature of 1370°C. In this way, it was possible to meet the conflicting demands for obtaining a dense mullite ceramic with anisotropic grains, ensuring good mechanical properties, while preserving a noticeable light transmittance.
COBISS.SI-ID: 29511719
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 a collaboration with Medical faculty, University of Ljubjana, we studied the influence of airborne-particle abrasion and ageing on materials with different grain sizes and therefore different transformability. Different grain sizes were obtained by applying two sintering temperatures (1400°C 2h or 1500°C 2h) to the nominally identical material. It was shown that pristine low-temperature sintered fine-grained ceramic exhibited superior LTD resistance, while the high-temperature sintered coarse-grained material experienced higher surface strengthening and a substantially improved ageing resistance upon airborne-particle abrasion. The finding is important when considering the recommended grain size values in the currently accepted standard ISO 13356 “Implants for surgery — Ceramic materials based on yttria-stabilized tetragonal zirconia (Y-TZP)” and the producers’ tendencies to apply finer grain sizes in order to increase the translucence.
COBISS.SI-ID: 29163303
An empirical modification of the Yodel model was developed for the prediction of the yield stress (YS) of paraffin-wax suspensions with a solids loading of 47‒57 vol.% used in the low-pressure injection moulding (LPIM). A practical validation of the empirical model, in terms of predicting the YS of suspensions made from several alumina powders and one zirconia powder yielded excellent agreement with the experimental results. It is shown that is possible to predict realistic YS across the whole of the solids-loading range suitable for LPIM just by making a single YS measurement for the desired volume fraction of solids in the paraffin-wax suspension.
COBISS.SI-ID: 29085479
Difficulties related to titanium processing and the problematic titanium-ceramic bond have been limiting the latter's application in prosthetic dentistry for many years. Despite efforts to improve titanium bonding to porcelain and to develop titanium compatible, low-fusing porcelains, many in vitro studies report bond strengths to titanium that are inferior to those for base metals and noble dental alloys. Current knowledge on titanium-ceramic bonding is here reviewed, focusing on the recent attempts to overcome the limitations of the system and on recent advances in titanium processing. Optimization of the currently available processing and surface conditioning methods seems to be necessary. Although most of the proposed surface preparation methods appear to show a certain degree of porcelain bond improvement, many of them require application of additional complex procedures. Simplification and improved efficiency therefore appear to be the essentials for implementation of these methods in clinical practice.
COBISS.SI-ID: 32738777