Papers by Author: Saša Novak

Abstract: This work presents deformation behaviour of gellan gum and gellan gum - bioactive glass composites as novel hydrophilic materials for production of scaffolds in the field of bone-tissue engineering. According to recent studies such materials are attractive for personalized design of implants thanks to their biocompatibility and wide range of available fabrication methods. Batch of samples was subjected to uni-axial compression loading in a custom designed loading device to obtain their elastic and plastic characteristics. However the testing procedure was challenging because of very low stiffness of the material acquired results show a significant reinforcement effect of bioactive glass and its influence to the elastic modulus.

Abstract: Electrophoretic deposition (EPD) was used to infiltrate 2D and 3D SiC fabrics with SiC submicron particles with the aim to verify the potential of the technique for the fabrication of dense SiC/SiC composites. Bulk SiC deposits were first prepared from aqueous suspensions with different dispersants using cathodic and anodic deposition. The most suitable composition of the suspensions and the conditions for the infiltration were determined on the basis of the analysis of green parts formed. Using a specially designed EPD cell a relatively high packing density of SiC particles in infiltrated 2D and 3D SiC-fiber fabrics was achieved.

Abstract: Electrophoretic deposition of silicon carbide in ethanol suspensions was studied with the aim to fabricate liquid-phase sintered (LPS) SiC-based ceramics densified at temperatures below 1500°C. The effect of suspensions composition (solids content, pH, sintering additives) on the deposition rate and the properties of the deposits was analysed. The consistency of deposits and their solids loading was found to be significantly dependent on composition of the starting suspension: the highest solids loading (54.5 vol. %) for pure SiC was obtained with the addition of citric acid, while for the suspension containing aluminum phosphate the deposition was more successful from alkaline suspensions.

Abstract: The preparation of functionally graded materials requires specially adapted shaping techniques and special attention need to be paid to changes in the amount of shrinkage through the cross-section of the graded material during sintering, to avoid high residual stresses leading to crack formation. In this work we report on the results of investigations of FGMs of Al2O3, ZrO2 and ZTA and their densification as a function of the starting suspensions’ properties (alumina/zirconia ratio, solids content and dispersion state), with the aim of compensating for the different amount of sintering shrinkage of the outer and inner materials in step-graded Al2O3-ZTA composites. The sintering studies revealed that the green density and hence the densification of the slip-cast ceramic parts are almost independent on the solids content, while significant effect was observed for dispersion state of the suspensions. Hence, different amounts of total sintering shrinkage in stepgraded Al2O3-ZTA may be achieved by modification of the zeta-potential by adjusting the pH of well-dispersed suspensions.

Abstract: Functionally graded alumina/zirconia-toughened alumina (ZTA) ceramics for biomedical applications were designed with a hard, wear-resistant alumina surface and a tough, zirconia-rich core. The main goal was to achieve an improved mechanical performance by introducing a residual compressive stress in the outer surfaces. Symmetrical, 7-layered samples were prepared by the sequential slip-casting of specimens from suspensions prepared at the inherent pH values, close to the pH values at which the maximum (negative) zetapotential was measured. No sintering or tunneling cracks were observed in the samples, but large defects, such as big agglomerates, air bubbles and large circular pores at layer interfaces, which resulted from preparing the samples using the slip-casting technique, were readily observed. The strength of the symmetrical composites is influenced by the presence of defects, which most probably originate from the shaping process. Therefore, the defects have to be regarded as the reason why the strength of the 7-layered composites is low.