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Sintering activation energies of anisotropic layered and particle alumina/zirconia-based composites and their mechanical response
(Elsevier, 2024-08-27) Drdlík, Daniel; Sokolov, Ilya; Hadraba, Hynek; Chlup, Zdeněk; Drdlíková, Katarina; Maca, Karel
Information on the sintering activation energy is currently focused on evaluation of single-phase ceramic systems. This work shows the results of high-temperature dilatometry measurements of layered and particle composites based on alumina and zirconia. Layered composites with different layer thickness ratios and particle composites with variable composition in the entire concentration range were prepared by electrophoretic deposition allowing manufacturing composites with precious design and strongly bonded interfaces. The phenomena observed during the high-temperature dilatometry measurements are discussed, and the data were used to calculate the sintering activation energies of composites using the modified Master Sintering Curve concept. By covering a wide range of composite designs, it was possible to determine differences in activation energies and to show their dependence on the direction in the case of laminate composites given by the directionally dependent sintering behaviour. Sintering activation energies of layered composites were always higher than for monoliths due to constrained sintering showing maximum sintering activation energies at lower volumes of zirconia in the layers for longitudinal and transversal orientation of the samples. A similar trend was identified in particle composites due to slowed down alumina densification by the pinning effect. Additionally, mechanical properties represented by Vickers hardness and indentation elastic modulus were related to the microstructure developed during sintering. The effects of interconnectivity of phases present in the composites together with other parameters of the microstructure were described.
Porous silica-doped calcium phosphate scaffolds prepared via in-situ foaming method
(ELSEVIER SCI LTD, 2024-11-01) Šiška Virágová, Eliška; Novotná, Lenka; Chlup, Zdeněk; Šťastný, Přemysl; Šárfy, Pavlína; Cihlář, Jaroslav; Kučírek, Martin; Benák, Leoš; Streit, Libor; Kocanda, Jan; Sklenský, Jan; Filipovič, Milan; Repko, Martin; Hampl, Aleš; Koutná, Irena; Částková, Klára
The effect of silica (SiO2) addition (0 wt%-20 wt%) on the microstructural and mechanical properties, as well as the in vitro response of calcium phosphate scaffolds for potential application in bone tissue engineering (BTE) was investigated in this research. Scaffolds characterized by high porosity (77%-88 %) and interconnected spherical pores with a broad range of pore sizes (5-600 mu m) were fabricated using in-situ foaming method. Incorporated silica affected the phase transformation of hydroxyapatite (HA) to beta-tricalcium phosphate (beta-TCP) and led to the development of new crystalline silica-rich phases like silicocarnotite and wollastonite. The reinforcement of silica became apparent during the tests of mechanical properties. Scaffolds with 5 wt% of SiO2 exhibited compressive strength (1.13 MPa) higher than pure HA scaffolds (0.93 MPa). Bone bonding potential of the materials was tested in simulated body fluid (SBF), demonstrating this potential in silica-doped samples. Additionally, degradation experiments showed gradual material degradation, making it suitable for BTE applications. Furthermore, cell culture studies using human mesenchymal stromal cells (MSC) confirmed the scaffold's non- toxicity and provided insights into how the silica content influences cell viability, morphology, and osteogenic potential. The findings of this study offer valuable insights into the design and development of advanced scaffolds with tailored properties for effective BTE applications.
Dilatometric and microstructural study of particle and functionally graded composites based on hydroxyapatite and crystalline bioglass
(2023-10-23) Drdlík, Daniel; Drdlíková, Katarina; Maca, Karel
Hydroxyapatite (HA) and bioglass (BG) ceramics have become of prime importance in bone tissue engineering. Besides the appropriate composition, the microstructure of bone replacement plays a crucial role. In the present work, particle composites and functionally graded material (FGM) based on HA and BG prepared by electrophoretic deposition were thoroughly characterised in terms of the preparation method, sintering process, phase composition and microstructure. The sintering was monitored by high-temperature dilatometry in two directions, the sintering rates were calculated, and the overall sintering process was discussed. The SEM showed the continuous change in the microstructure of FGM with gradual interconnected porosity favourable for bio-applications. The fundamental fractographic analysis proved the crack development in FGM related to the sintering process, and the recommendations for the reduction of the crack development were given. The phase transformations during thermal treatment were analysed using X-ray diffraction analysis and deeply discussed.
Improving the strength of -TCP scaffolds produced by Digital Light Processing using two-step sintering
(ELSEVIER SCI LTD, 2024-04-01) Paredes Sánchez, Claudia Isabel; Roleček, Jakub; Miranda, Pedro
Digital Light Processing is combined with two-step sintering to obtain bioactive scaffolds with improved strength and mechanical isotropy. Highly loaded photosensitive suspensions were prepared from beta-TCP powder to create scaffolds consisting of interpenetrating struts with two different designs. Two sintering methods were used: conventional sintering (CS) and two-step sintering (2SS). The latter resulted in a microstructure with uniformly shaped grains and reduced porosity. Their compressive strength was determined by uniaxial testing under two different load configurations, with the force applied parallel or perpendicular to the building plane of the scaffolds. Design optimisation and fine-tuning of the sintering process helped in reducing the presence of interlayer defects and minimise the shear-dominated fractures. Isotropic fracture behaviour was achieved, with similar central values of the Weibull distribution (49 +/- 1 MPa vs. 51 +/- 1 MPa) along both testing directions, showing a great potential for their use in load-bearing bone tissue engineering applications.
Thermal annealing effects in polycrystalline EuTiO3 and Eu2Ti2O7
(AIP Publishing, 2019-12-01) Schell, Juliana; Kamba, Stanislav; Kachlík, Martin; Maca, Karel; Drahokoupil, Jan; Rano, B. Rahman; Gonçalves, Joo Nuno Santos; Dang, Thien Thanh; Costa, Angelo; Noll, Cornelia; Vianden, Reiner; Lupascu, Doru C.
Using time-differential perturbed angular correlation of gamma rays, we investigated the electric-field gradient of polycrystalline EuTiO3 and Eu2Ti2O7, with Hf-181(Ta-181) as a probe, following different thermal treatments. The measurements were performed at ISOLDE-CERN following 80 keV implantation at the Bonn Radioisotope Separator. The experimental results indicated successful induction of different phases in the implantation recovery process at 1273 and 1373 K. These observations were combined with ab initio calculations and X-ray diffraction measurements. A comparison of ab initio calculated electric-field gradients with the measured values discriminates between different structures and defects and rules out many possible cases. The Ta probe at the Ti site in the Eu2Ti2O7 phase is found to be the most probable case of site occupation after annealing at 1373 K, while annealing at 1273 K keeps EuTiO3 in the vicinity of the Ta probe. A discussion of the hyperfine interactions that promote variation in the interaction strength at the Ta-181 site is presented.

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