Inovační technologie v keramice

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Macroporous bioceramic scaffolds based on tricalcium phosphates reinforced with silica: microstructural, mechanical, and biological evaluation
(Informa, 2022-03-27) Novotná, Lenka; Chlup, Zdeněk; Jaroš, Josef; Částková, Klára; Drdlík, Daniel; Pospíšil, Jakub; Hampl, Aleš; Koutná, Irena; Cihlář, Jaroslav
The positive effect of silica on microstructural, mechanical and biological properties of calcium phosphate scaffolds was investigated in this study. Scaffolds containing 3D interconnected spherical macropores with diameters in the range of 300-770 mu m were prepared by the polymer replica technique. Reinforcement was achieved by incorporating 5 to 20 wt % of colloidal silica into the initial hydroxyapatite (HA) powder. The HA was fully decomposed into alpha and beta-tricalcium phosphate, and silica was transformed into cristobalite at 1200 degrees C. Silica reinforced scaffolds exhibited compressive strength in the range of 0.3 to 30 MPa at the total porosity of 98-40%. At a nominal porosity of 75%, the compressive strength was doubled compared to scaffolds without silica. When immersed into a cultivation medium, the formation of an apatite layer on the surfaces of scaffolds indicated their bioactivity. The supportive effect of the silicon enriched scaffolds was examined using three different types of cells (human adipose-derived stromal cells, L929, and ARPE-19 cells). The cells firmly adhered to the surfaces of composite scaffolds with no sign of induced cell death. Scaffolds were non-cytotoxic and had good biocompatibility in vitro. They are promising candidates for therapeutic applications in regenerative medicine.
Tailoring a Refractory High Entropy Alloy by Powder Metallurgy Process Optimization
(MDPI, 2021-10-01) Moravčíková de Almeida Gouvea, Larissa; Moravčík, Igor; Pouchlý, Václav; Kováčová, Zuzana; Kitzmantel, Michael; Neubauer, Erich; Dlouhý, Ivo
This paper reports the microstructural evolution and mechanical properties of a low-density Al0.3NbTa0.8Ti1.5V0.2Zr refractory high-entropy alloy (RHEA) prepared by means of a combination of mechanical alloying and spark plasma sintering (SPS). Prior to sintering, the morphology, chemical homogeneity and crystal structures of the powders were thoroughly investigated by varying the milling times to find optimal conditions for densification. The sintered bulk RHEAs were produced with diverse feedstock powder conditions. The microstructural development of the materials was analyzed in terms of phase composition and constitution, chemical homogeneity, and crystallographic properties. Hardness and elastic constants also were measured. The calculation of phase diagrams (CALPHAD) was performed to predict the phase changes in the alloy, and the results were compared with the experiments. Milling time seems to play a significant role in the contamination level of the sintered materials. Even though a protective atmosphere was used in the entire manufacturing process, carbide formation was detected in the sintered bulks as early as after 3 h of powder milling. Oxides were observed after 30 h due to wear of the high-carbon steel milling media and SPS consolidation. Ten hours of milling seems sufficient for achieving an optimal equilibrium between microstructural homogeneity and refinement, high hardness and minimal contamination.
Comparative Study of PVDF Sheets and Their Sensitivity to Mechanical Vibrations: The Role of Dimensions, Molecular Weight, Stretching and Poling
(MDPI, 2021-06-22) Mrlík, Miroslav; Osička, Josef; Cvek, Martin; Ilčíková, Markéta; Srnec, Peter; Gorgol, Danila; Tofel, Pavel
This paper is focused on the comparative study of the vibration sensing capabilities of poly(vinylidene fluoride) (PVDF) sheets. The main parameters such as molecular weight, initial sample thickness, stretching and poling were systematically applied, and their impact on sensing behavior was examined. The mechanical properties of prepared sheets were investigated via tensile testing on the samples with various initial thicknesses. The transformation of the -phase to the electro-active -phase was analyzed using FTIR after applying stretching and poling procedures as crucial post-processing techniques. As a complementary method, the XRD was applied, and it confirmed the crystallinity data resulting from the FTIR analysis. The highest degree of phase transformation was found in the PVDF sheet with a moderate molecular weight (Mw of 275 kDa) after being subjected to the highest axial elongation (500%); in this case, the -phase content reached approximately 90%. Finally, the vibration sensing capability was systematically determined, and all the mentioned processing/molecular parameters were taken into consideration. The whole range of the elongations (from 50 to 500%) applied on the PVDF sheets with an Mw of 180 and 275 kDa and an initial thickness of 0.5 mm appeared to be sufficient for vibration sensing purposes, showing a d33 piezoelectric charge coefficient from 7 pC N1 to 9.9 pC N1. In terms of the d33, the PVDF sheets were suitable regardless of their Mw only after applying the elongation of 500%. Among all the investigated samples, those with an initial thickness of 1.0 mm did not seem to be suitable for vibration sensing purposes.
Poling procedures and piezoelectric response of (Ba0.85Ca0.15Zr0.1T0.9)O-3 ceramics
(Taylor & Francis, 2020-12-23) Bijalwan, Vijay; Sokolov, Ilya; Tofel, Pavel
The goal of the current report was to find the optimal poling conditions: poling field, poling time and poling temperature for lead-free (Ba0.85Ca0.15Zr0.1T0.9)O-3 ceramic. It has been noticed that the low poling field (< 2 kV/mm) was insufficient for obtaining ideal poling state (theta = 90 degrees) due to the incomplete switching of domains and thus low piezoelectric properties (d(33) <= 438 pC/N and k(p) <= 49%). However, relevance of higher poling voltage (> 2 kV/mm) may induce electric breakdown and physical defects such as cracks in the sample, which also leads degradation of piezoelectric properties. The optimal poling field, poling time and poling temperature was found to be 2 kV/mm, 10 min and 24 degrees C, i.e., near room temperature, respectively to achieve nearly ideal poling state (theta = 86 degrees) obtained by impedance spectra, and thus enhanced piezoelectric constant d(33) = 505 pC/N and k(p) = 56% at room temperature. The O-T phase transition point was identified at 32.6 degrees C, for which a peak value of d(33(E=0V)) = 622 pm/V was realized.
Properties of BaTiO3/Al2O3 Laminate Structure by Nanoindentation
(Elsevier, 2020-02-19) Chlup, Zdeněk; Drdlík, Daniel; Fides, Martin; Kovalčíková, Alexandra; Hadraba, Hynek
The proposed material design of BaTiO3/Al2O3/ZrO2 laminate structure predetermined for energy harvesters taking advantage of residual stresses developed during processing was prepared by electrophoretic deposition. The main aim of developed residual stresses is to enhance overall mechanical reliability of piezoceramic functional layers and/or to enhance piezoelectric effects acting in the laminate. The concept of co-sintered BaTiO3 piezo ceramic functional layers with protective ZrO2 and Al2O3 layers is based on strongly bonded layers. In this contribution will be described particular behaviour of the specific material configuration BaTiO3/Al2O3 laminate where an interface interlayer among other effects was formed. The influence of sintering conditions on the microstructure development of the laminate as well as the formation of the interlayer was investigated. The relationship between observed microstructural changes and resulting mechanical properties as hardness and indentation elastic modulus was analyzed by means of nanoindentation technique. The cracks propagation through the individual layers and specific formed interfaces were observed and analyzed. The crack deflection due to the presence of developed residual stresses during the cooling stage of sintering as well as the consequence of microstructural changes on mechanical properties was confirmed.

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