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- ItemSuperflux of an organic adlayer towards its local reactive immobilization(NATURE PORTFOLIO, 2023-10-18) Salamon, David; Bukvišová, Kristýna; Jan, Vít; Potoček, Michal; Čechal, JanOn-surface mass transport is the key process determining the kinetics and dynamics of on-surface reactions, including the formation of nanostructures, catalysis, or surface cleaning. Volatile organic compounds (VOC) localized on a majority of surfaces dramatically change their properties and act as reactants in many surface reactions. However, the fundamental question "How far and how fast can the molecules travel on the surface to react?" remains open. Here we show that isoprene, the natural VOC, can travel similar to 1 mu m s(-1), i.e., centimeters per day, quickly filling low-concentration areas if they become locally depleted. We show that VOC have high surface adhesion on ceramic surfaces and simultaneously high mobility providing a steady flow of resource material for focused electron beam synthesis, which is applicable also on rough or porous surfaces. Our work established the mass transport of reactants on solid surfaces and explored a route for nanofabrication using the natural VOC layer.
- ItemImproving 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, PedroDigital 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.
- ItemWhy freeze-casting brings different phase composition of calcium phosphates?(Elsevier, 2021-09-01) Mařáková, Lucie; Roleček, Jakub; Salamon, DavidThe impact of freeze-casting on the porosity, pore distribution, and phase composition was studied and compared with conventional shaping techniques. A bimodal pore size distribution was observed in freeze-cast + freeze-dried samples, in contrast to the unimodal one in freeze-cast + air-dried and conventionally prepared samples. The densification of freeze-cast + freeze-dried samples started at about 50 °C higher than their conventional counterparts (~870 °C vs. 920 °C). Diffusion seems to be a key parameter for the phase transformation of HAP into -TCP during sintering. The residual HAP content in the sintered samples was influenced by used freezing rate and varied from 4% to 30% (unimodal samples), and from 7% to 16% (bimodal samples). Although further experiments must be carried out, our results showed that the freeze-casting parameters affect the resulting porosity and phase composition regardless of whether the freeze-drying or air-drying was used afterward.
- ItemCoarsening Kinetics of Y2O3 Dispersoid in New Grade of Fe-Al-Cr-Based ODS Alloy(MDPI, 2022-01-23) Holzer, Jakub; Gamanov, Štěpán; Luptáková, Natália; Dlouhý, Antonín; Svoboda, JiříOxide dispersion strengthened (ODS) alloys with a high content of Al are candidate materials for extreme high temperature applications such as turbine blades and other components working at temperatures significantly above 1000 degrees C. While oxidation kinetics of Fe-Al ODS steels is frequently studied, the stability and growth kinetics of strengthening oxide dispersion is a rarely studied topic. The Fe-10Al-4Cr-4Y(2)O(3) is an experimental material, fabricated at IPM by powder metallurgy route and contains much higher volume fraction of Y2O3 than similar materials. Stability and growth kinetics of Y2O3 particles of our material are studied on 24 samples aged for 0.5, 1, 2, 4, 8, 16, 32 and 72 h at 1200 degrees C, 1300 degrees C and 1400 degrees C. The sizes of at least 600 individual Y2O3 particles are measured on each sample to obtain extensive statistical analysis of the particle growth. The average particle size coarsens from 28.6 +/- 0.7 nm to 36.9 +/- 0.9 nm in 1200 degrees C series and to 81.4 +/- 5.6 nm in 1400 degrees C series. The evaluated activation energy of coarsening of Y2O3 particles is 274 +/- 65 kJ. The effects of particle coarsening on mechanical properties is demonstrated by HV measurements, which is in very good agreement with the Orowan theory.
- ItemEffect of alumina or zirconia particles on the performance of lead-free BCZT piezoceramics(Elsevier, 2024-12-15) Mařák, Vojtěch; Drdlík, Daniel; Bijalwan, Vijay; Tofel, Pavel; Erhart, Jiří; Chlup, Zdeněk; Maca, KarelThe barium titanate derivative Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) offers high dielectric and piezoelectric performance but has poor mechanical properties. Ceramic composite materials combining BCZT with tougher Al2O3 or ZrO2 could be the solution to the inherent brittleness of electroceramics. This work focuses on BCZT with 1–5 vol% addition of reinforcing phase dispersed in the microstructure. While hardness was improved in all composites, especially in ZrO2-reinforced BCZT, toughness was positively affected only by Al2O3. The chemical reactivity of BCZT during sintering resulted in the formation of new barium aluminate phases at the grain boundaries and possibly also within the grains, which affected the electrical properties of the composites. The addition of zirconia resulted in the formation of BaZrO3 or Ba(Zr,Ti)O3, which is a natural part of the BCZT solid solution and shifts the phase composition towards relaxor behaviour. ZrO2-reinforced composites exhibited higher permittivity but lower ferroelectric properties, accompanied by a substantial Curie temperature decrease.