ÚMVI-odbor keramiky a polymerů

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    Effect 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, Karel
    The 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.
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    Basic microstructural, mechanical, electrical and optical characterisation of BaTiAl6O12 ceramics
    (Elsevier, 2024-06-27) Drdlík, Daniel; Mařák, Vojtěch; Klement, Róbert; Tofel, Pavel; Drdlíková, Katarina; Hadraba, Hynek; Chlup, Zdeněk
    In progressive particle or layered composites based on a combination of BaTiO3 and Al2O3, serving as e.g. ceramic harvesters, new phases are formed during heat treatment. The dominant one is BaTiAl6O12. This study provides information about the microstructural, mechanical and optical properties of the BaTiAl6O12 ceramics. The evolution of the phases during the solid-state reaction synthesis of the BaTiAl6O12 was monitored. The fully dense samples prepared by Spark Plasma Sintering had indentation Vickers hardness and indentation elastic modulus within ranges of 10.1 – 13.7 GPa and 132.0 – 187.0 GPa, depending on loading force. The three-point bending tests of the BaTiAl6O12 samples resulted in flexural strength of 129.9 MPa and fracture toughness of 1.8 MPa.m1/2.The sample showed blue broad-band emission under UV excitation due to the charge-transfer transition of the Ti4+ and defect sites. The BaTiAl6O12 evinced low permittivity (') = 16 and dielectric loss (tan ) < 0.0003 at a frequency 1 kHz.
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    Study of the Synthesis of Multi-Cationic Sm-Co-O, Sm-Ni-O, Al-Co-O, Al-Ni-O, and Al-Co-Ni-O Aerogels and Their Catalytic Activity in the Dry Reforming of Methane
    (MDPI, 2024-05-01) Cihlář, Jaroslav; Tkachenko, Serhii; Bednaříková, Vendula; Cihlář, Jaroslav; Částková, Klára; Trunec, Martin; Čelko, Ladislav
    Dense multi-cationic Sm-Co-O, Sm-Ni-O, Al-Co-O, Al-Ni-O, and Al-Ni-Co-O oxide aerogels were prepared by epoxide-driven sol-gel synthesis. Catalysts for dry reformation of methane, Sm2O3/Co, Sm2O3/Ni, Al2O3/Co, Al2O3/Ni, Al2O3/Co, and Ni were prepared by reduction of aerogels with hydrogen and their catalytic activities and C-deposition during dry reformation of methane were tested. Catalytic tests showed high methane conversion (93-98%) and C-deposition (0.01-4.35 mg C/gcat.h). The highest content of C-deposits after catalytic tests was determined for Al2O3/Co and Al2O3/Ni catalysts, which was related to the formation of Al alloys with Co and Ni. A uniform distribution of Co0 and Ni0 nanoparticles (in the form of a CoNi alloy) was found only for the Al2O3/Co and Ni catalysts, which showed the highest activity as well as low C deposition.
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    Enhancing Photocatalytic Properties of TiO2 Photocatalyst and Heterojunctions: A Comprehensive Review of the Impact of Biphasic Systems in Aerogels and Xerogels Synthesis, Methods, and Mechanisms for Environmental Applications
    (Gels, 2023-12-13) Tinoco Navarro, Lizeth Katherine; Cihlář, Jaroslav
    This review provides a detailed exploration of titanium dioxide (TiO2) photocatalysts, emphasizing structural phases, heterophase junctions, and their impact on efficiency. Key points include diverse synthesis methods, with a focus on the sol-gel route and variants like low-temperature hydrothermal synthesis (LTHT). The review delves into the influence of acid-base donors on gelation, dissects crucial drying techniques for TiO2 aerogel or xerogel catalysts, and meticulously examines mechanisms underlying photocatalytic activity. It highlights the role of physicochemical properties in charge diffusion, carrier recombination, and the impact of scavengers in photo-oxidation/reduction. Additionally, TiO2 doping techniques and heterostructures and their potential for enhancing efficiency are briefly discussed, all within the context of environmental applications.
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    Improving contact damage resistance of spinel translucent ceramics through a multi-layer design
    (Elsevier, 2025-04-01) Najafzadehkhoee, Aliasghar; Jabr, Abdullah; Talimian, Ali; Papšík, Roman; Drdlík, Daniel; Maca, Karel; Galusek, Dušan; Bermejo, Raul
    The brittle response of transparent spinel ceramics to contact damage is limiting their application as an alternative to glasses and single crystals. In this work, we explore a strategy to enhance the contact damage resistance of spinel ceramics by embedding alumina layers in a multi-layer architecture. Crack initiation upon Hertzian indentation was investigated in MgAl2O4 - Al2O3 laminates and compared to their corresponding monoliths. Contact stresses during loading were analyzed using finite element simulations by considering the elastic properties of the layers and contact non-linearities. Results were analyzed using Weibull statistics. It was found that the effect of in-plane residual stresses on crack formation in the laminate depends on the disposition of the compressive spinel layers, either at the surface or embedded in the structure. Embedding alumina between spinel layers increased the load-bearing capability before crack initiation by similar to 70 % compared to spinel, offering a promising approach to enhance contact damage resistance.