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- ItemA Comparative Study of the Impact of La2O3 and La2Zr2O7 Dispersions on Molybdenum Microstructure, Mechanical Properties, and Fracture(SPRINGER, 2024-10-23) Tkachenko, Serhii; Slámečka, Karel; Bednaříková, Vendula; Remešová, Michaela; Gejdoš, Pavel; Ksenzova, Olha; Valášek, Daniel; Dvořák, Karel; Šulák, Ivo; Gálíková, Markéta; Baláž, Matej; Deák, Andréa; Cihlář, Jaroslav; Čelko, LadislavWe report, for the first time, the effect of lanthanum zirconate (La2Zr2O7) particles on the microstructure and mechanical behavior of an experimental molybdenum oxide dispersion-strengthened alloy. The focus was on the preparation of the novel Mo-La2Zr2O7 composite using high-energy ball milling and spark plasma sintering and on the comparison of its microstructural and mechanical properties with pure Mo and Mo-La2O3 ODS alloy counterparts. Mechanical properties were assessed using a Vickers hardness test at room temperature and a three-point flexural test in the temperature range from - 150 to 150 degrees C. The microstructure of the studied materials and their fracture behavior were evaluated using x-ray diffraction, energy-dispersive x-ray spectroscopy, and scanning electron and transmission electron microscopy. The strengthening effect of La2Zr2O7 particles was found to be lower than that of La2O3 particles, resulting in a 30-35% lower yield stress and flexural strength of the Mo-La2Zr2O7 alloy compared to the Mo-La2O3 alloy. The experimental Mo-La2Zr2O7 alloy exhibited low plasticity and no distinct ductile-to-brittle transition temperature (DBTT) in the tested temperature range, unlike pure Mo and the Mo-La2O3 alloy, which had the DBTT of 63 and 1 degrees C, respectively. Fracture occurred mainly in a brittle intergranular manner in the entire testing temperature range, while the counterpart materials showed localized plastic stretching at grain boundaries and within grains at and above the transition region. The observed behavior was primarily related to lower strengthening and brittleness as well as less effective grain boundary purification.
- ItemMechanical Behavior of Oxide Dispersion Strengthened Steel Directly Consolidated by Rotary Swaging(MDPI, 2024-10-23) Kocich, Radim; Kunčická, Lenka; Dvořák, Karel; Král, PetrAmong the main benefits of powder-based materials is the possibility of combining different constituents to achieve enhanced properties of the fabricated bulk material. The presented study characterizes the micro- and sub-structures and related mechanical properties of ferritic steel strengthened with a fine dispersion of nano-sized Y2O3 oxide particles. Unlike the typical method of preparation via rolling, the material presented herein was fabricated by direct consolidation from a mixture of powders using the versatile method of hot rotary swaging. The mechanical properties were evaluated at room temperature and also at 1300 degrees C to document the suitability of the prepared steel for high-temperature applications. The results showed that the imposed shear strain, i.e., swaging ratio, is a crucial parameter influencing the microstructure and, thus, material behavior. The workpiece subjected to the swaging ratio of 1.4 already exhibited a sufficiently consolidated structure with ultra-fine grains and featured high room-temperature microhardness values (up to 690 HV0.5), as well as a relatively high maximum flow stress (similar to 88 MPa) when deformed at the temperature of 1300 degrees C with the strain rate of 0.5 s(-1). However, the dispersion of oxides within this sample exhibited local inhomogeneities. Increasing the swaging ratio to 2.5 substantially contributed to the homogenization of the distribution of the Y2O3 oxide particles, which resulted in increased homogeneity of mechanical properties (lower deviations from the average values), but their lower absolute values due to the occurrence of nucleating nano-sized recrystallized grains.
- ItemThe Usability of Metallurgical Production Waste as a Siliceous Component in Autoclaved Aerated Concrete Technology(MDPI, 2024-10-03) Mészárosová, Lenka; Černý, Vít; Melichar, Jindřich; Ondříčková, Pavlína; Drochytka, RostislavThe reconstruction of buildings is a complex process that often requires the consideration of the construction load when selecting correct building materials. Autoclaved aerated concrete (AAC)-which has a lower bulk density (compared to traditional masonry materials)-is very beneficial in such applications. A current trend in AAC development is the utilization of secondary raw materials in high-performance AAC, characterized by higher bulk density and compressive strength than regular AAC. The increase in bulk density is achieved by increasing the content of quartz sand in the mixing water. In this study, part of the siliceous component was replaced by ladle slag, foundry sand, furnace lining, and chamotte block powder. These materials are generated as by-products in metallurgy. The substitution rates were 10% and 30%. The samples were autoclaved in a laboratory autoclave for 8 h of isothermal duration at 190 degrees C with a saturated water vapor pressure of 1.4 MPa. The physical-mechanical parameters were determined, and the microstructure was described by XRD and SEM analyses. The results were compared with traditional AAC, with silica sand being used as the siliceous component. The measurement results show that sand substitution by the secondary raw material is possible, and it does not have a significant impact on the properties of AAC, and in a proper dosage, it can be beneficial for AAC production.
- ItemSubstantiation of the Effectiveness of Water-Soluble Hydrophobic Agents on the Properties of Cement Composites(MDPI, 2024-10-24) Hodul, Jakub; Beníková, Tatiana; Drochytka, RostislavThis paper aims to verify the effect of water-soluble hydrophobisations on cementitious composites such as concrete (S1) and cement-bonded particle boards (S2). The research was focused on the water-soluble hydrophobisations based on methylsilanolate (MS), a mixture of silanes and siloxanes (SS) and alcohol with the addition of nano-silica (N). The results provide a comprehensive overview of the benefits and effectiveness of water-soluble hydrophobisations in the context of building materials, outlining a direction towards the development of new, more environmentally friendly solutions in the construction industry. For this reason, alternative raw materials (brick recyclate and brick dust) were used for S1 substrate preparations. How the water-soluble hydrophobisations, including hydrophobisations with the addition of nano-silica (N), affect the process of water evaporation during hydration and the resulting water repellence of the S1 and S2 substrates were experimentally verified through a series of tests, e.g., measurement of the contact angle and depth of water penetration under pressure. The evaluation of the effect of hydrophobisations on the resistance of substrate to aggressive gaseous and liquid environments was observed by the determination of the resistance to carbonation and sulphation processes and the resistance of the concrete to aggressive liquid media (10% H2SO4, 10% CH3COOH). Although the hydrophobisations did not have a significant effect on some aspects of S1, such as the resistance to carbonation and sulphate attack, improvement was observed in other areas, such as the quadrupling increase in contact angle of the surface and 9 mm decrease in water pressure penetration into the concrete substrate.
- ItemUtilization of alternative wood particles for modern thermal insulation products(IOP PUBLISHING LTD, 2024-05-13) Zach, Jiří; Peterková, Jitka; Novák, Vítězslav; Korjenic, AzraThermal insulation materials play a vital role in minimising energy loss in building operation and also affect the amount of greenhouse gas emissions associated with heating and cooling. In this context, it is becoming an increasingly important milestone to find suitable thermal insulation materials that not only meet the technical requirements but also minimise their environmental impact. The trend towards the use of eco-friendly materials for thermal insulation reflects the construction industry's desire to contribute to environmental protection and the transition to more sustainable models of building construction and renovation. For more than 20 years, a number of research teams have been investigating the possibility of replacing synthetically produced materials such as mineral wool and polystyrene foam with natural fibre-based insulation materials. These alternatives include wood as a traditional, easily renewable raw material. This, together with the low energy intensity of processing and manufacturing wood materials, contributes to its low carbon footprint. Compared to traditional synthetic insulation materials, which are often energy intensive to produce, wood is a more environmentally friendly choice. However, with many European countries now facing a potential shortage of higher quality wood, it is necessary to look for alternative sources of wood, including in the field of thermal insulation materials, materials with a lower carbon footprint that can be produced from lower quality wood or from wood waste that would otherwise only have an energy use. The paper is devoted to the study and use of suitable wood waste and secondary raw materials from spruce wood (coarse wood chips, sawdust and wood flour) for the development of modern thermal insulations with the aim of an environmentally friendly and less energy-intensive production process compared to conventional insulants.