Development of yttrium and ytterbium silicates from their oxides and an oligosilazane precursor for coating applications to protect SI3N4 ceramics in hot gas environments

Environmental barrier coatings are required to protect Si3N4 against hot gas corrosion and enable its application in gas turbines. In comparison to other environmental barrier coatings, rare-earth silicate-based coatings stand out due to the very low corrosion rates in moist environments at high temperatures and the compatibility of thermal expansion coefficient to Si3N4 ceramics. Thus, the polymer-derived ceramic route was used to synthesize yttrium and ytterbium silicates in the temperature range of 1000-1500 °C for basic investigations regarding their intrinsic properties from a mixture of Y2O3 or Yb2O3 powders and the oligosilazane Durazane 1800. After pyrolysis above 1200 °C in air, the corresponding silicates are already the predominant phases. The corrosion behaviour of the resulting composites was assessed after exposure to flowing moist air at 1400 °C for 80 h. The material containing Yb2SiO5 and Yb2Si2O7 as main crystalline phases undergoes the lowest corrosion rate (-1.8 µg cm-2 h-1). In contrast, the corrosion rate of yttrium-based composites remained at least ten times higher. Lastly, the processing of Y2O3/Durazane 1800 as well-adherent, crack-free and thick (40 µm) coatings on Si3N4 was achieved after pyrolysis at 1400 °C in air. The resulting coating consisted of an Y2O3/Y2SiO5 top-layer and an Y2Si2O7 interlayer due to diffusion of silicon from the substrate and its interaction with the coating system

In Situ Generated Yb₂Si₂O₇ Environmental Barrier Coatings for Protection of Ceramic Components in the Next Generation of Gas Turbines

Abstract In face of an accelerating climate change, the reduction and substitution of fossil fuels is crucial to decarbonize energy production. Gas turbines can operate with versatile fuel sources like natural gas and future fuels such as hydrogen and ammonia. Furthermore, thermal efficiencies above 60% can be achieved using non‐oxide silicon‐based ceramic components. However, water vapor is one of the main combustion products leading to rapid corrosion because of volatilization of the protective SiO2 layer at 1200 °C. An in situ generated Yb2Si2O7 double layered environmental barrier coating system composed of silazanes and the active fillers Yb2O3 and Si processed at 1415 °C for 5 h in air protects a Si3N4 substrate very effectively from corrosion. It exhibits a dense microstructure with a total thickness of 68 µm, overcomes 15 thermal cycling tests between 1200 and 20 °C and shows almost no mass loss after very harsh hot gas corrosion at 1200 °C for 200 h (pH2O = 0.15 atm, v = 100 m s−1). The excellent adhesion strength (36.9 ± 6.2 MPa), hardness (6.9 ± 1.6 GPa) and scratch resistance (28 N) demonstrate that the coating system is very promising for application in the next generation of gas turbines

Роль и место иностранного языка в профессиональной компетентности преподавателей технических специальностей

Раскрывается состав профессиональной компетентности преподавателей неязыковых вузов для выявления особенностей типологии ключевых компетенций, определяющих содержание иноязычного компонента. Автор предлагает рассматривать иноязычную профессионально-коммуникативную компетенцию как эффективное средство реализации иноязычной переподготовки преподавателей неязыковых вузов

Synthesis and characterization of precursor derived TiN@Si–Al–C–N ceramic nanocomposites for oxygen reduction reaction

The development of efficient and durable catalysts is critical for the commercialization of fuel cells, as the catalysts’ durability and reactivity dictate their ultimate lifetime and activity. In this work, amorphous silicon-based ceramics (Si–C–N and Si–Al–C–N) and TiN@Si–Al–C–N nanocomposites were developed using a precursor derived ceramics approach. In TiN@Si–Al–C–N nanocomposites, TiN nanocrystals (with sizes in the range of 5–12 nm) were effectively anchored on an amorphous Si–Al–C–N support. The nanocomposites were found to be mesoporous in nature and exhibited a surface area as high as 132 m2/g. The average pore size of the nanocomposites was found to increase with an increase in the pyrolysis temperature, and a subsequent graphitization of free carbon was observed as revealed from the Raman spectra. The ceramics were investigated for electrocatalytic activity toward the oxygen reduction reaction using the rotating disk electrode method. The TiN@Si–Al–C–N nanocomposites showed an onset potential of 0.7 V versus reversible hydrogen electrode for oxygen reduction, which seems to indicate a 4-electron pathway at the pyrolysis temperature of 1000°C in contrast to a 2-electron pathway exhibited by the nanocomposites pyrolyzed at 750°C via the Koutecky–Levich plot