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Full-Text Articles in Materials Science and Engineering
Tungsten Doping Induced Superior Mechanical Properties Of Hafnium Oxide For Energy Applications, Ann Marie Uribe
Tungsten Doping Induced Superior Mechanical Properties Of Hafnium Oxide For Energy Applications, Ann Marie Uribe
Open Access Theses & Dissertations
Hafnium oxide, or hafnia, is a high temperature refractory material with good electrical, chemical, optical, and thermodynamic properties. The effects of dopants have been widely studied, especially after the discovery of ferroelectricity induced in hafnia thin films. While attractive and used in the opto-electronic, memory devices, and semiconductor industries, there is a lack in the literature on enhancing the mechanical properties of hafnium oxide, specifically through doping it with tungsten, another material of interest particularly for future high temperature device applications. Thus, this work aimed to grow hafnia thin films doped with varying amounts of tungsten. The samples were grown …
Gadolinia Doped Hafnia (Gd2o3- Hfo2) Thermal Barrier Coatings For Gas Turbine Applications, Satya Kiran Gullapalli
Gadolinia Doped Hafnia (Gd2o3- Hfo2) Thermal Barrier Coatings For Gas Turbine Applications, Satya Kiran Gullapalli
Open Access Theses & Dissertations
Thermal efficiency of the gas turbines is influenced by the operating temperature of the hot gas path components. The material used for the hot gas path components can only withstand temperature up to a certain limit. Thermal barrier coatings (TBC) provide the additional thermal protection for these components and help the gas turbine achieve higher firing temperatures. Traditionally available yttria stabilized zirconia (YSZ) TBCs have a limitation up to 1200 C due to their phase transformation. The present work focuses on gadolinia based hafnia (GSH) TBCs to study their potential to replace the YSZ coatings. Different compositions of gadolinia doped …
Crystal Structure, Phase, And Optical Properties Of Yttrium-Doped Hafnium Oxide Nanocrystalline Thin Films, Alejandro Ortega
Crystal Structure, Phase, And Optical Properties Of Yttrium-Doped Hafnium Oxide Nanocrystalline Thin Films, Alejandro Ortega
Open Access Theses & Dissertations
Yttrium-doped hafnium oxide (YDH) nanocrystalline films were produced by sputter-deposition at various substrate times and temperatures, to produce YDH films in a wide range of thicknesses, dYDH∼25 to 1100 nm. The deposition was made onto optical grade quartz and sapphire substrates. Samples deposited on sapphire were subject to post-deposition annealing (PDA) at various times (3-24 hr) and temperatures (1100 - 1500 °C). The effect of d[special characters omitted]YDH on the crystal structure, surface/interface morphology and optical properties of YDH films was investigated. X-ray diffraction analyses revealed the formation of monoclinic phase for relatively thin films (<150nm). The evolution towards stabilized cubic phase with increasing dYDH [special characters omitted]is observed. The scanning electron microscopy results indicate the dense, columnar structure of YDH films as a function of dYDH. Spectrophotometry analyses indicate that the grown YDH films are transparent and exhibit interference fringes. The band gap was found to be ∼ 5.60 eV for monoclinic YDH films while distinct separation and an increase in band gap to 6.03 eV is evident with increasing dYDH and formation cubic YDH films. The PDA films band gaps were found to be between 5.31 and 5.72 eV, all of which exhibit secondary gaps. A correlation between growth conditions, annealing, phase evolution, and optical properties of the YDH nanocrystalline thin films is established.
Hafnia-Based Nanostructured Thermal Barrier Coatings For Next Generation Gas Turbine Technology, Mohammed Noor-A-Alam
Hafnia-Based Nanostructured Thermal Barrier Coatings For Next Generation Gas Turbine Technology, Mohammed Noor-A-Alam
Open Access Theses & Dissertations
Extensive efforts have been directed in the last several decades towards improving thermodynamic efficiency of industrial gas turbines for power generation plants. The central theme of the efforts is to increase the turbine operating temperature and, thus, allowing higher efficiency. Thermal barrier coatings (TBC) constitute an advanced technology to protect the metallic surface from high temperature exposure for long time operation. The TBCs protect the gas turbine components from high temperature and allows further increase in engine operating temperature which subsequently increases the efficiency of the gas turbine power plant. However, the current TBC materials are capable of allowing the …