The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Robert A Miller - One of the best experts on this subject based on the ideXlab platform.
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Refractory Oxide coatings on sic ceramics
Mrs Bulletin, 1994Co-Authors: Nathan S Jacobson, Robert A MillerAbstract:Silicon-based ceramics are leading candidate materials for high-temperature structural applications such as heat exchangers, advanced gas turbine engines, and advanced internal combustion engines. They have excellent oxidation resistance in clean oxidizing environments due to the formation of a slow-growing silica scale (SiO 2 ). However, durability in high-temperature environments containing molten salts, water vapor, or a reducing atmosphere can limit their applications. Molten salts react with silica scale to form liquid silicates. Oxygen readily diffuses through liquid silicates and rapidly oxidizes the substrate. High water vapor levels lead to hydrated silica species, such as Si(OH) 4 ( g ) and subsequent evaporation of protective scale. Complex combustion atmospheres containing oxidizing (CO 2 , H 2 O) and reducing (CO, H 2 ) gases form SiO 2 and then reduce it to SiO( g ). In situations with extremely low partial pressures of oxidant, direct formation of SiO( g ) occurs. All these reactions can potentially limit the formation of a protective silica scale and thus lead to an accelerated or a catastrophic degradation. One approach overcoming these potential environmental limitations is to apply a barrier coating which is environmentally stable in molten salts, water vapor, and/or reducing atmospheres. Refractory Oxides such as mullite (3Al 2 O 3 · 2SiO 2 ), yttria-stabilized zirconia (ZrO 2 -Y 2 O 3 ), or alumina (Al 2 O 3 ) are promising candidate coating materials because of their excellent environmental stability in these severe conditions. Refractory Oxide coatings can also serve as thermal barrier coatings because of their low thermal conductivity. Key requirements for an adherent and durable barrier coating include coefficient of thermal expansion (CTE) match and chemical compatibility with the substrate. Mullite in general meets all the requirements and thus appears most promising.
Gurusampath A Kumar - One of the best experts on this subject based on the ideXlab platform.
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optimization of post deposition annealing temperature of direct current magnetron reactive sputtered zirconium titanate thin films for Refractory Oxide applications
Journal of Alloys and Compounds, 2017Co-Authors: Jhansi D Rani, Gurusampath A KumarAbstract:Abstract Nano crystalline Zirconium titanate thin films with Zr/Ti/O compositions of 51.22/45.32/3.46 have been deposited on to the glass substrates at a substrate temperature of 250 °C under ultra high vacuum conditions by employing direct current magnetron reactive sputtering. Later on the sputtered films were treated with post deposition rapid thermal annealing with temperatures ranging from 100 to 600 °C for 1 h in a flowing Oxygen (1 standard cubic centimeter) atmosphere. The micro structural, optical, electrical and morphological film properties have been analyzed as a function of annealing temperature by employing x ray diffraction in glancing incident angle mode, ultra violet visible spectroscopy, four point probe technique, atomic force microscopy, scanning electron microscopy and energy dispersive x ray analysis studies. The evolution of structural properties began at an annealing temperature of 300 °C and improved up to 500 °C. Annealing resulted in the re crystallization in the films. Once the re crystallization of amorphous films has occurred, the annealing temperature did not affect the film thickness. However higher temperatures promote inter diffusion of the substrate and film elements, which is undesirable. Here the films exhibited smooth, crack free, homogeneous micro structure and a consistent thickness of ∼400 nm. From the results obtained it is found that the optimal annealing temperature range is 400–500 °C.
C. Sanjeeviraja - One of the best experts on this subject based on the ideXlab platform.
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Fabrication techniques and material properties of dielectric MgO thin films-A status review
CIRP Journal of Manufacturing Science and Technology, 2010Co-Authors: A. Moses Ezhil Raj, Muthukumaran Jayachandran, C. SanjeevirajaAbstract:During the past few decades, considerable research effort has been directed towards the development of fundamental peculiarities of wide-gap (Eg > 5 eV) inorganic dielectric thin films. Wide-gap dielectrics are used for various technical and technological applications as laser materials, electronic components, radiation resistant materials, spectral transformers for luminescent lamps, detectors and dosimeters of several kind of radiations, various sensors and catalytic agents. The optical characteristics of intrinsic electronic excitations in inorganic wide-gap dielectric are shifted towards the vacuum ultra-violet spectral region and therefore being studied insufficiently that impedes the elaboration of new materials and the modernization of the existing ones based on wide-gap dielectrics. Besides, alkali halides, the value of energy band gap Eg >6 eV is typical of numerous wide-gap Oxides: MgO, CaO, Al2O3, SiO2, Y2O3, etc. Among this, magnesia (MgO) is a well-known Refractory Oxide, has the potential advantages of a wide band gap (Eg ∼ 7.8 eV) and is predominantly preferred to be used as lattice templates for growing oriented ferroelectric and superconducting over layers because of its higher Poisson's ratio and lower Gibb's free energy. Well-defined procedures to prepare MgO surfaces of very high quality is of importance in a number of areas of surface physics and imperfect due to their preparation kinetics, inclusion of foreign matter and compositional variations. Even though, increasing number of researchers, laboratories have engaged in the fabrication and characterization of MgO because of its excellent scientifically based applications. The scope of this review article is to summarize briefly the important research achievements on higher quality MgO thin films with novel physical properties and systematic interrelationship for fabrication conditions, crystal structure, composition predictions, surface morphology, electrical and optical characterizations. Particular attention is given to the secondary electron emission coefficient of the fabricated film due to their applications in the alternating current plasma display panel as a protecting layer of dielectrics to improve the discharge characteristics and the panel's lifetime. © 2010 CIRP.
Nathan S Jacobson - One of the best experts on this subject based on the ideXlab platform.
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Refractory Oxide coatings on sic ceramics
Mrs Bulletin, 1994Co-Authors: Nathan S Jacobson, Robert A MillerAbstract:Silicon-based ceramics are leading candidate materials for high-temperature structural applications such as heat exchangers, advanced gas turbine engines, and advanced internal combustion engines. They have excellent oxidation resistance in clean oxidizing environments due to the formation of a slow-growing silica scale (SiO 2 ). However, durability in high-temperature environments containing molten salts, water vapor, or a reducing atmosphere can limit their applications. Molten salts react with silica scale to form liquid silicates. Oxygen readily diffuses through liquid silicates and rapidly oxidizes the substrate. High water vapor levels lead to hydrated silica species, such as Si(OH) 4 ( g ) and subsequent evaporation of protective scale. Complex combustion atmospheres containing oxidizing (CO 2 , H 2 O) and reducing (CO, H 2 ) gases form SiO 2 and then reduce it to SiO( g ). In situations with extremely low partial pressures of oxidant, direct formation of SiO( g ) occurs. All these reactions can potentially limit the formation of a protective silica scale and thus lead to an accelerated or a catastrophic degradation. One approach overcoming these potential environmental limitations is to apply a barrier coating which is environmentally stable in molten salts, water vapor, and/or reducing atmospheres. Refractory Oxides such as mullite (3Al 2 O 3 · 2SiO 2 ), yttria-stabilized zirconia (ZrO 2 -Y 2 O 3 ), or alumina (Al 2 O 3 ) are promising candidate coating materials because of their excellent environmental stability in these severe conditions. Refractory Oxide coatings can also serve as thermal barrier coatings because of their low thermal conductivity. Key requirements for an adherent and durable barrier coating include coefficient of thermal expansion (CTE) match and chemical compatibility with the substrate. Mullite in general meets all the requirements and thus appears most promising.
Jhansi D Rani - One of the best experts on this subject based on the ideXlab platform.
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optimization of post deposition annealing temperature of direct current magnetron reactive sputtered zirconium titanate thin films for Refractory Oxide applications
Journal of Alloys and Compounds, 2017Co-Authors: Jhansi D Rani, Gurusampath A KumarAbstract:Abstract Nano crystalline Zirconium titanate thin films with Zr/Ti/O compositions of 51.22/45.32/3.46 have been deposited on to the glass substrates at a substrate temperature of 250 °C under ultra high vacuum conditions by employing direct current magnetron reactive sputtering. Later on the sputtered films were treated with post deposition rapid thermal annealing with temperatures ranging from 100 to 600 °C for 1 h in a flowing Oxygen (1 standard cubic centimeter) atmosphere. The micro structural, optical, electrical and morphological film properties have been analyzed as a function of annealing temperature by employing x ray diffraction in glancing incident angle mode, ultra violet visible spectroscopy, four point probe technique, atomic force microscopy, scanning electron microscopy and energy dispersive x ray analysis studies. The evolution of structural properties began at an annealing temperature of 300 °C and improved up to 500 °C. Annealing resulted in the re crystallization in the films. Once the re crystallization of amorphous films has occurred, the annealing temperature did not affect the film thickness. However higher temperatures promote inter diffusion of the substrate and film elements, which is undesirable. Here the films exhibited smooth, crack free, homogeneous micro structure and a consistent thickness of ∼400 nm. From the results obtained it is found that the optimal annealing temperature range is 400–500 °C.