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  • 1
    Electronic Resource
    Electronic Resource
    Semisolid solidification of high temperature superconducting oxides (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 179-190 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments are reported on two techniques for melt-texture processing Ba2YCu3O6.5 by directional solidification from a semisolid melt containing particles of BaY2CuO5 and a copper-rich liquid. One of these employs an electric resistance furnace with ambient or oxygen enriched atmosphere; the other is a laser-heated furnace operating at 1.3 atm oxygen. Solidification interface morphologies and other structural features were examined in quenched specimens. Depending on growth rate and temperature gradient, three different types of growth morphologies of the growing 123 phase were observed: "faceted plane front,'' "cellular dendritic'' or "equiaxed blocky.'' The interface temperature decreased markedly with increasing growth rate for the faceted plane front specimens. In the remaining specimens, solidification took place over a range of temperatures. The temperature of the "root'' of the solidification front dropped, but temperature of the solidification front "tip'' did not. A solidification model is developed and employed to interpret experimental observations. The model assumes limited diffusion of solute in the liquid during the growth of the superconducting phase. The model shows, in agreement with experiment, that growth rate of the low temperature solid phase has a strong effect on ability to obtain the desirable faceted plane front, and that thermal gradient has only a small effect. Interparticle spacing of the high temperature phase, BaY2CuO5, is also predicted to have a strong effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352155
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  • 2
    Electronic Resource
    Electronic Resource
    Metalorganic deposition of high-Jc Ba2YCu3O7−x thin films from trifluoroacetate precursors onto (100) SrTiO3 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4183-4187 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting thin films of Ba2YCu3O7-x were prepared on (100) SrTiO3 substrates by metalorganic deposition (MOD) of trifluoroacetate precursors. The best electrical transport properties were measured in films annealed at 750 °C in a humid, low PO2 gas mixture followed by slow cooling in oxygen. These specimens had sharp resistive transitions with Tc above 90 K and zero-field critical current densities in excess of 106 A/cm2 at 77 K. Critical current densities of this magnitude have not previously been reported in films produced by MOD. The highest Jc obtained in films fired only in humid oxygen was 3×105 A/cm2. Annealing at high temperature in the low PO2 atmosphere also resulted in a smoother surface morphology than was observed in the oxygen-fired films. Use of the low PO2 furnace gas appeared to suppress the formation of b-axis normal oriented grains in the superconducting films and to strengthen c-axis normal texture. X-ray powder diffraction indicated the presence of a-axis normal textured material in the films, although it was not present as separate microstructural features which could be identified by scanning electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346233
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of growth conditions on the properties and morphology of chemically derived epitaxial thin films of Ba2YCu3O7−x on (001) LaAlO3 (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1868-1877 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of Ba2YCu3O7−x (BYC) were prepared on (001) LaAlO3 single-crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high-temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low-oxygen partial pressures. Superconducting films of 70 nm thickness with zero-field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830 °C in 2.5 × 10−4–1 × 10−3 atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c-axis normal BYC near the film/substrate interface with the overlying material dominated by grains with c-axis in-plane crystallographic orientation. The transport Jc fell to 2–3×106 A/cm2 for films of 200–250-nm thickness annealed at 780 °C in 1 × 10−3 atm oxygen. As the P(O2) was raised to 0.032 atm at 780 °C, for films of the same thickness, the Jc at 77 K decreased to 0.7 × 106–1 × 106 A/cm2 and the Tc(R = 0) dropped to 89 K. Increasing the furnace P(O2) was also found to degrade the crystalline quality of the films, as characterized by ion channeling Rutherford backscattering spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351172
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  • 4
    Electronic Resource
    Electronic Resource
    Additive-Enhanced Redispersion of Ceramic Agglomerates (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Deagglomeration of ceramic powders is usually accomplished by immersion of powders in a surfactant-containing liquid vehicle, followed by milling. We seek alternative mechanisms to the classical milling approach by generating a chemical pressure to break up the agglomerate. This study explores the enhanced redispersion of TiO2 ceramic compacts that contain a nonionic water-soluble polymer, poly(ethylene glycol) (PEG). PEG forms a polymer solution within the agglomerated structure during redispersion. The resulting osmotic pressure gradient forces water into the porous structure and creates a tensile stress on the particle network with magnitudes as high as 0.6 MPa. Thus, the principle to achieving redispersion is to develop osmotic pressures that exceed the cohesive strength of the agglomerated structure. A critical PEG concentration of 2.0 vol% PEG 400 with respect to titania has been determined, below which redispersion is minimal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03501.x
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  • 5
    Electronic Resource
    Electronic Resource
    Ink-Jet Printing of Binders for Ceramic Components (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Layered manufacturing methods for fabricating ceramic components can involve selective deposition of binder using ink-jet printing. Selection of a proper binder plays a critical role in fabricating parts with good surface finish, dimensional accuracy, and high resolution. Several polymeric solution-phase binders were investigated in terms of their physical properties, printing performance, and binder-powder bed interaction. It was observed that the molecular weight should be 〈15 000 for the binder to be penetrated into dense powder compacts. Binder infiltration kinetics and printed line width were also significantly influenced by powder-bed characteristics, such as surface roughness and pore size, as well as the physical properties of the binder, such as viscosity and surface tension.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00168.x
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  • 6
    Electronic Resource
    Electronic Resource
    Corrosion of Aluminum Nitride (AlN) in Aqueous Cleaning Solutions (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The corrosion of aluminum nitride (AlN) in aqueous solutions has been evaluated in situ, using an ammonium/ammonia ion-selective electrode. The corrosion behavior of AlN over a pH range of 5.5–12 indicates that the corrosion products that are formed act as a protective barrier layer in the pH regime where they have the lowest stability. An insoluble barrier layer is formed via the oxidation of the AlN surface in air at a temperature of 750°C for 10 min. This oxynitride layer, which is 200 Å thick, prevents the corrosion of the AlN in a pH 9.5 aqueous solution; however, the thermal conductivity is reduced by 6.6%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01145.x
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  • 7
    Electronic Resource
    Electronic Resource
    Mixed-state behavior in large magnetic fields of high-temperature superconducting films prepared by metalorganic deposition (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2033-2035 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Films of Ba2YCu3O7−x prepared by metalorganic deposition (MOD) are demonstrated to have large critical current densities in high magnetic fields. The current-voltage (I-V) characteristics are reported for an MOD film in applied fields from 0 to 6 T at 77 K. The zero field critical current density was 600 000 A/cm2 and fell to 60 000 A/cm2 at 1 T. The critical current is approximately proportional to 1/H1/2. The variation in I-V curves above the critical current indicates the voltage has a power law behavior with values for the current exponent varying from 5.2 to 1.7 for magnetic fields from 0 to 6 T.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105004
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  • 8
    Electronic Resource
    Electronic Resource
    Epitaxial planarization of patterned yttria-stabilized zirconia substrates for multilayer structures (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1148-1150 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ planarization of epitaxial films has been demonstrated. This is a critical technology for the processing of any epitaxial multilayer device. Ion beam assisted deposition (IBAD) has been used to planarize patterned yttria-stabilized ZrO2 (YSZ)(001) substrates using YSZ films. X-ray diffraction measurements have shown that the IBAD YSZ grows homoepitaxially. The IBAD planarization mechanism has similarities to those previously observed for rf bias sputtering. Critical current densities of up to 7×105 A/cm2 at 77 K have been measured for Ba2YCu3O7−x (BYC) films deposited on planarized patterned YSZ substrates using pulsed laser deposition. In contrast, BYC deposited on unplanarized patterned YSZ substrates did not become fully superconducting for measurements down to 25 K. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114990
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  • 9
    Electronic Resource
    Electronic Resource
    Slurry Chemistry Control to Produce Easily Redispersible Ceramic Powder Compacts (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The slurry-based Three Dimensional Printing (3DPTM) process requires the production of an easily redispersible powder bed from a well-dispersed slurry. Understanding and control of the interparticle potential in the dispersed state, as well as in the dry consolidated state, are important. The strength of the particle–particle interactions in the dry state determines the redispersion efficiency. One factor that controls the interparticle strength is the chemical stability of the ceramic powders in the dispersed state. For unstable powders, a partial dissolution and/or hydration of the powders can occur and eventually impede the redispersion by forming insoluble salt bridges at the necks of the particles. Redispersion of the powder bed can be improved substantially by weakening the strength of the particle–particle bonds. The formation of strong chemical bonds between particles should be avoided by adjusting the slurry pH to an appropriate range where the powders are chemically stable in the slurry. Replacement of the chemical bonds by soluble physical bonds, using a low-molecular-weight hydrophilic polymer, also reduces the interparticle strength and enhances redispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01568.x
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  • 10
    Electronic Resource
    Electronic Resource
    Controlled Cracking of Multilayer Ceramic Bodies (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Cracking of granular ceramic films during drying is a well-known phenomenon. Previous work has shown that films cast above a critical thickness on nonporous substrates crack spontaneously. Films cast on previously cast layers crack at thicknesses that depend on the solids content of the slurry. Cracking occurs in this instance when films are cast above a critical saturation thickness (CST). The CST is defined as the thickness of granular material that would be 100% saturated by the liquid contained in the last cast layer. The CST is remarkably similar in magnitude to the critical cracking thickness obtained with similarly prepared slurries on dense substrates. For example, 0.5 µm Al2O3 slurries in water have a CST of 65 µm when cast on previously deposited layers of Al2O3. Similarly prepared slurries crack spontaneously when cast on single-crystal silicon at any thickness above ∼60 µm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02044.x
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