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  • 1
    Digitale Medien
    Digitale Medien
    Direct Coagulation Casting of Silicon Carbide Components (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: Direct coagulation casting is a novel near-net-shape method for forming ceramic green bodies from homogenous high-solids-loaded particle suspensions. It is based on the principle of the in situcoagulation of a powder suspension via a reaction-rate-controlled internal-enzyme(urease)-catalyzed reaction after casting. Low-viscosity (〈3 Pas) suspensions with a high solids loading (〉62 vol%) of SiC, boron, and carbon powder mixtures with a high surface area (〉7-10 m2/g) have been prepared at pH = 10. Salt ions (up to 1-2 mol/L) are created by the urease-catalyzed decomposition of urea, to destabilize the suspensions. The coagulation kinetics and the strength of the wet green bodies have been investigated. The reaction rate is strongly dependent on the temperature (in the range of 5°-30°C) and the enzyme concentration (for the range of 4-16 units/g SiC) and is independent of the substrate (urea) concentration for urea concentrations of 〈2 wt%, based on the powder content. The resulting green bodies show no shrinkage during coagulation and 1%-2% linear shrinkage during drying. The compressive strengths of the wet green bodies are as high as 60 kPa and increase as the coagulation time increases. The wet green strength of the coagulated suspensions scales with the solids content, according to a power law with an exponent of 11, in the range of 56-61 vol% solids content. The possibilities of fabricating high-solids-containing complex SiC green and sintered components with homogenous microstructures and high sintered densities are demonstrated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01886.x
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  • 2
    Digitale Medien
    Digitale Medien
    Experimental Phase Diagram Study and Thermodynamic Optimization of the Ag-Bi-O System (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The Ag-Bi-O system has been experimentally studied using differential thermal analysis (DTA) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), and thermodynamically optimized. The temperatures of the eutectic, monotectic, and Bi2O3 allotropic transformations have been measured in N2, in air, and in O2 by DTA. There are no ternary phases stable at ambient pressure. Presently measured transformation temperatures have been combined with existing oxygen activity measurements in the metal liquid to optimize thermodynamic parameters describing the liquid phase. The resulting fit is excellent. EDX measurements of the composition in the oxide liquid have a rather low precision but confirm the thermodynamic optimization. However, some uncertainties remain concerning the liquid composition at the eutectic transformation and the shape of the miscibility gap at higher temperatures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01821.x
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  • 3
    Digitale Medien
    Digitale Medien
    Experimental Phase Diagram in the Ag-Cu2O-CuO System (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: Phase equilibria in the Ag-CuO-Cu2O system were experimentally determined using thermal analysis, and structural and compositional studies. Three reactions were observed in air: (1) L1= CuO + Ag, (2) L2= CuO + L1, and (3) Cu2O = CuO + L2. The evolution and absorption of oxygen accompanied these reactions. At oxygen partial pressures below 0.02 bar, the reactions L1= Cu2O + Ag and L2= Cu2O + L1 were found. Based on isobaric projections in the Ag-CuO-Cu2O system, two invariant reactions, L1= CuO + Cu2O + Ag and L2= CuO + Cu2O + L1, were deduced.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02604.x
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  • 4
    Digitale Medien
    Digitale Medien
    Experimental Phase-Diagram Study and Thermodynamic Optimization of the Silver-Strontium-Copper-Oxygen (Ag-Sr-Cu-O) and Silver-Calcium-Copper-Oxygen (Ag-Ca-Cu-O) Systems (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The phase relations in the silver-strontium-copper-oxygen (Ag-Sr-Cu-O) and silver-calcium-copper-oxygen (Ag-Ca-Cu-O) systems were studied in oxygen, air, and nitrogen environments, using differential thermal analysis and energy-dispersive X-ray spectrometry. The presence of silver reduces the melting temperature of the oxide liquid to a monotectic in the strontium- and calcium-containing systems by 62 and 82 K, respectively (to 1222 and 1244 K, respectively) in oxygen. The oxide liquid dissolves silver (up to a metallic ratio of 0.17) in the Ag-Sr-Cu-O system in oxygen at a temperature slightly higher than that required for monotectic reaction. In the Ag-Ca-Cu-O system, the silver content has been measured to be 0.29 (metallic ratio). The oxide systems have been optimized using the experimental data from monotectics and those from lower-order systems that have been published previously. This work is part of a project to evaluate the phase relations within the silver-bismuth-strontium-calcium-copper-oxygen (Ag-Bi-Sr-Ca-Cu-O) system and, in particular, to focus on the influence of silver on the phase equilibria around the superconducting phases during partial-melt processing.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02283.x
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  • 5
    Digitale Medien
    Digitale Medien
    Thermodynamic Assessment of the Silver–Oxygen System (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: An assessment of the silver–oxygen system has been made, and a consistent set of thermodynamic parameters has been optimized. The calculated thermodynamic properties and phase relations are in good agreement with the experimental data. Ag2O is the only phase that is commonly found within the system. In air, it decomposes to silver and oxygen gas at 420 K. There is a eutectic between silver and Ag2O at a temperature of 804 K, an oxygen partial pressure (PO2) of 526 bar (5.26 × 107 Pa), and an oxygen mole fraction in the liquid phase of 0.25. Uncertainties remain on the Ag2O liquidus for PO2 〉 108 Pa. An ionic two-sublattice model has been used to describe the liquid phase. This work is part of a study of interactions between compounds from the bismuth-strontium-calcium-copper-oxygen system and silver.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03232.x
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  • 6
    Digitale Medien
    Digitale Medien
    Thermodynamic Assessment of the Bismuth–Calcium–Oxygen Oxide System (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The experimental data on the oxide part of the Bi-Ca-O system have been reviewed, and an optimized thermodynamic description is presented. There are six known stable ternary oxide phases, two of which show considerable solid-solution ranges. At least two phases—delta–Bi2O3 and the rhombohedral ß-phase–are good oxygen-ion conductors. Because all oxide phases are found on the Bi2O3–CaO line, the Bi2O3-CaO system can be treated as a true binary system. Most experimental data are in reasonable agreement with each other; however, there are fairly large uncertainties on the extension of the solid-solution phases and on the thermodynamic properties.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03165.x
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  • 7
    Digitale Medien
    Digitale Medien
    Thermodynamic Modeling and Calculation of Phase Equilibria in the Strontium–Calcium–CopperOxygen System at Ambient Pressure (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The phase-diagram and thermodynamic data on the Sr–Ca–CuO system at a total pressure of 105 Pa (1 bar) are reviewed and assessed. Gibbs energy functions for the (Sr,Ca) solid solutions and the liquid are optimized, and a consistent thermodynamic description is presented. Calculated phase relations are shown in various isothermal and isoplethal sections and compared to experimental data. Special attention is given to the stability of the infinite-layer compound, as a function of temperature and oxygen partial pressure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02865.x
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  • 8
    Digitale Medien
    Digitale Medien
    Thermodynamic Assessment of the Bismuth–Strontium–Oxygen Oxide System (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The experimental data on the oxide portion of the Bi–Sr–O system have been reviewed, and an optimized thermodynamic description is presented. There are at least seven stable ternary oxide phases, two of which show considerable solid-solution ranges. At least two phases—δ-Bi2O3 and the rhombohedral β-phase—are good oxygen-ion conductors. Most of the phases are confined to the Bi2O3-SrO line at ambient oxygen partial pressure; however, in the SrO-rich portion, there are at least two phases with oxygen in excess, i.e., with bismuth in the oxidation state Bi5+ instead of the usual Bi3+. There are rather large differences between different experimental data sets; nevertheless, a reasonably consistent set of data can be chosen for the optimization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02950.x
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  • 9
    Digitale Medien
    Digitale Medien
    Thermodynamic Assessment of the Strontium–Copper–Oxygen System (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The phase diagram and thermodynamic data on the Sr–Cu–O system at a total pressure of 105 Pa (1 bar) have been reviewed and assessed. Gibbs energy functions for the ternary oxides Sr2CuO3, SrCuO2, Sr14Cu24O41, SrCu2O2, and the liquid phase have been optimized, and a consistent thermodynamic description is presented. Calculated SrOCuOx phase diagrams in air and in 1.01 ×105 Pa (1.01 bar) O2, the oxygen potential diagram, and various thermodynamic properties are shown and compared to experimental data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02864.x
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  • 10
    Digitale Medien
    Digitale Medien
    Processing of β-Silicon Nitride from Water-Based alpha-Silicon Nitride, Alumina, and Yttria Powder Suspensions (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: A water-based route for processing ß-Si3N4 from alpha-Si3N4, Al2O3, and Y2O3 powder mixtures was established. The surface charges and isoelectric points of the three different powders were investigated within the pH range from pH 3 to pH 12. Citric acid diammonium salt was found to be an effective deflocculant for shifting the isoelectric points to pH 3.5 for Al2O3 and to pH 6 for Y2O3. Aluminum hydroxide (Al(OH)3) showed strong interaction with the Si3N4 powder, shifting the isoelectric point from pH 7 to pH 5.5. Low-viscosity, high-solids-loading suspensions (60-63 vol%) thus were possible at pH 9.7. The preparation of homogeneous and stable suspensions with a solids content of ≤61 vol% and a viscosity 〈1 Pa·s was limited to a pH regime between pH 9 and pH 10.5 because of the high solubility of yttria. The homogeneous suspensions were easily solidified by direct coagulation casting (DCC), using the urease-catalyzed decomposition of urea at pH 9 to pH 10, by forming salt. No shrinkage cracking, sedimentation, or phase separation was observed during coagulation or drying. The green-density distribution was homogeneous throughout all bodies, even for complex geometries.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02037.x
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