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  • 1
    Electronic Resource
    Electronic Resource
    Chemical Aspects of Direct Coagulation Casting of Alumina Suspensions (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), 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: This work presents a detailed description of urea decomposition during direct coagulation processing of alumina suspensions. We report on the chemical equilibria involved in the decomposition of urea in an aqueous environment with and without alumina particles. The model uses the logarithm of the concentrations as variables to ensure fast convergence and nonnegativity of the solutions, and is able to give a semiquantitative description of the experimentally observed development of pH and ionic strength (specific conductivity) during the decomposition of urea in a 30 vol% solid loading alumina suspension. Assuming local equilibrium, and a homogeneous distribution of the catalyst urease and the evolving educts, the results show an increasing solubility of CO2 with increasing pH. As a consequence the production of gaseous CO2 during the urea decomposition (direct coagulation casting (DCC) process), shifting the pH from 4 to 9 occurs only when a strong buffer is present at low and medium pH. This is advantageous for the preparation of defect-poor ceramic green bodies using this internal gellation reaction in the DCC process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01530.x
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  • 2
    Electronic Resource
    Electronic Resource
    Electrophoretic Deposition of Zirconia on Porous Anodic Substrates (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), 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 aim of the present work is the preparation of thin (〈20 μm) zirconia layers on porous substrates with the electrophoretic deposition process. The preparation was completed with a cosintering step of substrate and layer. Through adjustment of shrinkage and the shrinkage rate of the deposited zirconia layer on the presintered porous substrate, thin, dense layers without cracks were prepared. A method for direct control of the layer thickness during the electrophoretic deposition process was developed. The solid oxide fuel cell application with porous anode substrates and thin zirconia electrolytes was chosen to demonstrate the potential of the electrophoretic deposition process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00658.x
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  • 3
    Electronic Resource
    Electronic Resource
    Direct Coagulation Casting of Alumina Suspensions Using Jack Bean as a Urease Source (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: This paper reports on the use of Jack bean meal as an alternative source of urease for direct coagulation casting (DCC) processes. Al2O3 suspensions were prepared to compare the effect of Jack bean meal and pure urease on the hydrolysis of urea, the slurry coagulation rate, and the mechanical properties of consolidated bodies. Results indicate that the Jack bean meal is a promising economic alternative for the consolidation of ceramic parts, mainly because of its lower susceptibility to enzyme deactivation when exposed to room temperature and relatively humid environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00337.x
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  • 4
    Electronic Resource
    Electronic Resource
    Powder-Based Tin Oxide Microcomponents on Silicon Substrates Fabricated by Micromolding in Capillaries (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: With the introduction of soft lithography and micromolding in capillaries, low-cost microfabrication with liquid materials has become possible. In this article, we demonstrate how to fabricate porous ceramic lines of 10 μm width and several millimeter length on silicon wafer substrates by using colloidal suspensions of tin oxide. Microchannels of poly(dimethylsiloxane) (PDMS) served as molds that were spontaneously filled owing to capillary forces with suspensions of 0.1–40 vol% solid loading. The resulting ceramic lines have a height of about 7 μm and therefore differ from the usual ceramic thin film coatings. The capillary filling characteristics were observed under the microscope, and the implications of rheology and suspension chemistry are discussed and evaluated. Using the same capillaries, even smaller lines (2–3 μm width) of powder particles could easily be prepared by adjusting only the solid content of the suspensions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03313.x
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  • 5
    Electronic Resource
    Electronic Resource
    In Situ Coagulation of High-Alumina Zero-Cement Refractory Castables (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: Coagulation methods originally developed for colloidal processing were investigated in this paper as alternative approaches to consolidate high-alumina refractory castables free of hydraulic binders (zero-cement). Three in situ reactions based on the direct coagulation casting (DCC) technique were evaluated to promote castable coagulation: (1) the autocatalytic hydrolysis of gluconic acid lactone, (2) the gradual dissolution of hydroxyaluminum diacetate particles in water, and (3) the enzyme-catalyzed hydrolysis of urea. The coagulating behavior of castables and matrix-representative suspensions was investigated with the help of zeta potential analysis, pH measurements, castable free-flow evaluation, and oscillatory rheological tests. The enzyme-catalyzed hydrolysis of urea seemed to be the most appropriate mechanism to promote the coagulation of initially self-flow zero-cement refractory compositions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00386.x
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  • 6
    Electronic Resource
    Electronic Resource
    Gelling of Alumina Suspensions Using Alginic Acid Salt and Hydroxyaluminum Diacetate (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: This paper proposes a novel direct casting method of alumina suspensions using alginic acid salt and the coagulation agent hydroxyaluminum diacetate (HADA). These two compounds allowed the consolidation of alumina suspensions through a simultaneous time-delayed physical and chemical gelation process. The physical gel was formed by the gradual release of aluminum and acetate ions from the HADA in water, while the chemical gel originated from the cross-linking of alginate molecules by the polyvalent aluminum ions. Wet alumina green bodies displayed enhanced mechanical properties with the addition of minimal contents of organic material (〈0.1 wt%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00518.x
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  • 7
    Electronic Resource
    Electronic Resource
    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
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02283.x
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  • 8
    Electronic Resource
    Electronic Resource
    Thermodynamic Optimization of the Silver—Bismuth—Strontium—Calcium—Copper—Oxygen (Ag-Bi-Sr-Ca-Cu-O) System (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: Experimental data on the phase equilibria between the high-critical-temperature (high-Tc) superconducting compound 2212 and silver have been reviewed and assessed. Using these data, the interaction parameter of the Gibbs energy function of the liquid phase was optimized via the CALPHAD method. The calculation yields very good agreement with the experiment. This work is the final step in the optimization of the Ag-Bi-Sr-Ca-Cu-O system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01293.x
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  • 9
    Electronic Resource
    Electronic Resource
    Mechanical Properties of Coagulated Wet Particle Networks with Alkali-Swellable Thickeners (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), 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: Alkali-swellable thickeners (ASTs) such as Acusol 820 and Acusol 830, as well as poly(acrylic acid) homopolymers of various molar mass, have been used as additives in aqueous electrostatically stabilized alumina suspensions. These suspensions have been destabilized by internal enzyme-catalyzed reactions (a direct coagulation casting process) to form viscoelastic solids. The ASTs increase the strength and modulus of the wet green bodies on coagulation. The effect of their molecular architecture on the mechanical properties of wet particulate networks has been studied. At low pH (pH 4.5), ASTs are small insoluble polymer particles that have only minor influence on the low viscosity of the high-solids-loading suspensions. After shifting the pH toward the isoelectric point of α-Al2O3, the suspension coagulates and the AST polymer particles swell, thereby increasing the compressive strength and modulus of the alumina-particulate wet green bodies. The presence of small amounts of ASTs (0.4 wt%, based on the solids loading) results in a 10-fold increase in the strength of the wet green bodies. The compressive strength of the wet green bodies that contain ASTs correlates with the size of the expanded AST molecules at pH 9. A possible explanation is that swelling of the AST particles locally decreases the interparticle distance, which leads to increased van der Waals forces between the ceramic particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00900.x
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  • 10
    Electronic Resource
    Electronic Resource
    In Situ Rheological Investigation of the Coagulation in Aqueous Alumina Suspensions (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), 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: Electrostatically stabilized alumina suspensions can be destabilized by the enzyme-catalyzed decomposition of urea (direct coagulation casting). Depending on the conditions, this reaction can shift the pH of a suspension to the buffer pH of the reaction products or increase the ionic strength at the buffer pH. The coagulation for both mechanisms was investigated using in situ rheological measurements. Using a vane tool in oscillation mode, the measuring conditions were optimized to find a reasonable method for time-dependent measurements. Constant parameters (stress or strain) proved to be unsuitable, because the linear viscoelastic region shifted considerably during the coagulation. Furthermore, the gel structure produced on coagulation via increase of ionic strength (ΔI) was very sensitive to the oscillation. Therefore, for long-time experiments, a short continuous measurement with a low strain was followed by amplitude sweeps with increased intervals to determine the linear values of G′ and G″. In this way, the increase of the moduli G′ and G″ could be followed for longer times, and it was possible to demonstrate two results. First, the final G′ of the network was about 10 times higher for ΔI-coagulated material than for suspensions coagulated via pH shift (ΔpH). Second, particle rearrangement processes took place in ΔI-coagulated networks even after the chemical changes were finished, whereas ΔpH-coagulated samples were “frozen-in” when approaching the isoelectric point and showed no further physical changes afterward.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00907.x
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