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  • 1
    Electronic Resource
    Electronic Resource
    Influence of Short-Chain Carboxylic Acids on the Mechanical Properties and Structure of Coagulated Alumina Suspensions (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Three different short-chained carboxylic acids, formic, acetic, and propionic acid, were compared as additives to increase the green strength of wet particle networks produced with the direct coagulation casting process, which allows the internal coagulation of a suspension. Small acid additions do not alter the favorable low viscosity of the stabilized slurry, and yet increase the compressive strength of wet coagulated bodies. The strengthening effect increases with increasing chain length of the carboxylic acid. The maximum effect was observed upon addition of propionic acid (0.3 wt% to alumina), which resulted in a sixfold increase in compressive strength of wet coagulated bodies compared with that without propionic acid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00470.x
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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Mechanics and Microstructures of Concentrated Particle Gels (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: It is often assumed that the viscoelastic properties of dense colloids are determined by the colloid volume fraction, the interaction potential, as well as the particle size distribution and shape. The dependence of the viscoelastic behavior of particle suspensions and gels on these parameters has been widely studied, and is well understood in many cases. In contrast, our knowledge on the influence of microstructure on mechanical and rheological properties, in particular for high solid loading suspensions as used in ceramic processing, is much less developed. This aspect has been the focus of recent experiments, which show that small changes in microstructure can have dramatic effects on the mechanics and dynamics of concentrated colloidal gels. In this article, we attempt to give an overview of the influence of microstructure on the mechanical and rheological properties of colloidal systems. Particular attention is given to colloidal particle gels at high volume fractions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00622.x
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  • 5
    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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  • 6
    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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  • 7
    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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