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Journal ArticleDOI

Effects of microstructure on the compressive yield stress

01 Jan 2000-Aiche Journal (John Wiley & Sons, Ltd)-Vol. 46, Iss: 1, pp 72-78
TL;DR: In this paper, the effects of microstructure on the compressie properties of aggregated alumina suspensions are determined by intentionally introducing heterogeneities into the suspen- sion.
Abstract: The effects of microstructure on the compressie properties of aggregated alumina suspensions are determined by intentionally introducing heterogeneities into the suspen- sion. Suspensions are prepared at a higholume fraction and diluted with low shear hand mixing to a series of initial concentrations. As the initial concentration is in- creased, larger heterogeneities are introduced, and the suspension becomes more com- pressible relatie to the compressie yield stress of the uniform suspension. A simple model is proposed in which the heterogeneous suspensions compress by rearrangement ( of the dense aggregates until a critical concentration f , which coincides with the c ) ¤olume fraction prior to dilution is reached. Aboe f , the suspensions consolidate c ( identically to the uniform suspension. With a single fitting parameter the size of the ) heterogeneities , the model shows semiquantitatie agreement with the experimental data.

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Citations
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Journal ArticleDOI
TL;DR: The ability to pattern materials in 3D shapes without the need for expensive tooling, dies, or lithographic masks is critical for composites, microfluidics, photonics, and tissue engineering as discussed by the authors.
Abstract: The ability to pattern materials in three dimensions is critical for several technological applications, including composites, microfluidics, photonics, and tissue engineering. Direct-write assembly allows one to design and rapidly fabricate materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. Here, recent advances in direct ink writing are reviewed with an emphasis on the push towards finer feature sizes. Opportunities and challenges associated with direct ink writing are also highlighted.

1,226 citations

Journal ArticleDOI
TL;DR: In this article, both droplet-and filament-based direct ink writing (DIW) techniques are presented, and various ink designs and their corresponding rheological behavior, ink deposition mechanics, potential shapes and the toolpaths required.
Abstract: The ability to pattern ceramic materials in three dimensions (3D) is critical for structural, functional, and biomedical applications. One facile approach is direct ink writing (DIW), in which 3D structures are built layer-by-layer through the deposition of colloidal- or polymer-based inks. This approach allows one to design and rapidly fabricate ceramic materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. In this feature article, we present both droplet- and filament-based DIW techniques. We focus on the various ink designs and their corresponding rheological behavior, ink deposition mechanics, potential shapes and the toolpaths required, and representative examples of 3D ceramic structures assembled by each technique. The opportunities and challenges associated with DIW are also highlighted.

637 citations

Journal ArticleDOI
30 Jan 2007-Langmuir
TL;DR: This study synthesized dispersants with a molecular architecture that enables better control over the particle adlayer thickness that facilitates the fabrication of a wide range of products and intermediates in materials technology, cosmetics, pharmacy, and in all areas where concentrated nanoparticle suspensions are required.
Abstract: The stabilization of nanoparticles in concentrated aqueous suspensions is required in many manufacturing technologies and industrial products. Nanoparticles are commonly stabilized through the adsorption of a dispersant layer around the particle surface. The formation of a dispersant layer (adlayer) of appropriate thickness is crucial for the stabilization of suspensions containing high nanoparticle concentrations. Thick adlayers result in an excessive excluded volume around the particles, whereas thin adlayers lead to particle agglomeration. Both effects reduce the maximum concentration of nanoparticles in the suspension. However, conventional dispersants do not allow for a systematic control of the adlayer thickness on the particle surface. In this study, we synthesized dispersants with a molecular architecture that enables better control over the particle adlayer thickness. By tailoring the chemistry and length of these novel dispersants, we were able to prepare fluid suspensions (viscosity < 1 Pa.s at 100 s-1) with more than 40 vol % of 65-nm alumina particles in water, as opposed to the 30 vol % achieved with a state-of-the-art dispersing agent. This remarkably high concentration facilitates the fabrication of a wide range of products and intermediates in materials technology, cosmetics, pharmacy, and in all other areas where concentrated nanoparticle suspensions are required. On the basis of the proposed molecular architecture, one can also envisage other similar molecules that could be successfully applied for the functionalization of surfaces for biosensing, chromatography, medical imaging, drug delivery, and aqueous lubrication, among others.

243 citations

Journal ArticleDOI
TL;DR: The best dewaterability is observed for activated sludge that contains strong, compact flocs without single cells and dissolved extracellular polymeric substances.

218 citations

Journal ArticleDOI
TL;DR: In this paper, a mathematical framework exists for the dewatering of suspensions using three parameters: the compressi®e yield stress P, the y () hindered settling function r, and a solids diffusi®ity D.
Abstract: To characterize and optimize the compressi®e dewatering of suspensions, rapidly determinable material parameters are required. A mathematical framework exists for char() acterization of dewatering using three parameters: the compressi®e yield stress P , the y () ( ) hindered settling function r , and a solids diffusi®ity D .An ew®ariation on traditional constant pressure, batch filtration tests is described along with a computer-controlled filtration apparatus that enables complete characterization of a suspension with respect to dewatering in a matter of hours. The testing methods are ®alidated experimentally on flocculated zirconia suspensions along with calculation of the material dewatering parameters. Application of the calculated parameters to modeling of a real filtration test shows excellent agreement. Practical implications of the modeling are also discussed.

117 citations

References
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Journal ArticleDOI
TL;DR: In this article, it has been shown that the van der Waals interaction at the point of contact remains finite and that the electrostatic repulsion, for pH values sufficiently far from the isoelectric point, can become large enough to overcome the attraction, even at distances of closest approach.
Abstract: The adsorption of low molecular weight oxyanions onto oxide surfaces is known to limit the distance of the closest approach between particles in dispersions of such oxides. As a consequence, the value of van der Waals interactions at the point of contact remains finite. By calculating the forces for conditions where the charge density of the absorbed ions is small, it has been demonstrated that the electrostatic repulsion, for pH values sufficiently far from the isoelectric point (i.e.p.), can become large enough to overcome the attraction, even at distances of closest approach. More significantly, this conclusion remains true at high electrolyte concentrations. It has also been shown that the current results can account for the apparent narrowness of the experimental shear stress vs. pH curves, recently reported in a number of studies for oxide dispersions. It has been predicted that, regardless of the electrolyte concentration, coagulation for such systems can only occur over a limited range of pH values around the i.e.p. The significance of these results for the problem of peptisation, in dispersions with high acid contents, has also been briefly discussed.

12 citations


"Effects of microstructure on the co..." refers methods in this paper

  • ...Despite the appealing simplicity of this picture, models for predicting the magnitude of P remain in a poory Ž .state of development Buscall et al., 1997 ....

    [...]

Book ChapterDOI
01 Jan 1994
TL;DR: In this article, the authors present an overview of the research conducted in the Department of Chemical Engineering at the University of Melbourne in conjunction with Alcoa of Australia Limited and compare the rheology of highly concentrated bauxite residue suspensions in shear to results obtained in compression using techniques for compressive yield stress measurement.
Abstract: The paper presents an overview of the research conducted in the Department of Chemical Engineering at the University of Melbourne in conjunction with Alcoa of Australia Limited. The first part of the presentation reviews the shear rheology of bauxite residue suspensions and emphasises how an understanding of the fundamental flow properties of concentrated bauxite residue suspensions can be exploited in developing a semi-dry waste disposal scheme, which has been developed and proven by Alcoa in Western Australia and is now under consideration by a number of international alumina producing companies. The paper compares the rheology of highly concentrated bauxite residue suspensions in shear to results obtained in compression using techniques for compressive yield stress measurement developed at the University of Melbourne. It is shown how the compressive yield stress properties are particularly useful in the design and specification of thickeners for dewatering red mud suspensions.

6 citations


"Effects of microstructure on the co..." refers background in this paper

  • ...Green et al. 1994 investigated the compressive yield stress Ž .of Bauxite Residue that is, ‘‘red mud’’ ....

    [...]