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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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01 Jan 2012
TL;DR: The breakthrough pressure pb condition is defined in this article, which is critical for determining the performance of these processes, including the final cake solids and moisture content, and it is the condition when consolidation ends and desaturation begins.
Abstract: The desaturation and drying of suspensions is important to many industries such as paints, ceramics, minerals processing and pharmaceuticals. In such processes, cakes or films first consolidate due to the capillary pressure generated by solvent removal and, at a critical concentration, stop consolidating and begin to desaturate. The condition when consolidation ends and desaturation begins is termed the breakthrough pressure pb and is critical for determining the performance of these processes, including the final cake solids and moisture content. In many cases, cracking may occur once desaturation begins, which is generally detrimental. For example, cracking during vacuum filtration of minerals tailings or pharmaceutical products reduces the efficiency of solvent removal.
Posted Content
TL;DR: Using both light microscopy and mesoscale cell-level simulations, this article showed that erythrocytes form a soft-colloid gel, and the high volume fraction of erythropoietin (EPO) cells, their deformability, and weak attraction lead to unusual properties of this gel.
Abstract: The erythrocyte sedimentation rate is one of the oldest medical diagnostic methods whose physical mechanisms remain debatable up to date. Using both light microscopy and mesoscale cell-level simulations, we show that erythrocytes form a soft-colloid gel. Furthermore, the high volume fraction of erythrocytes, their deformability, and weak attraction lead to unusual properties of this gel. A theoretical model for the gravitational collapse is developed, whose predictions are in agreement with detailed macroscopic measurements of the interface velocity.
References
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Journal ArticleDOI
TL;DR: In this paper, the concentration or consolidation of suspensions of fine particles under the influence of a gravitational field has been analyzed and a constitutive equation is suggested for irreversibly flocculated suspensions undergoing consolidation which embodies the concept of a concentration-dependent yield stress Py(ϕ).
Abstract: The concentration or consolidation of suspensions of fine particles under the influence of a gravitational field has been analysed. The rate and extent of consolidation depends upon a balance of three forces, the gravitational driving force, the viscous drag force associated with flow of liquid in the sediment and a particle or network stress developed as a result of direct particle–particle interactions. In the case of colloidally stable suspensions, this particle stress is the osmotic pressure of the particles; in the case of flocculated or coagulated suspensions, it is the elastic stress developed in the network of particles. A constitutive equation is suggested for irreversibly flocculated suspensions undergoing consolidation which embodies the concept of a concentration-dependent yield stress Py(ϕ). This is then used to analyse the sedimentation behaviour of flocculated sediments and to derive expressions for the initial sedimentation rate. The initial rate of change of sediment height with time in a uniform gravitational or centrifugal field is given approximately by: [graphic ommitted] where B=Δρgϕ0H0/Py(ϕ0), u0 is the sedimentation rate of an isolated particle, ϕ0 is the initial (uniform) volume fraction of solids, r(ϕ0) is a dimensionless hydrodynamic interaction parameter, Δρ is the difference in density between solid and liquid, g is the gravitational or centrifugal acceleration and H0 is the initial sediment height. The theory accounts correctly for the equilibrium consolidation behaviour of strongly flocculated suspensions, and preliminary experimental data suggest that it is not inconsistent with their dynamic behaviour. The estimation of the yield stress Py(ϕ) from a batch centrifuge experiment is also described.

403 citations


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

  • ...Buscall and White 1987 describe a constitutive model for the compressive behavior of aggregated suspensions....

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  • ...Miller et al., 1996 , or 2 measuring the equilibrium height at Ž .a series of speeds Buscall, 1982; Buscall and White, 1987 ....

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Journal ArticleDOI
TL;DR: The instantaneous shear modulus G and compactive strength Py of aggregate networks formed from silica particles with a mean diameter of 26 nm have been determined as a function of particle concentration as mentioned in this paper.
Abstract: The instantaneous shear modulus G and compactive strength Py of aggregate networks formed from silica particles with a mean diameter of 26 nm have been determined as a function of particle concentration. The data are compared with similar data obtained earlier for a range of polystyrene spheres with diameters between 60 and 960 nm and with compactive strength data obtained for polystyrene spheres at higher volume fractions by Sutherland. It is shown that clusters of submicron spheres formed by rapid aggregation become spacefilling and form a network at a critical volume fraction Φg of ca. 0.05. Above this concentration the data for Py and G suggest that aggregate networks show universal behaviour which is consistent with the scalings G∼ϕµ, dPy(ϕ)//d ln ϕ∼G(ϕ), with µ= 4 ± 0.5. This latter value for the exponent agrees well with that predicted by Ball and Brown by assuming the clusters comprising the network are fractal. For diffusion-limited cluster–cluster aggregation (DCA) they obtained a value of µ= 3.6. The data for Py imply a particle size dependence of the type Py∼am with m between –2 and –3, where a is the particle radius. More data are required to establish the precise dependence; the observed trend is, however, not inconsistent with what might be expected from a consideration of interparticle forces which implies a scaling of a–2.3. The scaling behaviour of the yield stress in shear flow and the dependence of the shear modulus on strain for non-negligible strains is also discussed.

357 citations


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

  • ...While the term gelation is more precisely used for systems with interparticle interactions on the order of a few kT, it is often applied more broadly to systems where there is a liquid to solid transition, even in the presence of much stronger attracŽ .tions Buscall et al., 1988 ....

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  • ...Buscall et al. 1988 Ž .and Meeten 1994 present data on the compressive behavior of polystyrene latex, silica, and two clays, bentonite and attaŽ .pulgite....

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Journal ArticleDOI
TL;DR: In this paper, the consolidation behavior of flocculated alumina suspensions has been analyzed as a function of the interparticle energy, and it has been shown that strongly attractive interactions result in a particle network which resists consolidation and shows compressible behavior over a large stress range.
Abstract: The consolidation behavior of flocculated alumina suspensions has been analyzed as a function of the interparticle energy. Consolidation was performed by a centrifugal force field or by gravity, and both the time-dependent and equilibrium density profiles were measured by a gamma-ray absorption technique. The interparicle energy at contact was controlled by adsorbing fatty acids of varying molecular weight at the alumina/decalin interface. We found that strongly attractive interactions result in a particle network which resists consolidation and shows compressible behavior over a large stress range. The most weakly flocculated suspension showed an essentially incompressible, homogeneous density profile after consolidation at different centrifugal speeds. We also found a significant variation in the maximum volume fraction, φm, obtained, with φm∼ 0.54 for the most strongly flocculated suspension to φm∼ 0.63 for the most weakly flocculated suspension. The compresive yield stresses show a behavior which can be fitted to a modified power law. In this paper, we discuss possible correlations between the fitting parameters and physical properties of the flocculated suspensions.

194 citations


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

  • ...In centrifugation, compressive yield stress data can be obtained Ž .by two methods: 1 measuring the volume fraction profile of Žthe centrifuge bed at a single speed Bergstrom et al., 1992;¨ ....

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  • ...Bergstrom et al. 1992 studied the compressive behavior¨ Ž .of alumina particles suspended in decalin....

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Journal ArticleDOI
TL;DR: In this paper, a generalized approach to understand and prediction of solid-liquid separation methods based on the measurement of fundamental material properties is reviewed and applied to a variety of thickening and filtration processes.

169 citations


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

  • ...At this point, the applied load is the compressive yield stress at that volume fracŽ .tion Lange and Miller, 1987; Landman and White, 1994 ....

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Journal ArticleDOI
TL;DR: In this article, the shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction, and the links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.
Abstract: The shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction. Over a range of volume fractions, yield stresses, τy, elastic moduli, the strain delimiting the extent of the linear elastic response, and compressive yield stress, Py, are well described by power-law functions of volume fraction, while the role of interparticle attractions can be accounted for by expressing these mechanical properties as (ϕ/ϕg − 1)n, where ϕg captures the strength of particle attractions and n the microstructure. The links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.

167 citations


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

  • ...…curve is characteristic of the Žcompressive behavior observed in other systems Bergstrom¨ January 2000 Vol. 46, No. 1 AIChE Journal74 The curves presented are for suspensions with homoge- Ž u.neous microstructures that is, P .y et al., 1992; Channell and Zukoski, 1997; Miller et al., 1996; ....

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  • ...Similar effects are also observed for a variety of systems as the strength of Žthe particle network is varied Channell and Zukoski, 1997; ....

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  • ...The ability of small shear stresses to disrupt heterogeneities is a result of the shear yield stress being much smaller than the Ž .compressive yield stress Channell and Zukoski, 1997 and the continuous nature of the shearing action....

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