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Dive into the research topics where van Ajg Alois Diemen is active.

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Featured researches published by van Ajg Alois Diemen.


Colloids and Surfaces A: Physicochemical and Engineering Aspects | 1994

Efficient dewatering of waterworks sludge by electroosmosis

Pj Buijs; van Ajg Alois Diemen; Hn Stein

Abstract Electroosmotic dewatering of water treatment process sludge, in which a relatively high specific resistance causes difficulties with regard to water removal, is described. The dewatering can be both accelerated and made economically more attractive by additives which increase the absolute value of the ζ potential but do not lead to stable suspensions. An increase in ζ potential means an increase in electroosmotic water transport; simultaneously electric charges on the filter repel particles with electrical charges of the same sign, which causes a decrease in the clogging of the filtration material. Best results show an increase in final dry solid content from 4% (by weight) by pressure filtration only, to 16% (by weight) by a combination of electroosmosis with pressure filtration.


Journal of Colloid and Interface Science | 1983

Coagulation of aqueous dispersions of quartz in a shear field

van Ajg Alois Diemen; Hn Stein

The coagulation of aqueous dispersions of quartz shows, with increase particle radius (b) and increasing shear rate (γ), a transition from coagulation under the predominant influence of Hamaker attraction, to coagulation caused in the main by centrifugal pseudoforces. For b = 1.5 μm, the transition is at γ≃20 sec-1. For γ > 1000 sec-1, the capture efficiency of collisions between the suspended particles, in the initial stages of the coagulation, is small (0.005–0.01) but not strongly dependent on γ, due to most of the pairs breaking up shortly after their formation. The final aggregate size increases with increasing γ up to γ > 5000 sec-1this is ascribed to a smaller permeability of the aggregates formed at larger γ. At γ > 5000 sec-1, however, vortex formation after the aggregates retards their further growth.


Journal of Colloid and Interface Science | 1982

Energy dissipation during stationary flow of suspensions of hydrophilic and hydrophobic glass spheres in organic liquids

van Ajg Alois Diemen; Hn Stein

Abstract Suspensions of both hydrophilic and hydrophobic glass spheres in dioctylphthalate behave similarly to suspensions of hydrophilic glass spheres in glycerol + water mixtures: Newtonian behavior is shown up to a solid volume fraction (cv) of 0.4; at larger cv values, Bingham behavior is observed with a yield value steeply increasing at cv > 0.45. Suspensions of hydrophobic glass spheres in glycerol + water mixtures, on the other hand, already show deviations from Newtonian behavior at cv


Journal of Colloid and Interface Science | 1985

Rheology of suspensions of hydrophilic and hydrophobic solid particles in nonaqueous media

van Ajg Alois Diemen; Fwam Schreuder; Hn Stein

Abstract Coagulation of suspensions of hydrophobic particles becomes apparent if the hydrophilic/lipophilic balance (HLB) value of the medium is larger than 14; suspensions of hydrophilic solid particles show no distinct tendency toward coagulation in the media investigated (HLB ⪖ 4.5). As a criterion for coagulation, rheological, and sedimentation characteristics are employed. The rheological behavior of these suspensions indicates that both in the Newtonian and in the non-Newtonian range, the energy dissipation during stationary flow is proportional to the viscosity of the suspension medium. This excludes any significant contribution to this energy dissipation from the increase and decrease of potential energy between the suspended particles (breaking and renewed formation of interparticle bonds).


Journal of Colloid and Interface Science | 1986

Viscoelastic properties of concentrated suspensions

Fwam Schreuder; van Ajg Alois Diemen; Hn Stein

Abstract The deformation observed during oscillatory shear of concentrated suspensions indicates the alternate occurrence of two structures: the first at small deformations gives rise to approximately linear viscoelastic behavior, while the second is a virtually undeformable structure formed at large deformations. The behavior at small deformation is characterized by a dynamic viscosity which at low frequencies is inversely proportional to the frequency: at higher frequencies the viscosity levels off. This transition is ascribed to sheet formation by the suspended particles during shear in the low frequency region; in the high frequency region sheet formation is less developed. In accordance with this interpretation is the deformation at which the undeformable structure originates, as a function of frequency. The origin of this structure is attributed to the following: once the shear leads to an increase in solid content in a part of the system, the apparent viscosity there rises which causes an additional increase in solid content. This finally leads to a blocking of further deformation.


Journal of Colloid and Interface Science | 1978

Adsorption and electrokinetic potentials at solid/aqueous solution interfaces characterized by mutually stimulated adsorption of cations and anions

van Ajg Alois Diemen; Hn Stein

For interfaces of some Ca silicates with aqueous solutions, the change of the potential in the chemisorption plane with Ca2+ activity in the surrounding liquid is calculated from adsorption data. The potential, averaged over the Ca2+ sites, increases less with increasing Ca2+ activity than the ζ potential and the potential averaged over the whole chemisorption plane. In some cases, distances between the electrokinetic slipping and chemisorption planes may be calculated (1–2.5 nm); these distances may be too low because any surface disorder will increase these values, but they may be overestimated because any lowering of the relative dielectric constant near the surface will lead to lower values.


Advances in Colloid and Interface Science | 1999

Understanding the influence of gravity on perikinetic coagulation on the basis of the DLVO theory

Rudy Folkersma; van Ajg Alois Diemen; Hn Stein

Previous investigations had shown that perikinetic coagulation under microgravity conditions is faster than coagulation under terrestrial conditions. The results can be understood by calculating the interaction forces between doublets of particles, applying the DLVO theory to spheres with a certain degree of surface roughness in combination with convection flows in the continuous phase, caused by a temperature gradient.


Colloids and Surfaces | 1989

Influence of surfactants on electro-osmotic dewatering of sludges

van Ajg Alois Diemen; de Mjh Vet; Hn Stein

Abstract The influence of surfactants [C12H25OSO3Na, C16H33N(CH3)3Br] on the electro-osmotic dewatering of sludges is investigated at various pH values. Under favourable conditions, dewatering rate and final solid content can be increased and energy consumption can be lowered. In this investigation, two metal hydroxide sludges (from galvanotechnical industry), sewage sludge and pig manure have been considered.


Colloids and Surfaces | 1986

Coagulation of suspensions in shear fields of different characters

Hn Stein; Ehp Logtenberg; van Ajg Alois Diemen; Pj Peters

Abstract Coagulation is effected in: (a) the space between two coaxial cylinders, both under laminar and Taylor vortex flow conditions; and (b) a cylindrical vessel in which a flow field is generated by stirring. The former geometry permits a theoretical calculation of shear rates, while the latter resembles more closely conditions met in practice. In this case, shear rates are calculated from a model based on Laser Doppler anemometry measurements of local velocities. From the data, capture efficiencies (α 0 ) for the initial coagulation are calculated. At a given average shear rate, α 0 in laminar shear is larger than in Taylor vortex flow. This is ascribed to the partially elongational character of the latter type of flow stimulating breaking of aggregates. Deviations from a smooth spherical shape lead to a lower mutual attraction between two approaching particles on the one hand, but to a lower hydrodynamic interaction on the other. The former leads to a lower coagulation rate for quartz particles than expected for spheres, while the latter could be responsible for larger α 0 values than predicted by the theory of spherical bodies as observed in the case of ZnO.


Advances in Colloid and Interface Science | 1993

Influence of density differences between disperse and continuous phases on coagulation

Llm Bert Krutzer; Rudy Folkersma; van Ajg Alois Diemen; Hn Stein

Abstract Experimentally, a difference was found between coagulation rates of quartz in aqueous solutions, under μg conditions and under 1 g: at μg conditions, coagulation is faster than at 1g. This difference is contrary to theoretical expectations; however, at 1 g in dispersions in which there is no density difference between the disperse and continuous phases, coagulation rate is also higher than in dispersions in which there is such a density difference. Theoretically, a difference in coagulation rates is not expected from low Reynolds number hydrodynamics. Apparently the non-linear terms in the Navier-Stokes equation become important even for small (1–3 μm) particles, when they are close enough for the London-van der Waals forces to be important.

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Hn Stein

Eindhoven University of Technology

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Fwam Schreuder

Eindhoven University of Technology

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Llm Bert Krutzer

Eindhoven University of Technology

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Rudy Folkersma

Eindhoven University of Technology

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Ehp Logtenberg

Eindhoven University of Technology

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Pj Buijs

Eindhoven University of Technology

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Pj Peters

Eindhoven University of Technology

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de Mjh Vet

Eindhoven University of Technology

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