Papers at 5th World Congress on Particle Technology

5th World Congress on Particle Technology - WCPT5 - Orlando 2006

Use of multisample analytical centrifugation for evaluation of separation of fine particle slurries in the centrifugal field

T. Sobisch, D. Lerche, T. Detloff

Dispersion Stability & Particle Analysis, L.U.M. GmbH

Rudower Chaussee 31, 12489 Berlin, Germany,

info@lum-gmbh.de, www.lum-gmbh.com

Unit processes using centrifugal fields are often applied for separation, deliquoring and classification of fine grained materials. Modelling of these processes requires information about the separation behaviour of the suspensions to be processed. To this end direct measurements in centrifuges are obligatory. Moreover, these measurements have to gather kinetic information as function of the processing conditions, particle interaction and particle concentration.

The separation behaviour of quartz (stable dispersions) and limestone suspensions (moderately and strongly flocculated) was investigated as function of solid concentration and centrifugal acceleration using a multisample analytical photocentrifuge. The new multisample approach uses the STEP-technology. Space and time resolved extinction profiles quantify the alteration of particle concentration, the velocity distribution of particles and packing behaviour during centrifugation. Particle interactions are characterized by the packing density determined under defined conditions and by its variations under alternating centrifugal load.

Multisample analytical batch centrifugation with optical detection proved to be a versatile tool for the characterization of the separation of fine grained materials. This holds for information on the type of sedimentation behaviour (free sedimentation of individual particles, hindered settling, zone settling) on the sedimentation velocity distribution inside the centrate and on the packing, compression and elasticity behaviour, on the nature of particle interactions and the degree of flocculation as well.

The results of multisample analytical centrifugation with optical detection were in good agreement with the results derived by other methods (velocity distribution determined by manometric detection and average packing density obtained during compression in a disc centrifuge).

Characterization of interparticle forces in aqueous and nonaqueous dispersions using multisample analytical centrifugation

T. Sobisch, D. Lerche

info@lum-gmbh.de, www.lum-gmbh.com

The behaviour of dispersions in liquid media, i.e. dispersion stability, flow, separation and packing behaviour, is determined by the nature and degree of interparticle forces. This is of fundamental importance for their application in diverse fields such as nanomaterials, coating, paper making, ceramics, sludge dewatering, to name just a few.

The present work reports on the use of multisample analytical centrifugation for investigation of the packing and compression behaviour to characterize the colloidal stability and microstructure in aqueous and nonaqueous dispersed systems.

Packing density, obtained after compression, is related to the total interparticle potential energy. By using different additives interaction between particles can be shifted from nearly hard sphere behaviour to strong attraction which results in flocculated systems. Additional information could be obtained about the strength and elasticity of particle networks by analysing the relative change in sediment volume after increasing/decreasing the excess pressure in multiple cycles.

The multisample technique applied implies the potential for more systematic studies for targeted colloidal stability.

The new multisample approach uses the STEP-technology. Space and time resolved extinction profiles quantify the alteration of particle concentration and packing behaviour during centrifugation without the need for sample dilution. The latter is a necessary prerequisite for ensuring that the liquid dispersions maintain their original properties.

The paper further covers the influence of the nature of interparticle forces on segregation and deliquoring of common polydisperse fine particle slurries in the centrifugal field.

KEYWORDS: Multisample Analytical Centrifugation, Interparticle Forces, Particle Interactions, Packing Behaviour, Dispersion Stability, Consolidation, Compressibility

Characterization of liquid nanoparticle dispersions by multisample analytical centrifugation

Particle interaction, colloidal crystallization

T. Sobisch, D. Lerche

info@lum-gmbh.de, www.lum-gmbh.com

Reducing particle dimensions to nanoscale leads to qualitatively new properties. This holds also for liquid dispersions, which are the most often used form of application of nanoparticles.

For characterization of nanoparticle dispersions techniques are preferable, which avoid dilution, thus don’t modify dispersion properties. To this end multisample analytical centrifugation proved as an efficient tool.

The new multisample approach uses the STEP-technology. Space and time resolved extinction profiles quantify the alteration of particle concentration but also packing behaviour and phase separation during centrifugation.

Examples are presented for the detection of the presence of flocculation in nanoparticle suspensions, for examination of microgels and colloidal crystallization. The behaviour of microgels was characterized as function of centrifugal acceleration, temperature and concentration. Further, the effect of initial volume concentration and sediment pressure on the speed and extend of the crystallization process was studied.

KEYWORDS: Multisample Analytical Centrifugation, Nanoparticles, Microgels Interparticle Forces, Particle Interactions, Packing Behaviour, Colloidal Crystallization